The mechanical performance of fibre-reinforced ultra-high-performance
concrete based on alkali-activated slag was investigated, concentrating
on the use of steel fibres. The flexural strength is slightly higher
compared to the UHPC based on Ordinary Portland Cement (OPC) as the
binder. Correlating the flexural strength test with multiple
fibre-pullout tests, an increase in the bonding behaviour at the
interfacial-transition zone of the AAM-UHPC was found compared to the
OPC-UHPC. Microstructural investigations on the fibres after storage in
an artificial pore solution and a potassium waterglass indicated a
dissolution of the metallic surface. This occurred more strongly with
the potassium waterglass, which was used as an activator solution in the
case of the AAM-UHPC. From this, it can be assumed that the stronger
bond results from this initial etching for steel fibres in the AAM-UHPC
compared to the OPC-UHPC. The difference in the bond strength of both
fibre types, the brass-coated steel fibres and the stainless-steel
fibres, was rather low for the AAM-UHPC compared to the OPC-UHPC.