Current Knowledge and Pending Research on Sulfate Resistance of Recycled Aggregate Concrete
As mentioned before, the number of research papers on the performance of recycled concrete against sulfate attack still needs to be increased in order to understand the degree of influence of each intervening variable. Although there are several publications on this topic, they vary significantly regarding research objectives, setup parameters, and evaluation methods. Many of these studies focus on characterizing specific types of recycled concrete aggregates (RA) or evaluating eco-efficient concretes that incorporate RA together with SCMs. These studies examine various properties, including sulfate resistance, but cover only a few variables. Some research also considers sulfate attack in combination with other forms of deterioration, such as freezing and thawing. Each paper uses different test conditions and evaluation methods, making comparing results and drawing meaningful conclusions across different studies challenging.
The literature data was first classified based on the predominant type of sulfate attack: ESA, PSA, or ISA. In order to compare the results of studies with different experimental setups and evaluation methods, a numerical factor was defined: the degradation ratio, which is the relation between the degradation observed for each evaluated RAC (or RAM) and its corresponding reference concrete (or mortar) in a given time. One example is the final expansion of RAC divided by the final expansion of the reference NAC (same criteria for compressive strength loss, weight variation, SO3 incoming, et cetera). Degradation ratios greater than 1 indicate worse performance of RAC compared to NAC, while ratios below 1 indicate better performance.
3.2. ESA + PSA
As in the case of ESA, the results regarding ESA + PSA are not enough to establish consistent correlations, but they do confirm some points regarding the development of the sulfate attack in recycled concretes, such as the quality of the new matrix, the ambiguous effect of RA, and the very positive effect of SCM with RA.
Studies show that the aggregate sulfate limits set by regulations may be conservative. However, more experimental results are needed to better understand the effects of RA on the ISA under different conditions.
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