From the literature review, seven topics/issues were identified as deserving further research
and are very briefly analysed below. However only the last two of these topics are taken
forward for fuller analysis in the ensuing chapters: the others require the attention of other
researchers.
1. The relationship between the shape of IBs and the proportion of stabilizer required for the production mix.
There is a direct relationship between brick configuration and the quantity of
stabilizer/cement needed to strengthen the soil. The simpler the shape of the interlocking
strength requirements. More complicated shapes, with thin features (protrusions or tongues),
require stronger materials. Therefore there is a need to develop or choose the most favourable
shape of interlocking bricks to give best results, by using the minimum stabiliser and simple
moulding machine to attaining the required wall stability and strength.
2. Optimising the size of brick grooves and chamfers acting as key to plaster mortar.
The grooves made in bricks, for example of the Thai type (Figure 2.2) appear on the wall
face. Also the chamfers on the free edges of the brick form grooves where bricks meet. These
grooves differ in magnitude, and because of their volume may increase the render mortar
required, or they may reduce it because of the better “key” which they provide (allowing
thinner mortar). For best plaster and wall strength, the minimum size of groove consistent
with good keying should be identified. If un-plastered, big grooves are better as they save
material in brick. If plastered, small grooves are better because plaster is more expensive than
brick.
3. Constant-volume versus constant-pressure production of IBs
Blocks made in press moulding machines, i.e. where a defined pressure is applied, will vary
in size for several reasons. There are:
(i) Incorrect amounts of soil
(ii)Inconsistency of soil
(iii)Different moisture contents of soil
method is the constant-volume, which can easily control brick dimensions, which is more
important than achieving constant density in IBs. The first test is to check the density of fresh
brick from the press. If it resists the handling pressure to move brick from machine, it is
believed that both the volume of material and the moulding pressure are satisfactory. The
second test proposed by Montgomery (2002), is the “Indentation testing for green brick”. It’s
application therefore requires further experiment. This test defines the weight of a ‘rod
punch’, the height it is to be dropped from and the maximum allowable indentation it
produces. The indentation test may be easily tracked throughout curing duration.
4. Choice of direction of compacting/pressing bricks and dimensional error consequences on bricklaying
When moulding bricks, the compacted/compressed side in normal cases is the top or bottom.
The conventional method of pressing bricks with a piston and a moulding rectangular will
closely control two of the three-dimensions of the brick and less closely the third dimension.
The poorly controlled dimension is that in the direction of the piston stroke (Figure 2.21), for
example the brick height is impinges on the top of the brick. Moreover which the mould
walls will be parallel, the piston may not be exactly parallel with the base: thus the pressed
face may be at a slight angle to the opposite face. Depending on the type of locking features
the compaction force can be applied perpendicular to the end, top or front-back faces of the
brick.
(i) Compaction force is applied perpendicular to brick end faces (as for the Solbric
and Hydraform blocks)
For any given compaction pressure this will minimise the force that has to be applied since
strong. As shown Figure 2.21 the pressures inside the brick during moulding are likely to be
more variable, as which the piston-end (F2) of the brick experiences full pressure (P).
Figure 2.21 Press machine operations schema
Ppiston = F2/Aend-face
The opposite end of the brick experience a lower pressure
Pmould = (F1-τ)/Aend-face
Where,
τ
is the shear-force between the soil and the sides of the mould. For a length to width ratio of 2:1, Pmould may be as little as Ppiston/2 (Gooding 1993). Variability in pressure along abrick implies variability of density on ejection from the mould. F1 = F2, but while all of F2 is
transmitted to soil, only some of F1 is.
If the brick is controlled in its height and width, so a wall built using these bricks will have
(ii) Forces applied perpendicular to the brick’s top/bottom faces (as in Thai, Bamba,
Auram and Tanzanian types).
This mode of pressing is essential if the top and/or bottom face are of complex shape. It will
control brick width and length; so that, both internal and external wall surfaces will be flat
because of uniform brick width. From the accuracy of brick length it is easy to maintain
equal and constant overlaps for alternating courses, and therefore simplifies the process of
estimating the brick quantity required in the construction. It also facilitates the
standardisation of house measurements to multiples of brick length or width. Although for
constant-volume pressing all dimensions are fixed, only certain surfaces are ‘wiped’ during
moulding and ejection, which does not affect dimensions. However variation in brick
dimensions made in a fixed-volume press might be caused by:
• Air trapped at piston or at mould-end
• Expansion on release of pressure (in the direction of retreating piston)
• Distortion during de-moulding
• Rocking of the piston, so the pressed face is not perpendicular to other faces.
(iii) Force applied perpendicular to brick front/back faces
It will control the height and length of the brick, which will allow the wall to have one
uneven (internal) surface. To make the surface straight and even will lead to a small increase
in thickness of plaster.
