Wael Alnahhal

This paper reports on the results of an experimental study on the flexural performance of recycled-aggregate concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars. A total of eight reinforced concrete (RC) beams were prepared and tested under four-point loading. The parameters investigated included: (1) concrete mixture (0, 25, 50, and 100% use of recycled concrete aggregates (RCA)) and (2) reinforcement material (steel/BFRP). The results revealed minimal effects of the use of RCA on the flexural behavior of RC beams. Altering reinforcement material, on the other hand, showed a significant effect on the flexural behavior of RC beams: using BFRP (instead of steel) reinforcement reduced the deformational performance but yielded comparable ultimate capacity of RC beams at 0% and 100% RCA replacement ratios. The cracking loads and crack spacings of steel RC beams were generally higher compared to BFRP-RC beams at the same RCA replacement ratio. Theoretical investigations of ultimate capacities and service load deflections were performed for the tested beams based on contemporary design guides and were compared with the experimental results. The findings of this study underscored the potential of using RCA and BFRP bars as sustainable alternatives to the conventional materials in reinforced concrete.

Steel corrosion poses a serious threat to the structural performance of reinforced concrete (RC) structures. Thus, this study evaluates the flexural capacity of RC beams through machine learning (ML)-based techniques with six parameters used as input features: beam width, beam effective depth, concrete compressive strength, reinforcement ratio, reinforcement yield strength, and corrosion level. Four single and ensemble ML models are evaluated; namely, decision tree, support vector machine, adaptive boosting, and gradient boosting. Hyperparameters of each model were optimized using grid search and K-fold cross-validation with root mean squared error used as the performance index. The predictive performance of each model was assessed using four statistical performance metrics. The analysis results demonstrated that the decision tree model exhibited overfitting and limited generalization ability. The adaptive boosting model also had a slight overfitting issue. In addition, the support vector machine reported comparable accuracy to that of adaptive boosting. Conversely, the proposed gradient boosting ensemble model achieved the best performance with strong generalization ability, as indicated by its lowest mean absolute error of 2.78 kN.m, mean absolute percent error of 13.40%, and root mean squared error of 3.56 kN.m, and the highest coefficient of determination of 97.30% on the test dataset. The optimized gradient boosting model has been deployed into a graphical user interface, allowing for practical implementation of the model and enabling fast, efficient, and intelligent prediction of the flexural capacity of corroded RC beams.

Corrosion is a common condition encountered by steel reinforcing bars which has a considerable negative impact on the structural integrity of concrete structures. Nowadays, applying anti-corrosive composite materials such as fiber-reinforced polymer (FRP) bars as reinforcing bars instead of steel bars is a major area of interest among researchers. The current study presents an investigation on the influence of surface treatment of the basalt (B) FRP reinforcing bars on the shear strength ofone-way high-strength concrete slabs. Two types of BFRP bars were tested, one with a sand-coated surface and the other with a ribbed surface.The testing results showed that the ribbed BFRP bars resulted in a slightly higher shear strength than the slab reinforced with sand-coated bars. The ultimate shear capacity in the ribbed bars reinforced slab was recorded as 95.65 kN, whereas it was recorded as 90.08 kN in the sand-coated bars reinforced slab. Moreover, in comparison to the slab with sand-coated bars, the first flexural crack was delayedin the slab with ribbed bars.Also, reinforcing the one-way slab with ribbed BFRP bars has shown higher stiffness represented by lower midspan deflection at all loading stages compared to the sand-coated bars. As a result, this has induced lower stresses on the ribbed bars, which caused lower midspan strain values in the ribbed bars than the sand-coated bars.