Use of Crushed Stone sand & its impact on Concrete Performance

The Concrete has been traditionally made with use of Natural / River sand as fine aggregate. As sand contributes to around 25 to 35% of total concrete along with coarse aggregates, cement & water, the properties of the fine aggregates would be one of the major influencing factor in determining the fresh & hardened Concrete properties and performance with respect to workability, durability & target strengths. The advantage of natural sand is that the particles are cubical or rounded with smooth texture which gives good workability to the concrete. However the present implementation of environmental legislations on banning the use of natural sand has made the procurement of natural sand difficult & expensive and sand quarrying from riverbeds is heavily taxed / banned in many parts of India, which has resulted into not fulfilling the increasing demand of construction sector. The Licensed sand pits producing the required quality of sand are often located in remote locations, also contributes to the limited availability of natural sand due to much higher costs of transportation.

Under these circumstances, use of crushed sand /manufactured sand becomes inevitable to meet the construction demands in the country. As the crushed stone sand is a byproduct of quarrying of coarse aggregates and it is being generated and supplied with or without proper screening, grading & washing. To meet the increasing demand of construction, the more rocks need to be separately crushed to get crushed / manufactured sand as replacement to natural sand. The crushed sand generally contains  more angular particles with rough texture, flaky nature & variability in gradation, more micro fine particles compared to natural sand; performance of which depend on mineralogy  of rocks & process of generation.

Use of crushed sand though is economical & eco-friendly, the different characteristics of the crushed sand can lead to poor workability, increasing water demand which could also lead to increasing cement contents or higher admixture usage to get desired workability & Target strengths. At construction sites in the IHB segments, tend to have cracks due to uncontrolled size distribution & variability of its characteristics. This necessitates having good construction practices & adequate curing of fresh concrete. To adhere to such measures for use of crushed sand especially for smaller construction sites (IHB segments) would be very difficult.

It deals with the comparative evaluation of concrete performance with Natural/River Sand & different Crushed Sands & also highlights to some extent the avenues to overcome some of issues with use of crushed Sand & environmental impact of use of natural as well as crushed sands in constructions. . The paper was presented and published at the 14th NCB Int Seminar on Cement , Concrete and Building Materials