Concrete quality issues in multistory building construction in Ghana: Cases from Kumasi metropolis

Abstract

This study investigated concrete quality issues at eleven multistory building construction sites in Kumasi metropolis amid several cases of multistory building collapses in Ghana. The objective was to understand key aspects of concrete quality problems at multistory building construction sites in Ghana to help recommend strategies for improving building safety standards. Apart from observing construction practices at the eleven construction sites, fresh concrete and constituent materials were sampled from four of the sites. The materials were used to produce concrete cube specimens, generally replicating the mixing ratios utilized at the sites. The site- and laboratory-produced concrete was tested for 28-day compressive strength. The site observations indicated that aggregate sourcing, stockpiling and batching practices promoted variability in concrete quality. Concrete production at the sites followed the recipe method (nominal mixing ratios), employing either low-capacity concrete mixers or hand-mixing. Consolidation, curing and quality control testing of concrete were not regular practices, and segregation and honeycombs were common. The sites determined adequacy of mixing water by visual evaluation of concrete workability. Had water content been properly determined and measured, the compressive strength of the site-produced concrete, which ranged from 10 MPa to 18 MPa, could have been 26–100% higher. The compressive strengths of the site-produced concrete were 26–60% less than the minimum 28-day characteristic compressive cube strength of 25 MPa required for structural use in buildings in Ghana. If an appropriate water content had been used at the sites, the compressive strengths could have still been less than the specified 25 MPa by 9%, on average. These findings suggested that low concrete quality was a real issue and could pose significant building failure risk or performance inadequacy. While the Ghana Building Code contains several specifications that potentially promote high building construction quality, their enforcement was non-existent or weak. A collaborative system of construction quality assurance and training encompassing local government agencies, professional associations and laboratories of higher educational and research institutions is recommended to help improve access to material testing resources and high-quality technical expertise, as well as to disincentivize willful violation of construction regulations.

Keywords

• Multistory building collapse
• Structural failures
• Concrete defects
• Compressive strength
• Concrete mixture design
• Concrete quality