Study The Effect Of Axial Compressive Load On Chloride Ion Erosion In Concrete

Reiforced concrete structures have been used in civil engineering for hundred years.The corrosion of steel bar caused by chloride ion erosion has attracted people’s attention.There are many studies about chloride ion erosion in concrete, but many don’t take loadeffect or sustained load into consideration. While in practical engineering, the concretestructures are all under sustained compressive load. Therefor, it is very impormant tostudy the effect of axial compressive sustained load on chloride ion erosion in concrete.Based on this, the concrete prisms (100mm×100mm×300mm) of type A(W/C=0.4)and type C (W/C=0.6) are loaded at65%,75%, and85%of the compressive load for2,10,50,250, and1250minutes respectively. During the duration, the longitudinal andtransverse stress and strain was measured. The special crack area caused by micro-crackis caculated by the longitudinal and transverse strain. The longitudinal and transversecapillary water absorption and chloride ion content is determined. And the change ofpore structure of concrete prisms of type C, which is loaded at65%,75%, and85%ofthe compressive load for50,250and1250minutes respectively, is determined by MIPtest.The main results are as follows:(1) At the same stress level, with the increasing sustained time, the longitudinalcreep deformation can increase3~8times, the transverse creep deformation canincrease6~10times; the longitudinal residue strain can increase1~4times, thetransverse residue strain can increase2~12times. At the same sustained time, with theincreasing stress level, the longitudinal creep deformation can increase0.3~2times,the transverse creep deformation can increase0.2~1.5times; the longitudinal residuestrain can increase0.5~1.5times, the transverse residue strain can increase0.1~3.2times(2) The creep deformation and the residual strain of concrete prisms are raleted tothe concrete water cement ratio. At the same stress level and the same duration time, thelongitudinal creep deformation of concrete, whose water cement ratio is0.6, is1~3times of that whose water cement ratio is0.4, and the transverse creep deformation can be up to1~2times. The longitudinal residue strain of concrete, whose water cementratio is0.6, is1~2times of that whose water cement ratio is0.4, and the transverseresidue strain can be up to1~2.4times.(3) It finds that the development of the special crack is mainly occurred during theduration, when the sustained time is longer, so the damage caused by the creepdeformation can not be ignored.(4) Under much higher stress level (65%,75%, and85%), under the samesustained time, with the increase of stress level, the longitudinal capillary absorptioncoefficient can increase20%~30%times; the transverse capillary absorptioncoefficient can increase10%~40%times. the longitudinal chloride ion diffusioncoefficient can increase4%~6%; the transverse chloride ion diffusion coefficient canincrease5%~8%(5) The capillary water absorption and the chloride ion erosion of concrete aredifferent in the longitudinal and transverse direction. Under the same stress level, whenthe sustained time is less than250min, the capillary water absorption and the chlorideion erosion of concrete are little different in the longitudinal and transverse direction.But when the sustained time is1250min, the capillary water absorption in thetransverse direction is more than that in the longitudinal direction; the chloride ionerosion in the transverse direction is stronger than that in the longitudinal direction. Andwith the increase of stress level, the difference performs more obviously.(6) Load and the duration time can increase the porosity, loaded at the higherstress level (65%,75%and85%) for50min,250min,1250min, the porosity canincrease12%~48%, and with the increase of stress level and sustained time, theporosity amplifies. The critical aperture of concrete can increase9%~48%, and withthe increase of stress level and sustained time, the critical aperture of concrete amplifies.With the increase of stress level and sustained time, the harmless pores and the lessharmless pores decrease, the harmful pores and the more harmful pores increase.