# Analysis of the Aggregate Effect on the Compressive Strength of Concrete Using Dune Sand
## 3 Results and Discussion
### Aggregate Effect on Compressive Strength  
As specified above, mixtures with the same water-cement ratios and water contents had the same paste and aggregate volumes. However, there were differences in aggregate volume fractions for the different DS replacement ratios. Figure 9 shows the aggregate volume fractions and compressive strengths by age for each mixture with different water contents and DS/FA ratios. Because the mixtures with the same paste and aggregate volumes also had different compressive strengths depending on their aggregate volume fractions, we deduced that the aggregate volume fraction has an impact on the compressive strength of concrete. Figure 8: Mean compressive strengths and standard deviations of concrete mixtures with different water contents. Figure 7: Mean compressive strengths and standard deviations of concrete mixtures with different DS/FA ratios. In this study, to analyze the effect of aggregates on the compressive strength of concrete, the following equation was proposed that considers the change in the compressive strength of each mixture, the change in aggregate volume fractions, and the effect factors of each aggregate type on the compressive strength. In this study, the effect factor was used as a coefficient representing the properties of the aggregate that could affect the compressive strength of the concrete. The effect factor of each aggregate type on the compressive strength of the concrete is calculated as the coefficient representing the properties of the aggregate that could affect the compressive strength of the concrete. Figure 9: Aggregate volume fractions and compressive strengths of (**a**) W170, (**b**) W160, and (**c**) W150. strength of the concrete. In addition, although the relationship between the compressive strength of concrete and the aggregate properties may be expressed as a polynomial, a monomial expression was first adopted in this study. \[\Delta S=a\cdot\Delta DS+b\cdot\Delta CS+c\cdot\Delta CA \tag{1}\]  
where \(\Delta S\) is the change in compressive strength (Mpa), \(\Delta DS\) is the change in \(DS\) volume (\(\ell\)), \(\Delta CS\) is the change in \(CS\) volume (\(\ell\)), \(\Delta CA\) is the change in \(CA\) volume (\(\ell\)), \(a\) is the effect factor of \(DS\) on compressive strength (Mpa/\(\ell\)), \(b\) is the effect factor of \(CS\) on compressive strength (Mpa/\(\ell\)), and \(c\) is the effect factor of CA on compressive strength (Mpa/\(\ell\)). First, the changes in compressive strength and aggregate volume fractions were calculated for the mixtures that exhibited the highest compressive strength at each age among the mixtures with the same water contents. Among the W170 mixtures, the W170-D40 mixture was used as the reference mixture only for the W170-D20 mixture at an age of 3 days, whereas the W170-D20 mixture was used as the reference for the other ages. Among the W160 and W150 mixtures, the W160-D20 and W150-D20 mixtures were used as the reference mixtures. Table 3 lists the calculated changes in compressive strength and aggregate volume fractions of the mixtures with respect to the reference mixtures. Next, the influences of the magnitude of the effect factor of each aggregate type on the changes in the compressive strength of the concrete mixtures were examined. It has been reported that the compressive strength of concrete increases as the particle size of the CA increases [20; 21; 22; 23; 24; 25]. On the contrary, some studies have reported that the compressive strength of concrete increases as the particle size of the CA decreases [26; 27; 28; 29; 30]. Thus, it is difficult to assess the magnitude of the effect factor of each aggregate type on the concrete compressive strength based on the particle size of the aggregate. In addition to the aggregate particle size, other properties of an aggregate that could affect the compressive strength of concrete include its surface texture, particle shapes, and strength.