Fly ash is a waste product from burning coal so it contains unburned carbon. This carbon will adsorb surfactant admixtures, especially air entraining agents. This makes it difficult to entrain air in concrete containingfly ash with a high carbon content. For this reason, many states limit the carbon content of fly ash to 3 - 6 %, measured by loss in ignition (LOI). Unfortunately, this makes much of the fly ash produced in the US unusable. A method has been developed to coat the carbon with a blocking agent, which prevents adsorption of the admixtures. A testing program was developed to determine if the carbon blocking agent was effective. In general, concrete mixes made with treated fly ash entrained more air more consistently than mixes made with untreated ash. Mixes made with treated ash hadhigher slumps and slightly lower strengths; but these property differences could be completely correlated to the increased air content. The carbonblocking admixture did not show any negative reaction with admixtures, but it performed better with some admixture chemistries than with others.
Samenvatting