Hydration of calcium aluminate cement blended with anhydrite

Abstract

Calcium aluminate cements (CACs) are used in combination with calcium sulfates as binders in self-levelling mortars. The influence of commercial CAC/anhydrite ratio on the solid phase assemblage and pore solution at water to binder (w/b) ratios of 0•40 and 0•72 was investigated between 1•5 h and 91 d of hydration using a multi-method approach including x-ray diffraction, thermogravimetric analysis and thermodynamic calculations. The reduction of the extent of hydration at the lower w/b ratio can be explained by a lack of water for complete hydration and lack of space. In the system with a CAC/anhydrite weight ratio of 1, ettringite and AH 3 were the main hydration products, whereas in the case of a CAC/anhydrite ratio of 2•3, in addition to ettringite and AH 3 , monosulfate was present along with strätlingite and at a later age. In contrast to the thermodynamic modelling results, anhydrite persisted even at low calcium sulfate contents as the precipitation of AH 3 around the anhydrite grains seemed to lead to a chemical blocking.

Microstructural comparison of the AH3 phase in the hydration of three structural modifications of ye'elimite

“…Thus, the AH 3 phase formed during the hydration of three structural modifications of ye'elimite had a small crystal size presented in a microcrystalline or nanocrystalline structure. Some researchers, such as Cuesta et al and Lothenbach et al who studied the CA or CA 2 minerals in the calcium aluminate cements, also observed this particular state of AH 3 phase. They also confirmed that this broadening in diffraction peaks arising from the AH 3 phase clearly showed the microcrystalline or nanocrystalline structure.…”

“…It is interesting to note that the amorphous AH 3 phase may be present at an early age. Le Saoût et al who studied the hydration of calcium aluminate cement blended with anhydrite at a lower L/S ratio, observed that the pore solutions were strongly oversaturated by the calculated saturation indices with respect to microcrystalline AH 3 phase at an early age; however, experimentally, no or negligible amount of AH 3 phase was detected by XRD or TGA. Thus, the AH 3 phase might exist with an amorphous structure at an early age.…”

Nanostructural characterization of Al(OH)3 formed during the hydration of calcium sulfoaluminate cement

“…This XRD observation was previously shown to correspond with the formation of AH 3 ‐H with a microcrystalline size. Lothenbach et al, has analyzed the degree of crystallinity of AH 3 phase formed during the calcium aluminate cement at an early age . They observed that the pore solutions were highly oversaturated with respect to AH 3 at the beginning (before 1.5 hours), indicating that AH 3 could potentially form, but AH 3 phase was not detected experimentally at an early age, indicating that amorphous AH 3 may be present initially.…”

“…Lothenbach et al, has analyzed the degree of crystallinity of AH 3 phase formed during the calcium aluminate cement at an early age. 30,47,48 They observed that the pore solutions were highly oversaturated with respect to AH 3 at the beginning (before 1.5 hours), indicating that AH 3 could potentially form, but AH 3 phase was not detected experimentally at an early age, indicating that amorphous AH 3 may be present initially. With a tendency over time, amorphous AH 3 transformed into microcrystalline AH 3 .…”

Nghiên cứu ảnh hưởng của loại canxi sun phát đến độ co hoá học và nhiệt thủy hóa của vữa tự san phẳng sử dụng chất kết dính ettringite

“…Pic tỏa nhiệt thứ (2) tương ứng với sự hình thành khoáng ettringite, có thể thấy rằng khi cùng loại canxi sunphát, độ lớn của dòng nhiệt tăng lên khi tăng hàm lượng CAC do tốc độ thủy hóa của CAC diễn ra nhanh. Kết quả này tương hợp với các kết quả nghiên cứu khác [19][20][21]. Mặt khác, tốc độ hòa tan của hemihydrate nhanh hơn anhydrite vì vậy mà tốc độ hình thành ettringite diễn ra nhanh hơn và nhiệt tỏa ra nhiều hơn.…”