An experimental study on the guidelines for using higher contents of aggregate micro fines in portland cement concrete

The increase in production of crushed aggregates has resulted in an increase in manufactured fine aggregate (MFA). Standard specifications for fine aggregate for concrete contained in ASTM C 33 permit a maximum of 7 percent finer than the No. 200 sieve (75μm), if the fines consist of dust-of-fracture essentially free of clay or shale. Since the production process for MFA normally generates 10 to 20 percent of micro fines, more than permitted by specifications, excess fines must be separated from the desired sizes by screening or washing operations or both. It is estimated that over four billion tons of by-products have been stockpiled annually at quarry sites around the US. The amount of by-products will continue to grow due to production increases and environmental discharge restrictions. This dissertation focuses on experimental research for using higher micro fines contents in concrete and to develop guidelines for using high amounts of aggregate micro fines, defined as aggregates passing the No. 200 sieve (75μm). The testing program in this study consisted of four stages. The first stage was the selection of nine sources of aggregates to represent aggregates used in the US. The aggregate property-testing program was the second stage. The basic aggregate characteristic tests were conducted to select the aggregates to be tested in the next stage. Five tests were performed for 63 sands from seven rock types. The third stage was the mortar-testing program to evaluate the use of MFA in mortar. Two variables (fixed w/c and constant flow) were used to investigate the characteristics for each type of aggregate in mortar. The last stage was the concrete testing program to investigate concrete performance and the properties of concrete. After the third and fourth stages were finished, a statistical analysis was conducted to evaluate the effect of the characteristics of fine aggregate on the properties of mortar and concrete. Based on the analysis guidelines for using higher amount of micro fines in portland cement concrete are recommended.