Although silicate-based surface impregnants have been used to enhance the durability of concrete structures, their long-term performance remains unclear. In this study, the chemical changes that occur when cement paste is treated with a silicate-based impregnant and subsequently carbonated were examined using X-ray diffraction and solid-state NMR spectroscopy, based on a powder-based model system simulating the treatment process. As the carbonation progressed, the decalcified regions of C–A–S–H underwent structural rearrangements. Both Al3+ and Na+ were incorporated into these Ca-depleted domains, and the resulting phases exhibited characteristics of aluminosilicate hydrates, including structures similar to C–(N, A)–S–H. Increases in tetrahedral Al and polymerized silicate species were evident in the 27Al and 29Si spectra, whereas 23Na 3QMAS data showed that Na+ migrated from regular C–S–H interlayer sites to less symmetric Si–O– and Al–O–related environments. These results suggest that silicate treatment influences the chemical processes during carbonation by facilitating Na+ incorporation and promoting the formation of less-ordered aluminosilicate phases.

In cold climates, the durability of construction materials against freeze-thaw cycles is critical for ensuring long-term structural safety. To minimize environmental impact, blast furnace slag cement, incorporating varying proportions of blast-furnace slag fines, is increasingly being adopted as a sustainable alternative to ordinary cement. While the freeze-thaw resistance of such materials has been widely studied, their performance after repeated dry-wet cycling, which simulates moisture fluctuations that can occur in typical environments, has not been thoroughly investigated. This study evaluates the freeze-thaw resistance of blast furnace slag cement with different blast-furnace slag replacement ratios following repeated dry-wet exposure. The influence of entrained air, introduced via an air-entraining agent, was also examined. Freeze-thaw resistance was assessed using the RILEM CIF method, and microstructural characteristics were analyzed via mercury intrusion porosimetry. Results showed that, even though capillary pores became coarser with AE addition, the presence of adequate entrained air mitigated frost damage. In specimens without AE, increasing blast-furnace slag content improved resistance by reducing the prevalence of capillary voids formed during dry-wet cycling. These findings suggest that the microstructural changes induced by blast-furnace slag and AE agents play a crucial role in enhancing the frost durability of blast furnace slag cement under cyclic environmental stress.

Temperature and humidity changes affect the durability of buildings. Experiments can be conducted to simulate the changes in the temperature and humidity conditions in real environments through repeated dry and wet cycles, revealing the microstructural changes in hardened cement. Calcium-silicate-hydrate (C-S-H) is a hydration product with the greatest influence on the physical properties of concrete, resulting in changes in the pore structure of hardened ordinary cement with repeated dry and wet cycles. However, blended cements with blast furnace slag produce less microstructural changes under dry and wet cycles than ordinary cement. In this study, blast-furnace cements with different replacement ratios were employed to investigate the causes of fine pore structure changes in blast-furnace cements under repeated dry and wet cycles. The hydration products were quantified using solid-state nuclear magnetic resonance (NMR) spectroscopy, and the pore size distribution was confirmed by mercury injection porosimetry. The 27 Al MAS NMR results showed an increase in the Al/Si content after repeated dry and wet cycles, and from the Al content of Al[IV], it is inferred that AlO4 bonds to C-S-H and C-A-S-H is formed, which maintains the width of the C-S-H interlayer and reduces pore structure changes in the size range of 30-2000 nm than ordinary cement. In the future, blast furnace cement with different substitution rates may exhibit a better practical freezing resistance owing to reduction of microstructural changes with repeated drying and wetting of the cement.

