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An Evaluation of The Effects of Local Mix Design on the Compressive Strength of Concrete
Abstract
This is a report on an evaluation of the effect of local mix design of concrete on its compressive strength. In order to accomplish this research work, field survey was first undertaken with a well-structured questionnaire. This questionnaire was administered to the respondents who are directly involved in concrete production. Oral interview was also carried out in order to confirm the information given by the respondents concerning batching, mix ratio, etc. A study of contract document was undertaken with emphasis on specification of contract, bill of quantity and structural design in order to study how mix design is carried out in construction industry. Based on the information obtained from the respondents on how concrete is designed and specified in contract document and how such information is used in the production of concrete on construction sites, an experimental programme was set up in order to assess the extent of deviation from the normal. In the experiment, six different mixes were used. A total number of one hundred and twenty (120) cubes were cast; twenty (20) cubes were cast for each of the design mix specified. The samples were cured and crushed after 1,3,7,14,21 and 28 days of curing so as to determine the compressive strength. The test result shows that, the compressive strength for both mass and reinforced concrete produced in the construction firm are 3.13N/mm2 and 6.00N/mm2 respectively at 28 days, which are lower than that produced using the standard mixes and that produced using the target mixes. It is concluded that there is a very wider deviation from the normal in the concrete produced on site and it affects the strength of concrete and therefore, durable and qualitative concrete cannot be achieved through such means (their mix design). It is recommended that professionals should be involved in the production and supervision of concrete works so as to take care of quality control and guard against irregularities.
