Deterioration of dolomitic and calcitic based RPCC aggregates subjected to abrasion and their potential for precipitating tufa

Recycled Portland Cement Concrete (RPCC) aggregates are produced as a result of recycling of Portland Cement Concrete pavements. They are often used as base and subbase courses in pavement construction. RPCC aggregates of calcitic and dolomitic origin leach by interacting with acidic rainwater, leading to the partial dissolution of calcium ions. The calcium in suspension precipitates in the pavement underdrains. This precipitate is called tufa (CaCO₃). Tufa blocks pavement underdrains causing increased moisture presence in the pavement substructure, leading to early failure.; The extent to which RPCC aggregates leached out calcium ions is dependent on the total percentage of calcium-bearing minerals (like calcite, dolomite and portlandite) in the aggregate, and the extent of fines the aggregate produced as a result of mutual attrition and abrasion due to the road-traffic loads. Calcite and dolomite are minerals that provide strength to RPCC aggregate. Their dissolution makes RPCC aggregates weak in supporting traffic loads.; The current research investigates the deterioration and leaching characteristics of RPCC aggregates of calcitic and dolomitic origin subjected to abrasion. Thermogravimetric analysis (TG) establishes the composition of calcium-bearing minerals in RPCC aggregates. X-Ray diffraction analysis supplements the thermal analysis data. TG was used to obtain kinetic data for the complete decomposition of RPCC samples. The leaching test results are used to decide whether RPCC aggregates can be used as base/subbase courses.; A ratio of Mg/Ca ions >0.60 indicates that the aggregates have higher concentration of Ca+2 ions and may result in the precipitation of calcium carbonate or tufa. RPCC aggregates with pouring temperature below 50°F have shown a higher incidence of tufa precipitation. It may be due to incomplete hydration. It is recommended to establish Mg/Ca ratio before using RPCC as base/subbase course aggregates. It is recommended to limit the use of RPCC aggregates to coarse sizes only.; A mathematical model was developed to predict the rate of dissolution of calcium bearing minerals like calcite, dolomite and portlandite, which are present in RPCC aggregates. As a result of sensitivity analysis, the percentage of dolomite present in the RPCC sample was the most significant variable contributing to the total calcium ion concentration in solution.