Advanced Materials Research Vols. 250-253

Abstract: This paper studies the laws of crystal growth, percent conversion and the rate of reaction of α-calcium sulfate hemihydrate from FGD gypsum under different conditions using the hydrothermal method under atmospheric pressure. The crystal morphology was observed by using SEM, polarizing microscope profile, and percent conversion and the rate of reaction were obtained by assaying crystal water content and calculating. The results showed, (1) with the increase of reaction temperature, the dehydration rate increased and the formed α-calcium sulfate hemihydrate crystal had a larger particle size; (2) with the increase of salt concentration or slurry concentration, the formed α-calcium sulfate hemihydrate crystal was smaller, percent conversion and the rate of reaction was nearly unchanged; (3) with the increase of pH value of solution, the rate of reaction increased and percent conversion was nearly unchanged, and with pH value ranging from 5 to 7 the formed α-calcium sulfate hemihydrate crystal was crassitude. In conclusion, the perfect technological parameters were as follows: reaction temperature ranging from 95°C to 100°C, salt concentration ranging from 15% to 20%, slurry concentration ranging from 15% to 20%, pH value ranging from 5 to 7, and reaction time not exceeding 90min.

Abstract: To protect circumstance and improve of structure durability of Cao’e River floodgate, high volume industrial residue concrete (HVIRC) was prepared, and its mechanical property and durability were studied systematically. 10% of fly ash and 40% of ground granulated blast-furnace slag was used to replace 50% of cement in HVIRC. HVIRC had better anti-carking ability with larger tensile strength, larger ultimate tensile strain, larger tensile-compressive strength ratio and smaller elastic modulus-to-strength ratio. Dry shrinkage rate of HVIRC was similar with that of ordinary Portland concrete (OPC). HVIRC had higher compactness with smaller gas diffusion coefficient and relative permeability coefficient. Expansion caused by alkali-silica reaction reduced greatly by using high volume industrial residue and alkali-silica reaction was controlled markedly. HVIRC had better property of chloride ion penetration resistance with low effective diffusion coefficient. HVIRC could protect steel-bar from premature corrosions. Properties of sulfate resistance and frost resistance of HVIRC were also favorable. It’s proved that high volume industrial residue can enhance greatly mechanical property and durability of concrete and HVIRC can be used in Cao’e River floodgate.

Abstract: Insulation grout of glazed hollow beads is injected into the support structure of high temperature gallery. By this way, thermal insulation structure system is constructed. The paper measures the thermal conductivity of this material and sums up the calculating model and formulas of the heat transfer quantity from surrounding rock to airflow in a gallery. The paper provides the theoretical basis for energy conservation prediction, construction and design of this structure system.

Abstract: This paper suggests that deposition paste area is one of those leading control indicators of mix proportion design for the macroporous ecological concrete without sand. By analyzing the effect of water-cement ratio, amount of cement, and type of coarse aggregates on application properties of concrete, it puts forward that when carrying out the mix proportion design of the concrete, setting the water-cement ratio as 0.4 can help the macroporous ecological concrete without sand acquire satisfying application properties. Based on this idea, experiments to the later period strengths and the erosion resistance property of concretes are tried out. Finally, the result of this series of experiments shows that the macroporous ecological concrete without sand possesses necessary conditions for plants to survive and grow up.

Abstract: Combining with the utilization of waste, an new idea of using the waste to prepare high-strength artificial aggregates was put forward in this paper. The concrete was also prepared by using these aggregates. The demolished concrete could be recovered and used as cement raw meal to produce new cement clinker. In this study, the feasibility of making cement clinker with this kind of demolished concrete was studied. The concrete aggregates composed of steel slag, blast furnace slag, coal gangue and fly ash were prepared. The concrete was prepared using these aggregates with the water-cement ratio of 0.45, 0.50 and 0.55 respectively. The compressive strength of the concrete in 28 days is 52.8MPa, 46.4.2MPa and 42.6MPa, respectively, higher than that of ordinary concrete. In accordance with the ratio of cement raw meal, the cement clinker is produced by adding appropriate limestone, clay and other correction materials. After hydrated for 3 days, 7 days and 28 days, the cement paste compressive strength is 47.1 MPa, 59.8 MPa, 75.6 MPa, respectively, which reach the requirements of ordinary 42.5 Portland cement.

