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Development of Light Weight Foamed Bricks from Red Mud

  • Jawaharlal Nehru Aluminium Research Development and Design Centre,Nagpur,Maharashtra

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Development of Light Weight Foamed Bricks from Red Mud 1 P.A Mohamed Najar*, 1Manoj T. Nimje, 1S.U.Bagde, 1V.S.Pathak, 1S.S.Prajapati, 2B.K.Satpathy and 1J. Mukhopadhyay 1 Jawaharlal Nehru Aluminium Research Development and Design Centre Amaravati Road, Wadi, Nagpur – 440 023, India 2 National Aluminium Company Limited, Nayapalli, Bhubaneswar – 751 061, India ABSTRACT The present study demonstrates the potential utilization of red mud for the production of light weight foamed bricks (LWFB) for building and construction applications. A novel concept of self expanding raw material mix for the formation of LWFB has been realized. The salient features of LWFB produced by heat treatment (1000-1200 0C) of admixtures containing red mud, fly ash and foaming agents were discussed. The environmental impact on the durability was also evaluated with respect to its exposure to sunlight and moisture under different climatic conditions. Various physical and chemical parameters such as compressive strength, porosity, dry and wet density, leachability and vaporization of heavy metals, soda leaching, pH variations, efflorescence, radioactivity etc. were evaluated. The possibility of product modification and area of extended applications were also discussed. Key words: Red mud; Foamed Light Weight Bricks; Building and Construction, Toxic effect, Environmental Impact, Application
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Development of Light Wight Foamed Bricks from Red Mud
1 P.A Mohamed Najar*, 1Manoj T. Nimje, 1S.U.Bagde, 1V.S.Pathak,
1S.S.Prajapati, 2B.K.Satpathy and 1J. Mukhopadhyay
1Jawaharlal Nehru Aluminium Research Development and Design Centre
Amaravati Road, Wadi, Nagpur – 440 023, India
2National Aluminium Company Limited, Nayapalli, Bhubaneswar – 751 061, India
The present study demonstrates the potential utilization of red mud for the production
of light weight foamed bricks (LWFB) for building and construction applications. A
novel concept of self expanding raw material mix for the formation of LWFB has been
realized. The salient features of LWFB produced by heat treatment (1000-1200 0C) of
admixtures containing red mud, fly ash and foaming agents were discussed. The
environmental impact on the durability was also evaluated with respect to its exposure
to sunlight and moisture under different climatic conditions. Various physical and
chemical parameters such as compressive strength, porosity, dry and wet density,
leachability and vaporization of heavy metals, soda leaching, pH variations,
efflorescence, radioactivity etc. were evaluated. The possibility of product modification
and area of extended applications were also discussed.
Key words: Red mud; Foamed Light Weight Bricks; Building and Construction,
Toxic effect, Environmental Impact, Application
* Author for correspondence: Dr. P.A. Mohamed Najar, Scientist, Jawaharlal Nehru Aluminium
Research Development and Design Centre, Wadi, Amravati Road, Nagpur – 440 023, India.
E-mail:, web:
Fax:- +91 7104 220942, Phone:- +917104220017 Ext 235.
1. Introduction
The construction industries preferably use locally available and sustainable materials
for structural building applications. It is opined that sustainable building is an essential
aspect to achieve ecologically responsible world. Therefore the building materials
should be chosen and used without any adverse effects on the environment. All over the
world the market and production of both dense and lightweight concrete blocks is
already well established. Conversely, very recently the utilization of industrial waste in
these two types of bricks has received attention and their wide range of
commercialization is yet to be established. This is however heavily dependent on the
degree of technical suitability, economic viability and acceptability in the markets and
the society. Construction bricks can be prepared sun-dried or fired in a furnace at a
temperature ranging from 900–1200 °C [1,2]. However, fired bricks are usually
stronger than sun-dried bricks, especially if they are made of clay materials [3]. In
general bricks are categorized into various groups according to their major mineral
composition such as silica, zirconia, alumina, mullite, magnesite and dolomite bricks
[4]. The hardness of brick is attributed to the ceramic bond from the fusion phase of the
silica and alumina clay constituents [5]. Also, brick properties are affected as a result of
physical, chemical and mineralogical alteration. Besides cracks, compressive strength
and water absorption are two major physical properties of bricks that are potential
interpreters of their ability to sustain weathering effects without cracking [6]. The type
of materials and firing temperature are the two main factors affecting the final product
quality [1]. Additives are frequently used in brick production for imparting special
characteristics such as better durability, insulation and light weight. One way to
increase the insulation capacity of bricks is to generate porosity in the clay body.
Combustible pore-forming additives of organic origin are most frequently used for this
purpose [7]. Attempts have already been made for incorporating variety of industrial
wastes viz. rubber, limestone dust, wood sawdust, processed waste tea, fly ash, and
sludge in the production of bricks [8].
