The use of cement and concrete is becoming increasingly widespread all over the world. However, the high energy consumption required for the production of clinker and the greenhouse gas emissions generated during production negatively affect both the economy and the environment. In the studies conducted for many years, researchers have found that the substitution of various pozzolans with cement pro- vides both technical advantages and environmental benefits. The use of pozzolans in cementitious composites provides advantages such as the improvement of the phys- ical and mechanical properties of the material, the conservation of the environment and the economy in terms of the evaluation of industrial wastes. In recent years, stud- ies on the use of nanoparticles in cementitious composites are positively. In this study, it was aimed to investigate the properties of fresh and hardened cement mor- tars using micro silica as pozzolan and nano silica as nanoparticle. For this purpose, four different cement pastes and mortars mixtures were prepared by substituting 0%, 1%, 2%, 3% nano SiO 2 (silica) cement in mortar mixtures containing 5% micro silica. The effects of the nano silica on the micro silica-containing cement paste on the consistency and setting time were investigated. The mortar mixtures produced were subjected to flexural and compressive strength tests on days 7, 28 and 90 th . SEM im- ages of mortar mixtures were taken. As a result, it was found that 2% nano silica ad- mixture of 5% micro silica containing cement admixture affects the flexural and com- pressive strength positively, whereas 2% nano silica admixture increased the flex- ural strength by 13% and compressive strength by 7%.
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