Characterization of pore structure in cement-based materials using pressurization-depressurization cycling mercury intrusion porosimetry (PDC-MIP)

Numerous mercury intrusion porosimetry (MIP) studies have been carried out to investigate the pore structure in cement-based materials. However, the standard MIP often results in an underestimation of large pores and an overestimation of small pores because of its intrinsic limitation. In this paper, an innovative MIP method is developed in order to provide a more accurate estimation of pore size distribution. The new MIP measurements are conducted following a unique mercury intrusion procedure, in which the applied pressure is increased from the minimum to the maximum by repeating pressurization-depressurization cycles instead of a continuous pressurization followed by a continuous depressurization. Accordingly, this method is called pressurization-depressurization cycling MIP (PDC-MIP). By following the PDC-MIP testing sequence, the volumes of the throat pores and the corresponding ink-bottle pores can be determined at every pore size. These values are used to calculate pore size distribution by using the newly developed analysis method. This paper presents an application of PDC-MIP on the investigation of the pore size distribution in cement-based materials. The experimental results of PDC-MIP are compared with those measured by standard MIP. The PDC-MIP is further validated with the other experimental methods and numerical tool, including nitrogen sorption, backscanning electron (BSE) image analysis, Wood's metal intrusion porosimetry (WMIP) and the numerical simulation by the cement hydration model HYMOSTRUC3D.     

A method for the estimation of micropore volume and micropore surface area

Micropore volumes have been estimated by comparing the results of mercury intrusion with helium displacement in porous samples. Differences in the surface area measured by gas adsorption and mercury porosimetry afford an estimation of micropore surface area and the micropore surface to volume ratio gives a mean micropore radius.     

Rehydration and microstructure of cement paste after heating at temperatures up to 300 °C

This paper is concerned with the evolution of the microstructure of cementitious materials subjected to high temperatures and subsequent resaturation in the particular context of long-term storage of radioactive wastes, where diffusive and convective properties are of primary importance. Experimental results obtained by mercury intrusion porosimetry (MIP) are presented concerning the evolution of the pore network of ordinary portland cement (OPC) paste heated at temperatures varying between 80 and 300 °C. The consequences of heating on the macroscopic properties of cement paste are evaluated by measures of the residual gas permeabilities, elastic moduli and Poisson's ratio, obtained by nondestructive methods. Resaturation by direct water absorption and water vapour sorption are used to estimate the reversibility of dehydration. The results provide some evidence of the self-healing capacity of resaturated cement paste after heating at temperatures up to 300 °C.     

硬化水泥浆体气体渗透特征研究

渗透性直接决定了有害物质在混凝土等水泥基材料中的传输速度,是影响混凝土耐久性的关键指标。基于水泥浆体三维孔隙结构和压汞试验数据,分别采用Katz-Thompson方程和格子Boltzmann方法模拟计算水泥浆体试样的渗透率,并与气体渗透测试结果进行对比,其结果表明:硬化水泥净浆气体渗透率测试结果为3.82×10^-18~7.29×10^-18 m²;Katz-Thompson方程的预测结果仅具有数量级的准确度,不能真实准确地预测水泥浆体孔隙结构的渗透率;格子Boltzmann方法能够准确地预测水泥浆体的本质渗透率,为4.88×10^-19~15.48×10^-19 m²;气体渗透测试结果比模拟结果高约2~10倍,表明水泥浆体中毛细孔依然是渗透的主要路径,而气孔和微裂缝仅在局部起到了提高气体渗透率的作用。     

压汞法测定材料孔结构的误差分析

根据压汞法测量材料孔结构的基本原理分析了可能引起误差的来源。压汞法测定材料的孔径分布依据的是Washburn方程,基本的理论模型是圆柱孔模型,实际样品中的孔隙均存在异形孔,这给测量带来误差。汞的表面张力和汞与材料表面的接触角直接影响测量结果。     

Characterization of partially densified 3D Cf/SiC composites by using mercury intrusion porosimetry and nitrogen sorption

The microstructure of partially densified three-dimensional carbon fiber fabrics reinforced silicon carbide (C_f/SiC) composites are characterized by both mercury intrusion porosimetry (MIP) and isothermal nitrogen sorption (INS). By comparison, MIP is preferable to the characterization for its wide effective probing ranges. Based upon multiple measurements, in the C_f/SiC composite, exists a complicated three-dimensional porous network formed by the interconnecting pores and necks with various sizes, diverse shapes and rough surfaces.     

