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Evaluation of Concrete Strength by Partially Replacing Cement by Red Mud And Fly Ash

Guided By: Mr. Anil Kumar Suman
Submitted By: Rashmi Sahu

Chhattisgarh Swami Vivekanand Technical University
Bhilai (C.G.), India
Shri Shankaracharya Technical Campus
Ssgi-bhilai (C.G)

Red Mud is a hazardous waste generated in the Bayer process Alumina production (AL2O3) from Bauxite ore which contains high levels residual alkalinity and toxic heavy metal. Therefore, Red Mud is a hazardous waste of Alumina Industry. The volume of Red Mud which generated in the alumina processing plant depends on the quality of crude Bauxite ore, may be greater than the volume of alumina 1-1.5 times. The alumina processing plant usually disposes liquid Red Mud into reservoirs, which cause the risk of major environment pollution for lowland. The particle dimension of red mud usually less than 1mm . Therefore, dry red mud easy spread into the air and causes dust pollution. It is often exposured to dust cause skin and eyes diseases. Red mud in an liquid state causes harmful effect to human skin. Composition and properties of red mud in the world have been presented by many researchers in their publications.

Fly Ash is a byproduct of coal-fired electric generating plants. The coal is pulverized and blown into burning chamber for immediate combustion. Heavier ash particle (Bottom Ash or Slag) fall to the bottom burning chamber and the lighter ash (fly ash) fly out with exhaust gas, thus the term fly ash. Before leaving the stack, these fly ash particle are removed and collected by electrostatic precipitation, bag houses or other methods.

Aluminum is a light weight ,high strength and recyclable structural metal. It plays an important rate in social progress and has a pivotal contribution in transportation, food and beverage packaging, infrastructure, building and construction electronics and electrification, aerospace and defense. It is the third abundant element in the earth’s crust and is not found in the free state but in combined form with other combined form with other compounds. The commercially mined aluminum ore is bauxite, as it has the highest content of alumina with minerals like silica, iron oxide, and other impurities in minor or trace amount. The waste product derives its colour and and name from its iron oxide content. As the bauxite has been subjected to sodium hydroxide treatment the red mud is highly caustic with a PH in the range of 10.5-12.5. Bauxite posing a very serious and alarming environmental problems.

About 1 ton of alumina is produced from 3 tons of bauxite and about 1 ton aluminum is produced from 2 tons of alumina. Depending on the raw material processed,1-2.5 tons of ed mud is generated per ton of alumina produced.


The main aim of this research is to study the effect of chemical composition and physical properties of Indian fly ashes and red mud strength. The objectives of this thesis work are listed below.

1. To understand which of the characteristics of fly ash are important for strength development in mortar.
2. Utilization of red mud is established in brick manufacturing, partial cement refilling, in concrete industry and stabilization process.
3. To investigate the effect of fly ash characteristics on the rate of hydration of cement.
4. Awide variety of potential uses of red mud have been reviewed, yet there is no economically viable and environmentally acceptable solution for the utilization of large volumes of red mud.
5. To investigate the effect of fly ash characteristics on transport.
6. It should be easily adopted in field.
7. To model the effect of physical characteristics of fly ash on strength development of mortars.
8. Using the wastes in useful manner.
9. To reduce the cost of the construction.

• Kusum Deelwal, Kishan Dharavath and Mukul Kuleshreshtha- A wide variety of potential uses of red mud have been reviewed, yet there is no economically viable and environmentally acceptable solution for the utilization of large volumes of red mud. There is urgent need to undertake research and studying the metal speciation and the changes associated with red mud reuse in the construction purpose and during
the wet storage of red mud in ponds.

• Daniel Veras Riberio and Joao A. Labrincha- Tests performed in the actual work suggest that red mud generated from the alumina and aluminium production by the Bayer process an interesting candidate to be used in mortar and concretes for non-structural applications, in addition to ordinary Portland cement in the mixture.

• Sherwood and Ryley stated that fly ash possesses self-hardening features due to the presence of free lime in the form of calcium oxide or calcium hydroxide.

• McLaren and Digioiab presented that the specific gravity of fly ash is relatively lower than that of soils. The density of the ash fills gets reduced which is a major advantage in terms of its use as various filler materials. Now these fillers can be used in spongy walls and ridges particularly when the foundation is weak.

• Sridharan et al., studieds the micrographs of FA particles through SEM. These particles are mostly solid spheres with glassy appearance, hollow spheres with smooth-edged porous grains, asymmetrical agglomerates and irregular absorbent scraps of unburnt carbon. Presence of particles which are dark grey in color can be identified as pointed grain.

