Advanced Materials Research Vols. 306-307

Abstract: The influences of saline waterproof agent composed of carboxylic acid sodium (RCOONa), Al₂(SO₄)₃, K₂SO₄ on the hydration of semi-hydrated gypsum were investigated. The results showed: (1) with the concentration of K₂SO₄ increasing, the ζ potential rose due to the increasing K⁺ entering the electric double layer of gypsum; (2) with the concentration of Al₂(SO₄)₃ heightening, the ζ potential gradually decreased as a result of the formed AFt phase during the hydration process and the increasing Al³⁺ entering the electric double layer of gypsum. The ζ potential rose because the RCOO^- base groups adhered to the surface of gypsum crystal, which slowed down the growth rate of the gypsum crystal in direction c, and short hexahedron poles were produced.

Abstract: The effect of VAE latex modification on the physical properties of cement mortar is investigated. The porosity problem in cement mortar modified by vinyl acetate ester-ethylene (VAE) copolymer emulsion was successfully resolved by reasonable defoaming technique. It is shown that the bond strength and water resistance properties of modified cement mortar are better than unmodified cement mortar. When polymer-cement ratios ranged from 0 to 0.25, the bond strength and anti-permeability increased first and then decreased. The best value appeared at 0.1(polymer-cement ratio). SEM shows that the modified sample has compacted structure, polymeric films wrap the cement body and fill in the gap between cement and sand to improve the interfacial bond.

Abstract: Experiments on adiabatic temperature rise are systematically carried out in this paper, the characteristics of adiabatic temperature rise of concrete with different mineral admixtures are compared. The influence of binder amount, water-binder ratio, placing temperature and superplasticizer is also studied. The results reflect that binder is the main factor affecting adiabatic temperature rise, mineral admixtures such as fly ash can significantly reduce the rate and amount of heat development, large quantity substitution of slag in concrete can relieve the concentrative heat liberation, the retarded superplasticizer can prolong the exothermic process effectively and high placing temperature has adverse effect on temperature control of mass concrete.

Abstract: The influence of polymer coating on the shrinkage of cement-based materials is comparatively analyzed in this paper. First of all, the relationship between cement-based materials shrinkage and water loss is discussed. Furthermore, some surface topography differences and pore structure changes of cement-based materials causing by polymer coating are investigated. At last, the affecting mechanism of polymer coating on reducing cement-based materials shrinkage is investigated. The results show that polymer coating can significantly reduce the shrinkage of cement-based materials. A more thick coating gets a higher shrinkage reducing ratio. There is a close relationship between cement-based materials water loss ratio and shrinkage ratio. Polymer coating can make the micro-crack on cement-based materials surface disappear. The cement-based materials coated with polymer have a lower surface layer cumulative average porosity than blank control group. The evaporation of capillary water and the development of negative capillary pressure in cement-based materials are controlled by polymer coating, thus the shrinkage becomes small.

Abstract: Based on the experiments on 4 specimens with the dimension of 700mm×700mm and different thickness, the failure mode and anti-crack performance of the steel fiber reinforced high strength concrete four-pile cap was studied. The results show that the steel fiber mixed in high strength concrete in four-pile cap enhances its cracking load, limits the propagation of crack obviously and raises the ductility greatly. It also indicates that the ultimate load-carrying capacity of four-pile cap can be improved significantly with the increase of effective thickness.

Abstract: Gypsum and vesicant were used to manufacture foamed gypsum by physical foaming. The effect of different components of vesicant on the properties of bubbles and gypsum slurry were confirmed in the experiments. The changes of dry bulk density and thermal conductivity of foamed gypsum were studied in the conditions of adding bubbles. The results showed that the comprehensive performance was better when adding150ml bubble to 300g gypsum, compared with blank sample, the dry bulk density and thermal conductivity of the samples decreased by 38%, 36% respectively, the dry bulk density was 812 Kg/m³ and the thermal conductivity was 0.18 W/m•K.

Abstract: Effect of different blending amount of LaCrO₃, a composite additive, on the hydration resistance and crystallization properties of magnesia-calcium refractory were studied by measuring hydration rate, using X-ray diffraction and scanning electron microscopy. The results show that the LaCrO₃ at a low addition (≤1%) can significantly decrease the hydration resistance of the MgO-CaO material when the burning temperature is 1550°C, and the hydration rate is only 0.183%. LaCrO₃ can promote the growth of the CaO, while it has little effect on MgO. The Cr₂O₃ and CaO can melt into CaO·Cr₂O₃ in a high temperature. The CaO·Cr₂O₃ can not only promote sintering but also wrap on the CaO, which is negative for the grain to contact with water, and consequently improve the hydration resistance of magnesia-calcium refractory.

Abstract: Concrete lining is commonly used in large channel project to fixup soil slope and prevent channel seepage. Concrete lining is a type of thin plates structure which should have the high compression strength, crack resistance and durability. Two new high performance concrete (HPC) are used in lining project of south main channel of Yellow River-crossing project in east-route of the South-to-North Water Diversion Project. One is flyash HPC with manufactured-sand and the other is HPC with cementitious capillary crystalline waterproofing material (CCCW); meanwhile, the mix proportion of flyash HPC with manufactured-sand and HPC with CCCW are recommended. For flyash HPC with manufactured-sand, the recommendatory water-binder ratio is 0.4 and the recommendatory flyash content is 30%. For HPC with CCCW, the recommendatory water-binder ratio is 0.48 and the recommendatory CCCW content is 1.5%.With the wide application of new HPC, the compression strength, crack resistance and durability of lining concrete are improved, channel seepage discharge is reduced and a large amount of natural building materials are saved.

Abstract: Viscosity modifying admixtures (VMA), known as an important component, are water-soluble polymers that can increase the viscosity and cohesion of self-compacting concrete( SCC). This article presents the effect of four different types of VMA on the workability of SCC , which including flowability, filling ability, passing ability and segregation resistance ability of the fresh concrete. The results show that the low viscosity of VMA satisfies the workability requirement of fresh properties of SCC.

Abstract: In order to decrease the disadvantageous effect of ultraviolet light to asphalt, nano-scaled TiO₂ was selected as modifier to modify asphalt. The photooxidation properties of the modified asphalt were examined in a home-made ultraviolet radiation environment box. By comparing the before and after performance indexes of asphalt, the anti-photooxidation aging property of modified asphalt and the blank asphalt were studied. And the results showed that the sample of 5% TiO₂ modified asphalt possesses more stable ductility and smaller softening point changing ratio.TiO₂ doping can actively enhance the photooxidation properties of asphalt and TiO₂ modified asphalt is capable of resisting photooxidation aging.