| An epoxy resin adhesive is a kind of important engineering adhesive,which is nowadays widely used in architectures,semiconductor industry,and aerospace engineering,where strength,stiffness,and stability are the most important indices in these areas,Strength and stiffness are the ability of materials to withstand rupture and deformation,and stability is the durability of materials in the environment during service.Thus the adhesives used for structural reinforcement must satisfy these indices simultaneously.In terms of practical applications of these developed adhesives,for example,in the field of civil engineering,most of the work places are outside,even some remote places.Under these complex environmental conditions,the adhesives used for reinforcing engineering structures should be operated easily.In particular,the curing conditions should not be too complicated,since it is nearly impossible to cure the epoxy resin adhesive using external heating sources.Owing to the structural epoxy resin adhesive often subjected to various and extreme environmental conditions in applications,such as temperature and relative humidity,which could potentially affect the rheological mechanical performance of the adhesive and hence the structural integrity of the reinforced structures,the long-term durability of it should be considered and evaluated.As such,it is imperative to understand the influences of environmental conditions on the rheological mechanical properties of this kind of polymer materials.In this paper,combined closely with the Project of Hunan Provincial Science&Technology Department of P.R.China(NO.2010GK3110),the Key Project of the Education Department of Hunan Province of P.R.China(NO.10A130)and the Innovation Project of Postgraduate of Central South University of Forestry&Technology of P.R.China(NO.20181008),the main work and innovations were summarized as follows:(1)A new type of room temperature cured epoxy resin adhesive for civil engineering structures was synthesized and studied.The experimental results indicated that the storage modulus was 1.7GPa and the glass transition temperature was 108?after 7 days'cured under room temperature.The common shortcoming of this kind of adhesive on the marketwith low glass transition temperature was overcome.(2)Tensile tests of home-made epoxy resin adhesives have been carried out.The results showed that their tensile strength and break elongation got better of the requirements of structural adhesives based on concrete in the national standard?Technical code for safety appraisal of engineering structural strengthening materials?(GB50728-2011).Then the short-term static tensile creep tests of the adhesive under four different stress levels were carried out,and its creep behavior was analyzed,which proved that the epoxy resin adhesive was a typical viscoelastic material.The creep behavior of the epoxy adhesive was characterized acceleratly by time-stress equivalence principle.The results show that the observation time of creep behavior of the adhesive has been extended to some extent after accelerated characterization analysis.The experimental period has been effectively saved.The functional relationship between shift factor and stress increment of this home-made epoxy adhesives at the stress level of 36 MPa has been obtained,which was significant to predict the creep behavior of adhesives under the specific stresses.(3)The dynamic mechanical properties of the home-made epoxy resin adhesive were tested and also characterized acceleratly after thermal aging and hydrothermal aging.Because the effect of hydrothermal aging on the properties of polymers can only be observed in a long time,most of hydrothermal aging experiments were accelerated by placing in a constant temperature water pot,but there is still some differences between the method and the actual environment.In this paper,the hydrothermal aging experiments were all carried out in a constant temperature and humidity aging chamber,which was more consistent with the actual service environment.The results of hydrothermal aging test showed that the properties of this epoxy resin adhesive have little change after aging for 30 days at four different relative humidity levels,which proved that the adhesive had better hydrothermal aging resistance.In addition,by using the time-temperature equivalence principle,the time-aging time equivalence principle and the time-humidity equivalence principle,the generalized curves E'-lg f of epoxy resin adhesive aging for 20 days at relative humidity of 95%,70 ? and frequency with 20 magnitude orders were obtained,which effectively saved the experimental period.At the same time.it also provided a method for accelerating the characterization of the long-term mechanical properties of other polymers.by which the generalized curves can be obtained at specific humidity,temperature the and aging time.The results of thermal aging test showed that the properties of the epoxy resin adhesive did not change much after 30 days when the temperature were 80?,100 C and 120?.However,the properties of the epoxy resin adhesive were unstable and declined rapidly with the increase of aging time when the temperature was 140?,which indicated that the epoxy resin adhesive was suitable for the environment below 120?.In addition,the experiment of accelerating the characterization of mechanical properties of adhesive after thermal aging proved that when the aging temperature and the test temperature are inconsistent,the test temperature should be chosen as the reference temperature by using the time-temperature equivalence principle,and then the time-aging time equivalence principle should be used for the secondary acceleration characterization of this kind of adhesive.(4)The generalized curves of the epoxy resin adhesives in the condition of room temperature and tensile stress level of 36 MPa obtained by using time-stress equivalence principle were fitted by integer order Burgers model and fractional order KBurges model respectively.The results showed that compared with the Burgers model,the KBurgers model can predict the creep behavior of the new adhesive under room temperature.The experimental results and model predictions can provide guidance for various practical applications of this new adhesive in the future.(5)The properties of the epoxy resin adhesive for repairing and strengthening concrete with cracks and reinforcing bar(REBAR)based on concrete were studied experimentally at room temperature.In the experiments of repairing concrete blocks(150mm X 150mm X 300mm)with two symmetrical cracks(150mm X 30mm X 2mm)in the middle of the highth,the compressive strength of the concrete blocks with cracks decreased to 6J].6%of the original concrete blocks.After repairing with the adhesive,the compressive strength of the concrete blocks reached to 90.5%of the original concrete blocks.The results showed that the application of this adhesive greatly improved the compressive strength of the testing blocks,and the effect of repairing and strengthening on it was remarkable.In the experiments of bonding REBAR and concrete,the drawing force of t,wo kinds of specimens at three different dynamical even loaded tensile tests(0.2kN/s,0.5kN/s.0.8kN/s)were investigated.When the dynamical loading speed was lower(0.2kN/s).the cracks of the specimens are wide and the c.oncrete was broken.which indicated that the damage of concrete was the main,and the bondin,effect between REBAR and concrete was better.When the dynamical loading speed was higher(0.5kN/s,0.8kN/s),the cracks of the specimens were narrow,the concrete was not broken,and the REBAR was pulled out,which indicated that it was the main failure at this time.Therefore,when the dynamical loading speed was lower,the bonding effect between REBAR and concrete by this home-made adhesive was better. |
PDF Full Text Request