Fly Ash Concrete For Carbonation Resistance Of Steam Curing

Aiming at the durability problems of steam-curing concrete used in the railway sleeper and bridge prefabricate structures, the paper studied the hydrate properties, pore strucrure, pore liquid alkalinity and carbonation depth of fly-ash concrete. The effect of water to binder ratio, fly-ash content on the anti-carbonation properties was studied. And the carbonatin life of steam-curing concrete was predicted.The main results was showed as followed.1 .Compared the standard curing system, the whole porosity,air pore ratio and coarse capillary porosity was larger under the steam-curing system when the content of fly-ash was below 40%, and the whloe pores, air pores and coarse capillary pores was smaller. Increasing the content of fly ash, decreasing the pore liquid alkalinity.When the content of fly ash was below 30%,the pore liquid alkalinity of steam-curing concretewas higher.However, when the content was above 30%, the value under the standard curing system was lower.2.The carbonation depth of concete increases when the content of fly ash increases.When the content of fly ash was below 40%,the carbonation depth of steam-curing concete was larger the one under standard curing system. When the content was larger 40%,the depth in different age was smaller.3.The carbonation speed of steam-curing concrete increase when the content of fly ash increases, and the coefficient was different under different ages. The carbonation speed coefficient decreases when the ages increase.4. The carbonation rate coefficient of the steam-cured concrete is closely related with the alkalinity of pore liquid, pore structure.Its carbonation rate coefficient reduces as its alkalinity of pore liquid increases; and with the porosity increasing, the carbonation rate coefficient also increases in a whole.5.The carbonation life of steam-curing concrete was same as the normal concrete. When the strength grade was above C40, the CO₂ content was below 0.03%, and the protection thickness was larger than 25mm, the steam-curing concrete with 40% fly ash can satisfy the demand of 100 years working life.