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Zhao L.,Wuhan University of Technology | Zhao L.,Xinxiang University | Han Y.,Liaoning Building Science Research Institute | Wang B.,Dalian University of Technology | And 2 more authors.
Journal of Solid Waste Technology and Management | Year: 2015

The quick frost method was used to measure the mass loss rate and relative dynamic elastic modulus of rubberized concrete and ordinary concrete. The frost resistance property of the rubberized concrete in sodium sulfate solution environment was studied by comparing the difference of mass loss rate and relative dynamic elastic modulus between rubberized concrete and ordinary concrete. The results shown that rubberized concrete in sulfate behave superior antifreeze performance than the corresponding ordinary concrete. The scanning electron microscope, mercury intrusion method, hardening bubbles method were used to study the mechanism of rubberized concrete's freeze-thaw durability. Through analysis, it was known that rubber powder in concrete acts as a solid air-entraining agent. Freeze-thaw damage made the micropores increased. The crystallization of sodium sulfate blocked the micro-holes of concrete. Fine rubber powders reduce the bubbles spacing coefficient and increase the number of bubbles. Rubber powders as micro "solid stomatal" improve the porosity of concrete, so that the antifreeze performance enhanced. Through the microstructure observation of rubberized concrete during freeze-thaw cycles it was found that rubber powders do not participate in the hydration reaction, while they appear as filling material. Source

Zhu Y.,Dalian University of Technology | Zhu Y.,Liaoning Building Science Research Institute | Xu S.-L.,Dalian University of Technology | Zhao J.,Shenyang Railway Survey and Design Institute Co.
Dalian Ligong Daxue Xuebao/Journal of Dalian University of Technology | Year: 2011

The fracture properties of cement paste and mortar which are two most basal matrix materials of concrete were studied using three groups of three-point bending beams with different sizes and strengths. A complete P-CMOD curve was directly obtained, and the initial cracking load was determined. The experimental results show that the resistance to crack propagation in matrix is enhanced due to sand aggregate in the matrix, even though the grain size used is very small. Cement paste is not an ideal brittle material, an apparent stable crack propagation before unstable failure is observed in cement paste, and this stable stage is shortened with the compressive strength increasing. The larger the size is, the earlier the crack initiation is, and the longer the stable crack propagation stage becomes. Therefore, based on the hydraulic engineering concrete fracture testing specification, the double-K fracture parameters were calculated for cement paste and mortar. The discussion on the obtained results was made. Source

Wang B.-M.,Dalian University of Technology | Han Y.,Dalian University of Technology | Han Y.,Liaoning Building Science Research Institute | Liu Y.-R.,Manzhouli Civil Building Engineering Quality Testing Center | Tu N.,Dalian University of Technology
Jianzhu Cailiao Xuebao/Journal of Building Materials | Year: 2013

The influence of scrap rubber powder on alkali-aggregate reaction(AAR) was studied by the mortar bar length method. The effect of rubber powder contents and rubber powder sizes on AAR were compared. The results indicate that the incorporation of scrap rubber powder can suppress the expansion of samples which caused by alkali-aggregate reaction at the early age, and the inhibition rate of expansion can be more than 50%. The inhibition effect is weakened to 30% at the later age. The inhibition effect reaches ideal degree when the rubber content is 2.5%(by mass), its expansion inhibitory ratio can reach 35%. The growth of inhibition effect is not obvious with the increase of rubber powder content. Among the three different particle sizes of rubber, the 119μm has the best inhibition effect on AAR, but the improvement of inhibition is insignificant. The elastic scrap rubber powder with small particle sizes acts as concentration center of stress, they can reduce the emerging of crack effectively. The scrap rubber powder are hydrophobic, and they can induce air. Air bubble together with the scrap rubber powder plays a part in easing up the bulbs of pressure generated by AAR, then restricts the internal crack extension in cement mortar, and weakens the damage of AAR on the matrix. Source

Zhu Y.,Liaoning Building Science Research Institute | Xu S.-L.,Zhejiang University
Gongcheng Lixue/Engineering Mechanics | Year: 2011

Ultra High Toughness Cementitious Composites (UHTCC) can be used as reinforcement material because of its good performances on crack control, energy consumption, corrosion resistance etc. The fracture process of concrete three-point bending beams retrofitted with UHTCC on tension face was studied. Based on the assumption that the interface deformation is consistent and by neglecting the elastic deformation of uncracked regions of UHTCC, a method for determining the total crack width wu of UHTCC is proposed and a simplified model of σ-wu is obtained subsequently. According to the simplified model, stress value of UHTCC can be determined. Through the analysis of whole process of crack propagation of concrete three-point bending notched beams retrofitted with UHTCC, the initial fracture toughness KIc ini and the unstable toughness KIc un applicable for reinforced concrete were introduced. The double-K fracture criterion is used for describing the whole process of crack propagation of concrete three-point bending beams retrofitted with UHTCC, and then the applicability of the criterion is verified by tests. Source

Wang B.-M.,Dalian University of Technology | Liu S.,Dalian University of Technology | Han Y.,Liaoning Building Science Research Institute | Leng P.,Dalian University of Technology
Nanoscience and Nanotechnology Letters | Year: 2015

In this paper, the durability and microstructure of cement-based composites doped with multi-walled carbon nanotubes (MWNTs) were investigated with low MWNTs concentration of 0, 0.05%, 0.1% and 0.15% by weight of cement at 28 days. Ultrasonic processing and a commercially surfactant (Gum Arabic, (GA)) were utilized to achieve homogenous MWNTs suspensions. Chloride ion penetration resistance, sulfate attack resistance, and scanning electron microscopy (SEM) were used to characterize the durability of cement-based composites with MWNTs. Compared with the reference sample, the addition of MWNTs improved the chloride ion penetration resistance performance, sulfate attack resistance and microstructure of cement composites. The 0.1% weight fraction of MWNTs obtained excellent durability among the composites. The embedded MWNTs acted as bridges and networks across the voids and cracks in matrix, which guaranteed the load-transfer in case of tension. Copyright © 2015 American Scientific Publishers. Source

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