Cement and Concrete Research(2024 - 2025)
Multiscale analysis on microstructural changes in hardened cement paste dried under different relative humidity levels: A comparison with cement paste containing water-dispersible polyurethane ether compound
Asamoto S.; Takahashi K.; Sakamoto N.; Sampei T.; Matsui K.
Cement and Concrete Research, Elsevier Ltd., Vol.194, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107896)
Abstract
This study investigated microstructural changes in hardened cement paste with and without a water-dispersible polyurethane (PU) ether compound under varying relative humidity (RH) levels. The small-angle X-ray scattering technique was used to analyse the agglomeration, piling, and densification of calcium silicate hydrate (C-S-H) units. Mercury intrusion porosimetry and water vapour sorption isotherms were used to further characterise pore structures and surface areas, focusing on the C-S-H unit changes across different RH levels and the influence of PU. The presence of PU reduced variation in scattering profiles and subsequent calculated disc thickness at each RH, indicating the inhibition of C-S-H structural evolution during drying. These findings indicate less variation in the pore structure and surface area during the drying process than in the paste without PU. The length change isotherm of the cement paste with PU confirmed reduced shrinkage and hysteresis, which can be attributed to microstructural stabilisation. c 2025 The Author(s)
Mechanisms of change in accelerated carbonation progress in cement paste under different relative humidity conditions
Cheng L.; Kurihara R.; Ohkubo T.; Kitagaki R.; Teramoto A.; Suda Y.; Maruyama I.
Cement and Concrete Research, Elsevier Ltd., Vol.195, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107898)
Abstract
This study investigated the evolution of water content and carbonation in OPC cement paste under low, intermediate, and high relative humidity (RH) conditions, emphasizing the role of water in accelerated carbonation and microstructural modifications. Under high RH, the carbonation suppressed after 28 days owing to calcium ion accumulation at the surface, precipitating as calcite. This calcite formation leads to a dense calcium carbonate layer, reducing the gas?liquid interfacial area for CO? dissolution and blocking further water evaporation and carbonation process. Low RH conditions cause the agglomeration of calcium silicate aluminate hydrate (C?(A)?S?H), increasing empty space in the microstructure. This facilitates CO? penetration but limits CH carbonation due to insufficient water availability. These findings highlight the significance of water distribution and microstructural evolution in CO? sequestration, revealing that RH critically influences the progress of carbonation by altering the pore structure and subsequent water availability in cementitious materials. c 2025 The Authors
Air entrapment and reaction with absorbed liquids on the absorption of aerated concrete
Fukui K.; Kobayashi S.; Takada S.
Cement and Concrete Research, Elsevier Ltd., Vol.191, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107824)
Abstract
Aerated concrete exhibits anomalous water transport, similar to mortar and concrete. Several factors, including water sensitivity, air entrapment, and gravity, are considered to be the causes; however, they are currently not quantitatively understood. This study aimed to clarify the mechanisms underlying the anomalous absorption of aerated concrete through liquid absorption experiments and numerical simulations of liquid and air transfer. The experiments showed that, unlike mortar and concrete, aerated concrete exhibited decreasing absorption rates during the initial stage of absorption, even when organic liquids were absorbed. A comparison between the calculations of simultaneous air and liquid transfers and those of single-phase water transfer in a material revealed that increases in water content in the high-water-content region were significantly reduced by air-pressure buildup. Therefore, the water absorption of aerated concrete, which is characterized by coarse aerated pores, is sensitive to air entrapment in addition to the water sensitivity of the cement component. c 2025 The Authors
Rate effect on the pull-out load of individual fibers in concrete: A probabilistic modeling approach
Kanazawa T.; Bolander J.E.
