Investigations on optimum possibility of replacing cement partially by redmud in concrete

Red mud is an industrial waste material generated during production of alumina from bauxite by Bayer process. These industrial wastes hold some heavy metals which are hazardous in nature. The aim of the paper is to investigate the possibility of partially replacing Portland cement in concrete by red mud and evaluating its compressive and splitting tensile strength. This study examines the effect of red mud on the properties of hardened concrete and compares with the conventional concrete. The test results revealed that 15% of cement can be optimally replaced by red mud beyond which compressive strength, split tensile strength and flexural strength starts decreasing. Cement replacement by red mud up to 15% yields characteristic strength greater than the conventional cubes. Further increase in percentage of red mud by 20, 25 and 30% tends to decrease the compressive strength. However, the optimum replacement level was observed as 15% without decrease in strength.


INTRODUCTION
Red mud is the main waste generated from bauxite ore during production of aluminium and alumina by the Bayer process (Ashok and Suresh Kumar, 2014).The world's production of bauxite in 2009 was 205 million tons, and the main producing countries were Australia, China, Brazil, Guinea, India and Jamaica (Ribeiro et al., 2011).As per records of 2009, Brazil ranks third in bauxite production by producing 26.6 million tons of bauxite.It also holds the world's third largest bauxite ore reserves (around 3.5 billion tons), concentrated mainly in the northern part of the country.Roughly 0.3 to 1.0 tons of red mud waste are generated per ton of aluminium produced.Brazil has discarded about 10.6 million tons/year of caustic red mud in recent years and the worldwide generation of red mud exceeds 117 million tons/year.
For the betterment of waste management and generation of cost effective concrete, the inclusion of recycled waste material becomes essential.Most of the recent studies on concrete focus on the inclusion of waste material in concrete.This is due to the problems relating to the waste management.Thus the waste materials that resemble the properties required by concrete ingredients can be included for concreting.*Corresponding author.E-mail:linorametilda1971@gmail.comAuthor(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Fineness in sq.cm/gram 1000-3000 3. pH 10.5 -12.5 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)

MATERIALS AND METHODS
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.    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 1:1.462:2.695with 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.

RESULTS AND DISCUSSION
The compressive strength results are shown in Table 7.It was observed that the maximum compressive strength of 36.52 N/mm 2 was obtained at 15% replacement of cement by red mud.The compressive strength reduces 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/mm 2 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.

Conclusion
The effect of partial replacement of cement by red mud

(
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 byShetty 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.

Table 1 .
Properties of cement.

Table 2 .
Properties of red mud.

Table 3 .
Red mud composite materials.

Table 4 .
Properties of fine aggregate.

Table 5 .
Properties of coarse aggregate.

Table 6 .
Replacement of binding materials.
Fine aggregateRiver 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

Table 7 .
Compressive strength on concrete cubes.

Table 8 .
Split tensile strength on concrete cylinders.