Papers by Author: Tie Jun Zhao

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Authors: Xiao Mei Wan, F.H. Wittmann, Tie Jun Zhao, Fu Xiang Jiang
Abstract: Reinforced concrete structures may be exposed to an aggressive environment. In this case combined mechanical and environmental actions may act simultaneously and their synergetic influences have to be taken into consideration. In this contribution results of tests on two different types of concrete and mortars are presented and discussed. Capillary absorption of not carbonated and carbonated concrete has been determined. The influence of mechanical load on capillary suction has been studied separately. A moderate compressive load reduces the coefficient of capillary suction, while capillary suction is enhanced by higher mechanical loads as micro-cracks are formed. Chloride diffusion has been measured by means of the diffusion cell test. The diffusion coefficient observed in carbonated concrete is roughly speaking one order of magnitude higher than the value measured on not carbonated concrete.
Authors: Wei Qun Cao, Li Tian, Tie Jun Zhao
Abstract: Strain-hardening cement-based composites (SHCC) resist increased tensile stress after first crack formation, over a significant range of tensile strain. This increased strength and strain capacity is achieved by effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether the crack width limitation translates into increased durability through retardation of ingress of moisture, gas and other deleterious matter, is scrutinised in this paper. The potential of the comparatively new composite material becomes obvious, yet it is clearly outlined that further research is necessary before we fully understand the basic mechanisms underlying durability of SHCC.
Authors: Xin Yuan Zhang, Shao Chun Li, Tie Jun Zhao, Zu Quan Jin
Abstract: In this study, octyl-triethoxysilane emulsion was prepared using octyl-triethoxysilane monomer. The protective effect of the silane monomer and emulsion was investigated on the concrete with different water to cement ratios (0.4 and 0.5). The results showed that octyl-triethoxysilane emulsion displayed efficient protection of concrete. Octyl-triethoxysilane emulsion acquired excellent penetration depth (> 3.7 mm), the water absorption coefficient was reduced by 83.4%, and the chloride ion diffusion coefficient was only 1.8 × 1012 m2 s1, reduced by 71.3%. The emulsion also showed good resistance to carbonization and freezing-thawing. The carbonation depth of concrete was reduced by 42%, while the silane monomer has little effect on carbonization. Good protection performance was obtained in the freezing-thawing cycle tests. The relative dynamic elastic modulus was increased by 27%; the mass loss was reduced by 49% after 300 cycles. The protective effect of silane emulsion was also related with the water cement ratio of concrete and the test method. Silane monomer had good waterproof effect and chloride resistance, but poor resistance to carbonization and freezing-thawing. Silane emulsion was a better choice for concrete protection, for it displayed lower rate of volatilization, insignificant toxicity, and better retainment of the active ingredient.
Authors: Li Tian, Jing Ru Chen, Tie Jun Zhao, Zhu Ding
Abstract: The high brittleness of cement-based materials is the dominant reason that causes cracking, corrosion, and even losing the load bearing capacity of the structure. PVA fiber reinforced Strain-hardening Cement-based Materials (SHCC) which is characterized by strain-hardening and multi-micro cracking significantly improves the mechanics performance of cement-based materials. In this paper, 3-point-bending and direct tensile tests were conducted to contrast influence of the material mechanics on SHCC by aggregate gradation. Tests results demonstrate that appropriate particle gradation may improve the strain hardening section in the stress-strain curve. Therefore, the maximum diameter of aggregate can be enlarged from 110μm to 1.25mm. Comparatively large aggregate will be convenient for such materials in the practical application and popularization.
Authors: Rui Xue Wu, Tie Jun Zhao, Li Tian, Wan Ma
Abstract: As a new type of building materials, performance of SHCC admixed with silica fume and that exposed to different temperatures are of concern. Uniaxial tension test is conducted on specimens that with and without silica fume admixture, after being exposed to 6 different temperatures (20°C, 50°C, 100°C, 150°C, 200°C and 300°C) for 2 hours. The results show that the ultimate tensile strain of SHCC decreases along with the increase of temperature. However, the ultimate tensile strain remains above 1.2% when the temperature is less than 200°C. Incorporating silica fume into SHCC design indicates that the use of silica fume does not have much effect on the ultimate tensile strain of SHCC, but significantly improves the first cracking strength and ultimate strength of the material.
