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Home > Publications > 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.
Showing 1-5 of 11 Abstracts search results
Document:
SP270-05
Date:
March 1, 2010
Author(s):
N. Tregger, R. Ferron, M. Beacraft, J. H. Kim, K. Kuder, and S. P. Shah
Publication:
Symposium Papers
Volume:
270
Abstract:
Although clays such as metakaolin are typically incorporated into cement-based materials in order to improve hardened-state properties, recent findings at the Center for Advanced Cement-Based Materials (ACBM) have shown a large influence on the fresh-state. Furthermore, these benefits come at a much lower dosage, (~1% by mass of binder). A recent focus of ACBM has been the use of small dosages of clays in order to improve fresh-state properties such as extrudability and green strength. This paper summarizes several current projects at ACBM which demonstrate the effects of different commercial clays on relevant properties for three different scenarios: extrusion, formwork pressure of self-consolidating concrete (SCC) and slipform paving SCC. In each case, small additions of clays have shown marked improvements in the rheology of the cement composite. The use of two experimental methods to characterize the microstructural changes that occur with additions of clays is also reviewed.
DOI:
10.14359/51663738
SP270-02
D. A. Lange, Y. Jia, and Y.-S. Liu
X-ray nanotomography was explored for investigation of the microstructure of cement paste in various ages, including 1-day and 28-day. 2D and 3D images were obtained for quantitative analysis and morphological reconstruction. The technique also provided a prospect of viewing interfacial transition zone (ITZ), of which the microstructures were simulated and the evolution of components with respect to the distance from the interface was calculated.
10.14359/51663735
SP270-04
N. Neithalath and J. Jain
Electrical impedance based methods are frequently used to monitor the microstructural development in cement-based materials due to their non-invasive nature and the ability to make continuous measurements. This paper discusses two other applications of electrical impedance for two different classes of concretes—micro-porous conventional concretes and macro-porous pervious concretes. The effectiveness of a microstructural parameter derived from electrical impedance data to relate to the rapid chloride transport parameters of conventional concretes is described. The influence of the non-steady state migration test in changing the microstructure of concretes due to formation of new solid products through chloride binding of cement hydrates is also evaluated in detail through a combination of measured electrical impedance parameters and an equivalent electrical circuit model. The values of the components of the model determined before and after the migration test provide confirmation of the formation of binding products along the pore walls in concrete. Electrical impedance observations along with a modified Bergman equation are used to predict the porosity of pervious concretes. The experimentally determined and predicted porosities match adequately. The effective electrical conductivity can also be used in well known permeability prediction equations such as the Kozeny-Carman or Katz-Thompson equations for performance prediction of pervious concretes.
10.14359/51663737
SP270-03
Z. C. Grasley
Uniaxially passive restraint experiments (for example, “cracking frames”) provide enough information to extract useful viscoelastic constitutive properties when combined with free deformation and mass loss experiments (in the case of drying shrinkage). In this paper, analytical techniques are described for deriving a closed-form solution to extract the viscoelastic Young’s modulus from solidifying concrete in a uniaxial passive restraint test. In addition, for the particular case where drying shrinkage is restrained in the test, approximate closed-form solutions are derived for the non-uniform internal relative humidity (RH), free drying shrinkage, and stress gradients. An example problem demonstrates the utility of the derived solutions.
10.14359/51663736
SP270-10
Z. S. Metaxa, M. S. Konsta-Gdoutos, and S. P. Shah
There have been numerous studies that have aimed at improving the low tensile strength, stiffness, and toughness of cementitious materials. This study aims to show that all of these characteristics can be greatly improved by the addition of ladder scale reinforcement at the nano and micro scale. Carbon nanofibers (CNFs) as well as polyvinyl alcohol (PVA) microfibers were used as reinforcement. The mechanical properties of the nanocomposites were investigated by fracture mechanics three-point bending test. The microstructure and the morphology of nanocomposite samples were studied using an ultra high resolution scanning electron microscope (SEM). The results clearly illustrate that the incorporation of nanofibers and microfibers greatly improves the flexural strength, Young’s modulus, and toughness of the cement matrix.
10.14359/51663743
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