Research On The Influence Of Coupling Multi-factors Of Load And Corrosion Freeze-thaw And Recycled Coarse Aggregate On Durability Of Recycled Concrete

In order to research the influence of meso-factors on durability of recycled aggregate concrete.Firstly,a coupling mechanism of load,corrosion and freeze-thaw cycles used in the laboratory is designed in this paper,which is used to simulate the real working environment of concrete structure under multi-factor coupling action.On this basis,the influence of coupling action on durability of recycled concrete is studied.Then model recycle coarse aggregate(MRCA)and model recycle concrete(MRC)are made due to the consideration of meso-factors that are not easy to observe and difficult to control,it is used to study the effect of different mortar in initial damage,thickness and coverage on macro durability.Finally,The failure mechanism of recycled concrete under coupling action is analyzed by SEM and Finite Element,the conclusions was as follows:(1)In the coupling mechanism,the order of influence of the each single factor on the durability of recycled concrete was as follows: salt-solution freeze-thaw cycles > stress level of 50% > stress level of 30% > salt-solution,the influence under the condition of salt-solution was the least,the influence under the action of salt-solution freeze-thaw was the largest,the influence of action of loading increased with increase of the stress level.(2)With the alternative time of repetitive load increased,the rate of the compressive strength loss became faster with the increase of alternative times of repetitive load,the macrocracks on the surface of the specimen progressively are occurred and propagated,the deterioration of concrete is more serious.(3)The mechanism of this coupling mechanism was as follow: the loading action will make the initial micro crack developed;the numerous chemical corrosion products accumulated in microfracture produce will increase the swelling stress on micro cracks,which is accelerated the cracking of concrete;The brittleness of the specimen is increased by the freez-thaw cycles,which is aggravated the degree of deterioration of the specimen.Physical and chemical interactions promote each other until failure of the specimen.(4)The destruction of recycled concrete specimens always begins at the interface of old mortar.With the increase of the thickness and coverage of old mortar and initial damage of recycled coarse aggregate,the damage of recycled concrete increases and the durability becomes worse gradually.(5)Through microscopic image analysis between new and old interfaces,we can find some conclusions was as follows: Before the freeze-thaw cycles in salt-solution,there are a large number of cracks in the old ITZ,which can lead to poor connectivity of the old ITZ between aggravate and old cement mortar,the floc C-S-H gel is tightly bonded in the new ITZ,which can lead to increase the stability of the space structure;However,after the freeze-thaw cycles in salt-solution,a large number of chemical reaction products are filled at the old ITZ,the floc C-S-H gel at the new ITZ has been reduced greatly,a small number of p chemical reaction products have appeared in the new ITZ.It can be found that the deterioration rate of the old ITZ is faster than the new ITZ,it is further confirmed by the simulation analysis of finite element software.