Valorization of rice husk-derived cellulose microfibers as sustainable reinforcement in fiber-cement composites through mechanical and microstructural analysis

Valorization of rice husk-derived cellulose microfibers as sustainable reinforcement in fiber-cement composites through mechanical and microstructural analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Valorization of rice husk-derived cellulose microfibers as sustainable reinforcement in fiber-cement composites through mechanical and microstructural analysis DANIEL FERNANDO HINCAPIE ROJAS, Stefania Hurtado Paez This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9348799/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Fiber-cement composites are used in lightweight construction due to their favorable balance of mechanical and physical properties. This study investigates the influence of rice husk-derived cellulose microfibers on the performance of fiber-cement boards. Specimens were prepared with varying fiber concentrations (0.0%, 3.0%, 6.0%, 9.0%, and 12.0% wt.) and air-cured for 28 days. Characterization included X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), 3-point flexural testing to determine the Modulus of Rupture (MOR) and Modulus of Elasticity (MOE), and physical measurements of density and water absorption. Data were validated using one-way ANOVA at a 95% confidence level. Results showed that 9.0%wt. of cellulose as the optimal dosage, significantly enhancing the MOR by 159% and increasing the MOE by 59% compared to the control. Microstructural analysis revealed that the hydrophilic nature of the microfibers facilitates internal curing and secondary hydration, promoting calcium silicate hydrate gel formation. This mechanism densifies the matrix and improves fiber anchoring, as confirmed by SEM. Physically, the inclusion of cellulose reduces bulk density, favoring the development of lightweight materials, despite an increase in water absorption caused by inherent fiber porosity. Ultimately, the valorization of agro-industrial waste like rice husks not only optimizes the mechanical integrity of fiber-cement but also provides a sustainable, clean production alternative for the modern construction sector. Fibercement cellulose mechanical properties density lightweight building systems Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Fibercement (FC) is a material widely used in the construction industry specially in lightweight systems [1]. Currently urban buildings must be more resistant, durable, lightweight, lower costs, need faster installation times [2] and generate the least possible energy expenditure [3]. FC is a material composed of cement, silica, aluminum hydroxide and reinforced with fibers, which is cured in air that usually takes 28 days under conditions of ambient temperature, pressure and humidity. FC is characterized by low permeability, low density [4], low thermal conductivity, low shrinkage, thermal and/or acoustic insulation capacity, high heat resistance and transpiring properties [5]. The addition of fibers in the cementitious matrix has a positive impact on properties such as resistance to bending, cracks, impact, durability; and the results show that the addition of these fibers can improve the toughness and ductility of this material [6]. In recent years there has been a growing interest in the use of natural fibers such as wood and cellulose fibers, they are considered sustainable materials due to their rapid bio-renewability and biodegradability [7]. As a consequence of the hydrophilic and hygroscopic nature of vegetable fibers, they are considered good candidates for hydraulic matrices such as cement [8]. Some fibers used traditionally in industry (steel fibers, glass fibers, polymer fibers) have higher costs [6], it means that natural fibers obtained from renewable sources are considered as flashy substitutes for reinforcing material [9]. Additionally, the ecological aspects are taken into consideration to produce ecofriendly construction materials obtained from agricultural and forest wastes. The valorization of by-products in construction industry has increasingly attracted the attention from researchers, governments as well as industries [10]. For example, using rice husk as a natural source of cellulose microfibers in a cement-based matrix brings a lot of number of positive aspects [11]. Rice husk (RH) is a residue of production and refinement in this agricultural industry and is one of the highest lignocellulosic biomass, about 20% of the volume of the grain after milling corresponds to husk, it means that around 148 million tons of RH are generated each year [12], [13]. Depending on the characteristics, morphology, and crystallinity of the cellulose fraction of RH, it can be used as a filler or for reinforcing materials in cellulose and cement-based materials [14]. Cellulose microfibers have excellent mechanical properties, which can reach up to an elastic modulus of 200 GPa (higher than glass fibers of 65 GPa ), a tensile strength of 7.5 GPa . [15] and they also have a high surface area [16], [17]. Cellulose microfibers have applications that include the reinforcement of composite materials, thin film manufacturing, food packaging materials, aerosols, biomedical products, stabilizers for aqueous suspensions, and also as a raw material for the development of electronic components [18]. In the literature there are different reports on the mechanical properties, microstructure and durability of cement composites reinforced with cellulose fibers and manufactured by the Hatschek process. It is a semi-continuous process comprised of three steps: sheet formation, board formation, and curing [11]. The results of some investigations are focused on the mechanical properties of cement-based materials without delving into the interactions between cellulose fibers and cement particles and without determining how these interactions have an important effect on cement-based compounds [19]. Parveen et al.[15] showed in their study that the addition of cellulose microfibers improves the mechanical properties and the degree of hydration of the cement paste. The properties of the cement mortar with an addition of 0.3% by weight were comparable to those of the mortar without fibers. Nilsson et al.,[20] prepared Portland cement mortars with 0.11, 0.22 and 0.33 wt.% of recycled cellulose microfibers from the paper industry, in this research they characterized the changes in the viscosity of the mixture in the fresh state, changes in the mechanical properties and capillarity properties and absorption of the material in the hardened state. They determined that microfibers modify the rheology of the material, affecting the mechanical properties and concluded that they have a positive effect on water absorption, since microfibers modify the pore structure in cement mortars. Seongwoo Gwon et al.,[21] added cellulose microfibers in a proportion from 0.3–2.0% with respect of to the amount of cement, they determined that adding cellulose has a positive effect on the mechanical properties of the material and they determined that the optimal percentage of addition was 1% . Mohamed et al.,[22] studied the effect of adding microcellulose in a compacted concrete mixture. They determined that adding fibers by 21 wt/v.% increased compressive strength and flexural strength after 7 days of curing in air. It is observed that there are differences between the percentages of addition of cellulose microfibers used in the various studies and some of these are focused on mortars or concrete, not specifically on fiber-reinforced cement. Another drawback associated with the use of vegetable fibers is the degradation of the fiber constituents (lignin and hemicellulose) and reduction of the degree of polymerization in the alkaline environment of the matrix and the bonding between the individuals’ fibers [23], [24]. According to the different bibliographic sources, there are not enough studies that focus on analyzing the effect of the addition of cellulose microfibers in cementitious compounds for industrial applications and it is also not clear what is the maximum weight content of cellulosic fibers that can be incorporated into the composites [25]. On the other hand, some studies have shown that the presence of calcium hydroxide (Portlandite) in the cementitious matrix degrades the fibers due to the alkaline environment to which they are exposed which leads to a loss of the durability of this compound [26]. The mineralization of the fibers is caused by the migration of hydration products to the lumen and the pores of the fibers, in addition to the volume variation of the fibers due to their high water absorption. The extent of the attack will depend on the type of fiber, the composition of the cementitious matrix, the level of porosity in the matrix and the aging conditions of the material. Mohr et al. [27] established the following sequence of damages that occur to the fibers as a consequence of the aging of the matrix: a) loss of adherence between the fibers and the matrix; b) reprecipitation of the hydrated compounds within the void space in the old asbestos-cement interface and c) complete mineralization, and therefore the embrittlement of plant fibers. The objective of this work is to analyze the effects of the inclusion of different percentages of addition of cellulose microfibers (0.0, 3.0 6.0, 9.5 and 12.0%wt.) on the flexural strength, the modulus of elasticity, the density and the absorption of the fibers. fiber cement plates, to evaluate the effect of the inclusion of these fibers in the composite material. Additionally, a statistical analysis will be carried out by means of the Tukey comparison test to determine if there are significant differences in the different percentages of cellulose added on the properties of the material. 2. Materials and Methods The procedure followed to cellulose microfibers from rice husk and to manufacture the FC boards is described below. In addition, each of the characterization steps carried out on FC boards and the statistical analyses carried out with the results obtained from the design of experiments are described. 2.1 Materials Rice husk was obtained from Tolima, Colombia. Sodium hydroxide (Panreac 99% purity) was used for alkaline treatment. Sodium hypochlorite and acetic acid were used as bleaching agents (from Todo Químicos, Caldas, Colombia S.A.S.). All chemicals were of analytical grade and used without further purification. Ordinary Portland cement (OPC) type III produced by Cementos Argos, Colombia S.A. was used to prepare the fibercement boards, with a surface area (Blain) of 420 m 2 /kg and density aproximatelly 3129 kg/m 3 . The bentonite was purchased from Bentucol SAS, the silicon dioxide ( µ-SiO 2 ) from Pulverizar S.A. Manizales and aluminum hydroxide ( Al(OH) 3 ) in Spot Training. An ether-based polycarboxylic acid superplasticizer additive was used to promote the compaction and workability of the cementitious matrix during the manufacturing process. The chemical composition of the OPC used in this research is presented in Table 1 . Table 1 Chemical composition of Ordinary Portland Cement Minerals Content (%) \(\:{\varvec{S}\varvec{i}\varvec{O}}_{2}\) 20.25 \(\:\varvec{C}\varvec{a}\varvec{O}\) 64.10 \(\:{\varvec{K}}_{2}\varvec{O}\) 0.35 \(\:{\varvec{P}}_{2}{\varvec{O}}_{5}\) 0.31 \(\:\varvec{M}\varvec{g}\varvec{O}\) 2.48 \(\:{\varvec{A}\varvec{l}}_{2}{\varvec{O}}_{3}\) 4.15 \(\:\varvec{M}\varvec{n}\varvec{O}\) 0.09 \(\:{\varvec{F}\varvec{e}}_{2}{\varvec{O}}_{3}\) 3.56 \(\:\varvec{S}{\varvec{O}}_{3}\) 2.01 \(\:{\varvec{N}\varvec{a}}_{2}{\varvec{O}}_{3}\) 0.10 Otros 0.10 Fire losses 2.20 Free lime 0.30 2.2 Obtaining cellulose and silica from rice husk 2.2.1 Cellulose extraction from rice husk The extraction of cellulose fibers from HR was carried out on the basis of the methodology of previous research by Hincapié-Rojas et al [28]. Briefly, alkali treatment purified cellulose by removing hemicellulose and lignin from HR. The ground rice husk was treated with an 8 wt% NaOH alkali solution. The mixture was transferred to a round bottom flask and the treatment was carried out at reflux for 2 h at 100°C. The solid was then filtered and washed to a pH of 7. The paste obtained was dried at 50°C for 24 h. After the alkali treatment, the bleaching process of alkali-treated was completed using a buffer solution of 1.47% acetic acid, aqueous chlorite (1.7% by weight) and distilled water at reflux for 1 h at 70°C. The mixture was allowed to cool to room temperature and filtered with an excess of distilled water until the filtrate was colourless and a pH of 7 was obtained. The bleaching process was repeated twice until a completely white cellulose was obtained. 2.2.2 Silica extraction from rice husk The power with a high silica content was obtained according to the methodology proposed by Hincapie-Rojas et al. in a previous work [29]. Briefly, RH was washed to remove impurities. It was then dried in a conventional oven at 100 ºC for 3 h. The RH was then incinerated in a furnace to remove the organic materials and to reduce the carbonaceous materials in order to obtain the ash. A solution of nitric acid (HNO 3 ) was prepared at 1.0 M in order to remove the impurities by means of the chemical reaction between the acid and the inorganic impurities. These reacted metals are leached from the acidic solution during filtration. After leaching, a white powder rich in silica was obtained. 2.3 Processing of fibercement specimens Cement, water, cellulose fibers, bentonite, silicon dioxide and aluminum hydroxide were precisely mixed according to ASTM C-305 Standards [30], until obtaining a homogeneous and moldable paste. The water/cement ratio (w/cm) was kept at a constant value and equal to 0.4 [14]. After the mixing process, the specimens were compacted into prisms with dimensions of 150 mm x 200 mm x 10 mm according to ASTM C-78-09: Standard Test Method for Flexural Strength of Concrete Using Simple Beam with Third-Point Loading [31]. The samples were cured under laboratory conditions (temperature of 25 ± 2 ºC and 65 ± 5% humidity relative) for 28 days. Finally, the characterization of the specimens was carried out. Five formulations were elaborated, the first one corresponds to the control sample (without cellulose) and the other 4 with different percentages of addition of microfibers cellulose defined as 3.0, 6.0, 9.0 and 12.0 %wt. repectively. These variations were proposed to evaluate the effect of the inclusion of the fibers on the physical and mechanical properties of the FC. For this study, the amount of cellulose microfibers was calculated with respect to the total weight of the sample, and the specimens were labeled as C0.0, C3.0, C6.0, C9.0 and C12.0 according to the percentage of cellulose addition, respectively. 