Due to the development and increment in the construction industry, the scarcity of natural resources and building materials has been on a very large scale and the demand for the natural resources and materials is increasing day by day. At the same time, disposal of industrial waste or by-products has become more difficult and expensive as a result of the increasing stringent environmental regulations and shortages of suitable, nearby disposal sites. Industrial by-products also create environmental hazards as they may be toxic for the environment. So the usage of industrial by-products and solid waste materials as aggregates in concrete and in the soil stabilization for road and other types of construction work is the need of the hour. Some of the mines wastes at various places throughout the country are copper ore tailings, iron ore tailings, manganese ore tailings, gold ore tailings, zinc ore tailings, lead ore tailings, metal extracts etc [14].

Masonry is widely used to construct both small and large structures because of its structural versatility and attractive appearance [16]. Masonry is of considerable volume in most of the structures and masonry units are consumed in bulk quantities [15]. Compressive strength of masonry greatly depends on strength of the masonry units. In order to cater to the different needs of construction, various masonry units have been developed and used. Natural resources are indiscriminately extracted for construction needs. To reduce the adverse impact on nature, there is a large potential and scope for utilising industrial and mine solid wastes for the manufacture of construction products [1]. India generates huge volumes of mine wastes every year. In the present work, mine tailings which are waste generated after extraction of ore were investigated for production of stabilised mud bricks.

With the increase in population every year, the problem of providing housing is a herculean task for a developing country like ours and also frequent escalation of cost of materials keeps the common man beyond his reach for construction of shelter [6].

The stabilized mud blocks can be used for wall construction, as an alternative to mud walls. Soil lime and soil cement blocks are better than burnt bricks, where the prices of burnt bricks are very high [7].

It is a challenging problem to Civil Engineers to economize the cost of construction in these days of inflation. One of the ways to reduce the cost of construction is to utilize waste materials like fly ash, rice husk ash, coconut pith, metal tailings, slab etc. in construction [8].

The construction industry has developed a lot of stress on the environment by making use of many naturally available materials in the construction of houses and many other structures. The utilization of natural resources like sand, aggregate, soil etc in the construction is going unabated and probably in near future, the yield of all such natural resources may decrease and may give a threat to the construction sector [8, 9].

The use of stabilized mud blocks is an alternative to burnt bricks, where soil is being stabilized with the stabilizers like cement, lime, molasses etc. and pressing them under high compaction, thereby avoiding burning. In avoidance of the process of burning, it saves a lot of energy and hence it becomes economical [6, 7]. The question of economy and conservation energy arises, when burnt bricks are invariably used. The alternative, effective remedy is the use of stabilized blocks. Soil stabilization techniques have been used for improving the properties of soil viz., compressive strength, erosion resistance, absorption etc [10, 11]. The process of compaction can further improve the properties of stabilized soil. The process of compaction leads to higher densities, thereby higher compressive strength, better erosion resistance, lesser water absorption and permeability. The stabilized mud blocks can be used for wall construction, as an alternative to conventional walls [12, 13].

The above approach not only offers significant saving in fuel, energy consumption and conversion of materials, but also involves lower capital investment per ton of cement and provides solution to ecological problems created by disposal of waste [6, 7].

The stabilized mine ore-tailings cement blocks can serve the better purpose of replacing conventional burnt bricks and building blocks upto certain extent in and around Chitradurga and Davangere district, Karnataka.

Thus, the advantages of using the industrial wastes (mine ore-tailings) in the construction can be listed as below.

• Use of industrial wastes in construction reduces the environmental pollution.
• Use of industrial wastes in construction will save the natural resources.
• Use of some industrial wastes in construction may even improve the performance of the material.
• Use of industrial wastes in construction solves the problem of dumping area.
• Some time saving in energy and saving in cost can also be achieved by the use of industrial wastes, thus achieving economy.

