Abstract
At present, many modification methods have been proposed to improve the performance of recycled aggregate concrete (RAC). In this study, tests on the compressive strength and damping properties of modified RAC with the addition of different proportions of recycled coarse aggregate (RCA) (0, 50, 100%), rubber powder (10, 15, 20%), steel fibre (5, 7.5, 10%) and fly ash (15, 20, 5%) are carried out. To elucidate the effect of the modification method on the interfacial transition zone (ITZ) performance of RAC, model ITZ specimens are used for push-out tests. The results show that when the replacement rate of RCA reaches 100%, the loss factor of the RAC is 6.0% higher than that of natural aggregate concrete; however, the compressive strength of the RAC decreases by 22.6%. With the addition of 20% rubber powder, the damping capacity of the modified RAC increases by 213.7%, while the compressive strength of the modified RAC decreases by 47.5%. However, with the addition of steel fibre and fly ash, both the compressive strength and loss factor of the RAC specimens increase. With a steel fibre content of 10 wt%, the compressive strength and loss factor of the RAC increase by 21.9% and 15.2%, respectively. With a fly ash content of 25 wt%, the compressive strength and loss factor of the RAC increase by 8.6% and 6.9%, respectively. This demonstrates that steel fibre and fly ash are effective in improving both the damping properties and compressive strength of RAC, and steel fibre is more effective than fly ash. Two methods were used for modification of the RAC: reinforcing the RCA through impregnation with a 0.5% polyvinyl alcohol (PVA) emulsion and nano-SiO2 solution, and strengthening the RAC integrally through the addition of fly ash as an admixture. Both of these techniques can improve the ITZ bond strength between the RAC and new mortar. Replacing 10% of the cement with fly ash in the new mortar is shown to be the best method to improve the ITZ strength.
Highlights
With the growing interest in sustainable and environmentally friendly construction, recycled aggregate concrete (RAC) has been widely investigated and is gradually being incorporated into real engineering projects
When the coarse aggregate is completely replaced with recycled coarse aggregate (RCA), the loss factor of the RAC is increased by 6.0%, while the compressive strength of the RAC decreases by 22.6%
After adding 20% rubber powder, the damping capacity of the modified RAC is increased by 213.7%, while the compressive strength of the modified RAC decreases by 47.5%
Summary
With the growing interest in sustainable and environmentally friendly construction, recycled aggregate concrete (RAC) has been widely investigated and is gradually being incorporated into real engineering projects. Many studies have found that the mechanical properties of RAC decrease with an increasing replacement rate of recycled coarse aggregate (RCA) [1,2,3]. The compressive strength of RAC is generally 10–30% lower than that of natural aggregate concrete (NAC) [4,5,6], while the flexural strength is generally approximately 10% lower than that of NAC [5]. The tensile strength of RAC is generally approximately 6% lower than that of NAC, and the elastic modulus is generally 10–33% lower than that of NAC [5,7]. The addition of admixtures, fibres and aggregate impregnation has been investigated
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