Pore Structure Of Cement-based Materials Research Articles

Non-destructive characterization of pore structure and chloride diffusion coefficient of cementitious materials with modified non-contact electrical resistivity method

The intricate pore structure of cement-based materials passively influences chloride ion transport and mechanical properties. Existing non-contact electrical resistivity measurement (NC-ERM) methods lack precision for rigorous studies. the NC-ERM was upgraded in this research, which is suitable for assessing the pore structure and transport characteristics of hardened cementitious substrates. The results obtained from this method closely correspond to those obtained from CEMHYD3D, Mercury intrusion porosimetry (MIP), and other methods. Additionally, the impact of mixture proportions on the resistivity, pore structure parameters, and chloride ion diffusion coefficient of cementitious materials is discussed. With an increase in sand ratio and sand-to-stone ratio, the resistivity exhibits an initial rise followed by a decline. Chloride diffusion of 5 wt% NaCl-saturated specimens is 1.2–1.3 times higher than 3.5 wt% NaCl. This study provides a novel non-destructive, convenient and accurate method for characterising the pore structure and testing the transport properties of cementitious materials.

Simulation study on the impermeability improvement effect of cement-based materials with different pore structures

The impermeability of cement-based materials is the first line of defence for ensuring durability. Improvements in the impermeability of cement-based materials can be achieved by optimising their pore structure. However, the mechanism by which the improvement in impermeability of cement-based materials varies with their initial porosity remains unclear and requires systematic research. In this study, a simulation method was used to investigate this mechanism. It was found that for cement-based materials with different initial porosities, when the reduction in porosity resulting from pore structure optimisation was within the range of 0.8%–7%, as the initial porosity increased from 10.1% to 38%, the improvement in impermeability increased from 1.1% to 19.6% when the connectivity of the pore structure remained unchanged, and from 1.3% to 24.3% when the connectivity of the pore structure weakened. A mathematical relationship between the impermeability improvement effect and pore structure characteristics, including initial porosity, porosity reduction, and pore structure connectivity, was established, forming a macroscopic mechanism model for the impermeability improvement effect. According to this model, the macroscopic mechanism of nano-modified cement-based materials reveals that nano silica has more significant modification effects on the pore structure of cement-based materials with lower initial porosities.

New insight of solvent-replacement-induced damage to pores of cement stone by comparison with 1H NMR relaxometry, mercury intrusion porosimetry, and nitrogen adsorption

The consensus on the damage to pore structure of cement-based materials caused by solvent-displacement-drying method has yet not been achieved. This work explored the effect of replacing pore water with ethanol, methanol, isopropanol, cyclohexane and acetone on the pore parameters of hardened white cement paste by means of low field NMR, mercury intrusion porosimetry and nitrogen adsorption techniques, with direct-drying (oven-drying and vacuum-drying) as the control. The results show that the degree of damage to the pore structure after secondary-solvent-replacement is close to that of direct- drying in terms of porosity, total pore area, characteristic pore size and pore size distribution. The difference of pore parameters of samples dried by different solvent-displacement is caused by the physical properties of solvents and the reaction with hydration products. Furthermore, thermal analysis results have confirmed the reaction between acetone and hydration products to generate a dark brown substance. If the possible chemical reaction between organic solvents and hydration products is not considered, the pore structure of cement stone can be well protected by replacing pore water with methanol.

Understanding strengthening mechanisms of Ca-LDO on cementitious materials

The influence of CaAl-layered double oxide (Ca-LDO) on physical properties, mechanical properties, hydration process, and pore structure of cement-based materials was investigated systematically in this study. The results demonstrated that 0.5% and 1% of Ca-LDO contributed to the development of mechanical properties of mortar, which could be attributed to the integration of the seed effect, internal curing effect, and micro-filling effect. In contrast, more than 1% of Ca-LDO was deposited on the surface of cement hydration products. Besides, the polymerization degree of C–S–H gel was reduced and the growth of monosulfate (AFm) was inhibited, which hindered the cement hydration process. These findings are expected to provide theoretical guidance for the application of layered double hydroxides (LDHs) in cement-based materials.

