Refinement Of Pore Structure Research Articles

Incorporation of reduced graphene oxide in waste-based concrete including lead smelter slag and recycled coarse aggregate

Waste-based concrete stands as an environmentally friendly and sustainable optifon compared to conventional concrete. The waste-based concrete holds the potential to reduce the unfavorable ecological effects associated with the concrete production. In this research, along with ground granulated blast furnace slag (GGBS) and fly ash (FA) as alternative binders to cement, lead smelter slag (LSS) as sand and recycled coarse aggregate (RCA) have been utilized in the production of the waste-based concrete. The influence of reduced graphene oxide (rGO) on mechanical and durability characteristics of the waste-based concrete has been assessed. Four rGO dosages of 0%, 0.05%, 0.1% and 0.3% by weight of binder were incorporated. Scanning electron microscopy and thermogravimetric analysis were conducted to assess the rGO-reinforced concrete's microstructure. The findings indicate that rGO improves the characteristics of the waste-based concrete. 0.1% is the optimum dosage of rGO to increase the compressive strength (47%), splitting tensile strength (44%), and flexural strength (42%) and decrease the water absorption (45%) and drying shrinkage (35%) of the concrete. Further dosage leads to reduced properties of the concrete. In addition, the waste-based concrete incorporating 20% FA, 50% GGBS, 100% LSS, and 100% RCA reinforced with 0.1% rGO exhibits similar mechanical and durability properties to the conventional concrete. The enhanced performance of the waste-based concrete can be related to the reduced porosity, refined pore structure, densified hydration products and increased hydration degree of the concrete by incorporating rGO.

Nanoscale chloride diffusion in alkali-activated steel slag and ultrafine blast furnace slag considering the electrical double layer effect

Utilizations of industrial byproducts and wastes as much as possible, together with desirable durability, are essential to sustainable development of building materials. In this work, the chloride diffusion behavior of alkali-activated steel slag (SS) and ultrafine blast furnace slag (UFS) is studied, towards deeper insights into the effect of electrical double layer on the resistance to chloride penetration. The microstructure improvement of alkali-activated SS with increasing addition of UFS was examined by means of X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, mercury intrusion porosimetry and nitrogen sorption. The zeta potentials above the pore surface of various alkali-activated SS-UFS systems were measured and compared. The electrostatic resistance of the electrical double layer to chloride diffusion was analyzed and discussed. Results indicate that UFS dosages above 40% substantially refines the pore structure of alkali-activated SS and then the mechanism governing chloride penetration shifts from capillary transport to gel transport. The exposure of higher chloride sodium concentration results in the pore surface of alkali-activated SS-UFS systems to be less negatively charged and the zeta potential is reversed to be positive value after continuous ion exchange between sodium and calcium. The presence of UFS can remarkably increase the proportion of physically bound chloride that attains approximately 80% of the total binding capacity. The impediment of electrical double layer to chloride diffusivity becomes increasingly pronounced with pore structure refinement, especially for mixtures with diffusion coefficients below 5 × 10−12 m2/s obtained based on Fick's law of diffusion.

Sustainable utilization of alkali-activated steel slag material: Effects of silicate modulus and GBFS on fresh, mechanical and pore structure properties

To improve the sustainable utilization of alkali-activated steel slag material, experiments were conducted to systematically investigate effects of sodium silicate modulus and GBFS content on the setting time, workability, mechanical properties and pore structure of alkali-activated steel slag cementitious material. Results show that the setting time is prolonged and workability is reduced as silicate modulus increases. The setting time is first shortened and then prolonged and workability is slightly reduced as GBFS content increases. Increasing silicate modulus and adding GBFS have positive effects on the development of elastic modulus, compressive and splitting tensile strength of alkali-activated steel slag material due to more refined pore structure. The highest compressive strength at 28 d can reach C35 strength level. Manufacturing alkali-activated steel slag material can achieve low energy consumption and carbon emission. If chemical activators can be replaced by some industrial wastes, cost, energy consumption and carbon footprint will be further decreased.

