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International Concrete Abstracts Portal

Showing 1-5 of 104 Abstracts search results

Document: 

18-301

Date: 

March 1, 2021

Author(s):

Erik Stefan Bernard

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

It is well known that creep can affect the serviceability of concrete structures, including tunnel linings made using fiber-reinforced shotcrete (FRS). However, the possible effect of creep on the strength of structures is seldom explicitly considered in design. For cracked FRS loaded in tension or flexure, creep rupture of the fiber-concrete composite, either by pullout or rupture of fibers, can lead to structural collapse, at least when no alternative load path exists. In the present investigation, the influence of fiber geometry and surface roughness on creep rupture (expressed as the time-to- collapse) of FRS panel specimens subjected to a sustained flexural-tensile load has been assessed. The results suggest that geometric aspects of fiber design influence the propensity of the fiber composite to suffer creep rupture at a crack, and that collapse primarily occurs as a result of fiber pullout rather than tertiary creep of individual fibers. For the fibers presently investigated, geometric aspects of fiber design appear to exert a greater influence on creep rupture of the fiber composite than the properties of the material comprising the fibers.

DOI:

10.14359/51730410


Document: 

19-427

Date: 

November 1, 2020

Author(s):

Brock D. Hedegaard

Publication:

Materials Journal

Volume:

117

Issue:

6

Abstract:

This study presents a multi-scale model for predicting multidecade basic creep of concrete. Aging of cement is modeled through hydration, densification, and polymerization of the calcium- silicate-hydrate (C-S-H) phases. The model accounts for the separate mechanisms of viscoelastic compliance and aging viscous flow of the C-S-H, and for the dissolution-precipitation of elastic and viscoelastic phases during hydration that causes apparent creep in the composite. Upscaling is performed in the time-domain simultaneously for all loading ages. The results show that short-term viscoelastic compliance observed from nanoindentation tests dominates short-term creep, but cannot explain long-term creep rates observed in macroscopic concrete creep tests. Such observations can only be replicated by considering viscous flow that develops over time scales unobservable by minutes-long tests on the microscale. Dissolution creep may explain some irreversible basic creep at very early ages but rapidly diminishes in relevance as the concrete continues to age.

DOI:

10.14359/51728121


Document: 

19-459

Date: 

November 1, 2020

Author(s):

N. Saklani, B. M. Khaled, G. Banwat, B. Spencer, A. Giorla, G. Sant, S. Rajan, and N. Neithalath

Publication:

Materials Journal

Volume:

117

Issue:

6

Abstract:

Numerical implementation of an isotropic creep-damage model for concrete in multiphysics object-oriented simulation environment (MOOSE) finite element framework is presented in this paper. The constitutive model considers the combined effect of instantaneous and delayed strains on damage propagation. The implementation considers creep using generalized Maxwell or Kelvin-Voigt models. Using strain splitting assumptions, the total mechanical strains are split into elastic and creep components. Damage is considered to evolve as a function of the elastic and creep strains. This work considers damage as a function of fracture energy using the characteristic length of each finite element. This approach preserves the energy release rate of each element and avoids vanishing energy dissipation as the mesh is refined. A creep-damage parameter is used to quantify the effect of creep strain on damage. The model is tested against published results on notched three-point bending specimens involving non-linear creep and predicts that about a third of the creep strain contributes towards damage for the experiments simulated. Results show that the proposed framework has predictive capabilities, and the model can be extended for more complex systems.

DOI:

10.14359/51729312


Document: 

18-314

Date: 

September 1, 2019

Author(s):

Harikrishnan Nair and H. Celik Ozyildirim

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

Cracks in bridge decks facilitate the penetration of chlorides that induce corrosion of reinforcing steel. Formation of cracks is related to the shrinkage and properties of the concrete and the restraints to movement. Lightweight concrete with a low modulus of elasticity, high creep, and water in the aggregate pores for internal curing has a reduced cracking potential. To control cracking, shrinkage of concrete can be reduced by using a shrinkage-reducing admixture (SRA). A recent study at the Virginia Department of Transportation (VDOT) investigated the performance of both lightweight concretes and concretes with SRA containing normal-weight aggregates in the field and found that these concretes had no cracks or fewer cracks than were typical of decks constructed with normal-weight aggregates over the past 20 years. VDOT developed a new specification that included lightweight concretes or concretes with normal-weight aggregates and SRA and this specification is being used successfully to reduce cracking in bridge decks. This paper summarizes the work conducted to develop the new specification and includes information on field applications.

DOI:

10.14359/51716830


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


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