Damage resistance of calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) under vehicle-bridge coupling vibration

Damage resistance of calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) under vehicle-bridge coupling vibration | 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 Damage resistance of calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) under vehicle-bridge coupling vibration Sijia Liu, Long Yu, Biwan Xu, Ken Yang, Shunfeng Wang, Linglin Xu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3709566/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jun, 2024 Read the published version in Materials and Structures → Version 1 posted 3 You are reading this latest preprint version Abstract This study aims to develop the calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) to enhance the resistance of newly placed concrete against vibration-induced damage during highway bridge widening. The effects of vehicle-bridge coupled vibration on the mechanical properties of CSA-ECC including compressive strength, flexural strength and flexural toughness were investigated. The results indicate that the volume percentage of coarse air bubbles (> 1.0 mm 3 ) decreases from 54.70–25.94%, and the volume percentage of micro air bubbles (0-0.2 mm 3 ) increases from 30.89–54.19%. As a result, the microstructure of matrix and fiber/matrix interface are densified due to the redistribution of air bubbles caused by the coupling vibration. Therefore, the application of vibration significantly enhances the flexural strength and flexural toughness of CSA-ECC, ascribing to stronger matrix fracture toughness and fiber/matrix interfacial frictional bond. The digital image correlation (DIC) analysis also indicates that vibration delays the occurrence of main cracking and leads to more obvious multi-cracking characteristics. These indicate that the CSA-ECC has a promising application scenario in highway bridge widening projects with exceptional vibration-induced damage resistance ability. CSA-ECC Vehicle-bridge coupling vibration Damage resistance Flexural toughness Cracking behavior air bubbles Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction With the rapid development of vehicle industry and population, present highways struggle to meet the heavy traffic demand due to insufficient road width [ 1 ]. According to the National Highway Network Planning of China during 2013–2030, the reconstruction and widening projects of present 30000 km of highway roads and bridges are under planning and implementing. In this case, it is economic to tackle the increasing traffic demand by widening the existing highways [ 2 ]. Compared with the construction of highway roads, there are more difficulties in highway bridge widening projects. To ensure structural integrity, existing highway bridges are often widened transversely by building new bridges and casting in situ concrete stitches between the old and new bridges [ 3 ]. During the cast-in-situ concrete construction, the coupling vibration caused by vehicles passing over the old bridge under the open traffic construction conditions inevitably leads to damage the internal structure of the newly placed concrete [ 4 – 6 ]. The damage mechanism of conventional bridge-stitching concrete under vehicle-bridge coupled vibration has been extensively studied. In the early stage of setting and hardening, the hydration of cement is insufficient, leading to a fragile inner binding of concrete [ 7 ]. The poorly bound interfacial transition zone (ITZ) is the weakest region in concrete which highly determines the performance of concrete [ 8 ]. At this stage, concrete exhibits its highest sensitivity to internal stresses [ 9 ], making it particularly susceptible to external vibrations [ 10 ]. Previous studies have confirmed that vehicle-bridge coupled vibration intensify the stress on newly constructed concrete [ 11 ], which subsequently leads to segregation [ 12 ] and cracking [ 7 ]. As a result, the mechanical properties of the newly built concrete deteriorate, and its bond with the existing structure is compromised. Therefore, how to mitigate the detrimental effect caused by vibration is crucial for the bridge-stitching concrete. Interestingly, one of the promising materials for vibration-resistant construction, particularly in bridge-stitching concrete, is engineered cementitious composites (ECC). ECC is a class of fiber reinforced cement-based composite with ductile strain-hardening and fine multiple cracking behaviors [ 13 , 14 ]. It is generally prepared with Portland cement, fly ash, quartz sand, water, chemical additives, and randomly distributed fibers [ 15 – 17 ]. The high ductility of ECC is achieved by a systematic design, adjustment, and optimization of the materials based on principles of fracture mechanics and micromechanics [ 18 , 19 ]. In addition, ECC exhibits a series of advanced properties including high tensile strength [ 20 ], superior durability [ 21 ], high crack-control capacity [ 22 ] and self-healing ability [ 23 ]. Due to the excellent performances of ECC, it has been widely used in repairing, strengthening, and retrofitting reinforced concrete structures [ 24 , 25 ], and also as linking slab or bridge deck material for bridge structures [ 26 , 27 ]. However, the highway bridge construction cannot afford a long time-span due to the heavy daily service load, which requires that the bridge-stitching concrete is rapid-hardening and early-strengthened, leaving traditional Portland cement-based ECC unable to meet the demands. To address this limitation, calcium sulfoaluminate cement (CSA) has been innovatively incorporated into ECC for its advantages of rapid setting [ 28 ] and high early strength [ 29 ], as well as its better resistance to crack propagation [ 30 ]. Compared to traditional Portland concrete, CSA-ECC is anticipated to demonstrate rapid setting, high early strength, homogeneity, and superior crack-control capacity [ 31 ]. Therefore, this work aims to evaluate the effect of vehicle-bridge coupled vibration on the mechanical properties of CSA-ECC, while comparing the composite here with the ultra-high performance concrete (UHPC) in our previous work [ 32 ]. Mechanical response of CSA-ECC was evaluated from aspects of compressive strength, flexural strength and flexural performance. The crack propagation process was monitored by digital image correlation (DIC). The enhancement mechanism was accurately verified by the distribution of air bubbles determined via X-ray micro-computed tomography (X-ray CT). 2. Experimental 2.1. Raw materials and mixing proportion The CSA with strength grade of 42.5 used was supplied by Tangshan Polar Bear Building Materials, Co., Ltd., China. Class F fly ash (FA) was obtained from local coalfired thermal power station. The chemical compositions of CSA cement and FA were determined by X-ray fluorescence (XRF), are summarized in Table 1 . Quartz sand was provided by Shanghai Fengchen Powder Material Co., Ltd., with a specific surface area of 308 m 2 /kg. The particle size distributions of CSA cement, FA and quartz sand were measured by a laser particle size analyzer (Malvern Mastersizer 2000) as presented in Fig. 1 . Polycarboxylate-based superplasticizer (SP, Sika ViscoCrete®-325C) and industrial-grade sodium gluconate (SG, purity 99.8%) were used to adjust setting time and flowability of fresh CSA-ECC mixtures. Polyvinyl alcohol (PVA) fibers (Kuraray®) were used, of which the physical properties are provided in Table 2 . Table 1 Chemical compositions of CSA cement and FA (wt. %) Material CaO SiO 2 Fe 2 O 3 SO 3 Al 2 O 3 K 2 O MgO P 2 O 5 Others CSA cement 34.18 15.51 2.82 15.69 26.24 0.41 2.90 0.38 1.87 FA 3.15 44.87 2.79 0.86 44.34 0.54 0.58 0.50 2.37 Table 2 Physical properties of PVA fibers. Length (mm) Diameter (µm) Density (g/cm 3 ) Tensile strength (MPa) Young’s modulus (Gpa) Elongation at break (%) 12 40 1.3 1600 41 6.5 According to the design criteria of ECC with tensile strain capacity typically beyond 2%, the mix proportions of CSA-ECC were summarized in Table 3 . The preparation of CSA-ECC were as follows: (1) CSA cement, FA and quartz sand were added into JJ-5 planetary mixer in turn and stirred at low speed for 120 s to make them uniformly mixed; (2) Water, SP and SG were slowly poured into the mixer and stirred at low speed for 60 s and then at high speed for 120 s; (3) PVA fibers were added within 120 s at low speed and stirred at high speed until homogeneous mixtures were obtained. The tensile stress-strain curve of the CSA-ECC was obtained based on the Japanese Society of Civil Engineers (JSCE) recommendation, as shown in Fig. 2 . Table 3 Mix proportions of CSA- ECC mixtures (mass ratio). Sample Cement FA W / b a S/b b SP/b c SG/b d PVA (Vol.%) CSA-ECC 0.6 0.4 0.30 0.2 0.002 0.005 2.0 Note: a : water-to-binder ratio; b : sand-to-binder ratio; c : superplasticizer-to-binder ratio; d : sodium gluconate-to-binder ratio. 2.2. Simulated vehicle-bridge coupling vibration procedure A Full Functional and Vertical Vibration table (Shanghai Yihua Instrument Equipment Co., Ltd.) were used to simulate the vehicle-bridge coupling condition. The vibration parameters involved amplitude and frequency, which were obtained by monitoring an old bridge with a width of 1600 cm under half-way traffic construction conditions as stated in Ref. [ 32 ]. Two series of vibration procedure were applied, as shown in Table 4 . Series Ⅰ were the specifically amplitude set as 2–4 mm, while series Ⅱ were the specifically frequency set as 3–9 Hz. According to the situation in construction sites, the mixtures were vibrated for 15 s and stood for 45 s as one cycle [ 33 ]. The fresh CSA-ECC mixtures were cast into steel molds with the size of 40 × 40 × 160 mm 3 . These in-mold samples were placed on the Full Functional and Vertical Vibration table immediately and whole vibration lasted 1080 cycles (18 h). Then all the samples were demolded and transferred to the standard curing condition (20 ± 2 ℃, RH 95 ± 5%) until designated testing age. Table 4 Samples subjected to different simulated vehicle-bridge coupling vibrations Category Sample Amplitude (mm) Frequency (Hz) Control A0H0 0 0 Series Ⅰ A2H6 2 6 A3H6 3 6 A4H6 4 6 Series Ⅱ A3H3 3 3 A3H9 3 9 2.3. Testing methods 2.3.1 Compressive and flexural strengths Referring to Chinese standard GB/T 17671 − 2021, the compressive strength was determined on the specimens broken into two half parts from the flexural strength test. The loading rate for the determination of compressive strength was kept at 2400 N/s. Six specimens for each group were tested, for the calculation of average value. Flexural strength according to three-point bending test method adopts the prism specimens and a loading rate of 50 N/s. Three samples were testes and averaged as the representative strength value. The rate of change of compressive strength ( R c ) was characterized as the increase or decrease in percentage of compressive strength after vibration to that without vibration, as shown in Eq. 1 . where F vibrated was the compressive strength (Mpa) after the specimens vibrated for 18 h, and F non−vibrated was the compressive strength of the specimens without vibration. Similarly, the rate of change of flexural strength ( R f ) was also calculated to evaluate the variation of flexural strength after vibration. 