a b s t r a c tTime-dependent property changes in glass fibre reinforced cement (GRC) mainly result from a combination of the alkalinity of the matrix and densification of the matrix (e.g. due to calcium hydroxide precipitation) within and around the glass fibre strands. The microstructure of the interface between matrix and fibres in GRC has a significant impact on its durability. This paper describes a study of two GRC formulations (with OPC, and OPC plus calcium sulfoaluminate based matrices) aged for 10 years at 25°C. Thin-section petrography (TSP) and SEM are used to compare the microstructure of both polished surfaces and fractured surfaces. The aged OPC/ GRC demonstrates significantly brittle behaviour with substantial densification of C-S-H/CH intermixture occurring around glass fibres. In contrary, the aged composite made with the OPC plus calcium sulfoaluminate shows greatly retained toughness, accompanied by considerably flexible interfacial and interfilamentary areas around the glass fibres.
CSA/GFRC is an advanced composite material possessed with great ductility and durability. However, its bending performance and fibre condition, as well as intrinsic microstructural changes, under elevated temperature have not been understood so far. XRD was applied in this study to investigate the hydration mechanism of CSA cement under 50°C, 70°C, and 80°C. Bending performance was carried out to test the toughness of CSA/GFRC. SEM was applied to observe the underlying microstructural changes of CSA/GFRC under different curing regimes. It was found out that there was a gradual degradation of both ultimate tensile strength and ultimate strain of CSA/GFRC with elevated curing temperature and curing age, but glass fibre still shows considerable ability to carry stress alone by bridging cracks. Microstructural studies showed that, at accelerated temperatures of 50°C and 70°C, the space between fibres remained empty in general only with some hydration products adhering to the fibre surface occasionally. At a higher accelerated curing temperature of 80°C, densification of the interfilamentary spaces by larger and clustered hydration products can be observed at longer curing ages, causing the fibres to lose parts of the flexibility. Therefore, it can be concluded that densification of interfilamentary spaces may have a greater role to play in the strength degradation of CSA/GFRC than mechanisms associated with fibre weakening caused by chemical corrosion.
Concrete-filled steel tubular (CFST) columns are widely used in engineering structures, and they have many different cross section types. Among these, normal solid sections and concrete-filled double-skin steel tubular sections are often used. Although many studies have been conducted on CFST columns with these two section types, no studies have been conducted on their damage assessment under blast loading. In this study, experimental analysis and a numerical simulation method were integrated to evaluate the responses and assess the damage of two concrete-filled steel tubular (CFST) columns with different cross sections subjected to near-field blast loading. The results showed that for a scaled distance of 0.14 m/kg1/3, plastic bending deformation occurred on the surfaces of the two CFST columns facing the explosive. The antiexplosion performance of the normal solid-section (NSS) CFST column was better than that of the concrete-filled double-skin steel tubular (CFDST) column. The explosion centre was set at the same height as the middle of column, and the distributions of the peak pressure values of the two columns were similar: the peak pressures at the middle points of the columns were the greatest, and the peak pressures at the bottom were higher than those at the top. With the analysis of the duration of the positive pressure, the damage at the middle was the most severe when subjected to blast loading. Using pressure-impulse damage theory and the validated numerical simulations, two pressure-impulse damage evaluation curves for NSS and CFDST columns were established separately by analysing the experimental and simulation data. Finally, based on the two pressure-impulse damage evaluation curves, the two pressure-impulse damage criteria for these two different fixed-end CFST columns were defined based on the deflection of the surfaces facing the explosives. Furthermore, the mathematical formulae for the two different column types were established to generate pressure-impulse diagrams. With the established formulae, the damage of the CFST columns with these two cross section types can be evaluated. Damage to other similar CFST columns with different cross section types due to near-field blast loading can also be evaluated by this method.
High autogenous shrinkage property is one of the disadvantages of ultra-high-performance concrete (UHPC), which may induce early age cracking and threaten the safety of concrete structure. In the present study, different dosages of calcium sulfoaluminate (CSA) cement were added in UHPC as an effective expansive binder. Hydration mechanism, autogenous shrinkage property, and compressive strength of UHPC were carried out to investigate the effect of CSA addition on the mechanical properties of UHPC. Scanning electron microscopy was also employed to characterize the intrinsic microstructural reasons relating to the changes in macroproperties. Based on the XRD diagram, increasing formation of ettringite and Ca(OH)2 can be found with increasing CSA content up to 15%. In the heat flow results of UHPC with 10% CSA addition, the maximum heat release increases to 2.6 mW/g, which is 8.3% higher than the reference UHPC, suggesting a higher degree of hydration with CSA addition. The results in autogenous shrinkage show that CSA expansion agent plays a significantly beneficial role in improving the autogenous shrinkage of UHPC. The corresponding autogenous shrinkage of UHPC is −59.66 μ ε , −131.11 μ ε , and −182.31 μ ε , respectively, at 7 d with 5%, 10%, and 15% addition, which is 108%, 117%, and 123% reduction compared to the reference specimen without CSA. In terms of compressive strength, UHPC with 5%, 10%, 15%, and 20% CSA addition has 10.5%, 17.4%, 30.2%, and 22.1% higher compressive strength than that for the reference UHPC at 28 d. Microstructural study shows that there is an extremely dense microstructure in both the bulk matrix and interfacial transition zone of UHPC with 10% CSA addition, which can be attributed to the higher autogenous shrinkage property and can therefore result in higher mechanical performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.