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International Concrete Abstracts Portal

Showing 1-5 of 19 Abstracts search results

Document: 

SP227-17

Date: 

March 1, 2005

Author(s):

M. D. D’Ambrosia and D. A. Lange

Publication:

Symposium Papers

Volume:

227

Abstract:

Creep and shrinkage of concrete were studied under constant load and restrained conditions during the first week after casting. Concrete behavior was characterized by a uniaxial test that measures shrinkage deformation and restrained shrinkage stress. The extent of stress relaxation by tensile creep was determined using superposition analysis. The experimental measurements were compared with current creep and shrinkage models to assess their validity for early age prediction. The ACI 209 equation for creep is currently not applicable to early age, but modifications are proposed that fit a database of early age behavior. 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 with different w/c ratios are discussed.

DOI:

10.14359/14439


Document: 

SP227-16

Date: 

March 1, 2005

Author(s):

M. Pigeon, B. Bissonnette, J. Marchand, D. Boily, and L. Barcelo

Publication:

Symposium Papers

Volume:

227

Abstract:

This paper illustrates how stress relaxation can be used to obtain valuable information regarding the behavior of concrete at early ages. Five concrete mixtures were investigated using a so-called discretized restrained shrinkage (DRS) testing device, allowing the determination (from the time of casting) of the increase in load induced by autogenous shrinkage and the evaluation of the different strain components (free shrinkage, elastic strain, creep). Test results indicate that the stress due to early-age restrained autogenous shrinkage is quite variable, in good part due to the variation in the relaxation capacity of the mixtures. Both the relaxation ratio, defined as the stress generated divided by the theoretical stress, and the relative relaxation, defined as the absolute value of stress relaxation divided by the average applied stress, can be used to illustrate and analyze the variation of the relaxation phenomena as a function of the type of mixture tested.

DOI:

10.14359/14438


Document: 

SP227-03

Date: 

March 1, 2005

Author(s):

A. Al-Manaseer and S. Ristanovic

Publication:

Symposium Papers

Volume:

227

Abstract:

The purpose of this study was to conduct a sensitivity study on shrinkage prediction of concrete utilizing the ACI 209 (1), GL 2000 (2), B3 (3), and CEB MC 90-99 (4) models. The sensitivity of a prediction model is function of different parameters utilized in the equations describing the model. The influence of changing input parameters on shrinkage prediction was investigated. The study reveals that the change of relative humidity will result in similar sensitivity for different shrinkage models. The autogenous shrinkage component in the CEB MC 90-99 was found to be most sensitive to strength change at 28 days. The GL 2000 was found most sensitive to cement type while the B3 model was found to be most sensitive to specimen size and type of curing. In general the B3 was the most sensitive model while the ACI was the least sensitive.

DOI:

10.14359/14425


Document: 

SP227-02

Date: 

March 1, 2005

Author(s):

R. I. Gilbert

Publication:

Symposium Papers

Volume:

227

Abstract:

The Australian Standard for Concrete Structures, AS3600-2001 (1), is currently under review, with the intention to expand its scope to include concrete with characteristic compressive strengths up to 100 MPa. The procedures in the existing Standard for the estimation of the deformation characteristics of concrete, including the tensile strength, the elastic modulus, the creep coefficient and the shrinkage strain, are not applicable for high strength concrete. To provide reasonable agreement with the test data for Australian high strength concretes, new models for predicting the instantaneous and time-dependent material characteristics had to be developed. In this paper, the new models that have been adopted for inclusion in the next edition of AS3600 (due for release in 2006) are presented.

DOI:

10.14359/14424


Document: 

SP227-06

Date: 

March 1, 2005

Author(s):

M. A. Chiorino

Publication:

Symposium Papers

Volume:

227

Abstract:

The long-term service behavior of modern reinforced or prestressed concrete structures, whose final static configuration is frequently the result of a complex sequence of phases of loading and restraint conditions, are influenced largely by creep. Creep substantially modifies the initial stress and strain patterns, increasing the load induced deformations, relaxing the stresses due to imposed strains, either artificially introduced or due to natural causes, and activating the delayed restraints. The resulting influences on serviceability and durability are twofold, creep acting both positively and negatively on the long-term response of the structure. The paper shows that use of the four fundamental theorems of the theory of linear viscoelasticity for aging materials, and the related fundamental functions, offers a reliable and rational approach to estimate these effects. Extremely compact formulations are obtained, which are particularly helpful in the preliminary design, as well as in the control of the output of the final detailed numerical investigations and safety checks, and suitable for codes and technical guidance documents. Particular attention is dedicated to the problem of change of static system.

DOI:

10.14359/14428


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