Stress And Strain Field Induced By Corrosion Of Steel Bar In Concrete

Reinforced concrete is the most widely used engineering material in the world.Cracks of concrete due to dry or autogenous shrinkage will result in the penetration that seawater,salt fog and chlorine ion in deicing salt go into concrete rapidly,leading to steel corrosion next,which is an important factor leading to invalidation of reinforced concrete structures in marine environment.Aiming of the two major problems above（concrete shrinkage and steel corrosion）,the experiment adopts super absorbent polymer（SAP）as the curing material,and studies the influence of SAP on the basic properties of concrete.With the methods that constant potential accelerated corrosion,electrochemical measurement,digital image correlation technique and corrosion strain test,this dissertation investigates the corrosion damage behavior,corrosive force development and the evolution law of time varying strain field on concrete surface under the electric accelerated corrosion.The main results are as follows:（1）The effect of SAP on the basic properties of concrete was studied by adding different amount of SAP to concrete.The results show that SAP does damage to the early compressive strength of concrete,and the bigger the amount of SAP content,the bigger the loss of concrete strength.However,SAP contributes to the development of the late strength of concrete.SAP can significantly reduce the drying shrinkage of concrete,but too much SAP will be counterproductive;SAP reduces the permeability resistance of concrete,but help to improve the elastic modulus of concrete;the hydration product of SAP has no change by the XRD diffraction pattern analysis;It is concluded that the SAP has little effect on the early hydration of concrete by the Differential Thermal / Thermal Gravimetric（DTA/TG）analysis,and it is mainly to promote the late hydration.（2）Five kinds of reinforced concrete are under accelerated corrosion test by using independent research and development leakage test device,and the corrosion behavior of reinforcing steel bar and the law of crack propagation on the surface of concrete are studied.The results show that the research and development of the electric acceleration device can realize the non-uniform corrosion of the steel bar,which is more close to the actual;The electrochemical tests were carried out on concrete,finding that Fly ash and slag powder slows down the rate of steel corrosion in concrete,and the introduction of SAP accelerates the steel corrosion.With the increasing of SAP content,negative effect increases;By the real-time monitoring of concrete surface cracks in the process of electric acceleration,it is found that the crack development and the electric time accord with quadratic function;The rust of reinforced concrete specimens under the accelerated corrosion text is more dense and the oxygen content is obvious low compared to the rust caused by steel corrosion exposed in marine environment.（3）Real time characterization of corrosion development of steel bar can be realized by the monitoring of the reinforced internal strain in the process of reinforcement corrosion,and the time and position of the concrete cracks are judged by the strain value.（4）The experiment was carried out by using the self developed steel corrosion ring stress and strain test device,finding that the effect of corrosion solution on steel corrosion rate is as follows: the internal mixing seawater is larger than the inner 1%NaCl+5%Na₂SO₄ doped composite solution which is larger than the inner doped 5%Na₂SO₄ solution;the bigger the SAP content,the faster the corrosion rate of reinforcement.It can be concluded that the development of the expansion stress of concrete specimens with chloride content is faster than that of inner sulfate.The larger the diameter of the reinforcing bar is,the faster the development of the expansion stress;the greater the porosity of the mortar,the slower the development of the expansion stress by monitoring the stress development of the ring.（5）DIC technology can be used to realize the strain collection for the whole process of any point on the concrete surface.The whole process of cracking of concrete surface damage that caused by steel corrosion can be directly observed by relative surface deformation nephogram,which can also determine the initial cracking time and location accurately as well as the form and development trend of cracks.The result of DIC acquisition is consistent with the evolution law of strain acquisition.In the process of corrosion,the deformation of concrete surface mainly occurs around the steel bar.The upper surface of the reinforcement is corroded first and the tensile stress of concrete is produced,while the lower part of the concrete is subjected to the compressive stress.