Abstract
In order to investigate the internal curing effect of recycled brick aggregate (RBA) in recycled aggregate concrete (RAC) and calculate its contribution to the final compressive strength, two RAC groups with different recycled aggregates and 6 replacement ratios (r) under 4 curing ages were tested. Results show that the compressive strengths of RACI and RACII decrease steadily with the increase of r when below 40%, and that there is a significant drop once the r is higher than 60%. The internal curing effect for RAC with a low RBA ratio is mainly reflected during the curing age of 14–21 days, while for RAC with a high RBA ratio, this internal curing effect appears earlier, during 7–14 days, and becomes very obvious after 14 days. In addition, the actual tested compressive strength of RAC replaced by 100% RBA exceeds around 40% of the expected compressive strength at the age of 28 days. When the age of RAC entirely with RBA is 28 days, the compressive strength caused by the internal curing effect accounts for around 28% of the actual tested compressive strength. The most appropriate r of RBA for RAC production is between 40% to 60%. Finally, the equations for calculating the compressive strength of RAC are presented considering the curing ages, the replacement ratios and the internal curing effect of RBA. Further, a unified equation is suggested for convenience in calculation.
Highlights
Using recycled materials to replace natural aggregate (NA) in concrete is important from the environmental aspect of reuse
It should be noted that an aggregate fraction less than 5 mm is normally not used for recycled aggregate concrete (RAC) [21], so the sizes of most aggregates are between 10–30 mm
To the best knowledge of the authors, no research effort has been devoted to investigating the internal curing effect of recycled brick aggregate (RBA) in RAC, and there are no accurate calculations of compressive strength considering the internal curing effect
Summary
Using recycled materials to replace natural aggregate (NA) in concrete is important from the environmental aspect of reuse. Using crushed waste concrete and clay brick as alternative aggregates has particular significance since they can considerably reduce the problem of waste storage as well as help in the preservation of NA [1,2]. Recycled aggregate concrete (RAC) with waste concrete or clay brick as recycled aggregate (RA) is a green, interesting material with some unknown properties that need to be studied. A few studies have contributed to the research into using crushed clay brick as the coarse aggregate in concrete production. Many of them have focused on the mechanical properties of RAC directly, especially its compressive strength [3,4]. The results of Ghernouti et al [5] showed that it is possible to manufacture RAC blocks that are comparable in compressive strength to normal concrete, but with an appreciable reduction in weight. Miličević et al [6] tried to find the optimal replacement ratio, and their experimental research illustrated that with a 50% fine and 45% coarse NA replacement
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