Development of high-volume fly ash concrete with improved interfacial transition zone

The interfacial transition zone (ITZ) is a vulnerable region in concrete, particularly in high-volume fly ash (HVFA) concrete where a significant portion of fly ash particles remain unreacted. In order to improve the ITZ of HVFA concrete, this work introduces a novel approach by targeted employing slag in the ITZ. Slag-modified cement paste was used to coat coarse aggregate, which was further mixed with other materials to cast HVFA concrete. Various parameters during preparing the coated coarse aggregate, such as the water-to-cementitious material ratio of the cement paste, the slag content in cementitious materials, the mass ratio of coarse aggregate to cement paste, the mixing time of coarse aggregate and cement paste, and the drying time after mixing, were investigated to uncover their influence on the porosity of the ITZ in HVFA concrete. By using the optimized values of these variables of 0.35, 3.8%, 3.2, 10 min and 1 h, respectively, it is feasible to achieve ITZ in HVFA concrete characterized by a porosity of 23.6% and refined pore structure, alongside enhanced compressive strength of the concrete.

MgO/KH2PO4 and Curing Moisture Content in MKPC Matrices to Optimize the Immobilization of Pure Al and Al-Mg Alloys.

Magnesium Potassium Phosphate Cements (MKPCs) are considered a good alternative for the immobilization of aluminium radioactive waste. MKPC composition and moisture curing conditions are relevant issues to be evaluated. The corrosion of pure aluminium (A1050) and AlMg alloys (AA5754) with 3.5% of Mg is studied in MKPC systems prepared with different MgO/KH2PO4 (M/P) molar ratios (1, 2, and 3M) and moisture curing conditions (100% Relative Humidity (RH) and isolated in plastic containers (endogenous curing)). The Al corrosion potential (Ecorr) and corrosion kinetic (icorr and Vcorr) are evaluated over 90 days. Additionally, the pore ion evolution, the matrix electrical resistance, the pore structure, and compressive strength are analysed. The corrosion process of Al alloy is affected by the pH and ion content in the pore solution. The pore pH increases from near neutral for the 1M M/P ratio to 9 and 10 for the 2 and 3M M/P ratio, increasing in the same way the corrosion of pure Al (AA1050) and AlMg alloys (AA5754). The effect of Mg content in the alloy (AA5754) becomes more relevant with the increase in the M/P ratio. The presence of phosphate ions in the pore solution inhibits the corrosion process in both Al alloys. The MKPC physicochemical stability improved with the increase in the M/P ratio, higher mechanical strength, and more refined pore structure.

Chloride penetration resistance of ultra-high performance concrete with various multi-walled carbon nanotubes

Ultra-high performance concrete (UHPC) with outstanding chloride penetration resistance (CPR) exhibits excellent prospects for extending the service life of structures in the marine environment. This study investigates the effects of various types and contents of multi-walled carbon nanotube (MWCNT) on the CPR of UHPC, including pristine MWCNT with different sizes, MWCNT with surface modification, and MWCNT with special structures. The results show that 0.25% thick-short pristine MWCNT, 0.5% short hydroxyl functionalized MWCNT, and 0.25% helical MWCNT show more significant enhancement effect, improving the CPR by 74.14%, 72.91%, and 77.17%, respectively. The correlation analysis results suggest a negative linear correlation between the CPR and pore volume of the composites. The C-S-H gels and small capillary pores with a diameter below 50 nm are the significant factors determining the CPR of the composites. This illustrates that the CPR enhancement effects of various types of MWCNT change with the refinement of pore structure of UHPC. The enhancing mechanisms can be attributed to the nano-core effects of MWCNT, reducing the CH crystal size and primary cracks, inhibiting the growth and propagation of microcracks, refining the pore structure, optimizing the compactness of the cement paste matrix and interfacial transition zone, thus reducing the channels for chloride ion diffusion, while increasing the constrictivity and tortuosity of the channels.