The pore structure of hardened ordinary cement becomes coarser due to microstructural changes brought about by drying-wetting cycles. However, the production of blast furnace cement, which is a mixed cement, involves the production of calcium silicate aluminate hydrate (C-A-S-H); therefore, the microstructural changes are different from those of ordinary cement, and the degree of pore coarsening is small. Studies have also been conducted to examine the changes in the microstructure of ordinary and blast furnace cements by subjecting them to intermittent drying. However, no studies have been conducted on the influence of drying and wetting processes on the microstructure during drying-wetting cycles. In this study, microstructural changes in ordinary and blast furnace cements during high-temperature drying-wetting cycles were investigated. Solid-state NMR was used to analyze changes in the C-S-H structure. Additionally, pore structure and water content changes in the hardened material were examined using MIP and H-1 NMR. The results showed that for drying only, ordinary cement and blast furnace cement showed little change in C-S-H structure and pore structure from the first drying. Meanwhile, during the drying-wetting cycles, the microstructure converged to that between the initial dry and wet states. In this period, the C-S-H structure changed intermittently due to drying-induced polymerization and progressive moisture supply-induced hydration; however, the blast furnace cement reduced pore structural changes by producing more C-A-S-H. This study is expected to contribute to basic research on hardened cement in the future.

This study aimed to develop a cementitious repair material that can be constructed in cold weather conditions. The addition of nitrite/nitrate-based antifreezing agents has been shown to increase the initial strength of cementitious repair materials in cold weather. However, increasing the amount of these agents may lead to an increase in deformation behavior and shrinkage cracking. In this study, the effects of different types and amounts of nitrite/nitrate-based antifreezing agents on the strength development and deformation behavior of cementitious repair materials under low-temperature conditions were evaluated. As a result, it was found that the addition of a large amount of calcium nitrite can promote hydration and improve the initial strength of the repair material, irrespective of the type of antifreezing agent. However, this also leads to an increase in shrinkage and the concern of shrinkage cracking. Therefore, a repair material that is repairable in winter was developed by balancing the initial strength and deformation behavior through the appropriate selection of antifreezing agents. The developed repair material can be used to repair structures in cold weather conditions, which is of great significance for the construction industry in Hokkaido, Japan.

Nanocrystalline calcium???silicate???hydrate (C-S-H) is a typical heterogeneous material with a multiscale structure spanning a wide length scale from angstrom to micrometer, and whose structure is determined by the Ca/Si ratio. In this study, we directly applied compressive loads on synthetic C-S-H pastes with Ca/Si ratios of 0.6???1.2 and investigated their mechanical properties using the elastic modulus calculated at three length scale levels (i.e., angstrom to nanometer, micrometer, and millimeter) via in-situ synchrotron X-ray scattering, nanoindentation tests, and strain gauges, respectively. Further, 29Si nuclear magnetic resonance spectroscopy was conducted on the C-S-H pastes to elucidate the alterations in the silicate polymerization. The experimental results confirmed the deformation behavior of the C-S-H paste with different Ca/Si ratios under external loading, which was demonstrated to be transferred from the surface of the pastes to particles owing to the presence of multiscale pores.

This study investigated the potential of waste glass beads (WGB), a recycled porous lightweight material derived from waste glass, to enhance long-term curing of moisture-saturated cementitious construction materials. The macroscopic properties and microstructure development of a cement composite material blended with two types of WGB––spherical (B) and crushed (CB)––were analyzed. The primary objective was to provide practical guidelines for optimizing WGB utilization as a moisture release medium and thus contribute to sustainable concrete production by exploring waste glass applications. This study demonstrated the potential of WGB for improving strength and void structure and could help enhance the long-term durability of cement composites. Valuable insights were gained regarding the surface roughness and specific surface areas alongside curing methods to maximize WGB's effectiveness. The key contributions are as follows: (1) varying effects on high-strength concrete (HSC) strength with increased WGB content and surface roughness and specific surface areas were analyzed; (2) a proportional relationship between closed pore volume and modulus affecting macroscopic properties was revealed; (3) insights into hydration product presence in the ITZ and its relationship with WGB moisture content were gained; and (4) notable improvements in indentation tests for specimens with WGB were achieved, indicating enhanced ITZ hydration and increased density within both ITZ and paste.

