MATHEMATICAL MODELS FOR THE PREDICTION OF THE STRENGTH CHARACTERISTICS OF CONCRETE WITH COARSE AGGREGATES OF VARIABLE SOURCES

AUTHOR: UMEONYIAGU, IKECHUKWU ETIENNE

DEPARTMENT: CIVIL ENGINEERING

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

This research developed models for the prediction of the strength characteristics of concrete made with various coarse aggregates using Scheffe’s (4, 2) lattice polynomial. The coarse aggregates were unwashed and washed local gravels from Abagana, Anambra state and granite chippings from Abakaliki, Ebonyi state. The river sand used was from Amansea, also in Anambra State. A total of one hundred and eighty concrete cubes of dimensions 150 mm X 150mm X 150mm and one hundred and eighty concrete beams of dimensions 600mm X 150mm X 150mm were made, cured and tested. The mathematical models for the prediction of the compressive strength of the concrete developed were —Ŷ = 30 x1+ 32 x2+ 19 x3+ 12 x4+ 2.8 x1 x2 – 0.8 x1 x3 – 5.6 x1 x4 – 2.8 x2 x3 – 8 x2 x4+ 12 x3 x4, Ŷ = 20.67×1+ 22.01 x2+ 13.04 x3+ 8.26 x4+ 1.72 x1 x2 – 0.46 x1 x3 – 3.78 x1 x4 – 1.7 x2 x3 – 5.5 x2 x4+ 8.6×3 x4 , Ŷ = 23.46 x1+ 25.01 x2+ 14.83 x3+ 9.41 x4+ 2.06 x1 x2 – 0.78×1 x3 – 4.38 x1 x4 – 2.32 x2 x3 – 6.44 x2 x4+ 9.28 x3x4 for the chippings, unwashed local gravel and washed local gravel respectively. The mathematical models for the prediction of the flexural strength of the concrete developed were —Ŷ = 4.28 x1+ 4.42 x2+ 3.4 x3+ 2.71 x4+ 0.2 x1 x2 +0.04 x1 x3 – 0.14 x1 x4 – 0.08 x2 x3 – 0.3 x2 x4+ 1.22 x3 x4, Ŷ = 3.19 x1+ 3.29 x2+ 2.53 x3+ 2.02 x4+ 0.12 x1 x2 +0.04 x1 x3 – 0.1 x1 x4 – 0.04 x2 x3 – 0.22 x2 x4+ 0.94 x3 x4, Ŷ = 3.4 x1+ 3.51 x2+ 2.7 x3+ 2.15 x4+ 0.14 x1 x2 – 0.1 x1 x4 – 0.1 x2 x3 – 0.25×2 x4+ 0.94 x3 x4 for the chippings, unwashed local gravel and washed local gravel respectively. The student’s t-test and the Fisher’s test were used to test the validity of these models. The strengths predicted by the models were in complete agreement with the experimentally obtained values and the null hypothesis, H0 was accepted.

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