Experimental Study On The Influence Of Polymer Mortar On The Bond Strength Between New And Old Concrete

At present,during the process of the reinforcement of existing buildings,or the concrete repair of bridge pavement and embankment airport,project failures caused by insufficient bonding strength of old and new concrete interface have occurred.Using polymer mortar to bond with new and old concrete is a simple and effective method.This paper mainly studies factors affecting polymer mortar strength of new and old concrete bonding,including polymer mortar mixture ratio,bonding interface roughness degree of pulverization,polymer mortar and the old and new concrete strength.For the research of polymer mortar mixture ratio,ordinary Portland cement-sulfur-aluminate cement-gypsum is used as a small compound and early strength cement matrix.On the one hand,the mixing ratio of water-cement ratio,sand ratio,sand grain size composition is studied,on the other hand,acrylic acid emulsion,polypropylene fiber,cellulose ether,ultrafine silica fume mineral admixtures is used for modification research.On the basis of the research of mixing ratio,the influence of three factors on the bond strength such as bond interface roughness,the degree of pulverization of polymer mortar and the strength of old and new concrete is also analyzed.The main process of the experiment is:Firstly,the body strength test is carried out to determine the basic matching ratio.Then the bond strength test is conducted to determine the best ratio.Finally,the polymer mortar is applied to the test of reinforced flange beam,the bending test of simply supported beam in normal section is performed.Through analysis of experiment results,the influence of cracking bending moment,ultimate bearing capacity,deflection,crack of test beam on the bonding effect of polymer mortar is obtained.Results show that:(1)The smaller the water cement ratio of polymer mortar,the higher the compressive and flexural strength and the bond strength.But the mobility decreases.When the water cement ratio is 0.3,the bonding strength is the highest,which is able to meet the construction process requirement.The cement sand ratio is proportional to the bond strength,and the mortar strength is the highest when the glue ratio is 1:0.8.After the coarse sand is replaced by the middle sand,the workability of mortar is qualified.(2)Acrylic emulsion causes the compressive strength of mortar to decrease,the compressive strength increase,the pressure ratio decrease,and the bonding strength reaches the maximum when the polymer cement ratio is 3.6%.The polypropylene fiber can reduce the compressive strength of mortar,improve the compressive strength,and also improve the bond strength:When the cement sand ratio is 2‰,the is the bond strength is the highest.The silicon ash can improve the strength of mortar body,and also improve the bond strength,which is good at 10%of the content,and no segregation or bleeding occurs.The content of cellulose ether had little effect on the compressive and flexural strength of mortar.When the content of cellulose is 1%,the workability of mortar is good,bond strength is not obvious,excessive incorporation can introduce bubbles and reduce the bond strength.(3)The interface roughness influences the bond strength of the polymer mortar,and it is verified that the bond strength of new and old concrete is the highest when the roughness is 1?3mm.The influence of the strength of old and new concrete on the bond strength of polymer mortar has been verified by experiment.The difference between the bond strength of old concrete with C25 and C30 strength is not big.The higher the strength of new concrete,the higher the bond strength.The degree of mortar pulverization has an impact on the bond strength of polymer mortar.The mortar pulverization results in a large loss of bond strength after the test and verification.The wetting treatment after powdering can slightly increase the bond strength.(4)Through the application of polymer mortar ratio in the bending test of reinforced flange,the bond strength has played an important role in the beam loading process.The reinforcing part and the original beam part can form a whole,together bear the load.The application of polymer mortar makes the bearing capacity of the strengthened flange beam increase a little bit,delayed the crack initiation and deflection at the flange connection,and had no obvious effect on the cracking load.