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International Concrete Abstracts Portal

Showing 1-5 of 13 Abstracts search results

Document: 

SP220-08

Date: 

March 1, 2004

Author(s):

J.-P. Charron, B. Bissonnette, J. Marchand, and M. Pigeon

Publication:

Symposium Papers

Volume:

220

Abstract:

A restrained shrinkage apparatus was adapted to study the early-age behavior of hydrating cement-based materials in various thermal conditions. The intent of this paper is to provide information on the latest version of the DRS (Discretized restrained shrinkage) experimental setup and test procedure. In addition, the test reproducibility is evidenced through selected series of experiments. First, results that show the temperature control efficiency and the uniformity of the temperature field within the specimens are provided. Then, the results of tests performed to evaluate both hardware and material effects are presented. According to these results, the temperature controlled DRS test shows much promise in the quest of better understanding and characterizing the early-age behavior of cement-based materials. It definitely should help in tackling the related cracking problems.

DOI:

10.14359/13153

Document: 

SP220-12

Date: 

March 1, 2004

Author(s):

S. Zhutovsky, K. Kovler, and A. Bentur

Publication:

Symposium Papers

Volume:

220

Abstract:

The paper deals with internal curing of High-Strength Concrete using pre-soaked lightweight aggregate (LWA). The effect of internal curing depends directly on the distance over which the internal curing water can travel. The effectiveness of internal curing is a function of the ratio between the water penetration depth and the paste-lightweight aggregate proximity, which is related to the spacing between the aggregates. Estimates of these parameters were developed in this study, based on a combination of modeling and experimental work. The results indicate that water can penetrate from the LWA into the surrounding matrix to a distance of up to several millimeters during the first seven days of hydration. The water penetration was sensitive to the pore structure of the aggregate, ranging from about 1 to 6 mm, and it was reduced in systems having lower w/b ratio and silica fume by almost a factor of 2.

DOI:

10.14359/13157

Document: 

SP220-03

Date: 

March 1, 2004

Author(s):

K. S. Douglas and K. C. Hover

Publication:

Symposium Papers

Volume:

220

Abstract:

This paper evaluates a test method for measuring bulk, autogenous volume changes in cement paste and mortar. In this test method, paste and mortar were sealed in latex membranes and submerged in water. The weight of the specimens was recorded periodically, both in air and submerged in water, and their volume change was calculated using Archimedes' principle. Several sources of error in the test method were identified, and measures were taken to account for some of this error. It was concluded that the experimental error for this test may be quite substantial as the test duration increases, and therefore this test method is most suited for measuring the early age volume changes of cement paste and mortar.

DOI:

10.14359/13148

Document: 

SP220-04

Date: 

March 1, 2004

Author(s):

P. Lura, Y. E. Guang, and K. van Breugel

Publication:

Symposium Papers

Volume:

220

Abstract:

In this paper, measurements of non-evaporable water content, chemical shrinkage, autogenous deformation, internal relative humidity (RH), pore solution composition, and early-age elastic modulus are presented and discussed. All experiments were performed on Portland cement and blast-furnace slag (BFS) cement pastes. Self-desiccation shrinkage of the BFS cement paste was modeled based on the RH measurements, following the capillary-tension approach. The main findings of this study are: 1) self-desiccation shrinkage can be related to self-desiccation both for Portland and for BFS cement pastes, taking into account the influence of the dissolved salts in the pore solution, 2) the BFS cement paste studied shows pronounced self-desiccation and self-desiccation shrinkage, mainly caused by its very fine pore structure.

DOI:

10.14359/13149

Document: 

SP220-10

Date: 

March 1, 2004

Author(s):

P. Acker

Publication:

Symposium Papers

Volume:

220

Abstract:

Recent experimental results (creep tests and indentation tests at a nanometer scale) on Ductal®, a non-brittle (fiber-reinforced) ultrahigh-performance concrete (UHPC), show that only one constituent of this composite, the C-S-H phase, exhibits creep. Former creep tests on hydrated cement paste have shown a very high creep rate of the cement gel which decelerates very slowly (much more slowly than concrete creep). Furthermore, these results provide a clear explanation for the observations of a strong correlation between shrinkage and creep values. The reason is, when hydration rate becomes negligible (typically after a few weeks), the dominant part of shrinkage is nothing but the viscoplastic response of the cement gel to the internal stress which is applied by the liquid phase on the pore surface. This statement makes wrong the last argument against the explanation of shrinkage by capillary tension, the so-called argument of reversibility. Creep aging, as well as the very low creep of high-strength concretes can be explained by the consumption of creep potential by the hygral stress. Several coupling effects between creep and shrinkage can be explained, as for example the so-called PICKETT effect.

DOI:

10.14359/13155

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