Key Engineering Materials Vol. 599

Abstract: According to the vulnerable erosion ability of the ordinary hydraulic concrete, we adopt the method which adding both with superfine slag and super plasticizer to form the high performance concrete.The experiment about concrete erosion was carried out between the high performance concrete and the ordinary hydraulic concrete, the corrosion mechanism was studied respectively from the macro perspective and the micro perspective.From the experiment results we can conclude that the high performance concrete can resistance the sulfate attack which with the SO₄^2- concentration almost reached 20250 mg/L,it has better erosion resistance than the ordinary hydraulic concrete.

Abstract: As chloride ion diffusion in concrete theoretical model without considering the shortcomings of the concrete maturity,the improved maturity model is used to establish the relationship between the diffusion coefficient of concrete maturity. With the mathematical derivation, getting new chloride ion diffusion theoretically, which considers the maturity of the concrete, the chloride ion binding capacity, the degradation effects of chlorine ion diffusion equation,and consequently broadens the scope of the fick's second law of diffusion, besides, its form and solution completely consistent with the one in the second law of fick equation. By the calculation example,it can be found that the model is more accurate than the traditional ones, and it also applies to the high content of high-performance concrete.

Abstract: Mixed sands with different fineness are prepared by mixing iron tailing sand and manufactured sand at different ratio. It is shown that properties of concrete prepared with natural sand whose fineness is 2.3 are worse than that of concreter prepared with mixed sand whose fineness is between 2.6 to 3.0, but are better than that of concrete prepared with mixed sand whose fineness is 2.3. Mixed sand whose fineness is between 2.6 to 3.0 can be used in concrete.

Abstract: This paper gets two inventories of environmental load of two kinds of gypsum plasterboards by studying the production processes of the natural gypsum board and flue gas desulfurization (FGD) gypsum through life cycle assessment. The results show that the total life cycle environment load of the natural gypsum board is 6% higher than the FGD gypsum board. Human toxicity effect increases by 72% and the consumption of non-renewable resources is 76% higher than the total life cycle environment load of natural gypsum board.

Abstract: Steel slag, taking up about 20% of crude steel output in China, has caused many serious problems to environment, such as soil damage, water pollution. Research on the way of effective application of steel slag is always a hot topic. The utilization of steel slag in road construction as coarse aggregate is a promising way. Many researches on the mechanical characteristics of steel slag based HMA have been conducted in laboratory, and the quality indexes of steel slag such as angularity coefficient, dust content can be controlled by artificial way due to small demand for research destination. The lack of effective way to control the quality indexes of steel slag aggregate during processing is one of the main factors that limits its wide use in entity projects. In order to express the significance of quality control in steel slag aggregate production, this paper estimates the effect of different morphology on high-temperature performance of steel slag based HMA. High-temperature performances were carried out by wheel tracking test and permanent deformation test, results were discussed in this research.

Abstract: The formation of ettringite and the expansion associated with it were studied on paste made from Portland cement, two Al-bearing compounds such as calcium aluminate cement and calcium sulphoaluminate cement, and calcium sulfate with different reactivities (anhydrite, α-hemihydrate and gypsum). The hydration process and formation of ettringite in the binders with different content of calcium sulfate was investigated by free expansion testing, isothermal conduction calorimetry, X-ray diffraction (XRD) and environmental scanning electronic microscope (ESEM). Results showed that the reactivity and amount of the calcium sulfate determined the balance between the hydration products of ettringite and monosulfate, and also the early hydration kinetics including the formation content, size and location of ettringite. It was also found that all the ternary systems with higher addition of calcium sulfate expand significantly. When a higher content of α-hemihydrate was added, besides ettringite much secondary gypsum also forms in voids between cement granules, which exerted adverse effects on the properties of ternary systems. However, the formation content of ettringite appeared to have no connection with the expansion value.

Abstract: The effect of modified metakaolin (MMK) on the evaporable water and chemically bound water content of hardened cementitious materials have been investigated. Concrete specimens with 0%, 4%, 7% and 10% of MMK were included. Metakaolin was pre-modified in order to increase the dispersion and contact angle, which might further improve the workability of the concrete. The experimental results showed that both the evaporable water and bound water were increased with the increasing of the MMK content. MMK has a special layered structure. Water can get into the layers through this special layer during the mixing of concrete specimens. Part of MMK with water between the layers didn’t participate in the hydration reaction at the early stage of the hydration, which increased the evaporable water of the cementious materials. The water absorbed in MMK will be released to promote the formation of hydration products and thus the chemically bound water content will increase continuously at the later stages. It also reduced the autogenous shrinkage of the specimens which caused by the decrease of water in capillary pores at low water cement ratio (0.3).

Abstract: Layered double hydroxides (LDHs) materials could be used in cement and concrete for their ions capturing capacity and to enhance durability of concrete. In this work, properties and chloride binding capacity of different types of LDHs were compared, micro-mechanism of chloride binding of LDHs were analyzed and chloride binding of cement paste incorporating LDHs were investigated. The experimental results show that Mg-Al-NO₃ LDHs presents higher chloride ion binding capacity at initial time compared to LDOs calcinated at 500 °C while ion binding capacity of LDHs calms down and LDOs increases with increasing mixing time. Cement paste incorporating LDHs presents higher chloride binding capacity compared with reference sample. All types of LDHs performed beneficial effect on the chloride penetration resistance especially with addition of 1% Mg-Al-NO₃ LDOs.

Abstract: Calcium sulfoaluminate (CSA) cements were currently receiving a lot of attention because their manufacture produced less CO₂ than ordinary Portland cement (OPC). However, it was essential to understand all parameters which might affect the hydration process. This work dealt with the effect of two nanostructured materials, such as nanoSiO₂ (NS) and nanoTiO₂ (NT), on the properties of CSA pastes during early hydration. Isothermal calorimetry, X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were used to analyze the pastes. Results indicated that the influence of NS and NT on the early hydration of CSA showed different: when NS and NT were added by 5% (mass fraction), the early hydration of CSA cement can be significantly promoted by NS, and slightly accelerated by NT. X-ray diffraction and SEM analysis results showed that both of NS and NT can improve the microstructure of the cement pastes, which made the cement stone more uniform and dense. For the difference, during cement hydration, except for nucleation function, NS had a high pozzolanic activity. Whereas,the effect of NT on microstructure of hardened CSA-cement was mainly due to its seeding effect.