The beneficial use of cement in concrete, both from the economic and technical points of view, depends upon the ultimate degree of hydration possible under given conditions of service. The ultimate degree or hydration of cement in concrete which is allowed to dry, depends upon the degree of hydration at the time of exposure to drying and the relative rates of hydration and drying thereafter.
The rate and extent of hydration in concrete depends on the chemical activity coefficient and availability of pore water which, in the case of drying concrete, diminishes as the vapour pressure in pore space is decreased.
This paper deals with preliminary laboratory investigations conducted into the use of a new unit termed a disc bio-filter for sewage treatment. Some basic disadvantages of present day sewage treatment methods are analysed, and the reasoning which led to the creation of the disc bio-filter is set out. The manner in which this unit is expected to improve on existing treatment methods is expounded.
The paper descriptionbed tests carried out to determine the early strengths of concretes made with different types of cement, and to evaluate the effects of various percentages of calcium chloride used as an admixture. Curves were presented to serve as a guide to the selection of cement:water ratios suitable for required strengths of concrete.