Research On The Application Of High-content Mineral Admixture In Steam-cured Concrete

High-temperature steam curing is one of the main technical means for the production of precast concrete elements. The early activity of fly ash and slag is low, so their utilization rate in steam-cured concrete is very low. This thesis studied the influence of high-volume fly ash or slag on the performance of steam-cured concrete. The main results are listed as follows:(1) The length of pre-curing time(1 hour, 3 hours, 6 hours) has limited influence on the hydration degree of binder, the compressive strength and chloride permeability of concrete at late ages. If the length of pre-curing time is up to 3 hours, the concrete can obtain enough initial strength to resist the damage deriving from steam and temperature rise.(2) The promoting effect of increasing thermostatic time and improving thermostatic temperature on the hydration of composite binder is greater than that of the pure cement. When the thermostatic temperature is up to 70℃, further increasing the temperature has a negative effect on the hydration degree of cement. When the thermostatic temperature is up to 80℃, further increasing the temperature has a negative effect on the hydration degree of binder containing high-volume of fly ash or slag.(3) In order to obtain the ideal mould-stripping strength, the adding amount of fly ash should not exceed 40%, and the most appropriate temperature is 80℃. When the adding amount of slag is not more than 40%, the ideal mould-stripping strength can be obtained by increasing the steam-curing temperature to 80 ℃ or prolonging the thermostatic time at the steam-curing temperature of 60℃. When the adding amount of slag is larger than 40%, the ideal mould-stripping strength can be obtained by increasing the steam-curing temperature to 80℃ and also prolonging the thermostatic time. The resistance to chloride ion permeability of steam-cured concrete with fly ash or slag is much better than that of the pure cement concrete.(4) The phenomenon of delayed ettringite formation can not be observed in the paste with high-volume slag when the thermostatic temperature is 80℃, but a large amount of AFm can be observed in the paste with high-volume fly ash at late ages. The volume expansion ratio of the concrete with high-volume slag or fly ash under the condition of 80℃ at late ages is close to that of the pure cement concrete under the condition of 60℃ at late ages.