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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 60 Abstracts search results
Document:
SP178
Date:
June 1, 1998
Author(s):
Editor: V.M. Malhotra
Publication:
Symposium Papers
Volume:
178
Abstract:
SP-178 This Symposium Publication contains the proceedings of the Fourth CANMET/ACI/JCI International Conference held in Tokushima, Japan, in June 1998. Sixty-two refereed papers were accepted for presentation at this conference and for this publication.
DOI:
10.14359/14171
SP178-47
R.J. Flatt, Y.F. Houst, P. Bowen, H. Hofmann, J. Widmer, U. Sulser, U. Maeder and T.A. Burge
The behavior of superplasticizers has been studied in highly alkaline suspensions of magnesium hydroxide and silica fume, which can be considered as good model system for cementitious systems containing silica fume. Rheology showed that as superplasticizer dosage is increased, suspensions pass from behaving as Bingham fluids to Newtonian fluids. Beyond a critical concentration large dispersed particles sediment due to the absence of yield stress. The critical concentrations required to obtain Newtonian fluids has allowed to elucidate the dependence between adsorption and dispersion. Indeed, dispersion appears to be only linked to adsorbed polymers and can therefore be attributed either to electrostatic or steric repulsion mechanisms. On the other hand, superplasticizer requirement increases with silica fume fraction in particular with the less ionic polymer. This indicates important electrostatic interactions with the surface in the process of adsorption.
10.14359/6015
SP178-48
L. Gatty, S. Bonnamy, A. Feylessoufi, H. Van Damme and P. Richard
Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM) and Chemical Analysis investigations lead to a fine characterization of Reactive Powder Concretes elaborated under different conditions as pressure application during setting and post-set heat treatment. An abrasive thinning method followed by ionic etching allowed for the preparation of 100 nm thick specimens with wide observation surface areas while still avoiding any water or CO2 contact which may cause their alteration. Silica fume distribution and reactivity versus curing processes are studied. The Si diffusion interfacial zone between hydrated products and silica time, clinker particles or crushed quartz is measured in different curing cases. The Ca/Si ratio spatial distribution in hydrated products and its evolution with the curing processes are then analysed and shown to be strongly microheterogeneous.
10.14359/6016
SP178-49
A.C. Courault, A.K. Crumbie, D. Sorrentino and D. Damidot
Concrete samples made with and without blast furnace slag (BFS) and stored in saturated gypsum solutions for 40 years have been studied. After this long period of time, there still remains small amounts of anhydrous cement and unreacted BFS grains. The reacted BFS are easily identified by EPMA analyses by considering the Mg concentration ; Mg does not diffuse away from the BFS grains. On the contrary Al diffuses away from the BFS grains towards the paste, whereas Ca tends to diffuse from the paste towards the BFS grains. The evolution of Ca, Al, Si and Mg concentrations from slag grains to the paste, or to cement grains, can be described by a succession of local equilibria defined in the CaO-Si02 -A12 03 -MgO-S03 -H2 0 system. The formation of different phase assemblages in the presence of BFS may account for the finer pore structure found despite similar total porosities for both concretes. Moreover a calcite layer has been formed : this layer limits sulfate ions ingress into the paste for both concretes.
10.14359/6017
SP178-50
M. S. Zadeh, G. Debicki, P. Clastres and Y. Billard
Progressive utilisation of silica fume in concrete reactor containment walls that are susceptible to accident conditions, requires the study of leak tightness and the integrity of such structures, when exposing them to high temperatures. This paper deals with the influence of the silica fume dosage rate on the permeability coefficient for temperatures ranging from room temperature to 500°C. The use of silica fume reduces the oxygen permeability of concrete by 2 to 3.6 times at room temperature. When concrete, with or without silica fume, is exposed to heating up to 500°C free and bound water are released progressively; most hydrates are decomposed, the porous structure is modified and finally heating cracks are created, leading to concrete damage and an increase in the permeability coeffkient. However, the advantage of silica fume addition to decrease the loss of leak tightness integrity, depends strongly on the use of the optimum dosage rate of silica fume (i.e. 6-7% in these tests). The optimum dosage rate of silica fume can be estimated from 28 days compressive strength tests using silica fume dosage rates between 5 and 15%. A higher silica fume dosage rate leads to higher evaporable water content at T=lO5“C and for temperatures above 105’C leads to higher decomposing CSH, which causes the loss of more weight at any given temperature.
10.14359/6018
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