Experimental study on the effects of water content on the compression characteristics and particle breakage of calcareous sand

The particle breakage effect and compression characteristics of calcareous sand are related to the water content in the sand material. However, the effects of water content on the particle breakage and compression characteristics of calcareous sand have rarely been investigated. In this work, 50 sets of confined compression tests were conducted on calcareous sand specimens, and the compression characteristics and particle breakage effects of two single-particle-size groups (particle size ranges of 1-0.5 mm and 0.5-0.25 mm) of calcareous sand were investigated under five different water contents. The test results showed that with the increase in the water content, the final compression deformation of calcareous sand was positively correlated with the water content. The final compression deformation decreased when the water content reached a certain value. The water content corresponding to the peak final compression deformation was related to the gradation of the calcareous sand; the specific values were 10% and 15% for particle size ranges of 1-0.5 mm and 0.5-0.25 mm, respectively. With the increase in the water content, the slope of the loading curve of calcareous sand appeared to increase and then decrease, reaching maximum when the water content was 10%. Moreover, the slope of the loading curve was close to twice that of the loading curve of dry sand, whereas the slope of the unloading curve changed little. Under the same water content, the initial gradation had no effect on the compression and unloading characteristics of the specimens beyond a vertical pressure of 1 MPa. The effects of the variation in the water content on the particle breakage of calcareous sand were mainly reflected in the softening effect of water on the specimen particles, which reduced the Mohr strength of the particles.

The effect of reinforcement particle size on the mechanical and fracture properties of glass matrix composites

The strength and toughness of sealing glass are currently unable to meet increasingly severe application conditions, and composites are an effective way to solve this problem. The size of reinforcement particles significantly affects the material properties, while the underlying mechanism still eludes deeper understanding. In this paper, the influence of the embedded alumina size is investigated from the perspectives of mechanical and fracture properties by mechanical tests, fracture toughness tests and the finite element method. The results of the experiment and simulation indicate that the fracture energy is mainly consumed by interface debonding and particle breakage, and the former consumes more energy. Materials with large particles have better mechanical properties, while those with small particles have better fracture properties. This difference could be ascribed to the curvature of the particles rather than the size. Therefore, an ideal reinforcement particle shape with both mechanical and fracture advantages is proposed. The results shed light on the nature of particle enhancement and point out a new direction for the design of sealing glass composites.

Applications of the Linear Mass-Sectional Breakage Population Balance to Various Milling Process Configurations

After an initial grounding discussion, in which the linear mass-sectional population balance is described, and models for reducing the number of its parameters are discussed, this modeling approach is applied to a wide range of processes including batch mills, single-pass continuous mills, mills in series, mills with recycle, milling circuits including classification, and recycled-batch milling. The linearity of the model allows its straightforward inclusion in calculations for all of these processes. The sensitivity of the model to its inputs (order of rate kernel in size, fragment distribution) is explored for batch operations. Then, the effects of key continuous process design variables are explored including the (a) number of mill passes in pendulum milling (mills in series), (b) classifier properties in circuits with classification, and (c) ratio of feed tank-to-mill residence time in recycled-batch operations.

Triaxial compression behaviour of gangue solid wastes under effects of particle size and confining pressure

Underground coal mining leads to environmental problems such as gangue pollution, surface subsidence and soil erosion, etc. Solid backfilling coal mining (SBCM) can control the strata movement, reducing gangue discharge and environmental pollution in mining areas. Gangue solid wastes (GSW) are backfilled into the goaf space as the supports for the overburden strata in solid backfilling coal mining. In this case, GSW are under triaxial compression. The deformation characteristics of the GSW under this loading condition are the key factors determining the control efficiency of strata movement and surface subsidence. The influence of the particle size grade and the confining pressure condition on the deformation and breakage characteristics of the GSW is studied based on large-scale triaxial compression tests in this paper. Also, the effect of particle breakage on the deformation of the GSW is revealed. The results indicate that in the triaxial compression process, the GSW exhibits strain hardening characteristics and volume decrease under compressive loading. The maximum load-bearing stress is more sensitive to the confining pressure condition but less sensitive to the particle size grade. The maximum load-bearing stress increases linearly with the confining pressure. Particle breakage of the GSW is notably influenced by the particle size grade but almost independent of the confining pressure condition. The S1 specimen with a reasonable proportion has the minimum relative breakage index, while the S3 specimen that mainly contains large particles has the maximum relative breakage index. The research outcomes are significant to the understanding of the mechanical characteristics of GSW, the selection and preparation of the backfilling materials in the field practices and the ensurence of the backfilling efficiency.

A potential source for PM2.5: Analysis of fine particle generation mechanism in Wet Flue Gas Desulfurization System by modeling drying and breakage of slurry droplet

Aerosol particulate matter with dynamic diameter smaller than 2.5 μm (PM_2.5) is the main cause for haze pollution in China. As a dominant precursor of PM_2.5, SO₂ emitted from industrial process is now strictly controlled by using limestone/gypsum Wet Flue Gas Desulfurization (WFGD) system in China. However, a phenomenon that fine particle derived from WFGD is recently addressed, and is suggested to be a potential source of primary PM_2.5. Herein, a first investigation into the particle generation mechanism in WFGD system is conducted with a novel droplet (containing particles) drying and breakage model. The proposed model considers a random and porous crust instead of the previous regular crust assumption, and is verified by comparing the modeling results with measurements. An orthogonal test with four factors and three levels is carried out through modeling calculation, and flue gas temperature (T_g) in the inlet is found to be a governing parameter for PM_2.5 yields in WFGD. With T_g in range of 120-160 °C, PM_2.5 yields in desulfurizing tower can reach a maximum value at ∼2 × 10⁸ cm^-3 under typical WFGD condition. To avoid this situation and reduce the PM_2.5 generation, T_g is suggested to be lower than 120 °C. Additionally, a new insight of the elimination effect of gas-gas heater (GGH) on "gypsum rain" in WFGD system is provided.

Recycling of crushed waste rock as backfilling material in coal mine: effects of particle size on compaction behaviours

Crushed waste rocks can be used as materials for backfilling goafs, so as to achieve the simultaneous goals of processing solid waste and controlling surface subsidence; however, particle size distribution directly affects the compaction of crushed waste rocks. Therefore, by employing a self-designed bidirectional loading test system for granular materials, this study tested compaction characteristics of crushed waste rocks with four different particle size distributions. Moreover, this research tested the changes of parameters in lateral and axial loading of crushed waste rocks and analysed the influence of particle size distribution on lateral strain, axial strain, porosity, lateral stress, and lateral pressure coefficient during compaction. The test results show that (1) particle size distribution affects porosity, strain, and lateral pressure coefficient of crushed waste rocks under lateral and axial loading. (2) For the samples under particle size distribution ranging from 0 to 10 mm, the initial porosity is low and deformations are small under axial loading, so that particles can make contact and bear effective stress in grain-grain contact. Therefore, more stress is transferred to the lateral direction. (3) After compaction, the curves of the samples of crushed waste rocks under four particle size distributions all shift upwards in comparison with those before compaction, indicating that particles are crushed and the proportion of small particles constantly increases. (4) A reasonable particle size distribution can significantly improve stress characteristics, reduce crushing of particles in the samples, and increase the stiffness of the samples, so as to achieve better compaction effects.