2.3.2 Four-point bending test Due to the low operability of using direct tensile test of ECC in engineering practice [ 34 ], four-point bending test were used to investigate the toughness of CSA-ECC. The test was conducted using an electronic universal testing machine, with a displacement rate of 0.3 mm/min. The span length was 150 mm with a center span length of 50 mm. A linear variable displacement transducer (LVDT) was used to measure the mid-span deflection. The load-deflection curves could be recorded. Each curve was averaged from three parallel samples. Considering the strain capacity of CSA-ECC as illustrated in Fig. 2 , the flexure toughness parameters namely deformation hardening flexural strength ratio R h,m and deformation hardening flexural energy Q m are determined according to the study by Zhu et al. [ 35 ], which is given by Eq. 2 and Eq. 3 . where f h,m represents the equivalent flexural strength, Mpa, f ic is defined as the first-crack strength, Mpa, E m represents the area when the deflection is δ m , mm, and V p represents the volume of pure flexural section of the specimens, mm 3 . 2.3.3 DIC analysis Digital image correlation (DIC) is an optics-based nondestructive measurement, which provides the high-precision observation of non-contact strain field [ 36 ]. For the purpose of identifying deformation, a random, sprayed-on speckle pattern with a white-black point was sprayed onto the surface of the specimens (as shown in Fig. 3 (a)) as described in previous studies [ 37 , 38 ]. The image acquisition system with a high precision camera was employed for recording sequence frames during the four-point bending tests as exhibited in Fig. 3 (b). For accurate measurements, the image acquisition frequency was 1 frame/s. The full field strain/displacement maps were obtained through 2D image correlation analysis. 2.3.4 X-ray CT analysis X-ray CT was utilized to reconstruct 3D microstructures of prism samples with the size of 20 × 20 × 40 mm 3 , which were sawn from the pre-loaded four-point bending specimens. The distribution of air bubbles was characterized using the XTH255/320 LC (Nikon®, Japan) equipped with a high-resolution detector (2000 × 2000 pixels). During the test, the sample was scanned by X-ray released from the X-ray radiation source at 360° rotation. The accelerating voltage and beam current were set at 120 kV and 90 µA. A total of 2000 slice X-ray CT images were collected continuously for each sample. And then the 3D image was obtained by combinations of layered scanning images and the reconstruction of projections with VG Studio MAX 3.1 software. The total air bubble content and different size air bubbles percent of the samples was calculated. 3. Results 3.1. Compressive strength Figure 4 demonstrates the effect of vibration on the compressive strength of the CSA-ECC mixtures. The compressive strength of the control (A0H0) reaches 25.8 Mpa at age of 3 days and 39.9 Mpa at 28 days. This indicates that over 60% of compressive strength of CSA-ECC is achieved within the first 3 days. As previously noted, the rapid setting and early strength of CSA cement are attributed to the mechanical interlocking of ettringite generated during hydration [ 31 ]. This characteristic of CSA-ECC enhances construction efficiency [ 39 ], which is particularly beneficial for expediting traffic restoration during highway bridge widening projects. As shown in Fig. 4 , all vibrated specimens attained higher 3 days compressive strength than that of the non-vibrated specimens. This strength improvement is rather significant for the specimens vibrated under higher frequency or amplitude. It could be mainly attributed to the change of pore structure and actual water-binder ratio during vibration as previously indicated by many other studies [ 4 , 12 , 32 ]. Similar tendency could be found for 28 days: the vibration increased the compressive strength of CSA-ECC. Among different vibrated specimens, A3H9 had the highest compressive strength of 29.1 MPa at 3 days and 43.2 MPa at 28 days, indicating a relative increase of 13.0% and 8.3% on strength index respectively when compared to the control. This implies that vehicle-bridge coupling vibration has a slightly beneficial for the compressive strength of CSA-ECC. However, this benefit will diminish as the strength of CSA-ECC increases. In order to compare the effect of vibration on the compressive strength of CSA-ECC and UHPC, the rate of change of compressive strength ( R c ) is calculated. The mix proportion of UHPC and the results of compressive and flexural strengths are reported in our previous studies [ 32 ]. As can be seen from Fig. 5 , the increase in compressive strength of CSA-ECC after vibration is less than 9% at 28 days. This value is notably inferior to that of UHPC, which can exhibit a maximum increase of over 21% under comparable vibration conditions. The comparatively weaker effect on compressive strength in CSA-ECC, as compared to UHPC, can be attributed to the following reasons: (1) the duration of vibration before setting and hardening for CSA-ECC is typically less than that of UHPC; (2) the viscosity of CSA-ECC is generally higher than that of UHPC due to the hydrophilicity of PVA fibers. 3.2 Flexural strength The flexural strength of CSA-ECC mixtures with various vibration conditions are demonstrated in Fig. 6 . Different to the results of compressive strength, the variation of the flexural strength between CSA-ECC under different vibration conditions is more apparent. The result shows that the 3-day flexural strength of A3H3 and A2H6 is higher than that of the control, indicating that a positive impact of low vibration degree on flexural strength at early age. Whereas, under higher amplitude or frequency, an adverse effect on the flexural strength of CSA-ECC is observed. This minor loss in flexural strength may be associated with the fact that the flexural strength of cement-based materials is sensitive to the internal cracks and defects [ 22 ]. Such cracks and defects are known to be more easily generated and developed when subjected to higher levels of vibration. It is evident that the vibration considerably increases flexural strength of CSA-ECC with respect to control at late hydration stages. Increasing the amplitude to 4 mm or frequency to 9 Hz is also efficient in increasing the flexural strength, but with mitigated degree. The observed modification in the damage caused by vibrations can be attributed to the micro-cracking behavior and inherent self-healing ability of ECC. These characteristics enable CSA-ECC to resist damage caused by vibrations to a greater extent compared to conventional Portland concrete [ 40 ]. The positive effect for the enhanced strength of CSA-ECC overweighs the negative effect while simultaneously maintained a comparable mechanical property in the long term. Figure 7 illustrates the change rate of flexural strength ( R f ) of CSA-ECC and UHPC at 28 days. The flexural strength of UHPC decreases as the amplitude (from 2 mm to 4 mm) or frequency (from 3 Hz to 9 Hz) increased, with a maximum drop of nearly 40%, which is due to the non-uniform distribution of both air bubbles and steel fibers [ 32 ]. However, the vibration results in an increase in the flexural strength of CSA-ECC, with a maximum growth over 20% (A3H6). Based on these findings, it can be concluded that CSA-ECC exhibits significant advantages over UHPC when used as bridge-stitching concrete. 3.3 Flexural performance 3.3.1 Load-deflection response A typical tensile load-deflection curve of ECC is shown in Fig. 8 . Three characteristic points can be observed on load-deflection curve: the first cracking point, the peak point, and the point situated at 0.80 times the peak load during the post-peak regions. At this point, the deformation hardening stage of ECC has completed. According to the characteristic points, the response of ECC can be categorized into three stages [ 35 ]: a linear elastic segment, a multi fracture development segment and a destruction segment. Load-deflection curves for CSA-ECC mixtures obtained in the four-point bending test at 28 days are given in Fig. 9 . All the curves show the three stages as described above and obvious deflection-hardening are observed. During the first stage, the curves linearly increase until the first characteristic point. As given in Table 5, the effect of vibration on the first cracking load ( f 1 ) and the deflection at first crack ( d 1 ) are negligible. After the first characteristic point, the effect of vibration on the curves becomes obviously. Given that d 1 is relatively unaffected by vibration, the deflection at 0.8 times peak load ( d 0.8p ) can be used to evaluate the multi fracture development segment of CSA-ECC. It can be observed that the bending deformation hardening portion increases with amplitude and then significant reduced for A4H6. The deterioration of deflection-hardening may be related to the serious damage caused by the introduction of cracks and defects under a large amplitude (4 mm). Meanwhile, frequency plays no obvious positive role in the improved deflection-hardening of CSA-ECC mixtures. After the third characteristic point, the curve moves to destruction segment. During this stage, the PVA fibers are pulled out or broken from matrix against the physical frictional force between fiber and matrix interface. It results in the load on the composite decreasing at a linear rate. Except for A4H6, the load-bearing capacity of vibrated sample remains superior to that of non-vibrated specimen. Table 5. Key values for the four-point bending tests. Category Samples f 1 (kN) d 1 (mm) f p (kN) d p (mm) f 0.8p (kN) d 0.8p (mm) Control A0H0 1.92 0.15 4.10 1.36 3.28 3.30 Series Ⅰ A2H6 1.74 0.15 4.83 3.27 3.86 4.32 A3H6 1.63 0.14 5.25 4.47 4.20 5.00 A4H6 1.44 0.13 4.65 1.61 3.72 2.74 Series Ⅱ A3H3 1.48 0.15 4.91 2.23 3.93 5.21 A3H9 2.00 0.17 