Permeability Of Cementitious Materials Research Articles

Effect and mechanisms of surface treatment using nano titanium dioxide on the permeability of cementitious materials

Corrosive media typically penetrate the interior of cementitious materials through porous structures, causing corrosive damage. Strengthening the surface structure of the substrate is an effective method for enhancing the durability performance of such a material. This study investigates the effects of different concentrations of a nano titanium dioxide suspension (NTS) used for the surface treatment of cement specimens after 24 h of molding and the influence of this treatment on the impermeability of the substrate surface. The results indicate that at 28 d of hydration, water absorption by the 1 % NTS-treated specimens decreases by 45 %, and the resistance to chloride-ion penetration increases by 32.7 % with respect to that of the control group. Furthermore, results of the microscopic tests indicate that when NTS surface treatment is conducted on hardened cementitious materials, NTS provides nucleation sites to enhance the degree of cement hydration, fill minuscule voids, promote the dispersed growth of hydration products, optimize the surface pore structure, and increase the density of the microstructure, thereby improving the impermeability of the substrate surface. This study is expected to provide innovative ideas for the future utilization of nanomaterials for strengthening surface structures and enhancing the durability performances of cementitious materials.

Pore Structure and Permeability of Cementitious Materials Containing a Carboxylic Acid Type Hydrophobic Agent

Integral hydrophobic treatment is the most effective method to prolong the service life of the concrete by resisting the transport of water containing aggressive ions. The hydrophobicity phenomenon of cementitious materials with carboxylic acid type admixture has been presented, and experimental studies, including water adsorption, amount of hydration products, and pore system, are conducted to reveal the hydrophobicity mechanism. It is reported that cementitious materials containing hydrophobic admixture present excellent water resistance ability, and the experimental results of nitrogen adsorption isotherm show that carboxylic acid type admixture addition increases pore volume and surface area of cement pastes. In addition, the fractal geometry theory is applied to reveal the relation between the pore structure and the permeability coefficient of cement pastes with a hydrophobic agent. In conclusion, the high tortuosity fractal dimension and the hydrophobicity of the pore surface result in water resistance when the cementitious system is mixed with a new type of hydrophobic admixture.

Moisture diffusion in cement pastes with hydrophobic agent

Hydrophobic treatment of cement pastes is most effective ways to resist the penetration of water with aggressive ions to improve durability of cement-based materials. In this paper, the influence of carboxylic acid ammonium salt integral addition on hydrophobicity of cement-based materials is analyzed. The effects of carboxylic acid ammonium salt on hydrophobicity, moisture diffusion and hydration products are investigated by experimental methods. The results of water vapor sorption isotherm show that the addition of carboxylic acid ammonium salt increases the pore volume. The simplified analytical hydrodynamic model of cone type pore and Young’s relationship is proposed to analyze the relation between characteristic parameters of pore and the permeability of cementitious materials. It can be concluded that the hydrophobicity results from the change of pore structure and the hydrophobic surface of cone region. These results provide the guidance to design the durability and to develop the new hydrophobic agent used in cementitious material.

Permeability of cementitious materials using a multiscale pore network model

This paper presents a new multiscale pore network modelling framework for predicting saturated and unsaturated permeability of OPC-based cementitious materials using a novel algorithmic implementation. The framework fundamentally relies on the data on cement composition and current understanding of cement hydration kinetics and microstructural features. Central to the modelling framework is the ability to numerically estimate pore size distribution (PSD) from existing models and the ability to obtain snapshots of unsaturated microstructure for various degrees of saturation. The framework is an amalgamation of three important existing models: (i) particle packing model for predicting nanoscale PSD, (ii) cement hydration kinetics to estimate microscale PSD, and (iii) a pore network model to estimate the permeability. The proposed pore network modelling is validated against an extensive set of experimental data that includes a very wide range of materials. The predicted intrinsic permeability falls well within the accepted experimental range. Though fewer experimental data are available to compare, the predicted unsaturated permeability shows highly promising results.

Harmonic analysis on the effect of potential perturbations and electrodes arrangements on the electrochemical impedance (EIS) measurement of cementitious material

Electrochemical impedance spectroscopy (EIS) is an accurate method to measure material property development and permeability of cementitious materials. To obtain a reliable data set, however, an appropriate test parameter is required. Numerous studies used different perturbation amplitudes. But, the question of how these variations may influence the reliability and reproducibility of the impedance spectra is still unanswered. This study used the harmonic analysis to determine the stochastic and systematic errors during the EIS measurements. Sequential EIS measurements were conducted on cylindrical concrete specimens with embedded reinforcement steel under different amplitudes of potential perturbation varying from 5 mV up to 500 mV. Total harmonic distortion and noise-to-signal ratio analysis were employed to assess and optimize perturbation amplitude for EIS measurement. Results revealed that although increasing perturbation amplitudes decreases the noise-to-signal ratio, it may adversely influence the harmonic and the linearity of the responded current spectra and reduces the reliability of data at lower frequencies.

Empirical correlation between mortars mechanical and durability tests with different cementitious materials replacements

The durability of concrete against penetration of chloride ions is one of the most important factors that can affect the serviceability of structures. Many tests can measure or predict the durability of concrete structures during their lifespan. Recently, many researchers have tried to provide different relationships and correlations between durability tests. The rapid chloride migration test, the electrical resistivity test and the water absorption test are some of the common and practical tests that may be used for studying the durability and permeability of cementitious materials. Providing an empirical correlation among these tests could yield the opportunity to estimate the durability parameters. This study presents relationships between durability tests and their correlations with the compressive strength in mortars containing rice husk ash, nanosilica and sugar cane bagasse ash. The empirical correlation between electrical resistivity and the migration coefficient followed the Nernst–Einstein equation. A strong linear correlation between electrical resistivity and compressive strength of binary mixtures was found, whereas a weak correlation was found for ternary mixtures. Moreover, a strong power correlation between electrical resistivity and capillary absorption of mortars was found.

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.

Comportement différé des mortiers soumis au séchage et effet induit sur la perméabilité

ABSTRACT This study aims to give information, on the one hand, about the evolution of drying shrinkage according to mortar composition, and on the other hand, about the effects of hygro-mechanical microcracking on permeability of cementitious materials. It also deals with the influence of the interstitial fluid nature on the permeability. The results obtained demonstrate that the drying shrinkage of the two studied mortars versus weight loss shows three characteristic phases shown in literature. They also put in light, through the study carried out on the mortar with W/C=0.5, that the permeability of dried samples increases after creep while that in drying creep remains constant, compared to the dried samples without creep.