Applied Mechanics and Materials Vols. 438-439

Abstract: Combining the effect of polypropylene fibers, such as the decrease of cement base material shrinkage and plastic crack, and the increase of material toughness, with the improvement of polymer on the interface between the fiber and matrix, both polypropylene fibers and polymer modifier were used in the cement mortar at the same time to make more excellent cement mortar materials. The improvement for cement mortar from different length of polypropylene fiber, polymer modifier (waterborne epoxy emulsion), mineral powder and silica ash were studied. Results showed that compared with the short fiber, the long fiber has a more obvious effect on the toughness, the best dosage of which is 0.6 kg/m³; the waterborne epoxy emulsion improved the bonding properties of interface between polypropylene fiber and cement mortar matrix, and then, long fibers improved flexural strength of cement mortar greatly, in terms of short fiber, effect is not manifest; With the increase of mineral powder, all the mechanical index of polypropylene fiber reinforced polymer modified cement mortar were improved and the effect of silica ash was better than that of mineral powder, the optimal replacement ratio were 0.1 and 0.3 respectively.

Abstract: Test of basic properties of steel fiber reinforced concrete (SFRC) was carried out to further study the validity of the binary superposition mix proportion method. The strength grades of SFRC were CF40, CF50 and CF60. The key parameters of the study were the fraction of steel fiber by volume, the thickness of cement paste wrapping steel fibers and the water to cement ratio. The workability of fresh SFRC was measured firstly to satisfy the construction requirement. The compressive strength, tensile strength and flexural-tensile strength of SFRC were tested simultaneously. Based on the test data, the changes of above basic properties of SFRC are analyzed in view of the effects of the fraction of steel fiber by volume and the thickness of cement paste wrapping steel fibers. It shows that the optimum thickness of cement past wrapping steel fibers is 0.8mm. The influencing coefficients in formulas for calculating tensile strength and flexural-tensile strength of SFRC specified in the current technical specification are given out.

Abstract: Compared with ordinay concrete, weight of lightweight aggregate concrete could be lower 20%-40% under same bearing capacity. Mixed with some given steel fibers in it, crack resistance and flexural strength will be improved. Once lightweight aggregate concrete mixed with steel fibers meets the requirements of frost resistance, it could be applied to most civil engineerings in a cold area. In this paper, the frost resistance mechanism of steel fiber reinforced lightweight aggregate concrete is introduced. The research status of frost resistance of steel fiber reinforced lightweight aggregate concrete is reviewed including the effects of water cement ratio, aggregate, mineral admixture and amount of fiber, frost resistance experimatal methods and engineering applications etc. Some further researches are prospected.

Abstract: Based on the 9-year-experiment of self-stressing concrete (SSC for short), the stability of self-stress caused by steel bars and steel fibers is investigated. The results show that the losses of self-stress are only from 0.6 MPa to 1.2 MPa during 2.5 years. Meanwhile the matrix of steel fiber reinforced self-stressing concrete (SFRSSC for short) has the characteristic of secondary expansion. Finally, according to the existing theoretical models, formulas of the losses of self-stress created by SFRSSC are obtained.

Abstract: Pervious concrete is one kind of porous concrete which has skeleton structure. In this test the recycled coarse aggregate replacement ratio is 30%, by using recycled coarse aggregate which through high quality processing replaces ordinary coarse aggregate and adding PVA fiber (the mass of PVA fiber respectively are 0%, 0.5%, 1.0% and 1.5% of the cement), the influences of PVA fiber on the strength, effective porosity and permeable coefficient of porous concrete are studied. Besides, the dry shrinkage property and temperature contraction property of porous concrete are discussed. The results can provide the basis for the design and application of the recycled coarse aggregate porous concrete.

Abstract: Experiments were conducted to study the resistance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) to freezing and tharwing. The mix proportions of concrete in strength grade CF40 were designed according to the superposition mix design method, where five mass contents of polypropylene fiber changing in range of 0.3~1.5kg/m³ with 0.3kg/m³ increment while the fraction of steel fiber by volume was constant as 1.0%, and four fractions of steel fiber by volume changing in range of 0.5~2.0% with 0.5% increment while the mass content of polypropylene fiber was kept as 0.9kg/m³. The results show that the steel-polypropylene hybrid fiber can significantly increase the resistance of HFRC to freezing and thawing, the losses of dynamic elasticity modulus and flexural strength of HFRC decrease with the increasing mass content of polypropylene fiber and fraction of steel fiber by volume, there is the coupling effect of enhancing on resistance of HFRC to freezing and thawing by hybrid fibers.

Abstract: Tests were carried out to study the durability of fine aggregate concrete and composite concrete simultaneously provided by the wet-sieving technique for the thermal insulation composite wall as building envelops. The workability of every concrete satisfied the basic requirement of cast quality. The composition analyses of concrete showed that compared with the ordinary concrete, the volume percent of coarse aggregate was increased and the volume percent of cement mortar was decreased due to that the residual coarse aggregate stayed on the sieve was blended with ordinary concrete, which increased the resistances of composite concrete to chloride penetration, water penetration and carbonization. Meanwhile, the resistances of fine aggregate concrete to chloride penetration, water penetration and carbonization were reduced due to the obvious increase of the volume percent of cement mortar.

Abstract: This paper carried out the experimental study on the thermal conductivity of rock in different depth by transient hot-strip method and the analysis on the reliability of the data. The results show that thermal conductivity of pelitic siltstone has been less affected by the varying versus depth of the rock stratum than tuff, but the thermal conductivity of tuff slightly higher than pelitic siltstone.

Abstract: By the heat flow meter method, the thermal conductivity of reinforced concrete was experimental studied for the energy conservation design of reinforced concrete composite wall as building envelop. The steel bars were arranged as horizontal one-way, horizontal two-way and vertical in the reinforced concrete plates with different reinforcement volume ratio. Based on the test results, the effects of arrangement of steel bar and reinforcement volume ratio on thermal conductivity of reinforced concrete were analyzed. It can be concluded that the thermal conductivity of reinforced concrete was higher than that of concrete and increased with the reinforcement volume fraction, the steel bars in horizontal two-way arrangement brought the reinforced concrete with greater thermal conductivity than that in one-way arrangement, the vertical steel bar made the reinforced concrete with significantly higher thermal conductivity. The series-parallel model and parallel-series model are proposed for predicating the thermal conductivity of reinforced concrete with horizontal steel bars.

Abstract: In order to determine the thermal conductivity of the concrete for building reinforced concrete composite wall, the fine-aggregate concrete for the thermal insulation layer and the composite concrete for the reinforced concrete wall were made from the ordinary concrete by in-situ wet-sieving techniques. The compositions of these three kinds of fresh concrete were determined, which expressed by the volume fraction of crushed stone and the volume ratio of crushed stone to mortar. The thermal conductivity of concrete was measured by the one-dimensional steady heat flow meter. Based on the tests, the changes of thermal conductivity of concrete affected by the volume fraction of crushed stone and the volume ratio of crushed stone to mortar were analyzed. The correlation analysis shows that the correlation of the thermal conductivity is better with the volume ratio of crushed stone to mortar. The formula for forecasting the thermal conductivity of concrete is proposed.