5.23 3.61 4.18 5.20 3.3.2 Flexural toughness Flexural toughness is a crucial and representative indicator for evaluating the flexural performance of ECC, which reflects the ability to absorb energy and resist fracture failure [ 35 ]. The toughness evaluation index, including the deformation hardening flexural strength ratio R h,m and deformation hardening flexural energy Q m , are calculated to investigate the effect of vibration on flexural toughness of CSA-ECC mixtures. As shown in Fig. 10 (a), the R h,m of all samples increases by 20.5–51.9% compared with the control (A0H0), indicating the enhancement of equivalent flexural strength of CSA-ECC after vibration. The R h,m presents different tendency in response to variations in amplitude and frequency. With the increase of amplitude, R h,m gradually increases when the amplitude increased from 2 mm to 3 mm and then decreases when the amplitude is extended to 4 mm. As the frequency is increased from 3 Hz to 9 Hz, R h,m exhibits a decrease tendency, which is consistent with the results of bending deformation hardening portion elaborated in Section 3.3.1 . As shown in Fig. 10 (b), the Q m for most of the specimens is higher than that of the control specimen, except for A4H6, which showed a large vibration amplitude (4 mm) significantly reduces the energy consumption capacity of CSA-ECC. Q m of A3H6 is nearly double those of A0H0, indicating that the application of suitable vibrated amplitude is beneficial to the energy consumption capacity of CSA-ECC. In contrast, Q m is affected less remarkable by the frequency than the amplitude. As the frequency is increased from 3 Hz to 9 Hz, the resulting change in Q m is determined to be less than 11%. 3.3.3 Cracking behavior The crack propagation process of CSA-ECC mixtures under four-point bending test were captured by DIC method. Figure 11 compares the crack propagation process of the non-vibrated (A0H0) and vibrated specimens (A3H6) corresponding to the five typical moments that occurred in the whole fracture process. During the initial loading process, the CSA matrix and PVA fibers work in conjunction to bear the load. When the applied load exceeds the first cracking load, a microcrack could be observed visually for both A0H0 (Fig. 11 a(1)) and A3H6 (Fig. 11 b(1)). The PVA fibers situated in the tension region subsequently play a bridging role, which serves to limit further crack propagation and simultaneously transmit tensile forces carried by the PVA fibers to the cement matrix on both sides of the crack via the interfacial bonding [ 34 ]. With the continuous increase of load, the number of microcracks on the surface of specimens propagate gradually, as shown in Figs. 11 a(1–2) and Figs. 11 b(1–4). After the peak load, the main crack occurred at the bottom of prisms in the tensile area for A0H0 at a time 300 s as shown in Fig. 11 a(3). The main crack continuously expands with the load decreasing as the test preceded, as shown in Figs. 11 a(4–5). For A3H6, the main crack appears at a time 500 s as shown in Fig. 11 b(5). It can be found that both the vibrated samples (A3H6) and non-vibrated samples (A0H0) achieve desirable multi-cracking behavior. However, vibrated samples exhibit a later main cracking time and more obvious multi-cracking characteristics, which is mainly affected by the bridging performance of ECC [ 21 ]. 3.4 The distribution of air bubbles To further analyze the enhancement mechanism, X-ray CT measurement was used to visualize air bubbles distribution in 3D space, and the reconstructed 3D image is exhibited in Fig. 12 . Air bubbles with different volumes can be characterized with specific color. It can be observed from Fig. 12 that the air bubbles with different size are evenly distributed in both A0H0 and A3H6. However, after vibration, the proportion of air bubbles with different sizes undergoes significant changes, as indicated by Fig. 13 . Relative to the control group (30.89%), the volume percentages of micro air bubbles in A3H6 (54.19%) are increased. Additionally, the volume percentage of coarse air bubbles in A3H6 is 25.94%, even less than half of that of A0H0 (54.70%). It can be inferred that part of the coarse air bubbles at the bottom layer in the specimen tends to move upward to the middle layer and the upper layer and eventually overflow. In addition, it is worth noting that the total air bubbles content decreases from 2.13–1.61% after vibration, the result is consistent with previous studies [ 32 , 33 ]. Therefore, the redistribution of air bubbles caused by the coupling vibration refines the pore structure in the matrix and improves its microstructure, which increases the CSA-ECC strength. 3.5 Discussion Based on the experimental results, the vibration caused by vehicle-bridge coupling has a negligible effect on the compressive strength (shown in Fig. 4 ) of CSA-ECC, but it significantly enhances the flexural strength (shown in Fig. 6 ) and flexural toughness (shown in Fig. 10 ). The schematic diagram of the enhancement mechanism of CSA-ECC is illustrated in Fig. 14 . The application of vibration to CSA-ECC results in a significant reduction in the fraction of coarse air bubbles, while concurrently augmenting the fraction of micro air bubbles. This leads to the refinement of pore structure, as illustrated in Fig. 12 and Fig. 13 , which may potentially enhance the matrix fracture toughness. Simultaneously, the coupling vibration also affects the spatial distribution of PVA fibers, as well as the compactness and stiffness of the fiber/matrix interface, which in turn affects the toughness contribution of PVA fibers. As reported previously [ 32 ], the vibration influences the spatial distribution and inclination angle of steel fibers in UHPC, deteriorating its flexural and tensile strength. For ECC, the effect of fiber distribution on mechanical properties also plays an important role [ 41 ]. Considering that three-dimensional random distribution of PVA fibers in the matrix and the fiber/matrix interfacial bond could resist the heterogeneous redistribution of PVA fibers caused by coupling effects of frequency and amplitude to a certain extent. Therefore, the enhanced bending deformation hardening characteristics of CSA-ECC after vibration is mainly affected by the physical frictional force at the fiber/matrix interface. Combined with the transverse sections images of the prism samples as shown in Fig. 14 , it can be deduced that the coupling vibration has a beneficial effect on the refinement of pore structure around PVA fibers and its surrounding matrix. The A stronger fiber/matrix interfacial frictional bond formed due to vibration made it possible to effectively improve the fiber-bridging effect in the tension area (as illustrated in Fig. 14 ). As a result, a desirable multi cracking behavior along with enhanced flexural strength and flexural toughness occurs in the vibrated samples. 4. Conclusions This investigation studied the effect of vehicle-bridge coupling vibration on the mechanical properties of CSA-ECC. The underlying enhancement mechanism of flexural performance was systematically discussed. Based on the experimental results, the following conclusions could be obtained. (1) Vehicle-bridge coupling vibration positively impacts the compressive strength of both CSA-ECC and UHPC, with a more pronounced effect observed in UHPC. However, vibration contributes to opposite effect on the flexural strength of CSA-ECC and UHPC. CSA-ECC exhibits a significant improvement in flexural strength after undergoing vibration, with an increase of over 20%. (2) CSA-ECC specimens which subjected to vibration exhibit a significant increase in the distance of multi fracture development segment in the load-deflection curve, as well as enhanced flexural toughness. However, a large vibration amplitude (4 mm) leads to severe damage. DIC analysis further corroborates these findings by demonstrating that specimens subjected to vibration display more obvious multi-cracking characteristics and delayed main cracking time. (3) X-ray CT measurement has confirmed that vibrated specimens exhibit a smaller percentage of coarse air bubbles (> 1.0 mm 3 ) and a larger number of micro air bubbles (0-0.2 mm 3 ). The refinement of pore structure enhances the matrix fracture toughness and fiber/matrix interfacial frictional bond, which contributes to bending deformation hardening characteristics of CSA-ECC. In light of its exceptional vibration-induced damage resistance ability, CSA-ECC has proven to be particularly suitable for bridge widening projects. In the future, research will be conducted to assess the mechanical properties and durability of CSA-ECC in a broader range of engineering applications. Declarations Declaration of Competing Interest 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. Acknowledgments The authors gratefully acknowledge the financial support provided by the National Key Research and Development Projects of China (2022YFC3803400), the National Natural Science Foundation of China of China (52172022, 52378255), Shanghai Scientific Research Program (21DZ1200401), Guangdong Science and Technology Program(2021B1111610002), Shanghai Municipal Science and Technology Major Project (2021SHZDZX0100) and the Fundamental Research Funds for the Central Universities. References Wen QJ (2011) Long-term effect analysis of prestressed concrete box-girder bridge widening. Constr Build Mater 25:1580–1586 Tu B, Fang Z, Dong Y, Frangopol DM (2017) Time-variant reliability analysis of widened deteriorating prestressed concrete bridges considering shrinkage and creep. Eng Struct 153:1–16 Kwan AKH, Ng PL (2007) Effects of traffic vibration on curing concrete stitch: Part I - test method and control program. 