Influence of mix proportions on microstructure and gas permeability of cement pastes and mortars

This paper presents a study on the influence of mix proportions of cementitious materials on their transfer properties, namely porosity and gas permeability. These latter are known as durability indicators. The work is performed on a wide range of cement pastes and mortars (24 compositions). These compositions are defined by mix proportion parameters (water/cement ratio, limestone filler/cement ratio, and amount of superplasticizer and volume fraction of paste). To characterize these materials, an experimental campaign was carried out, including different types of test (water porosimetry, mercury intrusion porosimetry, desorption isotherms and gas permeability). The influence of the composition parameters on the studied durability indicators is highlighted and correlation between gas permeability and microstructural properties (total porosity and critical pore diameter) is established. Finally, a method to predict materials permeability from that of the cement paste is proposed.     

碳纤维－尼龙纤维混杂改性水泥力学性能及显微结构观察

碳纤维尼龙纤维混杂改性，既可提高水泥强度又可提高其韧性。通过电子显微镜和压汞试验所得结果对混杂改性机理进行了初步探讨     

Gas permeability and electrical conductivity of structural concretes: Impact of pore structure and pore saturation

This paper investigates the gas permeability and the electrical conductivity of structural concretes under different pore saturations. The gas permeability was measured by CemBureau device and the electrical conductivity by alternating current method. The pore structure was characterized by mercury intrusion porosimetry (MIP) and gravimetric methods. The Archie's law is used to interpret the tortuosity of the pore structure. The impact of pore saturation is evaluated through the Van Genuchten-Mualem (VGM) and Kozeny's models. The results show that (1) the global correlation between the gas permeability in dried state and the electrical conductivity in saturated sate is weak; (2) both VGM and Kozeny's models can describe the relative permeability/conductivity, but the VGM model gives more consistent exponents for permeability and conductivity; (3) as the pore gas and liquid phases are both percolated, the gas permeability is correlated to the electrical conductivity for arbitrary pore saturation.     

A three-parameter Kozeny–Carman generalized equation for fractal porous media

The Kozeny–Carman equation is a traditional permeability–porosity relationship which has been used in many models of real problems related to flows in porous media. In spite of this, some limitations of this well-known equation has motivated the conception of different versions, specialized for particular applications. In the present article, we deduce a three-parameter Kozeny–Carman equation obtained from a fractal structure involving the specific surface and the tortuosity of the porous medium. Here, a theoretical analysis indicates that the new equation is capable to generalize several models existent in the literature. Besides, parameter estimations fitting experimental data of different materials show that the present model can be used to describe the relationship between permeability and porosity of many materials, such as sandstones, sisal fiber mat and glass fiber fabrics.     

Size of polymeric particles forming hemodialysis membranes determined from water and solute permeabilities

Regarding hemodialysis membranes as layers packed with uniform polymeric particles, the size of the particles is determined using the Kozeny–Carman equation. Diameter of the spheres forming cellulosic membranes is the same order as the size of primary polymeric particles determined by electron microscopy in a previous article. Pore radii of the membranes calculated by the Kozeny–Carman equation are in agreement with those determined by the tortuous capillary pore model. The result suggests that an estimate of a pore radius of a membrane is feasible by the Kozeny–Carman equation only with water permeability of the membrane. Intramembrane diffusion coefficients of vitamin B₁₂ calculated from an equation derived from the analogy of heat conduction in heterogeneous media consisting of a continuous phase and particles are larger than the experimental values. The result suggests the failure of the analogy between heat conduction and diffusion of vitamin B₁₂ in a heterogeneous medium. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:833–840, 1998     

Non-destructive investigations of pore morphology of micropore carbon materials

Pore morphology of experimental micropore carbon materials was explored using non-destructive methods. The influence of the heat treatment on porosity of two micropore carbon materials was investigated using helium porosimetry (HP) and X-ray micro-computed tomography (µCT). Methodology of µCT image processing and separation of the total and the open porosity is presented. In both materials open pores were found over the whole height of the sample. The local pore thickness and tortuosity of the materials were calculated. The increase of the porosity after heat treatment is observed for both materials.     

The effect of bisphenol monomer structure on the gas permeability of aromatic polycarbonates

Permeability measurements for oxygen and, to a lesser extent, carbon dioxide were carried out on a series of 24 structurally different aromatic polycarbonates. Polymers were prepared from bisphenols bearing substituents on the aromatic rings and/or the central aliphatic carbon atom. A strong correlation between monomer structure and polymer permeability was found, with gas transport rates varying by over two orders of magnitude between the most and the least permeable materials. In addition, a semilogarithmic relationship was found between oxygen transmission rates and monomer composition for two series of copolycarbonates. Of several methods explored, an excess free volume model was found best able to relate the experimental permeability values to the polymer molecular structure.     

