Influence Of Sea Sand On Hydration Behavior And Steel Corrosion Resistance Of Cement Based Materials

In recent years, the infrastructure construction of our country has been developing on a large scale, and concrete materials are used progressively, which induces the shortage of building sand gradually. In the face of this shortage, exploiting and using sea sand is an adjust measure to local conditions in costal region. But it is well known that sea sand contains many harmful components to durability of concrete such as shells and chloride, and if sea sand is directly mixed in concrete mixtures without desalting, problems will be induced, for instance steel corrosion, the most considerable one. To utilize sea sand as fine aggregate, opening out the characteristics of sea sand and the influence of sea sand on properties of concrete must be done as preconditions. Under such a background, the characteristics of sea sand, the influence of sea sand on hydration of cement materials, chloride binding and steel corrosion in sea sand concrete are studied in this thesis. Main contents are listed as follow.1) Combining investigation with experimental research, the characteristics of sea sand, such as shells content, grading, salt content and so on, are discussed. Potential influences of these characteristics on properties of concrete are analyzed, as well as the influential factors of chloride content of sea sand. And it is proposed that chloride ions adsorbed on the surface of sea sand particles can not absolutely dissolve into mixing water after the mixing of concrete.2) By complementary methods like hydration heat releasing testing method, non-contacting resistivity testing method, EIS method, micro-pore structure analysis method and XRD method, the influence of sea sand on hydration behavior of cement based materials is studied. The influences of sea sand on hydration procedure and micro-pore structure of cement based materials are opened out, and the hydration product corresponding to chloride ions is found out.3) By standard methods, water soluble and acid soluble chloride ions contents in mortars are determined, which are used to calculate the binding ratio of chloride ions. In this way, binding ratio of chloride ions in mortars mixed with sea sand is studied compared with that in mortars mixed with salt water; theoretical analysis is carried out to study the influences of carbonation and wet-dry recycling on the inner diffusion of chloride ions concrete mixed with sea sand, and the distribution of chloride ions in concrete mixed with sea sand under complex service condition is obtained.4) Using corrosion testing apparatus, corrosion factors of steel bars embedded in mortars are detected continually. By comparison, the characteristics of corrosion of steels in sea sand mortars are studied. And the threshold value of chloride ions content to induce steel corrosion in sea sand mortar is discussed.5) Linking the binding laws of chloride ions and the rules of steel corrosion, analysis is done to open out the difference of binding rule between chloride ions introduced by sea sand and that introduced by salt water.