This paper presents a development of a ductile alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) based composite as an environmentally friendly material for structural concrete application. For this purpose, polyvinyl alcohol (PVA) fibres and sand aggregate were combined with alkali-activated paste. Workability, setting time, mechanical properties and failure mode of PVA fibres in the mixture were studied by slump test, Vicat needle test, flexural and compression tests, and Scanning Electron Microscopy (SEM) imaging, respectively. Although the mixture sets in a short period of time (less than 30 min), the workability was good and the developed fibre reinforced composite was used for a large scale application in a canoe. Casting a large volume (45 l compared to 3 l, as initially designed) did not affect the workability and the setting time of the mixture. Mechanical properties of specimens coming from “small” (3 l) and “large” (45 l) batches were tested at different ages (up to 120 days) and compared. It was shown that their flexural and compressive strength are similar, i.e. not affected by the upscaling. Furthermore, it was shown that the mixture with PVA fibres exhibits deflection hardening behaviour even with aggregate particles as large as 4 mm, although single crack localization led to failure. The SEM images of fractured surfaces indicated that combined fibre pull-out and fibre rupture occurred, with the latter one causing the final failure. The developed mixture, additionally reinforced with the plastic fiberglass mesh, was used in the 5.8 m long and 16 mm thick canoe for the student competition, which for the very first time, was constructed without the use of Ordinary Portland cement (OPC). The upscaling was successful and the results show the potential of fibre-reinforced alkali-activated FA and GBFS composite to be used as a durable and resistant material suitable for the structural application in thin shell elements, exemplified by the canoe. Such an application and a low risk project was suitable to gain the necessary experience and confidence with this innovative, “concrete like” material for which no codes or regulations are available. Furthermore, similar applications are the first step for larger scale structural applications, like structural elements in the building industry, bridges and other civil engineering structures.
- Alkali-activated composite
- PVA fibres