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High early pozzolanic reactivity of alumina-silica gel: A study of the hydration of composite cements with carbonated recycled concrete paste

2023; Elsevier BV; Volume: 175; Linguagem: Inglês

10.1016/j.cemconres.2023.107345

1873-3948

Maciej Zając, Jiayi Song, Patrick Ullrich, Jan Skoček, Mohsen Ben Haha, Jo̷rgen Skibsted,

Innovative concrete reinforcement materials

Carbonated recycled concrete paste (cRCP) is a unique supplementary cementitious material with pozzolanic properties stemming from the alumina-silica gel. This study reveals that the high early strength of composite cements with cRCP is attributed to its rapid pozzolanic reactivity. 27Al and 29Si NMR investigations show that the alumina-silica gel is consumed after only 7 days of hydration. The rapid gel reaction results in the formation of a C-(A)-S-H phase with a low Ca/Si ratio. After 7 days, belite and remains of alite react further and increases the Ca/Si ratio of the C-(A)-S-H phase to a level typical for blended cements. As a result, a lower porosity forms already at early age, resulting in high strength. The reactivity of cRCP is influenced by its origin and carbonation conditions. Carbonation in sulfate-rich solutions enhances the gel surface area and accelerates the reaction. Slag remnants in cRCP react aiding to microstructure and strength development.