Development of core-shell lightweight aggregate with carbon nanotube towards high elastic modulus : experiment and modeling

Abstract

The low strength and elastic modulus of lightweight aggregate (LWA) are the main factors restricting the development of lightweight concrete (LWC). To address this issue, a core-shell lightweight structure comprising a lightweight core and a strong shell toughened by carbon nanotubes (CNTs) was designed to fabricate high-strength LWA. Incorporating 0.3 % CNTs resulted in a remarkable reduction in LWA porosity by over 97 %, while the elastic modulus of LWC was enhanced by 31.7 %. Experiments and simulations were employed to elucidate the role of CNTs in toughening the hydrated cementitious shell from hydration to cracking. Through TEM, SEM, X-CT, and nanoindentation, it was demonstrated that CNTs played a limited role in nucleation and marginally accelerated the hydration process. The shell and the adjacent interfacial transition zone were enhanced mainly because CNTs significantly rendered a tighter packing of hydration products and optimized the interconnected pores in sphericity and volume. Simulation results revealed that achieving a high modulus hinged on establishing a multi-layer synergy between the shell and the matrix, which was accomplished by forming an evenly distributed dense CNT-cement composite to mitigate stress concentration. This work harnesses the potential of CNTs to refine the unique pore distribution of LWA and optimize the stress distribution pattern of the core-shell structure within the matrix, which would facilitate the realization of LWC applications with high strength and modulus.