Cement and Concrete Research, Elsevier Ltd., Vol.193, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107857)
Abstract
Understanding of the load-rate dependence of fiber pull-out from concrete has been hindered by the large scatter of test data. Relatively little attention has been given to the statistical nature of single-fiber pull-out under different loading rates. The present study is based on a probabilistic interpretation of the pull-out phenomenon, assessing the statistical fluctuations observed in the common finding that complete pull-out occurs at greater load levels under higher loading rates. Since progressive debonding along the fiber?matrix interface affects the pull-out behavior, interfacial crack growth is modeled using a fracture mechanics approach. Based on a theoretical justification, the transition probability to debonding is devised and implemented within a Markov chain model. The Markov model accounts for debonding propagation with each stress increment until complete pull-out. The results demonstrate that the probability distributions of stress at complete pull-out differ from a normal distribution. The coefficient of variation is also independent of the loading rates. These findings show reasonable agreement with statistical variations observed from test data. c 2025 Elsevier Ltd
Mechanical behavior of concrete under high water pressure: Water penetration as a critical factor for mechanical properties
Kunawisarut A.; Kawabata Y.; Iwanami M.
Cement and Concrete Research, Elsevier Ltd., Vol.190, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107820)
Abstract
The combined effects of water pressure and water penetration on the mechanical behavior of concrete under hydraulic loading were investigated. When concrete is subjected to water pressure, a saturated zone forms near the surface and gradually progresses toward the interior over time, resulting in a non-homogeneous hybrid state with a saturated envelope and humid core (hybrid saturated state) during the initial stages of hydraulic loading. However, the mechanical behavior of concrete with a hybrid saturated state has hardly been investigated. This study performed the experiments on concretes with water pressures (~50 MPa). The results show that concrete with a hybrid saturated state exhibits higher peak mechanical stress than unconfined concrete. In contrast, the peak mechanical stress of fully saturated concrete remains comparable to that of unconfined concrete. This indicates that water penetration strongly influences the triaxial strength of concrete under water pressure, especially in the initial stages of hydraulic loading. c 2025 Elsevier Ltd
Incorporation of boron into metakaolin-based geopolymers for radionuclide immobilisation and neutron capture potential
Niu X.; Elakneswaran Y.; Li A.; Seralathan S.; Kikuchi R.; Hiraki Y.; Sato J.; Osugi T.; Walkley B.
Cement and Concrete Research, Elsevier Ltd., Vol.190, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107814)
Abstract
Metakaolin-based geopolymers have attracted significant interest in decontaminating radioactive debris from the Fukushima nuclear accident. This study explored the incorporation of boron (B) into geopolymers using boric acid as the source, with the goal of developing B-enriched geopolymers for enhanced radionuclide immobilisation and neutron capture potential. The addition of boric acid lowered the pH of the alkali activator, reducing metakaolin solubility and impeding alkali-activated geopolymerisation. B formed an unstable BO4(xB, 4-xSi) structure with extra short-range Si tetrahedra in low-temperature curing conditions, making it prone to be leached out. High-temperature curing facilitated alkali-activated geopolymerisation, mitigating some negative effects of boric acid. It also promoted partial incorporation of BO4 into the framework, reducing leaching. Additionally, in acid-activated geopolymers, boric acid absorbed substantial reaction heat during the initial dealumination phase by reacting with PO4, thereby enhancing the overall geopolymerisation degree and increasing the relative content of near-Si terminal P and Al6 units. B could be incorporated into the framework by bonding with numerous Al-unsaturated Si tetrahedra to form a stable BO4(0B, 4Si) structure. Although B introduction slightly reduced the positive charge of the acid-activated geopolymer's structure, decreasing its capacity to immobilise anionic SeO32? through electrostatic adsorption, the decrease was negligible. Conversely, B introduction increased structural compactness, which improved Cs+ immobilisation through physical entrapment. Overall, the B-containing acid-activated geopolymer effectively incorporated B into the main matrix while maintaining radionuclide immobilisation capacity. This study provides valuable insights into the selection and incorporation mechanisms of the B-containing geopolymer matrix, contributing to effective strategies for radioactive waste disposal. c 2025 The Authors
Semi-dry natural carbonation at different relative humidities: Degree of carbonation and reaction kinetics of calcium hydrates in cement paste
Saeki N.; Kurihara R.; Ohkubo T.; Teramoto A.; Suda Y.; Kitagaki R.; Maruyama I.
