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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

SP312

Date: 

October 19, 2016

Publication:

Symposium Papers

Volume:

312

Abstract:

Editors: Mohammad Pour-Ghaz, Aali R. Alizadeh, and Jason Weiss

With the recent quest for developing sustainable infrastructure materials, there is a need for more advanced material characterization techniques at different length scales that can provide insight to the nature and fundamental behavior of the new classes of cementitious materials as they are becoming available. These methods can be used to predict the mechanical properties, microstructural aspects, and long-term performance of different cementitious systems. Examples of these novel techniques that have been recently used for material characterization include nuclear magnetic resonance spectroscopy, nano- and micro-indentation, X-Ray tomography, and atomic force microscopy. Recently, major progress has also been made in the development of novel cement-based systems such as C-S-H/polymer nanocomposites and self-healing materials. This Special Publication aims at providing a treatise on the current research in the areas related to innovative characterization methods and analytical techniques used in the cement and concrete research, as well as the development of novel basic and composite cementitious materials. This Special Publication is developed to honor the significant contributions made by Dr. James J. Beaudoin over the past four decades to the advancement of cement and concrete science. Dr. Beaudoin, a Researcher Emeritus, Fellow of the Royal Society of Canada, and Fellow of the American Ceramic Society, has authored more than 500 publications, including five books, 20 book chapters, encyclopedia contributions, more than 270 research journal papers, 17 patents, and numerous discussions and book reviews. He is the recipient of numerous prestigious awards, including the Della Roy Lecture Award on applications of nanotechnology in cement science (American Ceramic Society, 2005), the Wason Medal for Materials Research (American Concrete Institute, March 1999) and the Copeland Award (American Ceramic Society, 1998). The papers included in this Special Publication were presented in two sessions in ACI Fall 2014 Convention, Oct 26-30, 2014.


Document: 

SP312-03

Date: 

October 1, 2016

Author(s):

Danny Smyl, Milad Hallaji, Aku Seppänen and Mohammad Pour-Ghaz

Publication:

Symposium Papers

Volume:

312

Abstract:

The durability performance of cement-based materials is directly related to the rate of moisture ingress in them. Moisture ingress in cement-based materials can be assessed using electricallybased methods. Traditionally, the electrically-based assessment of the moisture transport in cement-based materials has relied on two or four-point measurements, enabling onedimensional (1D) moisture flow monitoring. However, moisture ingress in cement-based materials is most often three-dimensional (3D). The objective of this paper is to investigate the feasibility of 3D electrical imaging of moisture ingress in mortar using Electrical Impedance Tomography (EIT). The EIT reconstructions are compared with the results of unsaturated moisture transport simulations using 3D Finite Element Method. The results of this study support the feasibility of EIT for 3D imaging of moisture flow in cement-based materials.


Document: 

SP312-10

Date: 

October 1, 2016

Author(s):

William Hunnicutt, Paramita Mondal, and Leslie Struble

Publication:

Symposium Papers

Volume:

312

Abstract:

The viscoelastic nature of concrete is a topic of much study and the calcium-silicate-hydrate (C-S-H) phase is believed to be largely responsible for this viscoelastic behavior. In this study the viscoelastic properties of synthesized calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) are measured by quasi-static and dynamic nanoindentation. A protocol for synthesizing and preparing samples for chemical and mechanical characterization is presented. The addition of aluminum to C-S-H has been previously shown to modify its molecular structure, a modification that is expected to change the viscoelastic behavior. The results indicate that C-A-S-H behaves more viscously than C-S-H and a number of factors are discussed.


Document: 

SP312-09

Date: 

October 1, 2016

Author(s):

Qiang Li, R. James Kirkpatrick, Leslie J. Struble

Publication:

Symposium Papers

Volume:

312

Abstract:

Mortar bars made with silica glass aggregate were tested at 23°C (73°F) to evaluate the applicability of a previously proposed chemical model for the alkali silica reaction (ASR). The model, based on tests at 80°C (176°F), proposes that ASR gel does not form until portlandite (CH) in the hydrated paste is locally depleted and the calcium silicate hydrate (C-S-H) has been locally converted to a more highly polymerized and lower Ca/Si form. SEM-EDX, XRD, and 29Si NMR spectroscopy of the 23°C (73°F) mortars show that the same chemical processes operate at both temperatures. At 23°C (73°F) and up to 60 days, only a small amount (~1%) of ASR gel forms and is confined to cracks entirely within the aggregate grains, but this small amount of gel containing Na, K, and Ca is sufficient to cause substantial expansion. There is no large-scale depletion of CH or increase in the C-S-H polymerization in the paste due to the small amount of gel formed and its confinement in the aggregate grains. Local reduction in both the amount of CH and the Ca/Si ratio of C-S-H in the paste is observed near places where gel-filled cracks in the aggregate contact paste, consistent with the proposed chemical model.


Document: 

SP312-01

Date: 

October 1, 2016

Author(s):

Saamiya Seraj and Maria C.G. Juenger

Publication:

Symposium Papers

Volume:

312

Abstract:

Concerns about the future availability of traditional supplementary cementitious material (SCM) sources, like fly ash, have prompted the search for a wider variety of materials that could be used as SCMs in concrete. An important criterion for an SCM is pozzolanic reactivity, which is its ability to react with calcium hydroxide in the presence of water to form calcium silicate hydrate (C-S-H). ASTM criteria for SCMs address pozzolanic reactivity indirectly by measuring the compressive strength of SCM containing mortars, or more specifically the strength activity index (SAI). More direct methods of assessing pozzolanic reactivity include measuring the reduction of calcium hydroxide (CH) in cementitious pastes through methods like thermal gravimetric analysis (TGA). However, both direct and indirect tests to evaluate pozzolanic reactivity take a considerable amount of time due to the slow nature of certain pozzolanic reactions. Alternatively, the Chapelle test, which measures the amount of CH fixed by the SCM in solution at high temperatures, can serve as an accelerated test method for screening out potential SCMs. In this paper, the accuracy of the Chapelle test for measuring pozzolanic reactivity is evaluated for a variety of SCMs with different physical and chemical characteristics by comparing it with more traditional test methods like SAI and CH measurement through TGA.


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