Towards Better Understanding of Concrete Containing Recycled Concrete Aggregate

Abstract

The effect of using recycled concrete aggregates (RCA) on the basic properties of normal concrete is studied. First, recycled aggregate properties have been determined and compared to those of normal aggregates. Except for absorption, there was not a significant difference between the two. Later, recycled aggregates were introduced in concrete mixes. In these mixes, natural coarse aggregate was partly or totally replaced by recycled aggregates. Results show that the use of recycled aggregates has an adverse effect on the workability and air content of fresh concrete. Depending on the water/cement ratio and on the percent of the normal aggregate replaced by RCA, the concrete strength is reduced by 5% to 25%, while the tensile strength is reduced by 4% to 14%. All results are compared with previous research. As new in this research, the paper introduces a simple formula for the prediction of the modulus of elasticity of RCA concrete. Furthermore, the paper shows the variation of the air content of RAC.

X-ray computed tomography harnessed to determine 3D spacing of steel fibres in self compacting concrete (SCC) slabs

“…The authors are convinced that the future research programmes should cover the processes of concrete casting and placement of reinforcement. Saving large amounts of energy and time, during these technological steps would result in making the whole erecting process much greener, especially while harnessing recycled fibre [8] and waste aggregate [30] for its production. Compacting fresh concrete mix through vibrating and laborious placement of re-bars and stirrups significantly increase the amount of energy needed for erecting a concrete structure.…”

Effect of bitumen grade on hot asphalt mixes properties prepared using recycled coarse concrete aggregate

“…The RCA aggregate conformed to RILEM 1994 Type II [18]. Aggregate conforming to that specification showed acceptable behavior in normal concrete mixes [19]. Also RCA conformed to the requirements of RILEM TC 217.…”

“…Some of these researches are included in references [19][20][21][22][23][24][25][26]. Most of these researches consider that the use of RCA is environmentally efficient.…”

Two-lift concrete paving for sustainable pavements

“…One primary concern with recycled materials is the long-term durability performance, which is a function of the replacement level, water-to-cementitious-material ratio, concrete age, and moisture (Yehia et al, 2015). Even though recycled aggregate concrete typically results in lower mechanical properties (Brand et al, 2014), lower abrasion and ingress resistance (Thomas et al, 2013), and lower fresh concrete properties (Qasrawi and Marie, 2013), it can generally be produced to meet standard aggregate quality and grading requirements if adequate replacement level, proper care, and process control are taken into account. The incorporation of RCA, RAP, and/or FRAP into twolift concrete pavement provides economic, environmental, and sustainability advantages, and offers practical solutions.…”