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The problem of detecting the presence of the lignosullonate type of retarder or plasticizer in hardened cement paste is investigated by a spectrophotometric method based on ultraviolet absorbance measurements of aqueous extracts. The interaction of hydrating portland cement and lignosulfonate salt, whether in water suspension or in hardened paste, results in the disappearance of the characteristic 280 mμ maximum of the original lignosulfonate and the appearance of two new maxima at wavelengths of 245 and 350 mμ. This change is attributed to alkaline hydrolysis, with the formation of vanillin. The experimental results are discussed in relation to the qualitative and quantitative aspects of the method in detecting lignosulfonates in portland-cement products.
Director of Research, Miron and Frères Ltd., Montreal, P. Q.
Dean Emeritus of Graduate Studies, University of Saskatchewan, Saskatoon, Sask.