Mercury Intrusion Porosimetry Experiments Research Articles

Cracking behaviour of concrete with superabsorbent polymer (SAP) under rolling fatigue load and temperature coupling

ABSTRACT To explore the long-term crack resistance of pavement concrete containing superabsorbent polymer (SAP), a fatigue test was designed with the consideration of rolling fatigue load and temperature coupling. The four-point fracture and acoustic emission tests were combined to evaluate the evolution of crack resistance. Additionally, the enhancement mechanism was revealed through scanning electron microscopy and mercury intrusion porosimetry experiments. The results indicate that the coupling effects of rolling fatigue load and temperature accelerate the deterioration of the fracture performance of concrete, particularly the freeze–thaw conditions. The concrete with SAP had greater fracture toughness, with improvements of 9.3%, 11.9%, and 58.1% under the coupling rolling fatigue loading and high temperatures, low temperatures, and freeze‒thaw cycles, respectively. The fracture process of concrete with SAP includes fluctuation, fatigue accumulation, and fatigue failure periods, and the SAP delays the arrival time of cumulative ring count and energy, significantly reducing the rate of concrete damage. More fibrous C-S-H and ettringite were generated at the interface microcracks in the concrete containing SAP, confirming the greater degree of hydration. Moreover, the SAP reduced the porosity and average pore size, which enabled the concrete to better resist the impact of rolling fatigue loading and adverse environmental temperatures.

Degradation mechanism and evaluation of the carbonation resistance of concrete after high-temperature exposure

High-temperature exposure during fire decreases not only the mechanical properties of concrete structures but also their durability, especially their concrete carbonation resistance. However, the degradation of concrete carbonation resistance after fire exposure remains unclear. Concrete specimens with water/cement (w/c) ratios of 0.4, 0.5, and 0.6 were fabricated to solve such problems, and high-temperature experiments were performed at 400 °C, 500 °C, and 600 °C and sustained for one hour. Then, mechanical and accelerated carbonation experiments were conducted, and the carbonation depths and pH values of concrete were tested. X-ray diffraction, thermogravimetry analysis, and mercury intrusion porosimetry experiments were also performed on concrete with and without high-temperature treatment. Results showed that high-temperature exposure caused severe degradation in concrete compressive strength, relative dynamic modulus of elasticity, and carbonation resistance, and the carbonation resistance loss of concrete was higher than its mechanical property loss. Concrete with lower w/c ratio suffered more losses in mechanical properties, whereas w/c ratio had no obvious effect on the carbonation resistance degradation of fire-damaged concrete. The key mechanism of the decline in the carbonation resistance of concrete after fire was not mainly the alkalinity drop in concrete but the considerable increase in concrete porosity and harmful pores. Instead of the traditional phenolphthalein method, a new method of residual OH- concentration of superficial concrete after accelerated carbonation was proposed to evaluate the carbonation resistance of concrete after fire. The average carbonation resistance of the concrete with the three w/c ratios was reduced by 66.3 %, 84.2 % and 95.1 % after exposure to 400 °C, 500 °C, and 600 °C, respectively.

Fractal analysis of pore structures in transitional shale gas reservoirs in the Linxing area, Ordos Basin

Studying complex pore structures and fractal characteristics of gas shale provides significant guidance for clarifying the mechanism of shale gas accumulation and realizing its efficient development. In this paper, 12 samples of Taiyuan Formation shale are used as the research object, and the fractal theory is combined with mercury intrusion porosimetry and N2 adsorption technology to innovatively solve the problem of splicing point selection, which can reveal the full-scale pore size distribution of shale. The results demonstrate that the most common types of pores in the chosen samples are pores between or within clay minerals, micropores and mesopores inside organic matter, and microfractures, based on scanning electron microscopy imagery analyses. The pores of shale samples have fractal geometries. The fractal dimension DM1 values in the mercury intrusion porosimetry experiments range from 2.3060 to 2.6528. Two fractal dimensions, DN1 and DN2, may be obtained using the Frenkel-Halsey-Hill fractal method. DN1 values vary from 2.4780 to 2.6387, whereas DN2 values range from 2.5239 to 2.7388. Most macropores in shale samples have a size range of about 0.2 mm, with a wide pore size distribution, and the largest peak of the micro-mesopore volume is generally about 50 nm. The fractal dimension correlates positively with the corresponding pore volume, although the correlation between volume and composition is weak. The relatively strong correlation between fractals and the basic compositions of shale proves the fractal theory’s relevance in defining pore inhomogeneity. This study would contribute to the development of a fractal perspective-based method for pore splicing while also expanding our understanding of pore morphology and structure in transitional shale.

