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International Concrete Abstracts Portal

Showing 1-5 of 44 Abstracts search results

Document: 

22-409

Date: 

January 4, 2024

Author(s):

Ronan Chometon, Maxime Liard, Pascal Hébraud, Didier Lootens

Publication:

Materials Journal

Abstract:

The need to constantly improve the quality and properties of manufactured products leads to the development of hybrid materials that combine different elements complementing one another. Fiber-reinforced mortar is one of those products as the fibers are used to improve cementitious materials' flexural weakness. Experimental data on different metallic fibers dispersed in mortar demonstrate the correlation between early-age rheological properties and long-term mechanical strength. Both quantities depend on the ratio of the solid volume fraction of the fiber by a critical solid volume fraction characteristic of the form factors of the fiber. It is demonstrated that both effects arise from the packing stress of the fibers in the mortar when their concentrations are close to their maximum packing fraction. Geometric arguments are used to explain how this critical volume fraction is related to the fiber form factor. Then it enables the building of master curves using geometrical arguments.

DOI:

10.14359/51740371


Document: 

21-387

Date: 

July 1, 2022

Author(s):

Nghia P. Tran, Chamila Gunasekara, David W. Law, Shadi Houshyar, and Sujeeva Setunge

Publication:

Materials Journal

Volume:

119

Issue:

4

Abstract:

In this study, carpet waste fibers—namely, polypropylene (PP) and polytrimethylene terephthalate (PTT) in the form of mono microfibers and hybrid combinations—were studied. The optimization of mono fiber parameters for fiber content (0.1, 0.3, and 0.5%) and length (6, 12, and 24 mm [0.236, 0.742, and 0.945 in.]) were conducted to achieve the optimum strength properties and minimize drying shrinkage. The microstructure, pore structure, and fiber-matrix interfacial properties of the optimized samples were characterized at 7, 28, and 90 days by means of scanning electron microscopy (SEM), X-ray micro-computed tomography (CT), and nanoindentation. The research data revealed that the inclusion of either the optimized mono PP fiber (υf = 0.5% and l = 12 mm [0.472 in.]) or PTT fiber (υf = 0.1% and l = 12 mm [0.472 in.]) improved the compressive strength of 4.3% and 16.1%, and the flexural strength by 11.5% and 9.2% at 28 days, respectively. Hybrid carpet fibers (0.4% PP + 0.1% PTT) provided a greater enhancement in compressive strength of 6.6%, and flexural strength by 13% at 28 days. Drying shrinkage mitigation of mortar over 120 days was recorded as 18.4, 22.3, and 25.8%, corresponding to the addition of 0.5% PP fibers, 0.1% PTT fibers, and hybrid PP/PTT carpet fibers. A pore-refining effect was also observed for mortars with 0.5% PP and hybrid PP/PTT carpet microfibers. The SEM images indicated that the trilobal cross-sectional shape of PTT carpet fibers had a stronger anchoring effect with cement hydrates than the rounded shape of PP carpet fibers. Nanoindentation identified the thickness of the fiber-matrix interfacial transition zone (ITZ) as approximately 15 μm (5.9 × 10–4 in.) for both mono PP and PTT fibers. Approximately 50% of the phases in the vicinity of the fiber-matrix interface comprised a porous structure at 7 days. However, the hydration of clinker over the 90-day period promoted the formation of calcium-silicate-hydrate (C-S-H) and portlandite to form a dense microstructure.

DOI:

10.14359/51734688


Document: 

20-416

Date: 

January 1, 2022

Author(s):

B. S. Sindu and Saptarshi Sasmal

Publication:

Materials Journal

Volume:

119

Issue:

1

Abstract:

An attempt has been made to develop hierarchically crack-abridged, strain-hardened cementitious composite by judiciously incorporating hybrid fibers of three distinctly different length scales (nano-, micro-, and continuous fibers). Unlike textile-reinforced cement composites, here, the nano- to macrofibers are used to improve the cementitious matrix properties through appropriate crack bridging, and at the macroscale, only onedimensional (1-D) long fibers/yarns are used. A distinct and categorical improvement in the property(ies) is found to take place at each scale of bridging. The structural composite systems made using the developed composite exhibited very promising properties, such as high strength (flexural) of approximately 20 MPa (2.90 ksi), an ultimate strain of 8000 με, and rotational capacity of approximately 10 degrees. A detailed numerical model is developed to carry out nonlinear finite element analysis where the interface properties, strain state, and so on are the parameters. Finally, a constitutive model is proposed for the developed composite through inverse analysis. The proposed constitutive model will help engineers design structural components/retrofit schemes by employing the developed composite without complex analysis (using smeared properties).

DOI:

10.14359/51734193


Document: 

20-489

Date: 

January 1, 2022

Author(s):

Tayseer Z. Batran, Basem H. AbdelAleem, and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

119

Issue:

1

Abstract:

This investigation aimed to develop hybrid composite lightweight concrete beams with improved shear capacity and strength. A semi-lightweight high-performance engineered cementitious composite (ECC) layer was added to either the compression or tension side of the beam to improve the shear capacity while maintaining low average density of the composite beam. The ECC material was developed with different fiber types, including polyvinyl alcohol (PVA) fibers with 8 mm (0.31 in.) length, and steel fibers (SFs) with 35 mm (1.38 in.) length. The study compared the theoretical predictions of ultimate shear capacity calculated by design code models and proposed a model to the experimental results. The results indicated that the strategy of using a high-performance ECC layer in lightweight concrete beams can successfully alleviate the reduction in the shear strength of lightweight concrete, with a slight increase of no more than 9% in the density. For example, using an ECC layer with PVA fibers in the compression side of the lightweight control beam increased the density from 1727 to 1843 kg/m3 (107.81 to 115 lb/ft3) while it significantly improved the normalized shear strength, reaching a value that exceeded the normalized shear strength of the normalweight concrete beam with a density of 2276 kg/m3 (142.1 lb/ft3). Using an ECC layer in the compression side of the lightweight control beam also showed a noticeably higher post-diagonal-cracking shear resistance and post-cracking shear ductility compared to the control lightweight beam, full-cast ECC beams, and normalweight concrete beam.

DOI:

10.14359/51734256


Document: 

20-465

Date: 

November 1, 2021

Author(s):

AlaEddin Douba and Shiho Kawashima

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

A concrete system is identified as highly printable if it can offer minimal resistance to handling while sustaining high load resistance and structural stability. One of the major complexities of three-dimensional (3D) concrete printing lies in its sensitivity to materials and equipment that varies the time among layers, hydration time, and shear history. While nanoclays are effective additives for enhancing structural buildup, methylcellulose is introduced as a secondary additive to significantly amplify the nanoclays’ effect on the static yield stress while prolonging the open time between layers and increasing filament cohesiveness. The compatibility of these two systems at different contents is studied by characterizing rheological properties such as static yield stress, steady-state viscosity, and storage modulus, as well as the heat of hydration through isothermal calorimetry. The hybrid system is found to increase the static yield stress by up to 900% compared to the reference paste at only 3.0 wt.% total content by mass.

DOI:

10.14359/51733129


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