Table 2.4 summarises the effects of brick pressing to each of the three dimensional directions,
the strength and weaknesses are given for each compaction scenario and the errors expected
Table 2.4 Advantages and disadvantages of compaction scenarios S/No Compaction Stroke Direction Loading
Direction Advantages Disadvantages Remarks
(i) Along the brick length i.e. force applied to end faces Perpendicular to compaction
a). Easy to lay (level and plumb) bricks of controlled thickness and width. b). Straight and flat wall surfaces resulting in min. thickness of plaster. c). Low force for a given pressure as end area is small.
a). Unequal brick overlaps in alternating courses. Give unpleasant appearance.
b). In a given wall length may lead to brick cutting at site, which will increase - construction time, labour cost, also material waste.
c). Likely to have a high variation in density 4(i). d). Only compatible with sliding interlock.
Brick load bearing strength not known if compaction and loading are on different direction and surfaces.
(ii) Parallel with brick height i.e. onto top or bottom face
Normal to the surface of compaction
a). Min. thickness of plaster. b). Automatic laying equal and constant brick overlap (half brick).
c). Simplifies house measurement,
(standardisation to multiples of brick length or width). d). Easy and accurate estimate of brick quantity.
Levelling of brick courses may delay the
construction speed with dimensional differences in brick thickness.
a). A small amount of mortar will be needed to compensate or level the wall courses. b). Scraping to reduce excess brick thickness delays construction, and hence increases labour cost. (iii) Parallel with
brick width i.e. pressed front- to-back
Perpendicular to compaction direction
a). Easy to lay bricks. b). Equal and constant overlaps automatically formed.
c). Simplifies standardisation.
d). It is easy and accurate to estimate number of bricks.
Require thicker plaster on uneven wall surface to make it straight and flat. Not compatible with any interlock. Unknown strength of brick as direction and surface of compaction during production different to those of loading.
5. The effect of the brick locking mechanism on wall stability.
Wall alignment (stability) in mortarless construction depends entirely on the locking
mechanism, whereas in a conventional wall stability depends on mortar joints. Control is
needed over both the height and the length of a wall. To keep the dry bonded wall straight
Piers are inbuilt columns, protruding from the wall surface by a half brick or more. They are
built at intervals depending on the distance from one support to the next and on the height of
the wall. By building the piers, ribbed wall panel are formed. With piers less or equal to 3m
apart, the wall may be built up to three metres high without need for horizontal strengthening.
Increasing the distance between centres of piers up to 4.5m will require the wall to be
strengthened horizontally (Weinhuber, 1995) by beams at both cill level and lintel or below
the roof at ring beam level. Strengthening methods need to be assessed for economic
comparison for their comparative cost.
6. Brick tolerances Dimensions
The dimensions of the brick are the measurement of length (l), width (b) and height (T) as
shown in Figure 2.20.
In a mortarless technology, the bricks are to be laid one over the other with their top and
bottom surfaces in direct contact, so the dimensions of each brick needs to be to a tolerance
of ±1 millimetres. This will make the wall formed by these bricks to be flat (depending on the
constancy of the width of the bricks) on its surfaces, and the overlaps (depending on the
length) of the bricks will be equal or of a certain interval required. The horizontal and straight
Surfaces
A brick (Figure 2.20) has three pairs of parallel outside faces (two ends, front and back, top
and bottom). The flatness of the surfaces of these faces is paramount in mortarless brick
technology because of the absence of mortar.
In particular, the top and bottom surfaces of the bricks need to be flat, parallel and without
any deformations, which in practice is very difficulty to achieve. That’s why, in conventional
masonry, mortar is used to compensate and take care of gaps caused by brick inaccuracy. In
some cases the material needs to be flexible, so that when loaded will automatically adjust to
fit in whatever the tolerance will be. Usually we put conditions of tolerance in accordance
with allowable standard deviations that for interlocking brick have yet to be established. The
limits of allowable brick inaccuracy should be known for production quality control,
standardization, and wall construction accuracy performance.
Accuracy of alignment
Mortarless technology will not work if the bricks, to be assembled do not fit and lock to each
other. This locking mechanism, allows the units be arranged (bonded) one over the other to
form stable wall in a designed height and width, to a certain accuracy of verticality and
horizontality. The locking features (knobs and depressions) should provide enough tolerance
(±1 mm along the brick) to allow flexibility and ±¼ mm transversally for a minimal
allowance between male and female in arranging the bricks. This need to be done so, because
the material is brittle (stabilised soil can be easily broken if forced to fit).
1991. Nash 1983). All interlocking bricks support stretcher bond only (Figures 2.1, 2.2, 2.3, 2.5, 2.8, 2.11 and 2.12), and so have limited construction flexibility compared to
conventional/mortared bricks. Therefore we need to investigate alternatives and possibilities
of increasing mortarless-wall construction flexibility.