Methods for determining and tracking the residual cement paste content of recycled concrete

The attached cement paste on recycled concrete aggregates (RCA) is the main factor causing impaired quality of the new concrete. Since attached mortar is not as hard or strong as natural aggregates, its presence
weakens the overall performance of the RCA. Additionally, the attached mortar is known to cause a higher water absorption, an increased water cement ratio, and therefore a more porous and weaker concrete.
Due to the negative influence of the attached mortar on the RCA properties, ideally all mortar should be removed from the original natural aggregates, returning the recycled concrete into its original aggregates and hardened cement paste (HCP). In order to study the efficiency of treatments designed to achieve this purpose, methods for estimating the amount of HCP attached to the original aggregates need to be used. Such methods, which include e.g. composition tests (XRF, XRD), thermogravimetric analysis or chemical
methods are generally time-consuming and complex. In this study, a more straightforward method based on oxide composition is proposed and corroborated with the results from other test results.