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Materials 14:7743 Zhang Y, Zhang S, Deng M (2022) Four-point bending tests of ECC: Mechanical response and toughness evaluation, Case Stud. Constr Mater 17:e01573 Zhu M, Chen B, Wu M, Han J (2022) Effects of different mixing ratio parameters on mechanical properties of cost-effective green engineered cementitious composites (ECC), Constr. Build Mater 328:127093 Tang J, Chen X, Dai F, Wei M (2020) Experimental investigation of fracture damage of notched granite beams under cyclic loading using DIC and AE techniques, Fatigue Fract. Eng Mater Struct 43:1583–1596 Ding Y, Yu K-Q, Yu J, Xu S (2018) Structural behaviors of ultra-high performance engineered cementitious composites (UHP-ECC) beams subjected to bending-experimental study. Constr Build Mater 177:102–115 Hu G, Yang Q, Qiu X, Zhang D, Zhang W, Xiao S, Xu J (2022) Use of DIC and AE for investigating fracture behaviors of cold recycled asphalt emulsion mixtures with 100% RAP. Constr Build Mater 344:128278 Lv L, Šavija B, Li L, Cui H, Han N, Xing F (2021) Prehydration of calcium sulfoaluminate (CSA) clinker at different relative humidities. Cem Concr Res 144:106423 Shoji D, He Z, Zhang D, Li VC (2022) The greening of engineered cementitious composites (ECC): A review, Constr. Build Mater 327:126701 Guo X, Wang S, Zhang H (2021) Effects of Fiber Distribution and Content on Performance of Engineered Cementitious Composite (ECC). J Wuhan Univ Technol -Mat Sci Edit 36:569–577 Cite Share Download PDF Status: Published Journal Publication published 01 Jun, 2024 Read the published version in Materials and Structures → Version 1 posted Reviewers agreed at journal 15 Jan, 2024 Reviewers invited by journal 15 Jan, 2024 First submitted to journal 03 Dec, 2023 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. 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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-3709566","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":267218462,"identity":"cd7e1050-8e46-44b4-acdc-6b9b0249245f","order_by":0,"name":"Sijia Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDElEQVRIiWNgGAWjYBACPgaGBIMPFWz1+483gPhsPEDCAK8WNqCWwhln+BgbzhwmXgvDZ942OcaGG8lwQQJa+A883DizzYyZceb7g48LfvHJMLA3b5NgqLmDW4tEQrLBh3NpbMzSyczGM/uADuM5VibBcOwZHi0MaYYzyo7xsEkns0nz9gC1SOSYSTA2HMbnsPTfPGz/JXgkD0O1yL8hoIUhIcGYp43NQEKCmU2a5wfIFh4CWiQSEgxnnGFLMOBJNjbmbWDjYeNJK7ZIOIZbCz//GXBUJhiwH3z4mOfPMXt+9sMbb3yowa2FgYEnAcFmbDsGjimGBOxqoYD9ABLnTw1etaNgFIyCUTAyAQAewEuCDReISQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0009-0006-2298-1825","institution":"Tongji University","correspondingAuthor":true,"prefix":"","firstName":"Sijia","middleName":"","lastName":"Liu","suffix":""},{"id":267218463,"identity":"9187c9fd-4eba-4381-99ee-06c0f386b0ac","order_by":1,"name":"Long Yu","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Long","middleName":"","lastName":"Yu","suffix":""},{"id":267218464,"identity":"0014ba42-52e8-4526-86d2-403abdd52e1d","order_by":2,"name":"Biwan Xu","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Biwan","middleName":"","lastName":"Xu","suffix":""},{"id":267218465,"identity":"4889b892-d611-4cdb-ab87-543d2592370a","order_by":3,"name":"Ken Yang","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Ken","middleName":"","lastName":"Yang","suffix":""},{"id":267218466,"identity":"a28e64e5-9528-40ca-81a2-1254690fc5fd","order_by":4,"name":"Shunfeng Wang","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Shunfeng","middleName":"","lastName":"Wang","suffix":""},{"id":267218467,"identity":"030beccb-0ade-4a84-927d-a94b9b2bc039","order_by":5,"name":"Linglin Xu","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Linglin","middleName":"","lastName":"Xu","suffix":""},{"id":267218468,"identity":"a2bd1610-6672-4b37-a6cc-71fa45806706","order_by":6,"name":"Zhenghong Yang","email":"","orcid":"","institution":"Tongji University","correspondingAuthor":false,"prefix":"","firstName":"Zhenghong","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2023-12-05 11:28:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3709566/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3709566/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1617/s11527-024-02398-8","type":"published","date":"2024-06-01T14:11:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49762657,"identity":"3016bb1e-72bb-414b-98fa-168b290045b6","added_by":"auto","created_at":"2024-01-17 16:13:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":176997,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution of CSA cement, FA and quartz sand.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/5a9847eb9e01a9e17036580d.png"},{"id":49761930,"identity":"842e68cc-e3cd-4238-a1c3-42cf02026797","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":64972,"visible":true,"origin":"","legend":"\u003cp\u003eTensile stress-strain curve of CSA-ECC at 28 days.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/4f85c99943c97189ec0329df.png"},{"id":49761937,"identity":"7237f4d0-ab71-4901-a46c-4be2cf2a3911","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1992634,"visible":true,"origin":"","legend":"\u003cp\u003eRandom speckle pattern and experimental setup of four-point bending test with DIC.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/8eff78a80587eb9efd03fa29.png"},{"id":49763694,"identity":"7496d1bb-4d2b-409c-98a5-cebc3331d99e","added_by":"auto","created_at":"2024-01-17 16:21:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":179358,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of CSA-ECC mixtures under vehicle-bridge coupling vibrations consider the parameters of: (a) impact of amplitude and (b) impact of frequency.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/abd5ddd5f90646535a3170a9.png"},{"id":49762654,"identity":"b57b724a-bd75-4e43-8a3a-f8fcd74220f5","added_by":"auto","created_at":"2024-01-17 16:13:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":76468,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of (a) amplitude and (b) frequency on the change rate of compressive strength of CSA-ECC and UHPC [32] at 28 days.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/67d805b93072477b27bc42fe.png"},{"id":49761939,"identity":"7396d32a-5435-4081-9603-6861c6887472","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":169415,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural strength of CSA-ECC mixtures under vehicle-bridge coupling vibrations considering the parameters of: (a) impact of amplitude and (b) impact of frequency.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/063ed35690cceae6ba75b0b3.png"},{"id":49762655,"identity":"93c49ac8-25c2-4385-882c-6d0cc143021d","added_by":"auto","created_at":"2024-01-17 16:13:31","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":76566,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of (a) amplitude and (b) frequency on the change rate of flexural strength of CSA-ECC and UHPC [32] at 28 days.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/29cdca0d60621ec370727cb8.png"},{"id":49761931,"identity":"4a266604-b3ae-4494-9f2e-291ddffa3ac3","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":127845,"visible":true,"origin":"","legend":"\u003cp\u003eTypical load-deflection curve of ECC under flexural loading test.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/11df77455c0fbb09f9c2ec77.png"},{"id":49762658,"identity":"a79dd474-6d60-4a88-a7c5-b7a3020dc5cf","added_by":"auto","created_at":"2024-01-17 16:13:31","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":177111,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of amplitude (a) and frequency (b) on load-deflection curves of CSA-ECC mixtures under vehicle-bridge coupling vibrations.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/9f45d7e7bc481032a41e06ff.png"},{"id":49761940,"identity":"195e8218-72b6-445f-9c80-66510dad2391","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":76815,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of vehicle-bridge coupling vibration on the flexural toughness of CSA-ECC mixtures: (a) \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e and (b) \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/9124feb370001385426b490f.png"},{"id":49762659,"identity":"8a386a0f-88cf-469c-939e-07376bf1ff43","added_by":"auto","created_at":"2024-01-17 16:13:31","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1067816,"visible":true,"origin":"","legend":"\u003cp\u003eCrack propagation of the loaded CSA-ECC samples after specific times.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/cf1175a9380b18fc760c843a.png"},{"id":49761942,"identity":"a1a84a44-b72f-41b4-a8e2-db0d56172467","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1750065,"visible":true,"origin":"","legend":"\u003cp\u003eThree-dimensional reconstruction images of air bubbles in CSA-ECC mixtures.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/f8d0b5348f86fd4afc86bff8.png"},{"id":49761935,"identity":"9bb42643-59c5-4eff-973a-d2f60b4d72c4","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":108117,"visible":true,"origin":"","legend":"\u003cp\u003ePore volume distribution of CSA-ECC mixtures with different sizes: (a) A0H0 and (b) A3H6.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/049f94c70401710b02867031.png"},{"id":49761943,"identity":"20097d70-6c08-4d63-996b-d3c91aab63f9","added_by":"auto","created_at":"2024-01-17 16:05:31","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":734749,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of the effects vehicle-bridge coupling vibration in enhancing the mechanical properties of CSA-ECC mixtures.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/04ced8ff6ca3a0ae75b0db1c.png"},{"id":59116965,"identity":"d337d857-ddf8-41fd-9a7a-e49c6f8c56e1","added_by":"auto","created_at":"2024-06-26 14:11:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9131771,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3709566/v1/2388ffd8-8cbb-45cb-bd2d-efd344ff9736.pdf"}],"financialInterests":"","formattedTitle":"Damage resistance of calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) under vehicle-bridge coupling vibration","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the rapid development of vehicle industry and population, present highways struggle to meet the heavy traffic demand due to insufficient road width [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. According to the National Highway Network Planning of China during 2013\u0026ndash;2030, the reconstruction and widening projects of present 30000 km of highway roads and bridges are under planning and implementing. In this case, it is economic to tackle the increasing traffic demand by widening the existing highways [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Compared with the construction of highway roads, there are more difficulties in highway bridge widening projects.