The Department of Civil Engineering of The University of Asia Pacific (UAP) has taken an initiative for the sustainable development of concrete technology in Bangladesh. The department has planned to complete this study in four parts, such as Part 1, Part 2, Part 3 and Part 4 by a two-year period. Part 1 was carried out in Spring 2005, which covered the following investigations:
aggregates (brick chips/khoa) are commonly used in construction in Bangladesh.
Stone chips, shingles, and jhama brick chips are also used for some
constructions works. To compare the mechanical properties of concrete made with
these aggregates, an investigation was carried out. It was found that for a high
W/C (such as 0.5 or 0.55), concrete made with brick chips gives higher strength
compared to the same made with stone chips.
interfacial transition zone (ITZ) around the aggregates has a significant effect
on the compressive strength as well as tensile strength of concrete. When load
is applied to concrete, it is transferred to the aggregate
through the matrix and ITZ. Generally, ITZ is a weaker region around the
aggregates, and therefore cracks nucleate at ITZ after application of load and
propagate to the matrix with the addition of load. For brick aggregates, a
stronger ITZ is formed around the aggregates and therefore higher load is
necessary for the nucleation of cracks at ITZ.
get the benefit of the high strength aggregate (stone chips), it is necessary to
reduce the W/C (0.45 or lower) in construction. Unfortunately, in Bangladesh
stone chips is commonly used with a very high W/C (more than 0.55). Such a high
W/C, the brick aggregates give higher strength compared to the stone aggregates
due to its strong ITZ.
of concrete structures is commonly found in Bangladesh after 10 to 15 years of
service life or even earlier. To understand the causes of deterioration of
concrete structures in Bangladesh, a study was carried out. Concrete structures
in several districts were investigated and the causes of deterioration were
identified. The common cause of deterioration is the carbonation-induced
corrosion of steel bars in concrete. Poor workmanship, concrete mixing with a
high W/C, concrete mixing with dust in aggregate, high humidity and temperature,
etc. accelerate the process of carbonation of concrete.
factors at construction sites that accelerate early deterioration of concrete
structures in Bangladesh were investigated. Construction sites at different
districts were visited for this purpose. It was found that concrete with a high
W/C ratio is generally made at the constriction sites. It makes concrete highly
porous and therefore increase the rate of diffusion or ingress of harmful ions
into concrete. For this reason, carbonation rate of concrete is increased and
the carbonation front reaches the steel bars within couple of years after
construction. When the carbonation front reaches the steel bars, the corrosion
over the steel bars is commenced and due to a high corrosion rate (due to high
humidity and temperature in Bangladesh) spelling of cover concrete is occurred