No abstract

Cement composites prepared with nanoparticles have been widely studied in order to achieve superior performance structures. The incorporation of carbon nanotubes (CNTs) is an excellent alternative due to their mechanical, electrical, and thermal properties. However, effective dispersion is essential to ensure strength gains. In the present work, cement pastes were prepared incorporating CNTs in proportions up to 0.10% by weight of cement, dispersed on the surface of anhydrous cement particles in isopropanol suspension and using ultrasonic agitation. Digital image correlation was employed to obtain basic mechanical parameters of three-point bending tests. The results indicated a 34% gain in compressive strength and 12% in flexural tensile strength gains, respectively, as well as a 70% gain in fracture energy and 14% in fracture toughness in the presence of 0.05% CNTs were recorded. These results suggest that CNTs act as crack propagation controllers. Moreover, CNT presence contributes to pore volume reduction, increases the density of cement pastes, and suggests that CNTs additionally act as nucleation sites of the cement hydration products. Scanning electron microscopy images indicate effective dispersion as a result of the methodology adopted, plus strong bonding between CNTs and the cement hydration product. Therefore, CNTs can be used to obtain more resistant and durable cement-based composites.

Carbon nanotubes (CNTs) are hollow tubular channels, formed by graphene laminated sheets. They can be classified as single-walled (SWCNTs) when they have a simple cylindrical layer of graphene or as multiple-walled (MWCNTs) formed by the joining of two or more single cylindrical layers. Due to the extraordinary properties, as a high tensile strength, the incorporation of the CNTs in civil construction materials has been studied. Recent research has shown that the incorporation of this nanomaterial allows improvements in the mechanical properties of cementitious compounds [1-5]. However, the hydrophobic nature of CNTs makes the dispersion a

Due to the necessity to improve the mechanical properties of cement-based materials, carbon nanotubes (CNTs) have been studied to prepare cement composites. Once they present high tensile strength, if well dispersed and well adhered to the cement hydration products, they can improve the mechanical properties of a cement paste system. Because of that, an effective dispersion process is crucial. Studies involving CNTs dispersion in cement particles in presence of a non-aqueous media of isopropanol resulted in improvements in mechanical properties suggesting a good dispersion and strong bond between CNTs and cement particles. Considering that, the present paper analysed a cement paste reinforced with 0%, 0.05% and 0.10% of CNTs dispersed in a non-aqueous media of isopropanol through three-point bending tests in notched specimens and direct tensile tests. The influence of CNTs on the material fracture energy, flexural strength, and tensile strength was addressed. The results pointed out an improvement of 90% of fracture energy in composites with 0.05% of CNTs. The results of direct tensile tests indicate an improvement of about 20% tensile strength in cement paste with 0.05% of CNTs and images by scanning electron microscopy indicate a better dispersion by this proportion. These results suggest not only an effective dispersion of CNTs in cement matrix by the used dispersion methodology at a dosage of 0.05% of CNTs, but also that the cement composites properties may be improved by the presence of them.