A STUDY OF CONCRETE STRENGTH FROM WORKS TEST

Abstract

The. statistical analysis of concrete strength is of much importance to measure the variability and to jt;dge the quality of concrete. For a study of concrete strength from works test the data for the field concrete strength has been collected from Uttarkashi Power House, Maneri Bhali Dam and Tehri Dam Project sites for different grades of concrete. The concrete strength data of four thousand two hundred ninteen samples were collectea for five grades of concrete with seven and twenty eight days of curing. The collected data were subjected to statistical analysis including'outlier' test. The third and fourth statistical moments have also been computed along with mean and standard deviation. A comparison of assumed standard devi-ations as suggested by IS:456-1978 with observed average standard deviations has been presented. The histogram, frequency polygon were prepared and normal and lognormal distributions were tried. Chi-square and Kolmogorov Smirnov goodness of fit tests were applied. The cumulative density functions and K-S curves have also been plotted on the probability paper which predicts a fair and quick judg€:ment for suitability of 0 iv model. Both Chi-square and K-S tests show that log normal distribution holds good in more cases than normal_distri-bution in this study. Three different criterion based on ACI (1976 & 1977), IS: 456-1978 and Draft TRH-5--1977 have been used for accep-tance criteria and quality control of concrete. Higher coefficient of variation values have been observed indicating poor control of quality in cases of low grades of concrete in this study. The computed statistical parameters, three points moving average of mean and three point moving average of,.,range have been presented. Quality contol tables and charts as per draft TRH-5-1977 have also been included. Computer programs for computation of statistical parameters, outlier test and for quality contol and acce-ptance criteria as per ACT, IS-456 and Draft TRH-5 have been developed as a part of the present study.