Historically, a large percentage of sand has been produced from alluvial deposits. However we are now experiencing a global shortage of natural sand, and environmental pressures, costs and a shortage of this type of deposit has necessitated the manufacture of sand from quarried material.
One of the problems often experienced with natural sand is the presence of contaminants, which can be very difficult to remove.
These contaminants may be silt, organic matters and sometimes, harmful chemicals, such as sulphates and chlorides, all of which can have significant detrimental effects on the performance of structural concrete. Manufactured sand, on the other hand, comes directly from good quality rock, and thus very few, if any contaminants are present.
An Indian company was designing a dry crushing plant to produce concrete aggregate and manufactured sand from basalt rock. Their major concern was to find a crushing technology which would enable them to manufacture sand that was of a high enough quality for use in concrete.
SBM Minerals proposed the installation of a Barmac VSI crusher as a tertiary stage crusher, to process the product from the primary and secondary jaw crushers.
The Barmac crusher was installed in closed circuit with a screen to crush minus 25mm material, giving two products; 12 - 4.75mm and 4.75 - 0 mm.
The plant has a capacity of 30-35 tph of sand and 15-20 tph of minus 12mm aggregate.
The final sand product from this plant is of a consistent high quality, has good equidimensional shape, and falls well within specification. In fact, following test work, the producer has confirmed that:
• Concrete made using Barmac sand is more cohesive, has an increased density (making it more resistant to chemical attack) and performs better generally than an equivalent concrete made with natural sand.
• The sand has been successfully tested for structural concrete, plaster first coat, mortar and concrete blocks.
• Water demand to get the equivalent workability to a natural sand concrete is lower.
• Cement consumption is reduced by 10-15%.
• Barmac sand is, in fact, 17-18.5% less expensive to produce than the local natural sand.
This installation has created considerable interest in the Barmac for manufacturing sand. In fact, it has paved the way for some very significant Barmac sales into the industry.