Abstract: Conductive fine flake expanded graphite/polyaniline composites was prepared by emulsion polymerization with sodium dodecyl benzene sulfonate(SDBS) as emulsifying agent, ammonium persulfate as initiator, hydrochloride and fine flakeexpanded graphite as dopants. Effects of hydrochloric acid, dopant, emulsifier and initiator to the conductivity has also been found through orthogonal experiment. The best condition, under which the conductivity is over 2.0S/cm, is 6% doped graphite, 6ml hydrochloric acid, 5.00g emulsifier and 3.25g initiator. It also demonstrates the improvement of the conductivity of polyaniline (PANI) via addition of graphite.

Abstract: Due to the recycling of construction waste, recycled concrete has gradually become a viable material in the construction industry. To study the strength property of the recycled concrete after freeze-thawing experiments, recycled concrete and ordinary concrete were tested for their post-test strength after freeze-thawing for 0, 50, and 100 times. The result shows that the strength of the recycled concrete declined more quickly than that of normal concrete after freeze-thawing. In the paper, the two kinds of concrete underwent permeability test and the two kinds of aggregate underwent mercury intrusion. After the comparison of the inner structure of the concrete and aggregate was obtained, the influence of concrete pore structure on strength after freeze-thawing was further analyzed. The result of the permeability test shows that the porosity of recycled concrete is large when taken as a whole, and the water content is higher after steeping, which reduces the strength of the material. Mercury intrusion results also show that the pore structure of recycled aggregate is poor and that there are more internal micro-cracks. Therefore, in areas with regular freeze-thawing cycles, particularly in humid areas, the use of recycled concrete should be prudently used and handled accordingly.

Abstract: Studies about the resistance of carbonation capability of fly-ash (FA) concrete at different initial curing regimes and exposure time through accelerated carbonation experiments were made. Firstly, 30% replacement ratio fly-ash concrete specimens were fabricated and cured in 20°C, 30°C and 40°C water for 3d, 7d, 14d and 28d respectively, and cured in a standard air environment (20±2°C, relative humidity ≥95% ) for 28d. As a comparison, ordinary Portland concrete (OPC) specimens were also made and cured in 30°C water for 7d, and standard curing for 28d. After the initial curing, all the specimens were taken out and placed indoor natural environment. When specimen age reach 30d, 60d and 120d, 2 weeks accelerated carbonation experiments were made and concrete carbonation depth were measured. In addition to this, hydration degrees of fly ash at different initial curing conditions were measured using the selective dissolve method. Results show that the initial curing conditions play an important role in the carbonation resistance of FA concrete. Initial water curing is beneficial to the development of carbonation resistance of FA and OPC concrete. Prolonging initial curing time and increasing curing temperature is beneficial for the carbonation resistance of FA concrete. For the same curing conditions, carbonation rate of FA concrete is usually higher than OPC concrete, but with the increase of initial curing temperature, the difference can be reduced.

Abstract: This paper analyses the membrane structure’s building material, structural style and its deformability, through which we pointed out that the membrane structure features light-duty and sustainable characteristic. Besides, this article describes the advantage of membrane structure in the area of environment protection and energy-saving from three points of view: acoustic, optical and thermal properties. In addition, development trends of membrane structure in the future constructions as well as the applications in China’s construction development are discussed, leading to the conclusion that the membrane structure, as a kind of light-duty architecture, has great prospects for environment protection and energy-saving applications.

Abstract: The aim of this paper is to investigate effect on hydration activity of steel slag by modifying its mineralogical composition and structure incorporating electric arc furnace steel slag (EAFS) and fly ash (FA) into it at high temperature, and the process was simulated in laboratory that mineral admixtures were added to the melting slag during slag-discharging process. The mineralogical composition, microstructure of both basic oxygen steel slag (BOFS) and modified steel slag (MSS) were identified with XRD and optical microscopy. The results show that after modification, silicate minerals in MSS are decreased in amount with FA being increased; furthermore, silicate minerals in which are increased in amount with C/S molar ratio improvement. Three days cumulative hydration heat of GB_40-1350 is greater than that of BOFS by 1.9 times.