\u003c/p\u003e \u003cp\u003eTo ensure structural integrity, existing highway bridges are often widened transversely by building new bridges and casting in situ concrete stitches between the old and new bridges [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. During the cast-in-situ concrete construction, the coupling vibration caused by vehicles passing over the old bridge under the open traffic construction conditions inevitably leads to damage the internal structure of the newly placed concrete [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The damage mechanism of conventional bridge-stitching concrete under vehicle-bridge coupled vibration has been extensively studied. In the early stage of setting and hardening, the hydration of cement is insufficient, leading to a fragile inner binding of concrete [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The poorly bound interfacial transition zone (ITZ) is the weakest region in concrete which highly determines the performance of concrete [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. At this stage, concrete exhibits its highest sensitivity to internal stresses [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], making it particularly susceptible to external vibrations [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Previous studies have confirmed that vehicle-bridge coupled vibration intensify the stress on newly constructed concrete [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], which subsequently leads to segregation [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and cracking [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. As a result, the mechanical properties of the newly built concrete deteriorate, and its bond with the existing structure is compromised. Therefore, how to mitigate the detrimental effect caused by vibration is crucial for the bridge-stitching concrete.\u003c/p\u003e \u003cp\u003eInterestingly, one of the promising materials for vibration-resistant construction, particularly in bridge-stitching concrete, is engineered cementitious composites (ECC). ECC is a class of fiber reinforced cement-based composite with ductile strain-hardening and fine multiple cracking behaviors [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. It is generally prepared with Portland cement, fly ash, quartz sand, water, chemical additives, and randomly distributed fibers [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The high ductility of ECC is achieved by a systematic design, adjustment, and optimization of the materials based on principles of fracture mechanics and micromechanics [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. In addition, ECC exhibits a series of advanced properties including high tensile strength [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], superior durability [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], high crack-control capacity [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] and self-healing ability [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Due to the excellent performances of ECC, it has been widely used in repairing, strengthening, and retrofitting reinforced concrete structures [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], and also as linking slab or bridge deck material for bridge structures [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, the highway bridge construction cannot afford a long time-span due to the heavy daily service load, which requires that the bridge-stitching concrete is rapid-hardening and early-strengthened, leaving traditional Portland cement-based ECC unable to meet the demands. To address this limitation, calcium sulfoaluminate cement (CSA) has been innovatively incorporated into ECC for its advantages of rapid setting [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] and high early strength [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], as well as its better resistance to crack propagation [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Compared to traditional Portland concrete, CSA-ECC is anticipated to demonstrate rapid setting, high early strength, homogeneity, and superior crack-control capacity [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, this work aims to evaluate the effect of vehicle-bridge coupled vibration on the mechanical properties of CSA-ECC, while comparing the composite here with the ultra-high performance concrete (UHPC) in our previous work [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Mechanical response of CSA-ECC was evaluated from aspects of compressive strength, flexural strength and flexural performance. The crack propagation process was monitored by digital image correlation (DIC). The enhancement mechanism was accurately verified by the distribution of air bubbles determined via X-ray micro-computed tomography (X-ray CT).\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Raw materials and mixing proportion\u003c/h2\u003e\n \u003cp\u003eThe CSA with strength grade of 42.5 used was supplied by Tangshan Polar Bear Building Materials, Co., Ltd., China. Class F fly ash (FA) was obtained from local coalfired thermal power station. The chemical compositions of CSA cement and FA were determined by X-ray fluorescence (XRF), are summarized in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Quartz sand was provided by Shanghai Fengchen Powder Material Co., Ltd., with a specific surface area of 308 m\u003csup\u003e2\u003c/sup\u003e/kg. The particle size distributions of CSA cement, FA and quartz sand were measured by a laser particle size analyzer (Malvern Mastersizer 2000) as presented in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Polycarboxylate-based superplasticizer (SP, Sika ViscoCrete®-325C) and industrial-grade sodium gluconate (SG, purity 99.8%) were used to adjust setting time and flowability of fresh CSA-ECC mixtures. Polyvinyl alcohol (PVA) fibers (Kuraray®) were used, of which the physical properties are provided in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eChemical compositions of CSA cement and FA (wt. %)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"10\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMaterial\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCaO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMgO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCSA cement\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.37\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePhysical properties of PVA fibers.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLength\u003c/p\u003e\n \u003cp\u003e(mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDiameter\u003c/p\u003e\n \u003cp\u003e(µm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDensity\u003c/p\u003e\n \u003cp\u003e(g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTensile strength\u003c/p\u003e\n \u003cp\u003e(MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eYoung’s modulus\u003c/p\u003e\n \u003cp\u003e(Gpa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElongation at break\u003c/p\u003e\n \u003cp\u003e(%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eAccording to the design criteria of ECC with tensile strain capacity typically beyond 2%, the mix proportions of CSA-ECC were summarized in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The preparation of CSA-ECC were as follows: (1) CSA cement, FA and quartz sand were added into JJ-5 planetary mixer in turn and stirred at low speed for 120 s to make them uniformly mixed; (2) Water, SP and SG were slowly poured into the mixer and stirred at low speed for 60 s and then at high speed for 120 s; (3) PVA fibers were added within 120 s at low speed and stirred at high speed until homogeneous mixtures were obtained. The tensile stress-strain curve of the CSA-ECC was obtained based on the Japanese Society of Civil Engineers (JSCE) recommendation, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMix proportions of CSA- ECC mixtures (mass ratio).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"8\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eW\u003cem\u003e/\u003c/em\u003eb\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS/b\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSP/b\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSG/b\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePVA (Vol.%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCSA-ECC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"8\"\u003eNote: \u003csup\u003ea\u003c/sup\u003e: water-to-binder ratio; \u003csup\u003eb\u003c/sup\u003e: sand-to-binder ratio; \u003csup\u003ec\u003c/sup\u003e: superplasticizer-to-binder ratio; \u003csup\u003ed\u003c/sup\u003e: sodium gluconate-to-binder ratio.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Simulated vehicle-bridge coupling vibration procedure\u003c/h2\u003e\n \u003cp\u003eA Full Functional and Vertical Vibration table (Shanghai Yihua Instrument Equipment Co., Ltd.) were used to simulate the vehicle-bridge coupling condition. The vibration parameters involved amplitude and frequency, which were obtained by monitoring an old bridge with a width of 1600 cm under half-way traffic construction conditions as stated in Ref. [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Two series of vibration procedure were applied, as shown in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Series Ⅰ were the specifically amplitude set as 2–4 mm, while series Ⅱ were the specifically frequency set as 3–9 Hz. According to the situation in construction sites, the mixtures were vibrated for 15 s and stood for 45 s as one cycle [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe fresh CSA-ECC mixtures were cast into steel molds with the size of 40 × 40 × 160 mm\u003csup\u003e3\u003c/sup\u003e. These in-mold samples were placed on the Full Functional and Vertical Vibration table immediately and whole vibration lasted 1080 cycles (18 h). Then all the samples were demolded and transferred to the standard curing condition (20 ± 2 ℃, RH 95 ± 5%) until designated testing age.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSamples subjected to different simulated vehicle-bridge coupling vibrations\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAmplitude (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFrequency (Hz)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA0H0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSeries Ⅰ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA2H6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA3H6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA4H6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSeries Ⅱ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA3H3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA3H9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Testing methods\u003c/h2\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.1 Compressive and flexural strengths\u003c/h2\u003e\n \u003cp\u003eReferring to Chinese standard GB/T 17671 − 2021, the compressive strength was determined on the specimens broken into two half parts from the flexural strength test. The loading rate for the determination of compressive strength was kept at 2400 N/s. Six specimens for each group were tested, for the calculation of average value. Flexural strength according to three-point bending test method adopts the prism specimens and a loading rate of 50 N/s. Three samples were testes and averaged as the representative strength value.