4.Conclusions
This paper has presented an experimental investigation on the effect of the replacement of natural coarse aggregates with recycled aggregates on the compressive strength of the hardened concrete. The experiments involved the use of two types of recycled aggregates, namely RCA and RBA, and two types of concrete mixes (C25 and C50 grade concrete) which were achieved by using different water-to-cement ratios. From the obtained experimental results the following conclusions can be drawn.
The compressive strength of the hardened concrete decreases with the increased replacement of NCA by RCA or RBA and in general, the concrete with RCA has better performance than the concrete with RBA.
For C25 grade concrete the compressive strength of the concrete with RBA is close to that of the concrete with RCA. The 28-day compressive strength of the concrete drops only by 7.2% or 11% when the NCA is completely replaced with RCA or RBA.
For C50 grade concrete there is a remarkable difference between the compressive strengths of the concrete with RCA and RBA. The 28-day compressive strength of the concrete drops by 9.6% or 13% when the NCA is completely replaced with RCA or RBA.
For concrete with RCA the strength development continues after the 28 days curing; whereas for concrete with RBA the strength development becomes very slow after the 28 days curing. This is particularly so for the C50 grade concrete with high RBA replacement rate.
The comparison of the present experimental results with those reported in literature for hardened concrete with RCA or RBA demonstrates the effectiveness in improving the compressive strength by using the optimal gradation of recycled aggregates.
