Mechanical properties of reduced-sized limestone filler-cement pastes and their variability using an instrumented Point Load test

In spite of their relevance in the context of modelling of the mechanical properties of cementitious composites, the mechanical properties of cement pastes (without standard sand) and their variability are rarely determined, given the large experimental effort demanded. In the present work, an instrumented Point Load Test was used to measure the mechanical properties of reduced-sized limestone filler (LF)-cement pastes. Since limestone filler replacement can have different effects on the tensile strength of pastes, depending on how the mixture is proportioned, a Box–Behnken fractional factorial design, by varying the w/c and the w/s ratios, besides superplasticizer was employed for designing low-cement concretes. Indeed, limestone filler was used to reduce water to solids (w/s) ratio and the porosity of the pastes. For each w/s ratio, replacement of cement by LF increased the w/c ratio and the paste porosity (the dilution effect). The tensile strength of pastes depended essentially on the capillary porosity. For an equal capillary porosity, limestone filler contributed to increasing the strength due to the toughening effect, which was confirmed by the larger total displacements in load-displacement curves. The elastic modulus was mainly governed by total open porosity. Multiple regression equations were proposed to predict porosity and mechanical properties of limestone filler-cement pastes, whereas their variability was analyzed.