Agglomeration behavior of colloidal nano-silica and its effect on pore structure, mechanical properties and shrinkage of cement mortar

The pozzolanic activity of colloidal nano-silica (CNS) can promote cement hydration, thereby improving the performance of the cement-based materials. However, the CNS itself presents highly electronegative, upon contact with cementitious materials, the electrostatic repulsion between CNS particles is lost due to the high ionic strength and the presence of multivalent cations in cement paste, which could lead to the destabilization of CNS and the formation of CNS aggregate (CNSA). Furthermore, similar to CNS, the chemical composition of CNSA is still amorphous silica because no chemical reaction occurs during the CNS agglomeration process. In theory, CNSA has similar nano effect and chemical activity effect to CNS and it can obviously accelerate the hydration rate of cement, improve the mechanical properties and pore structure of cement-based materials. This study aims to investigate the agglomeration behavior of CNS in cement pore solution (i.e. particle size distribution, zeta potential, residue Ca2+, microstructure) and its impact on the workability, pore structure and mechanical properties of cement mortar. It is proved that CNSA was formed by the complex of CNS and Ca2+ by electrostatic adsorption. And CNS content played a significant role on obtaining stable and narrow dispersion of CNSA in cement pore solution and the optimal content was found out to be 0.4 wt% where the particle size of the CNSA was still in the nanometer scale and stable at 200 nm. Cement mortar properties were also significantly improved through addition of 0.4 wt% CNS. While the basic workability was maintained, the 28-day compressive strength and flexural strength of cement mortar were improved by 8.94 % and 8.75 % respectively, the 28-day porosity was reduced by 8.76 %.

Effects of incorporating large quantities of nickel slag with various particle sizes on the strength and pore structure of cement-based materials

Firstly, nickel slag sand with a concentrated particle size distribution in the range of 2.36–0.60 mm was used to replace the mechanism sand in the ratio of 0%, 25%, 30%, 50%, 70% and 100%. Second, partial particle size substitution was used to partially replace nickel slag sand with particle sizes of 2.36–1.18 mm and 1.18–0.60 mm in proportions of 0%, 30%, 50%, 60%, 70% and 100%, respectively, to optimize particle gradation of mixed sand. Cement mortar specimens were prepared using different mixed sands composed of the above two substitution methods and at a water-cement ratio of 0.5. Then, the effects of nickel slag sand with varying substitution methods on the strength and pore structure of cement-based materials were investigated by mechanical tests, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Standard sand was also used as an experimental control group. The experimental results revealed that the maximum flexural and compressive strength of nickel slag sand using a full-size substitution group corresponded to an optimal dosage of 30%, while the optimal dosage of nickel-slag sand using a specific-size substitution group was 60%. The water absorption of the two particle sizes replaced the specimens decreased and then increased with the inclusion of nickel slag sand. The results showed a consistent trend with the variations in electrical resistivity and total porosity of MIP. From the SEM photographic results of the SS, MS, NF30 and NP60 specimens, the cement paste can be more tightly wrapped around the round spherical nickel slag particles. NF30 and NP60 specimens showed a denser internal structure, multi-dimensional hydration products and a lack of pores and microcracks, which is fully consistent with experimental results of mechanical properties and microstructures.

Catalysis and Regulation of Graphene Oxide on Hydration Properties and Microstructure of Cement-Based Materials

Graphene oxide (GO) is a two-dimensional material that adds functionalized oxygen-containing groups on the surface of graphene through strong acid oxidation. The oxygen-containing functional groups on the surface make GO have good dispersion and surface activity. When GO is incorporated into cement-based materials, while providing nucleation sites for cement hydration, it can also react with ions released by cement hydration. Therefore, GO has a catalytic effect on the hydration process of cement and plays a role in regulating the morphology of the hydration products, which in turn affects the formation of the microstructure of cement-based materials. In this study, the catalytic and regulatory effects of GO on the hydration characteristics, pore structure, and internal interface of cement-based materials are reviewed. The analysis shows that the oxygen-containing functional groups on the surface of GO can absorb a large number of water molecules, promote the dissolution of cement particles in water, and adsorb the Ca2+ released by cement particles, thereby reducing the concentration of Ca2+ around the cement particles and shortening the induction period of cement hydration. In addition, GO can provide more nucleation sites for cement hydration and shorten the hydration acceleration period. GO promotes the formation of hydration products through the nucleation effect and gradually transforms needle-like and rod-like hydration products into flower-like or polyhedral-like crystals. In addition, GO optimizes the pore structure of cement-based materials when it affects cement hydration and the morphology of hydration products through the above-mentioned effects. In addition, it makes the connection between hydration products closer through the bridging effect, so that the total porosity of cement-based materials decreases, gel-pore content increases, capillary-pore content decreases, and pore structure is significantly optimized. Finally, while optimizing the pore structure of cement-based materials, GO has an obvious optimization effect on the interface transition zone (ITZ) of cement-based materials, which significantly reduces the ITZ width and increases the ITZ density.

