## 4 Conclusions  
This study allows a better understanding of the compressive strength of concrete made with aggregates of various geological natures (e.g., limestone, basalt, granite, and quartz) and qualities (WA, density, and LA abrasion). The following conclusions can be drawn from this study. Figure 9: Relationship between the actual and calculated compressive strength of concrete mixes made with 100% NA and RA classified in terms of their quality. The strength was calculated according to [PERSON]’s model. The physical quality of A aggregates is better than B, followed by C and D. (**a**) \(k\) values for NA and RA concrete mixes, (**b**) k1 and k2 are the upper and lower boundaries for the 95% confidence intervals, and (**c**) the average \(k\) value is the average of k1 and k2 from Figure 9b. The standard deviation for the \(k\) values was \(\approx\)0.51 in (**c**). The original ([PERSON], [PERSON], and ACI) and modified ([PERSON] and [PERSON]) models cannot accurately estimate the compressive strength of concrete when the characteristics of aggregates are neglected. In other words, the estimated strength of concrete based on the quality of cement paste only is not accurate, and the relationship between the actual and calculated strength for all the original models is poor when only \(w/c\) (with and without considering the volume of aggregates to the cement content) is considered as an influencing factor. The scatter between the calculated and experimental compressive strength of concrete, even if made with 100% NA, is significant. In other words, for the same mix composition (similar cement paste quality), there are significant differences between the results when various geological natures of NA (e.g., limestone, basalt, granite, sandstone) are used in concrete. The same is true when various qualities (WA, density, and LA abrasion) of aggregates are used. The modified models ([PERSON] and [PERSON]) work better than the original models ([PERSON], [PERSON], and [PERSON]) because they consider the strength class of cement as one of the factors. However, [PERSON]'s model does not consider the ratio of the volume of aggregates to cement paste, and [PERSON]'s model does not consider how the aggregates are obtained (e.g., rolled or crushed) as influencing factors. In most cases, the scatter between concrete mixes measured by the difference between the upper (k1) and lower (k2) boundaries (\(k=f_{\text{cm, calculated}}/f_{\text{cm, experimental}}\)) for a 95% confidence interval significantly decreased when they were split based on the geological nature of the aggregates used. The same occurred when the mixes were split based on the quality of their aggregates. According to both modified models ([PERSON] and [PERSON]), the calculated/actual strength ratio of the concrete mixes made with basalt is higher than that of the mixes with aggregates of other geological natures--in descending order, limestone, quartz, and granite. In terms of the physical characteristics of the aggregates, the calculated/actual strength ratio of concrete increases as the quality (high WA, low density, and LA abrasion) of the aggregates decreases. In order to further show the importance of considering the physical characteristics of aggregates, the strength of a few examples of concrete made with aggregates of various qualities (A, B, C, and D, according to Table 1), namely incorporating 100% coarse RA or NA, was calculated using [PERSON]'s model. For a 95% confidence interval, the scatter between the mixes made of NA (mostly classed as A) was slightly smaller than that of the mixes made with RA (generally classed as B-D), but still significant. This means that to estimate the compressive strength of concrete made with either NA or RA, the influence of the geological nature and physical quality cannot be ignored, and this should be included both in the standard formulas and in the codes.