• Mitchell and Brown said that the soil, FA and lime displays unique behavior and are much more dependent on the physicochemical properties of the fly ash and soil like porosity, segregation, lime content, time and pressure applied during compaction.

• Martinet al. stated that FA in wet but unsaturated state displays cohesive properties which are due to the tensile stress developed by the capillary action of water. Since this property limits the long term solidity of the compacts. He concluded that for improving the mechanical strength angle of shearing is more important.

• Indraratna et al. showed a comparison between the intercept of cohesion and angle of shearing resistance of dry and wet fly ash specimens. He reported that there is 100% loss of cohesion mainly to dry specimen with no change is resistant shearing angle.

• Rajasekhar specified that fly ash particles are mostly amorphous (glassy) with shape. Te low specific gravity is due to the existence of large number of small hollow spheres enclosed in big spheres (plero spheres). Reasons behind that the trapped air cannot be detached from hollow spheres or due to the differences in configuration of these particles.

• Singh and Panda determined shear strength of newly made fly ash compacts in the presence of different volumes of water content. He concluded that the shearing strength of the compacts is due to the internal friction.

EXPERIMENTAL WORK – Concrete mix design was carried out by using Indian Standard Method (IS:10262-1982). Mix design of grade M30 is used.

Cement – Ordinary Portland Cement (53 grade ) confirming to IS:269-1976 was used throughout the investigation. Different tests were performed on the cement to ensure that it confirms to the requirements of the IS specifications. The physical properties of the cement were determined as per IS: 4031-1968 and are presented in table.

Table :- Physical Properties of 53 Grade Cement.

01 Standard Consistency 53
02 Fineness of cement as retained on 90 micron sieve 3%
03 Initial setting time 30 minutes
04 Specific gravity 3.15
05 7 days compressive strength 37mpa

Table :- Chemical Properties of Cement.

01 Lime ( CaO ) 63%
02 Silica ( SiO2 ) 22%
03 Alumina ( Al2O3 ) 6%
04 Iron Oxide ( Fe2O3 ) 3%
05 Magnesium Oxide ( MgO ) 2.5%
06 Sulphur Trioxide & loss of ignition ( SO3 ) 1.5%
07 Alkalies 0.5%

Red Mud – Red Mud is composed of a mixture of solid and metallic oxide-bearing impurities, and presents one of the aluminium industries most important disposal problems. The red colour is caused by the oxidized iron present, which can make upto 60% of the mass of the red mud. In addition to iron, the other dominants particles include silica, unleached residual aluminium, and titanium oxide. Red mud cannot be disposed of easily. As a waste product of the bayes process the mud is highly basic with a pH ranging from 10 to 13.

Fly Ash –

Coarse Aggregates – 10mm (sp. Gr. =2.87) , 20mm (sp. Gr. =2.88)

Fine Aggregates – Natural Sand (sp. Gr. =2.76)

Aggregate tests-
1. Sieve analysis.
2. Aggregate specific gravity and water absorption test.

Sieve Analysis- sieve analysis helps to determine the particle size distribution of the coarse and fine aggregates. This is done by sieving the aggregates as per IS: 2386(PART-1)-
1963. In this we use different sieves as standardized by the IS code and then pass aggregates through them and thus collect different sized particles left over different sieves. The apparatus used are – 1.)

A set of IS sieves of sizes- 80mm, 63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 12.5mm, 10mm, 6.3mm, 4.75mm, 3.35mm, 2.36mm, 1.18mm, 600µm, 300µm, 150µm, 75µm.

2.) Balance or scale with an accuracy to measure 0.1 percent of the weight of the test sample.

Step 1: Take 5000grams of coarse aggregates by weighing the material in a digital scale. Weigh each of the clean sieve, along with the bottom pan, and record their weights.

Step 2: Place the aggregates in the mechanical sifter (sieve sizes used are 1 ½”, 1”, ¾”, ½”,3/8”, & #4). This apparatus is used for shaking the material (similar to the principle of a paint-mixing machine) and sieving it.

Step 3: Determine the aggregates that are retained in each individual sieve, as mentioned earlier in part-1, and record the data. To ensure that all materials are collected, use the steel brush to clean each sieve.

Step 4: Tabulate the data and determine the percent retained, and the percentage that would have been retained in each sieve, if that sieve alone was used to sieve the whole volume. The fineness modulus is
obtained by adding the percentage of material retained in all the sieve and dividing it by 100.

Step 5: Plot a graph of percent passing by weight vs. sieve sizes.
Note: All sieves have to be cleaned prior to experiment.

