Sessions & Events

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Issues and Potential Solutions for Achieving Uniform Dispersion of Nanoparticles in Cementitious Composites and Concrete for the Laboratory and Field

Thu, October 29, 2020 1:00 PM - 3:00 PM

Nano particles designed for cement composites and concrete have been successfully used in laboratory and field applications over the last 20 years to enhance both the strength and durability of concrete. The following session will identify the dispersion of nano-based additives and admixtures for commercial concrete that focus on increase the strength and durability of concrete to physical and chemical attack. This session will emphasize concrete laboratory and field applications have been at the forefront of construction for the last decade. Pros and cons will be discussed in the to facilitate a realistic view for new solutions to ongoing issues.
Learning Objectives:
(1) Identify ongoing concrete research projects from a wide range of research topics that focus nanotechnologies employed in laboratories, ready-mixed concrete facilities, and concrete job sites;
(2) Discuss recent dispersion techniques, rapid mobility methods, and procedures related to structural and material aspects of nano-enhanced concrete;
(3) Describe emerging ideas in concrete research to increase resistance to physical and chemical attack;
(4) Summarize recent information related to dispersion of additives and admixtures for nano-enhanced cementitious composites and concrete.

Max capacity for a live session is 1,000. This session will be available on demand, during convention week, within 24 hours after this session takes place.

This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.

Dispersion of CNT/CNF in Cementitious Materials: Lab to Industry

Presented By: Kavya Mendu
Affiliation: Northwestern University
Description: For the last 15 years, several studies incorporated Carbon Nano Tubes/Nano Fibers (CNTs/CNFs) as additives to improve the mechanical and electrical properties of cementitious composites. Due to the very high vanderwaal forces between the CNTs/CNFs and their hydrophobic nature, a well dispersed aqueous solution is the key to the achieve superior properties. At Northwestern University, a successful one-step lab scale production of the dispersion was achieved using ultrasonication energy and surfactants. The suspension containing well-dispersed CNTs/CNFs of very small dosages of 0.08-0.15% weight of cement content helped achieve an uncoupling effect between compressive strength and elastic modulus and in-turn improved the later by nearly 50% compared to control samples without nanomaterials. The current lab scale procedure produces nearly 360 ml of solution and is highly repeatable. In order to scale up the study to industry level, a dispersion study was carried out high shear mixer which yields up to 2 liters of solution. The stability of the above two dispersions are studied using Ultraviolet-Visible Spectroscopy. Furthermore, characterization and image analysis using advanced microscopy techniques help in statistical comparison of the geometrical size and shape parameters of CNFs/CNTs. The methods’ repeatability and scalability make nanomodified cement composites a potential tool for the industry applications.

Industrial Application of In-Situ Carbonate Nanoparticle Seeding

Presented By: Sean Monkman
Affiliation: CarbonCure Technologies
Description: A beneficial use of carbon dioxide in ready mixed concrete production has been developed and installed as a retrofit technology with industrial users. An optimum dose of CO2 is added to ready mixed concrete during mixing and batching; the CO2 mineralizes to form an in-situ nanoscale carbonate reaction product. The carbon conversion leads to finely distributed nanoparticles while avoiding dispersion issues commonly associated with ex-situ nanomaterial additions. The calcite development can improve the performance of the concrete. Increased compressive strength and cement efficiency provides a lever to adjust the mix designs. The use of carbon dioxide along with a lower cement loading reduces the carbon footprint of concrete.

