An investigation of the effect of aggregate on concrete compressible strength

Findings of an investigation were compiled whose objectives were to determine the significance of variation in the plastic properties of concrete as denoted by construction records; to isolate those variables that also have an affect on the hardened properties of concrete; to determine if rigid control of aggregate gradation could be justified by requiring the aggregate to be separate into several size fractions prior to field batching in order to produce a durable superior concrete; and to evaluate the microwave oven tehnique of determing the water-cement ratio of plastic concrete. The statistical analysis of ten years of concrete construction data showed that some sources of coarse aggregate had not met their expected strengths and that concretes made of type 2 cements were found to produce compressive strengths about eight percent higher than concrete made of type 1 cements. Findings from laboratory testing implied that improved durability may be obtained by requiring tight control on the coarse aggregate gradation by separating it into three size fractions. The microwave technique appears to be a viable method of determining the water cement ratio of plastic concrete.