2.3 Characterization of cellulose microfibers and silica from rice husk and fibercement-based composites 2.3.1 Thermogravimetric analysis of rice husk fibers To evaluate the thermal stability of the raw materials, thermogravimetric analysis (TGA) and differential thermal analysis (DTGA) were performed using a TGA Q500 instrument (TA Instruments, USA). Samples were heated at a rate of 10ºC/min from room temperature to 700ºC. All measurements were performed in an air atmosphere at a gas flow rate of 50 mL/min. The data were processed using Universal Analysis 2000 TA software. The maximum rate of reaction and the mass lost were determined from the peak in the derivative curve (DTGA). 2.3.2 Morphological analysis by Scanning Electron microscopy (SEM) A high vacuum scanning electronic microscope JEOL JSM-5910 LV was used with 10.00–15.00 kV electron acceleration voltage. The morphology of cellulose microfibers, silica and also the main hydrated products from fibercement-based composites with different percentages of cellulose was analyzed. Before the analysis the samples were fixed on copper specimen held on carbon adhesive tape. A gold layer ( 30 nm of thick approximately) was deposited by sputtering on samples to make them conductive. 2.3.3 Structural analysis by X-ray diffraction (XRD) The structure of cellulose fibers, silica and phases presents in fibercement added with different proportions of microcellulose fibers were identified using a RIGAKU diffractometer equipment, MINIFLEX II operated at room temperature, equipped with a Cu Kα radiation source ( λ = 1.540562 Å ), and a 30 kV and 15 mA X-ray source. Measurements were run between 5º and 70º on a 2θ scale with a step size of 0.02º/s . 2.3.4 Mechanical characterization of fibercement specimens Mechanical tests of fibercement composites with different content of cellulose microfibers at 28 days of curing were performed on a UNITED uniaxial universal testing machine, with a maximum load capacity of 100 kN. The bending strength \(\:\left({\sigma\:}_{bend}\right)\) and modulus of elasticity (E) of the boards was determined using the three-pointed method according to ASTM C-133-97 [32]. The specimens were placed on two parallel supports separated by a distance of 150 mm (spam). The load was applied parallel to the supports at a constant speed of 0.05 kN/s . Using Eqs. 1 and 2 [32] and with Proteus Versión 14.1.0 of the Universal Testing Machine, the bending strength ( \(\:{\sigma\:}_{bend}\) ) and the deformation \(\:\left(\epsilon\:\right)\) of FC was calculated. The modulus of elasticity was calculated as the slope of the stress-strain curve (in the elastic zone) for each sample. The analyzes were performed in quadruplicate and the mean and standard deviation of each variable were calculated. $$\:{\sigma\:}_{bend}=\frac{3WL}{2b{d}^{2}}$$ 1 $$\:\epsilon\:=\frac{6db}{{L}^{2}}$$ 2 Where W is the fracture load, L is the distance of the bar between the two supporting edges (spam), b is the width of the sample, and d is the sample depth at the fracture plane. 2.3.5 Dry bulk density, water absorption of FC composites The dry apparent density and water absorption indexes of the compound were determined according to ASTM C-830 00 standards [33]. After the mechanical analysis, 4 samples of each formulation were removed in an oven at 100º C for 24 h and subsequently immersed in water for another 24 h . The weight of each sample was recorded at each step as oven dry (dry weight), saturated mass after immersion (wet weight), and mass under water (apparent weight). Therefore, the dry bulk density \(\:\rho\:\) and water absorption \(\:{A}_{w}\) were determined by equations 3 and 4 respectively [34]. $$\:\rho\:=\frac{dry\:weight\:}{wet\:weight-apparent\:weight}*{\rho\:}_{w}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(2\right)$$ $$\:{A}_{w}=\frac{wet\:weight\:-\:dry\:weight}{dry\:weight}*100\:\%\:\:\:\:\:\:\:\:\:\:\:\:\left(3\right)$$ \(\:{\rho\:}_{w}\) represents the density of water, taken as 1 g/cm 3 . 2.3.6 Statistical analysis of the variables established for the experimentation with fibercement boards Statistical analysis was performed to correlate the results of the independent and dependent variables considering in the manufacture of the FC samples. The independent variable was the variation of mixing percentage of cellulose microfibers at three levels 0.0, 3.0%, 6.0%, 9.5%, and 12.0% wt. A randomized, replicated (1 original + 3 replicates), single block experiment was conducted. The following response variables were used: modulus of elasticity, bending strength, dry bulk density, and water absorption. An analysis of variance (ANOVA) with 95% confidence with only one factor (content of cellulose) was conducted. ANOVA was verified to comply with the assumptions of normality of residuals, homoscedasticity of residuals, and independence of data. Minitab® software versión19 was used for the statistical analysis. 3. Results and Discussion 3.1 Thermal, morphological and structural characterization of raw materials from rice husk: Cellulose microfibers and silica nanoparticles To investigate the thermal stability of raw RH and chemically treated rice husk fibers (microcellulose fibres), thermogravimetric analysis was carried out. The weight changes that occurred during the combustion of RH are shown by the TGA curve shown in Figure 1a , and the differential thermal analysis DTGA is also shown as an insert in each graph. The DTGA curve shows that the raw RH is decomposed in three stages. Stage 1 (25-140°C) involves the removal of moisture; stage 2 and stage 3, which occur in the temperature range of 155-350°C and 350-550°C respectively, involve organic compounds (hemicellulose, cellulose and lignin) and their decomposition [35]. Finally, after 550 °C, the mass remained stable. The residual ash is 25.57% and consists mainly of silica SiO 2 . Figure 1b shows the thermal analysis profile of cellulose microfibres. Two thermal degradation steps were observed in the decomposition of treated RH. Stage 1 is associated with weight loss due to moisture and evaporation of water due to the hydrophilic nature of lignocellulosic material at 30ºC - 130ºC [17]. In this case, 8.21% of the total weight of the sample was removed. The second stage is associated with the decomposition of cellulose and hemicellulose [36]. The mass loss in this range is approximately 70.03%, which is higher than the decomposition recorded for the raw RH (40.05%), indicating that components other than cellulose have been removed during the chemical treatment. In stage 2, higher mass loss at this stage is associated with high cellulose content in the fibers. Additionally, the onset in this stage was increasing at higher temperatures for the analysed samples. It started at 147.09 °C for RH and increased to 200.68 °C for the bleached husk, as seen in the DTG (see insert at the right-up position of each graph) curves in Figure 1 a, b. This phenomenon can be explained by the removal of non-cellulosic components that are subject to degradation at lower temperatures. These results are consistent with those obtained in other studies [37] . Stage 3 is characterised by the loss of lignin over 350 ºC, with a 5.0% reduction in the total weight of the sample. This decomposition is lower than that recorded in the RH, suggesting a reduced presence of lignin in the sample due to the chemical treatment. Furthermore, the intensity of the peak associated with the decomposition of lignin in the DTGA curve ( Figure 1b ) was observed to be lower in comparison to that of the RH curve ( Figure 1a ). The residue obtained was also found to be lower, with a percentage of 9.07%, indicating that the majority of inorganic components had also been removed during the chemical process (mainly silica). In addition to weight loss, the temperature decomposition peak for treated RH was higher in comparison to raw RH. Similar results were reported by Shailendrakumar et al., [38]. From the thermogram in Figure 1c , it can be seen that the silica obtained from rice husk had no mass loss during heating, this indicates the stability of this material. The chemical treatments used for cellulose purification from RH are also expected to induce morphological changes on the surface of the rice husk fibers. The structure of RH fibers was investigated by comparing the SEM micrographs ( Figure 1 d-e) . The rice husk micrograph shows a high level of structural organization and uniformity, featuring a smooth, flat surface resembling unidirectional sheets ( Figure 1d ). The non-cellulosic components are distributed across the entire surface, acting as a protective layer while preserving the overall structure, and hemicelluloses and lignin form a matrix that encapsulates the cellulose. The typical structure of the material includes cellular spaces coated with pectin, silica, and waxes, which at the extremities tend to cluster into spherical and spongy agglomerates. Ridge-like linear grooves are formed on the surface of rice husk fibers by densely coated silica crystals. These grooves contribute to the overall rigid texture of the material and this crystalline silica is the principal cause of its roughness [39]. As shown in Figure 1e, the initial bleaching process results in cellulose microfibers with a cylindrical shape and a cotton-like texture. This treatment effectively removes non-cellulosic components, yielding fibers with diameters ranging from 4 to 12 μm. The bleaching process involves the use of sodium hypochlorite, which cleaves lignin's aromatic rings through oxidation, and acetic acid, which regulates the pH level. These findings align with previous studies indicating that sodium hydroxide treatment enhances bleaching efficiency by increasing the exposed surface area of the fibers [40]. The addition of cellulose fibers to cement-based composites enhances mechanical properties, reduce crack propagation, and improve durability, as will be shown below. Figure 1f shows the morphology of the silica extracted from the rice husk reveals irregularly shaped particles, possibly with a porous distribution. The silica particles are found to be sub-metric in size, with a size distribution between 1 and 10 microns, and an average size of about 0.57 µm. The presence of a heterogeneous size distribution indicates the possibility of smaller primary particles and agglomerations originating from electrostatic forces [41] . XRD was used to evaluate the changes in the structure and to determine the crystallinity indices (CrI) of the fibers extracted from the rice husk after applying the two chemical treatments. Figure 1g shows the diffraction patterns of the three samples analyzed. The diffractogram of cellulose shows three peaks at 2θ = 15°-17°, 22.5° and 35°. These three peaks are characteristic of the cellulose type I allomorphism and are attributed to crystallographic planes (110), (200) and (004), respectively, with the peak of highest intensity at 2θ = 22.47°. These results are in agreement with those reported by Sabapathi et al., [42] . In addition, the peaks become narrower and sharper as the chemical treatments are applied. The crystallinity index (CrI) is a parameter that indicates changes in their structure due to such treatments. This value was calculated according to the method proposed by Segal et al., [43] . The crystallinity index was 38% and 64% for rice husk and cellulose microfibres respectively. These results are in agreement with those of Bhandar et al., [44] . These results show that chemical treatments increase the value of the crystallinity index due to the partial removal of amorphous components such as lignin and hemicellulose present in rice husk. Figure 1h shows the diffraction pattern of the silica extracted from the rice husk, which clearly identifies the silicon oxide phase as the predominant phase. The location of these peaks is also indicated, along with other phases with lower intensity that correspond to impurities found in the silica, such as phosphorus, sodium and aluminium-based oxides. The results were compared with PDF #39-1425 of silicon oxide, the unit cell of which is tetragonal and corresponds to the crystalline system of cristobalite. The addition of crystalline silica to cement-based composites has a positive effect on the mechanical, barrier and durability properties of these materials. In addition, its use contributes to sustainability by reducing clinker content and taking advantage of silica-rich industrial by-products. 