Mine (Iron ore, Copper and Manganese ore) tailings are industrial waste material obtained in the mines, after the extraction of concentration from the ore. Some percentage trace of ore properties will be left in the ore waste after the extraction process is completed, known as tailings. These ore tailings are produced in large quantities in the ore mines, which is unfit for farming and making the land barren [3, 4, 5, and 6].

The main aim of this experimental work was to make an attempt to utilize the mine ore tailings for preparing mineore tailings stabilized building blocks, where mine ore tailings are being utilized instead of soil and stabilized with various percentages of cement and sand. ITGE-VOTH machine (Block making machine using man power) was used for preparing stabilized mine ore tailings, building blocks of standard size for construction purpose.

1.1 Materials Used

Cement: The cement used in the experimentation was Ordinary Portland Cement-53 grade, which satisfies the requirements of IS: 12269-1987 specifications [2]. The physical properties of tested cement are given in Table 1.

Table 1. Physical properties of Ordinary Portland Cement-53 grade (IS: 12269-1987)

Iron-ore tailings: The rusty red colored waste material, obtained from Bhimasamudra mines; place which is situated at a distance of 25 to 30 Kms from Chitradurga, Karnataka. Million tons of Iron-ore tailings are being dumped in this area.

Manganese-ore tailings: The dark brown colored waste material, obtained from Hulihalu mines; place which is situated at a distance of 40 Kms from Davangere, Karnataka. Million tons of manganese ore tailings are being dumped in this area.

Copper-ore tailings: The grey colored waste material, resembling cement, obtained from copper mines, Ingaldhal, situated at a distance of 10 Kms from Chitradurga. About 1, 50,000 cum of copper ore tailings are being dumped in this area. The physical properties and chemical composition of mine tailings are given in Table 2 and Table 3.

Table 2. Physical properties of mine-ore tailings

Table 3. Chemical composition of mine-ore tailings in percentage

Fine aggregates: Locally available sand collected from the bed of river Bhadra was used as fine aggregate. The sand used was having fineness modulus 2.96 and confirmed to grading zone-III as per IS: 383-1970 specification [3].

Water: Ordinary potable water (pH = 7.60) free from organic content, turbidity and salts was used for mixing and curing throughout the investigation.

1.2 Experimental Procedure

As the mine-ore tailings dumped by intense consolidation excavation were necessary, excavating can be done manually with excavating tools. The tailings excavated were spread on the ground and left in that condition for few days for air dry.

The mine-ore tailings were first screened through a 4.75mm sieve, to remove the large sized particles if any. The screened dry tailings thoroughly mixed with cement in measured quantities manually. After mixing tailings and stabilizer uniformly, the required quantity of water was added to the dry mixture as per optimum moisture content test before by sprinkling using garden rose cane. Once again it was mixed thoroughly and uniformly without forming any lumps in it. Ready wet mix was tested for the moisture content, simply by making a ball in the palm of hand, where the dust should not stick to the hand in this process.

The mine-ore tailings were stabilized by cement in different percentages like 4%, 5%, 6% and 7% with extra percentage of sand as the case may be, and required quantities of blocks were prepared for testing of size 229mm x 178mm x 102mm using ITGE-VOTH machine, where in a pressure of 1.8 N/mm² was applied. The blockpressing machine was anchored temporarily by keeping sand bags on the adjacent sides of the machine.

The curing method used in this investigation was “Hay curing”. The paddy straw was spread over bricks, such that it completely covers them. The bricks were cured by sprinkling water gently on straws, thrice a day. The curing was continued for 7, 14 and 21days, as the case may be. Soon after the curing, the blocks were tested for dry compressive strength, wet compressive strength, water absorption, and erosion resistance.

The following tests were conducted on stone crusher dust blocks:

The blocks were dried in sunshine for 2 to 3 days, to remove moisture content inside the blocks completely for dry compression test. To conduct wet compression test, completely dried blocks were immersed in water for duration of 24 hours, the blocks were removed from water and the wetted surface was wiped out cleanly for test. For each average result, five blocks per set were taken and the blocks were tested for compression as per IS: 3495(Part 1)-1992 specification [4] on each specimen. The test results were tabulated in Table 4 to Table 9.

