Parameters For Good Site Concrete Production Management Practice In Nigeria

ABSTRACT

The versatility in-use of concrete for buildings and other infrastructures of necessity made concrete an important element of construction. Yet failure of concrete occurs more frequently at construction stage even when it seemed that mix ratio and design load calculations are adequate. This therefore suggests a missing gap in specification and the production of good site concrete. Literature survey confirms poor quality of concrete and use of sub-standard materials of concrete in the production of concrete as among the factors contributing to structural concrete failure in building. This research investigated presence and effect of deleterious substances in materials of concrete on the quality of the concrete structure. To achieve this, observations of concrete practice among project sites were undertaken and specimens of materials for concrete works from sampled ‘on-going’ project sites were obtained and investigated in the laboratory for the presence of deleterious substances, aggregate particle size distribution, aggregates specific gravity and compressive strength. The study further sampled and tested specimens of Ordinary Portland Cement for soundness and quality and fitness test was also conducted on sampled specimens of Water for the Works. Results obtained revealed excessive content of chloride, co2, nitrates, sulphates known to be destructive to concrete, in large quantities in some of the materials tested. The findings further revealed that their presence reduced drastically the compressive strength of the concrete elements produced with them. Data from results obtained were further tested using SPSS 17.0 statistical tools, ‘ANOVA’, ‘Paired T-Test’, ‘Chi-Square’ and ‘Quality Control Charts’ to test and validate the research hypothesis. The graphical results obtained from the QCC test indicated a non-random pattern which contradicted aspects of the quality control chart rules. The means, frequencies and standard deviations obtained from the ANOVA, Chi-square and Paired T-test statistical tools tested were at variance to one another in all the cases tested, thus corroborating the stud postulation. The study developed concrete production model as well as concrete check-list to guide site operators and managers in the regular production and management of site concrete. Recommendations include that concrete designers must urgently incorporate in the contract documents specifications for the compulsory test of proposed concrete materials by contractors before and during site concrete productions as an additional requirement to the traditional specification of mix ratios and compressive strength tests.