In this study, bauxite residue commonly known as red mud was used as the major
component for making special class of briquette specimens. In the production of
smelter grade alumina (Al2O3), by Bayer process (hydrothermal leaching of bauxite),
Red Mud is separated from sodium aluminate liquor before precipitation of alumina
hydrate (Al2O3.3H2O). Ever since the discovery of aluminium metal and Bayer process
for alumina, the disposal / utilization of bauxite residue has been a problem of intrigue
and despair. For each ton of alumina thus produced, on an average 1.10 - 1.50 ton of
red mud is generated. It is invariably accompanied by a liquor phase containing mainly
(alkaline) water with some amount of sodium salts formed during the process. Storage
or disposal of red mud is a major problem, with possible environmental hazards [9].
This generally results in the wet or dry disposal of huge volumes of mineral rich red
mud in selected areas of minimum human exposure. The chemical and mineralogical
compositions of red mud vary widely depending on the bauxite source and the process
parameters used for alumina extraction.
The red mud generation in India is approximated as 4.5 MT / annum and that is
expected to reach 13.7 MT / annum by 2012-14. Unfortunately, the recycling options
identified so far are not satisfactory in terms of bulk utilization, product generation and
economics involved with the process parameters [10-12]. High volume and low /
affordable cost utilization of red mud with minimum or no waste generation may be the
right choice of handling red mud issue. Also, it has been realized, no single processing
route can accomplish complete utilization of red mud [13,14]. In order to achieve
economic viability of processing options, industrial utilization and bulk disposal of red
mud a novel process route has been identified for the development of light weight
foamed bricks (LWFB). Recycling of red mud in this route offer potential processing
output for the bulk utilization of red mud in construction field without the generation of
byproducts and further waste generation.
2 Experimental
2.1 Apparatus and Instrumentation
Crushing of red mud blocks was carried out in ball mills for homogenization with fly
ash and foaming agents in dry mixer. Standard laboratory sieves of standard mesh 100
and 150 µ were used for preparing red mud samples for chemical analysis. Wooden
brick moulds (22cm x 11cm x 6cm) were used for making foamed bricks. Hot air oven
(100-150 0C) and rectangular heating furnace (900 -1200 0C) was also used for drying
and firing light weight bricks. Brick cutter was used for sizing and shaping for surface
finish. Various analytical instruments are also used different stages of the study for
quality evaluation of raw material and finished products. The details are described in
parenthesis wherever required.
2.2 Preparation of raw material
Red mud for the study was obtained from the alumina plants of National Aluminium
Company (NALCO), Damanjodi, Odisha. Fly ash was collected from local thermal
power plant, Koradi, Nagpur.
Table -1 Chemical composition of raw materials
% Chemical composition
Red Mud 16.35 54.20 6.15 5.41 10.40 4.82 1.62
Mn Cr Pb Cd Cu Fe Ti Ni Co
0.64 0.01 0.02 0.01 0.53 0.45 0.01 0.003 0.001
Hg As Zn Be
Nil 0.001 0.04 Nil
% Chemical composition
Fly Ash 30.58 5.17 59.62 1.96 0.38 0.36 0.81
Zn Mn Cr Pb Cd Cu Hg Be Ni Co
0.01 0.04 0.01 0.004 Nil 0.007 Nil Nil 0.006 0.003
The raw materials were subjected for chemical (Table-1) analysis for compositional
assessment. The red mud sample was crushed and powdered in ball mills and
homogenized with fly ash in a high speed dry mixer. Red mud composition in the dry
mix was maintained in the range 30-60%. The homogenized dry mixture was mixed
with two component foaming agent (0.25-1.0% with respect to red mud fly ash dry mix
composition). The main admixtures were thoroughly homogenized and dry mass was
transformed in to wet slurry with addition of calculated quantity of water.
2.3 Preparation of test sample
The wet slurry of red mud, fly ash and foaming agent components was transferred into
moulds for foam generation followed by drying at room temperature (30 - 35 0C). The
room dried mass in the moulds were carefully shifted to electric oven and heated at 100
± 10 0C for removal of water for about 2h. After cooling, the molds were removed and
dry foamed bricks were subjected for firing at 900 -1100 0C for 1-2 h. The heat treated
fire bricks (Fig 1) were labeled and stacked at room temperature.
Fig.1 Light weight foamed brick made from red mud
3. Results and Discussions
Since the infrastructural development across the country is booming and it has the
highest potential for consumption of large quantity of red mud in the form of building
materials. Accordingly, a profitable market is also expected for light weight foamed
bricks (LWFB) in constructional activities. Accordingly, an experimental model has
been designed for the development of light weight foamed bricks from red mud with
minimum processing steps. The results of these studies were summarized in Table 2 - 4
and Fig. 2-5 respectively.