Cement and Concrete Research, Elsevier Ltd., Vol.189, 2025, .
(https://doi.org/10.1016/j.cemconres.2024.107777)
Abstract
This study investigated semi-dry carbonation at different relative humidities (RH) under atmospheric CO2 concentrations to determine the effect of RH on the degree of carbonation (DoC) and reaction rates. The carbonation kinetics of each calcium-containing hydrate exhibited an initial rapid chemical-reaction-limited stage, followed by a significantly slower stage. DoC values plateaued after 200 days of carbonation, reaching 78 % at 95 % RH and 34 % at 33 % RH, aligning with EN 16757 values for sheltered outdoor and indoor environments, respectively. When the samples reached a stable DoC at a given RH, further carbonation occurred upon exposure to higher RH, implying that the DoC was governed by the highest RH to which the samples had been exposed. The phase assemblage was also affected, approaching thermodynamic equilibrium at higher RH but deviating at lower RH due to the formation of local equilibria and the presence of metastable phases. c 2024 The Author(s)
Durability of cementitious binders with blast furnace slag in deep sea conditions: Analysis of microstructure and phase transformation
Takahashi K.; Kawabata Y.; Kobayashi M.; Kasaya T.; Miyamoto S.; Wong H.S.
Cement and Concrete Research, Elsevier Ltd., Vol.196, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107942)
Abstract
Portland cement-blast furnace slag (PC-BFS) cement-based materials exhibit good durability in shallow marine environments but their performance in the deep-sea is poorly understood. This study investigates the degradation of PC-BFS cement pastes after one-year exposure in a deep-sea field site under high hydraulic pressure (3515 m depth) and low temperature (2 C) conditions. The results show that the main degradation mechanisms involve ettringite formation and Ca leaching, driven by low-temperature seawater ingress under pressure. SEM-EDS and XRD analyses revealed distinct microstructural changes such as Mg and Al enrichment and sulfate/chloride incorporation in BFS rims. Fluorescence imaging confirmed complete seawater infiltration, facilitating BFS dissolution and reprecipitation cycles. The findings highlight the vulnerability of PC-BFS systems to ettringite-induced damage due to their high alumina and low sulfate balance. These insights inform strategies to optimise cementitious materials for deep-sea applications under extreme environments. c 2025
Effects of Al in C?A?S?H gel on the chloride binding capacity of blended cement paste
Wang T.; Zheng Y.; Qian H.; Shi Z.; Medepalli S.; Zhou J.; He F.; Ishida T.; Hou D.; Zhang G.; Jiang Z.; Zhou Z.; Zhang W.
Cement and Concrete Research, Elsevier Ltd., Vol.190, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107805)
Abstract
This study quantitatively examines the impact of aluminum (Al) in C?A?S?H gelon the chloride binding capacity of blended cement paste containing supplementary cementitious materials (SCMs). The experimental results show that Al incorporation does not influence the physical chloride binding of C?A?S?H gel, which is governed by its Ca/Si ratio. However, in the presence of Cl? ions, the OH? ligands that stabilize high-coordination AlVI species (specifically [AlO?(OH)?]5?) can be replaced by Cl? ions. This replacement leads to the leaching of AlVI species from the C?A?S?H gel and an increase in OH? ion concentration in the solution. The released Al3+ ions then interact with Ca2+ and Cl? ions in the pore solution to form Friedel's salts (Fs), which further promotes the leaching of AlVI species. Consequently, the chemical chloride binding capacity of the cement paste increases as the Al/Si ratio of the C?A?S?H gel rises, along with refinements in paste microstructure. c 2025
Effects of Triethanolamine-Gallate on the workability, hydration and microstructure of steel slag supplementary cementitious materials
Zeng B.; Zhuang X.; Jia S.; Han W.; Zhong J.; Mo L.; Kishi T.
