Use of Stone Aggregates in Road Construction
Stone aggregates are extensively used in roads in pavement layers. They are obtained from natural rock. The following geological groups are commonly found in India:
(a) Igneous rocks, such as granite, ballast found in peninsular India and formed by hardening of molten material from volcanoes.
(b) Sedimentary rocks, such as sandstones found in Uttar Pradesh, Gujarat and Rajasthan, formed by deposition of granular material.
(c) Metamorphic rocks, such as quartzite found in the Aravali ridge in Delhi, Haryana and Rajasthan, formed by transformation of igneous or sedimentary rocks due to heat and pressure.
(d) Limestones formed in Rajasthan and Madhya Pradesh.
(e) Laterites, formed by decomposition of basalt and other rocks, found in Kerala, coastal Karnataka, Goa and Orissa.
(f) River borne shingles found in the rivers from the Himalayan hills, found in Punjab, Haryana, Uttara Khand and Uttar Pradesh.
It may be noted that the Gangetic plains of Uttar Pradesh, Bihar and West Bengal do not have natural rock outcrops. In these places, the aggregates have to be hauled over long distances of 200-300 Km. Because of this handicap, the use of brick pavement and over burnt brick ballast (called Jhama metal) in lower layers of the pavement is common in these areas.