Water-induced variations in micro characteristics of clay-bearing conglomerates at great depths in China

The micro characteristics, including micro-structural features of clay minerals and micro-pore textures of rock, change after the rock–water interaction and lead directly to rock deformation and deterioration. To understand the mechanism of the weakening process of rocks at great depths after interaction with water, we performed X-ray diffraction analysis, scanning electron microscopy, and mercury intrusion porosimetry experiments to investigate the mineral compositions, microstructures, and porosity characteristics of four clay-bearing conglomerate samples collected from Northeast China at great depths. In addition, the chemical analysis of the aqueous solutions was carried out to examine the variances of chemical compositions before and after the water absorption tests. The results showed that the dominant mineral components in the conglomerate samples were quartz, potash feldspar, plagioclase, and clay. The contents of clay minerals in all samples were relatively high and ranged from 8.9% to 14.9%, mostly containing a chlorite/montmorillonite mixed layer. The correlation analysis suggested that ion exchange occurred in the reactions between the conglomerate samples and water. The mixed layer of chlorite/montmorillonite expanded, spread, and flocculated after water absorption, jammed the pores, and reduced the porosity. A certain number of calcite particles formed on the surface of grains or surrounded the micro-pores, resulting in the blockage of pores and inducing the decrease in rock porosity. In addition, various occurrence features of the chlorite/montmorillonite mixed layer changed differently after interacting with water, leading to varied influences on the fractal characteristics of rocks.

Experimental Investigation on the Influence of Thermochemical Effect on the Pore–Water Status in Expansive Soil

The pore-water status, including adsorptive and capillary water, in expansive clay with different dry densities was investigated under the effect of temperature and saline solution via the nuclear magnetic resonance technique. Combined with a method of distinguishing the adsorptive and capillary water, the variations in the adsorptive water content with the thermochemical effect were obtained quantitatively. The experimental results show that the adsorptive water content decreases as the temperature increases, consistent with the theoretical conclusion, which is considered to be attributed to the increase of the chemical potential and the activity of the pore water. On the other hand, the volume of micropores decreases while the volume of macropores increases with the increasing temperature or concentration, resulting from the flocculation and agglomeration of soil particles. Meanwhile, the increase of salt concentration can suppress the electric double layer and decrease the micropore volume, resulting in a decrease in the adsorptive water content. In addition, due to ion hydration, the relaxation of water molecules accelerates, shifting the water distribution curves of soil leftward as concentration increases. This effect overshadows the suppression of electric double layers and the decrease of the micropores, rendering higher adsorptive water content. The microstructure and the pore size distribution, obtained by the scanning electron microscope and mercury intrusion porosimetry experiments, were used to validate the variation of the adsorptive and capillary water in the pores.

Properties of a double-layer EMW-absorbing structure containing a graded nano-sized absorbent combing extruded and sprayed 3D printing

