Influence of carbon nanotubes on concrete properties and bonding with steel bars

This thesis explores how carbon nanotubes (CNTs) can influence the properties of concrete properties and its bonding with steel bars, aiming to enhance mechanical behavior, reduce cement use, and promote sustainability. The research is divided into five chapters: the first three consist of literature reviews, which guide the two experimental ones. The first review focused on the parameters influencing steel-concrete (SC) bonding, highlighting fibers and CNTs' role in improving adhesion and identifying research gaps. The second one analyzed concrete with CNTs (CNT-concrete) bonding, addressing dispersion techniques, CNT types, and effects on bond strength, calling for more standardized studies. The third review examined CNT's impact on concrete's mechanical and durability properties, noting improvements in strength and porosity while emphasizing further research on durability aspects like carbonation resistance and electrical resistivity. Based on these studies, experimental approaches were conducted to assess CNT-concrete's physical and mechanical properties, with the CNTs being pre-dispersed in cement particles in an isopropanol medium to produce the concrete. Cylindrical samples were made with CNT contents up to 0.10% by weight of cement (wc) to evaluate ten different properties. Briefly, the findings demonstrated that CNT contents up to 0.05% wc improved compressive strength (+16%) and tensile strength (+29%) while reducing porosity (-12%). Finally, a detailed experimental investigation analyzed the effects of CNT incorporation (in aqueous suspension) on the SC bond strength using pull-out tests in cubic specimens, examining variables such as CNT content (up to 0.10% wc), bar diameter (d, 8 mm and 10 mm), roughness (plain and ribbed), and embedded length (4d, 5d, and 5.6d). The results showed that incorporating 0.05% CNT significantly improved bond strength, especially for larger diameter bars and longer embedded lengths, reducing the recommended embedment length from 5d to 4d without compromising adhesion. The study also explored applying CNTs only around the steel bars, though this approach yielded less effective results. Overall, this research concluded that CNT incorporation enhances concrete performance and offers a sustainable solution by reducing cement and steel consumption, contributing to improved structural efficiency and supporting decarbonization efforts in the construction industry.