Study On Interfacial Bonding And Cl~-corrosion Resistance Of MPC Modified By Nano-Silica

With the continuous advancement and opening of China ’s " eight vertical and eight horizontal " high-speed railway network,as of 2021,more than 80 % of the large and mediumsized cities have realized the opening and operation of high-speed railway.Cement concrete has become one of the most important materials in national infrastructure construction due to its high compressive strength,wide range of materials and low price.In recent years,super high-rise buildings,large span,intelligent buildings,green buildings and buildings and structures with special functional requirements have emerged worldwide;complex,extreme service environment and increasing traffic lead to a large number of road and bridge damage within the design life,which makes cement concrete face new opportunities and challenges.Magnesium phosphate cement(MPC)is an inorganic cementitious material with phosphate as the matrix phase,which is formed by acid-base neutralization reaction and physical action of components such as heavy(over)burned magnesia(Mg O),soluble acid phosphate,retarder and other mineral admixtures in acidic environment.MPC has excellent early mechanical properties,short setting time,strong adhesion and good adhesion,which is widely used in rapid repair of buildings in traffic maintenance industry.MPC started late in our country,setting speed is too fast,raw material performance is unstable,brittle,low bonding efficiency problems in the practice process frequently.In order to solve the problems of MPC in engineering practice,this thesis starts with the mixture ratio,and uses nano-Si O2(NS),polypropylene fiber(PP),and additives to modify MPC to regulate the retarding mechanism of MPC.Using magnesium phosphorus ratio(M /P),boron magnesium ratio(B / M)through compressive strength test,folding strength test,fluidity test,setting time test put forward a set of relatively excellent mix ratio;the effects of NS and PP fibers on the work and mechanical p0 roperties of MPC were studied.The effects of interfacial roughness,interfacial agent and curing age of matrix on the interfacial bonding properties of MPC were studied.The interfacial bonding mechanism between MPC and old concrete(OPC)was revealed by means of microscopic analysis technology,which realized the rapid integration of MPC and matrix structure,and improved its ability to maintain longterm strength and appearance integrity under Cl-erosion environment.The main conclusions are as follows : The fluidity and setting time of MPC decrease with the increase of M / P value,and the compressive strength and flexural strength increase first and then decrease with the increase of M / P value.Appropriate NS can significantly improve the compressive and flexural strength of MPC,and the incorporation of PP fiber can effectively improve the flexural strength of MPC.Interface roughness(f),MPC paste interfacial agent,and curing age of high matrix specimens all increased the interfacial bonding strength between MPC and OPC to varying degrees;the intervention of water molecules causes the corrosion of MPC hydration products,resulting in the decrease of mechanical properties.The microscopic study found that Cl-inflowed into the cement stone through the capillary channels,cracks and other channels,and reacted with the ionized Mg2 + to form Mg(Cl O2)6.6H2 O,which filled the cement stone.The results of total electric flux are : ordinary MPC > FA modified MPC >NS modified MPC.