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DESIGN OF INTERLOCKING BRICKS FOR ENHANCED WALL CONSTRUCTION FLEXIBILITY, ALIGNMENT ACCURACY AND LOAD BEARING
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ABSTRACT
The worldwide housing shortage has stimulated a search for appropriate, easy, fast and
cost-effective new ways of wall construction. Among many technologies found to
have promise is mortarless technology using dry-stack interlocking bricks/blocks.
This thesis is about such mortarless walling technology and in particular: how to
improve wall-construction flexibility, the effects of brick irregularities on wall
alignment accuracy and wall behaviour (stiffness, strength) when subject to lateral
forces.
The flexibility of mortarless technology (MT) has been enhanced by the development
of new bricks (centre-half bat and tee brick): the introduction of closer bricks led to
the formation of two new bonds (patterns) namely Shokse and Lijuja bonds. It is now
possible to construct more than half-brick-thick walls, to attach more than half-brickwide
piers (buttresses) onto walls, and, using special bricks, to construct polygonal
and curved walls using interlocking bricks.
Three methods (theoretical modeling, physical experiments and computer simulation)
were used to analyze the effects of brick imperfections on wall alignment accuracy.
Theoretical analysis confirmed that brick moulders should concentrate on achieving
parallel top and bottom faces rather than achieving true square-ness.
Physical column assembly compared three brick-laying strategies namely: “random”,
“reversing” and “replace”. The columns assembled using the “reversing” and
“replace” strategies realized alignment improvement factors of 1.6 and 2.9
respectively over “random” strategy. The research also revealed that grooving, to
prevent bricks making contact near their centre lines, improved column alignment by
factor 2.13 and stiffness by factor 2.0, thus allowing construction of longer and higher
walls without strengthening measures.
In order to attain alignment accuracy in accordance with BS 5628-3:2005 in a dry-stack
mortarless wall, this research recommends using full bricks with top and bottom surface
irregularities not exceeding ±0.5mm for un-grooved bricks, and up-to ±0.9mm for
grooved bricks.
Further analysis was undertaken with respect to resource-use implications (cement, water,
soil) of employing MT. Using MT will save 50% of wall construction cost and 50%
cement consumption, which ultimately will reduce 40% of carbon emissions.
1.0 INTRODUCTION
1.1 BACKGROUND
1.1.1 HOUSING DEFICIT
Housing is one of the basic human needs and is usually ranked third after food and clothing.
In most developing countries housing is inadequate and the housing backlog has been
increasing rapidly. One key reason for housing inadequacy is the increase in population
Racodi (1997). It is estimated that the World’s population is rising weekly by more than a
million people, a rate that new construction does not match Earth from the air. [Online].
(URL http://www.earthfromtheair.com.html). 2004. (Accessed 15 December 2004) due to
the high pace of urbanisation and socio-economic factors that include the rise in prices of
land and building materials, Those classified as poor are the majority and they cannot afford
proper housing McAuslan (1985). The outcome of this can be seen by the poor quality of the
houses of this majority in both urban and rural environments (Gilbert & Gugler 1992, Basu
1988).
The provision of affordable housing for the poor needs to be facilitated through the
development of innovative strategies (Webb 1983, Hamdi 1995). The persisting problem for
urban housing authorities in Africa is the worsening condition of slums and squatter
settlements due to the high rate of population growth. Public provision of mass low-cost
housing is always far below the actual demand Maasdorp & Humphreys, (1975). The
situation is being exacerbated because the more city facilities are improved; the faster is
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rural-urban migration. This must not be considered for its negative impact only, but should be
regarded as an inevitable and irreversible consequence of continuing development Spence &
Cook, (1983).
1.1.2 POVERTY
Despite the fact that most African countries have large resources of indigenous building
materials, to date the housing situation has not improved, due to economic hardship. New
housing by its nature requires capital. World trade market data shows that between 1990 and
2000 the capital of the 50 poorest countries fell from 4% to 2% of global capital Earth from
the air. [Online]. (URL http://www.earthfromtheair.com.html). 2004. (Accessed 15
December 2004). Several studies have revealed that more than 50% of African people live
below the poverty line, and more than 80% of the population living in rural areas have poor
shelter as well as inadequate sanitation, transport and communication systems. About 70% of
the urban population now lives in slums and squatter settlements, which lack the basic
facilities for a decent life World Bank, (1995). Worse, is the continent’s dependence on
imported building materials that are too expensive for the poor majority to afford.
