Using Quasielastic Neutron Spectroscopy to Investigate Cement:

Special Interactions of Tricalcium and Dicalcium Silicate during Hydration

Cement is the most widely used and most important building material in the world. Cement clinker is a complex calcium silicate mixture, and is interground with a small amount of gypsum to make cement powder. Cement paste is produced when cement powder is combined with water, where hydration processes take place during which the mixture gains strength.

Tricalcium silicate is the primary component of Portland cement clinker, comprising 50-70 wt.% of the total composition, and is the component responsible for early strength development in cement paste. Dicalcium silicate is the second most abundant component, comprising 15-30 wt.% of clinker. Although dicalcium silicate contributes little to early strength development, by one year its strength is greater than that of tricalcium silicate paste. Although there exist numerous studies on the separate hydration of tricalcium silicate and dicalcium silicate, almost no studies on their interaction have been made, and it is the complex interaction of these phases that makes cement different from its constituent components.

Quasi Elastic Neutron Scattering (QENS) allows the state of the water in hydrating cement paste to be studied in-situ with time. Hence, QENS provides a direct measure of the conversion of free water to structurally/chemically bound water and to water constrained in the pores of the cement paste. Here we report the interaction of hydrating tricalcium and dicalcium silicates by QENS. Mixtures of synthetic tricalcium and dicalcium silicate were hydrated and their reaction mechanics explored as a function of mixture composition. The time-dependent free, constrained, and bound water results were analyzed. The complex interactions of the components during hydration gave interesting results, and demonstrated that the reaction does not proceed monotonically as a function of mixture composition.

Subsequent compressive strength testing has verified this surprising interaction and demonstrated that the interactions translate into strength properties of the system.

 

Investigator: Vanessa Kate Peterson

Mentorís name: Dan A. Neumann

Division: Materials Science and Engineering Laboratory (856.02)

Laboratory: Center for Neutron Research

Room: E18

Building Address: Building 235

Mail Stop: 8562.

Telephone: 301 975 8377

FAX: 301 921 9847

Email: vanessa.peterson@nist.gov

Sigma Xi member: No

Category: Materials Chemistry †