The ever-increasing electromagnetic wave (EMW) energy and its reflections may impair human health and information security. An ordinary EMW-absorbing structure usually exhibits limited EMW-reflecting capacity given its ungraded structure in both the micro and macro scales. In this study, four nano-sized graded absorbents are explored by wrapping carbonyl-iron powder with nano-sized silicon dioxide. The micro-scale wrapping effects are assessed via a scanning electron microscopy experiment to identify the best sample, including a 5 wt% coupling agent and a 10 wt% dispersant in CIP ethanol. The 10 mm thick concrete matching layer containing the graded absorbent is built using spraying methodology, and the 15 mm thick absorption layer is fabricated using extruding methodology. The mercury intrusion porosimetry experiments show that the sprayed matching layer incurs maximum porosity at 19.8% while the 3D extruded layer ensures the minimum porosity at 11.13%, strengthening the laminar grading effect to improve the EMW impedance matching. The Naval Research Laboratory experiments corroborate that double-layer structures improve the EMW-reflecting capacity compared to their single-absorption-layer counterparts and that the double-layer element containing the best wrapping effect absorbent yields the best reflection loss value, with a minimum of −14.7 dB and a 9.72 GHz effective bandwidth. The EMW-reflecting mechanism for the novel graded double-layer structure containing the graded nano-sized absorbent is then summarized. Theoretical calculations using the transform line theory suggest that a 15 mm absorbing layer and a 15 mm impedance matching layer is specified as the most optimized configuration, with −10.47 dB in average reflection, −15.18 dB in maximum RL, and 9.56 GHz in effective bandwidth.

Investigation of pore structure characteristics and adsorption characteristics of coals with different destruction types

The occurrence of coal and gas outbursts is closely linked to the presence of tectonic coal. To study the pore structure characteristics and adsorption characteristics of different destruction types of coal, nondestructive coal, destructive coal, strongly destructive coal, pulverized coal, and fully pulverized coal are selected based on the coal and gas outburst mine identification specifications. The experimental methods used are liquid nitrogen adsorption, mercury intrusion porosimetry and CH4 isothermal adsorption. The results show that the pore volume obtained by the Barrett–Joyner–Halenda method and the specific surface area increase with increasing destruction type. For all tested coal samples, the N2 adsorption/desorption hysteresis loop is not closed when the relative pressure is low, indicating the existence of ink-bottle pores, an elastic structure of the coal and nitrogen affinity in the coal. With increasing tectonic stress, it becomes more advantageous to produce micropores. The pore volume obtained by the mercury intrusion porosimetry experiment increases with increasing destruction types except for the case of fully pulverized coal. High-pressure mercury causes pore deformation and collapse. When the f value is <0.5, the compression effect of the pores is obvious. The smaller the value of f is, the wider is the pore range affected by the high-pressure mercury. The degree of destruction is positively correlated with the porosity, specific surface area, and Langmuir volume. However, the degree of destruction is negatively correlated with the f value and mercury extrusion efficiency.

Theory and practice of micro water-oil displacement efficiency based on mathematical models

Theoretical study about quantitative influence of the micro parameters (interfacial tension, wetting angle, distance, unit length, bottom radius, boundary distance, etc.) on the macro parameters (oil displacement efficiency, pressure gradient, etc.) in water-oil displacement process is very important. This paper focuses on the micro oil displacement efficiency calculation method in oil reservoir, building a new bridge between these parameters. Combining fluid motion equation, continuity equation to pressure gradient equation, the occurrence radius equation of remaining oil in different capillary is established; Taking mercury intrusion porosimetry experiment and constructing the mathematical model, new normal probability distribution of pore radius is achieved, and then a new probability function for injected water entering pore throat is established based on the occurrence radius equation and pore radius distribution equation; By using the Darcy’s Law and definite integral theory, new micro oil displacement efficiency equation is obtained. The Nuclear Magnetic Resonance experiments show: new method gets high calculating accuracy, and can be used to guide oil reservoir development.

