Digital Library / Journals / Journal of Cement, Concrete and Aggregates (CCA) / Citation Page

ISSN: 0149-6123
Published Online: 4 December 2004
Page Count: 10

Influence of a Long-Term Retarder on the Hydration of Clinker and Cement
Rickert J, Thielen G

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 (CS, CA, CAF), 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 Ca per mole PBTC. If enough Ca 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 Ca causes a short-term acceleration in hydration of the reactive clinker phase CA. 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 CA.

Keywords:
CA, CAF, CS, hydration, long-term retarder, phosphonate, Portland cement clinker, Portland cement, retardation

Paper ID: CCA12315
DOI: 10.1520/CCA12315
ASTM International is a member of CrossRef.