Experimental and modelling investigation on chloride transport and flexural behaviour of RC beams subjected to simultaneous deteriorating factors of carbonation, FT cycles and multi-type sustained stress

Abstract

Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity.