Effect of low temperature on early strength of cemented paste backfill from a copper mine and engineering recommendations

Low winter temperatures are a widespread concern for mines in China that use cemented paste backfill (CPB). A low environmental temperature has a significant effect on the CPB temperature, which can affect its hydration rate and early strength. Using paste material from the Jiashi Copper Mine (JCM) in winter, this paper prepared a total of 129 specimens and investigated the effect on these specimens of different amounts of water and cement, the method for adding cement, the dosage of the pumping agent, and the amount of aggregate used. The prepared specimens had a temperature range of 8-12℃ and were cured in a standard curing box with a temperature of 20℃ and humidity of 95%. After curing periods of 3, 7, and 28 d, the paper performed uniaxial compressive strength (UCS) tests on the specimens. The test results show that the UCS values of the 7 d and 28 d specimens are 1.44-fold and 2.4-fold those of the 3 d specimens, respectively. The 7 d UCS evolution accords with a 2℃ hydration progress, which leads to gradual strength development. However, the 28 d UCS evolution accords with a 20℃ hydration progress. This indicates that the temperature of the paste has a slight effect on its long-term strength. Based on the effect of low temperature on the strength of the 7 d paste, the paper proposed the addition of high-temperature water to the paste backfill system. Using a practical paste ratio at the JCM, the paper calculated a theoretical high-temperature water flow of 6-8 m³·h^-1. When the water temperature ranges between 70-100℃, the temperature of the paste can be improved from 6℃ to 15-19℃. The paper recommends the use of an industrial water heater for providing the hot water, with a conservative power output of 400 kW. The use of this water heater will yield a cost improvement of 2.9 RMB per cube of filling material.