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Corrosion of steel bars embedded in reinforced concrete structures considerably reduces the service life and even causes early failure of the structure. This paper investigates the early corrosion behavior of an alloy corrosion-resistant steel bar in seawater–sea sand concrete (SWSSC) using various electrochemical measurements [electrochemical impedance spectroscopy (EIS) linear polarization resistance (LPR)] and surface characterization techniques [scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS)], in comparison to low carbon steel bar (LC) and stainless steel bar (SS). The results reveal that the Cr10Mo1 alloy corrosion-resistant steel bar (CR) in SWSSC shows significant increase in the radius of the capacitive arc in later stages, particularly in the low frequency region. This increase in CR can be attributed to the enhanced corrosion resistance of the passivation film, as well as the rise of impedance at the interface between the passivation film and the concrete matrix. These improvements have effectively inhibited the penetration of free chloride ions into the concrete, thereby impeding the initiation and propagation of corrosion in CR In addition, the mechanical properties, pore structure and the hydration production of SWSSC were investigated. Based on the interactions between steel substrate and concrete matrix, the possible resistance mechanism of CR was proposed. This study innovatively provides a comprehensive evaluation of the effectiveness of CR in SWSSC. [ABSTRACT FROM AUTHOR]

In this study, a series of polyethylene glycol (PEG)/hydrochloric acid-modified sepiolite (HSEP) composite phase change materials (PCMs) are fabricated via vacuum impregnation. HSEP exhibits high adsorption capacity, rendering it superior to natural sepiolite as carriers for PEG. The resulting composite PCMs possess a melting enthalpy of up to 88.9 J/g and maintain stable thermal performances and chemical structures over 100 heating–cooling cycles between room temperature and 65 °C, thus, indicating long-term reliability. Calorimetry studies on cement paste containing 30% composite PCMs reveal a 24.14% reduction in 3-day cumulative hydration heat. However, the mechanical strength and thermal conductivity of the cement paste are adversely affected. Hence, carbon fibers (CFs) are introduced as reinforcement, resulting in a 28-day compressive strength of 45.6 MPa for cement paste containing 20% composite PCMs and 0.6% CFs. The fabricated composite PCMs are promising functional materials for hydration heat control and energy storage in concrete structures. [ABSTRACT FROM AUTHOR]

In this paper, citric acid-modified chitosan (CAMC) was added to cement slurry and its adsorption and hydration regulation mechanism on cement particles was studied. The rheological properties, agglomeration properties, and adsorption properties were characterized by different testing techniques. The effect of CAMC on the evolution of C-S-H gel and aluminum hydrate was further studied by the NMR technique. The results show that the negatively charged CAMC will adsorb on the surface of cement and agglomerate cement particles. In addition to being adsorbed on the positively charged aluminate phase surface under the electrostatic effect, CAMC was also adsorbed on the negatively charged silicate phase through complexation between carboxyl groups and calcium ions. The formation of complexes on the surface of the silicate phase hinders the hydration of calcium silicate (C3S).CAMC significantly reduced the hydration rate of early cement, hindering the nucleation of C-S-H and ettringite (AFt). [ABSTRACT FROM AUTHOR]

In this study, citric acid-modified chitosan (CAMC) is prepared by an acylation reaction to regulate the exothermic process occurring in cement hydration. The thermodynamic process of cement hydration is characterized by isothermal calorimetry. The effects of various CAMC contents of 0%, 0.2%, 0.4%, and 0.6% on the hydration process were systematically studied by X-ray diffraction (XRD), inductively coupled plasma emission spectroscopy (ICP–OES), and proton nuclear magnetic resonance (1H-NMR). The results show that the adsorption effect delays the dissolution of alite (C3S). The content of CAMC is shown to have a significant effect on the formation time and amount of ettringite (AFt), and the competitive adsorption relationship increases the concentration of Ca2+. The increases in Ca2+ and SO42- concentrations resulted in an increase in the AFt amount. With prolongation of the hydration, the capillary pores of the cement paste are transformed into gel pores, and the cement slurry exhibits a self-drying phenomenon. Designed and prepared citric acid modified chitosan. Adsorption delays the dissolution of C 3 S and the formation of hydrated products. Competitive adsorption increases calcium ion concentration. CAMC delays the formation of AFt and increases the amount of AFt formation. [ABSTRACT FROM AUTHOR]

Recently, the use of aeolian sand for producing ultra-high-performance concrete (UHPC) was introduced. Preliminary investigations suggested that it was feasible to use aeolian sand to produce UHPC. In this study, systematic investigations on the workability, hydration, microstructure, and mechanical properties are conducted to unveil the dominant factors controlling the performance of the UHPC produced with aeolian sand. Moreover, an intensive mixing process is also introduced to promote the efficiency of using aeolian sand and steel fibers for producing UHPC. The results show that the UHPCs produced with aeolian sand by an intensive mixing process exhibit substantial improvements in workability, mechanical strength, fiber dispersibility, and porosity, although the degree of cement hydration is only slightly improved. The improvement in the performance of the UHPC is found to be mainly related to the improvement in dispersibility of steel fibers and thus the refinement in the pore structure. [ABSTRACT FROM AUTHOR]