دانلود رایگان مقاله انگلیسی کارایی انعطاف پذیر از تیرهای بتن مسلح ساخته شده با مصالح زبر بتن بازیافتی - الزویر 2017

ABSTRACT

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.

6. Conclusions

In this work, the flexural performance of recycled concretes has been determined. On the basis of these results the following conclusions can be drawn:

• The cracking moment decreases as the replacement percentage increases. This reduction is consistent with the lower tensile splitting strength of recycled concretes, which leads to a greater and earlier cracking than with conventional concrete.

• At serviceability, bending moments and deflections are slightly affected by the content of recycled coarse aggregate due to the low influence of material properties on structural response when structural members are designed to present a ductile behaviour.

• The ductile design of steel reinforcement leads to yielding and ultimate behaviour of recycled concretes similar to that of conventional concrete, even when high replacement percentages are used. Therefore, the decrease in cracking moment and the invariability of yielding and maximum moments confirms early cracking development in recycled concretes.

• The crack pattern shows, in general, a similar behaviour in both recycled and conventional concretes. In terms of crack spacing, the lower modulus of elasticity and tensile splitting strength of recycled concrete make the flexural cracks closer together and therefore, reduce the crack spacing. However, the lower bond strength of recycled concretes counteracts this effect. As a result, recycled concrete shows similar crack spacing to that of conventional concrete. Consequently, this similar crack spacing and the higher strains of concrete and steel reinforcement result in greater crack width in recycled concrete compared with conventional concrete.