| High-temperature steam curing, which could substantially improve the early strength and production efficiency of concrete, is one of the most important technologies for the production of precast concrete elements. Low early activity makes it extremely hard to employ fly ash and slag in steam cured concrete. The influences of high-volume fly ash and slag on the performance of steam curing concrete have been studied in this thesis in order to explore the application of mineral admixtures in steam curing concrete. The main results are listed as follows:(1) The early activity of fly ash is significantly different from which of slag. Concrete with high-volume slag (proportion of 30%,40%,50%) cured under 60℃ performed well at early strength meanwhile high-volume fly ash (proportion of 30%, 40%) caused an obviously decline, higher curing temperature which makes fly ash become much more active is more suited to concrete with high-volume fly ash. Thermostatic temperature of 80℃ could improve the early strength of concrete but it can reduce the late strength and durability at the same time. Both fly ash and slag could improve the durability of steam curing concrete.(2) Composite mineral admixture composed of fly ash and slag could increase the early strength and decrease the late strength of normal concrete. It could also decrease the strength of high strength concrete and could reduce the effect of high temperature curing on late strength of concrete. Fly ash composited with slag decreased the late strength of concrete less.(3) Higher thermostatic temperature could cause the phenomenon of delayed ettringite formation (DEF) and made the concrete perform more expansion, which could be decreased by admixing fly ash and slag, the expansion caused by DEF under the thermostatic temperature of 80℃ and 60℃ were similar to each other. Under the thermostatic temperature of 60℃, addition of fly ash increased the drying shrinkage of concrete which could be reduced by the addition of slag. Under the thermostatic temperature of 80℃, both fly ash and slag could reduce the drying shrinkage of the concrete.(4) Alkaline activator, which could even decrease the strength of concrete, has proven ineffective to cement-fly ash system and cement-slag system. Superfine slag is not applicable for normal concrete with low strength, but it could reduce the adverse effect of fly ash on the strength of concrete when admixed with it. |
