EFFECT OF CARBON NANOTUBES ON THE MECHANICAL FRACTURE PARAMETERS AND MICROSTRUCTURE OF ALKALI ACTIVATED SLAG MORTARS

Rovnaník P, Bayer P, Topolár L, Šimonová H, Schmid P

Abstract: Alkali activated slag has a great potential to be used in practice. The mechanical properties and application possibilities of alkali activated slag composites are very similar to ordinary cement based concrete. However, the major disadvantage of alkali activated slag is an increased shrinkage, which results in microcracking and deterioration of tensile and bending properties. The study investigates the possibility of using carbon nanotubes (CNTs) as nanosized reinforcement to reduce the cracking tendency of alkali activated slag composite. The effect of CNTs was evaluated by means of mechanical fracture tests and microscopic observations. Compressive strength has increased with 0.5% addition of CNTs but higher content of CNTs causes a deterioration of the compressive strength. Modulus of elasticity was also slightly higher in case of the mixture with 0.5% of CNTs. Effective fracture toughness and fracture energy values are in both cases lower than with reference mixture. Therefore, it can be assumed that such amounts of CNTs do not improve fracture parameters of AAS material. The micrographs revealed that CNTs were not able to eliminate the stress caused by a drying shrinkage of AAS matrix and still some cracks can be observed in the matrix.

Keywords: Slag, Alkaline activation, Carbon nanotubes, Microstructure and Fracture parameters

DOI: https://doi.org/10.15623/ijret.2014.0325009