Effect of Carbon Nanotubes on Chloride Penetration in Cement Mortars

New Materials and Technologies for Durability and Conservation of Building Heritage

The increase in concrete structures' durability is a milestone to improve the sustainability of buildings and infrastructures. In order to ensure a prolonged service life, it is necessary to detect the deterioration of materials by means of monitoring systems aimed at evaluating not only the penetration of aggressive substances into concrete but also the corrosion of carbon-steel reinforcement. Therefore, proper data collection makes it possible to plan suitable restoration works which can be carried out with traditional or innovative techniques and materials. This work focuses on building heritage and it highlights the most recent findings for the conservation and restoration of reinforced concrete structures and masonry buildings.

Mechanical and electrical properties of MWCNTs - high early strength cement - mortars composite: Dispersion of CNTs and effect of chemical admixtures

The objectives of this research were to study (1) the dispersion of MWCNTs in an aqueous system by three commercial admixtures (CAds) for concrete, and (2) the effect of CAds and MWCNTs on indirect tensile strength and electrical conductivity of MWCNTs-high early strength (HE) cement-mortar composites. To achieve the objectives, we dispersed MWCNTs in an aqueous system with (1) hydroxylated polymers-based water reducing plasticizer (HPs), a nonionic compound, (2) Naphthalene based superplasticizer (SNF), an anionic compound, and (3) calcium chloride-based accelerating agent (CC) a neutral amphoteric salt. We prepared a total of 242 samples grouped in three sets: (1) Plain mortar [PM] (water + HE cement + Sand), (2) [PM+CAd], and (3) [PM+CAd+MWCNTs]. The three CAds dispersed MWCNTs in an aqueous solution. The CC and HPs admixtures have a two-time bigger dispersing power than the SNF. They demand half of SNF's ultrasound energy for optimal dispersion. Although the SNF (anionic) based superplasticizer resulted incompatible with the HE cement, it improved the indirect tensile strength of [PM+SNF+MWCNTs] composite. In contrast, the CC (amphoteric) based accelerating agent was compatible with the HE cement; the CC adsorption on the MWCNTs surface favors an improvement in the electrical conductivity of [PM+CAd+MWCNTs] composite.

Comparative Overview of the Performance of Cementitious and Non-Cementitious Nanomaterials in Mortar at Normal and Elevated Temperatures

Nanotechnology has emerged as a field with promising applications in building materials. Nanotechnology-based mortars are examples of such building materials that have widespread applications in the construction industry. The main nanomaterials used in mortars include nano-silica, nano-magnesium oxide, nano-alumina, nano-titanium oxide, nano-zinc oxide, nano-clay, and nano-carbon. This review paper presents a summary of the properties and effects of these nanomaterials on cement mortar in terms of its fresh-state and hard-state properties. The fresh-state properties include the setting time, consistency, and workability, while the hard-state properties include mechanical properties such as compressive, flexural, tensile strengths, as well as the elasticity modulus, in addition to durability properties such as water absorption, shrinkage strain, strength loss due to freeze–thaw cycles, and chloride penetration, among others. Different nanomaterials cause different physical and chemical alterations within the microstructures of cement mortar. Therefore, the microstructural characterization and densification of mortar are discussed in detail at varying temperatures. In general, the involvement of nanomaterials in cement mortar influences the fresh-state properties, enhances the mechanical properties, and impacts the durability properties, while reducing the porosity present in the mortar matrix. Cementitious nanomaterials can create a pathway for the easy injection of binding materials into the internal microstructures of a hydration gel to impact the hydration process at different rates, whereas their non-cementitious counterparts can act as fillers. Furthermore, the research gaps and future outlook regarding the application of nanomaterials in mortar are discussed.

Nanomaterials in Cementitious Composites: An Update

This review is an update about the addition of nanomaterials in cementitious composites in order to improve their performance. The most common used nanomaterials for cementitious materials are carbon nanotubes, nanocellulose, nanographene, graphene oxide, nanosilica and nanoTiO2. All these nanomaterials can improve the physical, mechanical, thermal and electrical properties of cementitious composites, for example increase their compressive and tensile strength, accelerate hydration, decrease porosity and enhance fire resistance. Cement based materials have a very complex nanostructure consisting of hydration products, crystals, unhydrated cement particles and nanoporosity where traditional reinforcement, which is at the macro and micro scale, is not effective. Nanomaterials can reinforce the nanoscale, which wasn't possible heretofore, enhancing the performance of the cementitious matrix.

Electrochemical Corrosion of Galvanized Steel in Binary Sustainable Concrete Made with Sugar Cane Bagasse Ash (SCBA) and Silica Fume (SF) Exposed to Sulfates

This research evaluates the behavior corrosion of galvanized steel (GS) and AISI 1018 carbon steel (CS) embedded in conventional concrete (CC) made with 100% CPC 30R and two binary sustainable concretes (BSC1 and BSC2) made with sugar cane bagasse ash (SCBA) and silica fume (SF), respectively, after 300 days of exposure to 3.5 wt.% MgSO4 solution as aggressive medium. Electrochemical techniques were applied to monitor corrosion potential (Ecorr) according to ASTM C-876-15 and linear polarization resistance (LPR) according to ASTM G59 for determining corrosion current density (icorr). Ecorr and icorr results indicate after more than 300 days of exposure to the sulfate environment (3.5 wt.% MgSO4 solution), that the CS specimens embedded in BSC1 and BSC2 presented greater protection against corrosion in 3.5 wt.% MgSO4 than the specimens embedded in CC. It was also shown that this protection against sulfates is significantly increased when using GS reinforcements. The results indicate a higher resistance to corrosion by exposure to 3.5 wt.% magnesium sulfate two times greater for BSC1 and BSC2 specimens reinforced with GS than the specimens embedding CS. In summary, the combination of binary sustainable concrete with galvanized steel improves durability and lifetime in service, in addition to reducing the environmental impact of the civil engineering structures.

