Bahoria et al. (2013) on their literature study collectively pictured various researches on waste and recycled materials that can be used as concrete ingredients. Material obtained from sludge treatment plants such as sludge ash, screenings, etc., were included in studies on concrete material replacements (Sahu et al., 2013; Kosior-Kazberuk, 2011; Sakthieaswaran and Ganesan, 2013; Deotale et al., 2012; Ramesh et al., 2014). By using hazardous waste materials such as glass waste and plastic waste, the environmental sustainability can be increased. Waste materials from coal industries contribute most basic properties of concrete material. However for the generation of pozzolona cement, waste materials such as fly ash, bottom ash are included. Some waste materials are being used for landfilling such as China clay waste (CCW), spent bricks, etc., (Sawant et al., 2011, Shetty et al., 2014, Dayalan and Beulah, 2014).

 

Seeni et al. (2012) ensured the partial replacement of fine aggregate in concrete by using china clay industrial waste for an optimum of 30%. This replacement leads to the positive effects on concrete by reducing its cost with increase in strength. The effect of replacement of cement by neutralized red mud has been studied on design mix concrete of grade M50 (Sawant et al., 2013). Govindarajan and Jayalakshmi (2012) investigated of the influence of calcined red mud in cement hydration and concluded that compressive strength of cement containing 20% red mud was higher than the OPC at all hydration periods. Mohan Kushwaha et al. (2013) developed self compacting concrete using red mud. Manoj et al. (2014) developed brick from industrial waste red mud. compressive strength of concrete produced by replacing cement by unwashed red mud and when subjected to alternative wetting and drying for 50 cycles goes on increasing up to 10% replacement levels (Rudrasamy  and  Prakash,   2014).   Ankit   and   Jayesh  (2013) investigated the strength of concrete and optimum percentage of the partial replacement by replacing cement via stone waste. The fresh and hardened properties of self compacting concrete (SCC) using red mud as partial replacement for cementitious material along with used foundry sand as partial replacement for fine aggregate were evaluated by Shetty et al. (2014).

 

OBJECTIVE

 

(i) To find the optimum replacement of cement by red mud

(ii) To find the compressive strength, split tensile strength and flexural strength of red mud used concrete and conventional concrete.

(iii) To compare the compressive strength, split tensile strength and flexural strength of red mud concrete with the conventional concrete.

Virgin materials were chosen as raw materials for concreting. 43 grade OPC cement, red mud, crushed rock of maximum 20 mm size and potable water were invested for the experiments. Locally available good river sand passing through 4.75 mm sieve was used.

 

Cement

 

Ordinary Portland Cement (43 Grade) confirming to IS: 8112-1989 was used throughout this investigation. Various tests were conducted on the cement to ensure their property as recommended by IS 8112. The physical properties of the cement were found as per IS: 4031- (Part 1 to 15) and are presented in Table 1.

 

 

Red mud

 

Red mud is one of the major solid wastes obtained as by-product from Bayer process of alumina extraction. At present about 3 million tonnes of red mud is generated annually which is not being disposed or recycled satisfactorily (Sawant et al., 2012). Red mud properties were obtained from M/S Mallco (India) limited, data sheet (Table 2). The chemical composites was ensured by the same industries and tabulated in Table 3.

 

 

Fine aggregate

 

River sand was used as fine aggregate. The size of the sand used is less than 4.75 mm. The properties of fine aggregate investigated as per IS 383 - 1970 are presented in Table 4.

 

 

Coarse aggregate

 

Machine crushed granite obtained from a local quarry was used as coarse aggregate. The properties of the coarse aggregate are found as per IS 383-1970 code specification, shown in Table 5.

 

 

Water

 

Water used in this project was potable water.

 

Mix design

 

Based on the properties of the water, cement, fine aggregate and coarse aggregate design mix of M₃₀ were calculated by following the recommendations of IS code IS 10262 - 2009. The final mix ratio was arrived as 1:1.462:2.695 with water cement ratio of 0.44. The measurement of materials   was   done   by   weighing   using electronic weighing machine. Water was measured in weight. The red mud was used for replacing of cement by 5% intervals in weight up to 25% as shown in Table 6.

 

 

Casting and testing of specimens

 

M₃₀ grade of concrete was prepared as per IS 10262-2009. Three cube specimens (150 x 150 x 150 mm) and three cylinders (150 x 300 mm) were casted for determining compressive strength and split tensile strength respectively. Prisms (100 x 100 x 500 mm) of 3 numbers were casted and tested for flexural strength of concrete. Casted specimens were cured in the curing pool for 7, 14 and 28 days. After curing the cubes and cylinders were tested in hydraulic compression testing machine and prisms were tested in UTM as per IS 516-1959 code specifications. The values of compressive strength, spilt tensile strength and flexural strength are tabulated.

The compressive strength results are shown in Table 7. It was observed that the maximum compressive strength of 36.52 N/mm² was obtained at 15% replacement of cement by red mud. The compressive strength  reduces beyond 15% replacement of cement by red mud. As the concrete is weak in tension, tensile strength is one of the basic and important properties of concrete. The concrete is not usually expected to resist the direct tension because of its low tensile strength and brittle nature. Determination of tensile strength of concrete is necessary to determine the load at which the concrete members may crack. The load at which splitting of specimen took place is recorded in Table 8.

 

 

In case of split tensile strength test, the maximum strength was obtained at 15% replacement of cement by red mud. At 28 days curing the split tensile strength value was 4.61 N/mm² which was greater than conventional concrete strength. The Maximum 28 days cured, flexural strength of prism is obtained for R3 specimen (that is) 15% replacement of cement by red mud and the various flexural values for the samples are tabulated in Table 9. The optimum replacement level of cement by red mud was obtained at 15% from the experimental investigation. From the Figures 1, 2 and 3, it can be noticed that increase in the percentage of red mud has proportionate increase in strength for all the ages. For percentage above 15 the strength decreases. Also the strength parameters of red mud replaced concrete were found to be greater than the conventional concrete.

 

 

 

The effect of partial replacement of cement by red mud has been studied on design mix concrete of grade M30. It is observed that the rate of gain in strength properties namely compressive, spilt tensile and flexure increases with increase in red mud content up to  15%  and  beyondwhich it started decreasing. The above results show that the maximum utilization of red mud in concrete is 15% as a partial replacement of cement. This study concludes that red mud can be used as an innovative supplementary cementitious alternative.

The authors have not declared any conflict of interest.