MATHEMATICAL MODEL FOR PREDICTION OF FLEXURAL STRENGTH OF MOUND SOIL-CEMENT BLENDED CONCRETE

Abstract

The paper examined the optimization of flexural strength of a five-component-concrete mix. Mound Soil randomly selected from Iyeke-Ogba in Benin City was used as a case study.  The work applied Scheffe’s optimization technique for a five by two degree polynomial. This linear optimization technique assumed the proportions of the material components of concrete to be variables in, and that these proportions sum up to a whole, that is, unity. It obtained a mathematical model of the form. Where, are proportions of the concrete components namely; cement, fine aggregate, mound soil, coarse aggregates and water/cement ratio. The mound soil-cement blended proportions were mathematically optimized by using scheffe’s approach and the optimization model developed. A computer program predicting the mix proportion for the model was written. The optimal proportion by the program was used prepare beam samples measuring 150mm x 150mm x 750mm which were tested for flexural strength at 28 days and their results were compared with those of a standard 1:2:4 concrete mix. The results showed that the standard mix gave a flexural strength of 1.93N/mm² at a w/c of 0.5 while the Scheffe’s optimized mix of 1.00:1.59:0.46:3.34:0.53 gave a flexural strength of 0.31N/mm²representing 16.06% of the recommended mix. Results obtained by using the model showed reasonable agreement with that of experiment. Therefore, mound soil-cement blended concrete can be used in construction but the mound soil content should not exceed 7% by weight of the cement for optimal flexural strength performance. Some amount of flexural strength is required in horizontal structural elements such as beams. This will provide for the necessary cracking before ultimate failure during service.

http://dx.doi.org/10.4314/njt.v34i3.5