C.K. Anbazhagan, Namakkal, Tamil Nadu
Sand can be classified into three types based on grain sizes, as coarse, medium and fine. The determination of these fractions is important since they affect the engineering characteristics and performance of sands as pavement layers in terms of plasticity, strength and bearing capacity. The shape of sand particles affects its density and stability and overall engineering behaviour. Smooth rounded particles would offer less resistance to rearrangement than angular or elongated particles with rough surfaces
Sea and desert sands seldom satisfy the requirements of traditional specifications for use as a construction material, especially in their untreated state. Desert sand grains are finer and smoother so their surface chemistry would not be able to offer sufficient number of multidirectional chemical linkages. If their grain size is too small, the slurry slip and the concrete would have poor strength. Desert sands possess an open structure, and there is little interlock between sand grains. If this sand is kept dry, these bonding bridges provide considerable bearing strength. But if the sand becomes wet, the bridges soften and when overloaded, the bridges break and collapse.
Sea sand also tends to very fine and rounded. In sea water, chloride is present which will cause corrosion of steel and iron which ultimately leads to reducing carrying capacity of steel and iron, so that the structure built using this may not be sustainable.. Sea sand does not have high compressive strength, high tensile strength etc so it cannot be used in construction activities. In addition to this, the salt in sea sand tends to absorb moisture from atmosphere, bringing dampness. Dr. SAINUDEEN PATTAZHY, Kollam, Kerala.
This week’s questions
When a table fan is switched on, why does the breeze move only in the forward direction?
Chanchal P.V., Thrissur, Kerala
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