Title: Detection of Aggregate Clay Coatings and Impacts on Concrete

Author(s): Jose F. Munoz, M. Isabel Tejedor, Marc A. Anderson, and Steven M. Cramer

Publication: Materials Journal

Volume: 107

Issue: 4

Appears on pages(s): 387-395

Keywords: cation exchange capacity; clays; coarse aggregate; coatings; crystalline swelling; methylene blue; microfines

DOI: 10.14359/51663865

Date: 7/1/2010

Abstract:
Deleterious clay minerals often enter concrete as coatings on aggregates; the impacts of the certain clays introduced by this mechanism is the subject of this study. The effects of different clay properties, including cation exchange capacity (CEC) and the nature of the exchangeable cations on concrete, were measured. The material selected for this research was an igneous clean coarse aggregate which, for purposes of repeatability and experimental control, was lab-coated with four different clay suspensions (kaolin, illite, sodium montmorillonite, and calcium montmorillonite). The coated aggregate was then used to make concrete test specimens. The results clearly show that the impact of the clays is not only a function of the CEC of the clay but also of the nature of the exchangeable cation.