A full understanding of the characteristics of the granular skeleton comprising different percentages of conventional and recycled aggregates is requisite to the reusability of construction and demolition waste. This study analyzed the effect of partially replacing natural aggregate with recycled concrete (RCA) and mixed (RMA) aggregates on the performance of granular mixtures. Each type of aggregate was characterized physically, chemically, mineralogically, and mechanically, and the physical and mechanical properties of the mixtures were assessed. Correlations were established to predict the optimal mixture proportions. The recycled aggregates analyzed met most requirements laid down in the national legislation and complied with international recommendations. The mixtures exhibited a close linear correlation between the properties analyzed and the recycled aggregate replacement ratios. For concrete, the upper limit was 75% for RCA and RMA, and for the base and intermediate layers in medium/low traffic roads, 75% for RCA and 35% for RMA.

The dimensioning of structural systems in reinforced or prestressed concrete requires knowledge, among other properties, at least of the deformation modulus and compressive strength. However, concrete may present enough strength, whereas the structure rigidity might not be compatible with minimum required values for the verification of possible deformations. In Brazil, the estimate of deformation modulus is made using the NBR 6118 theoretical equation and internationally, the main theoretical models used are recommended in ACI 318, Eurocode 2, and the fib Model Code. But the bibliography indicates that there is no confidence in the models proposed. The present study aims to analyze the isolated effect of paste volume on the portland cement concrete deformation modulus. The results of the study indicate a significant influence of paste volume on the module value and, because a reduction in the amount of paste volume occurs, the concrete deformation modulus increases for all ages. The lack of consistency is also observed between experimental values and those obtained by theoretical equations, suggesting independency of the two magnitudes, compressive strength, and deformation modulus.

An experimental investigation was conducted to study the mechanical properties and shear strength of full-scale beams constructed with recycled concrete aggregate (RCA). This study included two RCA mixtures and one conventional concrete (CC) mixture. The two RCA mixtures are different in the amount of RCA replacement, with one mixture replacing 50% of the virgin aggregate with RCA (RAC50) and the other replacing 100% (RAC100). This experimental program consisted of 18 beams with three different longitudinal reinforcement ratios. The experimental shear strengths of the beams were compared with the shear provisions of both U.S. and international design codes. Furthermore, the shear strengths of the beams were evaluated based on fracture mechanics approaches, Modified Compression Field Theory (MCFT), and a shear database of CC specimens. In addition, statistical data analyses were performed to evaluate whether there is any statistically significant difference between the shear strength of the recycled-aggregate concrete (RAC) and CC beams. Results of this study show that the RAC100 has 11% lower shear strength, on average, compared with the RAC50 and CC beams; however, the RAC50 and CC beams showed similar shear resistance. The decrease in basic mechanical properties (splitting tensile strength, flexural strength, and fracture energy) for the RAC parallels the decrease in full-scale shear behavior and can be used as a predictor in mixtures containing recycled concrete as aggregate.

The aim of this study is to investigate the possibility of partially substituting natural aggregates with black/oxidizing electric arc furnace (EAF) slag for reinforced concrete (RC) structural elements. International research has been mainly focused on experimental tests on small specimens rather than investigating the behavior of RC structural elements. In this study, the experimental behavior of RC beams made with EAF slag as aggregate was studied showing that these beams have both ultimate flexural and shear capacity higher than the corresponding traditional beams. Some comparisons between experimental results and analytical predictions according to the European and U.S. recommendations were also shown. The main result of this study is that the use of steel slag as aggregate in RC structural elements is, in principle, possible, and the rate of substitution could reach the entire part of coarse aggregates, obtaining benefits both from an economical and environmental point of view.

To obtain adequate serviceability and good durability of structures, international standards limit the crack width either through a direct calculation or by adopting specific measures. However, cracking behavior is very complex because of the large number of parameters that can have a significant effect on it. This complexity is also confirmed by the high scattering of the test results or by the several formulas that are adopted to theoretically govern the phenomenon. The cracking behavior of reinforced concrete (RC) structures under bending, with or without axial forces, can be described with a model based on the bond stress-slip relationship, t-s, between concrete and steel. A model of this type based on the bond law proposed by CEB-FIP Model Code 1990 was developed in the literature to predict the mechanical behavior of an RC tie subjected to monotonic loading, both in the crack formation phase and the stabilized cracking phase. However, the adoption of the bond stress-slip relationship as it is fails to comply with the equilibrium condition and contradicts the experimental condition of the fixed crack pattern. These inconsistencies can be overcome considering the effect of the so-called Goto cracks or secondary cracks, which leads to a decreasing trend of the bond stresses around the crack. The effect of secondary cracks on the cracking behavior of an RC tie in the stabilized cracking phase is also analyzed through a parametric analysis, which highlights how and to what extent their influence zone varies as a function of the axial force, the concrete strength, the reinforcement ratio, and the bar diameter.