This paper investigates the feasibility of combining different solid alkali materials as activator to prepare one-part geopolymer mortars. The effects of different composite solid activators on aluminosilicate materia...
This paper investigates the feasibility of combining different solid alkali materials as activator to prepare one-part geopolymer mortars. The effects of different composite solid activators on aluminosilicate materials were studied and compared with the traditional water glass and sodium hydroxide composite solution activator through the measurement of fresh and harden properties and microstructural analysis. The results showed that sodium metasilicate pentahydrate was more suitable than quick-dissolving sodium silicate for preparation of geopolymer. The addition of sodium carbonate and calcium hydroxide in solid activator enhanced the compressive strength and decreased the setting time and flowability of the mixes. The highest compressive strength (47.4 MPa, 28 d) was obtained with the activators consisting of sodium metasilicate pentahydrate and sodium carbonate. While scanning electron microscope (SEM) analysis indicated that micro-pores left by the dissolution of metasilicate particles might have an adverse effect on the mechanical properties of mortar samples.
Using the strain-controlled direct shear equipment, some direct shear experiments were carried out on the soil samples of Nanyang expansive soil with different gravel ratios under the specific water content, and the s...
Using the strain-controlled direct shear equipment, some direct shear experiments were carried out on the soil samples of Nanyang expansive soil with different gravel ratios under the specific water content, and the shear strength, cohesion and internal friction angle of the expansive soil samples were studied. The experimental results show that the shear strength of the expansive soil samples increases with the increase of vertical pressure. As the proportion of gravel sand increases, the shear strength of expansive soil samples increases to varying degrees. The shear strength of expansive soil increases significantly when the proportion of gravel sand is in the range of 10%~40%, and the shear strength of remolded soil is the highest when the gravel sand content is 10% under the lower vertical pressure. Under the higher vertical pressure, the shear strength of the remolded soil is the largest when the gravel content is 20%, and the shear strength of expansive soil is close to that of pure expansive soil when the proportion of gravel sand is 50%. The cohesive force of the sample increases first and then decreases sharply with the increase of the proportion of gravel sand, and is maximum when the content of gravel sand is 10%. The internal friction angle increases first and then decreases slowly with the increase of the proportion of gravel sand, and is maximum when the gravel sand content is 40%. The results show that gravel sand can effectively enhance the shear strength index of expansive soil, which can be used as a good engineering application material for improving expansive soil.
Nowadays, pipe jacking method is usually adopted in the construction of urban underground pipelines. In order to ensure the construction quality of pipe jacking method, geophysical non-destructive prospecting methods ...
Nowadays, pipe jacking method is usually adopted in the construction of urban underground pipelines. In order to ensure the construction quality of pipe jacking method, geophysical non-destructive prospecting methods are used for detecting the compactness around the jacked pipes. Based on the theory of ground penetrating radar (GPR), the void models of jacked pipes with two different materials (i.e. cement pipe and steel pipe) were established, and the finite element method was used to simulate the 2D forward modeling of GPR. At the same time, combined with the urban underground jacked pipes construction project in Xiangtan city, hunanprovince, China, GPR was used to carry out field prospection of the quality of jacked pipes construction. The results of forward simulation and practical applications show that good results can be obtained when GPR is used to detect the construction quality of cement pipes, which is the same as that of using GPR to detect the construction quality of tunnel. But the collected signals are not effective when the steel pipes are detected, which is because the radar signal cannot penetrate the steel pipe, and there are multiple reflections between the radar antenna and the pipe wall. Therefore, new non-destructive prospecting methods are needed for void detection of steel jacked pipes.
The hydraulic behavior of rocks is significantly controlled by fracture geometries, such as aperture, contact areas, roughness, interconnections, and so on. However, these characteristics are strongly influenced by th...
The hydraulic behavior of rocks is significantly controlled by fracture geometries, such as aperture, contact areas, roughness, interconnections, and so on. However, these characteristics are strongly influenced by the confining pressure conditions. This paper experimentally investigated the nonlinear flow behaviors through single rock fractures subjected to a wide range confining pressures. A series of transient pulse tests were conducted on three fractured limestone samples by MTS815 Rock Mechanics Test System. The experimental results show that the pulse decay curves diverge from the classical exponential model due to nonlinearity, thus an empirical relationship between differential pressure and time is developed with consideration of nonlinearity. Subsequently, the nonlinear flow coefficient and permeability were calculated based on the Forchheimer equation. The calculated results show that nonlinear flow coefficient increases with confining pressure, and rougher fracture surface helps to stronger nonlinearity. As the confining pressure increases, the permeability first experiences a dramatic decrease and then behaviors a much slow-down drop. The critical confining pressure for climb-rush shifts increases with the fracture rouhghness.
Based on the triaxial creep test of siltstone under loading and unloading, the linear creep model with seven elements is set up which can overall reflect the characteristics of sample with its instantaneous elasticity...
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ISBN:
(纸本)9781921712456
Based on the triaxial creep test of siltstone under loading and unloading, the linear creep model with seven elements is set up which can overall reflect the characteristics of sample with its instantaneous elasticity, decelerating creep, even creep, etc. Using secondary development program interface of FLAC3D, the program of user-defined model is developed. Based on these, the triaxial numerical simulation test is carried out. The test results show that the numerical simulating results under different stress level are greatly coincided with test results for either strain magnitude or general tendency of creep. The instantaneous strain and creep in top of sample are clearer than that at the bottom, which reflects the process the stress passes on. But there is an obvious restraining effect on axial and radial creep for confining pressure. The confining pressure is greater;the axial and radial creep is smaller.
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