Research On Preparation And Durability Of Polymer Modified Sulphoaluminate Cement Based Reinforced Concrete

With the extension of the service life,the building is easy to be damaged under the action of the environment,resulting in the decrease of bearing capacity.It greatly affects the normal use and safe reliability of the building.Compared with demolition and reconstruction,reinforcement and reconstruction are favored by people because of the advantages of short construction period and low cost.Ordinary Portland cement concrete has disadvantage of low bonding strength,high shrinkage and poor water retention and waterproof performance.When used for concrete reinforcement,it is easy to crack and peel off and further leads to the reduction in durability.Therefore,this thesis used calcium sulphoaluminate as the cementing material for the preparation of reinforced concrete and PVA powder was used a modifier,in order to prepar a concrete with good water retention performance,high bonding strength,low shirinkage and high durability,which is suitable for building reinforcement of concrete structure and brick concrete structure.In this paper,firstly,the influence of PVA powder on the working performance of sulphoaluminate cement reinforced concrete was studied.The admixture was used to adjust the working performance of the concrete to meet the requirement of reinforcement engineering.Secondly,the influence of PVA powder on mechanical properties of sulphoaluminate cement reinforced concrete was studied,including compressive strength,flexural strength,splitting tensile strength and bonding strength.The effects of interfacial wetting,interfacial agent and interfacial roughness on the bonding strength were studied.Thirdly,the durability of PVA powder modified sulphoaluminate cement reinforced concrete was studied,including impermeability,frost resistance,chloride ion permeability resistance and carbonization resistance.Finally,the PVA powder modified sulphoaluminate cement concrete was applied in engineering.Through the above research,the following conclusions are drawn:（1）PVA powder can significantly reduce the fluidity of sulphoaluminate cement reinforced concrete,which is shown in the rapid reduction of slump flow.Although the slump flow can be controlled within the range of 600-700 mm by increasing the polycarboxylate superplasticizer content,the use of PVA powder still worsen the gap passability and filling ability of the reinforced concrete.Besides,PVA powder could obviously delay the setting time of sulphoaluminate cement reinforced concrete.（2）PVA powder can improve the flexural strength,splitting tensile strength and toughness of reinforced concrete.When the content of PVA powder is 1.0%,the flexural strength and splitting tensile strength of reinforced concrete can reach 6.14 MPa and 4.26 MPa at the hydration age of 28 d,which are increased by 13.28%and 13.29%,respectively.The compressive strength of reinforced concrete increases firstly and then decreases with the increase of PVA powder.When the PVA powder content is 0.5%,the compressive strength reaches 62.8 MPa at the hydration age of 28 d,which is increase by 7.71%.PVA powder can effectively improve the bonding properties of reinforced concrete,the bonding strengths between the reinforced concrete and the old concrete as well as the reinforced concrete and clay brick increase with the increase of PVA powder content.With 1.0%PVA powder,the bonding strength reaches 2.97 MPa and 1.13 MPa at the hydration age of 28 d,respectively,which increase by 13.79%and 50.66%,respectively.The interface wetting,interface agent and the increase of interface roughness are beneficial to improving the bonding strength.（3）PVA powder can reduce the porosity of the hardened sulphoaluminate cement reinforced concrete.After adding 1.0%PVA powder,the porosity decreases from 21.44%to17.99%.Besides,the PVA powder has the role of refining the pore size.The capillary and large pores are significantly reduced.The decrease of porosity and capillary pore space is beneficial to the improvement of permeability.Besides,PVA powder could reduce the connectivity of the pores,which clold also improve the permeability of the reinforced concrete.Therefore,for the PVA powder modified sulphoaluminate cement reinforced concrete,the impermeability grade can reach P12 and the impermeability pressure exceeds4.0 MPa.（4）PVA powder can increase the relative dynamic elastic modulus of reinforced concrete and reduce the quality loss and strength loss after freeze-thaw cycles.Adding 1.0%PVA powder,the frost resistance grade of reinforced concrete increases from F100 to F150.After100 freeze-thaw cycles,the quality loss and strength loss decrease 68.37%and 55.61%,respectively.After the same number of freeze-thaw cycles,the pore water saturation of reinforced concrete decreases gradually with the increase of the content of PVA rubber powder,and the water penetrating into the concrete decreases,resulting in less freeze-thaw damage.（5）PVA powder can improve the chloride ion permeability resistance of sulphoaluminate cement reinforced concrete.The electric flux and unsteady chloride diffusion coefficient of reinforced concrete decrease gradually with the increase of PVA powder content.With 1.0%PVA powder,the electric flux of reinforced concrete can reduce from 241C to 151C,and the unsteady chloride diffusion coefficient also reduces from 1.65×10^-12 m²/s to 0.79×10^-12 m²/s.After soaking in 3.5%Na Cl solution for 90 days,the content of calcium sulphoaluminate in reinforced concrete decreased,while the content of AFt increased significantly,and a small amount of Friedel’s salt appeared.After soaking in Na Cl solution,the porosity and the connectivity of the pore structure of reinforced concrete decrease,and the reinforced concrete without PVA powder decreased most significantly,by 9.04%and 4.19%respectively.（6）PVA powder can improve the carbonation resistance of sulphoaluminate cement reinforced concrete.After accelerated carbonization test,the carbonization depth of reinforced concrete decreases gradually with the increase of PVA rubber powder,while the compressive strength and bonding strength increase slightly.After 28 d of accelerated carbonization,the carbonization depth of reinforced concrete with 1.0%PVA rubber powder is 9.36 mm,which is 15.81%lower than that of blank group.The carbonization degree is significantly reduced,and the compressive strength and bond strength of new and old concrete are respectively improved 5.07%and 7.35%.Compared with uncarbonized reinforced concrete,AFt and AFm contents in carbonized reinforced concrete decreased significantly,while Ca CO₃ content increased.Carbonization could affect the pore structure of the reinforced concrete.After carbonization,the porosity of the reinforced concrete decreases.The large pores decrease and the small pores increase.Besides,the connectivity of the pore structure decreases.（7）PVA powder modified sulphoaluminate cement reinforced concrete has been used to reinforce the houses with brick and concrete structures in Shuiniudian village of Hebei Province.In the process of preparation,transportation and pouring of reinforced concrete,there is no bleeding segregation phenomenon,the fluidity is good and the setting time is controllable,and the surface is smooth after demoulding.The engineering application results show that PVA powder modified sulphoaluminate cement reinforced concrete has the advantages of good construction performance,fast hardening and early strength,high bonding strength and good impermeability,which can be popularized in building structural reinforcement engineering.