Parameters Affecting Tufa Precipitation from Recycled Concrete Aggregate: Fid-Bau Portal

Parameters Affecting Tufa Precipitation from Recycled Concrete Aggregate

Abbaspour, Aiyoub / Tanyu, Burak F.

Aggregate generated from concrete is one of the most considered recycled materials used in the U.S. for construction that requires earthwork. However, recycled concrete aggregate (RCA) is known to produce tufa. This study focuses on understanding the composition of the precipitated tufa material from RCA as well as the factors that affect the precipitation process. The precipitation experiments were conducted using PWP (Plummer–Wigley–Parkhurst) reaction vessel using a synthetic metastable RCA solution. Based on the identified parameters, a parametric study was also conducted to evaluate the effectiveness of the suggested mitigation method in the literature to remove and replace fine particles from RCA. Additionally, as part of this parametric study, the effects of contact time and blending with natural virgin aggregate (V.A.) were investigated as alternative mitigation methods. Minteq A2 and geochemical modeling were utilized to calculate the total solid-phase formation under equilibrium conditions from 100% RCA, 100% V.A., and different blends of the two materials. It is shown that the total ionic strength, availability of carbonate and bicarbonate ions, and saturation conditions of Ca and SO₄ ions control the mineralogy of the tufa precipitation. Depending on the mechanism, it was found that the calcium carbonate or calcium sulfate minerals can be the dominant forms of precipitation in RCA tufa. Other minor elements contributing to RCA tufa formation were found to be Na, K, Cl, and Si. The parametric study showed that the RCA tufa potential is not dependent on the particle size fractions of RCA but can be reduced by blending RCA with V.A. or decreasing the contact time between water and RCA particle by creating a highly permeable layer of RCA.