Effects of carboxylated styrene‐butadiene latex nanoparticles on channeling leakage and pore structure of oil well cement

AbstractThe exploitation efficiency of oil and gas resources depends on the cementing quality. In cementing engineering, interlayer migration occurs in the underground gas layer with cement hole as the main channel, which seriously threatens the sealing integrity of cement casing and leads to the failure of cementing operation. To improve the gas migration control ability of oil well cement (OWC), two carboxylated styrene‐butadiene latex nanomaterials styrene butadiene latex containing itaconic acid and sodium p‐styrene sulfonate (SBSI) and styrene‐butadiene latex containing methacrylic acid and sodium p‐styrene sulfonate (SBSM) were synthesized. The effects of SBSI and SBSM with different carboxyl structures on the gas migration control ability and pore structure of cement were investigated. The results show that the latex is densely packed on the cement matrix through the dissociation and adsorption behavior of carboxyl groups, and the smaller particle size and lower adsorption are more conducive to the formation of the film. The introduction of latex effectively shortened the transition time of cement gel state and significantly reduced the permeability of interlayer material migration. Compared with OWC, the transition time of cement containing SBSI and SBSM latex (SBSI/OWC and SBSM/OWC) decreased from 28 to 18 and 17 min, respectively, and the filter loss decreased from 60 to 40 and 36 mL, respectively. The isolation effect of the latex film on the interlayer gas and the provision of mechanical support have greatly improved the gas migration control ability of the cement and ensured the cementing quality. In addition, the refinement of cement pore structure caused by latex brings better rheological and mechanical properties to cement. This study clarified the change of latex in the gel transition stage of OWC from liquid to solid and revealed the mechanism of latex on the internal structure change of cement. It broadens the application range of latex nanomaterials in the field of OWC and provides a new possibility for the use of OWC in high temperature and high salt environment.

Improvement of shrinkage resistance and mechanical property of cement-fly ash-slag ternary blends by shrinkage-reducing polycarboxylate superplasticizer

Fly ash and slag are two commonly used supplementary cementitious materials (SCMs) in modern concrete, which can significantly enhance the long-term durability of concrete. However, their application is somewhat limited due to the negative impact on early strength development and shrinkage cracking. This study proposed using a recently developed shrinkage-reducing polycarboxylate admixture (SR-PCA) to alleviate the above problems. The effect of SR-PCA on compressive strength, drying shrinkage, autogenous shrinkage, mass loss, pore structure and hydration process were also investigated. The results showed that SR-PCA enhanced the 28d compressive strength due to the refinement of pore structure and improved hydration degree. With the addition of SR-PCA, the drying shrinkage and autogenous shrinkage were significantly reduced, particularly in the mixture blended with 50% fly ash, while showing a slight impact in the sample with 50% slag. SR-PCA decreased the drying shrinkage by lowering the hydrous compressibility factor (CF) value and mesopore volumetric percentage. The incorporation of SR-PCA retarded cement hydration at an early age, thereby reducing the early-age autogenous shrinkage, while the long-term autogenous shrinkage was mitigated due to the enhancement effect on the hydration degree at 28 days. Therefore, SR-PCA is a practical approach for enhancing shrinkage resistance and compressive strength in cement-fly ash-slag blends, thereby contributing to the broader application of these industrial by-products.

In-situ wet carbonation activation of red mud waste for sustainable grout materials

The low reactivity and high alkalinity of raw red mud (RRM) limit its utilization as supplementary cementitious materials (SCMs) in Portland cement-based grouts. This work develops an in-situ wet carbonation technique to improve the chemical reactivity of RRM using flue gas CO2. Systematic investigation of the RRM before and after carbonation revealed transformed composition and microstructure. The minerals and morphology changed significantly, with nano-CaCO3 and amorphous silica/silica-alumina gels formation. This enhanced the pozzolanic reactivity of RRM. Detailed evaluation of the effects of carbonated red mud (CRM) as SCMs on the properties of Portland cement-based grouts showed accelerated hydration kinetics and refined pore structure. Replacement of 30% cement by the CRM increased the 28 d compressive strength of the grout. The underlying mechanisms were analyzed via XRF, XRD, TGA, FT-IR, 29Si NMR, SEM, and N2 adsorption–desorption testing. The nano-CaCO3 and silica/silica-alumina gels from CRM participated in additional hydration and microstructure densification. This integrated approach enables the improved performance of grouting materials through CO2 mineralization and industrial waste recycling.