Study on the Preparation and Hydration Properties of a New Cementitious Material for Tailings Discharge

Blast furnace slag (BFS) is often used as a cement-based raw material for underground filling and surface cemented paste discharge of tailings during mining processes. This paper studied a new cement-based material (NCM) with BFS to replace ordinary Portland cement (OPC). A uniaxial compressive strength (UCS) experiment was used to test the mechanical strength of samples; X-ray diffraction and thermal gravity experiments were used to test the crystalline phases and amount of hydration products by samples; a scanning electron microscope experiment was used to observe the influence of the hydration products morphology by samples; mercury intrusion porosimetry experiment was used to analyze the pore size distribution of samples. The samples with NCM had an optimum UCS; the crystalline phases of the hydration products were similar in OPC and NCM. However, the amount of product formed in OPC was less than that in NCM at the same curing time; more ettringite and calcium silicate hydrate were produced in samples with NCM, which filled the pores and enhanced the UCS of the samples. The final mercury intrusion volume of the samples with NCM were lower than the samples with OPC at the same curing time, which showed that samples with NCM had lower porosities. For the samples with NCM and OPC cured from 7 days to 28 days, the mercury intrusion volume was reduced by 18% and 13%, and the most common pore size of the samples reduced by 53% and 29%, respectively. This showed after 21 days curing time, the pores of all the samples getting smaller; however, the samples with NCM were more compact. The main ingredients of the NCM were clinker, lime, gypsum and BFS, and its ratio was 14:6:10:70. The content of additives to NCM was 0.4%, and the ratio of sodium sulfate: alum: sodium fluorosilicate was 2:1:1.

Characterization of microscopic pore types and structures in marine shale: Examples from the Upper Permian Dalong formation, Northern Sichuan Basin, South China

We selected the Upper Permian Dalong shale in northern Sichuan Basin to qualitatively and quantitatively characterize the different types and sizes of pore system in marine shale. Field emission scanning electron microscopy, low-pressure N2/CO2 gas adsorption–desorption experiment, high-pressure mercury intrusion porosimetry experiment, and petrophysical model interpretation method were conducted. Results show that Dalong shales are rich in brittle minerals and organic matters (OMs). The pore system consists of four types of pores, namely, OM pores, intraparticle (intraP) pores, interparticle (interP) pores, and microfracture. OM pores and pores within brittle minerals dominate the pore system and account for 65.7% and 24.5% of the total porosity, respectively. Slit- and wedge-shaped pores are the major pore shapes in the shale pore system. These pores have good adsorbability and openness that can facilitate the storage and migration of shale gas. Pore size diameters are mainly distributed in the ranges of 0.40–0.90 nm, 200–600 nm and 20–80 μm. Both the specific surface area (SSA) and total pore volume (PV) decrease with the increasing average pore diameters. Micro- (<2 nm), meso- (2–50 nm), and macropores (>50 nm) contribute 78.23%, 6.18%, and 12.52%, respectively, of the total PV and 92.67%, 9.25%, and 1.15% of the total SSA. The pore diameter of <10 nm is predominant in the pore system and account for 86.83% of the total PV and 99.89% of the total SSA. OMs together with clay minerals jointly influence the total PV and SSA development, whereas brittle minerals inhibit pore development. The total organic carbon (TOC), brittle minerals and clay minerals discriminatively control the development of micro-, meso-, and macropores, which are discretely provided by OM pores within kerogen, pores within brittle minerals, and clay minerals, respectively. Fractal dimensions D1 and D2 were 2.153–2.561 and 2.672–2.772, respectively. These values indicate that the pore surface is substantially irregular, and the pore structure is significantly complex and heterogeneous, which is positively correlated with total PV and SSA but negatively correlated with pore size diameter. TOC content, thermal maturity, and clay minerals are positively correlated to fractal dimension; whereas high brittle mineral content may reduce the fractal dimension.

Study of Low-Permeability Sandstone by Unidirectional Mercury Intrusion Porosimetry

