Sodium silicate bonded waste foundry sand - A substitute for fine aggregates in concrete and a potential material for cement phase synthesis

Sodium silicate bonded Waste Foundry Sand (WFS) is being discarded by the foundries after single use. The studies so far are suggestive that the WFS after being discarded cannot be reclaimed by any physico-chemical methods and the silica transformation is within the crystal structure. Hence such sand utilisation in bulk quantity will be one of the options for managing the issue of sodium silicate bonded WFS. Recent research trend in construction materials involve utilization and blending of different industrial byproducts and waste materials to solve the environmental problems. In the present work, sodium silicate bonded WFS was used as a replacement for fine aggregates in concrete in varying percentages of 0%, 10%, 20%, 30%, 40% and 50% by weight. The 30% replacement showed better compressive strength compared to control samples. Further, these samples also passed the durability tests like rapid chloride penetration, water absorption, sorptivity, rebound hammer and ultrasonic pulse velocity. Both the strength and durability results can be attributed to the property of the sand in terms of its size, shape and its reactivity. To prove this hypothesis further fine sodium silicate bonded WFS (less than 45μm) was mixed with calcium carbonate in appropriate molar proportions. The mixture was calcined at 1400°C. This mixture was analyzed using XRD and the results revealed that alite and belite phases were generated during the reaction. This gives new dimension to utilize sodium silicate bonded WFS in concrete or as source of silica in cement industry