EVALUATE THE USE OF MINERAL ADMIXTURES IN CONCRETE TO MITIGATE ALKALI-SILICA REACTIVITY

The increased use of mineral admixtures in portland cement concrete demands a better understanding of their properties and effects on hardened concrete. One of several beneficial advantages of mineral admixtures like flyash and silica fume is their potential for controlling deleterious expansion due to the alkali-silica reaction (ASR) in concrete. The objective of this investigation was to investigate the effects of portland cement, aggregates, and mineral admixtures on the alkali-silica reaction in concrete with and without air entrainment. The experimental program utilized aggregates from two sources, portland cement with different alkali contents, flyashes, silica fume and natural pozzolanic materials. The mitigation of the alkali-silica reaction by addition of mineral admixtures was evaluated using ASTM C 227, Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar - Bar Method). The test results show that the effect of mineral admixtures on ASR expansion is highly variable and depends on the chemical makeup of the mineral admixture, alkali content of the cement, and replacement rates of cement by mineral admixture. Creep characteristics of pozzolan based concrete were also studied. Four mineral admixtures were used as a partial replacement of portland cement. Air entraining admixture was used in some of the mixes. The results show that the creep characteristics of concrete are not adversely affected by the use of mineral admixtures.