Due to their exceptional electrical properties, carbon nanotubes (CNTs) can be applied as conductive fillers to develop self-sensing cement-based matrices. In order to obtain an adequate self-sensing response, CNTs must be evenly dispersed through the cement matrix in a volume sufficient enough to create an electric percolation network. This is challenged by the difficulty of dispersing CNTs; therefore, there is a demand for an efficient dispersing agent that can be filled by superplasticiezers, which are products of known compatibility with cement and high availability. This research explores the use of four commercial superplasticizers available in Brazil, both naphthalene and ether polycarboxylate-based, as dispersing agents for CNTs in water. Ultrasonic energy was applied to aqueous solutions containing CNTs and superplasticizers. UV–Vis spectroscopy and ξ-potential measurements were used to investigate which superplasticizer was more effective to disperse the CNTs. Cement pastes were produced with the CNT dispersions and their electrical resistivity was measured. It was found that only superplasticizers without aliphatic groups in their structure were capable of dispersing CNTs in water. It was concluded that second-generation naphthalene-based superplasticizers were more efficient dispersing agents for CNTs than third-generation ether polycarboxylate-based ones for self-sensing applications.

Different types of nanomaterials are able to modify the properties of cement-based composites in fresh and hardened states, with mechanical performance enhancement being one of the most sought after modifications. Due to their small particle size and high specific surface area, nanomaterials interact with the hydration reaction of cement through four known physicochemical mechanisms: (i) filler effect, (ii) nucleation, (iii) pozzolanic activity, and (iv) bridging effect; these mechanisms lead to a less porous and more resistant matrix. The aim of this chapter is to summarize the influence of a set of nanomaterials on the mechanical performance of cement-based composites, discussing their application, potential, and limitations.

The self-sensing capability is a well-studied property of carbon nanotubes blended cement pastes intended for civil construction applications. Nevertheless, most of the studies that can be found in the literature were performed at room temperature, natural humidity and atmospheric pressure. It is necessary to understand how down-hole conditions affect the electrical response of this intelligent material to identify its potential application in the oil industry. This paper presents a study on the effect of relative humidity, internal moisture and temperature on the electric properties of self-sensing cement pastes. These pastes were manufactured with class G cement blended with carbon nanotubes and are intended to be used as an intelligent material capable of auto monitoring its internal stresses and deformations during the post-abandonment phase of a well. Carbon nanotubes blended cement pastes were molded in 2.5 × 2.5 × 11.5 cm3 prisms embedded with copper electrodes. The produced samples were exposed to different relative humidity, internal moisture and temperature conditions and their electrical resistivity was measured at each condition by connecting a DC power supply and a multimeter to the embedded electrodes. Relative humidity and temperature was varied in a climate chamber, already internal moisture was varied by saturating and partially drying the material. It was found that the electrical resistivity of the studied pastes is more highly sensible to internal moisture and temperature, while relative humidity had a lower effect under the studied conditions. These results lead to the conclusions that the electrical response of carbon nanotubes blended pastes is highly affected by environmental conditions, and that for oil-well applications it is necessary to develop correction models that allow an accurate measurement of the internal stresses and deformations of the material.