Assess the reliability of concrete cubes and rebound hammer tests in prediction of concrete strength of vertical elements on building construction sites in Kampala, Uganda

Abstract

The study intended to identify the relationship between concrete cubes and in situ test in prediction of concrete strength of vertical elements on building construction sites in Kampala. In order to obtain this, three specific objectives were measured; determining compressive strength of concrete cubes of RC vertical elements of buildings at 7,14 and 28 days, determining the in situ compressive strength of the corresponding RC vertical elements cast in place at 7,14 and 28 days and comparison between cube strength and RC vertical elements’ strength at 7,14 and 28 days. A survey was done to identify the most suitable building construction projects in Kampala. Compressive concrete cube strength data and in situ compressive strength data was collected. Three cubes and two vertical columns were tested for curing period of 28 days in interval of 7 days.15 sites were worked on.

The results indicated that there was an increase in the comprehensive strength for cubes and vertical columns with an increase in the curing days. With the cubes, it was observed that there was variation in comprehensive strength from the sampling units. This was also a case to the vertical columns. With comparison, results indicated that the comprehensive strength of the cubes was greater than the comprehensive strength for the vertical columns at different curing age from all sites. Therefore, the structural elements were found to be structurally adequate to support the building basing on the results obtained.

Testing of concrete cubes using a universal compressive machine gave better results due to even curing while rebound hammer test gave lower values for the compressive strength due to un-even curing.ie (effects of sunshine), way of compaction as well as the vibrations. Further studies may be carried out to determine the compressive strength of concrete for both waters cured concrete cubes and air cured concrete cubes and tested by both methods.