Li Beixing

The mechanical properties of polypropylene fiber reinforced concrete

The compressive, shear strengths and abrasion-erosion resistance as well as flexural properties of two polypropylene fiber reinforced concretes and the comparison with a steel fiber reinforced concrete were reported. The exprimental results show that a low content of polypropylene fiber (0.91 kg/m3 of concrete) slightly decreases the compressive and shear strengths, and appreciably increased the flexural strength, but obviously enhances the toughness index and fracture energy for the concrete with the same mix proportion, consequently it plays a role of anti-cracking and improving toughness in concrete. Moreover, the polypropylene mesh fiber is better than the polypropylene monofilament fiber in improving flexural strength and toughness of concrete, but the two types of polypropylene fibers are inferior to steel fiber. All the polypropylene and steel fibers have no great beneficial effect on the abrasion-erosion resistance of concrete.

Chemical reaction between polyvinyl alcohol and titanate coupling agent with x-ray photoelectron spectroscopy

The chemical reaction between polyvinyl alcohol (PVA) and tri (dioctylpyrophosphoryloxy) isopropyl titanate (NDZ-201) was studied using X-ray photoelectron spectroscopy (XPS). The results show that some C−OH functional groups of PVA react with the titanate coupling agent to form CPVA−O−Ti−O−CPVA bond. The cross-linking of the PVA chains occurs through the formation of CPVA−O−Ti−O−CPVA bonds and produces a three dimensional hydrophobic polymer network. Accordingly, the mechanism is proposed that the titanate coupling agent improves the noisture sensitivity of high alumina cement/polyvinyl alcohol (HAC/PVA) based macro defect free (MDF) composite material.

Preparation of super composite cement with a lower clinker content and a larger amount of industrial wastes

The effects of the grinding mode, fineness, gypsum kinds and dosage, mix proportions on properties of the composite cements consisting of slag, fly ash, limestone and a lower content clinker were investigated, respectively. The results show that when the proportions among slag, fly ash and limestone are appropriate, the grinding technology and system are reasonable, the optimized gypsums and additives are effective, the 52.5R grade cement (52.5R grade cement means a higher strength than 52.5 at early age) can be prepared by clinker dosage of 50% in weight, the 42.5R or 42.5, 32.5 grade composite cement containing 40% and 30% clinker also may be made, respectively. Moreover, the high performance concrete prepared from the above composite cements was studied experimentally.

Analysis of pore structures and their relations with strength of hardened cement paste

Three cement samples were prepared, including OPC consisted of 100wt% portland cement, PFA consisted of 70wt% portland cement and 30wt% fly-ash, and CA consisted of 70wt% portland cement and 30wt% modified fly ash. The strength of hardened cement paste of these samples was tested and their pore structures were determined by a mercury intrusion porosimeter. Moreover, the data of the pore structures of three samples were comprehensively analyzed. The relations between the pore structures and the compressive strength of the three samples were studied. The experimental results show that the relations between the porosity determined by the mercury intrusion porosimeter and the compressive strength are not notable, and the total pore surface area, the average pore diameter and the median pore diameter could be used to explain the difference of the strength of the tested samples.

Optimization of SO3 content in blended cementitious materials

Experimental investigation was conducted on the effects of gypsum types and SO3 content on the fluidity and strengths of different cementitious systems. The experimental results show that influences of gypsum in various cementitious materials are different. For cementitious materials blended with various proportions of slag-fly ash and 5% gypsum content, influences of gypsum and calcined gypsum on the fluidity and flexural/compressive strength are similar. It is revealed that “combination effect” and “synergistic effect” of slag and fly ash play an important role during hydration. For cementitious materials with 45% clinkers, 30% slag, 20% fly ash and 5% limestone, the optimized SO3 contents in gypsum and calcined gypsum are 3.13% and 3.51% respectively and the optimized gypsum content is 6.5%. While both of them are blended, the optimum ratio of gypsum to calcined gypsum is 40%:60% (total gypsum content 6.5%), correspondingly the optimum ratio of SO3 is 19.3%:32. 4%.