Potential for Tufa Precipitation from Crushed Concrete Containing Coarse Basaltic and Fine Coralline Sand Aggregates

摘要

Crushed recycled concrete aggregate (RCA) has been widely utilized as base and sub-base course and as backfill. Despite the advantages of RCA, one of the potential concerns in some states is that its use can lead to the precipitation of calcium carbonate, or tufa, which can impair drainage and clog filter fabrics, which in turn can lead to premature failure of roads and other infrastructure systems. Tufa precipitation of RCA has been studied in various states, but no studies have been conducted on RCA containing a coarse basaltic and a fine coralline sand aggregate. By passing carbon dioxide gas through RCA soaked in rainwater for over 3 months to simulate an accelerated exposure of RCA to the elements of nature, the potential for tufa precipitation was studied by examining the pH and chemical composition of rainwater over time, the makeup of the RCA aggregate before and after testing, and by visual observation of the aggregate itself. From these observations, there is no evidence indicating that RCA containing a coarse basaltic and fine coralline sand aggregate has a serious tufa precipitation potential.