Table 4. Test results of stabilized Iron-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers.

Table 5. Test results of stabilized Iron-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers plus 15% extra sand.

Table 6. Test results of stabilized Manganese-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers.

Table 7. Test results of stabilized Manganese-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers plus 20% extra sand.

Table 8. Test results of stabilized Copper-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers.

Table 9. Test results of stabilized Copper-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers plus 20% extra sand.

The dry weight (W_dry) of the blocks was taken and then it was immersed completely in clean potable water for 24 hours. After 24 hours, the blocks were removed from water and the wet surface is wiped out with a clean cloth and the weight was taken (W_wet) as per IS: 3495(Part-2)-1992 [5] specification. The absorption was given by the relation,

(1)

Five blocks per set were taken and the average of five results was considered as 'Water absorption' of the blocks. The results were tabulated in Table 4 to Table 9.

The test involves using a normal shower rose of 90mm diameter, with water flowing at a pressure of 1 KSC (1 N/mm²). The spray jet, which is horizontal, is then allowed to impinge on the surface of a pressed block. The shower rose has 226 holes of an average dia of 1.15mm, with a density of 3.2 holes/ Sq. cm. It can be seen that, the flow rate is such that the amount of water flowing in one minute is equal to a precipitation of 566mm.This means that a majority of blocks would be completely eroded by the spray in less than 2 hours.

The erosion of the blocks may be expressed in mm after drying, by visual observation. Also,

(2)

Where, d = Average depth of erosion in mm and t = test duration in minutes (5 minutes)

The results were tabulated in Table 4 to Table 9.

The following tables give the details of the experimental results.

Tables 4, 6 and 8 show the test results of stabilized mine ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers.

Tables 3, 6 and 9 shows the test results of mine-ore tailings building blocks with various percentages of cement (4%, 5%, 6% and 7%) stabilizers plus extra percentage of sand to make total sand content to 65%

Based on the experimental results and observation, the following discussions were made.

• In the developing countries like India, the increase in population has created problems for shelter, as the cost of the building materials such as cement, brick, tiles etc are very high, and it is beyond the reach of the common man for construction of shelter.
• The above problem can be solved up to some extent by the utilization of waste material like mine-ore tailings, in the form of stabilized–mine talings building blocks, an alternative to burnt bricks and concrete blocks in and around Chitradurga and Davanagere District, Karnataka.
• The percentage of economy determined can be considered seriously, since the masonry work costs above of estimated cost of the construction.
• As the stabilized mine ore tailings building blocks posses sufficient erosion resistance, only pointing sufficient, there by economizing the construction cost by 10%, by avoiding the plastering. Also, there will be a saving of 10% of mortar consumption in masonry.

Based on the experimental results, the following conclusions can be drawn

• The stabilized building blocks of mine-ore tailings with 7% addition of cement show maximum compressive strength (refer Tables 4, 6 and 8).
• The stabilized building blocks of mine ore tailings with 7% addition of cement and with extra percentage of sand (15% and 20% as the case may be) show the maximum compressive strength (refer Tables 5, 7 and 9).
• The ratio of wet to dry compressive strength lies between 0.50 and 0.73 in the case of stabilized Iron ore tailings building blocks.
• The ratio of wet to dry compressive strength lies between 0.40 and 0.50 in the case of stabilized Manganese-ore tailings and Copper-ore tailings stabilized building blocks.
• The stabilized building blocks of mine-ore tailings show an increasing trend in the erosion resistance with the increase in the curing period and stabilizer percentage.
• The stabilized building blocks of mine-ore tailings show a decrease in absorption with the increased stabilizer percentage and curing period.

The authors would like to thank Vice-Chancellor, Christ University, Fr. Benny Thomas, Director and Dr. Iven Jose, Associate Dean, Christ University Faculty of Engineering, Bangalore for their constant encouragement.