Highlights

Abstract

Keywords

۱٫ Introduction

۲٫ Research significance and objectives

۳٫ Experimental program

۳٫۱٫ Concrete specimens

۳٫۲٫ Test setup and instrumentation

۳٫۳٫ Concrete properties and test parameters

۴٫ Results and discussion

۴٫۱٫ Concrete deformations: Strains and deflections

۴٫۲٫ Recovery strains

۴٫۳٫ Deflection recovery

۴٫۴٫ Analysis of uncracked and cracked concrete beams

۵٫ Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

References

Abstract

The purpose of this research is to analyse the long-term deformations of reinforced concrete beams made of recycled coarse aggregates (RCA), using four different replacement ratios, 0%, 20%, 50% and 100%. For said purpose, three different loading stages were carried out: firstly, loading and sustained load for 1300 days, secondly, unloading and recovery where the deformations were registered over a one year period, and lastly, testing the concrete beams up to failure in order to analyse the effect of recycled aggregates on pre-cracked concrete members. The results led to the analysis of deformations under sustained load, as well as those produced after removing the load and the performance of pre-cracked members, while identifying the effect of recycled coarse aggregates on concrete performance in terms of plastic deformation, recoverability and concrete stiffness, and also on structural design.

۱٫ Introduction

In recent years, the use of construction and demolition waste as aggregates for structural concrete has been widely studied. Numerous authors have contributed to the increasing knowledge in this field, analysing the structural performance of recycled concrete and its properties, such as mechanical strength, modulus of elasticity, creep and shrinkage or durability [1], [2], [3]. As a result, several expressions and methods have been assessed for the design of structural concrete using recycled aggregates [4], [5], [6], [7], [8], [9], [10], [11], [12]. Most authors deal with the short and long-term behaviour of concrete while considering only the influence of creep and shrinkage [13], [14], [15] and very few include the ageing effect of concrete, its different cracking behaviour or its ability to recover from deformations after a load is varied or removed [16].

As common concrete structures are usually submitted to load variations during their service life, it is important to consider the effect of creep over time, including not only loading periods but also unloading the stages and the recoverability of concrete. As mentioned by Rossi et al. [17] understanding the behaviour of concrete structures is greatly simplified by the numerical modelling of their mechanical behaviour. However, progress needs to be made to predict the long-term behaviour of concrete with sufficient accuracy. In order to determine the deformational mechanism, it is also important to analyse the effect of cracking and residual strain i.e. the irreversible part of strain. Many factors influence deformation and the ability of concrete to recover after unloading. Once the hysteretic recovery has finished, the residual deformation can be defined as plastic deformation. Additionally, it can be assumed that concrete deformations under loading are mainly due to creep, especially for long periods of loading and therefore, the ability of deformations to recover after unloading is closely linked to creep recovery.