Experimental Research On Bond Behavior Of New And Old Concrete With Interface Agent

At present,some cases of the project failures often occur,due to the lack of bond strength between old and new concrete,no matter it is the reinforcement and reconstruction of the existing building,or the concrete repair of the bridge,road,airport and dam.However it is a simple and effective way to use interfacial agent to bond new and old concrete.The purpose of the paper is to develop a kind of modified mortar interface agent,which has the advantages of self closing,high compressive strength,high bonding strength and good frost resistance.The first objective is to determine a kind of composite cement matrix which is high strength and low shrinkage,and research effects of content and age on the mechanical properties of modified agent interface,by using polymer emulsion(acrylic resin emulsion powder,epoxy emulsion,styrene butadiene emulsion)and superfine mineral admixture(silica ash and superfine fly ash)modified it.Then through researching 24 groups of modified interface agent on the old and new concrete interface splitting tensile,shear performance,four kinds of modified interfacial agents were selected to bond the old and new concrete,and the shear test was carried out after freezing and thawing.Besides,there are four kinds of modified interfacial agents applied to the bending test of 8 pure bent concrete beams,which verified the common working performance of the new and old concrete.Test results show that:(1)Portland cement-sulphoaluminate cement-gypsum is a good composite cement matrix,when sulphoaluminate cement and gypsum on Portland cement substitution rate is 5%,the shrinkage of the cement matrix is small,the early fracture resistance and compressive strength are high.(2)The flexural strength of mortar interfacial agent is improved but the compressive strength is decreased in different degrees by the incorporation of polymer emulsion,When the acrylic resin emulsion powder interfacial agent content is less than 1%and the latex content is less than 10%,7d compressive strength is greater than 30MPa.(3)Through the split tensile test to study the influence of interface roughness on bond strength of old and new concrete,it is concluded that when the roughness is 1mm?2mm,the bonding effect of old and new concrete is the best.(4)The bond strength of the polymer modified mortar interface agent increases with the growth of age,and the modification effect of' styrene butadiene is the best.When the dosage of acrylic resin emulsion powder is 1%?3%and the dosage of styrene butadiene latex is 10%,the early bond strength of new and old concrete is higher,which close to the cast-in-place splitting tensile strength and shear strength of concrete members.(5)The bigger the water cement ratio is,the lower the bond strength is.With the increase of silica fume and superfine fly ash content,the bond strength increases first and then slowly,and the silica fume and superfine fly ash content are 10%and 5%respectively.When combined with mortar interface agent ratio of 0.3 water cement ratio,10%silica fume,10%ultra-fine fly ash and 5%butadiene styrene emulsion,28d bond strength of interface exceeds the cast-in-place specimen,the damage from the parent material.The Z type adhesive specimen shear strength in 92.7%freeze-thaw shear bond strength after 40 cycles the whole cast,showing good frost resistance.(6)In the experiment of replacing concrete beams in pure bending section,the cracking load of the beam with preferred interface agent is larger,and it is conducive to collaborative work.