Solution time: 2016 - 2018
Project No: 16-00567S
The main aim of the project was to prepare and provide a complex analysis of alkali-activated aluminosilicate composites with conductive functional fillers. For the realization of this aim, composites with five different functional fillers (graphite, carbon nanotubes, carbon black, carbon fibres, and steel fibres) with various dosage were prepared. All tested parameters were compared with plain alkali-activated slag mortars as a reference mixture, and since only few data of electrical properties were provided for alkali-activated materials, some essential comparison was also made for the plain cement mortar. The fresh mortars were tested for their rheological properties by means of rotational rheometry. The hardened mixtures were characterized from the viewpoint of their textural and structural characteristics and mechanical fracture properties. Complex electrical characterization of the composites was performed in both DC and AC mode using impedance spectroscopy method in two different frequency ranges – one between 40 Hz–1 MHz and the other between 10 MHz–3 GHz. The main objective of this measurement was to assess the percolation threshold for different types of functional fillers which is essential for the application of these composites as self-sensing or self-monitoring materials. The other task was the investigation, complex characterization and computational modelling of the thermal and hygric properties of prepared composites, the objective of which was to find the most suitable admixtures and their dosage for the application as self-heating materials or as embedded moisture sensors. In the final task, demonstration of the selfsensing properties in compression and flexure and self-heating performance of the selected mixture were performed.
According to the experimental results, the following most important conclusions can be considered:
– AAA composites showed quite good mechanical performance, although high portions of very fine conductive fillers aggravated their mechanical properties, mainly due to a higher demand of mixing water.
– Assessed amount of fillers for reaching the percolation threshold was 12% for graphite, 6% for carbon black, and 10% for steel fibres. In the case of carbon fibres and CNTs, the percolation threshold was not reached for a reasonable amount of the admixture.
– All AAA composites including plain alkali-activated slag showed improved electrical conductivity compared to p-cement mortar; however, the electrical properties are extremely moisture dependent.