Report On Factors Affecting Shrinkage And Creep Of Hardened Concrete PDF Download

A description is given of a series of tests and test results from an investigation of the mechanical properties of structural-grade lightweight and normal-weight concretes. The major part of the work was planned to obtain comparative values of compressive creep, drying shrinkage, strengths, and moduli of elasticity for concretes made with 24 lightweight and 5 natural, normal-weight aggregates and having the same nominal strength at the time the specimens were placed under load. Data are presented from a total of 76 different concretes which show that there is a wide range in values of the mechanical properties of concretes of the same nominal compressive strength. It is shown that relatively high values of creep and drying shrinkage are not always associated with lightweight concretes and that, in fact, some lightweight concretes have practically the same mechanical properties as some normal-weight concretes. In addition to environmental conditions, the two major factors affecting the creep of concrete appear to be the ratio of the applied stress to the strength at the time of loading, and the aggregate used. Curing conditions, type of cement, mix proportions, and several other variables appear to affect the creep chiefly insofar as they affect the stress-strength ratio. It was observed that the creep at the age of two years can be estimated from the 90-day results with reasonable accuracy. (Author).