\u003c/p\u003e\n \u003cp\u003eThe rate of change of compressive strength (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e) was characterized as the increase or decrease in percentage of compressive strength after vibration to that without vibration, as shown in Eq. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003ewhere \u003cem\u003eF\u003c/em\u003e\u003csub\u003evibrated\u003c/sub\u003e was the compressive strength (Mpa) after the specimens vibrated for 18 h, and \u003cem\u003eF\u003c/em\u003e\u003csub\u003enon−vibrated\u003c/sub\u003e was the compressive strength of the specimens without vibration. Similarly, the rate of change of flexural strength (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e) was also calculated to evaluate the variation of flexural strength after vibration.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.2 Four-point bending test\u003c/h2\u003e\n \u003cp\u003eDue to the low operability of using direct tensile test of ECC in engineering practice [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e], four-point bending test were used to investigate the toughness of CSA-ECC. The test was conducted using an electronic universal testing machine, with a displacement rate of 0.3 mm/min. The span length was 150 mm with a center span length of 50 mm. A linear variable displacement transducer (LVDT) was used to measure the mid-span deflection. The load-deflection curves could be recorded. Each curve was averaged from three parallel samples.\u003c/p\u003e\n \u003cp\u003eConsidering the strain capacity of CSA-ECC as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, the flexure toughness parameters namely deformation hardening flexural strength ratio \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e and deformation hardening flexural energy \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e are determined according to the study by Zhu et al. [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e], which is given by Eq. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Eq. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003ewhere \u003cem\u003ef\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e represents the equivalent flexural strength, Mpa, \u003cem\u003ef\u003c/em\u003e\u003csub\u003eic\u003c/sub\u003e is defined as the first-crack strength, Mpa, \u003cem\u003eE\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e represents the area when the deflection is \u003cem\u003eδ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e, mm, and \u003cem\u003eV\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e represents the volume of pure flexural section of the specimens, mm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.3 DIC analysis\u003c/h2\u003e\n \u003cp\u003eDigital image correlation (DIC) is an optics-based nondestructive measurement, which provides the high-precision observation of non-contact strain field [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. For the purpose of identifying deformation, a random, sprayed-on speckle pattern with a white-black point was sprayed onto the surface of the specimens (as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(a)) as described in previous studies [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. The image acquisition system with a high precision camera was employed for recording sequence frames during the four-point bending tests as exhibited in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b). For accurate measurements, the image acquisition frequency was 1 frame/s. The full field strain/displacement maps were obtained through 2D image correlation analysis.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.4 X-ray CT analysis\u003c/h2\u003e\n \u003cp\u003eX-ray CT was utilized to reconstruct 3D microstructures of prism samples with the size of 20 × 20 × 40 mm\u003csup\u003e3\u003c/sup\u003e, which were sawn from the pre-loaded four-point bending specimens. The distribution of air bubbles was characterized using the XTH255/320 LC (Nikon®, Japan) equipped with a high-resolution detector (2000 × 2000 pixels). During the test, the sample was scanned by X-ray released from the X-ray radiation source at 360° rotation. The accelerating voltage and beam current were set at 120 kV and 90 µA. A total of 2000 slice X-ray CT images were collected continuously for each sample. And then the 3D image was obtained by combinations of layered scanning images and the reconstruction of projections with VG Studio MAX 3.1 software. The total air bubble content and different size air bubbles percent of the samples was calculated.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1. Compressive strength\u003c/h2\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e demonstrates the effect of vibration on the compressive strength of the CSA-ECC mixtures. The compressive strength of the control (A0H0) reaches 25.8 Mpa at age of 3 days and 39.9 Mpa at 28 days. This indicates that over 60% of compressive strength of CSA-ECC is achieved within the first 3 days. As previously noted, the rapid setting and early strength of CSA cement are attributed to the mechanical interlocking of ettringite generated during hydration [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. This characteristic of CSA-ECC enhances construction efficiency [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e], which is particularly beneficial for expediting traffic restoration during highway bridge widening projects.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, all vibrated specimens attained higher 3 days compressive strength than that of the non-vibrated specimens. This strength improvement is rather significant for the specimens vibrated under higher frequency or amplitude. It could be mainly attributed to the change of pore structure and actual water-binder ratio during vibration as previously indicated by many other studies [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Similar tendency could be found for 28 days: the vibration increased the compressive strength of CSA-ECC. Among different vibrated specimens, A3H9 had the highest compressive strength of 29.1 MPa at 3 days and 43.2 MPa at 28 days, indicating a relative increase of 13.0% and 8.3% on strength index respectively when compared to the control. This implies that vehicle-bridge coupling vibration has a slightly beneficial for the compressive strength of CSA-ECC. However, this benefit will diminish as the strength of CSA-ECC increases.\u003c/p\u003e\n\u003cp\u003eIn order to compare the effect of vibration on the compressive strength of CSA-ECC and UHPC, the rate of change of compressive strength (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e) is calculated. The mix proportion of UHPC and the results of compressive and flexural strengths are reported in our previous studies [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. As can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, the increase in compressive strength of CSA-ECC after vibration is less than 9% at 28 days. This value is notably inferior to that of UHPC, which can exhibit a maximum increase of over 21% under comparable vibration conditions. The comparatively weaker effect on compressive strength in CSA-ECC, as compared to UHPC, can be attributed to the following reasons: (1) the duration of vibration before setting and hardening for CSA-ECC is typically less than that of UHPC; (2) the viscosity of CSA-ECC is generally higher than that of UHPC due to the hydrophilicity of PVA fibers.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Flexural strength\u003c/h2\u003e\n\u003cp\u003eThe flexural strength of CSA-ECC mixtures with various vibration conditions are demonstrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Different to the results of compressive strength, the variation of the flexural strength between CSA-ECC under different vibration conditions is more apparent. The result shows that the 3-day flexural strength of A3H3 and A2H6 is higher than that of the control, indicating that a positive impact of low vibration degree on flexural strength at early age. Whereas, under higher amplitude or frequency, an adverse effect on the flexural strength of CSA-ECC is observed. This minor loss in flexural strength may be associated with the fact that the flexural strength of cement-based materials is sensitive to the internal cracks and defects [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. Such cracks and defects are known to be more easily generated and developed when subjected to higher levels of vibration.\u003c/p\u003e\n\u003cp\u003eIt is evident that the vibration considerably increases flexural strength of CSA-ECC with respect to control at late hydration stages. Increasing the amplitude to 4 mm or frequency to 9 Hz is also efficient in increasing the flexural strength, but with mitigated degree. The observed modification in the damage caused by vibrations can be attributed to the micro-cracking behavior and inherent self-healing ability of ECC. These characteristics enable CSA-ECC to resist damage caused by vibrations to a greater extent compared to conventional Portland concrete [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. The positive effect for the enhanced strength of CSA-ECC overweighs the negative effect while simultaneously maintained a comparable mechanical property in the long term.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the change rate of flexural strength (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e) of CSA-ECC and UHPC at 28 days. The flexural strength of UHPC decreases as the amplitude (from 2 mm to 4 mm) or frequency (from 3 Hz to 9 Hz) increased, with a maximum drop of nearly 40%, which is due to the non-uniform distribution of both air bubbles and steel fibers [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. However, the vibration results in an increase in the flexural strength of CSA-ECC, with a maximum growth over 20% (A3H6). Based on these findings, it can be concluded that CSA-ECC exhibits significant advantages over UHPC when used as bridge-stitching concrete.