دانلود رایگان مقاله انگلیسی خواص مکانیکی بتن بازیافتی با مصالح بتی ضایعات تخریبی و مصالح آجر خاک رسی - الزویر 2018

Abstract

This paper presents an experimental investigation on the effect of the replacement of natural coarse aggregate (NCA) with either recycled concrete aggregate (RCA) or recycled clay brick aggregate (RBA) on the compressive strengths of the hardened concrete. Two grades (C25 and C50) of concrete were investigated, which were achieved by using different water-to-cement ratios. In each grade concrete five different replacement rates, 0%, 25%, 50%, 75% and 100% were considered. In order to improve the performance of the recycled aggregates in the concrete mixes, the RCA and RBA were carefully sieved by using the optimal degradation. In this way the largest reduction in the 28-day compressive strength was found to be only 7.2% and 9.6% for C25 and C50 recycled concrete when the NCA was replaced 100% by RCA, and 11% and 13% for C25 and C50 recycled concrete when the NCA was replaced 100% by RBA. In general, the concrete with RCA has better performance than the concrete with RBA. The comparison of the present experimental results with those reported in literature for hardened concrete with either RCA or RBA demonstrates the effectiveness in improving the compressive strength by using the optimal gradation of recycled aggregates.

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.