Time Variation of Mechanical Properties of Ultra-High Pumped Self-Compacting Concrete Within One Year of Age

In order to reveal the time-varying laws of the axial compressive strength, elastic modulus and splitting tensile strength of the pumped self-compacting concrete (SCC) in super high-rise buildings during the construction period, and to provide a basis for mechanical performance analysis of super high-rise buildings in construction stage, 120 specimens, including 96 cylindrical specimens and 24 cube specimens, were fabricated by pumping the SCC of a high-rise building over 400 m, their mechanical properties were tested at different ages, and the stress-strain curves of the ultra-high pumped SCC were obtained. Based on the tested results, formulas for calculating the time-varying relationship of the mechanical properties were proposed. The results show that the ultra-high pumped SCC has good compactness under vibration-free conditions. With the increase of age, the peak stress of the ultra-high pumped SCC increases, and the peak strain is significantly greater than that of ordinary concrete. The period of early 14 d is the key stage for the growth of various properties; the elastic modulus tends to stabilize after 90 d, while the axial compressive strength and split tensile strength still increase significantly after 28 d. When the age T ≤ 60 d, the axial compressive stiffness of the ultra-high pumped SCC increases with time, while the relative toughness decreases. When T > 60 d, both of them change little and tend to be stable. The improvement of strength of the pumped SCC in super high-rise buildings can accelerate the development of its early performance, and increase the axial compressive stiffness and relative toughness. The proposed calculation formulas of time-varying mechanical properties can provide a reliable basis for prediction and evaluation of mechanical performance of the pumped SCC in super high-rise buildings.