Effect of Pore water expression on solid composition of cement paste

Pore solution expression is the most commonly used method to obtain aqueous phase in cementitious material. However, the high pressure applied on the sample may affect solid phase composition. This paper presents an experimental study on the chemical and mineral composition of cement paste before and after the expression. Results indicate that a small part of the alkali contained in samples can be excluded during the pore solution expression, mainly depending on alkali concentration in the pore solution. Due to the expulsion of interlayer water in C-S-H under high pressure, the pore solution expression reduces bound water content measured by TGA. The portlandite content determined by TGA is not affected by pore solution expression, but it leads to an overestimation of portlandite in QXRD, because of the enhanced preferred orientation of the (001) plane under the applied high pressure. In addition, the size of portlandite crystal decreases to some extent due to the creep caused by pressure. The content of hemicarbonate phase is found to decrease slightly after pore solution expression, which may be aroused by the increased solubility under high pressure.

Porous Multiphase Microcharacteristics Research of New Cement-Based Grouting Material Concretion

As an excellent inorganic hydraulic cementitious material, new cement-based grouting material (abbreviated as NCG) has a wide application prospect in grouting engineering. Four types of water-cement ratio (W/C ratio) NCG concretions were systematically researched on the solid-phase composition, microscopic morphology, nanoscale pore characteristics and micron-scale multiphase microscopic characteristics through SEM, TGA-DSC, BET, MIP, and 3D-XRM in combination with hydration reaction mechanism. The NCG concretion is characterized as a spatial network structure formed by dendritic or columnar ettringite (AFt) crystals, filled with calcium silicate hydrate gel (C–S–H) and aluminum gel (AH3). In the solid phase, the mass of AFt is the highest, about 65%, the mass of C–S–H is about 20%, and the mass of AH3 is the least, about 15%. In nanoscale, the pore size of NCG concretion is concentrated in about 50 nm–3 μm, and the volume proportion reaches about 90%, which can be used as the characteristic parameter of pore-phase. With the increase of W/C ratio and age, the MPD of pore decreases, and the probability of the MPD-pore increases, and the dispersion of the probability of pores increases. In nanoscale, the porosity of NCG concretion is as high as 60%. With the increase of W/C ratio and age, the porosity of NCG concretion increases, but the effect on the density of solid-phase is little. In micron scale, the regular characteristics related to diameter of pore-phase and gel-phase are similar, showing a three stage formula: as their diameter increases, the number of monocases decreases and its rate of reduction gradually slows down, the volume-proportion decreases first and then increases, the differentiation of volume between the monocases increases gradually, and the differentiation between monocases shape and sphere is bigger, and its shape characteristics are more diverse and discrete.

A robust new tool for online solution-phase sampling of crystallizations

Current PAT tools struggle to provide real time solid-phase composition data for crystallizations. HPLC offers a variety of benefits over other solution-phase PATs and can be used to infer solid-phase...

Active wall through a porous media foam type: flow and transfer characterization

Despite the efforts to develop new solutions to achieve the objectives of positive buildings in energy, a few studies in this area has been performed using a porous media foam type. The aim of this paper is to present the behaviour transfers of flow through a multi-structured porous media and to achieve the influence of the porosity and the thermal conductivity properties of the skeletal phase, and the interaction with a cross flow in order to get the equivalent of a perfect insulator. Therefore, in a specially made device, a finite volume method was applied to study a flow through a porous media foam-type, which was simulated to characterize the properties of the equivalent medium in terms of permeability and thermal conductivity. The analysis demonstrates that the solid phase composition and the medium porosity, as well as the distribution of pore size, are preponderant characteristics to constitute a foam structured media. Furthermore, the thermal boundary layer given by a forced convection through the porous medium has demonstrated the important influence of the flow phenomenon in a thermodynamic coupling. Lastly, three optimum configurations for the construction envisaging a balance of depleted thermal and dynamic powers for a relative conductivity *=10 were found between the velocity 2 10-3 (m/s) and 4 10-3 (m/s).