The hydration of fast setting spray binder versus (aluminum sulfate) accelerated OPC
Lukas Briendl, Florian Mittermayr, Rudolf Röck, Florian Roman Steindl, Marlene Sakoparnig, Joachim Juhart, Fatemeh Iranshahi, Isabel Galán
Abstract
Abstract The (early) hydration mechanisms of two different binder systems used for shotcrete were investigated: the so far almost unexplored low sulfate binder (spray binder), used in the field of dry-mix shotcrete; and ordinary Portland cement, accelerated by aluminum sulfate, widely used for wet-mix shotcrete. The basis for the fast setting of the spray binder is the rapid dissolution of C 3 A and the subsequent formation of flaky CO 3 -AFm phases. Thereby induced high aluminum concentrations in the pore solution lead to a blockage of alite dissolution during the first hours of hydration. At later stages, higher amounts of portlandite are formed in the dry-mix, compared to the wet-mix system. The lower calcium availability for portlandite formation in the wet-mix system is explained by an enhanced formation of C–A–S–H phases with a higher Ca:Si ratio. Additionally, wet-mix systems show lower porosity and higher compressive strength after 1 d of hydration and beyond. Graphical abstract