Investigation the Effect of Perpendicularity and Flatness deviation of Cubic Molds on Concrete Compressive Strength Results

One of the influential factors on concrete compressive strength results, which is often neglected in construction and research projects, is the quality of specimen molds. In this study, the effect of six types of 150 mm×150 mm×150 mm cubic molds, including two types of steel molds and four types of plastic molds, on compressive strength (17 MPa to 67 MPa) results of fifteen concrete mixtures at different ages were investigated. It was found that using the worst of the studied molds led to an 18% reduction of the measured compressive strength compared to the best one. These results show that the effect of mold on the compressive strength of concrete can be very considerable. This issue can result in an inaccurate measurement of concrete strength produced in construction projects and incorrect mixture design and hence, legal and technical disputes among the sides involved in construction projects. In addition, in this paper, to quantify the quality of the studied molds, two parameters of flatness and perpendicularity deviation were defined. For applying a linear regression for the obtained results, an empirical formula with high accuracy was presented to predict the effect of the two parameters of molds on the concrete compressive strength reduction factor. This formula indicates that the reduction factor decreases when perpendicularity deviation and flatness deviation values increase. The values of perpendicularity and flatness deviation of the best mold were 0.007 mm and 0.042 mm, and the values of the worst mold were 1.485 mm and 0.335mm, respectively.