EXPERIMENTAL RESEARCH ON EARLY-AGE MECHANICAL PROPERTIES OF ULTRA-HIGH PUMPING SELF-COMPACTING CONCRETE

The early-age mechanical properties of ultra-high pumping self-compacting concrete (SCC) have an extremely important impact on the formulation of construction scheme of ultra-high buildings, and are the basic key problems of construction mechanics of ultra-high buildings. Thirty standard cylindrical specimens of 150 mm×300 mm were produced in the same batch for ultra-high pumping SCC used in a 400-meter high-rise building. The mechanical properties of the specimens at early age were tested, the failure process and failure modes of the specimens were observed, and the axial load-displacement curve, compressive strength and elastic modulus were obtained. The variation of various performance indexes with age was analyzed. The formulas for calculating the strength and elastic modulus of ultra-high pumping SCC at early age and the stress-strain constitutive equation were presented. The results showed that the ultra-high pumping SCC had good integrity. With the increase of age, the falling section of the axial load-displacement curve became more and more steep, indicating that the brittleness of concrete increased. The change trends of the axial compressive strength and elastic modulus with age were similar, when the age was not longer than 21 d, the growth rate of elastic modulus was greater than that of compressive strength, when the age was at 21 d to 56 d, the growth rate of elastic modulus was less than that of compressive strength, and the calculated value was close to the measured value according to the formula of mechanical properties at early age proposed in the paper. When the age was not longer than 14 d, the deformation capacity of the concrete attenvated faster, and when the age was longer than 14 d, the deformation capacity changed little. The curves of the variable constitutive equation agreed well with the measured ones.