本研究では、結合材に高炉スラグを用いたアルカリ活性セメント硬化体の乾湿繰り返しによる微細構造変化について29Si MAS NMRと27Al MAS NMRから生成物の構造変化を確認し、1H NMRとMIPから水分の変化挙動や細孔構造変化の検討を行った。その結果、乾燥や乾湿繰り返しによる細孔分布に変化は確認されなかったが細孔量が大幅に減少した。これは乾燥以前から緻密であったが、乾燥によって反応を促進されC-S-Hに置換されるAl量が増加し緻密化を引き起こした。また、乾燥によりC-S-Hレイヤーの水分が減少し層間の幅が縮まるが、C-A-S-Hの生成が進行することで幅を保つ可能性が考えられる。その後、湿潤を行うことにより層間に水分が供給され、ゲル空隙が粗大化する可能性がある。

In ordinary hardened cement, the pore structure changes with microstructural changes due to repeated dry and wet cycles. However, the calcium-silicate-hydrate (C-S-H) produced in blended cement is different from that of ordinary cement because blast furnace slag and fly ash are used in blended cement. In this study, microstructural changes in ordinary cement and hardened blast-furnace cement, which have different compositions of C-S-H, due to repeated dry and wet cycles at high temperatures, were analyzed by solid-state nuclear magnetic resonance (NMR) for structural changes in the products, and by time domain NMR and mercury intrusion porosimetry for changes in moisture and pore structure in the hardened cement. As a result, it was confirmed that the degree of coarsening of capillary porosity in blast-furnace cement was lower than in ordinary cement due to drying and repeated dry-wet cycles. This is believed to be because the aluminum contained in the blast furnace slag of the blast-furnace cement, which is present in the interlayer, improves the resistance of the C-S-H layer to compaction, resulting in less change in the pore structure. This study is expected to contribute to fundamental research on hardened cement in the future.

本研究では、結合材に高炉スラグを用いたアルカリ活性セメント硬化体の乾湿繰り返しによる微細構造変化について29Si MAS NMRと27Al MAS NMRから生成物の構造変化を確認し、1H NMRとMIPから水分の変化挙動や細孔構造変化の検討を行った。その結果、乾燥や乾湿繰り返しによる細孔分布に変化は確認されなかったが細孔量が大幅に減少した。これは乾燥以前から緻密であったが、乾燥によって反応を促進されC-S-Hに置換されるAl量が増加し緻密化を引き起こした。また、乾燥によりC-S-Hレイヤーの水分が減少し層間の幅が縮まるが、C-A-S-Hの生成が進行することで幅を保つ可能性が考えられる。その後、湿潤を行うことにより層間に水分が供給され、ゲル空隙が粗大化する可能性がある。

This study explored the effect of M-S-H formation on the local atomic arrangements and mechanical properties of C-S-H. The elastic moduli of the samples were calculated using shifted atomic distances (r) and d-spacings (d) acquired by applying an external load on the pastes during X-ray scattering experiments. The experimental results indicated that the crystal structure of C-S-H remained intact with MgCl2 addition. At the highest Mg/Si ratio (Ca/Si = 0.6, Mg/Si = 0.2), change in the dominant phase occurred from C-S-H to M-S-H because the low pH environment hindered the formation of C-S-H and facilitated the formation of M-S-H. The elastic modulus decreased with increasing Mg/Si ratio up to 0.1 owing to both C-S-H destabilization and low M-S-H content in the samples. Conversely, the elastic modulus increased in the paste synthesized with the highest Mg/Si ratio because considerable M-S-H had formed, which exhibited a higher elastic modulus than C-S-H.

