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International Concrete Abstracts Portal

Showing 1-5 of 263 Abstracts search results

Document: 

19-320

Date: 

July 1, 2020

Author(s):

Bruce Menu, Thomas Jacob-Vaillancourt, Marc Jolin, and Benoit Bissonnette

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The experimental program reported in this paper sought to evaluate the efficiency of a range of curing methods in view of minimizing the evaporation rate at the surface of freshly placed shotcrete and preventing the detrimental consequences of early-age shrinkage. CSA A23.1-14 states that severe drying conditions should be considered to exist when the surface moisture evaporation rate exceeds 0.50 kg/m2/h (0.1 lb/ft2/h). In fact, the environmental conditions that lead to such evaporation rates are regularly experienced on construction sites, requiring that adequate protection of the concrete surface be carried out in a timely manner after placement. This research effort is aimed at quantifying the influence of selected curing methods upon the early-age moisture loss and the resulting shrinkage. The results show that early-age volume change of freshly sprayed shotcrete can be significantly reduced by adequate surface protection. Among the investigated methods, moist curing is found to be the most effective.

DOI:

10.14359/51724624


Document: 

18-512

Date: 

July 1, 2020

Author(s):

Mahdi Valipour and Kamal H. Khayat

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

DOI:

10.14359/51724613


Document: 

18-417

Date: 

May 1, 2020

Author(s):

Kamran Amini, Kristen Cetin, Halil Ceylan, and Peter C. Taylor

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This paper compiles results from three different laboratory studies and employs multivariate regression analyses to model the effect of mixture parameters and concrete hardened properties on saltscaling performance. The correlations between concrete hardened properties and mixture proportions were also studied. The modeled mixture parameters included water-cementitious materials ratio (w/cm), slag cement, and air content. Concrete performance was evaluated through abrasion resistance, sorptivity, compressive strength, and salt scaling tests. According to the results obtained in this study, concrete scaling performance is affected, in the order of importance, by w/cm, slag-cement replacement, and air content. In addition, concrete hardened properties, especially abrasion resistance, were found useful in making reliable salt-scaling predictions. Based on the results derived from the regression analyses and the discussions provided in the reviewed literature, recommendations are given for proportioning of concrete to obtain adequate performance with respect to compressive strength, abrasion resistance, sorptivity, and salt-scaling resistance. In addition, the relationship between concrete properties, ingredients, and effective mechanisms are investigated.

DOI:

10.14359/51724614


Document: 

18-353

Date: 

May 1, 2020

Author(s):

Nabeel A. Farhan, M. Neaz Sheikh, and Muhammad N. S. Hadi

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

The effects of aspect ratio and volume fraction of steel fibers on the engineering properties of ambient-cured geopolymer concrete (GPC) were investigated. Straight macro steel fibers with an aspect ratio of 65 and straight micro steel fibers with an aspect ratio of 30 were added into the GPC mixtures. The test results showed that the engineering properties of GPC significantly improved with the addition of 2% macro steel fibers and 2% micro steel fibers by volume. The stress-strain behavior of GPC changed from brittle to ductile with significant improvement in the post-peak behavior by the addition of steel fibers. The compressive strength of GPC increased significantly with the addition of low-aspect-ratio steel fibers and the indirect tensile strength, flexural strength, direct tensile strength, and double punch tensile strength of GPC increased significantly with the addition of high-aspect-ratio steel fibers.

DOI:

10.14359/51724591


Document: 

19-196

Date: 

March 1, 2020

Author(s):

Kacie C. D’ Alessandro, Carin L. Roberts-Wollmann, and Thomas E. Cousins

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

Ultra-high-performance concrete (UHPC) is known for its high strength and advanced durability. Due to the unique formulation of this material, including a fine cementitious matrix and distributed steel fibers, UHPC displays different material behavior than conventional concrete. This paper examines the biaxial tension-compression behavior of UHPC using a novel biaxial test method and compares results to biaxial failure criterion of conventional concrete. A total of 62 specimens were tested to evaluate the effects of curing regimes and fiber orientations. While the compressive strength of UHPC increased significantly when steam treated, tensile strength did not increase to the same degree. Controlled fiber orientation provided more compressive stress resistance than random fiber orientation with the presence of increasing tensile stress. Comparing UHPC results to biaxial failure criterion recognized for conventional concrete, the Mohr-Coulomb biaxial failure criterion was shown to be a conservative model for UHPC for all fiber orientations and curing regimes.

DOI:

10.14359/51722404


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