Statistical evaluation of the effects of slump variations on the compressive strength of concrete specimens in different ages

The present paper reports a recent and extensive study on the effects of variations of slump values on the compressive strength of concrete samples from a statistical point of view. To this end, various properties of a bin of totally 2341 concrete samples including 218 factory-made and steam-cured samples, 340 factory-made and wet-cured samples and 1783 in-place and wet-cured samples in 1, 7, 11, 28 and 42 ages have been studied. Cements include Type I, Type II and Pozzolanic type specific to the west region of Iran (Kurdistan Province) as defined in the National Building Code of Iran (Part 9). The variations of different properties including the mean, standard deviations, coefficient of variations of compressive strength, etc. are calculated and compared for each group of samples. Results show that variations of slump values affect the mean and coefficient of variation of compressive strengths in different ages remarkably. The effects are more pronounced for samples with high cement amounts per cubic meters of concrete mix, samples made of non-pozzolanic cements, samples at higher ages and wet-cured samples compared to other samples in the bin. Coefficients of variations of mean strength of samples with 400 kg cement per cubic meters of concrete mix as well as factory-made samples are the least among all other cases. The study also reveals various properties of pozzolanic cements specific to the aforementioned region of Iran and their effects on the strength properties of concrete samples made with this type of cement.