Alternate for River Sand for Concrete Aggregate

Ordinary river sand is becoming extremely scarce due to the environmental impact of river bed dredging in the country. In some parts of the country, cost of sand is about Rs. 90 per cft whereas cost of cement may be about Rs. 180 per cft. Very ironically the inert inexpensive aggregate of concrete is now more costlier than cement in a nominal 1:1.5:3 concrete. Its cost share is much more high in cement mortar plasters, whose ratios may be nominal 1:5.

Replacement has been sought by manufacture of sand by crushing stones to sieve sizes of sand. Although appearing to be a less expensive solution, this has its own share of problems to the environment. There has also been apprehension about quality of grading and lack of quartzite composition of stone crushed fine aggregates.

One more alternative needs to be explored considering the gravitry of the problem, namely use of sea bed sand for fine aggregate in concrete. Over 15% of the sand and gravel currently used in England and Wales is won from the sea-bed and has been used in a wide range of reinforced concrete structures, according to a 1987 publication of Building Research Establishment UK [Gutt, W. and Collins, R. J.].According to the paper, the main difference between the majority of land-based aggregates and marine aggregate lies in the presence in the latter of sea salts, which usually have to be washed out to meet British Standard maximum limits for chloride and latest guidelines for limited alkali content to prevent alkali silica reaction (ASR).  Many island countries such as New Zealand are now exploring the possibilities.

Sea bed sand are not devoid of their own share of environmental problems. A summary of problems is presented at http://www.seafriends.org.nz/oceano/seasand.htm. The environmental and quality related apprehensions if addressed appropriately might lead to a significant solution to the construction industry in general.