Research On The Deterioration Law And Mechanism Of Marine Concrete Under Chemistry-Mechanical Coupled Effect

The environment that the marine concrete service in is extremly complex and harsh. First of all, the abundant chloride and sulphate salts are responsible for the chemical corrosion to the concretes. To make it worse, the damage to concretes in the tidal zone is exacerbated due to the wetting-drying cycles. For loaded concretes, increased internal micro-cracks and propagation of existing cracks were observed, resulting in a network of micro-cracks that may be potential transmission channels. In this paper, the degradation and erosion mechanism of marine concrete under the coupled effects of chemical and mechanical was studied; the main work is as follows:Marine concrete with excellent salt corrosion resistance was cast, followed by chemical analysis of chloride and sulphate ions, and microscopic detection means such as X-CT tomography, MIP pore testing, XRD phase analysis, DSC-TG thermal analysis and microscopic morphology to investigate the erosion mechanism of corrosive ions and the evolution of the internal micro structure during their exposure to a marine environment. Additionally, an indoor accelerated corrosion test was conducted. The effects of the corrosive environment, water-to-binder ratio, mineral admixtures, corrosion time and other factors on the durability of the marine concrete were studied.On the same diffusion depth, the corrosive ion content can be sorted by descending:wetting-drying cycles test>salt spray test>soaking test; the addition of mineral admixtures, especially the combined use of fly ash and slag can significantly reduce corrosive ion content; The Functional relation between the total chloride ion content (Ct) and the free chlorine ion content (Cf) was linear, and the chloride binding capacity R decreased with the concrete strength increasing; With the extension of exposure time, the cement paste structure in concrete had changed, and the porosity and the chloride ion diffusion coefficient decreased; When concrete was under bending loads, the CH content in tension zone was much lower than in the compression zone, indicating the degree of deterioration of the tension zone was more serious than the compression zone.The development law of dynamic elastic moduli{Ed) was sutdied through detecting changes in the ultrasonic velocity of the concrete specimens. Based on the similarity theory, the dynamic elastic moduli (Edx/GPa) of field test in marine environment and the dynamic elastic moduli (Eds/GPa) of the indoor corrosion test obey the following empirical formula:Edx=m×a^Eds+n, where n is determined by the 28d compressive strength of concrete, a is an empirical value adding mineral admixtures may be appropriate to reduce.Finally, the service life of the concrete in the marine field exposure environment was preliminarily predicted based on the modified model of chloride ion diffusion. The service life of concrete in the ocean tidal zone is much less than in the atmospheric zone, the former is about 1/4 of the latter; the thickness of the protective layer of concrete plays a decisive role in the service life, the protective layer thickness x increased 50%, the service life of concrete will increase about 2 times; decreasing the water-binder ratio, adding mineral admixtures, especially fly ash and slag blending together will greatly improve the service life of marine concrete.