| Epoxy resin structural adhesive is widely used in reinforcement of concretestructure due to its excellent mechanical properties and good durability. At present,the research of structural adhesive and engineering data is mostly carried out at roomtemperature, but as polymer material, the properties of structural adhesive are greatlyaffected by temperature, which has not be taken seriously in engineering applicationsat past. This situation may be changed now, because in the newly issued code"Technical code for safety appraisal of engineering structural strengtheningmaterials†firstly give out a requirement on the heat resistance performance, it useheat deformation temperature to limit the upper application temperature of structuraladhesive.In this paper, in order to provide research data for the preparation ofspecification and for engineering application, three heat resistance evaluationmethods are discussed; the relations between mechanical properties at differenttemperatures, heat deformation temperature, glass transition temperature and upperapplication temperature are analyzed. The influences of curing conditions and maincomponents on heat resistance performance are studied; and the formulation isoptimized according to engineering applications. The results show that:The mechanical properties of structural adhesive are significantly affected bytemperature, with the rising of temperature, tensile strength, shear strength, elasticmodulus are decreasing, tensile elongation at break and creep are increasingsignificantly. There is a relation between heat deformation temperature and glasstransition temperature, both of them can reflect heat resistance performance at acertain extent. Heat deformation temperature actually reflects the decreasing of elasticmodulus with the increasing of temperature; load value used in test can significantlyaffects the result, only use one load value to measure heat resistance performance haslimitation; two structural adhesive（sAã€B） with similar heat deformation temperaturehave large difference in mechanical properties at high temperature.The heat resistance performance is significantly affected by curing conditions.Rising cure temperature can significantly improve mechanical properties at hightemperature, and can also greatly increase heat deformation temperature and glasstransition temperature, because rising cure temperature can significantly increase the crosslink density of the structural adhesive. The extension of curing time can improveheat deformation temperature, but is less effective than rising cure temperature.The composition of structural adhesive has great influence on heat resistanceperformance. Phenolic epoxy resin structural adhesive has a slight higher heatdeformation temperature than bisphenol A epoxy resin structural adhesive. However,the viscosity of phenolic epoxy resin is too high and the failure is brittle, so phenolicepoxy resin is not suitable for structural adhesive. The type of curing agent has largeinfluence on heat deformation temperature. Mixing of suitable curing agent canimprove the heat deformation temperature of structural adhesive, but the effcet ismuch lower than rising cure temperature. As for pressure injection adhesive, it isproper to mix phenolic amine (high reactivity) with modified cycloaliphatic amine(good heat resistance and low viscosity) as curing agent; as for adhesive requirehigher heat resistance performance, aromatic amine can be used as curing agent, andrising cure temperature is necessary.Single epoxy function diluent has good dilution effect, but has great impact onthe heat deformation temperature; diluent with higher epoxy function has lowerimpact on heat deformation temperature and compressive strength, but has poorerdilution effect; mixing of single and double epoxy functional diluents can solve thisproblem well. Toughening agents decrease heat deformation temperature in varyingdegrees; however, the "island structure" rubber has smaller impact on heatdeformation temperature and has the best toughening effect. Adding of filler improvesthe heat deformation temperature of structural adhesive; quartz powder has a betterimprovement on heat deformation temperature.Based on the requirements in practical application and to ensure other propertiesof structural adhesive, two types of structural adhesives are abtained by theoptimization of formulation. One structural adhesive has good heat resistanceperformance and low viscosity, it can be used as pressure injection adhesive. Anotherstructural adhesive has excellent heat resistance performance, it can be used in projectwhich requires better heat resistance performance. |
