Study On Preparation Technology And Durability Of Reactive Powder Concrete

Reactive Powder Concrete（RPC）is a new type of super-high strength concrete with high strength and high performance,which was successfully developed by Bouygues Company in France at the end of the twentieth century.It has super-high strength,low brittleness,excellent durability and broad application prospects.Because the current RPC preparation process is not uniform,the durability system is imperfect.This paper follows the basic principles of RPC preparation,and based on the specification"Reactive Powder Concrete"GB/T 3187-2015,the preparation process of RPC is studied experimentally.On this basis,the durability properties such as carbonation resistance,chloride ion diffusion coefficient and corrosion resistance were tested and studied,so as to clarify the durability degradation law of RPC and improve its durability research system.（1）Study on preparation technology of RPC concrete:Through experiments,the effects of defoamer,vibration mode and template type on reducing the porosity of RPC were studied,and the effects of the existence of pore and the difference of curing conditions on the compressive strength of RPC were studied.The experimental results show that defoamer can effectively reduce the area of pore in RPC by about 50%;wood mould casting and layered vibration can further reduce the porosity;the existence of pore has little effect on the strength of RPC;high temperature curing can improve the compressive strength of RPC by about 37%.For RPC concrete,standard curing conditions can not replace high temperature hot water curing.Finally,the optimum mix ratio,general pouring method,admixture selection,template selection and maintenance method are summarized.（2）Study on carbonation resistance and chloride ion erosion resistance of RPC:Standard carbonization test and chloride ion penetration resistance test were carried out on RPC.The results showed that after 28 days carbonization test,RPC was rapidly determined by phenolphthalein indicator in the carbonized area of RPC,and the final carbonization depth was 0 mm.The 28d carbonation depth of C50 concrete is about 10.6mm.The unsteady chloride ion migration coefficient of RPC was0.87?10^-13m²/s¹.1?10^-13m²/s.The chloride diffusion coefficient of C50 concrete is7?10^-13m²/s⁹?10^-13m²/s.In conclusion,the carbonization resistance and chloride ion penetration resistance of RPC are very superior.（3）Experimental study on corrosion resistance of RPC concrete:Corrosion is one of the important reasons for durability degradation of hydraulic concrete structures.At present,there are few reports on the corrosion of RPC under flow surface contact.In order to study the corrosion resistance of RPC,a simulated river corrosion test device was designed in this paper.Under the conditions of NH₄Cl solution environment and common tap water environment,the corrosion resistance of RPC was tested for 90 days,and the change rule of material properties before and after the corrosion of RPC was studied.SEM scanning electron microscopy and X diffraction（XRD）tests were performed on the RPC specimens at each stage of dissolution to observe their microstructure changes and qualitatively analyze their composition changes,The test results show that:the NH₄Cl solution of 6M has a significant accelerating corrosion effect,and its calcium corrosion factor is 0.3696,which is about 52times of the corrosion effect of ordinary tap water environment.The compressive strength of RPC cube decreased with the increase of corrosion time.Compared with the uncorroded RPC specimen,the compressive strength of RPC cube decreased by 26%after 90 days of corrosion.（4）Numerical simulation of RPC corrosion resistance:Based on the test results,the correlation between the dissolution amount of RPC calcium and the dissolution time was analyzed,and the empirical formula was established;The physical field of thin matter transfer and convection-diffusion equation in COMSOL Multiphysics were used to establish the model of RPC calcium dissolution.Numerical simulation results were verified by corrosion test results,and an effective calcium corrosion transport model of RPC concrete was obtained.