Papers by Author: Nai Qian Feng

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: In this paper, the technical problems are discussed, and a couple of countermeasures are proposed. To solve the problems of HPC, such as autogenous-shrinkage caused cracking, cracking caused by swelling, and high plastic viscosity, the key parameters are water content and cement content in mix proportion. Coarse aggregate should comprise of two grades. Such HPC can inhibit autogenous-shrinkage caused cracking, cracking caused by swelling, and lower plastic viscosity and improve pumping performance. Incorporate polypropylene fiber can prevent explosive spalling under high temperature.

Abstract: This paper investigates the effects of vitreous slag powders on the rheological properties of fresh concrete. It was observed that the fluidity of concrete increased noticeably, and the plastic viscosity decreased when vitreous powders were substituted partially for cement. It was demonstrated in the experiments that the fluidity effect of vitreous powders on fresh concrete can be correlated with the vitreous content of the powders.

Abstract: A series of polycarboxylate-type water-reducers (MPCs) had been developed and tested. Through molecular design, macromers of polyethylene glycol unsaturated carboxylic esters, and other derivative of unsaturated vinyl monomer containing the carboxylic groups，sulphonic groups， graft groups of alkyleneglycol was introduced as the chemical structure unit of MPCs. The copolymers MPC-2 contained long and short PEO chains and ionic groups, possessed a high dispersing and good slump retaining behavior. Therefore, MPCs can be used as high range water-reducers to prepare high-flowing concrete, high-strength high performance concrete and high-durability concrete.

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: The mechanism of using mineral admixtures in concrete for suppressing alkali-silica reaction has been studied through analyzing pore solution and observing the surface of aggregates in mortar bars with scanning electron microscope (SEM). The results show that when mineral admixtures are used in the concrete, not only the alkali concentration in the pore solution can be reduced, but also the diffusion of alkali ions from the outside of concrete to the inside can be prevented, and the diffusion of alkali ions from the pore solution to the surface of the aggregates can also be prevented. Thus the attack of alkalis to aggregates is reduced, and the alkali-silica reaction is suppressed.