International Concrete Abstracts Portal

ABOUT THE INTERNATIONAL CONCRETE ABSTRACTS PORTAL

  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal

Showing 1-10 of 11 Abstracts search results

Document: 

SP312

Date: 

October 19, 2016

Publication:

Special Publication

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: 

SP312-10

Date: 

October 1, 2016

Author(s):

William Hunnicutt, Paramita Mondal, and Leslie Struble

Publication:

Special Publication

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:

Special Publication

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: 

SP312-08

Date: 

October 1, 2016

Author(s):

S. H. Aboubakr, M. L. Begaye, E. Soliman and M. M. Reda Taha

Publication:

Special Publication

Volume:

312

Abstract:

In this study we report on characterization of synthetic calcium silicate hydrate (C-S-H) produced at relatively low Cao to SiO2 (C/S) mixture ratio of 0.7 compared with C-S-H produced at 1.5 C/S mixture ratio. Synthetic C-S-H slurry was produced by mixing calcium oxide (CaO) to micro-silica (SiO2) with large amount of deionized water. The slurry was then dried to the standard 11% relative humidity to produce a powder C-S-H. The C-S-H powder was then compacted at compaction pressures of 300 (43.5) and 400 MPa (58.0 ksi) to produce solid C-S-H discs. Modulus-density scaling relationships of C-S-H synthesized at 0.7 and 1.5 C/S ratios were established and compared. Microstructural characterization of C-S-H including Brunauer-Emmett Teller (BET) N2, thermogravimetric analysis (TGA), and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) were performed. We show that porosity, water content, and silicate polymerization affected the elastic and viscoelastic properties of synthetic C-S-H. We also show that elastic and viscoelastic properties of C-S-H synthesized at 0.7 C/S ratio are more sensitive to porosity than those of C-S-H synthesized at 1.5 C/S ratio.


Document: 

SP312-07

Date: 

October 1, 2016

Author(s):

Laila Raki and Aali R. Alizadeh

Publication:

Special Publication

Volume:

312

Abstract:

Development of a new composite technology for programmed delivery and control of admixture effects in concrete and other cement-based materials present is described. A series of new organo-mineral phases have been developed by a “chimie douce” technique and analyzed using a combination of analytical techniques: X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM). Conduction calorimetry was utilized to monitor the effect of modified admixture on the hydration reactions. The slump loss characteristics of cement paste and mortar samples containing different amounts of these additives were investigated. The results showed that a good workability of the fresh mix was maintained over a relatively longer period.


Document: 

SP312-06

Date: 

October 1, 2016

Author(s):

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

Publication:

Special Publication

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.


Document: 

SP312-05

Date: 

October 1, 2016

Author(s):

Pouria Ghods and O. Burkan Isgor

Publication:

Special Publication

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.


Document: 

SP312-04

Date: 

October 1, 2016

Author(s):

C. Villani, C. Lucero, D. Bentz, D. Hussey, D.L. Jacobson and W. J. Weiss

Publication:

Special Publication

Volume:

312

Abstract:

Shrinkage Reducing Admixtures (SRAs) are increasingly being used in concrete as a method to minimize shrinkage and restrained shrinkage cracking. SRAs reduce shrinkage by decreasing the surface tension of the pore solution; however, SRAs also impact the fluid viscosity, contact angle and density. Consequently, the absorption and desorption processes of cementitious systems containing SRA are altered. This paper describes experimental measurements of drying in cementitious mortar samples with and without SRAs, focusing on three components. First, solution properties (surface tension, viscosity, and contact angle) were measured at different temperatures. Second, the vapor desorption curves were measured and the non-linear moisture diffusion coefficient was quantified at different relative humidity (degrees of saturation). Third, neutron radiography measurements were performed to visualize and quantify the effect of the presence of SRA in solution on the moisture profiles and drying front generated during the early stages of the drying process. The results will be discussed in terms of theoretical observations in an effort to place the modeling of moisture and shrinkage gradients in concrete on a more fundamental footing.


Document: 

SP312-03

Date: 

October 1, 2016

Author(s):

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

Publication:

Special Publication

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: 

SP312-02

Date: 

October 1, 2016

Author(s):

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

Publication:

Special Publication

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.


12

Results Per Page