Papers by Author: Quan Lin Niu

Abstract: Material composition, mix proportion and physical properties of a low carbon cement with 90% of industrial refuse, properties of the cement was measured according to chinese national standard GB1346-2001 and GB175-2008. It is seen that the cement had good soundness, long setting time, low water requirement for standard consistency, good initial fluidity and high final strength as well, the properties are beneficial for the construction of highway engineering, underwater engineering and large volume concrete engineering.

Abstract: Two kinds of the representative artifactitious aggregates, namely the calcium-base and silicon-base, were chosen in the experimental study. Through analysis of SEM, it was found that the former’s main chemical component is calcium carbonate with a structure of crystal granules, the later might be a rock of silicon-base in a state of sandwich. Through experiments of the paste fluidity, ZETA potential and concrete test with different water-reducers, it was shown that the calcium-base aggregate, which could be easily used to prepare high workability and high strength concrete with the polycarboxylic water-reducer, bears a lower water-sobbing ability and has a well adaptability with any water-reducer, and that the silicon-base aggregate, a higher water-sobbing ability, a higher ZETA potential value of its powders, a bad adaptability that there might be a problem of producing HPC though using the high property polycarboxylic water-reducer.

Abstract: Charge passed of mortars with different aggregate volume fractions was tested according to ASTM C1202, and the differential expression of the Ohm law was introduced to explain the relationship between charge passed data and aggregate fractions.Cl- penetration depth of the corresponding mortars and concretes was measured to illustrate the influence of the aggregate volume fraction on their chloride permeability. It was shown that the charge passed of mortar was negatively correlated with aggregate volume fractions, and high aggregate fraction bearing concrete with low charge passed did not necessarily mean low permeability. As a result, the influence of aggregate fraction on charge passed should be taken into consideration when charge passed data was employed to evaluate Cl- permeability of concrete.

Abstract: Corrosion resistance coefficient of mortars incorporating different mineral admixtures were tested according to GB2420, and the expansion ratio of mortar bar immersed in 5% Na2SO4 solution was measured according to ASTM C1012. It is shown that all the mineral admixtures, including ground granulated blast furnace slag (SL) fly ash (FA), natural zeolite (NZ) and metakaolin (MK) were effective in decreasing the 15-week expansion and increasing the corrosion resistance coefficient of the specimens immersed in Na2SO4 solution as well.

Abstract: Concrete conductivity is the reflection of the micro pore structure and the pore solution conductivity of concrete, but the conductivity of pore solution changes considerably as different mineral admixtures are added, though the change is not always relevant to permeability and Cl- diffusivity. Saturation of concrete capillary pore system with 1 mol/l KOH solution through vacuum processing was tempted to maintain the pore solution conductivity constant, after which the concrete conductivity was a reflection of concrete porosity and tortuousity that closely related to Cl- diffusivity. Charge passed of concrete was also measured for comparison. It is shown that the conductivity of alkali saturated concrete without mineral admixtures was the biggest, followed by the concrete with natural zeolite（20％）, fly ash（30％）, slag（40％）metakaolin 20% and 10% of silica fume.

Abstract: Absorption and d esorption of super plasticizer by zeoltie were investigated, and zeolite superplasticizer with zeolite as carrier was produced. The addition of zeolite superplasticizer in cement and concrete increases the paste fluidity and concrete slump, while the loss of fluidity and slump are effectively controlled.

Abstract: A slow-release type carboxylic polymer(SLPC) is synthesized with the monomer mixture at a certain Molecule ratio of methacrylic acid, methoxy polyethylene glycol methacrylate and polyethylene glycol di-methacrylate. Test results of the fluidity, Zeta potential and adsorption in cement paste show that the polymer SLPC has the remarkable anti-adsorbing and high fluid-retaining ability for enhancing fluidity of cement paste as time elapsed, concrete experimental results indicated that it could be used to substitute 30～50% polycarboxylic type water-reducer in the same quality for preparing high workability concrete and controlling its slump loss.

Abstract: Mineral powders play positive role in improving the durability of concrete subjected to alkaline and saline corrosion, where sulphate ion and chloride ion coexisted may cause serious deterioration to the reinforced concrete structures. Metakaolin, slag, fly ash and natural zeolite mixed in appropriate proportion were tested in inhibiting the deterioration. It is found that the composite powder might decreased AAR and the charge passed of concrete effectively，the while the 7d and 28d strength of cement and concrete are improved as well.

Abstract: Sulphate ion and chloride ion existed in the alkaline saline soils may cause serious problems on the durability of reinforced concrete structures, while it is found that superfine mineral powder plays positive role in the precaution of the alkaline saline corrosion. A composite cement named high performance cement (H.P.C) composed of clinker, metakaolin and fly ash powder in appropriate proportions is developed with good performance in preventing concrete from alkaline saline soil corrosion. Mortar bar test and visual examination showed that the cement could effectively control AAR and sulphate ion related expansion, and the charge passed tested according to ASTM C1202 was decreased to “negligible” level for concrete with W/B ratio of 0.3, and “very low” grade for concrete with W/B ratio of 0.45 and 0.55 when the high performance cement was used. Other properties such as low hydration heat and anti-freezing properties, as well as the uniformity of the fresh concrete (with no bleeding and segregation), made it an important material in the construction of concrete structure in alkaline saline soils.

Abstract: ASTM C1012 and GB2420 method were employed to evaluate the inhibiting effect of different mineral admixtures on sulfate attack of cement mortar, and the mass loss of mortar specimens after drying-wetting cycles was measured for comparison. It is shown that all the mineral admixtures, including ground blast furnace slag (SL), fly ash (FA), natural zeolite (NZ) and metakaolin (MK) were effective in decreasing the 15-week expansion and increasing the corrosion resistance coefficient of the specimens immersed in Na2SO4 solution. The wetting and drying test however, showed inconsistent result, as both physical and chemical attack may soon occur due to quick accumulation of sulfate by capillary absorption instead of diffusion mechanism.