3.2 Characterization of Fibercement composites 3.2.1 Morphological characterization by SEM To better understand the results obtained in this study, SEM images at lower magnification are shown first (see Figure 2 ), where the interactions between the cementitious matrix and the cellulose microfibers are evident. Subsequently, micrographs obtained at higher magnification are shown to identify the typical hydration products of FC (see Figure 3 ). Figure 2 shows micrographs of fiber cement boards at 100X magnification with the different percentages of cellulose addition detailed in the methodology section. When comparing the five samples, some differences can be observed in terms of matrix-fiber interaction. In Figure 2a , which corresponds to the fiber cement sample without cellulose addition C0.0 , it can be seen that the surface of the cementitious matrix is more homogeneous and denser, with some isolated microcracks and a more compact microstructure, without the presence of fibers. In Figure 2b , which corresponds to sample C3.0 (3.0% cellulose addition), microfibers begin to be observed distributed relatively uniformly over the cementitious matrix. These fibers appear to be well adhered to the matrix, with visible interface areas. The presence of microspaces around some fibers is also observed, possibly due to shrinkage of the material during drying or curing. In Figure 2c , which corresponds to sample C6.0 (6.0% cellulose addition), a greater number of visible fibers distributed throughout the surface and with better interconnection within the matrix is evident. The fiber-matrix interfaces are more defined, although slight separation is noticeable in some areas. An increase in local porosity is also observed, as well as in the stress redistribution capacity. In Figure 2d , which corresponds to sample C9.0 (9.0% cellulose addition), the micrograph shows a more abundant and dense distribution of fibers compared to the previous samples. The analyzed surface presents an interconnected network that generates an effective bond and reinforces the cementitious matrix. Although the fiber content has increased, the fibers continue to integrate adequately with the other components of the fiber cement, the fibers are homogeneously distributed in the matrix, and also the fibers have a partly lamellar structure. Additionally, a controlled increase in porosity is observed, which may be associated with better absorption and dissipation of energy under mechanical stress, favoring the toughness of the material, as will be shown later. Similar results were reported by Lavasani et al. [45] . In their research on the effect of fibers in asphalt matrices, they highlight that fibers allow for excellent crack bridging and stress distribution in the material. Finally, in Figure 2e, which corresponds to sample C12.0 (12.0% cellulose addition), the morphology of the cementitious matrix appears less compact, with more abundant and disordered fibers. The image shows larger voids and fiber-matrix separation, which could decrease the overall mechanical strength of the fiber cement. An increase in porosity and possible formation of microchannels can be observed. A greater increase in fiber content can lead to a loss of uniformity in the fiber cement, affecting its structural performance. At this magnification scale, the interconnection between the cementitious matrix and the fibers can be identified. The addition of these reinforcing fibers has an effect on the morphology and other properties of the composite material. A more mechanically resistant material requires adequate bonding between its different components. On the other hand, Figure 3 shows micrographs of fibercement boards at 5000X magnification of some of the samples analyzed ( C6.0, C9.0, and C12.0 ). At this magnification scale, it is possible to observe some typical products of fiber cement hydration such as C-S-H (calcium silicate hydrate), CH (calcium hydroxide or portlandite), and ettringite. In Figure 3a , corresponding to sample C6.0 , a relatively compact matrix is observed with the presence of C-S-H, visible as a dense, amorphous mass with an irregular and homogeneous texture. Dispersed hexagonal lamellar crystals, typical of calcium hydroxide, are also present. The surface shows low visible porosity, suggesting adequate hydration. Some fine acicular microcrystals were identified that may correspond to ettringite, indicating an active calcium aluminate reaction [46] . In Figure 3b , corresponding to sample C9.0 , the matrix exhibits a more complex morphology of hydration products, with dense areas of C-S-H intertwined with accumulations of CH crystals that are more visible than in sample C6.0 . There is a greater presence of ettringite in the form of thin needles, indicating a more reactive environment, possibly promoted by the incorporation of cellulose. According to Scrivener et al., [47] the presence of these intertwined structures and dense layers may be associated with a greater water retention capacity induced by cellulose, which favors secondary hydration. The texture identified in the sample is compact, with less evidence of voids, suggesting a more cohesive microstructure. In Figure 3c , corresponding to sample C12.0 , areas of incomplete hydration can be observed, with patches of discontinuous C-S-H and greater visibility of pores or capillary voids. CH crystals appear more abundant and disordered, which may indicate the release of water not used for complete hydration. Ettringite is still present, but with an irregular arrangement, and in some areas, there are signs of cohesion between phases. This sample shows a possible negative effect of excess cellulose, which absorbs water but does not release it efficiently, affecting the continuity of the C-S-H [48] . La tobermorita es uno de los productos de hidratación más importantes del cemento, y es el responsable de la armazón interna de la pasta de cementicia, de la adherencia de ésta con los áridos en los morteros y también de aportar de forma positiva a la resistencia mecánica de este material [49]. It should be noted that in samples with 9.0 and 12.0%wt. cellulose added, the typical morphology of the reaction between tobermorite and aluminum hydroxide can be observed. These reactions improve the properties of fiber cement, such as strength and durability. The typical morphology of pure tobermorite is in the form of small laminar crystals. On the other hand, tobermorite with Al substitution exhibits larger ribbon-like crystallites, as shown in Fig. 2 (b-c) [50] . 3.2.2 Structural characterization by XRD Structural analysis by XRD is a very important technique for identifying the crystalline structure and main phases in this type of material. It should be noted that structurally characterizing fiber cement is quite complex due to its heterogeneous nature and the presence of multiple phases; for this reason, the patterns show many peaks due to the multiple phases present in it. Figure 4 shows the diffraction patterns of the five samples analyzed. The diffractogram identifies the main diffraction peaks of fiber cement. The main phases found were: Portlandite (P), Cellulose (C), Quartz (Q), Calcium Carbonate or Calcite (CC), and Tetracalcium Silicate Alite (A). These phases were identified by quantitative analysis using the diffraction patterns in the PDF2 database as a reference. Portlandite (Ca(OH)) is identified at 2θ=18.0°, 34.1°, and 47.1°. This crystalline phase results from the hydration of calcium silicates (alite: C 3 S and belite: C 2 S). The increase in the intensity of the portlandite peak at 2θ=18.0° and 47.1° for samples with higher cellulose content suggests a heterogeneous nucleation effect, where microfibers act as heterogeneous nucleation sites for hydration products (ettringite, calcium silicate hydrated C-S-H, and portlandite), accelerating hydration. Likewise, the absorption capacity of cellulose could be favoring an internal curing mechanism, promoting more advanced hydration of the clinker compared to the control sample [51]. As for the peak associated with cellulose around 2θ=22.5°, an increase in its intensity and width is observed as the cellulose content in the mixture increases. This peak is characteristic of the (200) plane of Cellulose I with a semi-crystalline structure [52] The peak around 2θ=26.86° corresponds to crystalline quartz originating mainly from the siliceous material used as a filler in the manufacture of the plates. The results show that there are no variations in its intensity, which may indicate that cellulose has no effect on this type of phase. For the peak located at 2θ=29.51º, corresponding to the (104) plane of calcite (CaCO3), an increase in intensity is observed as the cellulose content increases, reaching its maximum intensity in the sample with C9.0. This phenomenon suggests an accelerated carbonation process, where the cellulose microfiber network acts as a diffusion channel that facilitates the penetration of atmospheric CO₂ into the core of the cementitious matrix during 28 days of air curing. The hygroscopicity of cellulose provides the internal moisture necessary for the dissolution of environmental CO₂, thereby converting Ca(OH)₂ into calcite and densifying the microstructure [53] . Finally, for the peak at 2θ=32.0º, which corresponds to the anhydrous phases of alite (C 3 S) and belite (C 2 S), a decrease in intensity is observed as the cellulose content increases. This suggests a lower concentration of unreacted C 3 S/C 2 S, indicating a higher degree of clinker hydration and the subsequent formation of more tobermorite-like gel (C-S-H) in the mixtures containing cellulose fibers compared to the control sample. Similar findings were reported bu Wu et al., they study the influence of cellulose fibers from cotton on hydration and microstructure of portland cement paste [54]. Additionally, the presence of calcium oxide (free lime) was identified at 2θ=62.39º. 3.2.3 Mechanical characterization The flexural strength of fiber-reinforced cementitious composites depends on the interaction and physicochemical adhesion between the fiber and matrix, the dispersion and orientation of the fibers, and the resulting microstructure. The appropriate addition of cellulose microfibers can improve the flexural strength of this type of material, especially when the amount and dispersion of the fibers are optimized [55] . Figure 5a and b show the flexural strength and modulus of elasticity of the samples as a function of the percentage of cellulose microfiber added after 28 days of curing, respectively. The analyses were performed using an original sample and three replicates. The graph shows the average value and standard deviation. According to the results shown in Figure 5a, sample C0.0 has the lowest flexural strength (5.80 MPa). In this type of composite material, the absence of fibers (see SEM in Figure 2a ) means that the material has a lower capacity to control the propagation of microcracks, which implies that the material may be more brittle. Although sample C3.0 shows a 53.62% improvement in flexural strength compared to control sample C0.0 , it is not as significant as the improvement achieved with the other cellulose additions used in this work. According to Xie et al., [7], a small amount of fibers (e.g., 3.0%) may cause them to be unevenly distributed in the cementitious matrix, with some areas of the sample having very little or no fibers, which could lead to initial cracks in these areas. Additionally, it can be observed that as the percentage of cellulose added increases, flexural strength also increases. The maximum value (17.52 MPa) is achieved for sample C9.0, which corresponds to an improvement of 202.07%, 96.63%, 50.9%, and 9.8% compared to samples C0.0, C3.0, C6.0, and C.12. The fibers form a three-dimensional mesh that restricts the propagation of microcracks, acting as effective internal barriers. In sample C9.0, an adequate balance is achieved between fiber quantity, distribution, and internal cohesion in the sample, which is reflected in its mechanical properties [45]. In the sample with the highest cellulose content ( C12.0 ), a decrease in this value is observed compared to sample C9.0. According to Soares et al., [56] high fiber contents can cause structural defects and loss of compressive strength due to agglomerations that can be generated in the composite material (see Figure 2.e ) [16]. A similar behavior is observed for the modulus of elasticity (MOE) of the samples (see Figure 5b ). Again, sample C0.0 has the lowest modulus of elasticity (3650.3 MPa). Additionally, the maximum MOE value (5804.1 MPa) is obtained for sample C9.0 , in this case achieving an increase of 59.0%, 32.7%, 26.9%, and 6.7% with respect to samples C0.0, C3.0, C6.0 , and C12.0 , respectively. Similar results were reported by Soydan et al., [57] who evaluated the effect of different types of cellulose fibers on fiber-cement composite mixtures. In this study, they reported flexural strength or modulus of rupture values ranging from 9.76 to 17.57 MPa and modulus of elasticity values ranging from 3790 to 5430 MPa. The improvement in mechanical strength parameters (MOR and MOE) may be due to the fact that cellulose fibers have a high elastic modulus and form a strong bond within the cementitious matrix [58] . This gradual increase in the flexural strength of the material is attributed to greater interaction at the matrix-fiber interface (as evidenced in the SEM scanning electron microscopy images shown in section 3.2.1), as well as an improvement in the energy absorption capacity of the composite against fracture (toughness). This factor allows the mechanical behavior of the material to be evaluated under real conditions when subjected to static, dynamic, or fatigue loads [59] . This improvement is also related to the increase in the degree of hydration in the cementitious matrix, since cellulose microfibers have a high-water retention capacity due to their hydrophilic and hygroscopic nature [16] . In this process, cellulose acts as an internal water reservoir within its fibrillar network, attracting calcium ions (Ca²⁺) through electrostatic interactions with its anionic surfaces. Additionally, water molecules diffuse more easily and quickly within the cellulose network compared to the surrounding matrix. These combined effects accelerate the formation of calcium silicate hydrate (C-S-H) gel at the fiber-matrix interface during hydration. As a result, hydration products accumulate at this interface, strengthening the physical bond between the fibers and the matrix, which improves mechanical strength and reduces fiber pull-out [60]. These results are consistent with those reported by Gómez et al. [61] and Xie et al. [6] , who demonstrate that the addition of cellulose microfibers has a positive effect on the strength of cement-based composites. The use of cellulose as a reinforcing additive in the production of fiber cement contributes to: (1) improving mechanical properties such as bond strength, MOE, and MOR; (2) modifying the rheology of the paste; (3) reducing porosity; and (4) enhancing interactions with other components of the mixture. Cellulose improves bond strength and enhances hardening, mainly after 7 days; reduces fiber pull-out and shrinkage (especially autogenous shrinkage during setting, reducing the risk of product loss); and reduces both porosity and thermal expansion [25] . The reinforcement does influence the modulus of rupture and modulus of elasticity rupture ( p -value<0.05) compared to the reference. These results corroborate those previously presented in the XRD analysis ( Figure 4 ). The increase in the intensity of the calcite peak, observed especially in sample C9.0 , may be related to an increase in the carbonation process facilitated by the microfiber network. The precipitation of these calcite crystals acts as a densification mechanism in the Interfacial Transition Zone (ITZ) between the cellulose microfiber and the cement matrix, which generates superior mechanical anchoring, increasing interfacial friction and optimizing stress transfer during flexural loading. Cellulose acts as an agent that modifies the curing kinetics and crystalline structure of the matrix, favoring a mineralogical configuration (rich in calcite and quartz) that maximizes the strength of fiber cement. On the other hand, portlandite crystals may be forming in greater proportion directly on the surface of the cellulose fiber (which can be corroborated by XRD analysis, especially for sample C9.0 ). This creates better chemical and physical anchoring in the cementitious matrix, and the transfer of mechanical stresses from the matrix to the fiber is more efficient, increasing its toughness [62]. 