Quality control chart for crushed granite concrete

Ewa Desmond, Okafor Fidelis, Ewa Desmond, Okafor Fidelis
A chart for assessing in-situ grade (strength) of concrete, has been developed in this study. Four grades of concrete after the Nigerian General Specification for Roads and bridges (NGSRB)-C20, C25, C30 and C35, is studied at different water-cement ratios for medium and high slump range. The concrete mixes are made from crushed granite rock as coarse aggregate with river sand as fine aggregate. Compression test on specimens are conducted at curing age of 1, 3, 7, 14, 21, 28 and 56 days. Results
more » ... nd 56 days. Results on concrete workability from slump values, and water-cement ratios revealed that specimens with lower water-cement ratio were less workable but had higher strength, compared to mixes with higher water cement ratio. A simple algorithm using nonlinear regression analysis performed on each experimental data set produced Strength-Age (S-A) curves which were used to establish a quality control chart. The accuracy of these curves were evaluated by computing average absolute error (AAS), the error of estimate (EoE) and the average absolute error of estimate (Abs EoE) for each concrete mix. These were done based on the actual average experimental strengths to measure how close the predicted values are to the experimental data set. The absolute average error of estimate (Abs. EoE) recorded was less than ±10% tolerance zone for concrete works.