Chemo-physical mechanisms of high-strength cement composites with suprastructure of graphene quantum dots

Recently, there has been considerable interest in utilizing various forms of graphene derivatives for producing high-strength concrete. Among these derivatives are superstructure of graphene quantum dots (GQDs), particularly in their assemblies of carbon dots, which is innovative in cement. This research investigates the impact of graphene derivatives known as supra-GQDs on the mechanical properties and microstructure analysis of cement composites, compared with the control mixture and GQDs solution. The results found that supra-GQDs exhibit enhanced mechanical characteristics. The composite containing 1.2 % supra-GQDs had higher compressive and flexural strengths than the control by 40 % and 108 %, respectively. The study also identified a microstructural bridging mechanism involving the seeding and crystal growth of the C-S-H phase, leading to refined pore structure and less nano-, meso-, and micro-pores. The measured total pore volume reduced by 30 % when compared to GQDs solution. This investigation provides novel insight into the potential of utilizing supra-GQDs in cement composites, opening promising possibilities for high-performance concrete in the construction industry.

Utilization of municipal solid waste incinerator bottom ash (MSWIBA) in concrete as partial replacement of fine aggregate

Enhancing sustainable economic development while maintaining environmental integrity is of paramount importance. In this context, the effective utilization of municipal solid waste incinerator bottom ash (MSWIBA) presents a significant opportunity. This study investigated an approach for harnessing the potential of MSWIBA by incorporating it as a partial replacement for fine aggregate in concrete mixtures. Twelve concrete samples were prepared with varying proportions of MSWIBA. The mechanical and microstructural properties of the samples were comprehensively investigated. Moreover, the environmental and economic advantages of these concrete formulations were assessed. The results revealed that the water absorption of the concrete samples without MSWIBA was higher than that of the concrete samples with MSWIBA, suggesting that the added MSWIBA could fill the internal pores of concretes. The water absorption rate curve could be divided into three stages, i.e., rapid decline, slow decline, and stable. The optimal replacement ratio of fine aggregate with MSWIBA was between 24.8% and 57.8%. Notably, when the replacement ratio surpassed 24.8%, MSWIBA positively influenced the development of compressive strength, but it still lower than that of composite Portland cement-based concrete (OPC). Furthermore, pore structure analysis indicated that the efficacy of pore refinement was achieved within a certain replacement threshold. However, the efficacy of pore structure refinement diminished beyond that threshold. The substitution of fine aggregate with MSWIBA aligns with the technical specifications and building material standards, thereby complying with the principles of effective utilization, sustainability, and environmental consideration pertinent to MSWIBA management.

Development and evaluation of basaltic volcanic ash based high performance concrete incorporating metakaolin, micro and nano-silica

High-performance concrete is an excellent choice for modern engineering structures due to its superior performance, low maintenance costs, and long service life. Therefore, this study was aimed to produce high-performance concrete by incorporating a high volume of basaltic volcanic ash along with metakaolin (MK), micro-silica (MS), and nano-silica (NS). An investigation was performed in regard to the mechanical and durability properties, autogenous and drying shrinkage, and microstructural and pore-structure properties. A control mix, binary mixes, and ternary mixes were examined. The binary mixes contained fine (VA) and ultra-fine (VAF) volcanic ashes, and the ternary mixes contained combinations of VA with MK, MS, and NS. Test results show that ternary mixes with 30% and 40% cement substitution demonstrated better strength development and higher resistance to chloride penetration and water absorption. All binary and ternary mixes displayed lower autogenous shrinkage, as well as lower or comparable drying shrinkage than the control mix. Moreover, the combination of VA with MK, MS, and NS up to 40% resulted in micro and pore structure refinement by forming high-density gels. The findings indicate that VA in combination with MK, MS, and NS, can effectively substitute cement at up to 40% for the production of sustainable high-performance concrete.