3.2.4 Dry bulk density and water absorption values Figure 6 shows that the addition of cellulose microfibers slightly decreases the density values of the fibercement composites with respect to the control sample (C0.0). This is because the density of cellulose (1500 kg/m 3 ) is much lower than that of cement (3129 kg/m 3 ), so adding more of these fibers is expected to result in a much lighter and more porous material [63] . Cellulose microfibers have a porous structure, which allows greater water entry into these pores and into their hydrophilic structure, causing an increase in the absorption of the matrix [34]. The density and absorption results are within the standardized values in the NTC 4373 standard for cement [64] . The fit line obtained from the linear regression of these values was also included in the graph. The intercept of the equation, whose value is 1.451 g/cm 3 , represents the density of the composites without the addition of cellulose microfibers. On the other hand, the slope of the fit line, (-0.016 g/cm 3 /%), indicates the value at which the density of the fibercement decreases for each 1% addition of cellulose. Similars results were reported by Soydan et al., [57] Figure 6b also shows the absorption values in the samples. It was observed that a higher percentage of addition of cellulose, implied increases in the absorption. Additionally, a major increase in the absorption of the samples C9.0 and C12.0 . In contrast to the decreasing trend observed in density, water absorption in fibercement composites increases proportionally to cellulose content. The presence of a dense network of hydroxyl (-OH) groups on the surface of cellulose facilitates the formation of hydrogen bonds with water molecules, promoting a chemical affinity for moisture [65]. The incorporation of higher percentages of fiber alters the morphology of the cementitious matrix by introducing a network of capillary porosity and interstitial spaces at the fiber-matrix interface that act as water transport conduits as can be seen in SEM images (Figure 2 d-e). The trend line obtained by a linear fit to absorption values was also presented in the graph. The intercept of equation (22.108%) represents the absorption of the samples without cellulose. On the other hand, the slope (1,137%) represents the increase in the absorption of the samples for each 1% of cellulose addition. All calculated density and absorption results are in agreement with NTC 4694-D8 (Norma Técnica Colombiana). Similarly to the mechanical properties, the reinforcement influences the density and water absorption values ( p<0.05 ) compared to the control sample C0.0 . Conclusions The experimental results identify 9.0% wt. as the critical threshold for reinforcement efficiency within the cementitious matrix. At this concentration, the distribution of microfibers reaches a state of spatial saturation that maximizes crack-bridging mechanisms without compromising the continuity of the cement paste. Below this level, the fiber density is insufficient to effectively intercept and arrest micro-crack propagation under mechanical stress. The microstructural analysis showed that cellulose microfibers function as internal curing agents. Due to the presence of hydroxyl groups, these fibers absorb significant amounts of water during the mixing phase. As the bulk cement hydration progresses and consumes the surrounding moisture, the fibers gradually release their stored water back into the Interfacial Transition Zone (ITZ). This localized humidity facilitates a more complete secondary hydration of anhydrous cement particles, leading to a denser and more homogenous growth of C-S-H gel directly onto the fiber surface. This hydration product strengthens the interfacial bond increasing the strength of the composite. Incorporating cellulose microfibers leads to a improvement in mechanical performance, increasing the modulus of rupture from 5.80 MPa to over 17 MPa (+ 193.10%) and the modulus of elasticity from 3650.30 MPa to over 5800 MPa (+ 59%) compared to the control sample when the cellulose content was 9.0%. The physical properties of cellulosic fibers reinforced cement-based composites are influenced by the content of fibers. The porosity and water absorption increase with increase of fiber content, but the bulk density decreases. While this facilitates the production of lightweight construction materials. The study demonstrates that rice husk can be transformed into high-value raw materials (cellulose and silica), offering a sustainable alternative to traditional reinforcements and reducing the environmental footprint of the fiber-cement industry. Declarations Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding information This work was supported by XXX through the development of this research under project number 924 − 151 in Convocatoria XXXX. Author Contribution DFHR: Conceptualization, methodology, investigation, data curation, formal analysis, writing – original draft, visualization, and supervision.SHP: Validation, investigation support, resources, and writing – review & editing. Acknowledgement Authors acknowledge the Research Unit of the Universidad Autónoma de Manizales for providing the resources for the development of this research under project number 924-151 in Convocatoria Interinstitucional de Investigación y Creación de la Red Mutis. 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Wang, “Flexural Characteristics of Coir Fiber Reinforced Cementitious Composites,” vol. 7, no. 3, pp. 286–294, 2006. Icontec, “NORMA TÉCNICA COLOMBIANA NTC 4373.pdf,” 1997. S. Fernando et al. , “Sustainable Cement Composite Integrating Waste Cellulose Fibre: A Comprehensive Review,” Feb. 01, 2023, MDPI . doi: 10.3390/polym15030520. Additional Declarations Competing interest reported. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9348799","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":628352445,"identity":"81101da1-bed6-4132-8a04-7c4320634bfc","order_by":0,"name":"DANIEL FERNANDO HINCAPIE ROJAS","email":"data:image/png;base64,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","orcid":"","institution":"Universidad Autonoma de Manizales","correspondingAuthor":true,"prefix":"","firstName":"DANIEL","middleName":"FERNANDO HINCAPIE","lastName":"ROJAS","suffix":""},{"id":628352447,"identity":"5bcbe631-3a56-4cd2-a077-8cec00cbdfe9","order_by":1,"name":"Stefania Hurtado Paez","email":"","orcid":"","institution":"National University of Colombia","correspondingAuthor":false,"prefix":"","firstName":"Stefania","middleName":"Hurtado","lastName":"Paez","suffix":""}],"badges":[],"createdAt":"2026-04-07 19:08:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9348799/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9348799/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108116823,"identity":"1b0cbccb-c06b-4ce1-bf32-5a111c18cc0b","added_by":"auto","created_at":"2026-04-29 13:49:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2175788,"visible":true,"origin":"","legend":"\u003cp\u003eThermal analysis profiles a) TGA and DTG of raw RH, b) cellulose microfibers and c) silica particles, SEM Micrographs of (d) raw RH, (e) cellulose microfibers, f) silica particles, XRD Patterns of g) Rice husk and cellulose and h) silica particles.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/b616282c79467eee8db30df6.png"},{"id":108182678,"identity":"b2e7fcb4-f5fa-45f4-bfd0-76ca6159518c","added_by":"auto","created_at":"2026-04-30 08:59:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":891288,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of fiber cement boards at 100x magnification: a) 0.0%, b) 3.0%, c) 6.0%, d) 9.0% cellulose addition, and e) 12.0% cellulose addition.\u003c/p\u003e","description":"","filename":"Figure2.SEMFibercement100X.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/f47432f004ca8fefa505b926.png"},{"id":108116825,"identity":"1d9cdb2c-95e3-4514-95a1-3dc40eb8406f","added_by":"auto","created_at":"2026-04-29 13:49:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":458920,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of fiber cement boards at 5000X magnification, a) 6.0%, b) 9.0%, and c) 12.0% cellulose addition.\u003c/p\u003e","description":"","filename":"Figure3.SEMFibercemento5000X.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/bf9f80ee95d9ee57d239a7d2.png"},{"id":108182602,"identity":"33fc4bb4-3cac-40a7-b4d9-fde722e48701","added_by":"auto","created_at":"2026-04-30 08:59:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":344685,"visible":true,"origin":"","legend":"\u003cp\u003eDiffractogram of fiber cement with different percentages of cellulose microfibers. P: Portlandite, C: Cellulose, Q: Quartz, CC: Calcite, and A: Alite.\u003c/p\u003e","description":"","filename":"Figure4.XRDFibercement.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/2c70bbe806f2a33e9466d824.png"},{"id":108181815,"identity":"2128181b-67de-4cce-8219-1e8ebbd08af6","added_by":"auto","created_at":"2026-04-30 08:58:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":392434,"visible":true,"origin":"","legend":"\u003cp\u003ea) Resistencia a la flexión, b) Módulo de elasticidad del fibrocemento en función del porcentaje de adición de celulosa\u003c/p\u003e","description":"","filename":"Figure5.MORMOE.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/846c336798a0f560aa9fdb8d.png"},{"id":108182488,"identity":"56eda9b5-3526-457e-a156-ca60c525c901","added_by":"auto","created_at":"2026-04-30 08:59:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":281123,"visible":true,"origin":"","legend":"\u003cp\u003ea) Density and b) Water absorption of fibercement composites.\u003c/p\u003e","description":"","filename":"Figure6.DensityAbsorption.png","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/4a835debcfed943de2b83050.png"},{"id":109249327,"identity":"df8243a3-752b-440c-89bf-14a5ab622272","added_by":"auto","created_at":"2026-05-14 08:48:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4944906,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9348799/v1/3da0556d-f71c-47a3-ae27-639f3046cc3c.pdf"}],"financialInterests":"Competing interest reported. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.","formattedTitle":"Valorization of rice husk-derived cellulose microfibers as sustainable reinforcement in fiber-cement composites through mechanical and microstructural analysis","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFibercement (FC) is a material widely used in the construction industry specially in lightweight systems [1]. Currently urban buildings must be more resistant, durable, lightweight, lower costs, need faster installation times [2] and generate the least possible energy expenditure [3]. FC is a material composed of cement, silica, aluminum hydroxide and reinforced with fibers, which is cured in air that usually takes \u003cem\u003e28\u003c/em\u003e days under conditions of ambient temperature, pressure and humidity. FC is characterized by low permeability, low density [4], low thermal conductivity, low shrinkage, thermal and/or acoustic insulation capacity, high heat resistance and transpiring properties [5]. The addition of fibers in the cementitious matrix has a positive impact on properties such as resistance to bending, cracks, impact, durability; and the results show that the addition of these fibers can improve the toughness and ductility of this material [6].\u003c/p\u003e \u003cp\u003eIn recent years there has been a growing interest in the use of natural fibers such as wood and cellulose fibers, they are considered sustainable materials due to their rapid bio-renewability and biodegradability [7]. As a consequence of the hydrophilic and hygroscopic nature of vegetable fibers, they are considered good candidates for hydraulic matrices such as cement [8]. Some fibers used traditionally in industry (steel fibers, glass fibers, polymer fibers) have higher costs [6], it means that natural fibers obtained from renewable sources are considered as flashy substitutes for reinforcing material [9]. Additionally, the ecological aspects are taken into consideration to produce ecofriendly construction materials obtained from agricultural and forest wastes. The valorization of by-products in construction industry has increasingly attracted the attention from researchers, governments as well as industries [10]. For example, using rice husk as a natural source of cellulose microfibers in a cement-based matrix brings a lot of number of positive aspects [11]. Rice husk (RH) is a residue of production and refinement in this agricultural industry and is one of the highest lignocellulosic biomass, about 20% of the volume of the grain after milling corresponds to husk, it means that around 148\u0026nbsp;million tons of RH are generated each year [12], [13]. Depending on the characteristics, morphology, and crystallinity of the cellulose fraction of RH, it can be used as a filler or for reinforcing materials in cellulose and cement-based materials [14]. Cellulose microfibers have excellent mechanical properties, which can reach up to an elastic modulus of \u003cem\u003e200 GPa\u003c/em\u003e (higher than glass fibers of \u003cem\u003e65 GPa\u003c/em\u003e), a tensile strength of \u003cem\u003e7.5 GPa\u003c/em\u003e. [15] and they also have a high surface area [16], [17]. Cellulose microfibers have applications that include the reinforcement of composite materials, thin film manufacturing, food packaging materials, aerosols, biomedical products, stabilizers for aqueous suspensions, and also as a raw material for the development of electronic components [18].