Detecting deleterious fine particles in concrete aggregates and defining their impact

Abstract

This study examined the types of microfines in aggregates found in northern Wisconsin and their influence on concrete prepared according to Wisconsin Department of Transportation (WisDOT) specifications. Aggregates were collected from 28 sources and 69 percent were found to contain clay particles known to be deleterious in concrete. Seven aggregates sources were selected from the 28 for detailed evaluation including concrete performance. The microfines from the aggregates were evaluated by x-ray diffraction and thermal gravimetric analysis. Concrete performance testing included strength, shrinkage, porosity and rapid chloride ion penetrability for concrete subject to standard wet curing and dry curing. A rapid field test for microfine identification was attempted but found to be unsuitable for field conditions but potentially useful for laboratory identification of microfines with further development. The results of this research suggest the current P200 threshold for naturally occurring microfines associated with coarse and fine aggregates in the WisDOT Standard Specification results in acceptable concrete performance when conditions are optimal and meet typical ASTM laboratory test requirements. When microfines are present in aggregates, if air entrainment, uncontrolled water additions, certain intentional or unintentional chemical additions, and curing are not carefully monitored and controlled, then microfines in Wisconsin concrete aggregates can and do cause deleterious impacts.