Aggregate specific gravity and water absorption test:- The specific gravity and water absorption of aggregates are important properties that are required for the design of concrete
and bituminous mixes. The specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. Because the aggregates may contain water-permeable voids, so two measures of specific gravity of aggregates are used: apparent specific gravity and bulk specific gravity.

Apparent Specific Gravity, Gapp, is computed on the basis of the net volume of aggregate i.e. the volume excluding water-permeable voids. Thus

Gapp = (Md/Vn)/W

Md= the dry mass of the aggregate,

Vn= the net volume of the aggregate excluding the volume of the absorbed matter,

W= the density of water.

Water Absorption This test helps to determine the water absorption of coarse aggregates as per IS:2386(part-3)-1963. For this tests a sample not less than 2000g should be used.

The apparatus used for this test are:- wire basket – perforated, electroplated or plastic coated with wire hangers for suspending it from the balance, water-tight container for suspending the basket, Dry soft absorbent cloth- 75cm*45cm (2nos), shallow tray of minimum 650 area, air-tight container of a capacity similar to the basket and oven. The difference between the apparent and bulk specific gravities is nothing but the water- permeable voids of the aggregates. We can measure the volume of such voids by weighing the aggregates dry and in a saturated, surface dry condition, with all permeable voids called with water. The difference of the above two is Mw. Mw is the weight of dry aggregates minus weight of aggregates saturated surface dry condition. Thus

Water absorption = (Mw/Md)*100

The specific gravity of aggregates normally used in road construction ranges from about 2.5 to 2.9 . Water absorption values ranges from 0.1 to about 2.0percent for aggregates normally used in road surfacing.

As per the mix design control mix was prepared. Study includes replacement of cement by red mud and fly ash. Hence we have replaced cement in varying percentage 15% and 20% .

Figure shows red mud and fly ash powder and red mud, fly ash , cement concrete cubes. These composite concrete specimens were tested after 7, 14, 21and 28 days water curing. The compressive and Tensile
strength of resultant concrete was found out and compared with controlled concrete results.


PROPERTIES OF RED MUD:- 1. Physical Properties of Red Mud:-
The following tests were conducted to evaluate Physical Properties-
1. Generally fineness of Red Mud is varies in between 1000-3000cm2/gm. We collected Red Mud from BALCO Industries Limited, Korba Chhattisgarh (INDIA). In our study we have taken Red Mud passing through 300 micron I.S. sieve.
2. Its PH is varies in between 10.5 to 12.5 hence alkaline in nature.
3. Specific Gravity of Red Mud is found to be 2.51 .

Fe2O3 30-60%
Al2O3 10-20%
SiO2 03-50%
CaO 02-08%
Na2O 02-10%
TiO2 Trance-25%

It indicates that percentage of CaO is very less hence it has no cementious properties but when it react with water and cements if starts gaining cementious properties. Also percentage of silica available,contributes to strength.

Effects of Red Mud on Environment:-
1. Ground water pollution- when the red mud gets mix with water.
2. Alkali seepage in to underground water- underground water resources such as wells, aquifer may get polluted.
3. Impact on plant life- Alkaline air born dust fly with air and effects on transpiration process of plant result in reduction of plant life.
4. Land disposal changes the property of soil and result in lesser fertility.
5. Vast areas of land consume.

Red Mud in Cement Replacement:- Dicalcium silicate in red mud is also one of the main phases in cement clinker, and red mud can play the role of crystallization in the production of cement clinker. Fly ash is mainly composed of SiO2 and Al2O3, thus can be used to absorb the water contained in the red mud improve the reactive silica content of the cement.

PROPERTIES OF FLY ASH :- Fly Ash is characterized by its physical, chemical and mineralogical properties that are greatly reliant on the essence of the parent coal, the combustion conditions, various emission control devices and the storage and treatment methods.

1. Physical Properties of Fly Ash :- Fly Ash comprises of fine, powdered particles mainly spherical in shape, either solid or hollow. These particles are primarily glassy (amorphous) in nature with possibly some crystalline phases. During combustion of coal oxidation occurs, therefore negligible amount of carbon and nitrogen is found in the Fly Ash. The colour of fly ash vary from grey to black due to the little changeable quantity of unburned carbon present in it. Carbon content material in the fly ash are angular in shape. There is no such big difference between the variation in particle size of a bituminous coal fly ash and silt. Usually it is less than 0.075mm. Sub-bituminous coal fly ash is little bit coarse than bituminous coal fly ash although both are sediment-sized. The specific gravity of fly ash lies between the range of 1.8-3.2 , while its specific surface area lies in the range of 180 to 1000m2/kg. The average diameter of these fly ash particles are less than 10 micrometer and size between 0.01-1000 micrometer. The spherical morphology, low bulk density and low specific gravity bring great limitation in limits the height of ash dykes generated for increasing the stronge capacity of ash ponds.

