Vibrated concrete and mortar cubes: distribution of compressive strength

Abstract

Summary: This paper studies the variation in compressive strength of vibrated mortar cubes and vibrated concrete cubes. Within each of the four series of tests (two mortar and two concrete) the water-cement ratio was constant, but varied from series to series. The effect on compressive strength of varying the grading of the fine aggregate in concrete was observed. The mixes (including water-cement ratio) in the two mortar series were identical, but in one series (M.1) the mortar was vibrated to complete compaction by an electro-magnetic vibrator and in the other mortar series (M.2) a vibrator of the type described in BS 12(1947) was used for the specified time of 2 minutes for each cube. The coefficient of variation of concrete strength was found to be less than 4 per cent and that of mortar strength to be more than 5 per cent. It was determined that wide variations in fine aggregate grading had no effect on the dispersion of the values of the compressive strength of concrete. The two methods of compaction used for mortar cubes resulted in widely different mean compressive strengths but the coefficients of variation obtained/or the two series were similar.