Investigation and Assessment of Quality of Bricks Prepared Using Iron ore Waste

Abstract

Mining is the backbone of many countries economy. Iron ore mining plays a significant role in production of steel and other metals, but at the same time generates massive waste which pollutes the environment and brings other issues related to its storage and handling. Hence there is a need to develop a comprehensive plan for utilisation, storage of iron ore waste fines from the point of view of saving resources and sustainable development. Iron ore waste fine has low percentage of Fe2O3, hence it is discarded. Iron ore waste is dumped at relevant place as per the approved mining plan. It occupies large area within the lease boundary, degrades surrounding land and also deteriorates the environment. In general, any building materials are directly or indirectly prepared from the earth’s crust. The basic composition of building materials is nearly same as the composition of earth (i.e. silica, aluminum oxide, iron etc.). In the recent years, there has been a significant demand for building materials in India as well as all over the world. Therefore, it is imperative to use mining and mineral wastes in the production of bricks, paving blocks and other value added products which are used in the construction industry. Since the need for building materials is growing at an alarming rate, therefore in order to meet the demand for new buildings, new ways and techniques must be evolved for brick making. Manufacturing of building materials like brick, cement, steel, aggregates, etc. which are consumed in bulk quantities, puts great pressure on natural resources and are highly energy demanding. Therefore, the use of alternative material for brick manufacturing should be encouraged. Hence, there is a scope for utilizing mine wastes for the manufacturing of building material and other products. Mine wastes and tailing can be converted into bricks/paving blocks, which can meet the demand of brick in metropolitan cities for the next 30 years or even more. Similarly, utilizing the ironore waste tailings can fulfill the requirements of bricks for Karnataka State for many decades. Thus, there is great potential for utilizing mine wastes to manufacture building materials and products. The crux of this investigation was the possibility of making bricks by mixing iron ore waste fines from iron ore mines with other additives like cement and fly ash. In this investigation, the iron ore waste percentage (by mass) was varied from 65 to 90, whereas that of cement was varied from 0 to 30. The cement percentage was restricted to a maximum of 30 %, based on the study carried out by various other investigators. Similarly the fly ash percentage by mass was varied from 0 to 30. Iron ore waste fines were collected from the run-off of dumps from a large opencast mine of M/S. Sandur Manganese & Iron Ore Limited located in the state of Karnataka. A total of nine iron ore waste fine samples were collected from nine different locations in consultation with the mine management. However, samples collected from only six locations were considered for this study based on the chemical composition, especially the Fe2O3. Three samples where in Fe2O3 was more than 30 % was not considered as waste as they could be upgraded to iron ore in near future. Fly ash for this investigation was collected from Udupi Power Corporation Ltd. It was found that around 90 % of the collected iron ore waste fines were below 600 µ size. Hence, iron ore waste fines are directly suitable for preparation of non-fired bricks without going for any crushing, grinding or screening processes. The investigation revealed that cement can be readily used as an additive/binding material for preparing non-fired bricks from iron ore waste fines found in iron ore mines. These bricks comply with IS Standards IS 13757:1993 of class designation 3.5, which can be used in the construction of simple temporary and cheap structures which are not exposed to heavy rains. Bricks with 9 % cement content as an additive in brick making along with fly ash and iron ore waste fines will meet the desired compressiveiv strength as per BIS guidelines of 3.5 MPa with 28 days of curing period. With 10 % cement content in the brick with varying percentage of fly ash and iron ore waste fines, the bricks with several combinations attain the desired strength as per BIS standards much below 28 days (7 days, 14 days and 21 days) and therefore can be used as a construction material even without 28 days of curing the details of which are presented in this thesis. All the bricks prepared with 9 % cement content as binding material and with curing of 7 days and above meet the BIS standards of water absorption. Investigation has revealed that bricks prepared with below 9 % cement as binding material will deform once removed from the mould and will have very low compressive strength of the order of 0.55 to 0.67 MPa with 28 days of curing. Fly ash from thermal power plants should also be used along with cement and iron ore waste fines in brick making process. The fine fly ash particles improves the concrete pore structure thereby stimulating early strength development and also increases the compressive strength of bricks. Further addition of fly ash in the brick, makes the brick lighter. It was found that there is a significant reduction in weight of the bricks of around 0.5 kg by using fly ash compared to that of bricks prepared without fly ash. Hence, it is recommended to use fly ash in the process of brick making using cement and iron ore waste fines. Further, use of fly ash in making brick is environmental friendly too. It was found that the bricks prepared with 30 % cement, 25 % cement, 20 % cement, 15 % cement and 10 % cement costs ₹ 10, ₹ 9.20, ₹ 8.70, ₹ 7.80 and ₹ 7.20 per brick (excluding profit), respectively, which is substantially below the cost of fired compressed bricks available in the market (costing ₹ 15 per brick). As the cost figures arrived in this research work are based on the cost computation of prepared bricks on laboratory scale, it is anticipated that the cost figures may reduce further when the brick preparation is done on industrial scale. A number of regression equations have been developed for predicting compressive strength and percentage of water absorption of prepared bricks with different days of curing. These equations can be readily used to find out the compressive strength and water absorption of bricks with acceptable level of accuracy. Results on the investigation of the impact of chemical composition of bricks on its compressive strength has revealed that there is no proper relationship of it with total percentages of SiO2 and Al2O3 present in a brick. With increase in total percentage of Fe2O3 present in a brick, its compressive strength was found to decrease gradually. Hence, it is suggested to prepare non fired bricks from iron ore waste fines containing low percentage of Fe2O3 which is also desirable from the point of view of mineral conservation. However, further work needs to be carried out in this direction to confirm the above mentioned results.