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International Concrete Abstracts Portal

Showing 1-10 of 19 Abstracts search results

Document: 

SP227-18

Date: 

March 1, 2005

Author(s):

M. A. Miltenberger, E. K. Attiogbe, and A. R. Stoddard

Publication:

Special Publication

Volume:

227

Abstract:

Temperature effects are the predominant cause for volume change in concrete pavements. This paper describes an experimental investigation of thermal volume change conducted to improve the understanding of joint movement in concrete pavement. Four slab strips containing embedded strain gauges and thermocouples were monitored in a controlled environment under four heating rates. Each strip was monitored for translation, rotation, and warping height. Key findings of the experiment include the internal strain distribution and non-linear thermal gradients produced by asymmetrical heating. The laboratory data are compared with long-term data from an instrumented parking lot pavement. Analysis of the data provides insight into the prediction of thermal movements and determination of thermal stress development in pavements.

10.14359/14440


Document: 

SP227-17

Date: 

March 1, 2005

Author(s):

M. D. D’Ambrosia and D. A. Lange

Publication:

Special Publication

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.

10.14359/14439


Document: 

SP227-16

Date: 

March 1, 2005

Author(s):

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

Publication:

Special Publication

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.

10.14359/14438


Document: 

SP227-15

Date: 

March 1, 2005

Author(s):

M. Lopez, L. Kahn, K. Kurtis, and B. Buchberg

Publication:

Special Publication

Volume:

227

Abstract:

Creep and shrinkage data for two high strength lightweight aggregate concretes were collected over a two-year period. The concretes, with unit weight of 1922 kg/m3 (120 pcf), were developed using expanded slate as coarse aggregate. Strengths of 55.2 MPa (8,000-psi) and 69.0 MPa (10,000-psi) were obtained at 56 days. Creep specimens were loaded to 40 or 60 percent of the initial compressive strength at 16 or 24 hours after casting. Based on this preliminary study, AASHTO-LRFD creep estimates of high strength, lightweight aggregate concrete were within 20% accuracy for ages later than one month. ACI-209 estimated creep of the 55.2 MPa lightweight concrete and shrinkage of the 69.0 MPa concrete within 20% accuracy, but greatly underestimated shrinkage of the 55.2 MPa mix. When compared with normal weight, high strength concrete of similar strength and similar cement paste content from previous research, the 69.0 MPa lightweight mix experienced lower total strain after two years.

10.14359/14437


Document: 

SP227-14

Date: 

March 1, 2005

Author(s):

H. T. See and E. K. Attiogbe

Publication:

Special Publication

Volume:

227

Abstract:

With the increasing use of self-consolidating concrete (SCC) in the concrete construction industry, its performance in restrained structural elements is of interest in order to assess the resistance to restrained shrinkage cracking. A new standard test method, ASTM C 1581, which uses an instrumented ring, is employed to assess the cracking potential of various SCC mixtures under restrained shrinkage on the basis of either the time to cracking or the rate of stress development in the material. The performance of the SCC mixtures is compared to that of conventional concrete mixtures to assess the effect of fluidity level on resistance to restrained shrinkage cracking. In addition, the SCC mixtures are evaluated for the effects of sand-to-aggregate ratio (S/A), paste content, aggregate shape, and use of a shrinkage-reducing admixture (SRA) on cracking potential. The results show that the cracking resistance of SCC is similar to that of conventional concrete, indicating that the higher fluidity of SCC is not detrimental to performance under restrained shrinkage. The cracking potential of the SCC mixtures is found to be influenced by the mixture composition.

10.14359/14436


Document: 

SP227-13

Date: 

March 1, 2005

Author(s):

B. Pease, H. Shah, and J. Weiss

Publication:

Special Publication

Volume:

227

Abstract:

Concrete shrinks as a result of drying, self-desiccation, chemical reaction, or temperature reduction. If this shrinkage is prevented by restraint, tensile stresses develop which may result in cracking. Various alternatives have been proposed to reduce the cracking propensity of a mixture including the use of commercial chemical admixtures called shrinkage reducing admixtures (SRA). To date however, little information has been presented to describe how the performance of mixtures containing SRA’s could be predicted. In addition, little guidance exists to determine the dosage rate of SRA that should be used to achieve a specific level of performance. This paper describes initial research results from a study that has been aimed at quantifying the role of SRA at early-ages. The surface tension of various solutions of water and SRA was measured. In addition, free shrinkage measurements were conducted for specimens exposed to sealed and drying conditions from the time of set. Results indicate that shrinkage can be directly related to the concentration of SRA. Restrained ring experiments were performed to investigate the influence of a SRA on residual stress development and cracking in mortar. It has been observed that the residual stress reduction is not directly proportional to the reduction in free shrinkage since the specimens with SRA demonstrate less stress relaxation.