Production of sustainable lime-based brick using carbonated recycled concrete fines: Mechanical, mineralogical and microstructure properties

A novel method for reusing construction waste and simultaneously sequestering CO2 in the form of mineral carbon is presented in this study. The method involves the production of construction bricks using waste concrete fines treated with carbonation. Initially, waste concrete is crushed and ground into recycled concrete fines (RCF), which are then subjected to a carbonation process to obtain carbonated recycled concrete fines (CRCF). Comprehensive characterization using XRD, TGA, FTIR, and zeta potential measurements reveals that CRCF exhibits a microstructure featuring silica-coated calcium carbonate particles on its surface, imparting significant reactivity to CRCF. In this investigation, RCF and CRCF are separately mixed with Ca(OH)2, molded, and compressed into bricks, with performance testing conducted under various material ratios and manufacturing conditions. The results indicate that bricks made with CRCF exhibit mechanical properties exceeding those of RCF-based bricks by more than two-fold. This improvement can be attributed to the refined pore structure observed in CRCF bricks. The highly reactive silica gel present on the surface of CRCF reacts with Ca(OH)2 to form C-S-H, providing a rationale for the superior strength displayed by CRCF bricks.

Particle size effect of pre-wet zeolites on autogenous shrinkage and mechanical properties of LECC

The conservation effects can vary significantly when utilizing zeolite internal curing (IC) agents of different particle sizes in Lightweight Engineered Cementitious Composites (LECC). This paper addresses this issue by investigating the impact of zeolites with varying particle sizes (with average particle sizes of 90 μm, 240 μm, and 410 μm) on the mechanical and shrinkage properties of LECC. Furthermore, it delves into the intrinsic influencing mechanisms through pore characterization parameters and quantitative techniques for assessing the degree of hydration. The results demonstrate that the particle size of zeolite exerts a substantial influence on the conservation efficiency of LECC. Specifically, small-sized zeolite effectively eliminates pores larger than 200 μm within the LECC matrix, resulting in significant enhancements in its mechanical properties (a 16% increase in compressive strength) and shrinkage resistance (a 54% reduction in shrinkage). Conversely, large-sized zeolite diminishes the mechanical properties of LECC, albeit contributing to some extent to improved shrinkage properties (a 32% reduction in shrinkage). The improved conservation effect of small-sized zeolite stems from the refined pore structure and the filling effect of volcanic ash. Pore structure analysis reveals that small-sized zeolite yields a finer pore structure, primarily distributed within the 12 μm range. This enhances water absorption and release, consequently improving conservation efficiency. Additionally, hydration product analysis indicates that small-sized zeolite promotes cement hydration, resulting in a 9% increase in the degree of cement hydration.

Impact of synthetic C-S-H seeds on early hydration and pore structure evolution of cement pastes: A study by 1H low-field NMR and path analysis

C-S-H seeds are highly-efficient in promoting hydration but not compromising the long-term performances of cement. Unfortunately, mechanisms of the C-S-H seeds properties affecting the early-age performances of cement are not very well understood. In this study, the influence of hydrothermal synthetic conditions on the C-S-H seeds properties is firstly investigated, followed by revealing the correlations of C-S-H seeds properties, hydration kinetics, and pastes performances by using in situ 1H LF-NMR and path analysis. It is found that low reactant concentrations and calcium-to-silicon ratios facilitate the production of C-S-H seeds with small size and high purity. Using C-S-H seeds with high effective surface area, i.e. nano-sized and high purity, the acceleration period of cement starts within 2 h and ends after 6 h, which in turn results in a refined pore structure and an enhanced strength, particularly at 12 h. An increased CH content leads to a decreased C-S-H growth rate.

The mechanical strength, microstructure, and transport properties of steel slag reinforced loess soil system

Steel slag, as an industrial byproduct obtained from the steel manufacturing industry, may cause land occupation, resource waste, and environmental pollution. The application of steel slag as a material for soil reinforcement in road engineering is very popular due to its potential hydration activity. The unconfined compression strength, microstructure, and transport properties of loess soil with cement, lime and steel slag were investigated. The results show that the loess soil can be reinforced by cement, lime, and steel slag to varying degrees. The reinforcement mechanism of cement for loess soil is realized by pore filling by cement hydration products such as CH, C-S-H and AFt, and their unconfined compression strength is improved by reducing the porosity. The reinforcement mechanism of lime for loess soil is achieved by pore filling by hydration products such as CH and CaCO3, and their strength is improved by a refined pore structure where the porosity has not been significantly reduced. The reinforcement mechanism of steel slag for loess soil is a combined mechanism of cement and lime, including pore filling and refined pores. The pore structure of reinforced soil can be studied at different scales by the MIP, LF NMR, and X-CT test methods. The transport properties including diffusivity and permeability of reinforcing soil can be well explored by Avizo software based on the microstructure obtained from X-CT.