3.1 Optimization of red mud and fly ash
The raw material composition was optimized (Fig.2) with respect to bulk density,
minimum rejects due to cracks and compressive strength as well as maximum input of
red mud in view of higher percentage of red mud utilization in LWFB. Accordingly
45% red mud and 0.75% foaming agent in the dry mix composition has identified
optimum for making LWFB. Stability of foam generated, plasticity and viscosity of wet
mix, mechanical strength before and after heat treatment as well as percentage weight
reduction was also taken into consideration.
Optimization of raw material composition
010 20 30 40 45 50
100 90 80 70 60 55 50
1530.75 0.75 0.5 0.5 2
% Component
% Composition
Red Mud
Fly Ash
Fig.2 Optimization of raw material composition
3.2 Optimization of temperature
The firing temperature of LWFB was optimized with respect to compressive strength,
porosity and durability. Different sets of LWFB prepared with optimized raw material
composition have fired at different temperature ranging from 700 to 1200 0C. The brick
samples were studied under scanning electron microscope (SEM) at 10000 X
magnification. The microstructure recorded at different temperature indicated that
rupturing of cenosphere and gibbsitic phases in fly ash and red mud started approximate
900 0C as shown in Fig 3. It is attributed that the bond formation is taking place at a
temperature above 900 0C and the firing temperature for LWFB was optimized in the
range 900 -1100 0C.
Fig. 3 SEM Studies indicating optimization of firing temperature for LWFB
3.3 Quality evaluation
The quality of LWFB was assessed on the basis of chemical and physical properties.
The chemical composition of LWFB prepared at optimized experimental condition is
shown in Table-2.
Table-2 Chemical composition of LWFB made of red mud
Sl.No. Test Parameters Compositing (%)
1 Al2O325.20 23.61
2 Fe2O316.96 27.90
3 Ti2O32.65 3.31
4 SiO249.24 38.74
5 Loss on ignition (LOI) 0.59 0.54
6 Na2O 1.37 2.02
7 CaO 1.08 1.08
8 Zn 0.010 0.010
9 Mn 0.071 0.070
10 Co 0.004 0.003
11 Ni 0.006 0.005
12 Cu 0.005 0.003
13 Cr 0.030 0.031
14 As 0.003 0.001
16 Pb 0.003 0.002
17 Cd 0.0005 0.0005
pH Variation with time
Distlled water
Tap water
Fig.4 Assessment of soda leaching from LWFB made of red mud
In order to study the pH effect, samples of LWFB were immersed in tap water and
distilled water for over a period of 40 days. The soda content in the water was
determined on weekly intervals by flame photometer. Slight increase in pH was
observed in distilled water during the first evaluation. Subsequent assessment have
revealed no significant increase of soda in both tap water and distilled water
respectively (Fig.4).
Similarly, the heavy metal leaching from LWFB was studied by assessing the leachate
by inductively coupled plasma emission spectroscopy (ICP). The leachate for the study
was prepared with two sets of brick samples fired at 900 0C and 1000 0C. The bricks
were immersed in tap water at 40 0C and 60 0C for seven days and the water samples
were assessed for the presence of heavy metals leached out from LWFB. Except Mn
(0.77ppm) all heavy metals viz. Cu, Hg, Cd, As, Pb, Zn, Cr, Co, Ni have reported less
than 0.001ppm in the leach solution. In addition the brick samples fired at different
temperature was subjected for chemical analysis for verifying heavy metal vaporization
during firing. The studies at 800 -1100 0C have not reported any change in composition.
3.4 Assessment of physical properties
The finished products (LWFB) of standard size construction bricks were characterized
with approximate 1.2 -1.4 kg weight, 0.93 g/cm3 dry density and 0.32 porosity value. It
has a compressive strength of 8.9 kN (1000 °C) and thermal conductivity 0.15 Wm-1K-1
(at 35 0C). Further, LWFB were characterized with stable colour, zero efflorescence,
and no deformation on exposure to sunlight, rain water and moisture. A comparative
assessment of porosity, dry density and water absorption of LWFB prepared with
change dry mix composition and firing temperature are shown in Fig. 5.
Physical properties of LWFB
LWFB prepared at different composition and temperature
% Values
Water Absorption %
Dry De ns ity Gm /cc
Fig.5 Comparison of physical properties of LWFB
3.5 Application
It is envisaged that the utilization of LWFB from red mud in urban housing and
construction activities will lead to (i) substantial reduction in the total weight of walls
and partitions in multi storied buildings; thus reducing the foundation costs and total
building cost (ii) the presence of all through tiny air filled cells (Fig. 1) provides
excellent acoustic performance of foamed bricks and they are highly suitable for
partition walls, floor screens / roofing and panel material in auditorium. (iii) The low
thermal conductivity of LWFB provides low thermal exchange between inner and outer
atmospheric conditions. Hence it reduces the load on air conditioner during summer
season and reduces energy consumption. The lightness and irregular porous structure in
the material increases resistance (Fig.6) against earthquake and causing less chance of
loss / damage to human lives.
