Influence of height and weight of drop hammer on impact strength and fracture toughness of two-stage fibrous concrete comprising nano carbon tubes

Concrete is the most extensively utilized and cheapest building material. The cracking and fracturing of concrete may cause catastrophic harm to the structures. Advancements in fibrous concretes have recently been emerged to mitigate these issues. Two-Stage Fibrous Concrete (TSFC) is a new cement composite made of fibres with surpassing mechanical properties and exceptional toughness values. The production of TSFC involves packing aggregates and fibres in the molding and filling the gaps between the aggregates with high flowability via the injection of cement grouts. Nevertheless, the influence of TSFC comprising multi-walled carbon nanotubes (MWCNT) on impact strength and fracture toughness requires particular attention since it is yet unexamined. The study was divided into two phases to address this knowledge gap. In the first phase, the influence of drop hammer weight and height on the impact resistance of TSFC were examined. Three different heights 600, 750 and 900 mm and three different hammer weights 9, 7.5 and 6 kg were used to assess the TSFC's impact strength. The fracture toughness under mode (I and III) and mixed-mode (I/III) of TSFC were evaluated in the second phase. For this, many notched specimens of circular disc shape were cast and tested. TSFC was produced with three different fibres; polypropylene fibre, short steel fibre, and long steel fibre with a dosage of 2.5 % by volume. Additionally, composites were created by adding 0.2 % MWCNT by weight of cement. Findings indicated that the failure impact numbers values of mixtures incorporating polypropylene fibre, short steel fibre and long steel fibre were higher than those of the reference plain mixture by 1444 to 1700 %, 3156 to 3786 % and 4322 to 5357 %, respectively. Adding fibre has a more significant impact on mode I and III crack development, with improvements ranging from 46.1 to 92.2 % for mode I and from 16.4 to 30.0 % for mode III, proving that fibres can substantially increase the TSFC's fracture resistance.