Analysis of Hardened Concrete for Admixture Content

摘要

Twenty concrete admixtures, including air-entraining agents, water reducing retarders, accelerators, and super plasticizers, were added, both alone and in common combinations, to cement pastes in amounts typically used in concrete practice. The hardened and cured pastes were crushed, and the organic constituents were extracted from the No. 4 - No. 16 fraction in a Soxhlet apparatus. Various extraction solvents were tried, and the one selected as best was a ternary axeotrope of 75 percent methylethyl ketone, 14 percent ethanol, and 11 percent water by volume. The extracts were evaporated to dryness and then dissolved in a carrier phase and subjected to high pressure liquid chromatography using both ultraviolet absorbance and refractive index detectors. A variety of carrier solvents, column packings, and types of chromatographic operations were tried before suitable conditions for separation and identification of these materials were found. The carrier solvent selected was 80 percent acetonitrile and 20 percent water by volume. The column packing selected as a micro - C18 material in reverse phase operation. The recorded ultraviolet detector output was found to give patterns that were unique for the admixture or admixture combinations used, so that identification of the materials is possible with this technique. Because the results are influenced by instrumental and technique variables, cement past standards containing the admixture(s) under test should be used.