Abstract
This paper presents an experimental research on mechanical properties of recycled aggregate concrete (RAC) at low and high water/binder (W/B) ratios. Concrete at two W/B ratios (0.255 and 0.586) was broken into recycled concrete aggregates (RCA). A type of thermal treatment was employed to remove mortar attached to RCA. The RAC at a certain (low or high) W/B ratio was prepared with RCA made from demolished concrete of the same W/B ratio. Tests were conducted on aggregate to measure water absorption and crushing values and on both RAC and natural aggregate concrete (NAC) to measure compressive strength, tensile splitting strength, and fracture energy. The mechanical properties of RAC were lower than those of NAC at an identical mix proportion. Moreover, the heating process caused a decrease in compressive strength and fracture energy in the case of low W/B ratio but caused an increase in those properties in the case of high W/B ratio. The main type of flaw in RCA from concrete at a low W/B ratio should be microcracks in gravel, and the main type of flaw in RCA from concrete at a high W/B ratio should be attached mortar.
Highlights
Recycling of demolished concrete is an important way of utilizing building waste as a resource of the whole society and an important part of the recycling process in the building and construction field
The recycled aggregate concrete (RAC) at a certain W/B ratio was prepared with recycled concrete aggregate (RCA) made from demolished concrete of the same W/B ratio; that is, both 255RAC and H-255RAC employed the original concrete (255NAC) at the W/B ratio of 0.255, while 586RAC and H586RAC employed the original concrete (586NAC) at the W/B ratio of 0.586
Since water absorption of RCA decreased from 4.07% to 2.89% and from 7.89% to 2.77%, respectively, after removal of attached mortar, attached mortar should be responsible for a part of the increment of water absorption of RCA on the base of NA
Summary
Recycling of demolished concrete is an important way of utilizing building waste as a resource of the whole society and an important part of the recycling process in the building and construction field. The normally used mechanical process of breaking blocks of demolished concrete into relatively small grains may cause RCA suffering internal damage such as microcracks [12,13,14,15] so that RAC has relatively lower strength compared to natural aggregate concrete (NAC) at the same water/binder (W/B) ratio [8, 12, 14, 16]. Some investigations found that a couple of approaches such as particle shaping and heating plus grinding can considerably improve the quality of RCA, in the forms of enhanced density and lowered crushing value of RCA, and improve mechanical strength of RAC [16,17,18]. The control concretes were processed via two approaches, that is, crushing and heating plus removal of attached mortar, to obtain RCA, which was used to prepare RAC. [2, 12, 20] would be prevented
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