Cement and Concrete Research, Elsevier Ltd., Vol.190, 2025, .
(https://doi.org/10.1016/j.cemconres.2025.107810)
Abstract
Widely used hydration promoters primarily improve the early strength of steel slag supplementary cementitious materials (SCMs) but offer limited enhancement to later strength and fail to mitigate early hydration inhibition by steel slag (SS). This study introduces a novel organic hydration promoter, Triethanolamine-Gallate (TG), synthesized by modifying gallic acid with triethanolamine. TG imparted hydrophobicity to the SS composite cement powder, enhanced fluidity and increased initial and final setting times, and moderated hydration rate but improved overall hydration efficiency of SS composite cement. At 28d, the compressive strength of PS-TG-0.05% (PS was 70% PC and 30% SS) mortar was 21.1% and 13.3% higher than that of PS-Control and PS-TEA-0.05% mortar, respectively. TG promoted the transformation of C3S, C2S, C4AF, Ca2FexAl2-xO5 and CaCO3 into more C-S-H and Mc (monocarboaluminate), especially the new iron-containing Mc. TG also significantly refined the pores and reduced the cumulative pore volume of the SS composite cement. c 2025 Elsevier Ltd
Effect of alkali-hydroxide on hydration kinetics and microstructure of high-volume fly ash blended cement pastes
Ahmad M.R.; Medepalli S.; Wang T.; Dai J.-G.; Zheng Y.; Ishida T.
Cement and Concrete Research, Elsevier Ltd., Vol.185, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107641)
Abstract
The influence of NaOH on pore structure, reaction kinetics, volume, and morphology of reaction products in high-volume-fly-ash mixtures was explored by two mixing methods: (i) direct addition of 0.2 M, 0.5 M and 1.0 M NaOH solution into cement-FA powder, and (ii) pre-dissolving FA into NaOH solution before mixing with cement. The pre-dissolution technique improved early-age mechanical performance by enhancing Si release, aiding the expedited precipitation of extra C-A-S-H gel. Both methods improved the degree of FA reaction and alite/belite hydration. However, 1.0 M NaOH negatively affected the strength and microstructure properties due to undesirable silica-gel formation, C-A-S-H gel carbonation, and increased capillary pore volume. NaOH concentration has affected the packing density of C-A-S-H gel, where high-pH systems exhibit loosely packed sheet-like clusters. Ca/Si of C-A-S-H gel in low and high pH systems evolved with increased curing age, with low pH system exhibiting high Ca/Si at 90 days. c 2024 Elsevier Ltd
Plugging effect of fine pore water in OPC and LC3 paste during accelerated carbonation monitored via single-sided nuclear magnetic resonance spectroscopy
Cheng L.; Kurihara R.; Ohkubo T.; Kitagaki R.; Teramoto A.; Suda Y.; Maruyama I.
Cement and Concrete Research, Elsevier Ltd., Vol.186, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107688)
Abstract
This study investigates the influence of CO2 concentration on the carbonation process in cementitious paste, focusing on water content distribution in ordinary Portlandite cement and limestone-calcined clay cement (LC3). Employing single-sided nuclear magnetic resonance spectroscopy for water profiling, we revealed that under accelerated carbonation of 5 % and 1 %, the water content in fine pores (interlayer space and gel pores) kept constant at the carbonation front, demonstrating the plugging effect where fine pore water removal governs carbonation progress. This effect was absent under natural carbonation conditions because evaporation precedes the carbonation process. This study emphasizes that to accurately characterize cementitious materials under natural carbonation conditions, CO2 concentrations in accelerated methods should be constrained to prevent the plugging effect. c 2024 The Authors
Full-scale observation of drying-induced microstructure change in hardened cement paste by water and 2-propanol 1H NMR relaxometry
Igami R.; Igarashi G.; Aili A.; Kurihara R.; Ohkubo T.; Maruyama I.
Cement and Concrete Research, Elsevier Ltd., Vol.186, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107698)
Abstract
To understand the microstructural changes in the hardened cement paste during the drying, hardened white Portland cement pastes were D-dried or dried under 11, 33, 40, and 75% relative humidity, and then, pastes were impregnated with 2-propanol or water under vacuum. Measurement of 1H NMR relaxometry was employed for the pastes before and after impregnation, and the full-scale microstructural changes of the hardened cement paste after drying were successfully visualized. It was observed that the volume of the coarse pores outside the agglomeration of calcium-silicate-hydrate (C-S-H) increased, and the volume of the C-S-H interlayer spaces and gel pores decreased as the drying relative humidity decreased. Thus, it was evidenced that interlayer space is decreasing during drying. It was also confirmed that 2-propanol can enter some of the interlayer space of C-S-H after harsh drying. c 2024 The Author(s)
Surface chemistry and radionuclide anion immobilisation potential of phosphoric acid-activated metakaolin-based geopolymers
Niu X.; Elakneswaran Y.; Hiroyoshi N.
Cement and Concrete Research, Elsevier Ltd., Vol.181, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107549)
Abstract
Phosphoric-acid-activated metakaolin-based geopolymers (PGPs) have been investigated as promising options for the disposal of radionuclides. However, a lack of understanding of the surface chemical properties of PGPs has hindered further research into them and their application. This study explored the structure-related electrostatic properties and anion immobilisation potentials of PGPs via zeta potential measurements, structural characterisation, and leaching experiments. These findings suggest that acid activation triggers the geopolymerisation of metakaolin, resulting in new Alx-PO units (x = IV, VI representing VI- and V-coordination), the ratio of which controls the surface charge of PGPs. PGPs possess a positive charge in the equilibrium pH range of approximately 2?5 and exhibit a maximum positive zeta potential at approximately pH 4. Under acidic conditions, the AlVI-PO unit within the surface structure is released, decreasing the zeta potential as the pH decreases. In contrast, in alkaline environments, the AlVI/Si-OH hydroxyl group loses protons, causing a decrease in the zeta potential with increasing pH. Furthermore, PGPs can effectively immobilise SeO32?, SeO42?, I?, and IO3? anions through stabilisation/solidification (S/S). This immobilisation is primarily facilitated by electrostatic attraction between the anions and the positively charged surface of the PGPs. Importantly, the immobilisation process does not cause significant alterations to the matrix structure of the PGPs, even after solidification or subsequent leaching. c 2024 Elsevier Ltd
Impact of alkalis and shrinkage-reducing admixtures on hydration and pore structure of hardened cement pastes
Rahoui H.; Maruyama I.; Vandamme M.; Pereira J.-M.; Mosquet M.
Cement and Concrete Research, Elsevier Ltd., Vol.184, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107620)
Abstract
The hydration and pore structure of hardened cement pastes containing various amounts of alkali and hexylene glycol -a shrinkage-reducing admixture (SRA)- are studied. Until three months, SRA retards cement paste hydration regardless of alkali content; after seven days at most, this retardation diminishes with time. Alkalis increase the hydration degree at early ages for all pastes. The pore structure coarsens with the SRA: both the specific surface area and the volume of pores with a 5 nm entry size decrease in the presence of the SRA. The magnitude by which the SRA impacts the pore structure reduces with alkali. In alkali media, the C-S-H gel uptakes alkalis and aluminum; modifying the C-S-H structure, the gel pore volume, and the interlayer space. The SRA depletes the alkalis from the solution and may increase the C-S-H alkali uptake, which could lead to changes in the gel pore volume and specific surface area. c 2024 Elsevier Ltd
Shrinkage reduction mechanism of low Ca/Si ratio C-A-S-H in cement pastes containing fly ash
Segawa M.; Kurihara R.; Aili A.; Igarashi G.; Maruyama I.
