Answer: Increased use of limestone cement in construction: This was of high quality. It hardened into concrete when mixed with stone chips. It made the construction of large structures easier and faster.

What are the main uses of limestone?

MINING & MARKETING –

In India, limestone mines are worked by opencast method. Captive mines are mechanized and supply feed to cement and iron & steel units. Some mines have well laid road-cum-rail routes. The large mines are developed by forming benches in overburden and limestone bed. The face length, width and height of the benches correspond to the mining machinery deployed and production schedule. Heavy earth-moving machinery like 3.3 to 4 cu m capacity hydraulic excavators in combination with 10-35 tonnes dumpers are normally used. Other mines are mainly worked by semi-mechanized and manual opencast mining methods.The threshold value of limestone has been revised by IBM, through a Notification in 2009, as follows: (i) For limestone deposits in Chhattisgarh, Gujarat, Himachal Pradesh, Madhya Pradesh, Maharashtra, Rajasthan, Uttarakhand & Uttar Pradesh – CaO – 34% (min), MgO – 4% (max). (ii) For limestone deposits of Andhra Pradesh, Jharkhand, Karnataka, Kerala, Odisha & Tamil Nadu – CaO – 35% (min), MgO – 4% (max), SiO2 – 18% (max) & Alkalies – 0.5% (max).

The principal use of limestone is in the Cement Industry. Other important uses are as raw material for the manufacture of quicklime (Calcium Oxide), slaked lime (Calcium hydroxide) and mortar.

What is the chemical composition of limestone in cement?

SPECIFICATIONS OF LIMESTONE – FOR CEMENT INDUSTRY

Cement is a binder, a substance used in construction that sets, hardens and adheres to other materials. Cement used in construction are usually inorganic, often lime or calcium silicate based. Magnesia, sulphur and phosphorus are regarded as deleterious elements. Limestone should have less than 3% magnesium oxide (MgO), maximum tolerance being 5 percent. The presence of P as P2O5 more than 1% slows down considerably the setting time of Portland Cement. Indian cement manufacturers prescribed that the limestone should have CaO 42% (min), Al2O3 1 to 2%, Fe2O3 1 to 2%, SiO2 12 to 16% and MgO 4% (max). The broad chemical specifications of cement grade limestone (r.o.m.) for cement manufacture suggested by the National Council for Cement and Building Materials, New Delhi, are in the table above.Portland cement: Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with other materials (such as clay ) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which then chemically combines with the other materials that have been included in the mix to form calcium silicates and other cementitious compounds. The resulting hard substance, called ‘clinker’, is then ground with a small amount of gypsum into a powder to make ‘ordinary Portland cement’, the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar and most non-specialty grout, The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate ( gravel and sand ), cement, and water, As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white.

The Clinker invariably composed of Tricalcium Silicate, Dicalcium Silicate, Tricalcium Aluminate & Tetra calcium Alumino-ferrite. FOR IRON & STEEL INDUSTRY

In Iron & Steel Industry, limestone is used both in blast furnace (BF) and steel melting shop (SMS) as a flux after calcining. It is also added as flux in self-fluxing iron ore sinters. It has two basic functions in steel making, first to lower the temperature of melting and second, to form calcium silicate which comes out as a slag, as it combines with silica in iron ore. For use in the blast furnace, the calcium carbonate (CaCO3) content in limestone should not be usually less than 90 percent. The combined SiO2 and Al2O3 should not exceed 6% though up to 11.5% is allowed; MgO should be within 4% and sulphur and phosphorus as low as possible. In Steel Melting Shop (SMS), insoluble in limestone should not exceed more than 4 percent.Good fluxing limestone should naturally be low in acid constituents like silica, alumina, sulphur and phosphorus. Limestone should be dense, massive, preferably fine-grained, compact and non-fritting on burning.

FOR CHEMICAL INDUSTRY The calcium carbide manufacturers generally prefer lime containing 95% CaO (min) with limitations of not more than 3% SiO2, not more than 0.95% phosphorus and other impurities not exceeding more than 2%. For the manufacture of bleaching powder, lime containing 95% and above CaO is required.

Total Fe2O3 +Al2O3 +MnO2 should be less than 2%; MgO should be below 2% and SiO2 less than 1.5%. Bleaching powder is prepared by absorption of chlorine by dry hydrated lime. The hydrated lime should not contain more than 2% excess water. Iron and manganese oxides lead to unsuitability of the product and iron oxides tend to discolor the bleached material.

Magnesia renders the bleaching powder hygroscopic. Silica and clay impede solution and settling of bleaching powder. FOR INDUSTRY & CONSUMPTION India was the second largest cement producing country in the world after China. There were 210 large cement plants having an installed capacity of 410 million tonnes in 2015-16 in addition to more than 350 mini cement plants having estimated capacity of around 11.10 million tonnes per annum.

The total installed capacity of cement in 2015-16 was thus about 421.10 million tpy against 356 million tpy in the preceding year. Besides, there are three white cement plants having a total 990,000 tpy capacity. The total production of cement reached 283.45 million tonnes in 2015-16. Cement was the major consuming industry accounting for 94% consumption, followed by iron & steel (4%) and chemical (2%).

The remaining consumption was reported by aluminum, alloy steel, sugar, paper, fertilizer, glass, metallurgy, foundry, etc. The Cement Industry in India is among the core Industries that is vital for economic growth and development. India the second largest producer of cement after China in the world.

• Cement is the basic building material and is used extensively in urban housing, industrial sector and infrastructure development.
• It has become synonymous with construction activity and the per capita consumption of cement is accepted as an important indicator of the country’s economic growth.
• READY MIX CONCRETE (RMC) Ready-mix Concrete (RMC) is a relatively nascent market in India accounting for only about 0.5% of the demand.

RMC is ready-to-use concrete blend of cement, sand & aggregate and water mixed in convenient proportion. It was first launched in Mumbai a few years ago and is gaining ground in other metros in India. RMC is a corollary to bulk handling and transportation of cement.

What kind of buildings were built in medieval India?

Rulers and Buildings – Medieval India –

• Between the 8th and the 18th centuries kings and their officers built two kinds of structures: First were forts, palaces and tombs. Second were structures meant for public activity including temples, mosques, tanks, wells, bazaars.
• By making structures for subjects’ use and comfort, rulers hoped to win their praise.
• Construction activity was also carried out by others, including merchants. However, domestic architecture – large mansions (havelis) of merchants – has survived only from the eighteenth century.

What is the reference material for this article on medieval India?

In this article on Medieval India, we plan to cover the topic ‘Rulers and Buildings – Medieval India’. The reference material for this post is NCERT History text for Class 7 (Our past -1). Only main points from the chapters are compiled below. These points might come quite handy during preparation of Prelims and Mains to get a quick grasp of the subject.