Applied Mechanics and Materials Vols. 174-177

Abstract: As a new composite wall system, because of advanced structure, excellent polystyrene insulation board, insulation effect, light weight, the simple and flexible construction method and well adaptability, polystyrene insulation board thin coating of exterior wall thermal insulation technology is widely used in China. In practical applications, thermal bridges and the board surface cracks that caused by improper handling of deformation joints and detailed structure are the main problem of the technology. In this paper, many problems are analyzed such as the crack causes, the plates overlap and the node structure treatment, and also corresponding solutions are proposed.

Abstract: Compressive strengths of recycled aggregate concrete(RAC) with different recycled aggregates(RA) replacement ratios at 7d, 28d, 60d ages are investigated respectively. Failure process and failure mode of RAC are analyzed, influences on compressive strength with same mix ratio and different RA replacement ratios are analyzed, and the reason is investigated in this paper. The experimental results indicate that compressive strength of recycled concrete at 28d age can reach the standard generally, it is feasible to mix concrete with recycled aggregates, compressive strength with 50% replacement ratio is relatively high.

Abstract: The effect of glass powder on strength and microstructure of ultra high performance cement-based materials was investigated in this paper, which aimed to provide an additional option for glass recycling and potentially reduce the high costs of this kind of materials. Compressive strength of pastes and mortars with different glass powder content were tested and their microstructure properties were analyzed by scanning electron microscopy (SEM). Test result showed that the compressive strength rose initially with the increase of the amount of glass powder, and reached to the peak at 20% replacement ratio, then decreased a little. The glass powder in ultra high performance cement-based materials had exhibited pozzolanic reaction and filling effect, contributing substantially to strength increase. In addition, no ASR micro-cracking ring was found around the large glass powder particle due to the enough fineness of glass powder and the existing of silica fume.

Abstract: The existed research shows that when SRC component is under stress, there is bond-slip happened between shape steel and concrete. And the bond-slip have a certain influence on the bearing capacity of SRC component, when component is loaded to ultimate load, the bearing capacity descends quickly because of the effect of bond-slip between shape steel and concrete. Finite method of fiber finite element is a useful way to simulate this kind of composite components, but it ignores the behavior of bond-slip between shape steel and concrete. So building a bond-slip formula for fiber element to simulate SRC component has a practical significance. It’s not only gets more precisely calculated results, but also make the simulation of failure model close to the practical situation. In this paper, in order to add bond-slip effect into fiber element theory, a formula was set up to adjust stress of steel material, which was based on constitutive equations of our bond-slip tests. The method was programmed in OpenSees and used to simulate tests of SRC frame under cycling load, the simulate results shows that the method suggested in this paper is an effective way to express behavior of bond-slip in SRC component.

Abstract: Exterior insulation is currently promoting a building energy-saving insulation technology. Compared with internal insulation, it is a reasonable technique and has its obvious advantages. However, in the insulation material, thermal insulation effect is better, fireproof performance is often worse. Through analyzing several external wall insulation materials’ insulation and fireproof performance, the article recommends a kind of external wall thermal insulation material with good insulation and fireproof performance, to meet the construction needs.

Abstract: In order to provide scientific basis for design and application of cast steel joint, this paper researches on mechanical properties of tubular-plate combined cast steel joint and tubular cast steel joint, which work in International Expo Center in the most unfavorable load condition. Finite Element Method (FEM) is employed to analysis the mechanical properties of the complex cast steel joint and an optimize solution is given. FEM based on large deformation theory and material nonlinearity obtained ultimate load and failure mode of the joints. The results show that, force transmission path of combined cast steel joint is complex for its cross-section shape of branch changes much; stress concentration is very obvious on the branch. In contrast, the force transmission path of tubular cast steel joint is clear and concise; the phenomenon of stress concentration alleviated effectively, the efficiency of material improved greatly; in the same amount of material, the ultimate bearing capacity of tubular cast steel joint increased by 9.5%. The joint design should follow the principle of simple and practical in premise of mechanical requirements.

Abstract: Due to flaws of foamed concrete (e.g. low strength, high shrinkage and easily cracking), a new-type foamed concrete with high-strength and low-shrinkage was prepared using a combination of polypropylene fiber reinforcement and alunite expansive agent compensating shrinkage. Compared to conventional foamed concrete prepared under the same conditions, the modified foamed concrete with the optimal parameters has notable improvements: the 28 d shrinkage falls by 50 %, the compressive strength and flexural strength increase by 21.7 % and 37.5 %, respectively. A model is proposed to explain the mechanism of the co-action of PPF and AEA.

Abstract: Objective:this paper would research the effects of different dosages of admixtures doped to the adobe wall materials' compressive strength, 30min soaking compressive strength loss rate, water resistance, water absorption rate and resistance drying and watering cycle can be modified by cement, stone powder and fly ash three admixtures which are single-doped into the samples. Result: The single-doped cement can enhance the durability of the adobe wall materials obviously. When the dosage of stone powder's single-doped is 0~5%, it can lower the 30min soaking compressive strength loss rate and water absorption rate. When the dosage of it's single-doped is 5~15%,it raises the 30min soaking compressive strength loss rate and water absorption rate. While the dosage of single-doped fly ash is increasing, it could lower the adobe wall materials' compressive strength, but other performance lowers after that first enhances,and the single-doped dosage of 5% is the turning point performance.Conclusion: Three kind of admixtures can modify the adobe wall materials' durability. When the dosage of stone powder and fly ash's single-doped are 5%,the sample's performance of water resistance is best.It meets the demands of the adobe wall materials' durability.

Abstract: Taking bridge pile of Beijing-Shanghai high speed railway as background, this paper studies frost resistance of high performance concrete resistance to chloride ion, including double-doped mineral (fly ash and slag powder) concrete, two minerals and preservative composition concrete. Quick frost method was adopted in the freeze-thaw cycle test, and frost resistance of high performance concrete was assessed by relative dynamic modulus of elasticity and mass loss ratios. Meanwhile, the electric flux values of specimens were measured after freeze-thaw cycles for assessing chloride ion penetration. Test results show: The frost resistance of both C35, C50 double-doped mineral concrete and C35 two minerals and preservative composition concrete is good, and chloride ion permeability is very low after freeze-thaw cycles.

Abstract: For now, the compressive strength of Portland set-cements which have been eroded by formation fluids for many years would decline to some extent. Therefore, we have taken into account that phosphoaluminate cement with better performance has a possibility of applying to cementing engineering. The thickening time of phosphoaluminate cement paste is too short; hence, this article has studied on the influence of several commonly used retarders for Portland cement. The research shows that the same retarder has greatly different effects on Portland cement and phosphoaluminate cement. At 75°C and atmospheric pressure, the thickening times of phosphoaluminate cement slurry with different retarders and various added amounts have been tested. By comparison, we conclude that citric acid has the most efficient retarding effect. In the tested range, the thickening time and added amount of citric acid demonstrate a regular linear relationship. As a hydroxyl acid, citric acid can be used as a retarder for phosphoaluminate cement.