Durability of GFRC Modified by Calcium Sulfoaluminate Cement under Elevated Curing Temperatures

Abstract

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.

Effect of Low Temperatures on the Mechanical Performance of GFRC Modified by Low Carbon Cement

“…It can be found out that low-temperature environments have very little effect on the type of hydration products of CSA modified cement. Crystalline CH is still absent, and large amounts of ettringite can be traced in all the specimens of CSA modified cement under low-curing temperatures, which is in agreement with the previous research [14,16]. e sharp peak of ettringite in the CSA paste cured at −5 °C suggests that hydration of CSA cement still continues at lower temperature, which is beneficial for the development of both strength and densified microstructure.…”

“…is degradation process is similar to the previous results on CSA/GFRC [5,16], in which CSA/GFRC indicates gradual and medium reduction on both strength and ductility under accelerated ageing.…”

“…It was reported that formation of ettringite was extremely sensitive to curing temperatures and decreased levels of ettringite are generated under low temperatures [12]. is is because lower curing temperature is not conducive to the breaking of chemical bond and thus may lead to a slower nucleation rate of ettringite, especially for those below 0 °C [16]. In addition, a broad peak at about 32 °indicates remnants of unhydrated belite clinker in all the specimens.…”

“…GFRC modified by CSA cement (CSA/GFRC) has aroused great attention among researchers, and many studies have been undertaken to investigate its mechanical properties and microstructural characteristics under different curing regimes [14][15][16]. Research by Pe ′ ra and Ambroise [17] showed that CSA/GFRC exhibited rapid development of modulus of rupture, which reaches 8 MPa at 3 h, 9.3 MPa at 24 h, and 20.5 MPa at 28 d. Song et al [15] demonstrated that CSA/GFRC still retained a large proportion of toughness after ageing for 10 years at 25 °C.…”

Influence of different additives on the creep property of oil well cement

“…Hydrated cement paste is a brittle material with low tensile strength and inferior resistance to crack propagation. Previous studies showed that its toughness would be improved by the addition of fiber reinforcements (Brandt, 2008;Song et al, 2019). Fibres can not only limit the crack expansion but can also withstand the external loads mutually with cement.…”