Ice-releasing strategy to improve the dispersion of CNTs in cement paste with enhanced reinforcing efficiency

Due to the over-concentrated CNTs at the moment of adding an aqueous solution of CNTs (as-CNTs) into fresh cement mixture, bulk aggregation of CNTs immediately happens and limits its reinforcing efficiency to cement-based materials. This study proposed a novel ice-releasing strategy by solid mixing of cement particles with micro-scaled ice particles containing well-dispersed CNTs (ice-CNTs) at first and then slowly releasing of CNTs during the ice-melting process, which significantly enlarged the initial distance among neighbored CNTs, reduced the aggregation size of CNTs and relieved the over-concentrated problem of CNTs, and a better dispersion and stability of ice-CNTs in simulated cement pore solution was thus achieved and verified by visual observation, UV–Vis absorbance and particle size distribution. In this way, compared with as-CNTs, 0.08 wt% addition of ice-CNTs was more effective to reduce cement hydration heat, fine the pore structure and reduce the total porosity of cement matrix, and enhance the 3, 7 and 14-day compressive strength of cement paste by 12.0%, 7.1% and 12.1%, respectively. In addition, water adsorption of cement paste with ice-CNTs became the lowest one in all mixes up to 14 days. In conclusion, the research outcomes open the door to improve the dispersion and stability of CNTs in cement mixture by a novel ice-releasing strategy, and effectively enhance the reinforcement of CNTs to cement paste in terms of porosity, mechanical strength and durability.