PROPORTIONING METHODS FOR CONCRETE WITH HIGH MICROFINES

Five concrete proportioning methods, including ACI 211, were used to proportion and analyze several concrete mixtures made of five aggregates with varied shape and texture, and varied amount of microfines. The slight differences in compressive and flexural strengths that were found indicate that the desired strength can be easily attained with a wide range of aggregate size distributions. However, the significant differences in slump and workability due to aggregate grading differences that were found suggest that grade of aggregates is a major variable and that proportioning methods should account for it. Important differences in slump and workability were found due to shape and texture as well as the type and amount of microfines. The ACI 211 method does not encourage aggregate optimization; it only indirectly considers shape and texture, and is not suitable for manufactured fine aggregate with high amounts of microfines. The "18-8" does not ensure proper grading. Shilstone's method allows grading optimization although it does not consider shape and texture. The compressible packing model, based on packing concepts, considers shape and texture as well as grading, and is able to make acceptable predictions of concrete properties.