Multifunctional Cement Mortars Enhanced with Graphene Nanoplatelets and Carbon Nanotubes

Recent findings have brought forward the potential of carbon nano-species, especially nanotubes and graphene, to impart exceptional multifunctional potential to cement, offering simultaneous enhancement of mechanical, fracture mechanical and electrical properties. While available knowledge on the topic is still limited, there is a complete absence of direct comparisons of the potential of the nano-species to improve strength and toughness and provide multifunctionality to the mortars. The study offers a comprehensive overview of these potentials, for mortars modified with pure graphene nanoplatelets and carbon nanotubes at consistent, directly comparable, concentrations up to 1.2 wt.%. Testing included flexure under pure bending moments, axial compression, electrical resistivity measurements and fracture tests under three point bending configuration; the latter were also independently assessed by acoustic emission. Differences in documented properties and optimal concentrations associated with improved mechanical performance were directly compared and rationalized in terms of nanospecies morphology. Dramatic, statistically consistent improvements in fracture behavior, up to 10-fold of control values, were documented for specific nanofiller concentrations, indicating an excellent potential of the material system for contemporary smart construction applications. An exceptionally favorable comparison of acoustic emission and fracture energy data confirmed that the non-destructive technique can independently assess the fracture performance of mortars with exceptional precision.

The Effect of Carbon Nanotubes on the Flowability, Mechanical, Microstructural and Durability Properties of Cementitious Composite: An Overview

Excellent mechanical properties and chemical stability make carbon nanotubes (CNTs) some of the most promising nanomaterials that can be used in cementitious composites to improve their performance. However, the difficulty of CNTs’ dispersion within the cementitious structure still exists and thus prevents the homogeneous distribution of CNTs. The homogeneous distribution of CNTs within a composite structure plays an essential role that can have a positive effect on the mechanical performance of CNT-cement composites. This paper introduces the methods for the production of CNTs and provides useful information about the influence of CNTs on the flowability, mechanical performance, microstructural changes and hydration of cement composites. The influences of water-cement ratio, used surfactants and various doses of CNTs on the properties of cementitious composites were also studied.

Effects of CNT Dosages in Cement Composites on the Mechanical Properties and Hydration Reaction with Low Water-to-Binder Ratio

This study aimed to investigate the potential use of carbon nanotubes (CNTs), which are an innovative construction material preferred by many researchers. Long-term microstructure enhancement and on-site application are major reasons to conduct research on CNT-cement composites; thus, a study on mechanical properties as well as the thermal conductivity of CNT-cement composites was carried out. As the CNT content increased, the thermal conductivity of CNT-cement composites was also enhanced. In addition, a couple of microstructure analyses such as isothermal calorimetry, thermal gravimetric analysis and SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) for observing hydration reaction rate and types of hydration products were conducted to establish the advantage of CNT use in cement composites. Strength development of CNT-cement composites at early ages was slow, although eventually CNTs containing water developed equivalent level of strengths at last as internal curing effects.

Crack Width Estimation of Mortar Specimen Using Gas Diffusion Experiment

Maintenance of structures using self-healing concrete technologies has recently been actively studied. However, unlike the technological development of self-healing concrete, research focused on evaluating the self-healing performance is insufficient. Although water permeability experiments are widely used, the reliability of the test results may be reduced due to the viscosity of water and the possibility of elution of material inside the specimen. In this study, we propose a gas diffusion test for estimating the crack width and eventually for application to evaluation of the self-healing performance. The results verified that the proposed method can be effectively applied to the estimation of crack width.

Multi-Walled Carbon Nanotubes

Since their discovery, multi-walled carbon nanotubes (MWCNTs) have received tremendous attention because of their unique electrical, optical, physical, chemical, and mechanical properties [...]

Evaluation of Carbon Nanotube Incorporation in Cementitious Composite Materials

Over the last decades, new materials with outstanding performance have been introduced in the construction industry. Considering these new technologies, it is worth mentioning that nanotechnology has revolutionized various areas of engineering. In the area of civil engineering and construction, cement is used for various purposes and the search to improve its performance has been receiving growing interest within the scientific community. The objective of this research was to evaluate the behavior of cement mortar produced by the addition of multi-walled carbon nanotubes (MWCNTs) in different concentrations by comparing their physical and mechanical properties with the properties of the nanotube-free composite. Motivated by the lack of consensus in the literature concerning to the optimal dosage of CNTs in cementitious matrices, three different carbon nanotube ratios, 0.20, 0.40 and 0.60 wt % Portland cement, were investigated with the aim of evaluating the mechanical properties. Destructive tests were carried out to determine the compressive strength, flexural strength and split tensile strength. Additionally, a non-destructive test was performed to determine the dynamic elastic modulus and density. Scanning electron microscopy (SEM) images showed the interaction between the MWCNTs and the hydration products of Portland cement mortar. The results indicated the potential contribution of 0.40 wt % cement CNTs to the enhancement of the mechanical properties of the cement composite as a promising construction material.