Browsing by Author "Anthony, Dratre"

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    Variability of concrete production in Kampala and Dar es Salaam
    (University of Dar es Salaam, 2008) Anthony, Dratre
    Quality control on structural concrete was studied in the light of samples taken from concretes prepared by various contractors based at different sites in Tanzania, the results suggested a conclusion that most contractors are unable to produce concrete of specified grade, and the test results could not stand a compliance strength test. Therefore, the engineers in Dar es Salaam-Tanzania use some approximate values of standard deviations table provided by BS 8110 (same as in CP110) in their mix design and there have been some cases of structural concrete failures in Tanzania and possibly in Uganda implying that, the assumptions of variability margin for concrete produced in East Africa might be too low. The objectives of the study were to make a comparison between the approximate standard deviations in BS 8110 (same as in CP 110) for quality control of concrete at sites with the variability of ongoing concrete constructions in Dar es Salaam and Kampala, compare the quality of concrete production in Dar es Salaam and Kampala, establish variability margin of concrete produced in Dar es Salaam and Kampala and recommend measures to improve quality of the concrete produced. Sites were ascertained and over 200 concrete cubes were picked from 36 sites in Kampala and Dar es Salaam. The Cubes were then cured in water for 28 days and their compressive strengths then tested. It was found out that for medium sites with poor uniformity of production the variability margin varies significantly from that which is currently being used for mix design. Sites in Kampala have a higher variability margin than sites in Dares Salaam. However, the strength of concrete produced in Kampala is better than the strength of concrete produced in Dar es Salaam for both medium and small sites. For example, for small sites with poor uniformity the average strengths are 12N/mm2 and 16Nimm2 for Dar es Salaam and Kampala respectively for grade 20. 97% of the sites did not meet compliance test requirements for compressive strength and small site compressive strengths were worse than for medium sites. It was concluded and recommended that Engineers involved in mix design, for sites predicted to have poor and good uniformity of productions in Kampala and Dar es Salaam should now use the actual standard deviations applicable in the region to avoid further collapse of structures.