A model for hydrated Portland cement paste as deduced from sorption-length change and mechanical properties

TLDR: In this article, the authors present a model for hydrated portland cement paste that recognizes surface areas and porosities obtained by N2 adsorption as the most reliable values, and attributes many of the phenomena observed, to the behaviour of interlayer hydrate water.

Abstract: Recent findings in DBR and other laboratories has made it necessary here to revise the accepted model for hydrated portland cement paste. The model recognizes surface areas and porosities obtained by N2 adsorption as the most reliable values, and attributes many of the phenomena observed, to the behaviour of interlayer hydrate water. The bonds between and within individual “crystallites» are clearly defined; it is shown that the “inter-crystallite” bonds do not separate when exposed to physically adsorbed water. The paper describes some of the thermodynamic equations pertinent to the phenomena of adsorption, length change and creep, and some basic principles governing physical adsorption and types of hystereses. The results were obtained from two areas of work: A. Surface chemical experiments. B. Measurement of mechanical properties of compacted and cast systems of hydrated cement and gypsum. The experiments in (A) included sorption and length change scanning isotherms of water and methanol and led to the following conclusions: The experiments in (B) included measurements of modulus and strength versus relative humidity, and porosity, and led to the following conclusions: