Combined effect of multi-walled carbon nanotubes, steel fibre and glass fibre mesh on novel two-stage expanded clay aggregate concrete against impact loading

The use of expanded clay aggregate (ECA) for developing lightweight concrete results in strength-reduction properties. However, the ECA-based concrete strength properties can be improved by adding steel fibre (SF), glass fibre mesh (GFM) and multi-walled nano-carbon tubes (MWCNT). The combined effect of MWCNT, GFM, SF and ECA-based concrete and its strength properties is still unexplored. It is worth drawing a logical conclusion concerning the impact on the strength of concrete by incorporating the materials mentioned above. Two-stage expanded clay aggregate fibrous concrete (TECAFC) is a new concrete type and an emerging research area in material engineering. The casting method of TECAFC includes the two essential phases as follows. First, ECA and fibres are filled into the empty cylindrical mould to develop a natural skeleton. Second, the grout comprising cement, sand and MWCNT, are injected into the developed skeleton to fill voids. In this research, eight mixtures were prepared with 0.1 and 0.2% of MWCNT, 2.5% dosage of SF and three different layers of GFM inserted between the two layers of concrete. These eight mixtures were divided into two series of three mixtures each, in addition to two reference mixtures that include no SF or GFM. The first series of mixtures was comprised of 0.1% of MWCNT and 2.5% of SF and one, two and three layers of GFM insertion. The second series was the same as the first series and the dosage of MWCNT was taken as 0.2%. All cylindrical specimens were tested under drop mass impact as per the suggestions made by the ACI Committee 544. The test results showed that incorporating steel fibres and GFM improved the cracking and failure impact resistance by more than 270 and 1100%, respectively, and increased the impact ductility index by more than 220%, significantly contributing to steel fibres.