Mercury intrusion porosimetry in concrete technology: tips in measurement,pore structure parameter acquisition and application

Mercury intrusion porosimetry (MIP) has been widely used to investigate the pore structure of cement based materials for many years. The purpose of this paper is to present views of how to make MIP results of similar materials from different research institutes compatible and how to use MIP results in modeling. Factors that influence MIP results are analyzed comprehensively considering characteristics of cement based materials, and recommendations corresponding to these factors are illustrated. According to these recommendations, when specific tests are unavailable, mercury surface tension of 480 mM/m and mercury-solid contact angle of 130° may be used in theoretical calculations of pore size; sampling by either sawing or core-drilling, maximum value of the minimum sample dimension of 5 mm, and solvent drying are recommended for sample preparation; and staged operation mode which set appropriate equilibrium time is recommended for MIP measurements of cement based materials. From a MIP result, the methods which are necessary to be unified to determine pore structure parameters are discussed. Besides, it is shown that sometimes pore structure parameters should be used carefully in physical models by considering their physical or statistical meanings.     

Electrohydraulic shock wave generation as a means to increase intrinsic permeability of mortar

This article discusses the influence of compressive shock waves on the permeability of cementitious materials. Shock waves are generated in water by Pulsed Arc Electrohydraulic Discharges (PAED). The practical aim is to increase the intrinsic permeability of the specimens. The maximum pressure amplitude of the shock wave is 250 MPa. It generates damage in the specimens and the evolution of damage is correlated with the intrinsic permeability of the mortar. A threshold of pressure is observed. From this threshold, the increase of permeability is linear in a semi-log plot. The influence of repeated shocks on permeability is also discussed. Qualitative X Ray Tomography illustrates the evolution of the microstructure of the material leading to the increase of permeability. Comparative results from mercury intrusion porosimetry (MIP) show that the micro-structural damage process starts at the sub-micrometric level and that the characteristic size of pores of growing volume increases.     

Use of nanocomposites as permeability reducing admixtures

Permeability is one of the fundamental properties of concrete structures as it is strictly related to durability. Mitigation of the degradation processes induced by aggressive solutions can be achieved by controlling water penetration through the pore network. In this study, we test the potential use of nanocomposites as waterproofing agents in concrete. Macroscopic measurements show that the addition of a small amount of nanoparticles effectively reduces the extent of the water permeation front. A combination of experiments, based on X‐ray tomography, mercury intrusion porosimetry, and BET nitrogen adsorption, and of numerical simulations, are used to interpret the macroscopic observations. These investigations show that C–S–H precipitation away from cement surfaces, induced by the presence of nanoparticles, leads to a refinement of the pore network. Such a microstructural change in the cement matrix results in a net reduction in the overall concrete permeability.     

A study on anticorrosion effect in high-performance concrete by the pozzolanic reaction of slag

The study examines the pozzolanic reaction brought by the addition of slag to the cement paste using the synchrotron radiation accelerator (SRA), the mercury intrusion porosimetry (MIP), and scanning electron microstructural analysis. The anticorrosion effect in high-performance concrete with and without slag added is also assessed by its electrical resistivity and permeability. Results show that pozzolanic reaction due to the addition of slag can decrease the amount of calcium hydroxide, reduce the volume of capillary pores (Pc), and lower its permeability, thus making the concrete more compact and durable. As evidenced by the enhanced electrical resistivity and reduced permeability, the addition of slag to high-performance concrete can indeed strength the anticorrosion effect.     

Assessment of permeation quality of concrete through mercury intrusion porosimetry

Permeation quality of laboratory cast concrete beams was determined through initial surface absorption test (ISAT). The pore system characteristics of the same concrete beam specimens were determined through mercury intrusion porosimetry (MIP). Data so obtained on the measured initial surface absorption rate of water by concrete and characteristics of pore system of concrete estimated from porosimetry results were used to develop correlations between them. Through these correlations, potential of MIP in assessing the durability quality of concrete in actual structure is demonstrated.     

Some comments on the microstructure of hardened cement pastes

The effect of water/cement ratio of hardened cement pastes in the range 0.23 to 0.71 on the micropore structure as revealed by mercury intrusion and nitrogen adsorption porosimetry is discussed. The relationship between these micropores and the solid minerals as revealed by electron microscopy is also discussed.     

Thermal Damage on LX‐04 Mock Material and Gas Permeability Assessment

RM‐04‐BR, a mock material for the plastic‐bonded HMX‐based explosive LX‐04, is characterized after being thermally damaged at 140 °C and 190 °C. We measured the following material properties before and after the thermal experiments: sample volume, density, sound speed, and gas permeability in the material. Thermal treatment of the mock material leads to de‐coloring and insignificant weight loss. The sample expanded, resulting in density reductions of 1.0% to 2.5% at 140 °C and 190 °C, respectively. Permeability in the mock samples was found to increase from 10⁻¹⁶ to 10⁻¹⁵ m², as the porosity increased. The permeability measurements are well represented by the Blake‐Kozeny equation for laminar flow through porous media. The results are similar to the gas permeability in PBX‐9501 obtained by other researchers [1, 2].