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International Concrete Abstracts Portal

Showing 1-10 of 13 Abstracts search results

Document: 

SP220-12

Date: 

March 1, 2004

Author(s):

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

Publication:

Special Publication

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.

10.14359/13157


Document: 

SP220-11

Date: 

March 1, 2004

Author(s):

B.S.M. Persson

Publication:

Special Publication

Volume:

220

Abstract:

An experimental investigation of HPSCC, is outlined. Optimizations were performed on a laboratory scale according to an ideal grading of the particles in the fresh concrete for SCC, with high strength, high durability in marine environment or with fire spoiling safety. SCC was introduced in the full-scale production of beams and piles. The results showed high slump flow and robustness that allowed for a reasonable variation of the water-cement ratio, w/c, keeping the fresh concrete properties within the limits of the full-scale production even at elevated temperature. Creep, shrinkage, salt frost scaling and sulphate resistance did not differ much from the corresponding properties of vibrated concrete, NC. Internal frost resistance was improved for SCC compared with NC but the chloride migration was larger in SCC with limestone powder than in NC. Spoiling of the concrete during fire, especially in low-w/c concrete, was avoided by use of polypropylene fibers.

10.14359/13156


Document: 

SP220-10

Date: 

March 1, 2004

Author(s):

P. Acker

Publication:

Special Publication

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.

10.14359/13155


Document: 

SP220-09

Date: 

March 1, 2004

Author(s):

O. Bjontegaard and E. J. Sellevold

Publication:

Special Publication

Volume:

220

Abstract:

High Performance Concretes (HPC) with water-to-binder (w/b) ratios of 0.40 and from 0 to 15% silica fume have been tested under 20° C isothermal conditions and under realistic (semi-adiabatic) temperature developments with maximum temperature in the range 60 to 65° C. The coefficient of thermal expansion is not very sensitive to silica fume content and its time/temperature dependence may be expressed by the maturity concept. The autogenous shrinkage is extremely temperature dependent, and, importantly, isothermal data cannot be used to predict the behavior during realistic temperature histories. The effect of silica fume (1:1 replacement of cement) is generally to increase the autogenous shrinkage; however, the increase depends strongly on the temperature history, and occurs primarily the first 2 days. Thus, the consequence for crack sensitivity is by no means obvious, and must be calculated for each particular structure.

10.14359/13154


Document: 

SP220-08

Date: 

March 1, 2004

Author(s):

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

Publication:

Special Publication

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.

10.14359/13153


Document: 

SP220-07

Date: 

March 1, 2004

Author(s):

M. D. D'Ambrosia, D. A. Lange, and Z. C. Grasley

Publication:

Special Publication

Volume:

220

Abstract:

Volumetric instability of concrete is a primary cause for early age cracking of concrete pavements and structures. Creep and shrinkage of concrete were studied under restrained conditions and under constant applied load during the first week after casting. Early age behavior was characterized by a uniaxial test that measures shrinkage strain and restrained shrinkage stress. The extent of stress relaxation by tensile creep is determined using simple superposition analysis. The experimental measurements are compared with some current creep and shrinkage models to assess their validity for early age prediction. The B3 model has been previously modified to accommodate early age creep, and this modification was employed in the current study. Test results for normal concrete mixes with different w/c are discussed and compared to model predictions. Comparisons show that the B3 model is accurate when the early age modifications are employed.

10.14359/13152


Document: 

SP220-06

Date: 

March 1, 2004

Author(s):

E. Tazawa

Publication:

Special Publication

Volume:

220

Abstract:

Investigation into the mechanism of shrinkage is essential for the engineering purposes to mitigate cracking of concrete structures. Because comprehensive analysis of unit processes of self deformations is inevitable for systematic understanding of interaction between various self deformations, such as drying shrinkage, autogenous shrinkage and thermal deformation etc.,or their influences on stress generation and crack extension or crack propagation. In this paper one example of this trial is presented based on analysis of relationship between weight loss and drying shrinkage measured by ASTM method. By this analysis, it is shown that unit processes involved in these physical phenomena are not so simple as can be stated by Fick's diffusion theory. Depending upon duration of underwater curing or degree of hydration, unit processes are drastically varied suggesting that variation in microstructure gives rise to quite different situations for desiccation and deformation. Based on these models, relation and interaction between drying shrinkage and autogenous shrinkage is discussed.

10.14359/13151


Document: 

SP220-05

Date: 

March 1, 2004

Author(s):

P.-C. Aitcin, G. Haddad, and R. Morin

Publication:

Special Publication

Volume:

220

Abstract:

High-performance concrete is very vulnerable to early cracking because it does not bleed and it develops within the first 24 hours a significant autogenous shrinkage when it still has a very weak tensile strength. Plastic shrinkage cannot always be fought with curing membrane: fog spraying is much more appropriate. Among the different means already available to fight early autogenous shrinkage external water curing is a very efficient one. Water curing must be extended for 7 days. At the present state of the technology concretes having a water/cement ratio of 0.36 are the more robust against early cracking when an external water curing is used. The cost of water curing can represent from 0.1 to 1.5% of the total construction cost of concrete structures, a good investment in a sustainable development perspective.

10.14359/13150


Document: 

SP220-04

Date: 

March 1, 2004

Author(s):

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

Publication:

Special Publication

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.

10.14359/13149


Document: 

SP220-03

Date: 

March 1, 2004

Author(s):

K. S. Douglas and K. C. Hover

Publication:

Special Publication

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.

10.14359/13148


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