\u003c/p\u003e \u003cp\u003eIn the literature there are different reports on the mechanical properties, microstructure and durability of cement composites reinforced with cellulose fibers and manufactured by the Hatschek process. It is a semi-continuous process comprised of three steps: sheet formation, board formation, and curing [11]. The results of some investigations are focused on the mechanical properties of cement-based materials without delving into the interactions between cellulose fibers and cement particles and without determining how these interactions have an important effect on cement-based compounds [19]. Parveen et al.[15] showed in their study that the addition of cellulose microfibers improves the mechanical properties and the degree of hydration of the cement paste. The properties of the cement mortar with an addition of \u003cem\u003e0.3%\u003c/em\u003e by weight were comparable to those of the mortar without fibers. Nilsson et al.,[20] prepared Portland cement mortars with \u003cem\u003e0.11, 0.22 and 0.33 wt.%\u003c/em\u003e of recycled cellulose microfibers from the paper industry, in this research they characterized the changes in the viscosity of the mixture in the fresh state, changes in the mechanical properties and capillarity properties and absorption of the material in the hardened state. They determined that microfibers modify the rheology of the material, affecting the mechanical properties and concluded that they have a positive effect on water absorption, since microfibers modify the pore structure in cement mortars. Seongwoo Gwon et al.,[21] added cellulose microfibers in a proportion from \u003cem\u003e0.3\u0026ndash;2.0%\u003c/em\u003e with respect of to the amount of cement, they determined that adding cellulose has a positive effect on the mechanical properties of the material and they determined that the optimal percentage of addition was \u003cem\u003e1%\u003c/em\u003e. Mohamed et al.,[22] studied the effect of adding microcellulose in a compacted concrete mixture. They determined that adding fibers by \u003cem\u003e21 wt/v.%\u003c/em\u003e increased compressive strength and flexural strength after \u003cem\u003e7\u003c/em\u003e days of curing in air.\u003c/p\u003e \u003cp\u003eIt is observed that there are differences between the percentages of addition of cellulose microfibers used in the various studies and some of these are focused on mortars or concrete, not specifically on fiber-reinforced cement. Another drawback associated with the use of vegetable fibers is the degradation of the fiber constituents (lignin and hemicellulose) and reduction of the degree of polymerization in the alkaline environment of the matrix and the bonding between the individuals\u0026rsquo; fibers [23], [24]. According to the different bibliographic sources, there are not enough studies that focus on analyzing the effect of the addition of cellulose microfibers in cementitious compounds for industrial applications and it is also not clear what is the maximum weight content of cellulosic fibers that can be incorporated into the composites [25]. On the other hand, some studies have shown that the presence of calcium hydroxide (Portlandite) in the cementitious matrix degrades the fibers due to the alkaline environment to which they are exposed which leads to a loss of the durability of this compound [26]. The mineralization of the fibers is caused by the migration of hydration products to the lumen and the pores of the fibers, in addition to the volume variation of the fibers due to their high water absorption. The extent of the attack will depend on the type of fiber, the composition of the cementitious matrix, the level of porosity in the matrix and the aging conditions of the material. Mohr et al. [27] established the following sequence of damages that occur to the fibers as a consequence of the aging of the matrix: a) loss of adherence between the fibers and the matrix; b) reprecipitation of the hydrated compounds within the void space in the old asbestos-cement interface and c) complete mineralization, and therefore the embrittlement of plant fibers.\u003c/p\u003e \u003cp\u003eThe objective of this work is to analyze the effects of the inclusion of different percentages of addition of cellulose microfibers (0.0, 3.0 6.0, 9.5 and 12.0%wt.) on the flexural strength, the modulus of elasticity, the density and the absorption of the fibers. fiber cement plates, to evaluate the effect of the inclusion of these fibers in the composite material. Additionally, a statistical analysis will be carried out by means of the Tukey comparison test to determine if there are significant differences in the different percentages of cellulose added on the properties of the material.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003eThe procedure followed to cellulose microfibers from rice husk and to manufacture the FC boards is described below. In addition, each of the characterization steps carried out on FC boards and the statistical analyses carried out with the results obtained from the design of experiments are described.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eRice husk was obtained from Tolima, Colombia. Sodium hydroxide (Panreac 99% purity) was used for alkaline treatment. Sodium hypochlorite and acetic acid were used as bleaching agents (from Todo Qu\u0026iacute;micos, Caldas, Colombia S.A.S.). All chemicals were of analytical grade and used without further purification. Ordinary Portland cement (OPC) type III produced by Cementos Argos, Colombia S.A. was used to prepare the fibercement boards, with a surface area (Blain) of 420 m\u003csup\u003e2\u003c/sup\u003e/kg and density aproximatelly 3129 kg/m\u003csup\u003e3\u003c/sup\u003e. The bentonite was purchased from Bentucol SAS, the silicon dioxide (\u003cem\u003e\u0026micro;-SiO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e) from Pulverizar S.A. Manizales and aluminum hydroxide (\u003cem\u003eAl(OH)\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e) in Spot Training. An ether-based polycarboxylic acid superplasticizer additive was used to promote the compaction and workability of the cementitious matrix during the manufacturing process. The chemical composition of the OPC used in this research is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of Ordinary Portland Cement\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinerals\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eContent (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{S}\\varvec{i}\\varvec{O}}_{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{C}\\varvec{a}\\varvec{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e64.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{K}}_{2}\\varvec{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{P}}_{2}{\\varvec{O}}_{5}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{M}\\varvec{g}\\varvec{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{A}\\varvec{l}}_{2}{\\varvec{O}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{M}\\varvec{n}\\varvec{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{F}\\varvec{e}}_{2}{\\varvec{O}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{S}{\\varvec{O}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{a}}_{2}{\\varvec{O}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOtros\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFire losses\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFree lime\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Obtaining cellulose and silica from rice husk\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Cellulose extraction from rice husk\u003c/h2\u003e \u003cp\u003eThe extraction of cellulose fibers from HR was carried out on the basis of the methodology of previous research by Hincapi\u0026eacute;-Rojas et al [28]. Briefly, alkali treatment purified cellulose by removing hemicellulose and lignin from HR. The ground rice husk was treated with an 8 wt% NaOH alkali solution. The mixture was transferred to a round bottom flask and the treatment was carried out at reflux for 2 h at 100\u0026deg;C. The solid was then filtered and washed to a pH of 7. The paste obtained was dried at 50\u0026deg;C for 24 h. After the alkali treatment, the bleaching process of alkali-treated was completed using a buffer solution of 1.47% acetic acid, aqueous chlorite (1.7% by weight) and distilled water at reflux for 1 h at 70\u0026deg;C. The mixture was allowed to cool to room temperature and filtered with an excess of distilled water until the filtrate was colourless and a pH of 7 was obtained. The bleaching process was repeated twice until a completely white cellulose was obtained.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Silica extraction from rice husk\u003c/h2\u003e \u003cp\u003eThe power with a high silica content was obtained according to the methodology proposed by Hincapie-Rojas et al. in a previous work [29]. Briefly, RH was washed to remove impurities. It was then dried in a conventional oven at 100 \u0026ordm;C for 3 h. The RH was then incinerated in a furnace to remove the organic materials and to reduce the carbonaceous materials in order to obtain the ash. A solution of nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e) was prepared at 1.0 M in order to remove the impurities by means of the chemical reaction between the acid and the inorganic impurities. These reacted metals are leached from the acidic solution during filtration. After leaching, a white powder rich in silica was obtained.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Processing of fibercement specimens\u003c/h2\u003e \u003cp\u003eCement, water, cellulose fibers, bentonite, silicon dioxide and aluminum hydroxide were precisely mixed according to \u003cem\u003eASTM C-305 Standards\u003c/em\u003e [30], until obtaining a homogeneous and moldable paste. The water/cement ratio \u003cem\u003e(w/cm)\u003c/em\u003e was kept at a constant value and equal to \u003cem\u003e0.4\u003c/em\u003e [14]. After the mixing process, the specimens were compacted into prisms with dimensions of \u003cem\u003e150 mm x 200 mm x 10 mm\u003c/em\u003e according to ASTM C-78-09: \u003cem\u003eStandard Test Method for Flexural Strength of Concrete Using Simple Beam with Third-Point Loading\u003c/em\u003e [31]. The samples were cured under laboratory conditions (temperature of \u003cem\u003e25\u0026thinsp;\u0026plusmn;\u0026thinsp;2 \u0026ordm;C\u003c/em\u003e and \u003cem\u003e65\u0026thinsp;\u0026plusmn;\u0026thinsp;5%\u003c/em\u003e humidity relative) for \u003cem\u003e28\u003c/em\u003e days. Finally, the characterization of the specimens was carried out. Five formulations were elaborated, the first one corresponds to the control sample (without cellulose) and the other \u003cem\u003e4\u003c/em\u003e with different percentages of addition of microfibers cellulose defined as \u003cem\u003e3.0, 6.0, 9.0 and 12.0 %wt.\u003c/em\u003e repectively. These variations were proposed to evaluate the effect of the inclusion of the fibers on the physical and mechanical properties of the FC. For this study, the amount of cellulose microfibers was calculated with respect to the total weight of the sample, and the specimens were labeled as \u003cem\u003eC0.0, C3.0, C6.0, C9.0\u003c/em\u003e and \u003cem\u003eC12.0\u003c/em\u003e according to the percentage of cellulose addition, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization of cellulose microfibers and silica from rice husk and fibercement-based composites\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Thermogravimetric analysis of rice husk fibers\u003c/h2\u003e \u003cp\u003eTo evaluate the thermal stability of the raw materials, thermogravimetric analysis (TGA) and differential thermal analysis (DTGA) were performed using a TGA Q500 instrument (TA Instruments, USA). Samples were heated at a rate of 10\u0026ordm;C/min from room temperature to 700\u0026ordm;C. All measurements were performed in an air atmosphere at a gas flow rate of 50 mL/min. The data were processed using Universal Analysis 2000 TA software. The maximum rate of reaction and the mass lost were determined from the peak in the derivative curve (DTGA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 Morphological analysis by Scanning Electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eA high vacuum scanning electronic microscope JEOL JSM-5910 LV was used with 10.00\u0026ndash;15.00 kV electron acceleration voltage. The morphology of cellulose microfibers, silica and also the main hydrated products from fibercement-based composites with different percentages of cellulose was analyzed. Before the analysis the samples were fixed on copper specimen held on carbon adhesive tape. A gold layer (\u003cem\u003e30 nm\u003c/em\u003e of thick approximately) was deposited by sputtering on samples to make them conductive.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3 Structural analysis by X-ray diffraction (XRD)\u003c/h2\u003e \u003cp\u003eThe structure of cellulose fibers, silica and phases presents in fibercement added with different proportions of microcellulose fibers were identified using a RIGAKU diffractometer equipment, MINIFLEX II operated at room temperature, equipped with a Cu Kα radiation source (\u003cem\u003eλ\u0026thinsp;=\u0026thinsp;1.540562 \u0026Aring;\u003c/em\u003e), and a \u003cem\u003e30 kV\u003c/em\u003e and \u003cem\u003e15 mA\u003c/em\u003e X-ray source. Measurements were run between \u003cem\u003e5\u0026ordm;\u003c/em\u003e and \u003cem\u003e70\u0026ordm;\u003c/em\u003e on a \u003cem\u003e2θ\u003c/em\u003e scale with a step size of \u003cem\u003e0.02\u0026ordm;/s\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.3.4 Mechanical characterization of fibercement specimens\u003c/h2\u003e \u003cp\u003eMechanical tests of fibercement composites with different content of cellulose microfibers at 28 days of curing were performed on a UNITED uniaxial universal testing machine, with a maximum load capacity of 100 kN. The bending strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left({\\sigma\\:}_{bend}\\right)\\)\u003c/span\u003e\u003c/span\u003e and modulus of elasticity \u003cem\u003e(E)\u003c/em\u003e of the boards was determined using the three-pointed method according to \u003cem\u003eASTM C-133-97\u003c/em\u003e [32]. The specimens were placed on two parallel supports separated by a distance of 150 mm (spam). The load was applied parallel to the supports at a constant speed of \u003cem\u003e0.05 kN/s\u003c/em\u003e. Using Eqs.