Investigation of the effect of different grading on the mechanical properties of reactive powder concrete

In this study, 11 designs with sand-to-cement ratios of 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, and 7 were used to investigate the impact of increasing the sand-to-cement ratio in reactive powder concrete. Laboratory results indicate a decrease in compressive and bending strength, following an increase in the ratio of sand to cement. Sample S7 with the highest ratio of sand to cement has the lowest bending strength and compressive strength at the ages of 1, 7, 14, 28, 42 and 56 days.In the second process, 1 % polymer resin was added to the sand-to-cement ratio from the first step. By analyzing the results, it was observed that the addition of 1 % of polymer resin causes a decrease of 40.8 % in compressive strength at the age of 1 day. The biggest one-day pressure drop is S6.75 with a drop of 68.1 %. As the samples age, adding 1 % of polymer resin increases the compressive strength at 11 sand-cement ratios, so that the 90-day compressive strength of the S4.75 sample reaches 59.7 MPa. The addition of 1 % polymer resin also increased the bending strength by 9.1 %. After examining the results of the first and second steps of the study, the sand to cement ratios of 5.5, 6, 6.25, 6.5 and 7 were selected as optimal and suitable samples. In the third step of the study, coarse aggregate with percentages of 10, 20, 30, 40 and 50 was added to the selected samples. The results showed that the addition of coarse aggregate caused a decrease of 41.1 % in the compressive strength of reactive powder concrete at the age of 1 day, compared to the control sample. In the third step, the maximum compressive strength at the ages of 28, 42, 56 and 90 days for sand-cement ratios of 5.5, 6, 6.25, 6.5 and 7 corresponds to the sample containing 50 % of coarse aggregate. The best samples of the third step in flexural strength are those with 50 % gravel, which increases flexural strength with increasing sand-cement ratio. On the other hand, with the addition of coarse aggregate, an increase in flexural strength was observed compared to the control sample of reactive powder concrete. In the fourth step of the study, 1 % of polymer resin was added to the samples of the third step. The results of this step show that, like the third step, the maximum compressive strength of the ages of 28, 42, 56 and 90 days for the sandcement ratios of 5.5, 6, 6.25, 6.5 and 7 for the sample with 50 % coarse aggregate. In the fourth step, by increasing the ratio of sand to cement, samples with a lower percentage of sand have higher bending strength.