Non-Contact Multiple-Frequency AC Impedance Instrument for Cement Hydration Based on a High-Frequency Weak Current Sensor

This paper presents a new non-contact alternating current impedance instrument (NCACII) with multiple frequencies to measure the electrical impedance during the hydration of cement-based materials. It implements two measurement techniques: the first technique is a frequency conversion measurement with a frequency variation range of 1–100 kHz. The second is to measure the variation in impedance with time. It provides a new way to analyze the pore structure of cement-based materials. In this instrument, we design a current sensor made from nanocrystalline T37. The experimental results demonstrate the detection accuracy of NCACII has been improved and indicates the superiority of nanocrystalline T37.

Upcycling of construction spoil powder as partial cement replacement for sustainable cement-based materials: Properties and modification

Construction spoil accounts for the main part of construction and demolition waste, the effective recycling of which has been paid less attention to by previous investigations. This work investigated the feasibility of utilizing waste spoil powder (WSP) ground from construction waste as partial cement replacement for preparing sustainable mortar, and a 800–1200 °C heat treatment was employed to modify the properties of WSP. The WSP with an irregular particle shape contains massive inert quartz, anorthite and kaoline, and mixing WSP reduces the hydration reaction and enlarges the pore structure of cement-based materials. However, new metakaolin and amorphous components are generated in heat-treated WSP, and heat-treated WSP has higher activity than untreated WSP; besides, the paste with heat-treated WSP has finer pore size than the paste with untreated WSP. The drying shrinkage of mortar increases by intermixing WSP; but the mix of heat-treated WSP reduces the drying shrinkage, and the maximum shrinkage of mortar with 30% WSP after 1200 °C treatment is 25.0% lower than that of plain mortar. Incorporating WSP reduces the mechanical strength and meanwhile increases the water absorption of mortar, but the mortar including heat-treated WSP has higher strength and lower water absorption than the mortar with untreated WSP. Decreasing WSP particle size further improves the properties of WSP blended mortar. It is noticed that incorporating heat-treated WSP together with active mineral admixture can prepare sustainable mortar with similar mechanical strength and lower water absorption than plain mortar without WSP.

Research on the sulfate resistance of cement-based materials incorporating dolomite powder

The effects of dolomite powder on the sulfate resistance of cement-based materials with water-binder ratio (w/b) of 0.55 and 0.36 were investigated in this manuscript. Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and pressure testing machine were used to determine the apparent morphology, micro-morphology, mass increase rate, flexural strength and compressive strength of cement-based materials containing dolomite powder. The sulfate resistance of mortars was improved with increasing dolomite powder dosage. Generally, the flexural strength and compressive strength of mortars in Na2SO4 solution were higher than those in water. Within 150 days of immersion, the corrosion resistance coefficient and compressive corrosion resistance coefficient of mortars increased with increasing dolomite powder dosage. The pore structure of cement-based materials became more compact with the addition of dolomite powder. Accordingly, the sulfate resistance was improved by controlling the dynamics stage due to the fact that the pore structure of cement-based materials was refined with the addition of dolomite powder. The 150-day compressive corrosion resistance coefficients of mortars with a w/b of 0.55 in the case of dolomite powder at 0 and 30 wt% replacement levels were less than 1, suggesting that long-term immersion in sulfate solution increased the deterioration rate of cement-based materials.

Improved Crack Resistance and Pore Structure of Cement-Based Materials by Adding EVA Powder

The improved properties of ethylene-vinyl acetate (EVA)-modified cement-based materials have not been fully clarified, especially crack resistance and pore structure. The purpose of this research was to investigate the influence of EVA copolymer on the mechanical performances and microstructural properties of cement paste. Strengths, autogenous and drying shrinkage, and water absorption expansion were investigated to evaluate the mechanical properties and volume stability. The ring restrained shrinkage and chloride permeability tests revealed the crack resistance and enhancement of impermeability. The microstructures of EVA-modified cement-based materials were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicated that mixing EVA into cement-based materials increased the flexural strength, reduced the crack propagation and chloride ion penetration, and reduced the negative capillary pressure by improving the water retention. The addition of EVA resulted the remarkable reduction of harmful pores. The optimal mass fraction of EVA powder was approximately 4%.