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e[32] and with \u003cem\u003eProteus Versi\u0026oacute;n 14.1.0\u003c/em\u003e of the \u003cem\u003eUniversal Testing Machine, the\u003c/em\u003e bending strength (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\sigma\\:}_{bend}\\)\u003c/span\u003e\u003c/span\u003e) and the deformation \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(\\epsilon\\:\\right)\\)\u003c/span\u003e\u003c/span\u003e of FC was calculated. The modulus of elasticity was calculated as the slope of the stress-strain curve (in the elastic zone) for each sample. The analyzes were performed in quadruplicate and the mean and standard deviation of each variable were calculated.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{\\sigma\\:}_{bend}=\\frac{3WL}{2b{d}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:\\epsilon\\:=\\frac{6db}{{L}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eW\u003c/em\u003e is the fracture load, \u003cem\u003eL\u003c/em\u003e is the distance of the bar between the two supporting edges (spam), \u003cem\u003eb\u003c/em\u003e is the width of the sample, and \u003cem\u003ed\u003c/em\u003e is the sample depth at the fracture plane.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.3.5 Dry bulk density, water absorption of FC composites\u003c/h2\u003e \u003cp\u003eThe dry apparent density and water absorption indexes of the compound were determined according to \u003cem\u003eASTM C-830 00 standards\u003c/em\u003e [33]. After the mechanical analysis, 4 samples of each formulation were removed in an oven at 100\u0026ordm; C for \u003cem\u003e24 h\u003c/em\u003e and subsequently immersed in water for another \u003cem\u003e24 h\u003c/em\u003e. The weight of each sample was recorded at each step as oven dry (dry weight), saturated mass after immersion (wet weight), and mass under water (apparent weight). Therefore, the dry bulk density \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e and water absorption \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{w}\\)\u003c/span\u003e\u003c/span\u003e were determined by equations 3 and 4 respectively [34].\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\rho\\:=\\frac{dry\\:weight\\:}{wet\\:weight-apparent\\:weight}*{\\rho\\:}_{w}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{A}_{w}=\\frac{wet\\:weight\\:-\\:dry\\:weight}{dry\\:weight}*100\\:\\%\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(3\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{w}\\)\u003c/span\u003e \u003c/span\u003e represents the density of water, taken as 1 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.3.6 Statistical analysis of the variables established for the experimentation with fibercement boards\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eStatistical analysis was performed to correlate the results of the independent and dependent variables considering in the manufacture of the FC samples. The independent variable was the variation of mixing percentage of cellulose microfibers at three levels 0.0, 3.0%, 6.0%, 9.5%, and 12.0% wt. A randomized, replicated (1 original\u0026thinsp;+\u0026thinsp;3 replicates), single block experiment was conducted. The following response variables were used: modulus of elasticity, bending strength, dry bulk density, and water absorption. An analysis of variance (ANOVA) with 95% confidence with only one factor (content of cellulose) was conducted. ANOVA was verified to comply with the assumptions of normality of residuals, homoscedasticity of residuals, and independence of data. Minitab\u0026reg; software versi\u0026oacute;n19 was used for the statistical analysis.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Thermal, morphological and structural characterization of raw materials from rice husk: Cellulose microfibers and silica nanoparticles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo investigate the thermal stability of raw RH and chemically treated rice husk fibers (microcellulose fibres), thermogravimetric analysis was carried out. The weight changes that occurred during the combustion of RH are shown by the TGA curve shown in \u003cstrong\u003eFigure 1a\u003c/strong\u003e, and the differential thermal analysis DTGA is also shown as an insert in each graph. The DTGA curve shows that the raw RH is decomposed in three stages. Stage 1 (25-140\u0026deg;C) involves the removal of moisture; stage 2 and stage 3, which occur in the temperature range of 155-350\u0026deg;C and 350-550\u0026deg;C respectively, involve organic compounds (hemicellulose, cellulose and lignin) and their decomposition\u0026nbsp;[35]. Finally, after 550 \u0026deg;C, the mass remained stable. The residual ash is 25.57% and consists mainly of silica SiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 1b\u003c/strong\u003e shows the thermal analysis profile of cellulose microfibres. Two thermal degradation steps were observed in the decomposition of treated RH. Stage 1 is associated with weight loss due to moisture and evaporation of water due to the hydrophilic nature of lignocellulosic material at 30\u0026ordm;C - 130\u0026ordm;C [17]. In this case, 8.21% of the total weight of the sample was removed. The second stage is associated with the decomposition of cellulose and hemicellulose [36]. The mass loss in this range is approximately 70.03%, which is higher than the decomposition recorded for the raw RH (40.05%), indicating that components other than cellulose have been removed during the chemical treatment. In stage 2, higher mass loss at this stage is associated with high cellulose content in the fibers. Additionally, the onset in this stage was increasing at higher temperatures for the analysed samples. It started at 147.09 \u0026deg;C for RH and increased to 200.68 \u0026deg;C for the bleached husk, as seen in the DTG (see insert at the right-up position of each graph) curves in \u003cstrong\u003eFigure 1 a, b.\u0026nbsp;\u003c/strong\u003eThis phenomenon can be explained by the removal of non-cellulosic components that are subject to degradation at lower temperatures. These results are consistent with those obtained in other studies \u003cspan lang=\"EN-US\"\u003e[37]\u003c/span\u003e. Stage 3 is characterised by the loss of lignin over 350 \u0026ordm;C, with a 5.0% reduction in the total weight of the sample. This decomposition is lower than that recorded in the RH, suggesting a reduced presence of lignin in the sample due to the chemical treatment. Furthermore, the intensity of the peak associated with the decomposition of lignin in the DTGA curve (\u003cstrong\u003eFigure 1b\u003c/strong\u003e) was observed to be lower in comparison to that of the RH curve (\u003cstrong\u003eFigure 1a\u003c/strong\u003e). The residue obtained was also found to be lower, with a percentage of 9.07%, indicating that the majority of inorganic components had also been removed during the chemical process (mainly silica). In addition to weight loss, the temperature decomposition peak for treated RH was higher in comparison to raw RH. Similar results were reported by Shailendrakumar et al., [38]. From the thermogram in \u003cstrong\u003eFigure 1c\u003c/strong\u003e, it can be seen that the silica obtained from rice husk had no mass loss during heating, this indicates the stability of this material.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe chemical treatments used for cellulose purification from RH are also expected to induce morphological changes on the surface of the rice husk fibers. The structure of RH fibers was investigated by comparing the SEM micrographs (\u003cstrong\u003eFigure 1 d-e)\u003c/strong\u003e. The rice husk micrograph shows a high level of structural organization and uniformity, featuring a smooth, flat surface resembling unidirectional sheets (\u003cstrong\u003eFigure 1d\u003c/strong\u003e). The non-cellulosic components are distributed across the entire surface, acting as a protective layer while preserving the overall structure, and hemicelluloses and lignin form a matrix that encapsulates the cellulose. The typical structure of the material includes cellular spaces coated with pectin, silica, and waxes, which at the extremities tend to cluster into spherical and spongy agglomerates. Ridge-like linear grooves are formed on the surface of rice husk fibers by densely coated silica crystals. These grooves contribute to the overall rigid texture of the material and this crystalline silica is the principal cause of its roughness [39]. As shown in \u003cstrong\u003eFigure 1e,\u003c/strong\u003e the initial bleaching process results in cellulose microfibers with a cylindrical shape and a cotton-like texture. This treatment effectively removes non-cellulosic components, yielding fibers with diameters ranging from 4 to 12 \u0026mu;m. The bleaching process involves the use of sodium hypochlorite, which cleaves lignin\u0026apos;s aromatic rings through oxidation, and acetic acid, which regulates the pH level. These findings align with previous studies indicating that sodium hydroxide treatment enhances bleaching efficiency by increasing the exposed surface area of the fibers [40].\u003c/p\u003e\n\u003cp\u003eThe addition of cellulose fibers to cement-based composites enhances mechanical properties, reduce crack propagation, and improve durability, as will be shown below.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 1f\u003c/strong\u003e shows the morphology of the silica extracted from the rice husk reveals irregularly shaped particles, possibly with a porous distribution. The silica particles are found to be sub-metric in size, with a size distribution between 1 and 10 microns, and an average size of about 0.57 \u0026micro;m. The presence of a heterogeneous size distribution indicates the possibility of smaller primary particles and agglomerations originating from electrostatic forces \u003cspan lang=\"EN-US\"\u003e[41]\u003c/span\u003e.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXRD was used to evaluate the changes in the structure and to determine the crystallinity indices (CrI) of the fibers extracted from the rice husk after applying the two chemical treatments. \u003cstrong\u003eFigure 1g\u003c/strong\u003e shows the diffraction patterns of the three samples analyzed. The diffractogram of cellulose shows three peaks at 2\u0026theta; = 15\u0026deg;-17\u0026deg;, 22.5\u0026deg; and 35\u0026deg;. These three peaks are characteristic of the cellulose type I allomorphism and are attributed to crystallographic planes (110), (200) and (004), respectively, with the peak of highest intensity at 2\u0026theta; = 22.47\u0026deg;. These results are in agreement with those reported by Sabapathi et al., \u003cspan lang=\"EN-US\"\u003e[42]\u003c/span\u003e. In addition, the peaks become narrower and sharper as the chemical treatments are applied. The crystallinity index (CrI) is a parameter that indicates changes in their structure due to such treatments. This value was calculated according to the method proposed by Segal et al., \u003cspan lang=\"EN-US\"\u003e[43]\u003c/span\u003e. The crystallinity index was 38% and 64% for rice husk and cellulose microfibres respectively. These results are in agreement with those of Bhandar et al., \u003cspan lang=\"EN-US\"\u003e[44]\u003c/span\u003e. These results show that chemical treatments increase the value of the crystallinity index due to the partial removal of amorphous components such as lignin and hemicellulose present in rice husk.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 1h\u0026nbsp;\u003c/strong\u003eshows the diffraction pattern of the silica extracted from the rice husk, which clearly identifies the silicon oxide phase as the predominant phase. The location of these peaks is also indicated, along with other phases with lower intensity that correspond to impurities found in the silica, such as phosphorus, sodium and aluminium-based oxides. The results were compared with \u003cem\u003ePDF #39-1425\u003c/em\u003e of silicon oxide, the unit cell of which is tetragonal and corresponds to the crystalline system of cristobalite. The addition of crystalline silica to cement-based composites has a positive effect on the mechanical, barrier and durability properties of these materials. In addition, its use contributes to sustainability by reducing clinker content and taking advantage of silica-rich industrial by-products.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Characterization of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFibercement composites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.1 Morphological characterization by SEM\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo better understand the results obtained in this study, SEM images at lower magnification are shown first (see \u003cstrong\u003eFigure 2\u003c/strong\u003e), where the interactions between the cementitious matrix and the cellulose microfibers are evident. Subsequently, micrographs obtained at higher magnification are shown to identify the typical hydration products of FC (see \u003cstrong\u003eFigure 3\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 2\u003c/strong\u003e shows micrographs of fiber cement boards at 100X magnification with the different percentages of cellulose addition detailed in the methodology section. When comparing the five samples, some differences can be observed in terms of matrix-fiber interaction.