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International Concrete Abstracts Portal

Showing 1-5 of 13 Abstracts search results

Document: 

SP194-03

Date: 

May 1, 2000

Author(s):

N. J. Gardner

Publication:

Symposium Papers

Volume:

194

Abstract:

This paper presents a simple design-office procedure for calculating the shrinkage and creep of concrete using the information available at design; namely the 28 day specified concrete strength, the concrete strength at end of curing or loading, element size and the relative humidity. The method includes strength development with age, relationship between modulus of elasticity and strength, and equations for predicting shrinkage and creep. The only arbitrary information are the factors appropriate to the cementitious material, which can be improved from measured strength age data. At the most basic level the proposed method requires only the information available to the design engi-neer. The prediction values can be improved by simply measuring concrete strength development with time and modulus of elasticity. Aggregate stiffness can be taken into account by back calculating a concrete pseudo strength from the measured modulus of elasticity. Measured short term shrinkage and creep values can be extrapolated to obtain long duration predictions for simi-lar sized elements. The predictions are compared with experimental results for seventy nine data sets for compliance and sixty three data sets for shrink-age. The comparisons indicate shrinkage and creep can be calculated within +/- 25%. The method can be used regardless of what chemical admixtures or mineral by-products are in the concrete, casting temperature or curing regime.

DOI:

10.14359/9891


Document: 

SP194-06

Date: 

May 1, 2000

Author(s):

M. A. Chiorino, L. Dezi, and A. M. Tarantino

Publication:

Symposium Papers

Volume:

194

Abstract:

Variation of statistical scheme of reinforced and prestressed concrete struc-tures is frequent in modern construction techniques. Construction sequences may include application of permanent loads and of prestressing in one or more steps, and connection of different portions of the structure, or introduction of additional restraints (sometime forcedly applied to correct the internal stress conditions), at different ages during or after the construction process. The resulting stress distribution is largely influenced by the time-dependent deformability of concrete. The paper presents a unified approach for its evalu-ation based on the linear theory of viscoelasticity for aging materials, which is normally adopted for modeling concrete creep, evidencing the important role played by the non-dimensional redistribution function (t, to, t1) describing the creep induced stress variation at time t for loading at t, and variation of re-straint conditions at t,. The obtained solutions are exact for all problems of variation of restraint conditions in homogeneous structures with rigid restraints, and normally suffkiently accurate for problems concerning structures charac-terized by heterogeneities in the properties of concrete along their structural configuration. Redistribution function may be computed from the creep function J characterizing the creep prediction model under consideration and made available in terms of design aids (graphs or tables). The computational procedure is illustrated and an example of application to a typical structural problem is presented.

DOI:

10.14359/9893


Document: 

SP194-11

Date: 

May 1, 2000

Author(s):

W. H. Dilger and C. Wang

Publication:

Symposium Papers

Volume:

194

Abstract:

Creep and shrinkage of concrete are important factors in the design and analysis of concrete structures, particularly for the long-term serviceability and durability and for the construction stage of long span, prestressed con-crete structures. Because of very low water-cementitious ratio (w/cm), chemical admixtures and sometimes mineral admixtures, the evolutions of moisture state and rate of cement hydration in high-performance concrete (HPC) are significantly different from those in normal concrete. For example, the cement hydration in HPC terminates earlier due to the lack of water, resulti ng in faster development of relative strength at early ages and little long-term strength gain. At the same time, self-desiccation in the form of a rapid decrease in internal relative humidity starts in HPC at very early ages. Consequently, base (autogenous) shrinkage of HPC is very high compared with normal concrete. The moisture permeability, which affects the development of creep and shrinkage of concrete, is at least one order smaller for HPC than for normal concrete. As a result well as creep and the development shrinkage property of strength and modulus of elasticity as es of HPC are remarkably different from those of normal concrete. The current prediction models for time-dependent properties, particularly creep and shrinkage, which have been derived from experimental data on normal concrete, are not applicable to HPC. This paper will discuss the main parameters affecting the time-dependent properties and the differences between HPC and normal concrete, based on the results of an extensive experimental program at the University of Calgary and data from the literature. A recently developed model to estimate creep and shrinkage of HPC is also presented and examined.

DOI:

10.14359/9899


Document: 

SP194-09

Date: 

May 1, 2000

Author(s):

I. N. Robertson

Publication:

Symposium Papers

Volume:

194

Abstract:

This paper presents a comparison between laboratory creep and shririkage data and the performance of a long-span box-girder bridge structure. As part of a long-term instrumentation and monitoring program on the North Halawa Valley Viaduct, a number of laboratory creep and shrinkage tests were performed on the concrete used in the viaduct. The data are compared with current theoretical models for the prediction of creep and shrinkage. These models all underestimate the long-term effects on the concrete used in this structure. This is attributed in part to the nature of the basalt aggregates available on the Hawaiian Islands. It is shown that with as little as 28 days of data from creep and shrinkage tests, the prediction models can be modified to provide a far more accurate prediction of the long-term performance of the structure.

DOI:

10.14359/9897


Document: 

SP194

Date: 

May 1, 2000

Author(s):

Editor: Akthem Al-Manaseer / Sponsored by: ACI Committee 209

Publication:

Symposium Papers

Volume:

194

Abstract:

This Symposium Publication contains 12 papers presented at the Adam Neville Symposium in Atlanta, Georgia, in 1997. Topics relating to creep and shrinkage include admixture and cementitious materials effects, special high-performance considerations, temperature and humidity influences, reinforced and prestressed concrete analysis and design procedures, and much more. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP194

DOI:

10.14359/14228


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