Example: Tanzania is one of 20 poorest countries on earth. In the year 2000, the annual
housing demand was about 800,000 units, but supply was below 20% of this figure. In that
year there were about 9.8 million urban dwellers needing about 2.4 million housing units.
The actual number of units built was only 0.6 million indicating a 75% deficit URT –
NHSDP, (2000). This poor situation is reflected in other developing countries.
APPROPRIATE HOUSING SOLUTIONS
However, researchers worldwide have made significant efforts to find sustainable and
affordable technologies to arrest the situation. The best approach so far is the development of
technologies to increase the utilization of locally available building materials.
Appropriate solution for affordable housing will vary from one location to another. Some
general rules, however, apply to construction methods and housing systems. Affordability
and availability of course are the basic requirements for the low-cost housing industry
(Harlae and Marten, 1990, Laquian, 1983, Spence & Cook, 1983). But, the cultural
backgrounds and the particular needs of the communities must also be considered. With the
increasing rate of unemployment in Africa, there is still a need for labour-intensive
production methods in some parts of the industry. To enable the community to profit from
construction projects, systems making effective use of unskilled labour and local resources
are usually the most appropriate.
Development of appropriate technologies for the production of low-cost building materials of
good quality will speed up the provision of affordable urban housing in developing countries.
One such technology is the use of stabilised-soil bricks. These have been in use in developing
(African) countries for many years and have passed various stages of improvement in the
production processes and quality of the products.
1.1.4 EARTH WALLING
Recent research has been conducted at Warwick University (Gooding 1994, Kerali 2001,
Montgomery 2002) on building materials for low-cost housing, including literature reviews
from the 18th century to the end of 20th century, on the use of earth or soil as a dominant
building material. It was found that soil can be much improved through stabilisation. The
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durability of cement soil stabilised blocks (CSSB) can further be improved by using bestpractice
curing regimes Kerali, (2001) and their strength increased by impact compaction,
which gives better material consolidation than simple pressing Montgomery, (2002).
Burroughs, (2001) discussed selection of soil for wall construction and made a contribution
to the development of stabilised soil for rammed-earth walls. A valuable survey by
Maniatidis & Walker, (2003) shows clearly the development of rammed-earth construction
worldwide. The economic analysis in these various studies suggests use of earth material for
wall construction will continue and that such material will remain a cost effective and lowenergy
alternative to more ‘modern’ walling materials in the coming centuries.
1.1.5 MORTARLESS WALL BUILDING
Mortarless brick construction, usually employing interlocking bricks, is growing in popularity
round the world, indicative of acceptability. Mortarless techniques demonstrate the following
advantages: increase of construction productivity (Grimm 1974, Whelan 1985), reduction in
construction duration and labour (Anand & Ramamurthy 2003, Ramamurthy & Nambiar
2004) and reduced construction cost. Because of its technological simplicity and local
resource dependence, mortarless-brick construction is more appropriate to many local
communities than conventional mortared-brick techniques.
Designers have developed machines of different types (manually operated, hydraulic,
electrically operated, automatic or semi-automatic) for producing different shapes and sizes
of stabilised-soil bricks/blocks for Mortarless wall: Allan block system, Auram system,
Bamba systems and Haener blocks, Hydraform systems, Putra blocks and Solbric systems
etc. A variety of interlocking brick/block shapes was analysed by Thanoon et al. (2004),
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Ramamurthy and Nambiar (2004) concluded that a key requirement of interlocking bricks, if
they are to improve construction by semiskilled labourers, is that they be self-aligning.
The Interlocking Stabilised-Soil Brick (ISSB) is a technology that pioneers the idea of drystacking
bricks during construction; hence they are called mortarless bricks. Montgomery,
(2002) assume mortarless construction is a good idea but only if it is used in conjunction with
in-wall curing of very-low-cement homogenous blocks. For this technology to be successful
the bricks require very high dimensional accuracy. The cost of construction of a wall using
ISSB is estimated to be 40% lower than that using more conventional materials (Etherington
1983, Hines 1992, Anand & Ramamurthy 2003).
