ISSN: 0149-6123
Page Count: 10

Influence of a Long-Term Retarder on the Hydration of Clinker and Cement
Thielen, G
Prof. Dr.-Ing., Managing Director, German Cement Works Association (VDZ),

Rickert, J
Dr.-Ing., Research Engineer, German Cement Works Association (VDZ),

Abstract

This paper summarizes the results of investigations on the effects of a long-term retarder (LTR) based on phosphonic acid (PBTC) on the hydration of several clinker phases (C³S, C³A, C⁴AF), Portland cement clinker, and Portland cement. It could be shown that long-term retardation is due to a thin sparingly soluble layer of calcium phosphonate on the particle surface. The formation of sparingly soluble calcium phosphonate requires 2.5 moles Ca²⁺ per mole PBTC. If enough Ca²⁺ is available, sparingly soluble calcium phosphonate precipitates and forms a layer around the cement particles, which retards further hydration immediately. In the contrary a lack of Ca²⁺ causes a short-term acceleration in hydration of the reactive clinker phase C³A. The investigations show that a controlled long-term retardation can only be achieved if the cement shows an optimal “natural” setting retardation; hence, when the sulphate ingredient is fully compatible with the reactivity of C³A.

Keywords:
C3A, C4AF, C3S, hydration, long-term retarder, phosphonate, Portland cement clinker, Portland cement, retardation

Paper ID: CCA12315
DOI: 10.1520/CCA12315
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