Relationships between composition, structure and mechanical properties of very low porosity cementitious systems

Relationships between composition, structure and mechanical properties of very low-porosity cementitious materials have been investigated. It has been found that the principle factor determining the development of structure and strength is initial porosity which depends on the compacting pressure. The maximum degree of hydration was much higher than the limit described by Powers. A non-linear relationship between porosity and degree of hydration was found. The density of hydration products at an early age was found to be much lower that at later times. The hydration process appeared to proceed as if pore space was present in the structure of cement paste. It was proposed that the presence of a large quantity of clinker in the mature structure may be a harmful factor on the stability and durability of very low-porosity cementitious materials, because the chemical energy stored in clinker would be released through hydration in confined space. The development of structure and properties has shown that porosity was reduced sharply and compressive strength increased considerably during the early stage of hydration. The relation between compressive strength and porosity can be described by Schiller's equation using parameters obtained from helium and mercury porosity. It was suggested that the helium porosity-compressive strength relation is suitable to describe the behavior of very low-porosity cementitious materials.