Fig. 6 Comparison of compressive strength of clay brick and LWFB
The feasibility of developing such light weight slabs and tiles as shown in Fig. 7 was
also studied. The possibility of utilizing LWFB for construction application was also
verified on the basis of prism test. Excellent bonding between bricks and mortar have
achieved without interlocking cavities possibly due to highly porous surface (Fig.8).
The test results have reported that LWFB can be utilized for making boundary walls
and partition walls.
Fig.7 Light weight foamed slabs and tiles s made from red mud
Fig.8 Partition wall made of LWFB made of red mud
Based on the laboratory studies, the approximate cost for LWFB of standard
construction brick is calculated as Rs 1.50 per piece (using coal / flu gas for providing
firing temperature). Mini-pilot plant studies for the production of 300 bricks per cycle
are in progress for evaluating technical feasibility of the process and economical
viability for plant scale production.
The authors thank Shri.C.S.Gundewar, Director JNARDDC for his encouragement,
useful suggestions and permission for publishing the R & D work. National
Aluminium Company (NALCO) is thanked for the financial support for the project
“Management of Bauxite Residue”, raw material supply and technical input.
1. Cultrone G, Sebasti´an E, de la Torre M J, Mineralogical and physical behavior
of solid bricks with additives, Construct Build Mater 19 (2005) 39-48.
2. Jackson N, Ravindra K D, Civil Engineering and Materials, 5th edn, Mac-
Millan Education Press, New York, pp 49 (1996) 5-8.
3. Okunade E A, The effect of wood ash and sawdust admixtures on the
engineering properties of a burnt laterite-clay brick, J. Applied Sci.., 8, (2008)
4. Ahmad S, Lqbal Y, Ghani F, Phase and microstructure of brick-clay soil and
fired clay-bricks from some areas in Peshawar, Pakistan. J. Pakistan Mater
Soc., 2 (2008)33-9.
5. Adeola J O, A review of masonry block/brick types used for building in
Nigeria. Mech. Eng. Thesis, Univ of Benin. (1977)
6. Karaman S, Ersahin S, Gunal H, Firing temperature and firing time influence
on mechanical and physical properties of clay bricks. J Sci Ind. Res., 65
7. Demir I, Effect of organic residues addition on the technological properties of
clay bricks, Waste Manag,. 28, (2008) 622-7.
8. Abdul Kadir A, Mohajerani A, Roddick F, Buckeridge J, Density, strength,
thermal conductivity and leachate characteristics of light-weight fired clay
bricks incorporating cigarette butts. Int. J Civ. Environ. Eng. , 2 (2010)179-84.
9. Hind A R, Bhargawa S K, Grocott S C, The surface chemistry of Bayer process
solids: a review, Colloids Surf. A, 146 (1999) 359-74.
10. Schwarz M, Lalík V, Possibilities of Exploitation of Bauxite Residue from
Alumina Production, Recent Researches in Metallurgical Engineering - From
Extraction to Forming, Mohammad Nusheh (Ed.), ISBN: 978-953-51-0356-1.
11. Amritphale S S, Patel M, Utilization of red mud, fly ash for manufacturing
bricks with pyrophyllite. Silicates Industriels. 52, No.3-4 (1987) 31-35.
12. Amritphale S S, Anshul, A, Chandra N, Ramakrishnan N, A novel process for
making radiopaque materials using bauxite - Red mud, Journal of the European
Ceramic Society,.27 (4) (2007) 1945-1951
13. Anand, P, Modak, J M, Natarajan K A, Biobeneficiation of bauxite using
Bacillus polymyxa: calcium and iron removal, . International Journal of
Mineral Processing 48, No:1-2, November 1996, 51-60.
14. Rai S, Wsewar K L, Mukhopadhyay J, Yoo C K, Uslu H, Neutralization and
utilization of red mud for its better waste management, Arch. Environ. Sci,
... e study has proven the potential use of red mud manufacturing brick as substitute up to 25% to clay [9]. Studies have proved that lightweight foamed bricks can be made from red mud, and these bricks can be envisaged in urban development activities as partition walls in multistoried buildings which lowers the total weight of the wall, the foundation, and the construction cost [10]. e study has proven that the red mud-fly ash-based geopolymer coating to concrete blocks has increased the strength, durability, and thermal stability of blocks with the increment in morality of 6M and 12M [11]. ...
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