Applied Mechanics and Materials Vols. 204-208

Abstract: Abstract. This investigation was done based on the concrete filled steel tube (CFST) winter construction of Ganhaizi Bridge. Steel fiber reinforced micro-expansive concrete (SREC) with high frost-resistance ability, excellent fluidity and good self-compacting ability was prepared. Strength development mode under low temperature was illustrated. Scanning electron microscope (SEM) was used to analyze the morphology features of hydration products at the age of 28 days. It was confirmed that when the content of sodium nitrite was 0.4%, SREC did not frost under -5°C. In addition, SEM showed that ettringite and CSH gels were in good growth state, and concrete structure was very dense. Furthermore, 6 CFST short columns were poured in the winter construction site of Ganhaizi Bridge, and another 27 short columns were cut from emitting slurry pipe filling with concrete emitted from main girder. The bearing capacity of all the CFST specimens was tested when the environment temperature rose to about 25°C. The experimental results indicated that the mechanical performances of CFST specimens with anti-freezing admixture did not exhibit degradation when cast in site under a low temperature and tested at 24.3°C. The concrete presented in this research substantially met the need of Ganhaizi Bridge CFST construction in winter.

Abstract: The compressive and flexural strength of ordinary mortar and fiber reinforced mortar with five different pp fiber content were tested in this paper. The results show that the compressive strength reduced gradually with PP fiber increasing, and the flexural strength increased when the fiber volume fraction is no more than 0.12%. The higher water ratio can weaken the cohesiveness of the fiber and cement material, and the influence of polypropylene fiber on the flexural strength of mortar decreased after soaking. The major strength damage in the process of curing is caused in the early age and appropriate amount of fiber is beneficial to reduce strength damage.

Abstract: Considering the damage that composite material under loading may occur, acoustic emission (AE) technique is adopted to perform non-destructive evaluation (NDE). In order to obtain the acoustic emission emitted from the composite material, a novel fiber optic AE sensor which is based on single mode fiber optical fused-tapered coupler design is developed. Futhermore, its fabrication process was described and performance was studied. Results of a pencil break test on the composite laminate show that the fiber optic AE sensor have better frequency response than the commercial piezoelectric sensor. During a tension experiment of a carbon fiber composite specimen , the fiber optic sensor which was mounted on it detected the enormous acoustic emission signals. To analyze their characteristic parameter, such as amplitude, duration, can identify the type of failure to composite materials, including Matrix cracking , Interface stripping, fiber breakage. Experimental results would offer the reference to damage identification to complicate composite structures.

Abstract: As a part of a large research program aiming at the cementitious materials containing recycled materials at Central Queensland University – Australia, the current paper presents the preliminary results of a study on the effects of fly ash, which is used to replace cement in concrete, on the concrete compressive strength. For this purpose, systematic experiments have been carried out to investigate the influences of fly ash ratio and age. The compressive strength of concrete specimens with replacement ratios of 15%, 30% and 45%, and aged 7 and 28 days are measured and are compared with those of the concrete specimens without fly ash at the same ages. The results demonstrate that the strength of fly ash containing concrete improves more slowly but more strongly with aging, than their fly ash free counterparts, and an optimum fly ash replacement ratio exists where the maximum compressive strength of fly ash containing concrete can be achieved, and the maximum strength for the specimens aged 28 days and above is higher that of fly ash free concrete. Furthermore, the observation strength behaviours are analysed and discussed in terms of the influences of fly ash on interface reactions and interface bonding strength.

Abstract: Functions of the wall and some of wall materials are introduced. Basalt filaments possess excellent properties with high strength, high temperature resistance, corrosion resistance, small hygroscopicity, small thermal conductivity and high sound absorption coefficient. High performance basalt fabrics can be gelatinized into compound cementitious materials with cement or gypsum. The performance of basalt compound boards mainly rely on the performance of basalt filaments. So basalt compound boards possess excellent characteristics with light-weight, high strength, fire prevention, sound insulation and heat preservation. It is green initiative and easy construction as new wall materials. Basalt compound cementitious materials possess good application prospect in the wall materials along with the development of production technology.

Abstract: The shape memory alloys (SMAs) have received increasing interest attributed to their unique superelastic effect and the shape memory effect. The existing models of superelastic SMAs are generally complex for practical use. In this paper, cyclic loading tests of superelastic SMA wires are first performed. Based on the experiments, a simple constitutive model is set up. Simulations testify that the model can approximately describe the hysteretic characteristics of the superelastic SMA and the simulated mechanical parameters agree well with the experimental values.

Abstract: This study investigates the tensile response of reinforced ultra high strength strain- hardening cement composite (UHS-SHCC) ties in directly monotonic and cyclic tension. The UHS-SHCC exhibits valuable material properties such as high compressive strength, tensile strain-hardening and ductility. However, UHS-SHCC requires high volume of cement, which leads to more shrinkage than conventional concrete. Authors have considered replacing a part of cement by the expansive admixture (EXA) for compensating the shrinkage of UHS-SHCC. Specifically, this paper explores the structural application of a shrinkage-compensating UHS-SHCC to improve tension stiffening in structural members. The cement composite type and EXA replacement were taken as experimental parameters. All specimens had a square cross-section dimension of 100 x 100mm and length of 1,500mm. The test results indicate that the shrinkage compensating UHS-SHCC is very effective to improve tension stiffening behavior and initial crack load of reinforced cement composite ties.

Abstract: The effect of heat-curing procedure on strength of reactive powder concrete (RPC) having high volume of mineral admixtures, such as ultra-fine fly ash (UFFA), steel slag powder (SS) and silica fume (SF) was studied in this paper. Moreover, the effect of the cuing temperature (20°C, 60°C and 90°C) and the duration (1 day and 3 days) of heat-curing both on microstructure of RPCs’ samples were investigated by SEM-EDXA. The results indicate that the heat-curing procedure has a great influence on strength of this RPC; the compressive strength of specimens cured in a appropriate condition could achieve more than 190 MPa. Moreover, a high curing temperature or a long duration of heat-curing will cause not only a high degree of pozzolanic reaction but also a low n(Ca)/n(Si) ratio of hydration product. Thus, the microstructure of the paste becomes more compact, which would definitely improve the mechanic properties of the hardened paste.

Abstract: In this paper, flame-retardant fiberboard was prepared by blend mastication and hot-pressing method, using abandoned glass fiber and polypropylene as raw materials and magnesium hydroxide as flame-retardant reagent. The optimized processing conditions were concluded through orthogonal experiment and the range analysis: magnesium hydroxide mass fraction 25% , polypropylene mass fraction 70% , hot-pressing temperature 180, hot-pressing pressure 10 Mpa. Under these conditions, properties of fiberboard were as follow: tensile strength 20.55 Mpa , bending strength 30.98 Mpa , impact strength 3.65 Mpa , limiting oxygen index 28.2%.

Abstract: The ultrafine fibers based on the composites of polyethylene glycol(PEG) and polyvinylpyrrolidone(PVP) were prepared successfully via electrospinning as phase change materials. The thermal properties and morphology of the composite fibers were studied by differential scanning calorimetry(DSC) and scanning electron microscopy(SEM), respectively.