The Compatibility Between Sulphoaluminate (Sr) Calcium Cement And Liquid Erosion Environment

Concrete structures exposed to the environment affected by the environmental inevitably. Analysis of the erosion mechanisms of environment on the cement and the establishment of model to assess their durability life has same significance for the practical engineering application.The erosion behavior of sulphoaluminate (Sr) calcium cement in different liquid erosion environment was studied in this paper. The samples samples were put in kinds of sulfate and chloride solutions which consistency different. The test was done in the condition of replacing the erosion. Study the effect of the various erosion solutions on Sulphoaluminate (Sr) calcium cement compressive strength, while exploring the changes of ionic concentration and the whereabouts of ions in order to study the role of the ions in the erosion process. And we study the mechanism of erosion with the stereo microscope, X-ray diffraction (XRD) and scanning electron microscopy. The results show that:There are different degrees of erosion on the samples in variety of erosion liquid. The strength of samples in erosion solutions were slightly lower than those in water, and calcium and sulfate ions in samples have a certain degree of precipitation. The erosion of variety of solutions to the samples gradually weakened with the growth of age. Compared with sodium and magnesium salts under the same concentration, magnesium erosion to sulphoaluminate cement is more serious than of sodium. The higher concentration of erosion solutions the stronger erosion to samples, and this law has nothing with the erosion kind; different kinds of solutions have different effect to samples, and this law has nothing with the erosion concentration.In the four erosion solution, the highest 28d strength of sulphoaluminate cement samples was in sodium chloride solution up to 68.8 MPa, the lowest only 49.0 MPa in magnesium chloride solution. In sulfate solution, some sulfate ions jion in the cement hydration process forming the secondary ettringite. Some magnesium ions and chloride ions penetrate into the samples which caused the expansion of the samples. The surfaces of samples in magnesium chloride solution appear obvious cracks. With the concentration of erosion increasing, the dissolution of calcium ion from samples and various ions access to the internal samples rising. The highest strength of samples appeared at 7 days, and reduced from the maximum 90.6 MPa to 78.1 MPa with the increasing of Na2SO4 concentration. The 28 d strength of samples appeared shrinkage phenomenon, especially when the concentrations of sodium sulfate solution large. The samples strength in 10% sodium sulfate solution was down from the 78.1 MPa to 50.9 MPa.Fick's second law is used to the establishment of chloride ion diffusion model. The relationship between chloride concentration at different measuring point and the distance of measuring point to the samples surface meet the exponential relationship. And the order of the diffusion coefficient of chloride is 10-13. We inferred that the life of the concrete structure protected by sulphoaluminate cement is 51.5 years at least based on the model.Self-structural damage of samples caused by sulfate environment meet the Newton's cooling law similarly. We build durability model of sulphoaluminate cement under sulfate environment with the correction factor which come from the sulfate concentration and calcium concentration. We predict the life of sulphoaluminate cement structure is 66.1 years.The strength at any age of sulphoaluminate strontium calcium cement samples is higher than sulphoaluminate cement in any erosion, and growth as the age growth does not retraction like sulphoaluminate cement. Sulphoaluminate strontium calcium cement has better corrosion resistance in water and chloride solution while worse in the magnesium salt solution than sulphoaluminate cement. Sulphoaluminate strontium calcium cement is basically no sulfate ions dissolved in the experiment, and all of sulfate ions in sulfate solution involved in the hydration reaction of samples. The chloride erosion model was bulid with Fick's second law also applies to sulphoaluminate strontium calcium cement, while sulfate erosion model building with Newton's cooling law may not.