![]() They reported that an optimal graduating of lightweight aggregates could reduce the porosity of lightweight aggregate concrete and improve mechanical performance. Kurpińska and Ferenc 24, 25 investigated the importance of grading of lightweight aggregates. Mechanical properties of lightweight aggregate concrete also depend on the desired density of the composite decreasing the density reduces the mechanical properties of composite 23. However, the strength properties of lightweight aggregates are also much lower than the conventional aggregates due to this fact, cement composites utilizing lightweight aggregates generally achieve lower mechanical properties and densities 22. Lightweight aggregates are 25–35% lighter than the conventionally used aggregates 19. Expanded glass aggregates is also a thermal conducting material with porous structure 21. Silica aerogel is a lightweight thermal insulating material having low density and high specific surface area, allowing its application in many areas 20. With the increase in the consumption of natural aggregates, researchers are mainly focused on conserving the natural eco-system that leads to the use of lightweight aggregates such as expanded glass aggregates, silica aerogel 19. The strength development of cementitious composite also depends on the properties of aggregates and what kind of pozzolanic materials were used. The highest improvement in compressive and flexural strength was observed 83.33% 15 and 30% 16 for cement paste ~ 35% 3 and 28.04% 17 for mortar 38.62% and 38.63% for concrete 18, respectively. The improvement in cementitious composites were found different for cement mortar, cement paste, and concrete. Without proper dispersion technique, agglomeration of CNTs can be noticed in the concrete structure due to the strong van der Waals forces and can influence the mechanical and microstructural properties. ![]() 14 reported that polycarboxylate-based superplasticizer plays a double dispersion mechanism to disperse the cement and CNTs within the composite. 10 reported that ultrasonication energy and polycarboxylate-based superplasticizer could significantly influence the mechanical and microstructural properties of CNT incorporated cementitious composites by optimally dispersing the CNTs within a concrete structure 8, 10. The reinforcing efficiency of carbon nanotubes can be influenced by several parameters such as type of CNTs 3, the concentration of CNT 4, dispersion surfactants 5, treatment of CNTs 6, 7, dispersion technique 8, the interaction with cementitious materials and bond strength 9, the water–cement ratio 10, 11 and geometry of CNTs 12, 13. Inclusion of small doses of MWCNT can effectively improve the mechanical properties of cementitious composites improving early age and long-term durability 2. Carbon nanotubes can be categorized into single-wall carbon nanotube (SWCNT) and multiwall carbon nanotube (MWCNT). The nanoscale diameters and smooth surfaces of CNT’s could affect the early age hydration of cementitious materials 1. Carbon nanotubes (CNTs) are an allotrope of carbon composed of coaxial hexagonal carbon rings, cylindrical in shape having around 132,000,000:1 length–diameter ratio. Nowadays, the use of carbon nanotubes in cementitious materials is getting attention for the improvement of physical and mechanical characteristics. ![]() Additionally, flowability, water absorption, microscopy, X-ray powder diffraction, and semi-adiabatic calorimetry results were analyzed in this study. Besides, agglomeration of carbon nanotubes and the presence of ettringites was observed in the transition zone between the silica aerogel and cementitious materials. SEM image of the composite shows presence of C–S–H gel surrounding the carbon nanotubes, which confirms the cites of nanotubes for the higher growth of C–S–H gel. SEM image of lightweight concrete shows a homogeneous dispersal of carbon nanotubes within the concrete structure. The addition of carbon nanotubes gained almost 41% improvement in compressive strength. Study results show that incorporating multi-wall carbon nanotubes significantly influences the compressive strength and microstructural performance of aerogel based lightweight concrete. Carbon nanotubes were sonicated in the water with polycarboxylate superplasticizer by ultrasonication energy for 3 min. Combinations of expanded glass (55%) and hydrophobic silica aerogel particles (45%) were used as lightweight aggregates. This study is aimed to investigate the effect of carbon nanotubes on the properties of lightweight aggregate concrete containing expanded glass and silica aerogel.
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