Use of γ-Al2O3 to prevent alkali-silica reaction by altering solid and aqueous compositions of hydrated cement paste

Formulating Portland cement–reactive alumina blend through thermodynamic modeling to prevent the alkali–silica reaction

“…Region B (4.5% ≤RA < 5.75%) is a transitional stage, in which the predicted Al concentration increases rapidly from ∼0.3 to 0.8 mmol/L, corresponding to the formation of (SO 4 -OH) AFm solid solution. 14,18,40 As discussed above, the complete conversion of ettringite takes place at the end of region A, and C-S-H cannot incorporate more Al within this stage as its Al/Si ratio reaches 0.22. Therefore, the dissolved Al begins to form a less stable (SO 4 -OH) AFm solid solution, increasing Al concentration rapidly.…”

“…The particle size distribution of the raw materials position, and physical properties of the used materials are shown in Figure 1 and 14 The expansion (14 days) of the three aggregates measured according to ASTM C1260 is 0.18%, 0.30%, and 0.35% (Appendix B), respectively. 23 Rutile (Kronos 2300 TiO 2 , 96.4 wt.…”

“…25,26 If the Al uptake into C-S-H is not considered in the thermodynamic modeling, this leads to over-predicted katoite in comparison. 14 In order to improve the accuracy of the thermodynamic modeling, the Al uptake in C-S-H was corrected by subtracting the Al incorporated in C-S-H from the total incorporated alumina, because this part of Al does not contribute to forming hydrated aluminate phases (AFm phase and/or katoite). The correction was based on the measured atomic ratio of Al/Si in C-S-H in the hydrated blend containing 10% RA (hydrated for 90 days) by scanning electron microscopy/energy disperisive X-ray spectroscopy (SEM/EDS) point analysis, in which the formation of katoite has also been confirmed by the XRD and TGA.…”

“…In the previous study, the replacement of 10% Portland cement with reactive alumina (RA) led to the precipitation of katoite, and the Al concentration in the pore solution increased to 0.8 mmol/L correspondingly. 14 However, the use of RA at such a high cement replacement level resulted in some problems. First, the used RA mainly consists of γ-Al 2 O 3 , and the fast dissolution of γ-Al 2 O 3 leads to remarkably high initial heat release, flash setting, and hindering strength gain at early ages.…”

Experimental Study on Strengthening and Sealing Materials and Their Application in Coal Mines

“…(1) Aluminium powder: the main component of cement is silicate, which is soluble in water and weakly alkaline after hydrolysis. After adding aluminium powder into the cement, the chemical reaction of aluminium powder in the alkaline solution produces hydrogen, which will cause the volumetric expansion of the cement, compensate for the shrinkage of the cement slurry, play the role of expansion filling, and improve the sealing performance of the cement [34]. e principle of chemical expansion is as follows:…”