Recently, many researchers have revealed that addition of nanoparticles can provide synergy to improve physical and chemical properties of concrete materials. Nanoparticles can act like fillers to refine pore structure and immobilize water movement in cement paste. They can function like seeds for CSH nucleation to accelerate cement hydration, thus compensating the delayed hydration and strength development caused by commonly used supplementary cementitious materials (SCMs) like fly ash in concrete. Many nanoparticles can also interact with SCMs to produce stable and/or cementing reaction products, thus further enhancing concrete strength and durability. The objectives of this technical session are to summarize the recent progress on the use of nanoparticles in cement-based materials containing SCMs, to have a better understanding of the synergic effects of nanoparticles and SCMs, and to recognize challenges in the use of nanoparticles in cement-based materials.
(1) Discover recent research progress and innovations resulting from use of nanoparticles in cement-based materials;
(2) Develop knowledge of the interactions between nanoparticles and supplementary cementitious materials and their effects on cement hydration and concrete properties;
(3) Understand the key issues in use of nanoparticles in cement-based materials;
(4) Realize the synergy and benefits of use of nanoparticles in concrete containing supplementary cementitious materials.
Ultra-Piezoresistive Cement Mortars with CNTs and Fly Ash Admixtures for Structural Health Monitoring
Presented By: Mimi Zhan
Affiliation: The Hong Kong University of Science and Technology
Description: The use of fly ash (FA) as cement replacement is one of the most successful strategies to reduce carbon emissions in cement production. However, negative effects caused by the slow pozzolanic reaction of FA make it difficult to take this strategy further. Here we try to use FA as a dispersing agent for carbon nanotubes (CNTs) by in-situ synthesis technique to diminish the negative effects and seek a new application for FA. Upon microwave irradiation, CNTs were successfully synthesized on surfaces of FA particles in 30-40 s. Optical microscopy measurement showed that CNTs on FA dispersed well in water with average 52 µm2 of agglomerated area, about two orders of magnitude lower than the average 1367 µm2 of agglomerated area that the reference CNTs had. The good dispersion of CNTs coated on FA enabled cement mortars to exhibit an ultra-sensitive piezoresistive behavior under compressive loading. The sensitivity to strain of cement mortar containing CNTs coated on FA was 6544 with around 70% of resistivity change within elastic range. This ultra-high sensitivity indicates the huge potential of CNTs coated FA in the fabrication of cement sensor for structural health monitoring, and it opens a new application of FA for the cement industry.
The Effect of Nano-Additives on the Hydration Behavior and Durability of Concrete Containing Fly Ash
Presented By: Jan Olek
Affiliation: Purdue University
Description: Incorporation of fly ash in cementitious systems containing ordinary portland cement (OPCs) increases their long-term strength and durability. However, inclusion of fly ash also reduces the heat of hydration of such systems and their hydration rate. Thus, its use slows the development of strength at early ages. The reduced rate of hydration, and the associated lower early-age strength, can increase the risk of durability problems such as early surface deterioration (scaling) if young concrete is exposed to challenging environmental conditions.
The purpose of this research was to assess the influence of nano-additives (including titanium dioxide nanoparticles/nano-TiO2 and nano-silica) on the hydration process and the durability of fly ash concrete. The experiments were performed on cementitious composites containing class C fly ash (24% by weight of cement) and various levels of nano-additives.
The isothermal calorimetry (IC), thermogravimetric analysis (TGA), and Vicat setting time tests were carried out to investigate the effect of nano-additives on the hydration process of fly ash pastes. The influence of nano-additives on the permeability of concrete containing fly ash was determined by water absorption test using different methods of sample conditioning.
Furthermore, the scaling test was performed to evaluate the influence of the nano-additives on the scaling resistance of concrete containing fly ash. Preliminary results indicated that the addition of nano-additives can accelerate hydration process, reduce water permeability, and improve scaling resistance of concrete containing fly ash.
Effect and Mechanisms of Carbon Nanotube on the Early Age Hydration Performance of Cement-Based Materials
Presented By: Zhen Li
Affiliation: Harbin Engineering University
Description: The macroscale properties of cement-based materials are largely depended on their hydration performance. The effects and mechanisms of graphene oxide (GO)/graphene (GR) on the hydration performance of cement-based materials are not clear and should be further investigated. This paper aims at studying the effect of GO (0.01 wt.% and 0.03 wt.%) and GR (0.1 wt.%, 0.3 wt.% and 0.5 wt.%) on the hydration performance of cement-based materials, respectively. Results demonstrated that the addition of 0.01 wt.% and 0.03 wt.% GO has a limited accelerating effect on the cement hydration of fly ash-cement-based materials (FA-CBM) at the early stage. However, it can affect the overall hydration of FA-CBM by accelerating the secondary hydration of FA at the later stage. In addition, GO can decrease the total pore volume and the harmful pore volume, refine the CH crystal. The peaks of the heat flow and the total cumulative hydration heat of CBM can be improved by 0.34h and 8.08 J/g due to the inclusion of 0.1 wt.% of GR. Furthermore, GR can increase the polymerization degree of C-S-H and the amount of CH crystal, which may be helpful to improve the macroscale properties of CBM.
Corrosion Behavior of Steel Rebar Embedded in Concrete Incorporating Seawater, Sea Sand, Supplementary Cementitious Materials and Nanomaterials
Presented By: Liang Fan
Affiliation: Washington State University
Description: Recent years have seen increasing exploration of using sea sand and seawater to produce concrete components and structures, in light of the depletion and shortage of river sand and the desire of utilizing raw materials locally available in coastal environment. The high concentration of chloride anions in sea sand and seawater, however, poses a considerable risk to the durability of concrete infrastructure with steel reinforcement and thus hinders the application of such unconventional concrete. This laboratory study evaluates the corrosion behavior of steel rebar embedded in concrete incorporating seawater, sea sand, supplementary cementitious materials (SCMs) and nanomaterials, aimed to produce concrete mixtures with outstanding durability and lower environmental footprints than ordinary Portland cement (OPC) concrete. Specifically, two types of SCMs (fly ash and ground limestone) and two types of nanomaterials (nanosilica and montmorillonite nanoclay) were evaluated, each at three different dosages. A statistical design of experiments was followed to evaluate the effect of mix design factors on the chloride diffusion coefficient, chloride binding capacity, chloride threshold, and pore solution pH of hardened pastes. Furthermore, the effect of mix design factors on the corrosion behavior of steel rebar in mortar specimens exposed to 3.5 wt.% NaCl solution was assessed using electrochemical tests, including: open circuit potential (OCP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). Advanced characterization tools (SEM, EDX, etc.) were employed to shed light on the chemistry and microstructure of hydration products and key interfaces in selected concrete specimens.
Colloidal Silica and Class F Fly Ash for Concrete
Presented By: JON BELKOWITZ
Affiliation: INTELLIGENT CONCRETE LLC
Description: Colloidal silica has been successfully used in construction over the last 20 years to enhance both the strength and durability of concrete. The following presentation will identify focus on the progress of colloidal silica for concrete that has been combined with Class F Fly Ash. The presentation will cover an overview of colloidal silica and Class F Fly Ash technologies, ACI and ASTM activities to develop guides and standards, and two case studies that spans over 7-years (Eagle County Airport) and current case studies (Indiana DOT) that are showing the potential for concrete durability. The impetus of this presentation is to give a bird’s eye of the colloidal silica growth in the concrete and construction industry as Class F Fly Ash depletes.