Spring 2005

  Sustainable Development of Concrete Technology in Bangladesh Part 1

  Abdullah-Al-Mamunur Rashid, Md. Mamun Rashid, Md. Abdullah Al Mamun

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:  

  1. Strength of Concrete Made with Available Aggregates in Bangladesh

Brick 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.

The 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. 

To 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.

  1. Causes of Deterioration of Concrete Structures in Service in Bangladesh

Deterioration 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.

  1. Factors Identified at Construction Sites Associated with Early Deterioration of Concrete Structures in Bangladesh

The 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 very quickly.