| Self-compacting Concrete(SCC)has been widely used in tunnel structures due to its advantages such as self-compacting,high strength and easy construction.However,SCC will burst and flake off because of its high density and low permeability when exposed to tunnel fire.This is due to the internal pore water pressure can not be released in time,which further leads to a sharp decline in the bearing capacity of the structure.Aerogel cement paste(ACP),as a kind of fire resistant coating,can effectively limit the heat transfer between concrete structure and flame.Therefore,it has been widely concerned.To better improve the protection effect of ACP composite SCC in tunnel fire(1100 ℃,2.5 h),the effects of wet curing,curing temperature and early curing on the performance of ACP were studied.These curing regimes are based on site construction curing regime.Combined with the mass loss rate of ACP before and after simulated fire,macroscopic morphology,SEM,XRD,TG/DTG and other microscopic analysis,the influence mechanism of curing regime on fire resistance of ACP was explored.The main research contents and conclusions are as follows:(1)By changing the wet curing time of ACP(7 d wet curing,14 d wet curing,21 d wet curing,28 d wet curing),the physical properties of ACP were tested.The residual compressive strength of ACP composite SCC was analyzed.The results showed that the non-composite C40 SCC burst in tunnel fire,while the ACP composite SCC with different curing regimes did not burst.The looser the ACP microstructure,the more microcracks were generated at high temperatures,The microcracks accelerated the damage of the cement slurry and reduced the fire resistance of the ACP.14 d wet curing was the optimal curing method.(2)The curing temperature of ACP(5 ℃,20 ℃,35 ℃,50 ℃,65 ℃,80 ℃)was changed by simulating the natural environment temperature and the construction site temperature.The mechanical properties,thermal conductivity and porosity of ACP were tested.The interface temperature of ACP composite SCC was analyzed.The results showed that 50 ℃ was the best curing temperature for ACP.Higher curing temperature was conducive to hydration reaction and pozzolanic reaction,and was conducive to the generation of more stable hydration products(such as thenardite,tobermorite and C-S-H gels).When the thermal conductivity difference was very small,dense microstructure and stable material were more conducive to strengthen the fire insulation of ACP.In practical engineering applications,the thickness of ACP protective layer can be further optimized when ACP was cured at about 50 ℃.(3)The properties of ACP were tested by changing the early curing temperature(10 ℃,20 ℃,30 ℃,40 ℃,50 ℃,60 ℃)in combination with the optimal wet curing regime.The results showed that the high early curing temperature increased the coarse hole and connected hole,and reduce the thermal conductivity.However,it also accelerated the damage rate at high temperature,and then reduced the tunnel fire resistance of ACP.The best curing regime for ACP was 40 ℃ early curing+14 d wet curing,which had a relatively low cost and was more conducive to practical engineering application. |
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