مقاله انگلیسی رایگان در مورد کارایی انعطاف پذیر از تیرهای بتن مسلح ساخته شده با توده زبر بتن بازیافت شده – الزویر 2018

This work deals with the flexural performance of recycled concrete subjected to increasing loads up to failure. For this purpose, eight reinforced concrete beams were made with recycled coarse aggregates using two different water to cement ratios (0.50 and 0.65) and four replacement percentages (0%, 20%, 50% and 100%). Firstly, the basic concrete properties were determined (mechanical strengths and modulus of elasticity) and then, beam specimens were loaded up to failure using a four-point bending test at 28 days. As a result, bending moments, deflections, strains and curvatures were obtained at different load levels (cracking, service, yielding and ultimate state conditions), and also, the crack pattern. On the basis of these results, it can be noted that service, yielding and ultimate state of recycled concrete exhibits, in general, a similar trend to that of conventional concrete. However, the cracking behaviour shows differences between recycled and conventional concrete. Finally, code-based expressions were used to calculate bending moments and deflections under flexural load, taking into account the different content of recycled coarse aggregate.

Introduction

In order to promote the sustainability of concrete, efforts have been made to address some of the environmental problems associated with concrete waste. In line with this, numerous researches have been conducted to analyse the structural performance of recycled concrete [1–13]. However, its use in real building and civil engineering applications requires more full scale studies, to assess the load-deformation response of recycled concrete that leads to good agreement on structural design. Regarding flexural performance of structural recycled concrete, different investigations have been carried out [4,8,9,12]. However, the number of studies on concretes with high replacement percentages is scarce and additionally, some contradicting conclusions have been detected. While some authors [1,9,10,13] have found that recycled concrete beams show higher deflections, and cracking moments lower or similar to those of the conventional, others [6,8] have reported no significant difference between recycled and conventional concrete in terms of flexural performance. On the basis of the literature review, it can be seen that the codebased procedures for conventional concrete can also be applied to recycled concrete predictions for flexural behaviour [2,6,9], although some differences have been detected. In line with this, the increase in recycled coarse aggregate results in the reduction of concrete stiffness [9], which is consistent with the increased beam deflections of recycled concrete. Most authors [2,8–10] point out similar yielding and ultimate behaviour, but some [7] have found little differences in cracking behaviour, in terms of crack spacing and pattern. In general, it can be said that recycled concretes are able to fulfill strength and serviceability requirements similarly to conventional reinforced concrete. However, in order to encourage its use as structural concrete, it is important to be able to design reinforced concrete members made with recycled coarse aggregate, using existing design methods [6]. Accordingly, recent publications [2,9] have indicated that more full-scale research should be done to stablish a good agreement on its flexural performance and increase the results database for structural recycled concrete. This would lead to concrete properties, service-load and ultimate–load behaviour being predicted with the same approximation degree as conventional concrete. Furthermore, with the aim of carrying out an accurate structural design, some concrete parameters have to be considered such as, tension stiffening, strength capacity or cracking behaviour. Tension stiffening is known as the concrete contribution after cracking and has significant importance in structural design. This parameter is required to accurately design concrete structures as customary serviceability conditions occur after cracking.