Cement and Concrete Research, Elsevier Ltd., Vol.186, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107683)
Abstract
Understanding the drying shrinkage of low Ca/Si ratio cement pastes is crucial for promoting the use of low-clinker ratio cementitious materials and reducing the environmental impact of cement production. We prepared well-hydrated cement paste samples with various fly ash replacement and water-to-cement ratios. The long-term drying shrinkage was measured by 1 mm-thick samples. Results showed that fly ash containing samples exhibited lower shrinkage and the irreversible part of drying shrinkage was less compared to those without fly ash. Chemical composition analysis of the calcium aluminate-silicates hydrate (C-A-S-H) was conducted using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). Additionally, water vapor sorption isotherms and proton nuclear magnetic resonance (1H NMR) relaxometry were used to determine specific surface area and pore structure. By analyzing these results in conjunction with the C-A-S-H model, we attributed the reduced and more reversible drying shrinkage in fly ash cement to lower Ca ion amounts in the interlayer space and fewer trapped larger pores. c 2024 The Author(s)
Retardation effect of the pozzolanic reaction of low-calcium supplementary cementitious materials on clinker hydration at later age: Effects of pore solution, foreign ions, and pH
Wang T.; Medepalli S.; Zheng Y.; Zhang W.; Ishida T.; Bishnoi S.; Hou D.; Shi Z.
Cement and Concrete Research, Elsevier Ltd., Vol.177, 2024, .
(https://doi.org/10.1016/j.cemconres.2023.107416)
Abstract
Clinker hydration at later age in blended cement pastes was found to be retarded by the pozzolanic reaction of low-calcium supplementary cementitious materials (SCMs). Various mechanisms were explored, including the consumption of pore solution, the presence of foreign ions, and pH-related effects. Experimental results indicated that the dissolution of the foreign ions from SCMs was a secondary effect. The primary cause of the retardation effect was the reduction in pH caused by the pozzolanic reaction. Aqueous precipitation tests yielded the following findings related to pH: (1) At lower pH levels, the precipitation of C?A?S?H gel was reduced due to the decreased nano-adhesion force. (2) The morphology of aluminium-incorporated calcium silicate hydrate (C?A?S?H) gel consisted of small spherical particles at lower pH levels, resulting in a denser capillary pore structure. The latter led to increased water retention within the fine gel pores but a reduced amount of pore solution available in the capillary pores for cement hydration. c 2023 Elsevier Ltd
Unified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates
Yu Y.; Gunasekara C.; Elakneswaran Y.; Robert D.; Law D.W.; Setunge S.
Cement and Concrete Research, Elsevier Ltd., Vol.180, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107487)
Abstract
Developments of binary, ternary, and even quaternary cementitious binder materials have been widely recognised in research and practices to elevate the sustainability of modern construction industry. To this end, a robust method to predict the hydration of novel binder systems is essential to facilitate informed material designs, yet extremely lacking. In this study, focusing on fly ash cement binders, a unified hydration model, applicable to multi-blend systems that further incorporate hydrated lime and/or nano silica, is freshly established. The proposed method features kinetic models to predict reaction degree for each binder component that are further coupled with a thermodynamic model to evaluate phase assemblage during hydration. The proposed model is carefully calibrated and verified against separate sets of experimental data. It is demonstrated to be applicable to binders incorporating up to 80 % of total cement replacement, and capable of robustly assessing the influence of multi-blend compositions on the hydrating systems. c 2024 The Authors
New insights in the adsorption behavior of triethanolamine on OPC by experimental and theoretical study
Zhai Q.; Kurumisawa K.; Manzano H.; Moon J.; Hwang I.-H.
