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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.

DOI:

10.14359/51689378


Document: 

SP312-06

Date: 

October 1, 2016

Author(s):

Akash Dakhane, Zihui Peng, Robert Marzke, and Narayanan Neithalath

Publication:

Symposium Papers

Volume:

312

Abstract:

The influence of alkali cation (M = Na or K) on the alkaline activation of fly ash and slag are evaluated. NaOH, KOH (4M and 8M), or Na or K silicates (SiO2/M2O = 2.0) are used as the activators for fly ash systems which are then heat-cured, while Na or K silicates (SiO2/M2O = 1.5 and 2.5) are used to activate slag systems, which are then cured in ambient conditions. For alkali activated systems proportioned using Na-based activators, the compressive strengths were found to be higher for both the source materials. For the fly ash based systems, 29Si MAS NMR spectroscopy identifies abundance of Q4 structures with Al incorporation (N-A-S-H gel). An increase in gel structural order and the presence of higher amounts of Si-rich units as the activator alkalinity increases are noted, along with a higher degree of disorder for the K-based systems. The reaction product signature for the activated slag systems, dominated by the Q2 species are consistent with Al-substituted C-S-H (C-A-S-H) gel.

DOI:

10.14359/51689370


Document: 

SP312-05

Date: 

October 1, 2016

Author(s):

Pouria Ghods and O. Burkan Isgor

Publication:

Symposium Papers

Volume:

312

Abstract:

Many analytical surface characterization techniques exist to study steel passivity and corrosion in concrete. Some of these techniques, such as EIS and polarization resistance methods, have been used for decades to provide macro-scale data to characterize electrochemical activity on metal surfaces. More recently, advanced nanoscale spectroscopic methods, such as XPS and EELS, as well as analytical TEM have been shown to be quite useful to study compositional and crystallographic structures of oxides that form on steel. Despite these advances, researchers studying the interface between reinforcing steel and concrete in different scales are faced with several challenges with respect to the selection and the utilization of the available techniques. Each technique has advantages and disadvantages when compared with others; however, literature on these are quite limited in the study of steel/concrete interface. Since most of these techniques are not performed in situ, the interpretation of the data they provide requires careful examination. In addition, since most analytical studies to study passivity and corrosion in concrete are conducted in simulated environments, representativeness of the test setups are generally questioned. This paper presents a review of the commonly-used electrochemical as well as more recent analytical surface characterization techniques for the study of steel passivity and corrosion in concrete structures. The paper addresses the challenges with respect to the selection and the use of these techniques, pitfalls related to interpretation of the data, and common errors in test setups.

DOI:

10.14359/51689368


Document: 

SP312-02

Date: 

October 1, 2016

Author(s):

J. Marchand, S. Laurens, Y. Protière, E. Samson

Publication:

Symposium Papers

Volume:

312

Abstract:

The evaluation of steel corrosion in reinforced concrete is commonly carried out using techniques like half-cell potential (HCP) and linear polarization resistance (LPR) measurements. The latter is however the subject of interrogations concerning the relevance of the method and the actual steel area polarized by the external current Ice applied from a surface counter-electrode. To control the path of the polarizing current Ice towards a specific steel area, a current-confining device (guard-ring) is used in some LPR instruments, which imposes an additional current Igr around the counter-electrode. The impact of this guard-ring on LPR measurements is deduced from the uniform corrosion assumption. However, previous works have shown that the polarizing current spreading in macrocell corrosion systems is more complex and does not verify the uniform corrosion hypothesis. This paper presents the results of a 2D numerical study providing new insights on the theoretical impact of a guard-ring in case of galvanostatic pulse measurements performed on a macrocell corrosion system. The polarizing and confining currents are spread in a similar way over the macrocell system. In the case of an anodic polarization, both Ice and Igr are collected by the active steel area. In the cathodic direction, both Ice and Igr are spread over the passive areas. Consequently, numerical results show that the assumed confining effect cannot be achieved in presence of corrosion macrocells and it is actually impossible to define a specific polarized area. Moreover, since polarizing and confining currents have similar distributions, the confining current fully contributes to the system polarization, while it is not considered in LPR measurement analyses.

DOI:

10.14359/51689365


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.

DOI:

10.14359/51689364


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