scholarly journals Deterioration of Coal Microstructure under Discontinuous Cyclic Loading Based on Nuclear Magnetic Resonance

2021 ◽  
Vol 11 (1) ◽  
pp. 462
Author(s):  
Zhe Xiang ◽  
Nong Zhang ◽  
Zhengzheng Xie ◽  
Chenghao Zhang
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Compressive Strength ◽  
Magnetic Resonance ◽  
Cyclic Loading ◽  
Uniaxial Compressive Strength ◽  
Coal Sample ◽  
Cyclic Load ◽  
Coal Pillar ◽  
Holding Time

To study the damage and destruction behavior of small coal pillars in coal mine roadway driving along gobs under long-term in-situ stress and multiple engineering disturbances, an unconfined compression experiment under a discontinuous cyclic load was designed, with the holding time as a variable. An electro-hydraulic servo rock testing machine was used to impose a discontinuous cyclic load on the coal sample and perform a final uniaxial compressive strength test. The changes in pore number and diameter in the coal under stress were monitored by nuclear magnetic resonance analysis. An increase in holding time in the discontinuous cyclic loading resulted in a significant increase in the number and diameter of pores in the coal sample; the coal porosity continued to increase, and the proportion of pores in the coal changed. The proportion of micropores decreased gradually, whereas the proportion of mesopores and macropores (cracks) increased. The degree of internal specimen damage increased with an increase of holding time, which resulted in a gradual decrease in final uniaxial compressive strength. Therefore, under the action of a long-term stress, to improve the bearing capacity of the coal pillar while avoiding gas and water influx into the working face in the goaf, the coal pillar should be reinforced with multi-layer and multi-grain grouting.

scholarly journals Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2303
Author(s):  
Congyu Zhong ◽  
Liwen Cao ◽  
Jishi Geng ◽  
Zhihao Jiang ◽  
Shuai Zhang
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Coalbed Methane ◽  
Coal Sample ◽  
Fine Particles ◽  
Particle Sizes ◽  
Tectonic Coal

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

scholarly journals Study on the Fatigue and Durability Behavior of Structural Expanded Polystyrene Concretes

Materials ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 2882 ◽  
Author(s):  
Quan You ◽  
Linchang Miao ◽  
Chao Li ◽  
Huanglei Fang ◽  
Xiaodong Liang
Keyword(s):  
Cyclic Loading ◽  
Cyclic Load ◽  
Dynamic Performance ◽  
Plain Concrete ◽  
Expanded Polystyrene ◽  
Structural Elements ◽  
Sulfate Resistance ◽  
Erosion Test ◽  
Test Process

The fatigue and durability characteristics of structural expanded polystyrene concrete (EPS) are especially important when it was applied for structural elements in long-term service. In order to study the fatigue and durability behavior of structural EPS concrete, the long-term cyclic loading experiments and wetting–drying (W-D) cyclic experiments were conducted, respectively. The structural EPS concrete was found to have a relatively large damping and a fairly low dynamic elastic modulus under long-term cyclic load, which illustrated that it had a better energy absorption effect and toughness than plain concrete of the same strength level. Even if fine cracks appeared during the cyclic loading process, the relevant dynamic performance remained stable, which indicated that the structural EPS concrete had superior fatigue stability. In W-D cyclic experiments, the structural EPS concrete exhibited superior sulfate resistance. During the erosion test process, there was a positive correlation between the mass change and the evolution of the compressive strength of the structural EPS concrete, which indicated that ΔmB could be substituted for Δf to evaluate the degree of the structural EPS concrete eroded by sulfate attack. The study focuses on the fatigue performance and sulfate resistance of structural EPS concrete and is of important engineering value for promoting practical long-term operations.

scholarly journals Flexural Strength Prediction Models for Soil–Cement from Unconfined Compressive Strength at Seven Days

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 387 ◽  
Author(s):  
Alaitz Linares-Unamunzaga ◽  
Heriberto Pérez-Acebo ◽  
Marta Rojo ◽  
Hernán Gonzalo-Orden
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Uniaxial Compressive Strength ◽  
Prediction Models ◽  
Road Construction ◽  
Engineering Properties ◽  
Construction Technique ◽  
Soil Cement ◽  
Over Exploitation

Soil–cement is an environmentally friendly road construction technique for base and subbase materials, which allows employing soils placed in the right-of-way of the road or in the surroundings, by improving its engineering properties. With this technique, it is possible to reduce the over-exploitation of quarries, the necessity of landfills and the pollutant gas emission due to the reduction of aggregate fabrication and transport. The manufacturing of soil–cement is generally controlled by means of the Uniaxial Compressive Strength (UCS) test at seven days, according to the regulations of each country. Nonetheless, one of the properties that best defines the performance of soil–cement is the Flexural Strength (FS) at long term, usually at 90 days. The aim of this paper is to develop new equations to correlate the UCS and the FS at long term and the UCS at seven days and at 90 days. Obtained results validate the proposed models and, hence, the flexural strength can be predicted from the Uniaxial Compressive Strength at seven days, allowing, if necessary, correcting measures (recalculation or rejection) in early stages of the curing time to be taken.

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