Direct observation of the moisture distribution in calcium aluminate cement and hydratable alumina‐bonded castables during first‐drying: An NMR study

Calcium aluminate cement (CAC) and hydratable alumina (HA) are the most widely used binders for refractory castables. Nevertheless, CAC as the binder for refractory castable generates some low melting point phases when coupled with SiO2, which deteriorate the high temperature performance of refractory castables. Although hydratable alumina (HA) bonded castables overcome the drawbacks of CAC bonded ones, they demand a longer mixing time and higher water contents due to HA's high specific surface area, as well as increasing the shear stress and viscosity of HA bonded castables. Therefore, in this paper, CAC combined with HA was used as the binder for corundum- spinel castables to obtain better performance. Sodium tripolyphosphate (STPP), dispersing alumina (ADS) and polycarboxylate ether dispersant (FS60) were used as dispersants, and their effects on the rheological behaviors of CAC-HA bonded corundum-spinel castables suspensions had been investigated. According to the viscosity-shear rate and stress-shear rate curves of suspensions with different dispersants, it was suggested that STPP, ADS, FS60 were all helpful for rheological performance of suspensions. Suspensions achieved much better rheological behavior with 0.3 wt.% of STPP, 1.0wt.% of ADS and 0.1wt.% of FS60, respectively. Suspensions with ADS and FS60 presented to be pseudo plastic fluid, which was helpful for the installation process of CAC-HA bonded corundum-spinel castables. And FS60 could simultaneously impart electrostatic and steric stabilization to the given suspension. Considering the actual rheological performance of CAC-HA bonded corundum-spinel castables, FS60 was much better than ADS.

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Physicochemical, Mineralogical, and Mechanical Properties of Calcium Aluminate Cement Concrete Exposed to Elevated Temperatures

Materials ◽

10.3390/ma14143855 ◽

2021 ◽

Vol 14 (14) ◽

pp. 3855

Author(s):

Amirmohamad Abolhasani ◽

Bijan Samali ◽

Fatemeh Aslani

Keyword(s):

Temperature Rise ◽

Calcium Aluminate ◽

Elevated Temperatures ◽

Ultrasonic Pulse Velocity ◽

Pulse Velocity ◽

Calcium Aluminate Cement ◽

Cement Concrete ◽

Sem Images ◽

Strength Deterioration ◽

Aluminate Cement

One commonly used cement type for thermal applications is CAC containing 38–40% alumina, although the postheated behavior of this cement subjected to elevated temperature has not been studied yet. Here, through extensive experimentation, the postheated mineralogical and physicochemical features of calcium aluminate cement concrete (CACC) were examined via DTA/TGA, X-ray diffraction (XRD), and scanning electron microscopy (SEM) imaging and the variation in the concrete physical features and the compressive strength deterioration with temperature rise were examined through ultrasonic pulse velocity (UPV) values. In addition, other mechanical features that were addressed were the residual tensile strength and elastic modulus. According to the XRD test results, with the temperature rise, the dehydration of the C3AH6 structure occurred, which, in turn, led to the crystallization of the monocalcium dialuminate (CA2) and alumina (Al2O3) structures. The SEM images indicated specific variations in morphology that corresponded to concrete deterioration due to heat.

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