High-purity vaterite CaCO3 recovery through wet carbonation of magnesium slag and leaching residue utilization in cement

This work turned industrial waste of magnesium slag (MS) into two value-added products, high-purity vaterite and supplementary cementitious materials, through “leaching-carbonation” method. The various parameters on the leaching rate of Ca2+ from MS by using NH4Cl solution were investigated. The spherical vaterite with high purity of 96.5 % and high surface area (27.89 m2/g) could be successfully produced through wet carbonation of leachate with addition of glycine as crystal modifiers. In addition, the leachate solid residue (LSR) obtained from leaching process of MS had a smaller size destruction and higher surface area in comparison to Portland cement, resulting in an accelerated hydration process. The amorphous silica gel in LSR had a high pozzolanic effect, which resulted in a higher compressive strength development and refined pore structure in comparison to control samples. This work provides a novel treatment and can realize the high value-added utilization of MS.

Characteristic microstructural phase evolution and the compressive strength development mechanisms of tricalcium silicate pastes under various initial carbonation curing environments

The effects of various initial carbonation curing environments on the phase evolution and resulting mechanical characteristics of tricalcium silicate paste were studied. For the analyses of the reaction products and microstructure, synchrotron X-ray diffraction, thermogravimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and high-resolution X-ray computed tomography were utilized. C3S cured under carbonation environment pressurized by 0.1 MPa showed excellent mechanical properties owing to the highest degree of reaction and homogeneous generation of CaCO3 with low-Ca/Si calcium silicate hydrates, resulting in a dense matrix with refined pore structure. C3S paste treated under other carbonation conditions underwent deteriorative microstructural phase transitions, including void evolution by decalcification of C–S–H and an inhomogeneous composition of crystalline phases, resulting in inferior properties.

Bio-functionalization of metakaolin for better performance of metakaolin mortars

This study was conducted to investigate the influence of gallic acid (GA), the smallest molecular unit of tannic acid, on the performance of metakaolin (MK) mortars. GA was added directly as an admixture (Method I) or pre-mixed with MK (Method II) for bio-functionalization. Experimental results showed that GA improved the dispersion of MK by generating electrostatic repulsion and spatial site resistance between particles. The GA functionalization of MK by Method II displayed superior efficiencies in adjusting the fluidity of mortars owing to better dispersibility. The functionalization of MK by GA could enhance the pore filling effect resulting from the dispersed MK, and enable more products to be generated owing to the formation of GA ∼ Ca intermediates, contributing refined pore structure and increased compressive strength to mortars. The compressive strength of MK mortars has been optimally increased by 13.0—18.0% when using 0.1% GA.

Pore structure profile of ambient temperature-cured geopolymer concrete and its effect on engineering properties

Ambient temperature-cured geopolymer concrete (GPC) with solid alkali activators are attracting attention as an eco-friendly alternative to OPC-based concrete (OPCC) for industrial applications. This research investigates the pore structure and microstructural characteristics of GPC via porosimetry and micrography and strives to connect the micro-scale characteristics to macro-scale engineering properties. The dominance of slag and low water content resulted in a denser and more homogenous microstructure in the binder with fewer microcracks and voids. Furthermore, a refined pore structure was observed when the fly ash/slag ratio was 60/40. The porosimetry analysis demonstrated that OPCC possessed a uniform pore structure with a similar porosity profile throughout the concrete cross-section. GPC showed a descending pore gradation profile from top to bottom. The difference in the pore structure profiles can explain the previously witnessed shrinkage behaviour of GPC and OPCC in restrained conditions.