EFFECT OF RECYCLED CONCRETE AGGREGATE QUALITY ON PROPERTIES OF CONCRETE

The possibility of the use of recycled aggregates from the construction industry in green concrete production is of increasing importance to reduce the negative environmental impact associated with construction and demolition wastes.The objective of this study is to investigate the effect of recycled concrete aggregate(RCA)quality on the properties of hardened concrete properties such as compressive strength,splitting tensile strength,density,water absorption capacity and porosity accessible to water.The RCA used in this study was obtained from the crushing of waste concrete with two different compressive strengths(LRCA obtained from the crushing of waste concrete having compressive strengths below 30 MPa and HRCA obtained from the crushing of waste concrete having compressive strengths above 30 MPa).The natural coarse limestone aggregate was 100%replaced with coarse LRCA and HRCA.As a result of the study,the use of 100%HRCA and%100 LRCA instead of limestone coarse aggregate in the concrete adversely affected its mechanical and physical properties.In addition,HRCA showed better performance in terms of compressive strength,tensile strength,water absorption and porosity compared to the use of LRCA.Furthermore,the percentage of adhered mortar on the surface of LRCA and HRCA was analyzed using a computerized micro tomography device,and it was found that the percentages of attached mortar and aggregates are 61%and 35.5%for LRCA,whilst the attached mortar and aggregate contents for HRCA are 45.9%and 53.7%,respectively.

Performance studies on recycled aggregate concrete with treated recycled aggregates

Excessive construction activities generate huge quantities of waste that are disposed of in nearby sites,leading to environmental degradation.Recycling the concrete fractions of construction wastes for their utilization as aggregates has been predominant among industrialists and researchers in recent years.However,the smearance of cement mortar on the recycled aggregates affects the concrete properties.Fewer treatments were developed to remove the weak cement mortar or seal the micro-pores on the adhered cement mortar of recycled aggregates.This paper investigates the comparative efficiency of acid and carbonation treatment on recycled coarse aggregate(RCA)properties and its behaviour on recycled aggregate concrete(RAC).The RCA was treated with HCl acid at 0.1 mol/L,0.5 mol/L,and 0.8 mol/L and CO_(2) at 0.1 bar,0.2 bar,and 0.4 bar and tested for their physical properties,and the concrete mixtures with treated recycled aggregates were tested for fresh and hardened properties.It could be observed that the properties of RAC were affected owing to the smearance of weak mortar,whereas for the concrete with carbonated(RACc)and chemically treated aggregates(RACa),the concrete properties tended to improve.The strength of RAC was 28.59%less than that of normal aggregate concrete(NAC),whereas the strength of RACc and RACa was enhanced by 16.44%and 9.7%compared to that of RAC at 28 days.The water absorption of RAC was 47.51%more than that of NAC,whereas the water absorption of RACa and RACc was 28.67%and 33.75%lesser than RAC.Pre-soaking the RCA with acids removes the adhered mortar due to its acidic activity.In contrast,in carbonation,the CO_(2) reacts with the Ca(OH)_(2) on the cement mortar to form CaCO_(3),filling the micro-cracks in the cement mortar on the RCA.