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Flexural performance\u003c/h2\u003e\n\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.1 Load-deflection response\u003c/h2\u003e\n\u003cp\u003eA typical tensile load-deflection curve of ECC is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Three characteristic points can be observed on load-deflection curve: the first cracking point, the peak point, and the point situated at 0.80 times the peak load during the post-peak regions. At this point, the deformation hardening stage of ECC has completed. According to the characteristic points, the response of ECC can be categorized into three stages [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]: a linear elastic segment, a multi fracture development segment and a destruction segment.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLoad-deflection curves for CSA-ECC mixtures obtained in the four-point bending test at 28 days are given in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e. All the curves show the three stages as described above and obvious deflection-hardening are observed. During the first stage, the curves linearly increase until the first characteristic point. As given in Table\u0026nbsp;5, the effect of vibration on the first cracking load (\u003cem\u003ef\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) and the deflection at first crack (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) are negligible. After the first characteristic point, the effect of vibration on the curves becomes obviously. Given that \u003cem\u003ed\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e is relatively unaffected by vibration, the deflection at 0.8 times peak load (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e0.8p\u003c/sub\u003e) can be used to evaluate the multi fracture development segment of CSA-ECC. It can be observed that the bending deformation hardening portion increases with amplitude and then significant reduced for A4H6. The deterioration of deflection-hardening may be related to the serious damage caused by the introduction of cracks and defects under a large amplitude (4 mm). Meanwhile, frequency plays no obvious positive role in the improved deflection-hardening of CSA-ECC mixtures. After the third characteristic point, the curve moves to destruction segment. During this stage, the PVA fibers are pulled out or broken from matrix against the physical frictional force between fiber and matrix interface. It results in the load on the composite decreasing at a linear rate. Except for A4H6, the load-bearing capacity of vibrated sample remains superior to that of non-vibrated specimen.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;5.\u003c/strong\u003e Key values for the four-point bending tests.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tabb\" border=\"1\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCategory\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSamples\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(kN)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ed\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(kN)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ed\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e0.8p\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(kN)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ed\u003c/em\u003e\u003csub\u003e0.8p\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mm)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eControl\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA0H0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.92\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.36\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.30\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSeries Ⅰ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA2H6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.74\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.83\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.27\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.86\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.32\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA3H6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.25\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.00\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA4H6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.72\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.74\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSeries Ⅱ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA3H3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.91\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.93\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.21\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eA3H9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.00\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.17\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4.18\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.20\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.2 Flexural toughness\u003c/h2\u003e\n\u003cp\u003eFlexural toughness is a crucial and representative indicator for evaluating the flexural performance of ECC, which reflects the ability to absorb energy and resist fracture failure [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. The toughness evaluation index, including the deformation hardening flexural strength ratio \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e and deformation hardening flexural energy \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e, are calculated to investigate the effect of vibration on flexural toughness of CSA-ECC mixtures.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e(a), the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e of all samples increases by 20.5\u0026ndash;51.9% compared with the control (A0H0), indicating the enhancement of equivalent flexural strength of CSA-ECC after vibration. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e presents different tendency in response to variations in amplitude and frequency. With the increase of amplitude, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e gradually increases when the amplitude increased from 2 mm to 3 mm and then decreases when the amplitude is extended to 4 mm. As the frequency is increased from 3 Hz to 9 Hz, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eh,m\u003c/sub\u003e exhibits a decrease tendency, which is consistent with the results of bending deformation hardening portion elaborated in Section \u003cspan class=\"InternalRef\"\u003e3.3.1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e(b), the \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e for most of the specimens is higher than that of the control specimen, except for A4H6, which showed a large vibration amplitude (4 mm) significantly reduces the energy consumption capacity of CSA-ECC. \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e of A3H6 is nearly double those of A0H0, indicating that the application of suitable vibrated amplitude is beneficial to the energy consumption capacity of CSA-ECC. In contrast, \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is affected less remarkable by the frequency than the amplitude. As the frequency is increased from 3 Hz to 9 Hz, the resulting change in \u003cem\u003eQ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is determined to be less than 11%.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n\u003ch2\u003e3.3.3 Cracking behavior\u003c/h2\u003e\n\u003cp\u003eThe crack propagation process of CSA-ECC mixtures under four-point bending test were captured by DIC method. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e compares the crack propagation process of the non-vibrated (A0H0) and vibrated specimens (A3H6) corresponding to the five typical moments that occurred in the whole fracture process.\u003c/p\u003e\n\u003cp\u003eDuring the initial loading process, the CSA matrix and PVA fibers work in conjunction to bear the load. When the applied load exceeds the first cracking load, a microcrack could be observed visually for both A0H0 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea(1)) and A3H6 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003eb(1)). The PVA fibers situated in the tension region subsequently play a bridging role, which serves to limit further crack propagation and simultaneously transmit tensile forces carried by the PVA fibers to the cement matrix on both sides of the crack via the interfacial bonding [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. With the continuous increase of load, the number of microcracks on the surface of specimens propagate gradually, as shown in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea(1\u0026ndash;2) and Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003eb(1\u0026ndash;4).\u003c/p\u003e\n\u003cp\u003eAfter the peak load, the main crack occurred at the bottom of prisms in the tensile area for A0H0 at a time 300 s as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea(3). The main crack continuously expands with the load decreasing as the test preceded, as shown in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea(4\u0026ndash;5). For A3H6, the main crack appears at a time 500 s as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003eb(5). It can be found that both the vibrated samples (A3H6) and non-vibrated samples (A0H0) achieve desirable multi-cracking behavior. However, vibrated samples exhibit a later main cracking time and more obvious multi-cracking characteristics, which is mainly affected by the bridging performance of ECC [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4 The distribution of air bubbles\u003c/h2\u003e\n\u003cp\u003eTo further analyze the enhancement mechanism, X-ray CT measurement was used to visualize air bubbles distribution in 3D space, and the reconstructed 3D image is exhibited in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e. Air bubbles with different volumes can be characterized with specific color. It can be observed from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e that the air bubbles with different size are evenly distributed in both A0H0 and A3H6. However, after vibration, the proportion of air bubbles with different sizes undergoes significant changes, as indicated by Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e13\u003c/span\u003e. Relative to the control group (30.89%), the volume percentages of micro air bubbles in A3H6 (54.19%) are increased. Additionally, the volume percentage of coarse air bubbles in A3H6 is 25.94%, even less than half of that of A0H0 (54.70%). It can be inferred that part of the coarse air bubbles at the bottom layer in the specimen tends to move upward to the middle layer and the upper layer and eventually overflow. In addition, it is worth noting that the total air bubbles content decreases from 2.13\u0026ndash;1.61% after vibration, the result is consistent with previous studies [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. Therefore, the redistribution of air bubbles caused by the coupling vibration refines the pore structure in the matrix and improves its microstructure, which increases the CSA-ECC strength.