Volume 18, Issue 3 (2018)                   IQBQ 2018, 18(3): 153-167 | Back to browse issues page

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Investigation on the Correlations Between Different Physical and Mechanical Properties of Concrete Made with Recycled Concrete Aggregate. IQBQ. 2018; 18 (3) :153-167
URL: http://journals.modares.ac.ir/article-16-25738-en.html
Abstract:   (437 Views)
In the last few years, increase in construction rate has caused several new challenges, including waste storage problems, environmental pollution problems, excessive mining of natural resources, and shortage in sand and gravels sources. One way to address these problems and reduce the negative environmental impacts is reusing concrete waste as a new material in construction. Concrete waste could be crushed, graded, and used as aggregate, referred to as recycled concrete aggregate (RCA), in producing new concrete. There is a common agreement that recycled aggregate concrete (RAC) has inferior properties compared to natural aggregate. Nevertheless, structural usage of RAC has been growing in the last decade. However, due to different engineering properties of RCAs compared to natural aggregates (NA), it seems that the existing correlations between different mechanical properties for normal concrete cannot be used for RACs. This research focused on this topic with the aim of finding suitable correlations between different parameters such as water absorption coefficient, compressive strength, tensile strength, and flexural strength for RACs. In this research, two different types of coarse recycled concrete aggregates [CRCA-1 and CRCA-2] and one type of fine recycled concrete aggregate [FRCA] were considered. Also, for improving the mechanical properties of RACs, two types of supplementary cementitious materials (SCMs), namely 8% silica fume and 15% zeolite were used. A total of 18 concrete mixes were considered and various physical and mechanical tests were conducted on concrete samples made according to the designated mix designs. Concrete mixes were categorized in two different groups. In the first group, both FRCA and CRCA-1 were used. As for the second group, 11 mixes were considered in order to investigate the effect of SCMs on the mechanical properties of RACs. Correlations between results of water absorption coefficient, compressive strength, tensile strength, and flexural strength were investigated and compared to those for normal concretes. The results showed that substitution of NA with CRCA resulted in inferior mechanical properties of concrete. It is worth to note that FRCA had a more significant impact on the mechanical properties of concrete compared with CRCA-1. Also, utilization of 8% silica fume or 15% zeolite as a SCM had a positive effect on the mechanical properties of RACs, such that mixes containing 30% CRCA-2 and 8% silica fume or 15% zeolite had similar 28-day compressive strength to the reference mix. On the other hand, the results showed that existing correlations for normal concrete cannot be used for RACs due to different behavior of RACs compared to normal concrete. The correlation between 28-day tensile strength and 28-day compressive strength for RACs had a bigger coefficient (0.52) compared to normal concrete (0.49). As well correlation between 28-day flexural strength and 28-day compressive strength for RACs in the chosen range of compressive strength (22-43 MPa) overestimated the flexural strength compared to ACI 318's. On the basis of this research, using the equations proposed by ACI 318 for estimating the mechanical properties of RACs is not recommended, and leads to misleading results.
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Received: 2018/10/2 | Accepted: 2018/10/2 | Published: 2018/10/2

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