Experimental Study On Mass Transport In High Strength Concrete(HSC) With Blast Furnace Slag Under Short-term Sustained Compressive Loading

In the de-icing salt environment and offshore environment,the erosion effect of harmful media transport process is the main factor affecting the deterioration of mechanical properties and durability of RC structures.Usually,the concrete structures in tidal and splash zone are at the highest risk of reinforcement corrosion,because a large amount of aggregessive agents(i.e.chloride ions)are transported into the unsaturated concrete due to water transport,resulting in the deterioration of concrete durability and reinforcement corrosion.Concrete structures are mostly subjected to various loadings in the service process.However,the action of sustained loading will cause the vatiation to pore structure of concrete,and even the initiation and interconnection of cracks,which will accelerate the ingress of water and aggregessive agents.With the upgrading of engineering requirement,mineral admixtures and HSC are widely used.Therefore,for marine or de-icing environments,it is of great significance to investigate the transport mechanism and the distribution of water and chloride ions in unsaturated concrete subjected to susutained loading for durability analysis and service life prediction of reinforced concrete structures.Based on the above-mentioned considerations,the experimental investigation on the influence of short-term sustained compressive loading action and the granulated blast furnace slag(GBFS)content on transport properties of water and chloride in high strength concrete are carried out.The specificcontents of the research work and main conclusions are summarized as follows:(1)An improved water absorption device of concrete was designed based on the principle of communicating vessels,and hollow cylindrical specimens are prepared with prefabricated molds,which can realize the coupled process of sustained loading and mass transport.A series of capillary water absorption tests of completely dry HSC were carried out using this device under different stress levels(ranging in 0 to 60%),analyzing the influence of stress level and GBFS content on capillary water absorption property of HSC.And the relational model between the average water sorptivity and stress levels was set up.The results show that the cumulative water absorption curves of concrete with different GBFS content under each stress level are bilinear.In addition,within the range of a certain stress level,the cumulative water content and water sorptivity of concrete decrease first and then increase with an increase of compressive stress level,and the stress level threshold is the 40% stress level.Moreover,with the increase of GBFS content,the capillary water sorptivity of HSC increased first and then decreased for the GBFS contents tested in this paper,among which the HSC with no admixture and 20% GBFS content can better slow down the capillary water absorption than that with addition of just 10%.(2)A series of chloride transport tests of HSC under short-term sustained compressive loading were carried out by the test setup and method above,analyzing the influence and mechanism of the stress level and GBFS content on the chloride ion penetration depth of concrete and chloride concentration distribution.The results show that the influence of the stress level on the penetration depth and its concentration distribution of chloride ions in concrete is consistent with that on the sorptivity of concrete,which decreases first and then increases with the increase of the stress level.However,the influence of GBFS content on chloride penetration depth and its concentration distribution of concrete is different: with the increase of GBFS content,the lower the chloride penetration depth and and its concentration distribution of concrete are.And the results also verifies that the saturation time(water curing time)has a great influence on the mass transport property of concrete.(3)Based on the unsaturated flow theory,the water content distributions in concrete were predicted by means of the exponential law and power functions.And the predicted values were in good agreement with the experimental results,which verifies the accuracy of the prediction model.According to the corresponding relation between the relative water content in concrete and the chloride ion content in solution,a prediction model was established to predict the chloride concentration distribution by water content distribution.By comparing the predicted values with the measured results,it was found that the predicted values were different with the measured results because of not considering the hysteresis effect and the binding effect of chloride ions in the model.It was also found from the comparison of water permeation depth and chloride penetration depth that their transport processes were asynchronous,and the chloride ions migration lagged behind the water transport obviously.