In this study, the change in frost resistance and pore structure of concrete containing blast furnace slag with various replacement ratio due to carbonation were investigated. As a result, there is a close relationship between the carbonation speed and 28-day compressive strength in blast furnace slag concrete. The frost resistance, carbonation resistance and scaling resistance of blast furnace slag cement concrete decrease as blast furnace slag replacement ratio increases. Furthermore, due to carbonation, the frost durability of ordinary Portland cement concrete and the concrete with a low replacement ratio of blast furnace slag tends to decrease. However, the concrete with a high replacement ratio of blast furnace slag tends to increase. Under the carbonation conditions, the pore volume decreases due to carbonation of calcium hydroxide, and the pore structure will be coarsened due to carbonation of C-S-H. In addition, it is expected that permeability of concrete is raised and scaling is inhibited due to carbonation, and the surface area with a certain thickness in the carbonated concrete will be scaled due to freeze–thaw.

In this study, the frost and scaling resistance of concrete with various fly ash (FA) replacement ratios exposure to air and accelerated carbonation conditions were investigated. The changes in water absorption were measured by RILEM / CIF test and in pore structure were measured by the Archimedes method and the mercury intrusion porosimetry method due to carbonation. Results show that the influence of FA and carbonation on the frost and scaling resistance of concrete can be ignored due to air bubbles by air entraining (AE) admixture in case of AE FA concrete. For Non-AE FA concrete, carbonation of FA concrete does not change the gel porosity/capillary porosity ratio, which is the reason for the frost resistance is not influenced by carbonation of FA concrete. Additionally, it is noteworthy to note that the scaling resistance is strongly connected to the pore volume above 75 nm, and that when exposed to carbonation, the scaling resistance tends to rise as a result of the increase in pore volume above 75 nm that occurs as a result of carbonation. Because of the addition of FA and carbonation, the frost and scaling resistance are far more reliant on the changes in pore structure than they are on the water absorption.

軽量気泡コンクリート（ALC）の主要構成鉱物がトバモライトであるのに対し、これをゾノトライトとした場合、より熱特性に優れた建築材料になることが期待される。本研究ではこのゾノトライトを主要構成鉱物とした軽量硬化体（Xo-ALC）の炭酸化による基礎物性への影響を検討した。その結果、圧縮強度は若干の増加を示し、乾燥収縮は増加し、細孔構造は細孔径のピークが粗大径側にシフトし、総細孔量が減少した。また、Xo-ALCはALCよりも細孔が粗大であり炭酸ガスの侵入が容易であるため炭酸化収縮が早く生じる特徴がある。また、Xo-ALCの炭酸化収縮のメカニズムはALCと同様に、シリケートイオン2重鎖構造からシリカゲル構造へと縮重合するためと考えられた。

In this paper, experiments were conducted on the effects of aesthetic and durability of three representative surface protective material under accelerated weathering test for 5000 h. First, the adaptability of the surface protective material coating to the substrate was proven by examining the aesthetic properties and the water permeability of the building materials. Second, the pollutant resistance of the surface protective material coating to artificial stain was assessed using xenon-arc light. The result shows that the appearance of the silane types did not change significantly, and the water permeability was improved. In addition, the silicate types did not improve water permeability and the surface color was changed. Fluor- resin types effectively improved the water permeability, but the surface color became dark. Sample measurements showed changes in the average width of the contamination after weathering, with an increase after spray cleaning and ultrasonic cleaning. However, it was observed that after washing the pollution average width of all specimens due to weathering at 5000 h was almost as much or smaller than the initial value.

The frost resistance of cement-based materials can be improved, by using the admixtures such as nitrite corrosion inhibitor (NCI) and paraffin waterproofing agent (PWA). In this work, we studied the influence of water curing and dry curing on frost resistance of mortars when these admixtures are added alone or in combination. Here, the cross sections of mortar samples were observed using the microscope equipped with a charge coupled device (CCD) camera and the pore structure was measured using mercury intrusion porosimetry. The results show that the frost resistance is similar to that of the reference mortars regardless of the addition amount, for the water-cement ratio W/C = 35%, but the frost resistance decreases regardless of the addition amount, for W/C = 55% when NCI is added alone. It is confirmed that the NCI may produce nitrite-type hydrocalumite and decreases frost resistance with the coarsening of pores. Furthermore, the PWA improves frost resistance by suppressing the effect of frost damage of hydrophobic compounds. This improvement is lessened when both admixtures are added in combination. This study advances understanding of the mechanism of suppressing frost damage by hydrophobic compounds. (C) 2021 Elsevier Ltd. All rights reserved.

