A Comparative Study on Mortar Removal Methods and their Influence on Recycled Aggregate Properties

Abstract

The adhered mortar attached to recycled aggregate (RA) is one of the main causes of weakening the mechanical properties and durability performance of recycled aggregate concrete (RAC). Therefore, in order to improve the performance of RA and RAC, several methods have been proposed to remove the adhered mortar in RA. However, knowing the adhered mortar content is as important as removing it. This is because concrete mix designs considering the amount of adhered mortar have been proposed and better strength, durability and environmental benefits of these mix designs were reported compared to conventional RAC mix design. Therefore, in this study, the adhered mortar was removed by using two methods of ‘acid treatment’ and ‘chemical and mechanical stress treatment’ for three types of RA, and the test results obtained from each method were comparatively analyzed. The results showed that the adhered mortar contents determined by the two methods were different for the same aggregate, and neither allowed the complete removal of the adhered mortar from RA. It also showed that the test environment of the chemical-mechanical stress method can be harsh enough to damage the original aggregate in RA, and that the acid treatment can cause corrosion of RA depending on the type of aggregate.

Effect of Maximum Aggregate Size and Powder Content on the Properties of Self-compacting Recycled Aggregate Concrete

“…The density of SCC using 19 mm MAS was 0.6% to 2% higher than that of SCC with The SCC mixture with a w/b ratio of 0.39 increased the density by 0.6% when the MAS was increased from 9.5 mm to 19 mm, whereas the mixture with a w/b ratio of 0.45 increased by 2% for a given MAS. Smaller RAs have a higher adhered mortar content than larger RAs, resulting in lower density and higher water absorption [14]. Hence, SCC mixtures made from RA with large MAS exhibit higher density than mixtures with smaller MAS, which is consistent with the results reported in [24].…”

“…The adhered mortar absorbs mixing water and deteriorates the workability. In our previous study [14], it was reported that the smaller the aggregate size, the higher the adhered mortar content. Therefore, the workability of the SCC with 9.5 mm MAS is inferior to that of the SCC with 19 mm MAS.…”

“…The increase in elastic modulus due to larger MAS can be attributed to the characteristics of RA. Because of the adhered mortar, the modulus of RA is lower than that of NA, and in particular, it has been frequently reported that the adhered mortar content is likely to be higher in small sized RA [14]. Thus, RA with a larger particle size has a higher stiffness than RA with a smaller particle size due to a relatively lower adhered mortar content, which also explains the higher elastic modulus in SCC incorporating RA with a large MAS.…”

“…The density, water absorption, and fineness modulus of river sand were 2.52 g/cm 3 , 1.98%, and 2.68, respectively. In a previous study by the authors [14], adhered mortar content, a characteristic feature of RA, was determined for each size fraction of RA using hydrochloric acid treatment. The adhered mortar contents of 4.75-9.5 mm, 9.5-12.5 mm and 12.5-19 mm RA were 11.5%, 10.5% and 10.0%, respectively.…”