EVALUATION OF OPTIMUM PERCENTAGES OF ADDITIVES IN CONCRETE WITH RECYCLED AGGREGATES

Construction and Demolition waste is available in very large quantities in all Urban Areas of all Cities in any Country throughout the World year after year, since Demolition takes place due to some reason or the other. Disposal of this waste is highly expensive, and normally these are dumped in open spaces, which are very harmful to the public health, and pollute the atmosphere. Also Natural Fine Aggregate is very costly these days. Hence an attempt is made to utilize the demolished concrete as a Partial replacement for Natural Coarse Aggregate, and Manufactured Sand as a Total replacement for Natural Fine Aggregate in Concrete, leading towards Green Buildings Concepts, and economical structures. As per the IS :10262-2019, Proportions by weight for Cement, Natural Coarse aggregate, Natural fine aggregate, water cement ratio, were followed for M40 grade concrete. Compressive Strength on Concrete cubes were evaluated for seven days and twenty eight days with Natural Coarse aggregate(50%), and Demolished concrete(50%),and m-sand (100%). It was observed that the twenty eight day compressive strength was less than 40Mpa which is not satisfactory. The reason may be because of the use of demolished concrete being used as a partial replacement for Natural coarse aggregate and m-sand being used as a total replacement for natural fine aggregate. Additives like Nano Silica, Wollastonite Powder and Basalt fibres which are available at competent rates, were tried individually and compressive strength for seven days and twenty eight days were evaluated with various percentages of Nano silica like 1%, 1.5%, 2% by weight of cement added to Concrete. It was found that 1.5% Nano silica by weight of cement gave the maximum compressive strength. Similarly Wollastonite powder was mixed in concrete with 5%, 10%, 15% by weight of cement, and 10% wollastonite powder by weight of cement was the optimum percentage obtained. Also basalt fibres were added to concrete with 1%, 2% and 3% by weight of cement, and experimental results showed that 1% basalt fibre was the optimum percentage. Thus using these optimum percentages of Nano silica, Wollastonite powder and Basalt fibres in concrete we have got the compressive strength of concrete for twenty eight days exceeding 40Mpa. Thus we can conclude that the addition of optimum percentages Nano silica, Wollastonite power and Basalt fibres individually helps to regain the compressive strength of concrete to satisfactory levels, so that the concrete with demolished concrete as coarse aggregates and m-sand as fine aggregates could be used in all structural members of any structure. Water cement ratio of 0.45 was adopted. And super plasticizer(LIQUIFIX) was used to enhance the workability as per the IS code provisions.