Extenuating the Influence of Clay Content of Aggregates on Concrete Performance

One of the most important ingredients of concrete is aggregates whose property should be achieved before using it. Aggregates should be free from impurities; hence cleaning of aggregates is most desirable. The present study concentrates on extenuating the influence of clay content of aggregates (FA and CA) on performance of concrete. During monsoons in cities like Mumbai, there is reduction in strength of concrete in all grades due to contamination of FA and CA because of presence of clay. During runoff, clay sticks to the surface of aggregates as a result bond strength is affected. Clay forms a cover or coating on the cement and interferes in hydration process resulting in drop in strength. It is believed to interfere with the aggregate cement paste and hence bond becomes weaker. Generally the sand which comes for use in construction industry is coated with clay or impurities in some form. It is not in the pure form and adulterated which is undesirable to use. Usually clay coatings comprises of clay particles which are held tightly to aggregate surface. Clay found on aggregates in Mumbai city may in the form of kaolin, illite, sodium montmorillonite (NaM), calcium montmorillonite (CaM). There is need to understand the effect of clay on concrete because of lack of awareness among the stakeholders. Construction industry is not able to find out the correct solution for lessening the effect of clay content on both fresh and hardened concrete. Hence study can be carried out by preparing trial mixes by adding 0%, 1%, 3%, 5%, 7% and 9% clay by weight of sand for M-40 designed concrete mix. For each trial mix compressive strength, impermeability and flexural strength can be found out to understand to what extent percentage of clay can be present in concrete and also whether any construction chemical can be used for lessening this effect at minimum cost. The outcome of this study will be the analysis of the test results and comparing the results leading to an optimum solution with required strength and with substantial saving in cost. If at all clay is present in aggregates then which measures should be adopted to lessen the impact of clay.