The effect of cement replacement and homogenization procedure on concrete mechanical properties

Supplementary cementitious materials (SCM) are used in concrete for two main reasons – to reduce the amount of cement used and to improve material properties. A material that is more sustainable, durable, environmental friendly and economical compared to the traditional Portland cement concrete can be obtained. This paper investigates the effect of two important factors on mechanical properties of highperformance concrete (HPC) containing SCM. The first factor is the content of selected SCM, the second one is the homogenization procedure used for preparation of concrete. In the first part of the research program, 10 different mixtures were compared: reference mixture with no SCM and mixtures where 10 %, 20 % or 30 % of cement weight were replaced by microsilica, fly ash or metakaolin. In the second part, three mixtures with selected replacement levels were prepared by four different homogenization procedures and studied. Tests of bulk density, compressive strength, splitting tensile strength, flexural tensile strength, dynamic and static elastic modulus and depth of penetration of water under pressure were carried out for the tested mixtures. The best results were reached when cement was partially replaced by fly ash. Resistance of concrete to penetration of water under pressure was significantly improved by all SCM. The homogenization procedure in which the SCM was added to the mixture after water led to slightly better properties than the standard mixing technique in case of mixtures containing microsilica and metakaolin. The paper provides an extensive database that can serve as a benchmark for the design of HPC containing SCM.