Cement and Concrete Research, Elsevier Ltd., Vol.184, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107610)
Abstract
The influence of triethanolamine (TEA) on the hydration of cement-based materials is closely linked to its adsorption behavior in Ordinary Portland Cement (OPC). This study investigated the adsorption process and mechanism of TEA on OPC and pure mineral phases?alite, gypsum, aluminate+gypsum, and calcium hydroxide (CH)?in the first 8 h. The results revealed that in all single phases, TEA adsorption was associated with alite and CH. The crystal structure of CH did not change during adsorption, likely due to the physical adsorption of TEA. During OPC hydration, the adsorption of TEA was primarily associated with the hydration of alite. In the initial hydration stage, only CH served as the main adsorption receptor, which was supported by adsorption energy simulations using molecular dynamics. As alite hydration progresses, the role of the receptor may shift toward calcium silicate hydrate (C-S-H), as indicated by the calculated adsorption limit of CH. Furthermore, density functional theory (DFT) demonstrated that TEA?Ca2+ has the lowest complexation energy when the ligand-to-metal ratio is 1:1 and becomes even more stable when the ligand-to-metal ratio is 2:1. c 2024 Elsevier Ltd
Modeling the ionic diffusion coefficient of unsaturated hardened cement paste: A micromechanical approach
Zhang M.; Lin D.; He Z.; Yang R.
Cement and Concrete Research, Elsevier Ltd., Vol.177, 2024, .
(https://doi.org/10.1016/j.cemconres.2023.107415)
Abstract
Most of the concrete structures in service are unsaturated, estimating the ionic diffusion coefficient of unsaturated cement-based material is of paramount significance to assessment of corrosion of reinforced concrete. Taking account of the contributions from different water configurations at multi-scale (water films, interlayer water, large gel pore (LGP) water and capillary pore water) and the corresponding diffusion mechanisms of each type of water, a micromechanical model for estimating the ionic diffusion coefficient of unsaturated hardened cement paste (UHCP), is developed in this study. Model results show that the interconnectivity of the spheroidal capillary pore water is closely related to the aspect ratio of spheroidal capillary pore, the slender the prolate pore, the higher the interconnectivity of the capillary pore water; when the capillary pore water is totally drained, water films and interlayer water within C-S-H governs the ionic diffusion, the higher the water to cement ratio (w/c), the less the contribution of interlayer water, and the greater the contribution of water film, to ionic diffusion within UHCP. Application on saturated hardened cement paste and UHCP shows the capability of the model to accurately reproduce the experimental results. c 2023 Elsevier Ltd
Recyclable calcium carbonate-based concrete: Utilizing calcium carbonate to bond recycled concrete fines through an in-situ heterogeneous dual-precipitation approach
Zhou Q.; Wang W.; Noguchi T.
Cement and Concrete Research, Elsevier Ltd., Vol.186, 2024, .
(https://doi.org/10.1016/j.cemconres.2024.107679)
Abstract
This study introduces a novel approach for in-situ CO2 sequestration using recycled concrete fines (RCFs). The method employs heterogeneous dual?calcium carbonate (Cc) precipitation from wet carbonation and calcium bicarbonate (Ca(HCO3)2) solution to form a Cc binder between RCFs. The results demonstrate that metastable aragonite is significantly promoted and stabilized in wet carbonation by leveraging the seeding effects from semi-dry carbonated RCFs. A carbonated cement paste layer attached to the surface of RCFs facilitates the combination of precipitated aragonite crystals, while K (Na)-feldspar and quartz-based aggregates exhibit a relatively lower affinity for combining with Cc. The entanglement of aragonite crystals provides most of the strength in the carbonated RCF system. In the non?carbonated recycled cement paste powders system, wet carbonation primarily produces calcite, while precipitation from Ca(HCO3)2 yields aragonite, forming a Cc solid skeleton that contributes to the strength. c 2024 Elsevier Ltd