【正文】 tructures. 2. Experimental research The experiments were conducted for the steel S500s tempcore, which is similar to the BSt500S steel of DIN 488 part 1 [20]. A stress–strain graph of the uncorroded material is shown in Fig. 1. The chemical position (maximum allowable % in final product) of the alloy S500s is: C, %。 P, %。 S, %。 N, % [21]. (13K) Fig. 1. Stress–strain graph of uncorroded BSt 500s alloy. The material was produced by a Greek industry by using the tempcore method (hot rolling followed by quenching and self tempering) and was delivered in the form of ribbed bars. The nominal diameter of the bars was 8 mm (216。8). From the bars, tensile specimens of 230 mm length were cut. The gauge length was 120 mm according to the specification DIN 488 Part 3 [22]. Prior to the tensile tests, the specimens were precorroded using accelerated laboratory corrosion tests in salt spray environment. . Salt spray testing Salt spray (fog) tests were conducted according to the ASTM B11794 specification [23]. For the tests, a special apparatus, model SF 450 made by Cand W. Specialist Equipment Ltd. was used. The salt solution was prepared by dissolving 5 parts by mass of Sodium Chloride (NaCl) into 95 parts of distilled water. The pH of the salt spray solution was such that when dissolved at 35 176。C, the solution was in the pH range from to . The pH measurements were made at 25 176。C. The temperature in the zone of the reinforcement material exposed inside the salt spray chamber was maintained at 35 176。C + – 176。C. When exposure was pleted, the specimens were washed with clean running water to remove any salt deposits from their surfaces, and then were dried. In addition, a number of steel bars of the same length were exposed to the salt spray for 1, 2 and 4 days to monitor the corrosion damage evolution. . Mechanical testing procedure The precorroded specimens were subjected to tensile tests. All mechanical tests are summarized in Table 1. Table 1. Tensile tests for S500s 216。8 tempcore steel Test series Test series description Corrosion exposure prior to tensile test Number of tests conducted 1 Tensile tests on noncorroded control specimens None 4 2 Tensile tests on corroded specimens Salt spray corrosion for 10 days 3 3 Tensile tests on corroded specimens Salt spray corrosion for 20 days 3 4 Tensile tests on corroded specimens Salt spray corrosion for 30 days 3 5 Tensile tests on corroded specimens Salt spray corrosion for 40 days 3 6 Tensile tests on corroded specimens Salt spray corrosion for 60 days 3 7 Tensile tests on corroded specimens Salt spray corrosion for 90 days 3 The performed tensile tests aim to provide information on: 1. the gradual deterioration of the mechanical properties of the S500s tempcore steel reinforcement during salt spray corrosion。 2. whether the exposure of the specimens to salt spray might degrade their tensile property values such that they do no longer meet the limits set by the Hellenic standards for using steel in reinforced concrete structures, . [1] and [24]. The tensile tests were performed according to the DIN 488 specification [22]. For the tests a servohydraulic MTS 250 KN machine was used. The deformation rate was 2 mm/min. The tensile properties: yield stress Rp, ultimate stress Rm, elongation to fracture fu and energy density W0 were evaluated. The energy density is calculated from the area under the true stress–true strain curve. In the present work, the energy density has been evaluated from the engineering stress–engineering strain curves as (1) as an engineering approximation. 3. Results and discussion As expected, corrosion damage increases with increasing exposure time to salt spray. The exposure of the specimens to the salt spray environment causes the production of an oxide layer which covers the specimen and increases in thickness with increasing exposure time of the specimen. Removal of the oxide layer by using a bristle brush according to the ASTM G190 [25] specification has shown extensive pitting of the specimens already after 10 days of exposure to salt spray. The stereoscopic image of a specimen after exposure to salt spray for 10 days is shown in Fig. 2. It is pared against the image of the uncorroded material. It was observed that the corrosion attack started at the rib roots and advanced towards the area between the ribs. The indentations of the corrosion attack left on the specimen surface after removal of the oxide layer increase in dimensions and depth with increasing duration of the exposure. (84K) Fig. 2. Stereoscopic images (35) of (a) uncorroded specimen and (b) specimen exposed to salt spray corrosion for 10 days. The production of the oxide layer is associated to an appreciable loss of the specimen’s mass. The dependency of the obtained mass loss on the salt spray duration is displayed in Fig. 3. The derived dependency may be fitted by the Weibull function (2) The determined Weibull values C1 to C4 are given in Table 2. As it can be seen for salt spray duration of 90 days the mass loss of the corroded specimen is about 35% of the mass of the uncorroded specimen. It is worth noting that the involved salt spray test is an accelerated corrosion test which is performed at the laboratory. Although the salt spray test environment, to some extent, simulates qualitatively the natural corrosion in coastal environment, it is much more aggressive and causes a very severe corrosion attack in a short time. Currently, there is no direct correlation between the accelerated laboratory salt spray test and the natural corrosion of reinforcing steels such as to assess a realistic duration for the accelerated laboratory salt spray tests. Fig. 4 shows a photograph taken from a building constructed in 1978 at a coastal site in Greece. The corr