Abstract
ABSTRACTDue to rapid construction, necessity for raw materials of concrete, especially coarse aggregate, tends to increase the danger of early exhaustion of the natural resources. An alternative source of raw materials would perhaps delay the advent of this early exhaustion. Recycled coarse aggregate (RCA) plays a great role as an alternative raw material that can replace the natural coarse aggregate (NCA) for concrete. Previous studies show that the properties of RCA concrete are inferior in quality compared to NCA concrete. This article attempts to study the improvement of properties of RCA concrete with the addition of bacteria named as Bacillus subtilis. The experimental investigation was carried out to evaluate the improvement of the compressive strength, capillary water absorption, and drying shrinkage of RCA concrete incorporating bacteria. The compressive strength of RCA concrete is found to be increased by about 20% when the cell concentration of B. subtilis is 106 cells/ml. The capillary water absorption as well as drying shrinkage of RCA are reduced when bacteria is incorporated. The improvement of RCA concrete is confirmed to be due to the calcium carbonate precipitation as observed from the microstructure studies carried out on it such as EDX, SEM, and XRD.
Highlights
Crushed concrete that results from the demolition of old structures is generated nowadays in large quantities
The experimental investigation is carried out to study the enhancement of properties such as compressive strength, drying shrinkage, air content, and capillary water absorption of Recycled coarse aggregate (RCA) concrete with the addition of B. subtilis
The salient conclusions of the present study are as follows: (1) Properties of RCA concrete such as compressive strength, capillary water absorption, and drying shrinkage are improved by the addition of B. subtilis
Summary
Crushed concrete that results from the demolition of old structures is generated nowadays in large quantities. Many attempts to develop structural concrete with RCA have been reported in the literature From these studies, it is worth noting that a certain amount of mortar from the parent concrete remains adhered to the stone particles in RCA. This adhered mortar forms a weak porous interface, which influences the strength and performance of RCA concrete [5,6,7] and subsequently results in concrete with lower quality [8,9,10,11,12,13]. This is considered to be one of the most significant differences between RCA and NCA concrete
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