Effects of incorporating large quantities of copper tailings with various particle sizes on the strength and pore structure of cement-based materials

Although it is estimated that approximately 300 million tons of copper tailing is produced in China annually, only about 8.2% of this byproduct is reused. Therefore, to promote natural material sustainability, and value-added utilization of copper tailings in China, tailings from Hubei (HT) and Jiangxi (JT) were explored as replacement materials for the fine natural aggregate. The water/cement ratio was fixed at 0.50, and various proportions of fine aggregate were replaced (0%, 30%, 50%, 70%, and 100%). The size distribution of the tailings particles was as follows: HT (1.18 to 0.15 mm) and JT (0.60 to 0.15 mm). This study was made to match the size distribution of the tailings with that of the fine aggregate it replaced. The mechanical properties and pore structure were assessed using the methylene blue test, flexural tensile strength test, compressive strength test, absorption test, fluidity test, mercury intrusion porosimetry (MIP) test, and scanning electron microscopy (SEM). The control group (without tailings) presented the highest flexural strength but the lowest compressive strength. The experiment group achieved the highest flexural and compressive strength under 50% HT content or 70% JT content. Overall, MIP results show that inclusions in tailings tend to reduce “harmless pores” (pores < 20 nm). SEM observations at 7 days revealed that unreacted tailings particles filled the macropores between fine aggregate and paste. Observations at 28 days revealed fewer unreacted tailings particles. The finer tailings particles reacted with calcium hydroxide in cement to form hydrated calcium silicate gel and fill pores, thereby enhancing the strength of cement mortar.

The effect of powder activated carbon on mechanical properties and pore structures of cement-based mortars

Powdered activated carbon (PAC) has a well-developed micropore structure for adsorbing nitrous oxides, volatile organic chemicals (VOCs) and erosion ions in cement-based materials with the potential to improve their durability and the multi-functionality. The mechanical properties, water absorption ratio and pore structure of cement-based mortars were investigated with PAC of 0.5%, 1.0% and 2.0% by weight of cement and fly ash (FA). As PAC incorporation ratio increased, the compressive and flexural strengths of the mortars with and without FA both increased. PAC had a significant impact on the evolution of the pore structure of the cement pastes with and without fly ash, causing changes in the water absorption ratio of the mortars. As the PAC incorporation ratio increased from 0.5% to 2.0% by mass of the binders, the total porosity of the cement pastes without FA increased, but the total porosity of the FA-blended cement pastes decreased. When PAC and FA were used together in cement pates, PAC was excellently compatible with the cement matrix, dispersing well into the hardened cement pastes in 3-dimensional space. The volume fraction in the micron-scale pore structures using 3-dinmensional visualization was decreasing with an increase of the incorporation of PAC and the degree of reaction of fly ash. Therefore, PAC is an effectively porous material for improving the mechanical properties and pore structure of cement-based materials.

Segmented Fractal Pore Structure in Cement-Based Materials Blended with Dolomite Powder

The macroscopic property of cement-based materials depends on their pore structure. Due to the complex and disordered pore structure of cement-based materials, traditional parameters like porosity and mean distribution radius are not accurate enough for strength predictions. Fractal geometry was employed to characterize the complexity of pore structure more accurately than existing parameters, especially the scale-dependent fractal properties, which are more dependent on the pore ranges. In this study, the pore size range of cement-based materials containing dolomite powder was regularly segmented to characterize the scale-dependent fractal nature of the pore structure. The relationship between the segmented fractal dimension and the compressive strength was discussed. Results based on the mercury intrusion porosimetry (MIP) and mechanical property tests showed that the difference existed in the relationship between segmented fractal dimension and dolomite powder content under various pore ranges. The relationships between compressive strength and fractal dimension of gel pores and fractal dimension of large pores presented positive and negative linear function, respectively. The strength equations expressed in terms of the segmented fractal dimension were proposed. Regression analysis proved that the equations in this study had high prediction accuracy.

The waterproofing effect and mechanism of graphene oxide/silane composite emulsion on cement-based materials under compressive stress

The influence of the water-to-binder ratio and compressive stress on the waterproofing effect of graphene oxide/isobutyltriethoxysilane (GS) composite emulsion on cement-based materials was investigated. The results show that GS combines with calcium silicate hydrate to form a hydrophobic film, which prevents the intrusion of external water and carbon dioxide. In addition, after undergoing self-condensation, silanol reacts with calcium hydroxide to generate calcium silicate hydrate gel, which improves the microstructure of cement-based materials. Furthermore, the increase in the water-to-binder ratio and stress ratio leads to the expansion and connection of the pore structure of cement-based materials, resulting in an increase in the capillary water absorption coefficient. Meanwhile, the higher porosity is conducive to the penetration of the emulsion in cement-based materials and the formation of a waterproof layer. Thus, the waterproofing effect of GS composite emulsion on the specimen was improved.