In light of the fact that the results of conventional mercury intrusion porosimetry experiments may not always be accurate, unidirectional (linear) mercury intrusion porosimetry was employed to construct capillary pressure curves, determine the pore size distribution and pore structure of four low-permeability sandstones under different effective stress. Analysis results show that for the same sandstone sample, the capillary pressure curve obtained by unidirectional mercury intrusion porosimetry deviates from the curve obtained by conventional mercury intrusion porosimetry, and the deviation becomes more apparent with increasing effective stress; the inlet capillary pressure in the unidirectional mercury intrusion porosimetry experiment is higher than that in the conventional mercury intrusion porosimetry experiment; with the same mercury saturation, the capillary pressure in the unidirectional mercury intrusion porosimetry experiment is higher than that in the conventional mercury intrusion porosimehy experiment; the maximum mercury injection saturation in the unidirectional mercury intrusion porosimetry experiment is lower than that in the conventional mercury intrusion porosimehy experiment and decreases with increasing effective stress; the average mercury injection value in the unidirectional mercury intrusion porosimetry experiment is higher than that in the conventional mercury intrusion porosimetry experiment and increases with increasing effective stress; the sorting coefficient determined by unidirectional mercury intrusion porosimetry is slightly different from that found by conventional mercury intrusion porosimetry; finally, the skewness of the capillary pressure curve obtained by unidirectional mercury intrusion porosimetry is greater than that obtained by conventional mercury intrusion porosimetry. Therefore, unidirectional mercury intrusion porosimetry makes it possible to measure capillary pressure with a high level of accuracy.

Effect of the Pyrolysis Temperature on the Grindability of Semi-cokes Produced by Two Kinds of Low-Rank Coals

ABSTRCT: Variations in the grindability of semi-cokes produced by two low-rank coals at different pyrolysis temperatures were studied. The grindability of semi-cokes prepared by XiMeng lignite (XL) had minimal changes at varying pyrolysis temperature and was nearly similar to that of a dehydrated sample. The pore structure of XL was fully developed after dehydration and had no significant change during pyrolysis, as indicated by the observations obtained through scanning electron microscopy and results of the mercury intrusion porosimetry experiment. Thus, its grindability showed little change during pyrolysis. Meanwhile, the grindability of ShenHua sub-bituminous coal (SC) decreased considerably when pyrolysis temperature reached 550 °C. As shown by the results of thermal gravimetric (TG) experiments, X-ray diffraction (XRD) and fractal analysis of pore structure, the coal matrix of SC had a plastic stage. Meanwhile, its volatile matter rapidly releases in this stage. After the plastic stage, considerabl...

Geomechanical and water vapor absorption characteristics of clay-bearing soft rocks at great depth

The geological and physico-mechanical properties characterization of deep soft rocks is one of the critical scientific issues for deep soft rock engineering. In the present study, X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 clay-bearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and water-induced strength degradation effect of the investigated deep soft rock samples. The results show that the dominant mineral components in mudstone, coarse sandstone and fine sandstone samples were calcite, quartz and clay respectively. The contents of clay minerals in all samples were relatively high and ranged from 12.3% (N-4) to 56.5% (XS-1). Water vapor absorption processes of all the soft rock samples follow an exponential law which is very similar to the water vapor absorption behavior of conglomerate samples reported in our earlier study. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples. Furthermore, it was found that vapor absorption was not correlated with the porosity for mudstone, however, positive correlation relationship was found between them for sandstone. Correlation analysis between UCS, modulus of elasticity and water content demonstrated that both of them tend to decrease with the increase of their water content due to water absorption.

Tailoring the microstructure of porous MgO supports for asymmetric oxygen separation membranes: Optimization of thermoplastic feedstock systems

Porous magnesium oxide (MgO) structures were prepared by thermoplastic processing for use as supports in asymmetric thin film oxygen transport membranes (OTMs). The open porosity, pore size distribution, and resulting gas permeability of the MgO structures were measured for different feedstock compositions and sintering temperatures. For a composition with 19vol% graphite as a pore-former, sintering temperatures of 1300°C and 1400°C, resulted in support porosities of 36% and 26%, respectively, and gas permeabilities of 1.4×10−16m2 and 3.1×10−16m2. Electron microscopy showed that the unexpected increase in gas permeability at temperatures above 1300°C was a result of the growth of macro-pores and the opening of bottle-neck pores which resulted in improved pore connectivity. Mercury intrusion porosimetry experiments confirmed an increase in average pore size for samples sintered above 1300°C, despite a significant decrease in total porosity.