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n\u003ch2\u003e3.5 Discussion\u003c/h2\u003e\n\u003cp\u003eBased on the experimental results, the vibration caused by vehicle-bridge coupling has a negligible effect on the compressive strength (shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) of CSA-ECC, but it significantly enhances the flexural strength (shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) and flexural toughness (shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e). The schematic diagram of the enhancement mechanism of CSA-ECC is illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e. The application of vibration to CSA-ECC results in a significant reduction in the fraction of coarse air bubbles, while concurrently augmenting the fraction of micro air bubbles. This leads to the refinement of pore structure, as illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e13\u003c/span\u003e, which may potentially enhance the matrix fracture toughness.\u003c/p\u003e\n\u003cp\u003eSimultaneously, the coupling vibration also affects the spatial distribution of PVA fibers, as well as the compactness and stiffness of the fiber/matrix interface, which in turn affects the toughness contribution of PVA fibers. As reported previously [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e], the vibration influences the spatial distribution and inclination angle of steel fibers in UHPC, deteriorating its flexural and tensile strength. For ECC, the effect of fiber distribution on mechanical properties also plays an important role [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. Considering that three-dimensional random distribution of PVA fibers in the matrix and the fiber/matrix interfacial bond could resist the heterogeneous redistribution of PVA fibers caused by coupling effects of frequency and amplitude to a certain extent. Therefore, the enhanced bending deformation hardening characteristics of CSA-ECC after vibration is mainly affected by the physical frictional force at the fiber/matrix interface.\u003c/p\u003e\n\u003cp\u003eCombined with the transverse sections images of the prism samples as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e, it can be deduced that the coupling vibration has a beneficial effect on the refinement of pore structure around PVA fibers and its surrounding matrix. The A stronger fiber/matrix interfacial frictional bond formed due to vibration made it possible to effectively improve the fiber-bridging effect in the tension area (as illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e). As a result, a desirable multi cracking behavior along with enhanced flexural strength and flexural toughness occurs in the vibrated samples.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis investigation studied the effect of vehicle-bridge coupling vibration on the mechanical properties of CSA-ECC. The underlying enhancement mechanism of flexural performance was systematically discussed. Based on the experimental results, the following conclusions could be obtained.\u003c/p\u003e \u003cp\u003e(1) Vehicle-bridge coupling vibration positively impacts the compressive strength of both CSA-ECC and UHPC, with a more pronounced effect observed in UHPC. However, vibration contributes to opposite effect on the flexural strength of CSA-ECC and UHPC. CSA-ECC exhibits a significant improvement in flexural strength after undergoing vibration, with an increase of over 20%.\u003c/p\u003e \u003cp\u003e(2) CSA-ECC specimens which subjected to vibration exhibit a significant increase in the distance of multi fracture development segment in the load-deflection curve, as well as enhanced flexural toughness. However, a large vibration amplitude (4 mm) leads to severe damage. DIC analysis further corroborates these findings by demonstrating that specimens subjected to vibration display more obvious multi-cracking characteristics and delayed main cracking time.\u003c/p\u003e \u003cp\u003e(3) X-ray CT measurement has confirmed that vibrated specimens exhibit a smaller percentage of coarse air bubbles (\u0026gt;\u0026thinsp;1.0 mm\u003csup\u003e3\u003c/sup\u003e) and a larger number of micro air bubbles (0-0.2 mm\u003csup\u003e3\u003c/sup\u003e). The refinement of pore structure enhances the matrix fracture toughness and fiber/matrix interfacial frictional bond, which contributes to bending deformation hardening characteristics of CSA-ECC.\u003c/p\u003e \u003cp\u003eIn light of its exceptional vibration-induced damage resistance ability, CSA-ECC has proven to be particularly suitable for bridge widening projects. In the future, research will be conducted to assess the mechanical properties and durability of CSA-ECC in a broader range of engineering applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of Competing Interest\u003c/h2\u003e \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 \u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors gratefully acknowledge the financial support provided by the National Key Research and Development Projects of China (2022YFC3803400), the National Natural Science Foundation of China of China (52172022, 52378255), Shanghai Scientific Research Program (21DZ1200401), Guangdong Science and Technology Program(2021B1111610002), Shanghai Municipal Science and Technology Major Project (2021SHZDZX0100) and the Fundamental Research Funds for the Central Universities.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWen QJ (2011) Long-term effect analysis of prestressed concrete box-girder bridge widening. 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Constr Build Mater 344:128278\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLv L, Šavija B, Li L, Cui H, Han N, Xing F (2021) Prehydration of calcium sulfoaluminate (CSA) clinker at different relative humidities. Cem Concr Res 144:106423\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShoji D, He Z, Zhang D, Li VC (2022) The greening of engineered cementitious composites (ECC): A review, Constr. Build Mater 327:126701\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo X, Wang S, Zhang H (2021) Effects of Fiber Distribution and Content on Performance of Engineered Cementitious Composite (ECC). J Wuhan Univ Technol -Mat Sci Edit 36:569\u0026ndash;577\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"materials-and-structures","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"maas","sideBox":"Learn more about [Materials and Structures](http://link.springer.com/journal/11527)","snPcode":"11527","submissionUrl":"https://www.editorialmanager.com/maas/default2.aspx","title":"Materials and Structures","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"CSA-ECC, Vehicle-bridge coupling vibration, Damage resistance, Flexural toughness, Cracking behavior, air bubbles","lastPublishedDoi":"10.21203/rs.3.rs-3709566/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3709566/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aims to develop the calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) to enhance the resistance of newly placed concrete against vibration-induced damage during highway bridge widening. The effects of vehicle-bridge coupled vibration on the mechanical properties of CSA-ECC including compressive strength, flexural strength and flexural toughness were investigated. The results indicate that the volume percentage of coarse air bubbles (\u0026gt;\u0026thinsp;1.0 mm\u003csup\u003e3\u003c/sup\u003e) decreases from 54.70\u0026ndash;25.94%, and the volume percentage of micro air bubbles (0-0.2 mm\u003csup\u003e3\u003c/sup\u003e) increases from 30.89\u0026ndash;54.19%. As a result, the microstructure of matrix and fiber/matrix interface are densified due to the redistribution of air bubbles caused by the coupling vibration. Therefore, the application of vibration significantly enhances the flexural strength and flexural toughness of CSA-ECC, ascribing to stronger matrix fracture toughness and fiber/matrix interfacial frictional bond. The digital image correlation (DIC) analysis also indicates that vibration delays the occurrence of main cracking and leads to more obvious multi-cracking characteristics. These indicate that the CSA-ECC has a promising application scenario in highway bridge widening projects with exceptional vibration-induced damage resistance ability.\u003c/p\u003e","manuscriptTitle":"Damage resistance of calcium sulfoaluminate cement-based engineered cementitious composites (CSA-ECC) under vehicle-bridge coupling vibration","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-17 16:05:26","doi":"10.21203/rs.3.rs-3709566/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-01-15T19:15:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-15T09:17:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Materials and Structures","date":"2023-12-04T02:44:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"materials-and-structures","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"maas","sideBox":"Learn more about [Materials and Structures](http://link.springer.com/journal/11527)","snPcode":"11527","submissionUrl":"https://www.editorialmanager.com/maas/default2.aspx","title":"Materials and Structures","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"51c95f8d-0c65-44c9-99d0-c1941ca8a19b","owner":[],"postedDate":"January 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-06-26T14:11:14+00:00","versionOfRecord":{"articleIdentity":"rs-3709566","link":"https://doi.org/10.1617/s11527-024-02398-8","journal":{"identity":"materials-and-structures","isVorOnly":false,"title":"Materials and Structures"},"publishedOn":"2024-06-01 14:11:13","publishedOnDateReadable":"June 1st, 2024"},"versionCreatedAt":"2024-01-17 16:05:26","video":"","vorDoi":"10.1617/s11527-024-02398-8","vorDoiUrl":"https://doi.org/10.1617/s11527-024-02398-8","workflowStages":[]},"version":"v1","identity":"rs-3709566","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3709566","identity":"rs-3709566","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}