During the heavy floods we experienced this past spring, our concrete sand was contaminated with lignite. We don't have enough room to build another sand stockpile, and I want to avoid hauling it back to the quarry and paying rehandling costs. Is there any way I can use the contaminated sand but avoid potential surface defects?
Anti-washout admixtures (AWAs) might solve your problem. AWAs are water-soluble polymers that thicken the cement paste by physically binding the mixing water in concrete. They were developed for concrete placed under water. Most consist of microbial polysaccharides such as welan gums or polysaccharide derivatives such as hydroxpropyl methyl cellulose or hydroethyl cellulose. AWAs decrease concrete slump, so you might need to add a high-range water reducer (HRWR) to counteract that effect without reducing strength or durability. Since the cost of both an AWA and HRWR may too high, an alternative approach is to provide concrete with a maximum slump of 4 inches. Fewer lignite particles float to the surface in lower-slump concretes.