10.14359/14435


Document: 

SP227-12

Date: 

March 1, 2005

Author(s):

N. Suksawang and H. H. Nassif

Publication:

Special Publication

Volume:

227

Abstract:

The use of pozzolanic material, such as fly ash and silica fume, is becoming more popular in producing high performance/high strength concrete (HP/HSC) for various structural applications. Many studies have addressed the mechanical properties as well as durability of HP/HSC, however, the effect of pozzolans on the shrinkage and creep behaviors are not clearly addressed. There is a need to understand and identify how changes in the composition and porosity of HP/HSC, and consequently the elastic modulus, would affect its early age as well its long term performance. The main objective of this paper is to examine the effect of using various models for modulus of elasticity on the prediction of creep of high strength concrete (HSC) containing pozzolans. The study included an experimental program and a comparison of available analytical models for predicting the compressive creep and modulus of elasticity of HSC. Results from creep tests performed on different mixes (with compressive strength up to 90 MPa) were compared with those from prediction models available in the literature. Three creep models, ACI 209, CEB 90, and GL 2000, were used. In addition, various values of modulus of elasticity obtained from experimental calculation, ACI 318, ACI 363, CEB 90, Gardner, and from an equation proposed by the authors were evaluated. Results show that the modulus of elasticity has high impact on the accuracy of predicted creep and that available modulus of elasticity models needs to be revised to reflect HSC containing pozzolans.

10.14359/14434


Document: 

SP227-11

Date: 

March 1, 2005

Author(s):

M. Sassone and M. A. Chiorino

Publication:

Special Publication

Volume:

227

Abstract:

Many structural problems involving creep in concrete structures can be solved in very compact closed forms through the fundamental theorems of linear viscoelasticity of aging materials. This general approach requires the knowledge of three basic functions: the compliance function J, derived directly from the creep prediction models available in the literature and in technical guidance documents, and the relaxation (R) and redistribution () functions, that can be calculated from J. This paper presents an interactive web site for quick automatic calculation of these three basic functions, with reference to the principal creep models presently considered by international civil engineering societies. Starting from the approach suggested by Bazant for the numerical solution of the fundamental Volterra integral equation relating R to J, identically applied to derive ~ from J, a complete procedure has been developed, including the user interface necessary for setting input data and handling output results. The immediate availability of the basic functions allows extended comparisons of the outputs of the different models and evaluation of the influence that the selection of a particular model has on the assessment of structures. The web site has a flexible architecture and will be progressively extended to include calculation of other functions of interest for the creep analysis of structures, e.g. the aging coefficient X of the age-adjusted-effective-modulus-method, and the reduced relaxation functions R* that extend the field of application of the fundamental theorems to the analysis of heterogeneous structures, such as e.g. cable-stayed bridges.

10.14359/14433


Document: 

SP227-10

Date: 

March 1, 2005

Author(s):

D. W. Mokarem, R. E. Weyers, and M. M. Sprinkel

Publication:

Special Publication

Volume:

227

Abstract:

The study included A3 – General Paving (21 MPa at 28 days), A4 – General Bridge Deck (28 MPa at 28 days), and A5 – General Prestress (35 MPa at 28 days) concrete mixtures approved by the Virginia Department of Transportation (VDOT). The study also included a lightweight, high strength concrete mixture (LTHSC) used in the prestressed beams of the Chickahominy River Bridge, and a high strength (HSC) concrete mixture used in the prestressed beams of the Pinner’s Point Bridge. For the A3, A4, and A5 portland cement concrete mixtures, the CEB 90 model appears to be the best predictor. However, there is little difference in prediction capabilities between the CEB 90, GL2000 and B3 models. For mixtures containing supplemental cementitious materials, slag and fly ash, the GL2000 model appears to be the best predictor. For the LTHSC concrete mixture, the CEB-C90 model appears to be the best early age predictor, while the Bazant B3 model appears to be the best predictor a later ages. And for the HSC concrete mixture, the Gardner/Lockman model appears to be the best predictor.

10.14359/14432


Document: 

SP227-09

Date: 

March 1, 2005

Author(s):

M. W. Paulsen, S. D. B. Alexander, and D. M. Rogowsky

Publication:

Special Publication

Volume:

227

Abstract:

Continuous highway overpass structures are often governed by serviceability rather than ultimate conditions. Deflection prediction and control is vital to avoid cracking. A two span overpass in Calgary was chosen as a case study. Deflections and strains in two precast prestressed girders were monitored from fabrication to erection, and a comprehensive material testing program was done on the concrete mix. The results of the case study show that the CEB MC-90 model code underestimated the time-dependent response by a maximum of 16% while ACI 209 overestimated by 19%. By tuning ACI 209 and CEB MC-90 to the concrete material testing data, predictions were increased to within 8% and 7%, respectively. A variability analysis on the two tuned models showed that while they give nearly the same prediction, the CEB MC-90 format induces less uncertainty in predictions. In addition, extrapolation to long-term ages shows a substantial divergence between predictions of the two models.

10.14359/14431


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