A ‘How-To’ on Employing a Colloidal Silica Admixture in Ready-Mixed Concrete for the Mitigation of Damage from Freeze-Thaw and Deicing Salt

Presented By: Whitney Le Belkowitz
Affiliation: Intelligent Concrete
Description: The purpose of this presentation is to review a colloidal silica technologically used in a ready-mixed concrete to increase the resistance to the damaging effects of winter season freeze-thaw cycles and deicing salts and brines. The nano-enhanced concrete (NEC) needed to be easy to batch and place as conventional concrete. Particularly, it had to develop fresh and hardened properties suitable for all construction sites and applications. The colloidal silica mix gives properly placed and cured concrete a significantly higher ultimate compressive strength with a substantially decreased permeability. Ultimately, the ready-mixed concrete producer wanted to deliver a tougher concrete surface and substrate that had decreased permeability. The end result translated directly to greater resistance to the damage caused by freeze-thaw conditions and heavy deicer applications.

Relationship Between the Carbon Nanotube Dispersion State, Electrochemical Impedance and Capacitance and Mechanical Properties of Percolative Nanoreinforced OPC Mortars

Presented By: Maria Konsta
Affiliation: University of Texas at Arlington
Description: The presentation develops a novel method to evaluate the state of nanotube dispersion in CNT reinforced mortars based on the electrochemical impedance and capacitance of the cementitious nanocomposites. The observed correlation between AC capacitance values, flexural strength and modulus of elasticity provides valuable information on how the actual CNT dispersion state and the presence of CNT agglomerates affects the mechanical properties of percolative nano-reinforced cementitious materials.

Amendment of Cement Paste with Low Concentrations of Well-Dispersed Partially Unzipped Carbon Nanotubes

Presented By: Shohana Iffat
Affiliation: University of South Carolina
Description: This presentation introduces partially unzipped carbon nanotubes (PUCNTs) as nano-amendments for cement composites. Oxidized PUCNTs are of interest because they combine the aspect ratio and mechanical strength of multiwalled carbon nanotubes (MWCNTs), and the high graphene edge content and dispersibility of graphene nanoplatelets. In addition, PUCNTs offer a greater specific surface area than MWCNTs, which makes them suitable for exploring reduced concentrations. Cement paste samples were manufactured with oxidized PUCNT concentrations of 0, 0.001, 0.005 and 0.05 in weight of cement (wt%). Through dynamic light scattering analysis, a stable dispersion in aqueous solution was verified for equivalent concentrations of 0.001 and 0.005 wt%; instead, unstable suspensions were obtained for 0.05 wt%, which is often used as a lower-bound concentration for MWCNTs. Potential implications on strength and dispersibility in cement paste were investigated through uniaxial compression tests on 25 × 25 × 76 mm prism specimens, which were moist-cured for 28 days, and visual inspection of scanning electron microscopy (SEM) micrographs. Compared to plain cement paste, the incorporation of 0.001, 0.005 and 0.05 wt% of PUCNTs resulted in an average increase in compressive strength of 10%, 29%, and 14% respectively. These results were supported by SEM micrographs, which showed PUCNT agglomerates for a concentration of 0.05 wt%; instead, for 0.001 and 0.005 wt%, well-dispersed PUCNTs were noted together with a preferential formation of cement hydrates.

Role of Dispersion Degree of Nanoclays In Controlling Viscoelastic Properties of Fresh Cement Pastes

Presented By: Ala Eddin Douba
Affiliation: Columbia University
Description: Nanoclays (NC) have been explored as a thixotropy modifier for many concrete applications, including reducing self-consolidating concrete formwork pressure, improving slipform paving, and reducing rebound during shotcreting. Given their ability to enhance structural build-up, they are also a strong candidate for achieving shape stability of deposited layers during extrusion-based 3D concrete printing. However, early studies have indicated that typical dosing of ~ 0.5 wt % is not sufficient to meet the high rheological demands of this technique. And with current processing methods, higher dosing while achieving sufficient dispersion is difficult to achieve. This study explores various NC processing techniques and examines their efficiency in altering yield stress and elasticity of cement pastes, as well as reaching higher dosages. Results show that with the new processing technique a 16x increase in yield stress and 6x increase in storage modulus is achieved with 4 wt % NC, with limited impact on steady-state viscosity. Insights into underlying mechanisms and connections to 3D printing performance will also be discussed.

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