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H=Hyatt Regency Dallas; U=Union Station

Characterizing and Controlling Interfaces in Concrete, Part 2 of 2

Monday, October 24, 2022  1:30 PM - 3:30 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; 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.

Learning Objectives:
(1) Discuss the methods for characterizing interfaces at the nanoscale to enhance understanding of concrete properties;
(2) Identify characteristics of the Interfacial Transition Zone at the nano and microscale;
(3) Define the importance of interfacial chemistry in strength and durability;
(4) Recognize the mechanical and fracture properties of the nanofiber-matrix interfaces in concrete.

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


Characterization of the Impedance Profiles of Nanostructured Carbon-Based Material/Cement Interfaces

Presented By: Panagiotis Danoglidis
Affiliation: University of Texas At Arlington
Description: The effect of nanostructured carbon-based materials with strategically functionalized surface in controlling the electron transport through the nanomaterial/cement interfaces was evaluated. 1D and 2D functionalized carbon nanotubes (CNTs), nanofibers (CNFs) and graphene nanoplatelets (GNPs) with different intrinsic conductivity were used. The Impedance, namely conductivity and reactance, of the carbon/cementitious material nanostructured interfaces were evaluated via measuring and mapping their nanometer current signal (nA). The characterization of the interface’s Impedance profile was used to define the optimum conductive network into the cementitious matrix, necessary to achieve a percolative-like behavior of the nanocomposites desired for novel, powerful functionalities.


Nano Engineering the Interfacial Properties of PVA Fibers in Strain-Hardening Cementitious Composites

Presented By: Ousmane Hisseine
Affiliation: Laboratory of Nano- and Micro-Mechanics, Laval Uni
Description: Nano-engineering concrete properties has now emerged as a novel tool for the deployment of advanced cementitious composites necessary for the 21st century civil infrastructure. This study is aimed at characterizing the interface properties of polyvinyl-alcohol (PVA) fibers in strain-hardening cementitious composites (SHCC) incorporating high-volume GP (HVGP) at 0-100% replacement of FA. Single fiber pull-out tests were conducted to characterize the interface properties (i.e., frictional bond, chemical bond, and slip-hardening coefficient) necessary for micromechanical tailoring of SHCC. Results indicate that nanomodification of SHCC matrix and interface properties using nanocellulose (at rates of 0.03-0.10% per cement mass) enabled to significantly alter the pull-out behavior. In fact, the common frictional sliding behavior is shifted to a slip-hardening behavior due to a twofold mechanism imparted by nanomodification (i) meshing the matrix, and (ii) creating a jamming effect, interfering with the pull-out of PVA fibers. This characteristic slip-hardening effect contributed towards enhancing the strain-hardening capacity of SHCC as experimentally validated by uniaxial tensile tests.


Probing Texture and Mechanical Properties of the Interfacial Transition Zone (ITZ) in Fly Ash – Cement Systems via Locally Coupled Nanoindentation and Mass Spectrometry

Presented By: Konrad Krakowiak
Affiliation: University of Houston
Description: The macro-behavior of concrete strongly depends on the mechanical and textural attributes of the interfacial transition zone (ITZ) around the aggregate. Similarly, the micro-level properties of the cement paste in blended systems are controlled by the ITZ developed between fly ash and calcium-silicate-hydrate matrix. Therefore, understanding its evolution with progress in hydration and/or the advancement of pozzolanic reaction is of significant importance. In this work, the texture and micro-scale mechanical properties of interfacial transition zone developed around low calcium fly ash are studied. For this purpose, the small-scale indentation mapping technique was coupled with electron spectrometry. Such a combination of experimental methods allowed for the quantitative correlative analysis of indentation hardness, stiffness, and phase chemistry across the ITZ developed in the cement systems hydrated from 7 to 28 days. The discussion of the obtained results will be presented including the individual contributions of various hydration products to ITZ texture and the evolution of the nano-scale packing of C-S-H within the interfacial zone.


Contact Mechanical Insight into Carbon Nanoreinforced Composites Interactions

Presented By: Raul Marrero
Affiliation: Northwestern University
Description: Carbon nanoreinforcements, carbon nanofibers (CNFs) and carbon nanotubes (CNTs), have been incorporated in small percentages to cementitious matrices. These inclusions have shown enhancements in the elastic, fracture, and decrease shrinkage in the macro composite. Through Atomic Force Microscopy Quantitative Nanomechanical Mapping (AFM-QNM) and Scanning Electron Microscopy Energy Dispersive X-Ray Spectroscopy (SEM-EDS) measurements, the Interfacial Transition Zone (ITZ) between aggregate and bulk cement paste shows a localized increase in both contact modulus and presence of C-S-H rich regions compared to the bulk paste. This raises the hypothesis that carbon nanofibers through interaction with different constituents creates effect in the matrix. A different behavior not frequently observed in other micro- and macro- fibers. A modified AFM-QNM probe was developed to further understand the adhesion interactions between the carbon nanotubes and anhydrate/hydrated cement phases through a benchmarked couple SEM-EDS technique. Results shows a decrease in adhesion with lower Ca+2 concentration in C-S-H rich regions, and distinct interactions between intermix/C-S-H regions. Furthermore, gathered nanoindentation data is used to measure the effect of addition of carbon reinforcement in the creep behavior of the matrix in the submicron scales. Insights into the adhesion interactions and contact creep behavior through contact mechanics will increase the understanding of carbon nanoreinforced composite’s mechanics in the pathway for structural applications.


Microstructure and Freezing-Thawing Resistance of Concrete with Air-Entraining Agent (AEA) and Polymeric Microspheres

Presented By: Na Lu
Affiliation: Purdue University
Description: Air-entraining agent (AEA) has long been used as an effective means in protecting concrete from cyclic freezing-thawing damage. The addition of AEA in concrete can introduce micro-meter scale air voids which provide space for ice crystals growth, reliving the internal tensile stress during the freezing process. However, the effectiveness of AEA is influenced by the ambient environment and the mixture compositions which usually lead to the inconsistent result of AEA application. Moreover, the addition of AEA can lower the strength of concrete. An increase of 1% air content may result in 5% strength loss. Consequently, the mixture adjustments (i.e., decreased water-cement ratio value, increased cement content) are required to meet the strength and durability demands. This work reports the addition of the impermeable polymeric microspheres in concrete in providing the resistance of cyclic freezing-thawing damage. The particle size distribution of microspheres was tested by particle sizer. The morphology of the microspheres was characterized by optical microscope and SEM. The air content of fresh concrete with various dosages of AEA and microspheres were measured by air meter in accordance with ASTM C231. The compressive strength development of concrete was tested. In order to evaluate the freezing-thawing resistance, the ASTM C666 procedure A method was adopted. The dynamic modulus of elasticity of concrete specimens was tested as per ASTM C215. The relative dynamic modulus of elasticity, durability factor and scaling mass loss of concrete over freezing-thawing cycles were reported. The microstructure of concrete with AEA and microspheres were characterized by mercury intrusion porosimetry (MIP) method to explain the reason of freezing-thawing resistance of concrete. The achieved results indicates that microspheres can be a promising solution to improv the freezing-thawing resistance of concrete without strength loss and the requirement of mixture adjustments.

Upper Level Sponsors

Ash Grove
Baker
Conseal
Controls Group
Euclid Chemical
GCP
Master Builders
PoreShield
PS=0
ACI Northeast Texas Chapter

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