Porosity Of Cement-based Materials Research Articles

Convection-diffusion-electromigration coupled numerical simulation of water and chloride in cement-based materials

The transport of chloride in cement-based materials is influenced by various factors, and the chloride diffusion coefficient in numerical models should be the steady-state value under specific conditions, which is difficult to obtain through traditional experiments. In this article, based on an improved non-contact resistivity instrument, the steady-state chloride diffusion coefficient and porosity of cement-based materials are characterized. Considering the acceleration effect of moisture convection and electric field on chloride transport, a numerical model for moisture and chloride transport coupling diffusion, convection, and electromigration is established. Based on the measured steady-state chloride diffusion coefficient and porosity values, the influence of interface transition zone (ITZ), electric field type, chloride binding effect, initial conditions, and boundary conditions on moisture and chloride transport is numerically analyzed. It is found that the increase of ITZ thickness, electric field strength, boundary concentration, and initial concentration can accelerate chloride transport. The chloride concentration distribution curve exhibits a “shoulder peak” caused by chloride binding effect, and its peak height and width are positively correlated with the chloride binding coefficient. In conclusion, this study aims to better understand the ion transport behavior inside cement-based materials under coupling of convection, diffusion, and electromigration, and identify the key factors influencing this behavior, which provide a feasible scheme for durable design of concrete construction in environments rich in erosive media.

Influence and mechanism analysis of different types of water reducing agents on volume shrinkage of cement mortar

This study investigated the impact of five commonly employed water-reducing agents on the fluidity of cement paste at varying dosages firstly. The agents considered in this research are sodium lignosulfonate (LS), naphthalene superplasticizer (PNS), aliphatic superplasticizer (HSB), and two types of polycarboxylate superplasticizers (PCEs), specifically PCE-5C and PCE-6C. Subsequently, the impact of water reducing agents on both the total drying shrinkage and autogenous shrinkage of cement mortar was investigated. This was done by maintaining a consistent water-cement ratio, ensuring good workability, and adjusting the dosage of various water-reducing agents to achieve comparable slump flow in the mortar. Furthermore, the study delved into the mechanisms behind the influence of different types of water-reducing agents. The findings indicate the following: 1) Polycarboxylate superplasticizers (PCEs) exhibit superior dispersion performance with cement, trailed by naphthalene superplasticizer (PNS) and aliphatic superplasticizer (HSB), while sodium lignosulfonate (LS) demonstrates the least effective dispersion performance. The fluidity of cement paste is most responsive to variations in the dosage of PCEs, followed by PNS and HSB, whereas the fluidity of cement paste undergoes minimal changes when the dosage of LS is increased. 2) The effects of various water reducing agents on the volume shrinkage of cement mortar are distinct, and their influence is the outcome of multiple factors working in tandem. These factors include the postponement of the exothermic peak during cement hydration, reduction in solution surface tension, and decrease in the proportion of larger pores and smaller-sized capillary pores within the porosity of cement-based materials, and all these aspects collectively contribute to minimizing the volume shrinkage of cement-based materials. 3) In the realm of concrete engineering, opting for PCEs as water-reducing agents has proven effective in reducing the overall drying shrinkage of cement-based materials. Notably, PCE-5C demonstrates a superior ability in minimizing shrinkage compared to PCE-6C.

Review of the Influence of Acrylate Lotion on the Properties of Cement-Based Materials.

Polymer-modified cement-based materials have been widely used in the construction field. Acrylate lotion significantly improves durability, toughness, and bending resistance, especially durability, because the porosity of cement-based materials is reduced, preventing the entry of harmful ions and water. When acrylate lotion was at 20%, the resistance of cement-based materials to chloride ion penetration increased by 40%. At the same time, the fracture toughness of cement-based materials modified with acrylate lotion and carbon nanotubes increased by 10-15%. The flexural strength of cement-based materials modified by acrylate lotion and fiber increased by 29%. Additives such as TiO2 have a unique impact on the modification of cement-based materials, which has attracted the interest of researchers. This paper reviewed the performance of acrylate lotion-modified cement-based materials and the application of acrylate lotion in the field, which systematically increased the durability, mechanical properties, and waterproof properties of cement-based materials when acrylate lotion was modified, acrylate lotion was modified with nanomaterials, acrylate lotion was modified with other polymers, acrylate lotion was modified with fiber, and when acrylate lotion was modified with other additives. The shortcomings of acrylate lotion modification with different materials were reviewed and evaluated, and the comprehensive performance of cement-based materials modified by acrylate lotion was expected to achieve maximum strength improvement under the synergistic effect of various modifications.

The effect of bleeding on ice formation and water transport in blended cement systems

The presented paper aims to investigate how bleeding affects the ice formation and transport properties of blended cement systems. Three compositions of cement paste were studied, i.e., consisting of pure Portland cement, and containing silica fume and granulated blast furnace slag respectively. The ice content along with the distance from the surface was monitored using differential scanning calorimetry. The amount of ice formed in pore system decreased along with sample depth. However, bleeding mainly affects the crystallization within the connected capillary pores occurring above −30 °C. It was shown that the application of supplementary cementitious materials shortens the zone affected by bleeding and reduces the ice content. The porosimetric study revealed that the porosity of cement-based materials is not homogeneous along with depth. The large pores of diameter from 200 to 800 nm, which are similar to the ones resulting from the excess water introduced to cement paste with high water-to-cement ratio, appear in the vicinity of the surface. In order to investigate this effect in concrete, the water transport properties were studied. The results of capillary rise and water permeability tests evince that the fluid movement is increased if it occurs through the surface zone.