Recently, there has been increased use of calcium-nitrite and calcium-nitrate as the main components of chloride- and alkali-free anti-freezing agents to promote concrete hydration in cold weather concreting. As the amount of nitrite/nitrate-based accelerators increases, the hydration of tricalcium aluminate (C3A phase) and tricalcium silicate (C3S phase) in cement is accelerated, thereby improving the early strength of cement and effectively preventing initial frost damage. Nitrite/nitrate-based accelerators are used in larger amounts than usual in low temperature areas below −10 °C. However, the correlation between the hydration process and strength development in concrete containing considerable nitrite/nitrate-based accelerators remains to be clearly identified. In this study, the hydrate composition (via X-ray diffraction and nuclear magnetic resonance), pore structures (via mercury intrusion porosimetry), and crystal form (via scanning electron microscopy) were determined, and investigations were performed to elucidate the effect of nitrite/nitrate-based accelerators on the initial strength development and hydrate formation of cement. Nitrite/nitrate-AFm (aluminate-ferret-monosulfate; AFm) was produced in addition to ettringite at the initial stage of hydration of cement by adding a nitrite/nitrate-based accelerator. The amount of the hydrates was attributed to an increase in the absolute amounts of NO2− and NO3− ions reacting with Al2O3 in the tricalcium aluminate (C3A phase). Further, by effectively filling the pores, it greatly contributed to the enhancement of the strength of the hardened cement product, and the degree of the contribution tended to increase with the amount of addition. On the other hand, in addition to the occurrence of cracks due to the release of a large amount of heat of hydration, the amount of expansion and contraction may increase, and it is considered necessary to adjust the amount used for each concrete work.

Alkali-activated cements prepared from aluminosilicate powders, such as blast furnace slag and fly ash, are rapidly attracting attention as alternatives to cement because they can significantly reduce CO2 emissions compared to conventional cement concrete. In this study, we investigated the relationship between the physical and chemical changes by accelerated carbonation conditions of alkali-activated cements. Alkali-activated cements were prepared from binders composed of blast furnace slag and fly ash as well as alkali activators sodium silicate and sodium hydroxide. Physical changes were analyzed from compressive strength, pH, and neutralization depth, and chemical changes were analyzed from XRD, TG-DTG, and 29Si MAS NMR. The C–(N)–A–S–H structure is noted to change via carbonation, and the compressive strength is observed to decrease. However, in the case of Na-rich specimens, the compressive strength does not decrease by accelerated carbonation. This work is expected to contribute to the field of alkali-activated cements in the future.

In this work, the instant mechanical recovery and the thermal resistance of nanosilica(NS)-incorporated cement composites were investigated. The composites were exposed to various heating temperatures (200, 500, 800, and 1000 °C) and rehydration conditions (25 °C/65% RH or water rehydration), and weight, surface morphology, density, compressive strength, and X-ray diffraction were assessed. 29Si nuclear magnetic resonance was used to analyze the relationship between the mean chain length (MCL) of calcium silicate hydrates (C–S–H) and instant mechanical recovery. Increasing the NS content substantially increased the compressive strength after heating and strength recovery through rehydration at 25 °C/65% RH, particularly after exposure at 500 and 800 °C. The NS pozzolanic reaction afforded strength recovery and was linearly related to increasing MCL of C–S–H. The pozzolanic reaction produced a compact matrix; therefore, the strength recovered considerably following rehydration in water, even after heating to 800 °C, because of the combined effect of hydrate formation and the resistance of the matrix to thermal shock.