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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

SP254-03

Date: 

October 1, 2008

Author(s):

A. Gmira, J. Minet, A. Franceschini, N. Lequeux, R.J.-M. Pellenq, and H. Van Damme

Publication:

Symposium Papers

Volume:

254

Abstract:

On the basis of recent molecular simulation or experimental studies, we discuss two possible strategies for improving the mechanical properties of cementitious materials by modifying the bonding scheme in the hydrates at molecular level. We focus on the calcium silicate hydrates (C-S-H). A first strategy would be based on the strengthening of the cohesion forces acting between the individual C-S-H lamellae or between their crystallites. Monte Carlo simulations in the primitive model framework and ab initio atomistic calculations suggest that the cohesion of C-S-H is mainly due to a combination of sub-nano range ionic-covalent forces and meso-range ionic correlation forces. Both types of forces may be modified, at least in theory, by changing the nature of the interstitial ions, their hydration state, or the charge density on the C-S-H lamellae.

DOI:

10.14359/20209


Document: 

SP254-06

Date: 

October 1, 2008

Author(s):

H.J.H. (Jos) Brouwers

Publication:

Symposium Papers

Volume:

254

Abstract:

The present paper addresses several topics in regard to the sustainable design and use of concrete and the role of nanotechnology. First, major features concerning the sustainable aspects of the material concrete are summarized. Then the major constituent, cement, (from an environmental point of view), is discussed in detail, particularly the hydration and application of slag cement. The intelligent combining of mineral oxides, which are found in clinker, slag, and fly ashes, is designated as mineral oxide engineering. It results, among others, in environmentally friendly binders, recipes for soil stabilization (new building products), and impermeable/durable concretes. Subsequently, the mixture design of concrete is treated, whereby distinction is made between self-consolidating concrete and earthmoist concrete. By combining the particle sizes of all components, including the powders (cement, fillers), optimum mixtures in regard to workability/compactability and hardened state properties are obtained. This so-called particle size engineering results in concretes that meet all technical requirements, but that also make optimum use of the cement it is containing. This paper concludes with summarizing the opportunities and challenges involved with the introduction of both approaches, viz. mineral oxide engineering and particle size engineering, in the construction industry.

DOI:

10.14359/20212


Document: 

SP254-09

Date: 

October 1, 2008

Author(s):

H. Li, H. Xiao, and J. Ou

Publication:

Symposium Papers

Volume:

254

Abstract:

The electrical properties of nanophase carbon black-filled cement-based composites are sensitive to moisture content. Previous studies indicate that cementbased composites filled with 120 nm carbon black (CB) in the amounts of 15% (A-15) and 25% (A-25) by weight of cement have promising strain self-sensing properties (that is, piezoresistance properties), thus, this study investigated the effects of moisture on the electrical properties of A-15 and A-25. The results indicate that the initial resistance of composites increases with moisture content. Additionally, the resistance of specimens with certain moisture content increases with measurement time. These two phenomena are mainly attributed to a polarization effect. A waterproof measurement (that is, a specimen encapsulated by epoxy) was developed to insulate the composites from ambient moisture for the composites as strain self-sensing materials. The initial resistance of the specimens encapsulated with epoxy and dipped into water stayed constant during measurement time, and their piezoresistance properties were almost the same as those of the specimens exposed to ambient moisture.

DOI:

10.14359/20215


Document: 

SP254-05

Date: 

October 1, 2008

Author(s):

M. Sonebi

Publication:

Symposium Papers

Volume:

254

Abstract:

Nano-technology based on depth-sensing microindentation apparatus was used to evaluate the elastic modulus and micro-hardness of the interfacial transition zone (ITZ) and to estimate the extent of the ITZ around the aggregate-matrix interface for underwater concrete (UWC) and around steel reinforcement for selfconsolidating concrete (SCC) and vibrated concrete. The micromechanical properties of ITZ near to aggregates of concrete cast in water were lower than those of concrete cast in air. The modulus elasticity and the microstrength of concrete cast in water were lower than those of concrete cast in air. It is attributed to the dilution of paste cement and fines particles in water causing reduction of strength and increasing the porosity of concrete. The results of the interfacial properties between selfconsolidating concrete and conventional concrete revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixtures than for the corresponding control mixtures.

DOI:

10.14359/20211


Document: 

SP254-04

Date: 

October 1, 2008

Author(s):

P. Mondal, S.P. Shah, and L.D. Marks

Publication:

Symposium Papers

Volume:

254

Abstract:

In this research, sample preparation techniques were developed to image the nano- and microstructure of hardened cement paste and to determine local mechanical properties. An atomic force microscope (AFM) was used to image the nanostructure of hardened cement paste. AFM and a Hysitron Triboindenter equipped with an in-situ scanning probe microscopy were used to determine the Young’s modulus of cement paste at the nanoscale.

DOI:

10.14359/20210


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