Earth was one of earliest materials used for construction of human shelters. In its raw
state, it does not meet the basic physical properties required of a material for use in
construction, i. e. compressive strength and durability (water resistance). The raw
material can be stabilised to improve these properties through chemical, physical and
mechanical methods. Chemical and physical methods involve mixing and compacting
the earth with various materials to increase its compressive strength and reduce its
propensity to shrink and swell. Mechanical methods of stabilisation involve only
compaction of the raw material to produce blocks.
Stabilised blocks have adequate compressive strength and durability for use in lowincome
housing. They are also easy to handle, can be moulded to a variety of shapes
and are suitable for use as structural blocks. The latest developments in the design of
moulding machines means that stabilised blocks can be produced on-site at
approximately half the cost of the next cheapest construction material (hollow concrete
block).
The most important consideration in the stabilisation process is the choice of material
for mixing. The choice is based on three criteria: (i) composition of the earth, (ii) local
availability of the stabilising material and (iii) cost of the stabilising material. For
example, in terms of composition, earth with a high clay content, such as the samples
used in this study from Sindh Province, Pakistan, was found unsuitable for construction
purposes. This is because the clay minerals cause excessive shrinkage and expansion of
the material. However, work conducted in this study found that the effects of clay can
be mitigated by correcting particle size distribution and stabilisation.
Specimens of stabilised material were produced to measure the affects of mixing
various additives, including cement, lime, linseed oil, and calcium chloride, with earth.
The key findings from research carried out on these specimens are:
(a) Cement can not be used without correction of particle size distribution.
(b) Previous research work has found lime to be the most effective stabiliser in terms of improving compressive strength. However, it was found that, in the case of the high
clay content earth used in this study, cement provided better results.
(c) In earth stabilised through correction of particle size distribution, linseed oil provided the most improvement to water resistance.
(d) Calcium Chloride is not suitable for use as a stabiliser with earth containing a high proportion of clay minerals. This is because it reacts with the clay minerals to produce water.
-(e) A comparative study of the cost and engineering benefits of various stabilised specimens showed that cement provides the greatest improvement to durability, but at the highest cost. Lime was found to be the best stabilising material for high clay
content earth in terms of overall cost and engineering benefit. It provides adequate improvement to durability at low cost. Linseed oil was the cheapest stabilising material but, although greatly improving water resistance, it provided little
improvement to compressive strength.