1.2 RESEARCH JUSTIFICATION
Interlocking bricks may be made of fired clay or cement-stabilized soil (sand). They are
usually manufactured by a process using presses rather than slop-moulds, in order to achieve
greater uniformity. In Africa this would make them uncompetitive with conventional clampfired
bricks, were not the latter being adversely affected by growing firewood scarcity, and
the high price of the cement for the mortar.
Production and laying of ISSB are labour intensive, making use of unskilled labour. Apart
from saving cost, this will create more jobs and empower youth. Moreover building with
ISSB reduces the use of industrial products like cement and depends on local resources. It is
considered to an environmental friendly technology, because it consumes less production
energy, reduces deforestation, reduces the use of non-renewable resources and produce less
waste from construction process than the main walling alternatives (fired bricks, cement-sand
blocks) Walker, (1995).
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However concerning ISSB, little has been published about:
• Modes of deterioration,
• Failure mechanisms,
• Maintenance requirements,
• Construction procedures
• Architectural (design) flexibilities,
• The relationship between brick accuracy and wall alignment, and
• The stability and stiffness of mortarless wall (Marzahn, 1999).
These unknown parameters need to be established by experimentation.
The objectives of the work reported in this thesis were to investigate: -
• ISSB wall architectural flexibility in terms of patterns, bonds and buildable
configurations.
• Factors that influence the accuracy of mortarless walls.
• Stability and stiffness of mortarless wall during and after construction.
• Maximum height and length of ISSB walling that can be managed before requiring
strengthening,
• Economics of ISSB walls compared to conventional systems.
Forecasting the prospects for ISSB use in developing countries is difficult Croft, (1993)
because existing building standards, regulations and rules create negative attitudes towards
new technologies Beall, (2000). However the adoption of new technologies requires enough
time to prove their durability and advantages compared to existing ones, so it may take
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decades before they are widely accepted (Kua and Lee 2000, Spence & Cook 1983). The role
of the building industry should be both to develop and adopt beneficial changes Housing
Forum, (2001).
1.3 RESEARCH METHODOLOGY
The research recorded in this thesis employed three main methods, namely:
1. Literature review
2. Survey of existing structures built of ISSB (mortarless bricks) and design of a more
(architecturally) flexible form of ISSB.
3. Analysis, and experimentation;
a. Theoretical analysis of dry-stacking of interlocking bricks,
b. Physical testing of using half-scale interlocking bricks and
c. Computer simulation of dry-stacking interlocking bricks into walls and
columns.
1.4 STRUCTURE OF THE THESIS
The thesis is presented in seven chapters as follows:
Chapter 1 introduces the research topic, constructs the rationale for the study, and
develops the objectives of the research.
Chapter 2 has the literature review that surveys the existing knowledge of “Mortarless
Technology”, and presents a history of interlocking bricks. The review identifies the
knowledge gaps that determined the work developed in chapters 3 to 7.
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Chapter 3 discusses the benefits of using MT to minimise environmental impact. It
analyses the cost comparison between mortarless technology and conventional.
Chapter 4 describes the many patterns/bonds used by tradition bricklaying (compared to
the only one bond used by mortarless technology before this research). The design of new
ISSB parts enabled the invention of two new brick-bonds and the application of ISSB to a
wide range of conventional bonds. The chapter demonstrates the performance improvement
in the construction of variety of joints, thicker walls, and different wall configurations i.e.
polygon, curve etc.
Chapter 5 discusses the types of brick irregularity, their causes and remedial measures to
reduce them.
Chapter 6 describes the series of laboratory experiments performed in this research. It
addresses the variables to be measured and the measuring techniques that were employed to
obtain the required test results. It relates theoretical analyses to physical experiments and
scrutinises disagreements between them with the help of the computer model. It draws
conclusions concerning the relationship between the variability of a wall and the accuracy of
the ISSBs with which it is built.
Chapter 7 theoretically analyses the difference between solid column and dry-stacked
column subjected to lateral forces. It relates theoretical analysis to physical experiment.
Chapter 8 summarises and comments on the thesis findings. The chapter also highlights
the applications of the research findings and identifies areas for further research.
The References are presented at the end of the thesis.