The impacts of different replacement levels of micro silica (MS), fly ash (FA), and the combined usage of MS and FA on the behavior of concrete were investigated. Design of experts has been used incorporating the response surface methodology to find the synergetic effect of FA and MS on fresh and hardened concrete properties. A total of 15 and 30% of the binder content were replaced by FA. As well as a total of 5 and 10% of the binder content were replaced by MS. Experimental results of concrete mixtures have been used to construct ANOVA models. These models have also been confirmed to expect the properties of concrete mixtures based on different fractions of FA ash and MS. All statistical models are significant because P-value is less than 5%, and the difference between predicted R ² and adjusted R ² is lower than 20%. The variation between confirmation tests for the optimized mixture and test results are lower than 5%.

This article presents a mathematical model developed using the M5P tree to predict the shear strength of steel-fiber-reinforced concrete (SFRC) for slender beams using soft computing techniques. This method is becoming increasingly popular for addressing complex technical problems. Other approaches, such as semi-empirical equations, can show known inaccuracies, and some soft computing methods may not produce predictive equations. The model was trained and tested using 332 samples from an experimental database found in the previous literature, and it takes into account independent variables such as the effective depth d, beam width b_w, longitudinal reinforcement ratio ρ, concrete compressive strength f_c, shear span to effective depth ratio a/d, and steel fiber factor F_sf. The predictive performance of the proposed M5P-based model was also compared with the one of existing models proposed in the previous literature. The evaluation revealed that the M5P-based model provided a more consistent and accurate prediction of the actual strength compared to the existing models, achieving an R² value of 0.969 and an RMSE value of 37.307 for the testing dataset. It was found to be a reliable and also straightforward model. The proposed model is likely to be highly helpful in assessing the shear capacity of SFRC beams during the pre-planning and pre-design stages and could also be useful to help for future revisions of design standards.

Waste glass in combination with recycled aggregate used in concrete under effect of sulfate attack is not yet explored. This research studies the possibility of using the wastes materials in two types of concrete applications, i.e., normal and aggressive environmental conditions for specimens of mechanical properties and RC beam models for shear behavior studies. The results demonstrated that the mechanical properties of concrete did not change when replacing recycled aggregate with recycled bricks with 50% gravel. While strength deterioration becomes evident at high rates of 100% thermestone, since non-structural concrete weakens the overall structure due to high porosity and water absorption. Also, the research investigates the effect of glass powder is used as a replacement of cement weight percentages: 0%, 10%, and 20%. Beams containing 20% glass powder showed good resistance and satisfactory shear performance under aggressive conditions.