2. Chemical Properties of Fly Ash :- Fly ash properties are greatly influenced on various parameters like nature of coal, methods for handling, storage and treatment of different types of coal found in nature. These are bituminous, sub-bituminous anthracite and lignite. Each type of coal is chemically distinct with others and varies significantly with respect to its calorific value, chemical configuration, amount of ash present, and in geographical origin. Oxides of silicon, aluminum, and iron are the chief components of bituminous coal. Variable amount of unbrunt carbon present can be measured by the loss on Ignition which is one of the most significant chemical properties of Fly Ash.

The ash generated from lignite coal is rich in Ca and Mg oxides typically ranges between 12-25% with decreased amount of silica and oxides of iron (Fe2O3, Fe3O4), as compared to bituminous coal Fly Ash. Very little amount of carbon can also be found in lignite coal fly ash. Apart from the handling condition of ash i.e. either wet or dry there is several more classification out of which the ash coming out from coal is one. Anthracite coal fly ash finds little usage due to the large amount of carbon present in it. Only some amount of anthracite coal is combusted in utility boilers, thus generating low concentration of fly ash. Move over lignite and sub bituminous coal fly ash possesses greater concentration sulphate ions.

Fly Ash Disposal- Curse of Environment:- Large amount of solid wastes in the form of fly ash have been generated from thermal power plant. These wastes are widely utilized in various construction materials and other sectors. Apart from fulfilling the needs, the disposal of fly ash is burning problem and creates hindrance in developing a pollution free nation. Hence it’s a matter of great concern some of the problem regarding fly ash disposal are mentioned below.

1. Fly ash particles are available in both the dry and wet state. These ashes are disposed in bulk which occupies thousands of hectares of land and destroy the fertility of top soil.
2. Handling of fly ash particles in dry condition is a tough job. Since these ashes are very fine and dispersive in nature. The fine tiny bits of fly ash destroy the structural shells and affects cultivation.
3. It hampers the ecosystem through various modes of pollution i.e. soil, air and water.
4. Since fly ash are disposed in open atmosphere which ultimately results in various air borne disease due to long intake of air.
5. The biological features of soil and overall yield of crops also get hampered when fly ash is disposed in the nearby areas before any treatment.

SIZE AND SHAPE:- Fly ash is typically finer than Portland cement and lime. Fly ash consists of silt-sized particles which are generally spherical, typical ranging in size between 10 and 100 micron.

These small glass spheres improve the fluidity and workability of fresh concrete. Fineness is one of the important properties contributing to the pozzolanic reactivity of fly ash.

CHEMISTRY:- Fly ash consists primarily of oxides of silicon, aluminum iron and calcium, magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. When used as a mineral admixture in concrete, fly ash is classified as either class C or class F ash based on its chemical composition. American Association of State Highway Transportation Officials defines the chemical composition of class C and class F fly ash.

Class C ashes are generally derived from sub-bituminous coals and consists primarily of calcium alumino- sulfate glass, as well as quartz, tricalcium aluminate, and free lime ( CaO ). Class C ash is also referred to as high calcium fly ash because it typically contains more than 20% CaO.

Class F ashes are typically derived from bituminous and anthracite coals and consist primarily of an alumino- silicate glass, with quartz, mullite, and magnetite also present. Class F, or low calcium fly ash has less than 10% CaO.

Table :- sample oxide analysis of ash and Portland

Compound Fly ash class F Fly ash class C Portland cement
SiO2 55 40 23
Al2O3 26 17 4
Fe2O3 7 6 2
CaO 9 24 64
MgO 2 5 2
SO3 1 3 2

COLOR:- Fly ash can be tan to dark gray, depending on its chemical and mineral constitutions. Tan and light colors are typically associated with high lime content. A brownish color is typically associated with the iron content. A dark gray to black color is typically attributed to an elevated unburned carbon content. Fly ash color is usually very consistent for each power plant and coal sources.

QUALITY OF FLY ASH:- Quality requirements for fly ash vary depending on the intended use. Fly ash quality is affected by fuel characteristics ( coal ), co-firing of fuels ( bituminous and sub-bituminous coals ), and various aspects of the combustion and flue gas cleaning/ collection processes. The four most relevant characteristics of fly ash for use in concrete are loss on ignition ( LOI ), fineness,chemical composition and uniformity.

