Papers by Author: Wu Yao

Abstract: Cement clinker with low CO₂ emission was prepared in laboratory, which mainly consist of belite (C₂S), calcium sulfoaluminate (C₄A₃S), and ferrite (C₄AF). The mineral composition of clinker was optimized for better compressive strength development. The chemical and physical properties of this prepared cement were characterized through X-ray diffraction (XRD), back scattered electron-scanning electron microscopy (BSE-SEM) and differential thermal analysis (DTA). The results reveal that C₄A₃S governs most of the compressive strength at early ages, while C₂S contributes to the later strength development. C₄AF is in liquid when fired to 1300°C, beneficial to the mass transfer but causing high crystallinity of C₂S when excessive. Finally the results of experiments suggest that the optimal composition of clinker is 50wt. % C₂S, 40wt. % C₄A₃S and 10wt. % C₄AF.

Abstract: By combining the three-point bending beam test with theoretical derivation, the elastic modulus, fracture toughness, surface energy and the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials were obtained. The fracture properties were studied with the water to binder ratios (W/B) from 0.18 to 0.14. Test results showed that the ultra-high strength cement-based materials are quasi-brittle and the net bending strength of specimen decreased substantially when there was a notch. The elastic modulus of ultra-high strength cement-based materials can be up to 74.0 GPa, obviously higher than that of ordinary cement-based materials, showing greater elastic deformation resistance. Moreover, with decrease of W/B ratio, the compressive strength, fracture toughness, critical strain energy release rate as well as the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials increased significantly, indicating that the anti-cracking ability increased with the decrease of W/B ratio.

Abstract: Portland cement production leads to significant carbon dioxide emission and greenhouse effect. Magnesium oxide eco-cement, which is a mixture of Portland cement, magnesium oxide and fly ash, may be an alternative production. In this paper, the issue is focused on the carbon dioxide absorption ability and mechanical performance of this eco-cement. Several mix proportions of eco-cement were designed to conduct forced carbonation, strength and expansion tests. Also, microstructure analysis after carbonation was conducted. The results indicate that magnesium oxide eco-cement can efficiently absorb carbon dioxide and carbonation can improve mechanical performance substantially, also expansion of the eco-cement is found to fall within the safe limits and possesses good stability and soundness.

Abstract: Quantitative X-Ray Diffraction (QXRD) with Rietveld full pattern fitting method and the hyphenated technique of ThermoGravimetry (TG) with Differential Scanning Calorimetry (DSC) were used to explore the effects of silica fume (SF) on hydration process of composite cementitious system (CCS) as well as the pozzolanic reaction (PR) of SF in this system. Results indicate that the PR of SF has started at the end of the first day but proceeds very slowly during the rest days due to the agglomeration of SF particles; and the starting point of PR is far earlier than that of drop of CH content, which implies that it is not suitable to mark conventionally the drop of CH content as the starting point of PR.

Abstract: Using orthogonal experimental design, the influence of water-to-cement ratio, silica fume content, and fiber surface treatment on the electrical and mechanical properties of carbon fiber reinforced cement was studied. Moreover, the surface appearance of fibers with and without surface treatment was investigated by means of scanning electron microscopy. The results show that the effect of water-to-cement ratio on conductivity is the largest among all the three factors. Fiber surface treatment plays an important role in the mechanical properties of CFRC and the optimum way is HNO3 treatment. By adopting the method of efficiency coefficient, the best combination can be determined effectively.

Abstract: The water distribution in hardened cement paste with different ages, water to cement ratio (w/c) and different cured methods were investigated by low field NMR. The transverse relaxation time, T₂, was used as a parameter to describe the water phase constrained in pores. The results show that the T₂ distributions of pastes in the early age are bimodal distribution. As the curing time increase, the T₂ distribution peaks shift gradually to the short T₂ values reflecting the decrease of mean pore dimension as well as the increase of specific surface area resulted from the gel products. In addition, the influences of initial water to cement ratio and cure methods on water distribution are occurred mainly during the early age. When cured to 28 days, the differences of water distribution in various samples are unconspicuous.

Abstract: As an important part of cement-based materials，water plays an important role during hydration and self-desiccation so the measurement of relative humidity or internal moisture in the research of cement-based materials is vital. In this paper, the measurement samples are blended cement pastes in sealed with different water to cement ratios and different kind of mineral admixtures. The measurement was taken at different ages during hydration to investigate the changes of relative humidity. The result showed that the water to cement ratio was the key factor of affecting the change of relative humidity, and the effect of mineral admixture kind was not very obvious in this experiment.

Abstract: Thermoelectric properties of steel slag-carbon fiber/cement composites were studied in this paper. The effect of steel slag content on thermoelectric properties was focused on especially. The experimental results show that the addition of steel slag leads to an increase in the positive thermoelectric power of the cabon fiber/cement composites. The highest absolute thermoelectric power of carbon fiber/cement composites was rendered as positive as 14.4µV/°C by using steel slag, which had a high concentration of holes. Beside, a good linear relationship was observed between thermoelectric power and temperature differential on the specimen.

Abstract: The ultimate load, fracture energy and equivalent bending strength of hybrid steel fiber reinforced mortar were investigated with a constant fiber volume fraction in this paper. The results showed that ultimate load of hybrid steel-fiber reinforced mortar was higher than that of mono-fiber reinforced mortar; fracture energy and equivalent bending strength increased with the volume fraction of steel fiber with end hooks.

Abstract: This paper presents the first use of ultrasound technique during electrochemical chloride extraction (ECE). The effect of ultrasound on the extraction efficiency was studied, and the mechanism of ultrasound in improving the extraction efficiency was also discussed in this paper. Testing results showed that ultrasound was conducive to enhance the efficiency of chloride removal to a certain extent, especially in the first 3 weeks. Ultimately, compared with ECE treatment, the chloride removal efficiency of ultrasonic-assisted ECE nearly increased 10%. In addition, the corrosion potentials measured 2 months after treatment indicated the effectiveness of ultrasonic-assisted ECE in protecting eroded rebars from further corrosion.