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn \u003cstrong\u003eFigure 2a\u003c/strong\u003e, which corresponds to the fiber cement sample without cellulose addition \u003cem\u003eC0.0\u003c/em\u003e, it can be seen that the surface of the cementitious matrix is more homogeneous and denser, with some isolated microcracks and a more compact microstructure, without the presence of fibers. In \u003cstrong\u003eFigure 2b\u003c/strong\u003e, which corresponds to sample \u003cem\u003eC3.0\u003c/em\u003e (3.0% cellulose addition), microfibers begin to be observed distributed relatively uniformly over the cementitious matrix. These fibers appear to be well adhered to the matrix, with visible interface areas. The presence of microspaces around some fibers is also observed, possibly due to shrinkage of the material during drying or curing. In \u003cstrong\u003eFigure 2c\u003c/strong\u003e, which corresponds to sample \u003cem\u003eC6.0\u003c/em\u003e (6.0% cellulose addition), a greater number of visible fibers distributed throughout the surface and with better interconnection within the matrix is evident. The fiber-matrix interfaces are more defined, although slight separation is noticeable in some areas. An increase in local porosity is also observed, as well as in the stress redistribution capacity. In \u003cstrong\u003eFigure 2d\u003c/strong\u003e, which corresponds to sample \u003cem\u003eC9.0\u003c/em\u003e (9.0% cellulose addition), the micrograph shows a more abundant and dense distribution of fibers compared to the previous samples. The analyzed surface presents an interconnected network that generates an effective bond and reinforces the cementitious matrix. Although the fiber content has increased, the fibers continue to integrate adequately with the other components of the fiber cement, the fibers are homogeneously distributed in the matrix, and also the fibers have a partly lamellar structure. Additionally, a controlled increase in porosity is observed, which may be associated with better absorption and dissipation of energy under mechanical stress, favoring the toughness of the material, as will be shown later. Similar results were reported by Lavasani et al. \u003cspan lang=\"EN-US\"\u003e[45]\u003c/span\u003e. In their research on the effect of fibers in asphalt matrices, they highlight that fibers allow for excellent crack bridging and stress distribution in the material. Finally, in \u003cstrong\u003eFigure 2e,\u003c/strong\u003e which corresponds to sample \u003cem\u003eC12.0\u003c/em\u003e (12.0% cellulose addition), the morphology of the cementitious matrix appears less compact, with more abundant and disordered fibers. The image shows larger voids and fiber-matrix separation, which could decrease the overall mechanical strength of the fiber cement. An increase in porosity and possible formation of microchannels can be observed. A greater increase in fiber content can lead to a loss of uniformity in the fiber cement, affecting its structural performance.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAt this magnification scale, the interconnection between the cementitious matrix and the fibers can be identified. The addition of these reinforcing fibers has an effect on the morphology and other properties of the composite material. A more mechanically resistant material requires adequate bonding between its different components.\u003c/p\u003e\n\u003cp\u003eOn the other hand, \u003cstrong\u003eFigure 3\u003c/strong\u003e shows micrographs of fibercement boards at 5000X magnification of some of the samples analyzed (\u003cem\u003eC6.0, C9.0, and C12.0\u003c/em\u003e). At this magnification scale, it is possible to observe some typical products of fiber cement hydration such as C-S-H (calcium silicate hydrate), CH (calcium hydroxide or portlandite), and ettringite.\u003c/p\u003e\n\u003cp\u003eIn \u003cstrong\u003eFigure 3a\u003c/strong\u003e, corresponding to sample \u003cem\u003eC6.0\u003c/em\u003e, a relatively compact matrix is observed with the presence of C-S-H, visible as a dense, amorphous mass with an irregular and homogeneous texture. Dispersed hexagonal lamellar crystals, typical of calcium hydroxide, are also present. The surface shows low visible porosity, suggesting adequate hydration. Some fine acicular microcrystals were identified that may correspond to ettringite, indicating an active calcium aluminate reaction \u003cspan lang=\"EN-US\"\u003e[46]\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eIn \u003cstrong\u003eFigure 3b\u003c/strong\u003e, corresponding to sample \u003cem\u003eC9.0\u003c/em\u003e, the matrix exhibits a more complex morphology of hydration products, with dense areas of C-S-H intertwined with accumulations of CH crystals that are more visible than in sample \u003cem\u003eC6.0\u003c/em\u003e. There is a greater presence of ettringite in the form of thin needles, indicating a more reactive environment, possibly promoted by the incorporation of cellulose. According to Scrivener et al., \u003cspan lang=\"EN-US\"\u003e[47]\u003c/span\u003e the presence of these intertwined structures and dense layers may be associated with a greater water retention capacity induced by cellulose, which favors secondary hydration. The texture identified in the sample is compact, with less evidence of voids, suggesting a more cohesive microstructure.\u003c/p\u003e\n\u003cp\u003eIn \u003cstrong\u003eFigure 3c\u003c/strong\u003e, corresponding to sample \u003cem\u003eC12.0\u003c/em\u003e, areas of incomplete hydration can be observed, with patches of discontinuous C-S-H and greater visibility of pores or capillary voids. CH crystals appear more abundant and disordered, which may indicate the release of water not used for complete hydration. Ettringite is still present, but with an irregular arrangement, and in some areas, there are signs of cohesion between phases. This sample shows a possible negative effect of excess cellulose, which absorbs water but does not release it efficiently, affecting the continuity of the C-S-H \u003cspan lang=\"EN-US\"\u003e[48]\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eLa tobermorita es uno de los productos de hidrataci\u0026oacute;n m\u0026aacute;s importantes del cemento, y es el responsable de la armaz\u0026oacute;n interna de la pasta de cementicia, de la adherencia de \u0026eacute;sta con los \u0026aacute;ridos en los morteros y tambi\u0026eacute;n de aportar de forma positiva a la resistencia mec\u0026aacute;nica de este material [49].\u003c/p\u003e\n\u003cp\u003eIt should be noted that in samples with 9.0 and 12.0%wt. cellulose added, the typical morphology of the reaction between tobermorite and aluminum hydroxide can be observed. These reactions improve the properties of fiber cement, such as strength and durability. \u0026nbsp;The typical morphology of pure tobermorite is in the form of small laminar crystals. On the other hand, tobermorite with Al substitution exhibits larger ribbon-like crystallites, as shown in \u003cstrong\u003eFig. 2 (b-c)\u003c/strong\u003e \u003cspan lang=\"EN-US\"\u003e[50]\u003c/span\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.2 Structural characterization by XRD\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStructural analysis by XRD is a very important technique for identifying the crystalline structure and main phases in this type of material. It should be noted that structurally characterizing fiber cement is quite complex due to its heterogeneous nature and the presence of multiple phases; for this reason, the patterns show many peaks due to the multiple phases present in it.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 4\u003c/strong\u003e shows the diffraction patterns of the five samples analyzed. The diffractogram identifies the main diffraction peaks of fiber cement. The main phases found were: Portlandite (P), Cellulose (C), Quartz (Q), Calcium Carbonate or Calcite (CC), and Tetracalcium Silicate Alite (A). These phases were identified by quantitative analysis using the diffraction patterns in the PDF2 database as a reference.\u003c/p\u003e\n\u003cp\u003ePortlandite (Ca(OH)) is identified at 2\u0026theta;=18.0\u0026deg;, 34.1\u0026deg;, and 47.1\u0026deg;. This crystalline phase results from the hydration of calcium silicates (alite: C\u003csub\u003e3\u003c/sub\u003eS and belite: C\u003csub\u003e2\u003c/sub\u003eS). The increase in the intensity of the portlandite peak at 2\u0026theta;=18.0\u0026deg; and 47.1\u0026deg; for samples with higher cellulose content suggests a heterogeneous nucleation effect, where microfibers act as heterogeneous nucleation sites for hydration products (ettringite, calcium silicate hydrated C-S-H, and portlandite), accelerating hydration. Likewise, the absorption capacity of cellulose could be favoring an internal curing mechanism, promoting more advanced hydration of the clinker compared to the control sample [51].\u003c/p\u003e\n\u003cp\u003eAs for the peak associated with cellulose around 2\u0026theta;=22.5\u0026deg;, an increase in its intensity and width is observed as the cellulose content in the mixture increases. This peak is characteristic of the (200) plane of Cellulose I with a semi-crystalline structure \u003cspan lang=\"EN-US\"\u003e[52]\u003c/span\u003e The peak around 2\u0026theta;=26.86\u0026deg; corresponds to crystalline quartz originating mainly from the siliceous material used as a filler in the manufacture of the plates. The results show that there are no variations in its intensity, which may indicate that cellulose has no effect on this type of phase.\u003c/p\u003e\n\u003cp\u003eFor the peak located at 2\u0026theta;=29.51\u0026ordm;, corresponding to the (104) plane of calcite (CaCO3), an increase in intensity is observed as the cellulose content increases, reaching its maximum intensity in the sample with C9.0. This phenomenon suggests an accelerated carbonation process, where the cellulose microfiber network acts as a diffusion channel that facilitates the penetration of atmospheric CO₂ into the core of the cementitious matrix during 28 days of air curing. The hygroscopicity of cellulose provides the internal moisture necessary for the dissolution of environmental CO₂, thereby converting Ca(OH)₂ into calcite and densifying the microstructure \u003cspan lang=\"EN-US\"\u003e[53]\u003c/span\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFinally, for the peak at 2\u0026theta;=32.0\u0026ordm;, which corresponds to the anhydrous phases of alite (C\u003csub\u003e3\u003c/sub\u003eS) and belite (C\u003csub\u003e2\u003c/sub\u003eS), a decrease in intensity is observed as the cellulose content increases. This suggests a lower concentration of unreacted C\u003csub\u003e3\u003c/sub\u003eS/C\u003csub\u003e2\u003c/sub\u003eS, indicating a higher degree of clinker hydration and the subsequent formation of more tobermorite-like gel (C-S-H) in the mixtures containing cellulose fibers compared to the control sample. Similar findings were reported bu Wu et al., they study the influence of cellulose fibers from cotton on hydration and microstructure of portland cement\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003epaste [54]. Additionally, the presence of calcium oxide (free lime) was identified at 2\u0026theta;=62.39\u0026ordm;.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.3 Mechanical characterization\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe flexural strength of fiber-reinforced cementitious composites depends on the interaction and physicochemical adhesion between the fiber and matrix, the dispersion and orientation of the fibers, and the resulting microstructure. The appropriate addition of cellulose microfibers can improve the flexural strength of this type of material, especially when the amount and dispersion of the fibers are optimized \u003cspan lang=\"EN-US\"\u003e[55]\u003c/span\u003e. \u003cstrong\u003eFigure 5a and b\u003c/strong\u003e show the flexural strength and modulus of elasticity of the samples as a function of the percentage of cellulose microfiber added after 28 days of curing, respectively. The analyses were performed using an original sample and three replicates. The graph shows the average value and standard deviation.\u003c/p\u003e\n\u003cp\u003eAccording to the results shown in Figure 5a, sample \u003cem\u003eC0.0\u003c/em\u003e has the lowest flexural strength (5.80 MPa). In this type of composite material, the absence of fibers (see SEM in \u003cstrong\u003eFigure 2a\u003c/strong\u003e) means that the material has a lower capacity to control the propagation of microcracks, which implies that the material may be more brittle. Although sample \u003cem\u003eC3.0\u003c/em\u003e shows a 53.62% improvement in flexural strength compared to control sample \u003cem\u003eC0.0\u003c/em\u003e, it is not as significant as the improvement achieved with the other cellulose additions used in this work. According to Xie et al., [7], a small amount of fibers (e.g., 3.0%) may cause them to be unevenly distributed in the cementitious matrix, with some areas of the sample having very little or no fibers, which could lead to initial cracks in these areas.\u0026nbsp;Additionally, it can be observed that as the percentage of cellulose added increases, flexural strength also increases. The maximum value (17.52 MPa) is achieved for sample C9.0, which corresponds to an improvement of 202.07%, 96.63%, 50.9%, and 9.8% compared to samples C0.0, C3.0, C6.0, and C.12. The fibers form a three-dimensional mesh that restricts the propagation of microcracks, acting as effective internal barriers. In sample C9.0, an adequate balance is achieved between fiber quantity, distribution, and internal cohesion in the sample, which is reflected in its mechanical properties [45]. In the sample with the highest cellulose content (\u003cem\u003eC12.0\u003c/em\u003e), a decrease in this value is observed compared to sample C9.0. According to Soares et al., \u003cspan lang=\"EN-US\"\u003e[56]\u003c/span\u003e high fiber contents can cause structural defects and loss of compressive strength due to agglomerations that can be generated in the composite material (see \u003cstrong\u003eFigure 2.e\u003c/strong\u003e)\u0026nbsp;[16].\u003c/p\u003e\n\u003cp\u003eA similar behavior is observed for the modulus of elasticity (MOE) of the samples (see \u003cstrong\u003eFigure 5b\u003c/strong\u003e). Again, sample \u003cem\u003eC0.0\u003c/em\u003e has the lowest modulus of elasticity (3650.3 MPa). Additionally, the maximum MOE value (5804.1 MPa) is obtained for sample \u003cem\u003eC9.0\u003c/em\u003e, in this case achieving an increase of 59.0%, 32.7%, 26.9%, and 6.7% with respect to samples \u003cem\u003eC0.0, C3.0, C6.0\u003c/em\u003e, and \u003cem\u003eC12.0\u003c/em\u003e, respectively. Similar results were reported by Soydan et al., \u003cspan lang=\"EN-US\"\u003e[57]\u003c/span\u003e who evaluated the effect of different types of cellulose fibers on fiber-cement composite mixtures. In this study, they reported flexural strength or modulus of rupture values ranging from 9.76 to 17.57 MPa and modulus of elasticity values ranging from 3790 to 5430 MPa.