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Characterizing and Controlling Interfaces in Concrete, Part 1 of 2
Monday, October 24, 2022 11:00 AM - 1:00 PM, H-Reunion C
This session will highlight recent research on nanoscale and microscale interaction mechanisms at the interfaces between the cementitious hydration products and nanomaterials; and methods to characterize, control and strengthen these interactions; quantitative analysis of the interfaces and nanoscale texture of interfacial transition zone, and the link between atomic interactions, interfaces, and bulk concrete properties.
Investigation of the Effect of the Colloidal Nanosilica (CNS) on the New-and-Old Portland Cement Concrete Interface
Presented By: Na Lu
Affiliation: Purdue University
Description: The bonding between new-and-old concrete greatly affects the quality of the concrete pouring and patching. This study was performed to investigate the advantage of using colloidal nanosilica (CNS) in Portland cement concrete by studying the quality of the interface between the new-and-old concrete. It is hypothesized that the seeding and filling effect of the nanoparticles favors the densification of the cement matrix, while the improved curing quality caused by the CNS may also contribute to the formation of stronger bonding between concrete layers. Mercury intrusion porosimetry (MIP) and image analysis were carried out to study the interface of the prepared concrete layers. The experimental result indicates that the density of the interface region was increased with the incorporation of the CNS, which suggests an improvement in the bonding quality. More-over, the image analysis indicates that the incorporation of the CNS may improve the durability of the concrete by refining the voids in the cement matrix. In addition, it was found that an increased strength to density ratio was achieved by using CNS, which suggests that a lower amount of the cement can be used to reach the same targeted strength requirement.
The Significance of Interfacial Chemistry on the Strength of Fly Ash-Cement Composites
Presented By: Konrad Krakowiak
Affiliation: University of Houston
Description: Despite the large number of studies on supplementary cementitious materials, the under-lying physicochemical interfacial processes that govern their strength remain obscure. To address this knowledge gap, this work strives to establish a relation between the chemical composition of fly ash (FA) at the molecular level and the macroscopic compressive strength in cement hydrates-FA composites. We develop a multiscale modeling framework that links the fundamental physicochemical attributes of calcium silicate hydrate (C-S-H)-FA interfaces across molecular (~1 nm), mesoscopic (~100 nm), and microscopic (~10 µm) length scales. We observe that FA's chemical composition affects the interfacial properties across all scales. FAs with higher network-modifier cation concentration show stronger molecular and mesoscale interfacial properties and statistically significant higher macroscopic compressive strength. This is particularly interesting for Class F FA, where early-age reactivity is negligible.
Strengthening Interface Interactions in Carbon Based Nanomaterials/Cementitious Nanocomposites via Functionalization
Presented By: Maria Konsta
Affiliation: University of Texas at Arlington
Description: In this presentation we demonstrate an effective control of the yet unexplored nanoscale interfacial interactions between the nanomaterials and cement hydration products, via nanomaterial functionalization, optimizing the uniformity and homogeneity of nanoreinforced concrete. Monodispersed nanomaterial-suspensions were produced and their perfect dispersibility and long-term stability was evaluated by Spectroscopic methods, UV-Vis, Dynamic Light Scattering and Electrochemical Impedance. The dispersed nano-material’s functionalization was assessed by identifying new chemical bonding on their surface through FTIR and Raman Spectroscopy. NanoIR mapping and testing findings on nanomaterial/C-S-H interface shown that the local nanostructure was radically modified due to the effective functionalization of the nanomaterial’s surface. Nano-mechanical characterization was followed to specify the types of monodispersed/functionalized nanomaterials that can be used to optimize interface’s interactions. It was shown that functionalization significantly promoted the strengthening and toughening mechanism of the Interfacial Transition Zone (ITZ) between the nanomodified cementitious hydrates and aggregates.
Interfacial Characterization of Nanomodified Cementitious Composites
Presented By: Kavya Mendu
Affiliation: Northwestern University
Description: Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) when added to cementitious materials improve mechanical properties. Studies showed that this improvement is not only observed at the macroscale but also at the nano and submicron scales as shown by atomic force microscopy quantitative nanomechanical mapping especially at that of the interfacial transition zone (ITZ). Scanning electron microscope energy dispersive spectroscopy recorded changes in calcium silica ratios in the presence of CNFs which indicates possible chemical changes in the ITZ due to nanomodification. Recent advances in synchrotron research at Argonne National Laboratory enables 3D X-ray tomography of cement composites at the micro and nano scales. The high voxel resolutions in the orders of 16nm to 45nm helps detect the structural changes in the hydrated cement phases due to CNF addition. 3D structural scans at resolutions of 6 µm are used to obtain time dependent evolution of hydration products with or without the presence of carbon nanomaterials. In addition, AFM nano infrared spectroscopy is used to conduct chemical analysis on cement samples at different ages while mapping the data with the nanomechanical tests. The 3D tomography technique combined with AFM nano infrared spectroscopy helps achieve a unique correlation between morphology, mechanical and chemical characteristics of nanomodified cementitious composites especially at that of the ITZ. This investigation will help better understand the fundamental effects of nanomodification in construction materials.
Comparison on Properties of ITZs in Fly Ash-Based Geopolymer and Portland Cement Concretes with Equivalent Flowability
Presented By: Wengui Li
Affiliation: University of Technology Sydney
Description: Comparison on properties of ITZs in fly ash-based geopolymer and Portland cement concretes with equivalent flowability.