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International Concrete Abstracts Portal

Showing 1-10 of 341 Abstracts search results

Document: 

18-013

Date: 

January 1, 2019

Author(s):

Chamila Gunasekera, Sujeeva Setunge, and David W. Law

Publication:

Materials Journal

Volume:

116

Issue:

1

Abstract:

Fly ash geopolymer concrete is a sustainable green construction material that has outstanding mechanical performance and is a low-energy material with a low carbon footprint. In this study, a detailed investigation of the long-term creep and drying shrinkage of three different 100% fly ash geopolymer concretes was carried out up to 1 year of age. Two geopolymers, produced from Gladstone and Pt. Augusta fly ashes, achieved approximately 700 microstrain at the end of 1 year—equivalent to the total creep strain displayed by portland cement (PC) concrete. Moreover, both geopolymer concretes displayed a lower creep coefficient than PC concrete. Hence, AS 3600 or the CEB-FIP model could be conservatively used to predict creep coefficient for two geopolymers. However, the Tarong fly ash geopolymer concrete differed significantly from the other geopolymers and achieved approximately 1900 microstrain after 1 year. The drying shrinkage of Gladstone and Pt. Augusta geopolymer concretes at 1 year are 175 and 190 microstrain, respectively, while Tarong geopolymer and PC concrete achieved 615 and 475 microstrain, respectively. All the fly ash geopolymer concrete showed lower drying shrinkage than the maximum permitted value recommended by AS3600. Incorporation of calcium-aluminasilicate-hydrate (C-A-S-H) gel with the sodium-alumina-silicatehydrate (N-A-S-H) geopolymeric gel was seen to positively affect the packing density of the gel phase. The degree of uniformity and compactness of aluminosilicate gel matrix together with the macroporosity in the 50 nm to 1 μm range was identified as determining the long-term creep and drying shrinkage of the 100% low-calcium fly ash geopolymer concrete.

DOI:

10.14359/51706941


Document: 

17-465

Date: 

September 1, 2018

Author(s):

Akthem Al-Manaseer and Rami Zayed

Publication:

Materials Journal

Volume:

115

Issue:

5

Abstract:

An experimental study was conducted on unsealed concrete I-beam specimens to investigate early-age tensile creep. The tests were conducted on concrete specimens that were moist-cured for 24 hours. The specimens were loaded at 30% of their tensile failure load and tensile creep was monitored for 72 hours. Companion shrinkage specimens were used to measure drying shrinkage while the tensile creep test was performed. The investigation shows that the magnitude of early-age shrinkage exceeds the tensile creep values. The results showed that combined creep and shrinkage strains were increasing when the applied load was increased.

DOI:

10.14359/51706843


Document: 

17-214

Date: 

May 1, 2018

Author(s):

Michael R. Brandes and Yahya C. Kurama

Publication:

Structural Journal

Volume:

115

Issue:

3

Abstract:

This paper describes an experimental investigation on the use of recycled concrete aggregates (RCAs) as replacement for coarse natural aggregates (NAs) in precast/prestressed concrete structures. Specifically, sustained service load tests were conducted on 18 pretensioned beams with two different levels of RCA (50% and 100% by aggregate volume), two sources of high-quality RCA (from both rejected precast members and a construction demolition recycling yard), two different concrete mixture designs, concrete ages of 7 days and 28 days at superimposed service loading, and two different levels of prestressing (to result in beams that are uncracked or cracked under the superimposed load). The loss of prestress over time and midspan deflections of the beam specimens were monitored. Creep and shrinkage strains of accompanying concrete cylinders were also measured. The results showed that the effect of RCA on the service-load behavior of the beams was modest, even at full (100%) aggregate replacement. Additionally, the ability of current code approaches to estimate the measured immediate and sustained load deflections of the beams was not affected by the use of RCA.

