Influence Of Frost Damage On Fracture Properties Of Concrete

Most of the territory of China locate in cold region, For building structures such asreinforced concrete in the cold areas are frequently damaged by freeze-thaw cycle. Dueto actions repeatedly suffered repeated freeze-thaw cycle and low temperature cause aspalling damage of the concrete, and when the cracks carried out formation andextending, it will has a great influence on the fracture energy(the energy which isneeded to resistance to cracking) of concrete, ultimately leading to steel bar corrosionand the durability of concrete structure degradation or even failure. therefore anti-frostproperty of the concrete is a very important aspect in endurance durability of reinforcedconcrete,it is the crucial value that we do the research on the fracture energy ofconcrete for the cracks formation and strength, and the compressive strength is aimportant indicator of the mechanics performance of concrete, which is a majorpractical engineering inspection, because the loss of the strength is directly related tothe structure of the performance security, So far a lot of research has been carried out inorder to study the degradation of compressive strength as function of the number offreeze-thaw cycles. In most countries there exist standard test methods on how todetermine frost resistance of concrete. It may be expected that freeze-thaw cycles alsoreduce fracture energy of concrete. But this has not been checked in a systematic way sofar. Reduction of fracture energy, however, makes the material more brittle andtherefore more sensitive with respect to crack formation. Crack formation is a majorrisk for durability and service life of reinforced concrete structures. Crack is the mainfactor affecting the permeability of concrete, and the permeability of concrete is also themain influence factors of the durability of concrete structure, therefore, the generationand expansion of crack formation is one of the main reasons which causing durability ofconcrete structure and service life become weakness.After the effect of freeze-thaw cycle, both frost resistance of concrete andmechanical iproperties are significant degradation, The aim of this project is essentiallyto study the influence of frost damage on fracture properties of concrete, effect ofdiferent freeze-thaw cycles on different water cement ratio,different admixtures andmixing air entraning agent with concrete of elastic modulus,compressive strength andfracture energy and strain softening tests. With the wedge splitting test method for splitting test of concrete after freeze-thaw, and then get the load-deformation curve ofconcrete specimen, the strain softening of concrete is abtained by consoft softwarereverse analysis curve and fracture energy value, combining the analysis of the concreteafter different frost damage of fracture properties and resistance to softening of the loadcapacity, To solve above problems, the experimental study is mainly on the followingaspects:(一) study is in different water cement ratio of normal concrete after differentfreeze-thaw cycles of relative loss modulus and the loss rate of strength, systemicdiscussing the influence law of mechanical properties of concrete after freeze-thawcycles, analysing transformation rule of the relative dynamic modulus loss rate,compressive strength and frost resistance, the relationship between the study of thefracture energy of concrete and the function of the strain softening with freeze-thawcycle.(二) Research on normal concrete mixed with air-entraining agent, and concretewith air-entraining agentfrost resistance performance, study the influence of freeze-thawon the relative dynamic modulus loss rate, strength and the fracture energy and strainsoftening curve, it will be found that it can be predicted in the same conditions, concretewith air-entraining agent compared with normal concrete have the positive role forproperties and fracture performance of concrete under freeze-thaw environmentfrostresistance;(三) mixed with admixture of concrete after different freeze-thaw cycles,relative dynamic modulus loss rate and compressive strength and fracture energy of thelaw of development;applying the principle and method of application of fracturemechanics to derive the wedge splitting method for geting formula and fracture energyof concrete and strain softening curve.(四) After effect of freeze-thaw cycle on concrete specimen by the wedgesplitting test, due to frost effect of the surfaces of the concrete specimen have differentdegree of flaking, even hardened cement paste of concrete specimen are exposed andthe concrete is clearly observed the fracture development from the rule after splitting inhalf. It is a certain rule in the future that it can be predicted which making the researchon the forming regular of development of the cracks.