Impact of calcium ions leaching caused by biogenic acid attack on durability of cement composites

Leaching of calcium ions increases the porosity of cement-based materials, consequently resulting in a negative effect on durability since it provides an entry for aggressive harmful ions, causing corrosion of concrete. Sulphuric acid corrosion of concrete can be caused due to attack of aggressive media naturally existing in the environment. Another possibility of corrosion formation is biogenic acid effect through the agency of microorganisms. The paper is focused on the investigation of the influence of biogenic acid attack on the cement composites affected with bacteria Acidithiobacillus thiooxidans. The concrete specimens with 95% wt. addition of antimicrobial activated granulated blast furnace slag as durability increasing factor as well as without any addition were studied. The experiments proceeded during the nine 7-day cycles. The pH values and chemical composition of leachates were measured and evaluated after each cycle. The higher resistance of concrete samples with the addition of 95% wt. of antimicrobial activated granulated blast furnace slag to the aggressive environment was confirmed. The leaching of calcium ions of concrete sample affected with bacteria Acidithiobacillus thiooxidans was 1.13 times lower (736.6 mg/L of leachate) for concrete sample with antimicrobial activated granulated blast furnace slag addition comparing to concrete sample of ordinary CEM I Portland cement without any additives (832.0 mg/L of leachate).

Methods for Porosity Characterization of Cement Based Materials

ABSTRACTImportant pore structure parameters related to mechanical properties and durability of cement-based materials can be determined by techniques such as scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and low temperature calorimetry (LTC). The methods provide information on porosity characteristics as pore volume, pore thresholds and/or pore size distribution in different size ranges and do therefore to a large extent supplement each other. Pastes of w/b=0.4 with 0%, 40% or 70% slag by volume were cured saturated at 20ºC for up to two years. The porosity was characterized by LTC, MIP, and SEM. Higher volume of pores was obtained by MIP compared to results obtained using LTC and SEM. Measured porosity was correlated with predicted porosity using information on the density and degree of hydration of the cement and slag. Porosity estimation showed best agreement with the porosity data measured by MIP. The use of slag showed the same trend for all tests: a higher total volume of pores, but a lower threshold pore size when compared with Portland cement paste. The findings illustrate the importance of measuring not only pore volume but also threshold pore sizes when characterizing porosity of cement-based materials with different binder compositions.

Capillary porosity depercolation in cement-based materials: Measurement techniques and factors which influence their interpretation

The connectivity of the capillary porosity in cement-based materials impacts fluid-and-ion transport and thus material durability, the interpretation of experimental measurements such as chemical shrinkage, and the timing and duration of curing operations. While several methods have been used to assess the connectivity of the capillary pores, the interpretation of some experimental procedures can be complicated by the addition of certain chemical admixtures. This paper assesses capillary porosity depercolation in cement pastes using measurements of chemical shrinkage, low temperature calorimetry (LTC), and electrical impedance spectroscopy. The experimental results are analyzed to identify the time of capillary porosity depercolation. In addition, the factors that influence the interpretation of each technique are discussed. Experimental evidence suggests that capillary porosity depercolation, as defined by Powers, occurs after hydration has reduced the capillary porosity to around 20% in cement paste systems. The influence of capillary porosity depercolation on the transport properties is demonstrated in terms of a reduction in the electrical conductivity of the cementitious material. Special attention is paid to understand and interpret the influence of shrinkage-reducing admixtures (SRAs) on the freezing behavior of cementitious systems, particularly in regard to the inapplicability of using LTC to detect porosity depercolation in cement pastes containing such organic admixtures.

Influence of Cover Porosity on Steel Corrosion in Cement-Based Materials

A detailed investigation has been carried out to clarify the effect of porosity on steel corrosion in cement-based materials. Corrosion behaviours of steel were studied by means of corrosion potential, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS), while the porosity of cover zone cement-based materials were investigated by evaporative water method (EWM) and mercury intrusion porosimetry (MIP). The results highlight that the corrosion parameters of steel are strongly related with porosity of cement-based materials. A linear relationship between porosity and corrosion rate of steel has been established which is in good agreement with the principle that the diffusion of chloride ions through porous cementitious materials may accelerate the anodic reaction of steel corrosion as well as oxygen diffusion for the cathodic reaction simultaneously.

The Preparation of Porous Materials Using Liquid Metal Impregnation for BSE Characterization with a Scanning Electron Microscope

The infiltration of porous and particulate materials for metallographic examination with low-melting alloys was first described by Rose and DeRoos . The use of Wood's metal to fill porosity in sandstone was reported by Craze , by Dullien , and by Yadev et al. . Changes in pore structure and phase dispersions in iron ore pellets after simulated blast furnace reduction were reported by Shultz et al. , wherein liquid Bi-Sn impregnation was used to prepare cross sections of deformed and reduced pellets for backscatter electron imaging. Steele and Engel also applied the technique to examine the microstructure in commercial boron nitride (BN). In that study porosity formed by leaching the B2O3phase was filled with liquid metal to allow argon-ion etching to expose the BN microstructure. The characterization of cracks and porosity in cement-based materials after filling with Wood's metal has been reported by Nemati et al. . Cracks developed during compression testing of marble were studied byin-situmetal impregnation in Chang et al. .

Characterization of the development of microstructure and porosity of cement-based materials by numerical simulation and ESEM image analysis

Characterization of the development of microstructure and porosity of cement-based materials by numerical simulation and ESEM image analysis