Key Engineering Materials Vols. 405-406

Abstract: This paper presents the whole procedures that should be followed when carrying out the simulation analysis on the damage by fire to high-performance concrete (HPC). The whole procedures consist of temperature field determination, mechanical analysis, identification of damage to HPC related to thermal and mechanical behavior, structural behavior simulation and cooling stage simulation analysis. That the first two parts are essential to the whole analysis has been pointed out. The present simulation analysis situation is analyzed as well.

Abstract: In this paper, the influence of polypropylene fibers (PPF) and silica fume (SF) on chloride penetration of high performance concrete (HPC) containing fly ash (FA) was examined. Three different HPC in which the amount of ordinary Portland cement is 360 kg/m3, via., A concrete with 120 kg/m3 of FA, B concrete with 0.9 kg/m3 of PPF and 120 kg/m3 of FA, C concrete with 0.9 kg/m3 of PPF and 96 kg/m3 of FA and 24 kg/m3 of SF were used for the study. Chloride resistance of concrete was evaluated. From the tests, it is found that the incorporation of PPF and no SF has less influence on the chloride resistance of the fly ash concrete at the age of 28 days. SEM examines B and C concretes specimens illustrating that just incorporating PPF induced more porous fiber-matrix interfacial zone (FMIZ) in B concrete which is detrimental to the chloride resistance, but the microstructures of both the matrix and FMIZ in C concrete with PPF and SF are denser. The plastic shrinkage cracking test proves that the cracking areas on the surface of B and C concrete with PPF are 12.2% and 20.7% of A concrete without PPF respectively.

Abstract: In order to investigate the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of the corroded beams, the flexural behaviors of corroded RC beams strengthened with AFRP sheets under different degrees of corrosion (minor: reinforcement mass loss is 2.0％, medium: reinforcement mass loss is 6.0％) are researched experimentally in this paper, and compared with that of the control beams (un-corroded) and un-strengthened corroded beams. The results show that，compared with un-strengthened corroded beams under same degrees of corrosion, the cracking load, yield load and ultimate load of minor corroded RC beam strengthened with AFRP sheets is respectively increased by 20%, 27% and 60%, and increased by 15%, 36% and 83% for medium corroded RC beam strengthened with AFRP sheets respectively; The ultimate deflection of the medium corroded beam strengthened with AFRP sheets is 166% larger than that of corroded un-strengthened beam. AFRP sheets can improve significantly the bearing capacity and deformation for corroded RC beams.

Abstract: Through accelerating the hydration by heighening the curing temperature, the effect of the hydration of the unreacted cement in the hardened mortar with low W/C on the long-term strength was investigated. The results show that in the hardened mortar with low W/C, there exists a lot of unreacted cement at the age of 28 days, and when these cement particles hydrate again at the long age, it is disadvantageous to the long-term strength of the mortar. Moreover, the lower the W/C, the lower the hydration degree at the earlier age, and the more disadvantageous to the development of strength at the long age.

Abstract: The strengthening effect of phosphorus slag powder (PSP) in cement-based materials was researched by model of strengthening effect of mineral admixes, and the mechanism of strengthening effect of PSP was also studied by SEM. The results indicate that, in early hydration period, the strengthening effect of PSP on strength of cement mortars is zero. At 90 days, strengthening effect has been exerted, and increases with the amount of PSP when that is no more than 40%, but decreases with larger content of PSP. At 180 days, the strengthening effect was further enhanced, the greater the amount of PSP, the greater its effect. For compressive strength of cement mortars, the strengthening effect of PSP is more than that of PSP on flexural strength. The results analyses of SEM show that, strengthening effect of PSP mainly come from its pozzolana reaction. With double excitation of cement hydration product hydroxide and gypsum, the low alkalinity C-S-H was produced.

Abstract: This paper investigated a new type of admixture which can be used to enhance the resistance of concrete surface to deicing salt deteriorating. Physical and mechanical properties of concrete incorporating this salt-scaling resistant admixture were measured. Practical application on site has proved that this admixture is effective for concrete to resist salt-scaling action.

Abstract: Through the experiment, this paper carries on the appraisal to the cracking risk of cross-sea bridge concrete. Analyzed the influence of active admixture, sand ratio, cement content and water-cement ratio to the cracked degree of concrete. And proposed control measure of the plastic shrinkage cracking of concrete. Finally, through research to the concrete used in pile cap of the Shanghai Yangtze River Bridge, it obtains that all can be allowed to reduce the cracking risk of concrete by reducing active admixture, increasing to fly ash amount, reducing sand ratio, the slag powder has little effect the cracking risk of concrete, the silica fume can increase the cracking risk of concrete.

Abstract: This paper reports the experimental study on the mechanical characteristics of bending component with ground granulated blastfurnace slag (ggbs). A laboratory study has carried out to investigate the influence of replacement ratio of GGBS on the mechanics and deformation of concrete bending specimen; the harmonious working of concrete and reinforced bar is discussed as well. The results indicate that although the proportion of slag improve the strength of the concrete, the mechanical performance of GGBS concrete bending specimen is quite similar to that of common concrete, and the design expressions of common concrete girder is available to GGBS concrete girder. The specimen experiment also proves the existance of optimum slag proportion in GGBS concrete specimen, and the girder performs well when replace 20% cement with slag.

Abstract: Inorganic salts are important admixtures usually used in cold weather concrete. As research basic of influence of salts on concrete durability, effects of inorganic salts on pore structure of cement paste were studied in this paper, and possible implications of concrete property with pore structure was also analyzed. Pore structure of paste added CaCl2, NaCl, Na2SO4, NaNO2, Ca(NO3)2 and Ca(NO2)2 curing for 3 days and 28 days were tested through mercury intrusion porosimetry (MIP). The results showed that no matter 0.3 or 0.5 water-cement ratio, the pores whose diameter <50nm in paste with salts increased at 3 days, which was harmful for the control of concrete shrinkage and cracking at early age. Adding Ca (NO3)2 increased coarse pores (>200nm) of paste at 3 days, but these coarse pores turned into fine pores and reduced significantly at 28 days. Adding NaCl and Na2SO4 into cement paste raised coarse pores with size>1000nm at 3 days and 28days, which were harmful for the pore structure.