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe improvement in mechanical strength parameters (MOR and MOE) may be due to the fact that cellulose fibers have a high elastic modulus and form a strong bond within the cementitious matrix \u003cspan lang=\"EN-US\"\u003e[58]\u003c/span\u003e. This gradual increase in the flexural strength of the material is attributed to greater interaction at the matrix-fiber interface (as evidenced in the SEM scanning electron microscopy images shown in section 3.2.1), as well as an improvement in the energy absorption capacity of the composite against fracture (toughness). This factor allows the mechanical behavior of the material to be evaluated under real conditions when subjected to static, dynamic, or fatigue loads \u003cspan lang=\"EN-US\"\u003e[59]\u003c/span\u003e. This improvement is also related to the increase in the degree of hydration in the cementitious matrix, since cellulose microfibers have a high-water retention capacity due to their hydrophilic and hygroscopic nature \u003cspan lang=\"EN-US\"\u003e[16]\u003c/span\u003e. In this process, cellulose acts as an internal water reservoir within its fibrillar network, attracting calcium ions (Ca\u0026sup2;⁺) through electrostatic interactions with its anionic surfaces. Additionally, water molecules diffuse more easily and quickly within the cellulose network compared to the surrounding matrix. These combined effects accelerate the formation of calcium silicate hydrate (C-S-H) gel at the fiber-matrix interface during hydration. As a result, hydration products accumulate at this interface, strengthening the physical bond between the fibers and the matrix, which improves mechanical strength and reduces fiber pull-out [60]. These results are consistent with those reported by G\u0026oacute;mez et al. \u003cspan lang=\"EN-US\"\u003e[61]\u003c/span\u003e and Xie et al. \u003cspan lang=\"EN-US\"\u003e[6]\u003c/span\u003e, who demonstrate that the addition of cellulose microfibers has a positive effect on the strength of cement-based composites. The use of cellulose as a reinforcing additive in the production of fiber cement contributes to: (1) improving mechanical properties such as bond strength, MOE, and MOR; (2) modifying the rheology of the paste; (3) reducing porosity; and (4) enhancing interactions with other components of the mixture. Cellulose improves bond strength and enhances hardening, mainly after 7 days; reduces fiber pull-out and shrinkage (especially autogenous shrinkage during setting, reducing the risk of product loss); and reduces both porosity and thermal expansion \u003cspan lang=\"EN-US\"\u003e[25]\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe reinforcement does influence the modulus of rupture and modulus of elasticity rupture (\u003cem\u003ep\u003c/em\u003e-value\u0026lt;0.05) compared to the reference.\u003c/p\u003e\n\u003cp\u003eThese results corroborate those previously presented in the XRD analysis (\u003cstrong\u003eFigure 4\u003c/strong\u003e). The increase in the intensity of the calcite peak, observed especially in sample \u003cem\u003eC9.0\u003c/em\u003e, may be related to an increase in the carbonation process facilitated by the microfiber network. The precipitation of these calcite crystals acts as a densification mechanism in the Interfacial Transition Zone (ITZ) between the cellulose microfiber and the cement matrix, which generates superior mechanical anchoring, increasing interfacial friction and optimizing stress transfer during flexural loading. \u0026nbsp; Cellulose acts as an agent that modifies the curing kinetics and crystalline structure of the matrix, favoring a mineralogical configuration (rich in calcite and quartz) that maximizes the strength of fiber cement. On the other hand, portlandite crystals may be forming in greater proportion directly on the surface of the cellulose fiber (which can be corroborated by XRD analysis, especially for sample \u003cem\u003eC9.0\u003c/em\u003e). This creates better chemical and physical anchoring in the cementitious matrix, and the transfer of mechanical stresses from the matrix to the fiber is more efficient, increasing its toughness [62].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.4 Dry bulk density and water absorption values\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 6\u003c/strong\u003e shows that the addition of cellulose microfibers slightly decreases the density values of the fibercement composites with respect to the control sample (C0.0). This is because the density of cellulose (1500 kg/m\u003csup\u003e3\u003c/sup\u003e) is much lower than that of cement (3129 kg/m\u003csup\u003e3\u003c/sup\u003e), so adding more of these fibers is expected to result in a much lighter and more porous material \u003cspan lang=\"EN-US\"\u003e[63]\u003c/span\u003e. Cellulose microfibers have a porous structure, which allows greater water entry into these pores and into their hydrophilic structure, causing an increase in the absorption of the matrix [34]. The density and absorption results are within the standardized values in the NTC 4373 standard for cement \u003cspan lang=\"EN-US\"\u003e[64]\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe fit line obtained from the linear regression of these values was also included in the graph. The intercept of the equation, whose value is 1.451 g/cm\u003csup\u003e3\u003c/sup\u003e, represents the density of the composites without the addition of cellulose microfibers. On the other hand, the slope of the fit line, (-0.016 g/cm\u003csup\u003e3\u003c/sup\u003e/%), indicates the value at which the density of the fibercement decreases for each 1% addition of cellulose. Similars results were reported by Soydan et al., [57]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 6b\u003c/strong\u003e also shows the absorption values in the samples. It was observed that a higher percentage of addition of cellulose, implied increases in the absorption. Additionally, a major increase in the absorption of the samples \u003cem\u003eC9.0\u003c/em\u003e and\u003cem\u003e\u0026nbsp;C12.0\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast to the decreasing trend observed in density, water absorption in fibercement composites increases proportionally to cellulose content. The presence of a dense network of hydroxyl (-OH) groups on the surface of cellulose facilitates the formation of hydrogen bonds with water molecules, promoting a chemical affinity for moisture [65]. The incorporation of higher percentages of fiber alters the morphology of the cementitious matrix by introducing a network of capillary porosity and interstitial spaces at the fiber-matrix interface that act as water transport conduits as can be seen in SEM images (Figure 2 d-e).\u003c/p\u003e\n\u003cp\u003eThe trend line obtained by a linear fit to absorption values was also presented in the graph. The intercept of equation (22.108%) represents the absorption of the samples without cellulose. On the other hand, the slope (1,137%) represents the increase in the absorption of the samples for each 1% of cellulose addition. All calculated density and absorption results are in agreement with NTC 4694-D8 (Norma T\u0026eacute;cnica Colombiana).\u003c/p\u003e\n\u003cp\u003eSimilarly to the mechanical properties, the reinforcement influences the density and water absorption values (\u003cem\u003ep\u0026lt;0.05\u003c/em\u003e) compared to the control sample \u003cem\u003eC0.0\u003c/em\u003e.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe experimental results identify 9.0% wt. as the critical threshold for reinforcement efficiency within the cementitious matrix. At this concentration, the distribution of microfibers reaches a state of spatial saturation that maximizes crack-bridging mechanisms without compromising the continuity of the cement paste. Below this level, the fiber density is insufficient to effectively intercept and arrest micro-crack propagation under mechanical stress.\u003c/p\u003e \u003cp\u003eThe microstructural analysis showed that cellulose microfibers function as internal curing agents. Due to the presence of hydroxyl groups, these fibers absorb significant amounts of water during the mixing phase. As the bulk cement hydration progresses and consumes the surrounding moisture, the fibers gradually release their stored water back into the Interfacial Transition Zone (ITZ). This localized humidity facilitates a more complete secondary hydration of anhydrous cement particles, leading to a denser and more homogenous growth of C-S-H gel directly onto the fiber surface. This hydration product strengthens the interfacial bond increasing the strength of the composite.\u003c/p\u003e \u003cp\u003eIncorporating cellulose microfibers leads to a improvement in mechanical performance, increasing the modulus of rupture from 5.80 MPa to over 17 MPa (+\u0026thinsp;193.10%) and the modulus of elasticity from 3650.30 MPa to over 5800 MPa (+\u0026thinsp;59%) compared to the control sample when the cellulose content was 9.0%.\u003c/p\u003e \u003cp\u003eThe physical properties of cellulosic fibers reinforced cement-based composites are influenced by the content of fibers. The porosity and water absorption increase with increase of fiber content, but the bulk density decreases. While this facilitates the production of lightweight construction materials.\u003c/p\u003e \u003cp\u003eThe study demonstrates that rice husk can be transformed into high-value raw materials (cellulose and silica), offering a sustainable alternative to traditional reinforcements and reducing the environmental footprint of the fiber-cement industry.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003ch2\u003eFunding information\u003c/h2\u003e\n\u003cp\u003eThis work was supported by XXX through the development of this research under project number 924\u0026thinsp;\u0026minus;\u0026thinsp;151 in Convocatoria XXXX.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eDFHR: Conceptualization, methodology, investigation, data curation, formal analysis, writing \u0026ndash; original draft, visualization, and supervision.SHP: Validation, investigation support, resources, and writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eAuthors acknowledge the Research Unit of the Universidad Aut\u0026oacute;noma de Manizales for providing the resources for the development of this research under project number 924-151 in Convocatoria Interinstitucional de Investigaci\u0026oacute;n y Creaci\u0026oacute;n de la Red Mutis. We also thank Minciencias that, under the Bicentenario Doctoral Excellence scholarships, also contributed with the financial resources for the development of this research.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eData will be made available on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eW. Wongkeo, P. Thongsanitgarn, K. Pimraksa, and A. Chaipanich, \u0026ldquo;Compressive strength , flexural strength and thermal conductivity of autoclaved concrete block made using bottom ash as cement replacement materials,\u0026rdquo; \u003cem\u003eMater. Des.\u003c/em\u003e, vol. 35, pp. 434\u0026ndash;439, 2012, doi: 10.1016/j.matdes.2011.08.046.\u003c/li\u003e\n\u003cli\u003eG. Pachideh and M. Gholhaki, \u0026ldquo;Effect of pozzolanic materials on mechanical properties and water absorption of autoclaved aerated concrete,\u0026rdquo; \u003cem\u003eJournal of Building Engineering\u003c/em\u003e, vol. 26, no. 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Fernando \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Sustainable Cement Composite Integrating Waste Cellulose Fibre: A Comprehensive Review,\u0026rdquo; Feb. 01, 2023, \u003cem\u003eMDPI\u003c/em\u003e. doi: 10.3390/polym15030520. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Fibercement, cellulose, mechanical properties, density, lightweight building systems","lastPublishedDoi":"10.21203/rs.3.rs-9348799/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9348799/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFiber-cement composites are used in lightweight construction due to their favorable balance of mechanical and physical properties. This study investigates the influence of rice husk-derived cellulose microfibers on the performance of fiber-cement boards. Specimens were prepared with varying fiber concentrations (0.0%, 3.0%, 6.0%, 9.0%, and 12.0% wt.) and air-cured for 28 days. Characterization included X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), 3-point flexural testing to determine the Modulus of Rupture (MOR) and Modulus of Elasticity (MOE), and physical measurements of density and water absorption. Data were validated using one-way ANOVA at a 95% confidence level. Results showed that 9.0%wt. of cellulose as the optimal dosage, significantly enhancing the MOR by 159% and increasing the MOE by 59% compared to the control. Microstructural analysis revealed that the hydrophilic nature of the microfibers facilitates internal curing and secondary hydration, promoting calcium silicate hydrate gel formation. This mechanism densifies the matrix and improves fiber anchoring, as confirmed by SEM. Physically, the inclusion of cellulose reduces bulk density, favoring the development of lightweight materials, despite an increase in water absorption caused by inherent fiber porosity. Ultimately, the valorization of agro-industrial waste like rice husks not only optimizes the mechanical integrity of fiber-cement but also provides a sustainable, clean production alternative for the modern construction sector.\u003c/p\u003e","manuscriptTitle":"Valorization of rice husk-derived cellulose microfibers as sustainable reinforcement in fiber-cement composites through mechanical and microstructural analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-29 13:49:28","doi":"10.21203/rs.3.rs-9348799/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"71c737e5-1e6e-4226-a4d7-6e4a146fb718","owner":[],"postedDate":"April 29th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T13:49:28+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-29 13:49:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9348799","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9348799","identity":"rs-9348799","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}