An Experimental Study On Chloride Ion Transport In Uniaxial Tension Fatigue Damaged Concrete

Chloride ion penetration is an important factor the affects the durability of reinforced concrete structures. The study on the transport mechanism of chloride ions in fatigue damaged concrete is of important practical significance for the durability assessment and design of reinforced concrete structures. The tension fatigue of concrete subjected to different levels of stresses was studied in this paper. The immersion and dry-wet cycle tests were conducted on fatigue damaged concrete. The effects of the degree of fatigue damage and mineral admixture on chloride ion transport in concrete were analyzed. The conclusions of this study are summarized in the following points:(1) When the fatigue load is 15 kN, the strain in concrete with different admixtures is basically the same. When the fatigue load increases from 15 kN to 27 kN, the maximum strain in ordinary concrete increases from 70 × 10-6 to 195 × 10-6. The rate of strain increase is small during the initial stage but becomes large during the later stage with the increase of the fatigue load.(2) For a given depth, the maximum chloride ion concentration in ordinary concrete increases approximately by 55% when the fatigue load increases from 15 kN to 27 k N. For a given fatigue load, the chloride ion concentrations at the depth of 0~20 mm in concrete made with slag and fly ash are smaller than that in ordinary concrete by 14 % and 20 %, respectively.(3) Under the dry-wet cycle condition, the concentration of free chloride ion in concrete for a given location and time increases with the fatigue load and with the number of dry-wet cycles. At the depth of 0~5 mm in concrete, the chloride ion concentration reaches the maximum value.(4) For a given fatigue load, the maximum penetration depth at the critical concentration 0.15% of ordinary concrete is larger than that of concrete made with fly ash and slag by approximately 15 mm and 20 mm, respectively.(5) For a given material and penetration depth, the chloride ion concentration of concrete under the condition of dry-wet cycles is one to two times larger than that under the immersion condition.(6) With the increase of time, the chloride ion concentration in concrete increases gradually, but both the rate of increase and the chloride diffusion coefficient decrease.