Water exchange and migration of superabsorbent polymers (SAP) in cement paste is a very complicated process and governs the effectiveness of internal curing in concrete. The early state of SAP in ...real pore fluids was investigated under different water-cement ratios and hydration time. It is found out water absorption of SAP is not a constant value, but varies depending on these two factors. The absorption and desorption behavior of SAP is demonstrated in the shifted hydration peak location and the water-rich region around the SAP gels. The water exchange between SAP and cement pastes is quantified by the measured water content with time, from which a characteristic “two-stage desorption” driven by osmotic pressure and humidity gradient, respectively, is identified. The humidity-controlled desorption that is beneficial for internal curing is calculated. It is indicated the internal curing efficiency could be improved by shortening the osmotic stage and prolonging the humidity stage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Damping capacity significantly increases with the increase of LAP or LAW.•LAP and LAW in low volume (<45%) has no considerable effect on strength of concrete.•Young’s modulus and dynamic elastic ...modulus decrease with an increase of LAP or LAW.
In this study, the mechanical and dynamic properties of high strength concrete were experimentally investigated. Lightweight aggregate presaturated water (LAW) and lightweight aggregate presaturated polymer emulsion (LAP) was used as a partial replacement for coarse aggregate at 15, 30, 45 and 70v%. Compressive strength and splitting tensile strength decreased as the percentage of LAW or LAP increased. The decreasing tendency was unconspicuous when the percentage of lightweight aggregate (LA) replacement was no more than 45%, exceeding this range, it became obvious. The Young’s modulus and dynamic modulus of elasticity decreased as the proportion of LA substitution increased. Damping ratio of the modified concrete increased distinctly with the increase of LA volume fractions, the increasing tendency produced by the LA replacements was much more obvious than that induced by the LAW replacements at the same volume fraction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Pore structure of HFPC concrete is obviously optimized by addition of SF.•MK contributes to form more aluminate hydrates enhancing binding capacity of chloride.•The elevated temperature is ...detrimental to resistance of chloride penetration.
As a typical kind of sulphate resistance Portland cement (SRPC), high-ferrite Portland cement (HFPC) has drawn extensive interesting, and is expected to be used in marine environment, but the low chloride resistance is a primary issue and requires to be notably enhanced. This study therefore has investigated the effects of the curing temperature and supplementary cementitious materials (SCMs) on chloride migration in HFPC precast concrete. The results show that two representative SCMs, namely, silica fume (SF) and metakaolin (MK), could significantly improve the resistance of steam cured HFPC concrete to chloride permeation. The improving mechanism of SF is based on optimization of the pore structure to retard migration of chloride, while MK is based on promotion of the chloride binding capacity. This study could give an insight into a new type of precast concrete with excellent sulphate and chloride resistance in marine environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A calcium carbonate (CaCO3)-based coating with gamma-C2S (γ-C2S) as the main carbonatable binder is proposed to protect the metal substrate against corrosion in this paper. Here, the morphology and ...phase assemblage of the coatings are studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the corrosion resistance of the coating is evaluated by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Results show that the carbonated coating has excellent properties in terms of ultraviolet (UV) aging resistance, salt fog resistance, and electrochemical corrosion resistance. The porosity of deposited coating on steel substrates decreases by 47.1% after carbonation due to the compacted calcium carbonate formation, which is recognized as a self-compacting process during carbonation. The coating also exhibits rapid strength development within the first 2 h of carbonation; both the CO2 uptake efficiency and degree of carbonation (DOC) can reach more than 95% of the total CO2 uptake efficiency and final DOC values. This study provides a novel insight to extend the category of inorganic coating with additional benefits of CO2 solidification.
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► Water erosion of CAM was studied at varied temperature and pressure. ► Compressive strength of CAM decreases with increases of water temperature. ► Compressive strength of CAM decreases with ...increases of water pressure.
Water erosion is one of the major factors for performance degradation of cement asphalt mortar (CAM). In the paper, the strength variations of CAM exposed to water was investigated at various water temperatures (20°C, 40°C and 60°C) and pressures (0.0MPa, 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa and 0.5MPa) and the microstructure evolution was analyzed by mercury intrusion porosimetry (MIP) and scan electronic microscope (SEM). Results indicate that temperature and pressure both cause the deterioration of CAM, the compressive strength of CAM decreases with higher water temperature and its compressive strength decreases with increases of water pressure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The mechanical properties compatibility of CAM and repair mortar was evaluated.•A modified test method was developed for CAM compatibility evaluation.•CAM compatibility criteria with repair ...materials was summarized.
The compatibility of the mechanical properties of low-modulus cement and asphalt mortar (CAM) and repair materials was studied using the four-point bending test method. According to the bearing characteristics of CAMs, a four-point bending fatigue test was further developed to evaluate the compatibility of this material with the repair material. With the help of a finite element model, the effect of the difference in the modulus of the substrate mortar and the repair mortar on the stress and strain distribution of a composite sample was studied. The results indicated that the CAM compatibility criteria with repair materials were different from those of the concrete repair system. The difference in the moduli of the substrate mortar and repair mortar determined the loading transfer efficiency and failure mode, which mainly influenced the compatibility of the mechanical properties. The repair materials were compatible with substrate CA mortar when its modulus was approximately 0.75–1.28 times the substrate mortar modulus according to the experimental results. The four-point fatigue test met the requirements of the bearing characteristics of the CA mortar and the present quantitative experimental results, which provide supplementary information for compatibility evaluation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► The influence of cement hydration on emulsion stability was studied. ► Zeta potential was well related with the microstructure of emulsion. ► The nonionic emulsifier improves the alkali resistance ...property of emulsion. ► Water loss significantly influenced both cationic and anionic emulsions stability. ► pH value increase showed different effect on cationic and anionic emulsions.
The effect of pH value, Ca2+ concentration and water loss induced by cement hydration on emulsion stability was investigated by measuring the Zeta potential of asphalt droplets. The microstructure of emulsion was also observed by optical microscope. The results indicate that the chemical stability of cationic emulsion is strongly affected by pH value increase and the addition of nonionic emulsifier improves the alkali resistance property of emulsion. However, the chemical stability of anionic emulsion was slightly improved by pH increase. Ca2+ slightly influences the cationic and anionic emulsions due to its small concentration in the cement paste pore solution. The Zeta potentials of both cationic and anionic emulsions were sharply decreased due to water loss.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•A microstructural approach was used to study the bonding mechanism.•SACR was bonded with CA mortar by mechanical interlocking effect.•Resin mortar was bonded with CA mortar by van der Waals ...force.•The bonding results could be well explained by bonding mechanism.
Cement and asphalt mortar (CA mortar) is the key component for high-speed railway with high asphalt content to obtain low modulus which makes it difficult to bond with repair materials. The purpose of this work was to investigate the bonding mechanism of CA mortar to two type repair materials – SAC-AE composite mortar (short for SACR) and resin mortar (short for RM) based on microstructural evaluation of substrate CAM/repair materials by scanning electron microscopy (SEM) with EDS spectra. Results indicate that the porous structure of CA mortar had provided the space for mechanical interlocking with SAC-AE composite mortar which led to a nice bonding. However, CA mortar was bonded with resin mortar by van der Waals force which led to a weak bonding. The mode of rupture was mix-mode interfacial-cohesive failure and mostly interfacial failure for SACR-CAM and RM-CAM, respectively. The effect of asphalt content and curing age on the bonding strength between substrate CAM and repair materials was also studied which could be well explained by bonding mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Amide proton transfer (APT) imaging is a novel MRI technique, in which the amide protons of endogenous proteins and peptides are irradiated to accomplish indirect detection using the bulk water ...signal. In this paper, the APT approach was added to a standard brain MRI protocol at 3T, and twelve patients with high-grade gliomas confirmed by histopathology were scanned. It is shown that all tumors, including one with minor gadolinium enhancement, showed heterogeneous hyperintensity on the APT images. The average APT signal intensities of the viable tumor cores were significantly higher than those of peritumoral edema and normal-appearing white matter (P<0.001). The average APT signal intensities were significantly lower in the necrotic regions than in the viable tumor cores (P=0.004). The APT signal intensities of the cystic cavities were similar to those of the viable tumor cores (P>0.2). The initial results show that APT imaging at the protein and peptide level may enhance non-invasive identification of tissue heterogeneity in high-grade brain tumors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Steel slag as an alkaline industrial solid waste, possesses the inherent capacity to engage in carbonation reactions with carbon dioxide (CO2). Capitalizing on this property, the current research ...undertakes a systematic investigation into the fabrication of high-carbonation precast concrete (HCPC). This is achieved by substituting a portion of the cementitious materials with steel slag during the carbonation curing process. The study examines the influence of varying water–binder ratios, silica fume dosages, steel slag dosages, and sand content on the compressive strength of HCPC. Findings indicate that adjusting the water–binder ratio to 0.18, adding 8% silica fume, and a sand volume ratio of 40% can significantly enhance the compressive strength of HCPC, which can reach up to 104.9 MPa. Additionally, the robust frost resistance of HCPC is substantiated by appearance damage analysis, mass loss rate, and compressive strength loss rate, after 50 freeze–thaw cycles the mass loss, and the compressive strength loss rate can meet the specification requirements. The study also corroborates the high-temperature stability of HCPC. This study optimized the preparation of HCPC and provided a feasibility for its application in precast concrete.
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