Volume 2, Issue 2 (March 1974)
The Effect of Cement Properties and the Thermal Compatibility of Aggregates on the Strength of Accelerated Cured Concrete
Most research work on the effect of the thermal expansion of the constituents of concrete has concentrated chiefly on hardened concrete. Its resistance to heating and cooling and to freezing and thawing has been used for purposes of assessment. The works of different investigators have led to considerable contradiction and no definite conclusion can be drawn on the effect of differences between the coefficients of thermal expansion of the constituents of concrete. Findings show effects on the durability under repeated cycles of freezing and thawing and the compressive strength of concrete subjected to temperature change. There is some evidence that the relative expansions of the constituents of fresh concrete cause a reduction of its ultimate strength under conditions of accelerated curing.
In the present research, when electric curing was adopted, the complete elimination of any temperature gradients throughout the test specimens was effected by precisely controlled conditions. This made it easier to detect small differences as the conditions were changed.
The factors investigated were the ratio of the strengths obtained by (1) one-day accelerated curing and 28-day normal curing and (2) one-day accelerated curing plus 27-day normal curing and 28-day normal curing.
It was found that coarse aggregates having a low coefficient of thermal expansion caused a significant drop in the one-day accelerated cured compressive strength. The coefficient of thermal expansion of the coarse aggregate did not have much effect on the 28-day accelerated cured strength. It was thought that this was due to autogenous healing during the 27 days of normal curing, rectifying any cracking caused through stresses arising from thermal incompatibilities during the one day of accelerated curing. Residual expansion after heating and cooling of certain aggregates was liable to cause decreases in strength. Further evidence is given of the importance of the C3A content of cement in determining the ultimate strength obtained when the concrete is subjected initially to accelerated curing.