Experimental Study On Durability Of Recycled Aggregate Thermal Insulation Concrete Under Carbonization

As a new type of ecological concrete,Recycled Aggregate Thermal Insulation Concrete(RATIC)has great significance to resources and energy conservation in China.With its gradual application in daily engineering construction,the change of mechanical properties and durability after carbonization have increasingly become the focus of attention.Due to the addition of recycled aggregate and thermal insulation aggregate,the internal microstructure and interface characteristics of RATIC after carbonization are more complex than other concrete under the coupling of double admixture,which leads to the greater difference between the carbonation resistance of RATIC and the ordinary concrete,and the research is imminent.In this context,this paper focuses on the main factors affecting the anti-carbonization performance of RATIC,and the changes in the microstructure of RATIC and common concrete(NC),recycled concrete(RAC)and thermal insulating concrete(TIC)are compared and analyzed under carbonization,and the corrosion and change rules of the steel in RATIC are determined after carbonization.The main work and main conclusions of this paper are as follows:(1)Considering the anti carbonation properties of RATIC,the mix design is studied.Water cement ratio,fly ash,rate of recycled coarse aggregate replacement and initial water rate of recycled coarse aggregate,these four teams influence factors are selected to analyze effects of various factors on RATIC anti-carbonation performance.Research shows that in a certain range,anti-carbonation properties of RATIC decreases with the increase of water cement ratio,the best dosage of fly ash is 10%,and the best replacement rate of recycled coarse aggregate is 50%,and its resistance to carbonation with initial water rate of recycled coarse aggregate has little relationship.(2)Through 3d,7d,14d,28d,56d,90d carbonization tests of NC,TIC,RAC,RATIC,the carbonization depth in different environments is measured and the difference of its carbonization resistance is determined.After that,four kinds of concrete after 28d carbonization are scanned under the industrial CT scanner.The reasons for the difference of carbonation resistance of different concrete are analyzed at the mesoscopic level.Four kinds of concrete carbonization models are established by 3d,7d,14d and 28d carbonization data,and the rationality of carbonization model is verified by 56d and 90d carbonization depth data.Then the carbonization model is established by the RATIC short-term carbonization depth test under atmospheric environment,and the normal service life of RATIC in the atmosphere is predicted.The study shows that the carbonization depth of four kinds of concrete at the same age of carbonization is NC<RAC<TIC<RATIC,respectively.The resistance to carbonization performance is NC>RAC>TIC>RATIC,respectively.The porosity and pore structure of four kinds of concrete are analyzed by CT.The results show that with the addition of recycled coarse aggregate and thermal aggregate,the porosity of RATIC and NC is close to the porosity of NC,and the inner pore size of RATIC is smaller,which makes the contact surface of CO2 and concrete more extensive and the neutral reaction is more sufficient,which leads to the weakening of the carbonation resistance of RATIC.The carbonization coefficients of NC,RAC,TIC and RATIC in the rapid carbonization environment are 12.276,17.691,45.492 and 45.198 respectively.The carbonization model is suitable for the prediction of carbonization depth of NC,RAC,TIC and RATIC.The RATIC carbonation model in atmospheric environment predicts that the carbonization depth will reach 20mm for 39.6 years,and the carbonization depth will reach 22.5mm after 50 years of normal use.(3)After 28d,56d,90d carbonation,comparative analysis of the relationship between the two-way and one-way carbonation is studied to determine different usages of RATIC in different parts of building;analysis of potential changes in the overall test block by semi potentiometric method is done,using the principle of concrete carbonization to determine how carbonization of RATIC effects steel corrosion;according to the "standard test method for long-term performance and durability of ordinary concrete"(GB-T50082-2009)steel bar corrosion test is done to comparatively analyze morphological changes of steel before and after carbonization and measure corrosion weight loss rate.The research shows that there is a certain difference between the carbonization depth of RATIC components in unidirectional carbonization and bidirectional carbonization in carbonation environment,and the carbonation coefficient correction coefficient of carbonization is introduced.Under the condition of unidirectional carbonization,its value is 1,and under the condition of bi-directional carbonization its value is 1.33.After carbonization of 28d,56d and 90d,the corrosion activities of steel bars in RATIC are 0%,10.09%and 71.56%respectively.With the growth of carbonization time,the corrosion loss rate and carbonization depth of rebar corrosion in regenerated reinforced concrete increase.After 90d carbonization,the weight loss rate of the internal reinforcement is only 0.65%.Under carbonation,RATIC has an effective protective effect on the internal reinforcement.The durability of RATIC after carbonization is the basis of its application.Through the above properties obtained from tests in carbonation environment,reliable theory reference for the promotion and application of RATIC is proposed.This paper provides a theoretical basis for the material optimization and durability design of RATIC after carbonation,which aims to meet the needs of the development of building energy saving,recycling of construction waste use.In a word,it has a huge significance to the engineering application.