The effect of layered double hydroxides intercalated with vitamin B3 on the mechanical properties, hydration and pore structure of cement-based materials

Layered double hydroxides (LDHs) intercalated with corrosion inhibitors (INT-LDHs) are often used for corrosion inhibition of reinforced concrete. However, the environmentally friendly inhibitor intercalation LDHs is rare, and the law of the influence of INT-LDHs on the properties of cement-based materials is still unclear. In this paper, green inhibitor vitamin B3 intercalated LDHs (VB3-LDHs) were prepared, and its effects on the hydration, pore structure and mechanical properties of cement-based materials were systematically studied. As the results shown, a suitable amount of VB3-LDHs could improve the pore characteristics of cement paste by promoting cement hydration and filling effect. When the content of VB3-LDHs was 3%, the 28d compressive and flexural strength increased by 9.87% and 14.18%, respectively. 1% and 6% VB3-LDHs have no significant effect on mechanical properties of cement-based materials.

Pore Size Distribution and Surface Multifractal Dimension by Multicycle Mercury Intrusion Porosimetry of GGBFS and Limestone Powder Blended Concrete

Eco-friendly concrete mixtures make efficient use of constituents with reduced environmental impact to secure durable structures. Ternary mixes containing Portland cement, ground granulated blast-furnace slag (GGBFS) and limestone powder (LP) have demonstrated a good balance between environmental impact, economic cost and technical performance. The pore structure of cement-based materials determines the transport of species; hence its description is a valuable tool for predicting their durability performance. In this paper, textural analysis of the pore structure of Portland cement concrete and GGBFS and limestone powder blended concrete is assessed by multicycle mercury intrusion porosimetry (MIP). Results from three intrusion-extrusion cycles were used for determining pore volume, size distribution and surface multifractal dimension. The hysteresis during the experiments is mainly explained by the combined effects of ink-bottle pores and different contact angles for the intrusion and retraction. The analysis of the surface multifractal dimension of the pore structure showed no significant effects of GGBFS and limestone powder on the pore wall texture of concrete samples. The outcome depicts the advantages of using multiple intrusion-extrusion cycles during MIP experiments, as well as the effect of 35 wt.% GGBFS, 25 wt.% GGBFS + 10 wt.% LP, and 25 wt.% of LP, on concrete pore structure.

Improved non-contact variable-frequency AC impedance instrument for cement hydration and pore structure based on SVM calibration method

The non-contact alternating current (AC) impedance method is widely used in the study of electrochemical properties of cement-based materials,the instrument of this paper provide a new way for the study of pore structure of cement-based materials. Due to the loss of magnetic materials and the parasitic capacitance of measuring circuit, the ratio difference and phase difference of current sensor inevitably exit. Traditionally the standard resistor calibration method is used to determine the ratio error and phase error under different frequencies based on polynomial fitting (FT). In this paper, a machine-learning support vector machine (SVM) model is used to predict the calibration data with a small test sample. For the accuracy assessment, SVM model has the best comprehensive performance among FT, artificial neural network (ANN). The actual impedance test of typical cement-based materials under different frequencies is given and the results verify the excellent performance of SVM.

Physicochemical Characteristics and Pore Structure of Cement-Based Materials Subjected to External Multi-Ions Attacks and Drying-Wetting Cycles

Physicochemical Characteristics and Pore Structure of Cement-Based Materials Subjected to External Multi-Ions Attacks and Drying-Wetting Cycles

Influence of Neutralization Accelerated by the Soak Method on the Radon Exhalation of Cement-based Materials.

Radon is considered a significant contaminant that affects indoor air quality. Neutralization is one of the most important environmental factors in changing pore structure of cement-based materials that may release radon. Therefore, it is necessary to study the radon exhalation of cement-based materials impacted by neutralization, which is extremely lacking. Some concrete blocks were accelerated to neutralization by soaking in sodium bicarbonate solution, and the radon activity concentrations over the blocks were measured to investigate the effect of neutralization on radon exhalation. Controlled experiments were conducted with blocks in the initial dry state and soaked in pure water. The results show that the radon activity concentration exhaled from block is promoted by neutralization, and the promoting role of water is quite limited. The radon surface exhalation rate increases by increasing the sodium bicarbonate solution concentration from 0.5% to saturation.