Authors: Chun Hong Hu, Tie Jun Zhao, Tao Rong
Abstract: Strain Hardening Cementitious Composites (SHCC) varied with mixture proportion was preparated with normal engineering materials in our area, tensile performance of dumbbell specimens under uniaxial tensile load was experimentally investigated in this paper, and tensile stress versus strain curves as well as crack development of SHCC with different mixture proportion were obtained. The results showed that all specimens had strain-hardening and multiple-cracking characteristics obviously, among them, ultimate tensile strain of No.A and C series could exceed 3%. SHCC with excellent stable tensile performance was preparated based on normal river sand but not quartz sand, which can reduce project cost and promote the application and development of SHCC in practical engineering.
Authors: Peng Zhang, Tie Jun Zhao, F.H. Wittmann, Shao Chun Li
Abstract: Polymers are often applied in concrete for multiple purposes and aims. For instance, surface impregnation of concrete with silanes is a reliable technology to protect cement-based materials from ingress of aggressive solutions into the materials. An alternative method is to add silane emulsion into fresh concrete or mortar to produce integral water repellent materials. In this contribution integral water repellent concrete was prepared by adding 1 %, 2 %, 3 %, 4 % and 6 % of silane emulsion. The influence of silane emulsion on the compressive strength, porosity and pore size distribution, water capillary suction and chloride penetration have been investigated. The results indicate that addition of silane emulsion moderately reduced compressive strength of concrete. With 3 % of silane emulsion the reduction is about 10 %. The addition of silane emulsion hardly has influence on pore size distribution. Silane does not block the capillary pores, but only forms a hydrophobic film on the walls of capillary pores. Addition of silane emulsion reduces water capillary suction significantly. The reduction rate is higher than 89 %. Even the surface of integral water repellent concrete is abraded off 7 mm, the material still demonstrates high water repellency because the entire volume is hydrophobic. In addition, chloride penetration also can be reduced substantially.
Authors: Shao Chun Li, Peng Zhang, Tie Jun Zhao, Zu Quan Jin, Song Gao
Abstract: In this paper, the gel-tape-casting process was applied to manufacture multilayer green sheets of SiCw /Al2O3 composite. The influence of SiCw, ball milling time and solids loading on the rheological behaviors of SiCw/Al2O3 slurries were investigated. It was found that the slurries exhibited a shear thinning behavior. The viscosity of the slurry increased with increasing of the fraction of SiCw. A stable slurry with 40 vol.% solids loading was prepared when 20 vol.% of SiCw was added. The flexural strength of the green sheet showed a trend of increasing firstly and then decreasing with SiCw increasing. The optimal mechanical properties of 40.2 MPa for flexural strength was obtained when SiCw contents was 20 vol.%. SEM observation indicated that significant whisker alignment was present in the composite tape, which was considered as one of parameters affecting toughening process.
Authors: Xiao Mei Wan, Wei Qun Cao, Tie Jun Zhao, Hong Fan
Abstract: A carbonation model of reinforced concrete structures subjected to mechanical load based on experimental work is proposed in the paper. Correspondingly, a series of reliability analysis and service life prediction is carried out and reasonable results are acquired. Besides the effect of concrete cover, it indicates that mechanical load impacts the reliability and service life of the reinforced concrete structures significantly through example calculation. In the case of concrete cover of 40mm, the service life is shortened nearly half under a tensile load of 60% while the service life is lengthened 30% under a compressive load of 30%. In service life design or long term performance assessment, more work should be done with the consideration of the mechanical load effect.
Authors: Zu Quan Jin, Peng Zhang, Tie Jun Zhao, Bao Rong Hou
Abstract: In this paper, preparation, property study of ultra-strength mortars with mineral admixture and clear river sand was carried out. The mineral admixture include fly ash, ultra-fine GGBS and silica fume. The experimental results show that the compressive strength of mortar improves with increasing amount of silica fume or ultra-fine GGBS. When the content of silica fume or ultra-fine GGBS is 30~35%, the compressive strength and flexural strength of mortar in curing age of 7 days are 100 MPa and 20MPa, respectively. But strength of mortar decreases with the increase replacement rate of fly ash. When the mortar mixes with combined of silica fume and ultra-fine GGBS, the optimum proportion of siliaca fume to ultra-fine GGBS is 2:3. And the compressive strength of mortar in curing age of 7 days is 75~100MPa when the mixed mineral admixture is 40~60%. The compressive strength of mortar is about 90MPa as it mix 60% of cement, 15% of silica fume, 15% of GGBS and 10% of fly ash. Moreover, the ultra strength mortar refines its pore structure and its capiliary pore (≥100nm) amount reduces by 78% compared to ordinary mortar.
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