DOI:

10.14359/51702133


Document: 

17-192

Date: 

March 1, 2018

Author(s):

C. Gunasekera, X. H. Ling, S. Setunge, D. W. Law, and I. Patnaikuni

Publication:

Materials Journal

Volume:

115

Issue:

2

Abstract:

The use of concrete containing high-volume fly ash (HVFA) has recently gained popularity as a resource-efficient, durable, and sustainable option for a variety of concrete applications. The longterm creep and drying shrinkage of HVFA concrete containing 65% fly ash (HVFA-65) incorporating lime water has been investigated up to 1 year. Moreover, tensile strength and elastic modulus of HVFA-65 concrete have been examined in conjunction with microstructural development. The HVFA-65 concrete achieved ~200 microstrain of creep at the first 50 days; however, it only obtained approximately 100 microstrain between 50 and 365 days. This is equivalent to one-third of total creep strain displayed by portland-cement (PC) concrete, and also half of the predicted creep strain in accordance with AS 3600. Amalgamation of calciumalumina-silicate-hydrate (C-A-S-H) gel with calcium-silicatehydrate (C-S-H) gel was seen to positively affect the compactness and packing density of the gel matrix, which in turn influences the strength and elastic modulus development in HVFA-65 concrete. Early-age curing is also identified as significant in controlling drying shrinkage of the concrete.

DOI:

10.14359/51701238


Document: 

16-369

Date: 

March 1, 2018

Author(s):

Alireza Gholamhoseini, R. Ian Gilbert, and Mark Bradford

Publication:

Structural Journal

Volume:

115

Issue:

2

Abstract:

Relatively little research has been reported on the time-dependent in-service behavior of continuous composite concrete slabs with profiled steel decking as permanent formwork and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, and this has only recently been quantified. This paper presents the results of long-term laboratory tests on continuous composite slabs subjected to both drying shrinkage and different levels of sustained load. It provides experimental evidence of the dominant role played by drying shrinkage in the long-term deflection and redistribution of internal actions in continuous composite slabs. An analytical procedure for determination of the time-dependent deflections in continuous composite slabs is described and the results of analyses are presented and compared with the test data.

DOI:

10.14359/51701133


Document: 

17-019

Date: 

January 1, 2018

Author(s):

Adam M. Knaack and Yahya C. Kurama

Publication:

Structural Journal

Volume:

115

Issue:

1

Abstract:

This paper describes the development and validation of a time-dependent fiber-based (that is, layered) numerical model for the service-load deflection analysis of reinforced concrete structures. Specifically, the model is applied to analyze the effect of recycled concrete aggregates (RCA) on the deflections of beams. Previous research has shown that increased deflections (rather than reduced strength) may be a greater limitation for the use of RCA to replace natural coarse aggregates (for example, gravel and crushed limestone) for increased sustainability. Analysis and design tools are needed to quantify this increase in deflections so that limits on the use of recycled aggregates can be established. To aid in quantifying these increased deflections, a new time-dependent concrete fiber including creep and shrinkage strains was developed in the open-source structural analysis program, OpenSees (Open System for Earthquake Engineering Simulation). This paper describes the validation of the model, including recent data from service-load tests of slender cracked and uncracked RCA concrete beams. The model was able to predict the time-dependent deflections of reinforced concrete structural members under various load scenarios; however, the initial (instantaneous) deflections were generally underestimated because of underestimations in the extent of cracking. The model was also able to predict the total strains and increased neutral axis depth over time as a result of creep and shrinkage strains, except for the tension strains that were underestimated because of the inability of the model to accurately predict the amount of cracking. It was found that the shrinkage strains had a large effect on the time-dependent deflections of the beam test specimens, which was not a finding available from the experimental measurements. While the paper focuses on RCA concrete applications, the numerical model is a general-purpose tool that can be used to analyze the time-dependent axial-flexural deformations of conventional reinforced concrete structures as well.

