| An investigation was conducted of the physical properties of concrete at early ages. Four different concrete mixes with 28 day strength varying from about 4,000 to 10,000 pounds per square inch were tested. Tests were performed on 6 by 12-inch concrete cylinders at ages of 6 hours and 12 hours, and at 1, 2, 3, 7, and 28 days. Physical properties measured at each age included the compressive strength, the static elastic modulus, the splitting tensile strength, and Poisson's ratio. Investigation was also conducted on the effects of steam curing on these physical properties. The applicability of some physical property prediction equations to concrete at early ages as well as to high strength concrete was looked into.; The compressive strength, the tensile strength, and the elastic modulus are all related, and an increase in one is, in general, similarly reflected in increases in the others. The period within the first 12 hours after casting was observed to be the period of fastest development of physical properties. The elastic modulus developed much faster than either the tensile or the compressive strengths which developed at approximately the same rate. Poisson's ratio did not change substantially with both richness of mix and age of concrete.; The commonly accepted relationship that the tensile strength and the elastic modulus of concrete are proportional to the 0.5 power of the cylinder compressive strength with time was found to be accurate for the elastic modulus but inaccurate for the tensile strength. In fact, the tensile strength was found to be proportional to the 0.79 power of cylinder strength with respect to age. An alternate relation between the tensile and the compressive strengths was proposed.; Plowman's relation for compressive strength prediction has been found to be inaccurate at low maturities. An alternate relation was proposed to take care of these deficiencies. Similarly, a more representative relation between the seven and twenty-eight day strengths was proposed as an alternate to Hool's relation of 1935.; Steam curing increased physical property development at early ages at the expense of strength development at later ages. |
