Effects of carbon nanotubes and high surface area graphite on cement paste

This research aims at exploring the potential effects of carbon-based nanomaterials, such as carbon nanotubes (CNTs) and high surface area graphite (HSAG) on mechanical characteristics and durability of cement paste. CNTs and HSAG have remarkable mechanical, electrical, and thermal properties and their incorporation within the cement matrix is expected to enhance its performance through several mechanisms like densification of micro-structure, crack-bridging, and hydration promotion. Obtaining such attributes, however, necessitates a uniform distribution of nano-additions within the cement matrix which is a major challenge to overcome. Therefore, in this study a novel and well-tested dispersion approach is employed and the integration of CNTs and HSAG in cement paste is assessed through various experimental tests. Different mixtures with varying concentrations of nano-additions were prepared using aqueous suspensions of CNTs/HSAG, once dispersed with the proposed technique and another time utilizing only sonication. Furthermore, an additional set of samples were produced only with water and cement to be used as the reference. The results of mechanical tests revealed that the flexural strength of most samples with nano-addition increased up to an optimal concentration, with respect to the flexural strength of the control sample and regardless of the type of nano-addition and utilized dispersion approach. However, the compressive strengths of specimens were not significantly influenced by the presence of CNTs and HSAG. Moreover, tests on durability characteristics of samples, such as electrical resistivity and carbonation resistance, demonstrated positive effects of CNTs and HSAG additions on reducing the porosity of the cement paste and densifying its microstructure. Nevertheless, no marked distinctions were found in the comparison between CNTs and HSAG nano-additions or between the treated and pristine types of each specimen.

Lo scopo di questo lavoro di ricerca è quello di andare a studiare i potenziali effetti dei nanomateriali a base di carbonio, come i nanotubi di carbonio (CNT) e la grafite ad alta superficie (HSAG) sulle caratteristiche meccaniche e sulla durabilità dell’impasto cementizio. CNT e HSAG hanno notevoli qualità meccaniche, elettriche e termiche e la loro incorporazione all'interno della matrice cementizia, attraverso diversi meccanismi come l'addensamento della microstruttura, il crack bridging e la promozione dell'idratazione, dovrebbe migliorarne le prestazioni. L'ottenimento di tali miglioramenti prestazionali richiede una distribuzione uniforme delle nano-addizioni all'interno della matrice cementizia, questo sarà il requisito fondamentale e più difficile da raggiungere. Pertanto, in questo studio è stato utilizzato un nuovo metodo e l'integrazione di CNT e HSAG nell’impasto cementizio è stata valutata attraverso vari test sperimentali.