LOI is a measurement of unburned carbon ( coal ) remaining in the ash and is a critical characteristics of fly ash, especially for concrete applications. High carbon levels, the type of carbon ( i.e. activated ), the interaction of soluble ions in fly ash and the variability of carbon content can result in significant air-entrainment problems in fresh concrete and adversely affect the durability of concrete.

Some fly ash uses are not affected by the LOI. Filler in asphalt, flowable fill, and structural fills can accept fly ash with elevated carbon contents.

FINENESS:- Fineness of fly ash is the most closely related to the operating condition of the coal crushers and the grindability of the coal itself. For fly ash use in concrete applications, fineness is defined as the percent by weight of the material retained on the 0.044mm. A coarse gradation can result in a less reactive ash and could contain higher carbon contents. Limits on fineness are addressed by Americal Society for Testing and materials and state transportation department specification to improve its fineness and reactivity.

Some non-concrete applications, such as structural fills are not affected by fly ash fineness. However, other applications such as asphalt filler, are greatly dependent on the fly ash fineness and its particle size distribution.

CHEMICAL COMPOSITION:- Chemical composition of fly ash relates directly to the mineral chemistry of the parent coal and any additional fuels or additives used in the combustion or post-combustion processes. The pollution control technology that is used can also affect the chemical composition of the fly ash. Electric generating stations burn large volumes of coal from multiple sources. Coals may be blended to maximize generation efficiency or to improve the station environmental performance. The chemistry of the fly ash is constantly tested and evaluated for specific use applications. Some stations selectively burn specific coals or modify their additives formulation to avoid degrading the ash quality or to impart a desired fly ash chemistry and characteristics.

UNIFORMITY :- Uniformity of fly ash characteristics from shipment to shipment is imperative in order to supply a consistent product. Fly ash chemistry and characteristics are typically known in advance so concrete mixes are designed and tested for performance.

QUALITY ASSURANCE AND QUALITY CONTROL :- criteria vary for each use of fly ash from state to state and source to source. Some states require certified samples from the soil on a specified basis for testing and approval before use. Others maintain lists of approved sources and accept project suppliers certification of fly ash quality. The degree of quality control requirements depends on the intended use, the particular fly ash, and its variability.

OVERVIEW:- Fly ash is used in concrete admixtures to enhance the performance of concrete. Portland cement contains about 65% lime. Some of this lime become free and available during the hydration process. When fly ash is present with free lime, it reacts chemically to form additional cementitious materials, improving many of the properties of the concrete.

BENEFITS :- Benefits to concrete vary depending on the type of fly ash, properties used, other mix ingredients, mixing procedure, field conditions and placement. Some of the benefits of fly ash in concrete.

1. Higher ultimate strength.
2. Improved workability.
3. Reduced bleeding.
4. Reduced heat of hydration.
5. Reduced permeability.
6. Increased resistance to sulfate attack.
7. Increased resistance to alkali- silica reactivity ( ASR ).
8. Lowered costs.
9. Reduced shrinkage.
10. Increased durability.

CAUTIONS :- Care should be taken when using fly ash in concrete due to –
1. Potential for decreased air entraining ability with high carbon fly ash may reduce durability.
2. Reduced early strength.
3. Reduced heat of hydration in colder climates.


1. The percentage of water cement ratio is depends on quantity of RED MUD and FLY ASH used in concrete. Because RED MUD is highly porous material.

2. Compressive strength increases with the increase in the percentage of FLY ASH and RED MUD up to replacement ( 20%FA and 20%RM ) of cement in concrete for different mix proportions.

3. Compressive strength increase by addition of quarry sand in addition to FLY ASH and RED MUD.

1. For experimental work it was found that increase in red mud and fly ash content decreases the compressive as well as tensile strength of concrete.

2. Optimum percentage of the replacement of cement by weight is found to be 25% by the replacement results got are nearly equal to the results of controlled concrete.

3. Concrete prepared by using red mud is suitable in ornamental works and gives aesthetically pleasant appearance.

4. Workability of concrete may get affected with increases of fly ash and red mud.

5. We use mixture of red mud, fly ash and cement for non-structural work. There is future scope for the use of red mud concrete in structural point of view.

6. A wide variety of potential uses of red mud have been reviewed, yet there is no economically viable and environmentally acceptable solution for the utilization of large volumes of red mud.

7. The addition of red mud promotes on increases of pH of fresh paste. This is due to a concentration of hydroxyl ions ( OH-), from the solution and aluminium hydroxides detected in the red mud.

8. The mortar workability is considerably reduced by adding the red mud. Moreover water retention is reasonably increased.


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We at are thankful to Rashmi Sahu for submitting this paper to us

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Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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