Analysis on the characteristics of spatiotemporal distribution and their causes of temperature and strength in three-graded mass concrete

The use of prefabricated mass concrete blocks have gained increasing attention in construction industry. However, excessive temperature due to hydration can easily cause cracks, and the development of strength influences the lift and transportation time, thus affecting the efficiency of the precast yard. In this paper, the temperature field of three-graded mass concrete was simulated using Midas Civil, and compared to the measured results. In addition, the strength of concrete at different ages and locations was tested with different methods, and the influence of temperature inside the mass concrete on strength was explored. The results show that the finite element simulation basically agrees with the experimental temperature and can provide scientific guidance for the construction of three-graded mass concrete. The compressive strength of the specimens under the same conditions is consistent with that of the surface core samples of solid concrete blocks, and the rebound strength at different ages is lower than the compressive strength of the surface core samples. The temperature inside mass concrete has both positive and negative effects on the formation of concrete microstructure, high temperature can promote cement hydration and pozzolanic effect of fly ash to form more compact C-S-H gel. But under prolonged high temperature conditions, it can also cause morphology of CH to be coarse and loose, forming scattered needle shaped AFt. At different ages, the compressive strength of the core samples inside the concrete block is greater than that of the surface core samples. As the age increases, the concrete strength at the core location with the highest temperature may not necessarily be the highest. As the age increases, for example, at 7 days, the concrete strength at the core location with the highest temperature is 6.46 % higher than that at the surface, while the concrete strength is 15.6 % lower than that at locations with relatively lower temperatures.