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H=Hyatt Regency Dallas; U=Union Station

The A to Zs of Supplementary Cementitious Material Reactivity, Part 1 of 2

Tuesday, October 25, 2022  1:30 PM - 3:30 PM, H-Reunion C

In order to ensure sustainable and durable concrete, we must use novel supplementary cementitious materials in concrete. Arguably the most important property of supplementary cementitious materials that governs their use is their reactivity. This session covers all aspects of supplementary cementitious materials reactivity - from fundamental modeling studies, to reactivity test methods, to links between reactivity and durability, to thoughts on changes in specifications. The session is aimed at students, researchers, and the industry, who will learn fundamental and applied science and engineering of supplementary cementitious materials reactivity.
Learning Objectives:
(1) Discuss the reactivity of amorphous calcium aluminosilicate glass systems;
(2) Explain the importance of early-age reactivity and reaction kinetics for supplementary cementitious materials (SCMs);
(3) Explain the importance of SCM reactivity and other inputs for thermodynamic modeling;
(4) Evaluate the impacts of processing/benefication on SCM reactivity.

This session has been AIA/ICC approved for 2 CEU/PDH credits.

Metakaolin Reactivity via Exfoliation & Dissolution

Presented By: Nishant Garg
Affiliation: University of Illinois at Urbana-Champaign
Description: Understanding and (potentially) enhancing the reactivity of calcined clays is a fundamental key to enable their widespread use as a supplementary cementitious material (SCM). Considering that the pozzolanic reaction of these SCMs is essentially a dissolution-precipitation reaction, there has been a growing interest in measuring dissolution rates of calcined clays. While this reactivity has been studied in terms of dissolution kinetics, not much is known about the evolution of clay morphology upon dissolution. In this talk, I'll outline our recent quantitative imaging approaches to statistically quantify the extent of morphological changes that occur in dissolving kaolinite and metakaolin at multiple scales. Using in situ optical microscopy on clays undergoing dissolution, we find significant differences in the disintegration pattern for kaolinite and metakaolin. Moreover, using scanning electron microscopy, we report an evidence of layer thinning (of ~20nm) in metakaolin layers upon dissolution. Together, these new quantitative results on morphological changes in 1:1 clays upon dissolution could pave towards fundamental understanding of clay reactivity as well as widespread usage in cementitious systems.

Early-Age Reactions and Precipitation of Hydrates in Cementitious Materials Containing Calcined Clays and Limestone

Presented By: Franco Zunino
Affiliation: ETH Zurich
Description: The adoption of blended cements is the only realistic alternative for a rapid, widespread and substantial reduction of the CO2 emissions associated with the concrete industry. The combination of calcined clays and limestone enables a reduction of the clinker content to 50%, while retaining the same strength as OPC and enhancing some of its durability properties. The high reactivity of calcined clays lead to an early contribution of the pozzolanic reaction to mechanical properties. In addition, the synergic reaction between limestone and the alumina from metakaolin increases the amount of carboaluminates precipitated, significantly increasing the early-age performance of the material. Understanding how this highly reactive aluminosilicate influences sulfate balance and the early-age kinetics of the different reactions taking place is crucial for further optimization and successful deployment of this technology.

Determining the Reaction Kinetics of Supplementary Cementitious Materials for Input into Thermodynamic-Kinetic Models

Presented By: Maria Juenger
Affiliation: University of Texas at Austin
Description: Strategic blending of supplementary cementitious materials (SCMs) into the ordinary portland cement (OPC) helps reduce energy use and greenhouse gas emissions from concrete. Thermodynamic simulation is a powerful tool to predict hydrated cement phase assemblages and chemical compositions; however, reaction kinetics of specific SCMs components in pastes are generally unknown, impeding accurate incorporation of reactive components of SCMs into thermodynamic simulation. This study obtained reacted components of SCMs in simulated pore solutions via alkaline dissolution experiments and determined reactivity of SCMs in cement pastes via a selective dissolution approach. Reactivity of each amorphous oxide phase was then determined by linking the mass loss of amorphous oxide phases in both pore solution dissolution and paste hydration. A modified Parrot-Killoh model was used to obtain values of empirical kinetic parameters by fitting the obtained reactivity data. The empirical kinetic parameters can be used to calculate reactive phases of OPC pastes containing SCMs over time under non-equilibrium conditions, which can be used as input for the thermodynamic simulation.

Activation of Low-Amorphous Content Materials

Presented By: Prannoy Suraneni
Affiliation: University of Miami
Description: In recent years, changes in industrialization trends have caused a shortfall of conventional supplementary cementitious materials (SCMs) such as fly ash and slag. There is thus a need to identify, characterize, and ultimately utilized novel SCMs to ensure the production of sustainable and durable concrete. Due to their high-volume global availability, low-amorphous quarry fines and other related materials are potentially attractive SCM sources. However, the low amorphous content results in low reactivity, necessitating activation before such materials can be used as SCMs. In this study, the effects of thermal activation and mechanochemical activation were evaluated on basaltic fines. Physiochemical changes in the material after grinding were investigated using X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and other techniques. Reactivity was evaluated using the modified the rapid, robust, and relevant (R3) reactivity test. Beyond a certain level of grinding energy/heating temperature, the tested materials showed significant reactivity, confirming activation. This activation is linked to a loss of crystallinity, confirmed by XRD and FTIR. Process-structure-reactivity relationships during the different activation processes were explored.

Reactivity and Durability of Beneficiated Harvested Class C Fly Ash

Presented By: Kyle Riding
Affiliation: University of Florida
Description: Interest has been growing in alternative supplementary cementitious materials (SCM) as traditional sources of SCMs have become more expensive or scarce. Many millions of tons of coal combustion ash have been stored outdoors over the last several decades because at the time fly ash supply outstripped demand. Harvested fly ash has become a potential source of SCMs that could be used in place of fresh fly ash if it has sufficient reactivity. Class C fly ash will hydrate and carbonate when stored outdoors in wet conditions, however the ash may still contain sufficient material to be reactive in concrete. In this study, the reactivity and durability of harvested and beneficiated Class C fly ash was quantified for three different ashes. The findings showed that the ashes can have sufficient pozzolanic material after storage to serve as an SCM and can improve the concrete durability, with many similarities to fresh Class C fly ash.

So You’ve Measured Reactivity – Now What?

Presented By: Keshav Bharadwaj Ravi
Affiliation: Oregon State University
Description: Over the last five years, there has been an interest in measuring the reactivity of SCM. Several tests have emerged. This presentation discusses the implications of this information on the design of concrete mixtures for durability. Specifically, this presentation will discuss how the reactivity test can be used to predict the performance of concrete both in the near term and over the service life. The work also discusses the impact of this work on producing more sustainable concrete.

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