The effect of size and shape of specimen upon the unconfined compressive strength of cement-stabilized materials

Abstract

Synopsis An investigation has been carried out into the effect of the shape and size of the specimen upon the unconfined compressive strength of cement-stabilized gravelsand-clay, well graded sand and fine crushed rock. A range of cement contents was used with each material to give a range of strengths up to about 14 N/mm2 after 7 days' curing. To enable valid comparisons of strength to be made, the specimens were compacted to produce similar dry densities. Relationships were obtained between the strength of cylindrical specimens of different height to diameter ratios and between the strengths of cubes and cylindrical specimens. The average ratios of the strength of cylindrical specimens with a height:diameter ratio of 2:1 to the strength of specimens with a height: diameter ratio of 1:1 were 0·89, 0·74 and 0·65 for 150, 100 and 50 mm diameter specimens respectively. The differences in strength between specimens with height:diameter ratios of 1:1 and 2:1 is thought to be associated with the effect of the end restraint imposed on the specimens by the platens of the testing machine in producing different modes of failure with the specimens of different height. The average ratio for the strength of 150 mm cubes to the strength of 300 mm high by 150 mm diameter cylinders made from the materials studied was found to be 1·29, which agrees closely with the value of 4/3 commonly accepted for concrete test specimens.