DOI:

10.14359/51701153


Document: 

15-382

Date: 

January 1, 2018

Author(s):

Yue Huang, Ehab Hamed, Zhen-Tian Chang, and Stephen J. Foster

Publication:

Structural Journal

Volume:

115

Issue:

1

Abstract:

The results of nine full-scale high-strength concrete panels tested under eccentric sustained loads are presented in this paper. The panels were uniaxially loaded for up to 4 months. Four panels failed due to creep buckling at different times under sustained loads that are lower than their short-term capacities. The other panels exhibited a long-term stable behavior; they were then loaded to failure without the release of the existing sustained loads and exhibited a reduction in their residual strength due to creep. The study investigates the influences of aging of concrete, magnitude of the applied load, and the slenderness ratio. The experimental results are compared to theoretical predictions generated from a theoretical analysis that was previously developed by the authors. The formulation is based on the rheological generalized Maxwell model and it accounts for large deformation kinematics in the structural level. A close correlation is achieved between the experimental and theoretical results.

DOI:

10.14359/51700913


Document: 

16-371

Date: 

November 1, 2017

Author(s):

H. Alfisa Saifullah, K. Nakarai, V. Piseth, N. Chijiwa, and K. Maekawa

Publication:

Structural Journal

Volume:

114

Issue:

6

Abstract:

This study aims at investigating the effects of sustained loads on the shear strengths of reinforced concrete (RC) slender beams. Slow loading rates (that were 100 and 1000 times slower than the normal loading rate) were selected to reveal creep effects. The slower loading rate indicated that increased creep occurred during the loading test. However, the shear strength was almost constant during the occurrence of significant diagonal cracking and it increased slightly at failure. It showed that a reduction factor for the shear strengths of the slender RC beams under sustained loads was not required in the design.

DOI:

10.14359/51700916


Document: 

16-342

Date: 

July 1, 2017

Author(s):

Inamullah Khan, Arnaud Castel, and Raymond Ian Gilbert

Publication:

Materials Journal

Volume:

114

Issue:

4

Abstract:

This paper focuses on the effects of fly ash on early-age mechanical and viscoelastic properties of concrete and on early-age cracking. Fly ash is a supplementary cementitious material that is mainly used to increase the durability of concrete. The effect on shrinkage-induced cracking of replacing some ordinary portland cement (OPC) with fly ash has not been studied previously. Material properties such as compressive strength, indirect tensile strength, and elastic modulus were measured with different percentage replacements of OPC with fly ash. Tensile creep and drying shrinkage were also measured on two types of specimens by using two different experimental techniques. The cracking age of plain concrete was observed by using a restrained ring test. Results revealed that the strength evolution of fly-ash-blended concrete is lower than the corresponding OPC concrete and the age at which restrained shrinkage cracking first occurs is also reduced. Slightly higher tensile creep coefficients were observed for fly-ash-blended concrete compared to OPC concrete, but drying shrinkage was not altered to any great extent.

DOI:

10.14359/51689898


Document: 

16-227

Date: 

March 1, 2017

Author(s):

Anton K. Schindler, Robert W. Barnes, Jonas Kammoe Kamgang, and Bryan Kavanaugh

Publication:

Materials Journal

Volume:

114

Issue:

2

Abstract:

Estimating the time-dependent behavior of self-consolidating concrete (SCC) is essential for its successful use in prestressed concrete applications. Compliance is the total load-induced strain (elastic and creep strain) at any age per unit stress caused by a sustained applied load. Compliance of SCC is compared to that of conventional-slump concrete (CSC). Four SCC and one CSC mixtures were made under controlled laboratory conditions and tested under sustained load applied at either 18 hours, 2 days, 7 days, 28 days, or 90 days. All SCC mixtures cured under elevated or standard laboratory temperatures exhibited compliance values less than or similar to the CSC mixture. The accuracy of six compliance prediction methods was also investigated. The compliance prediction accuracy achieved for SCC is similar to that for CSC. The CEB 2010 model was the most accurate compliance prediction method regardless of concrete type or curing condition.

DOI:

10.14359/51689594


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