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International Concrete Abstracts Portal

Showing 1-5 of 417 Abstracts search results

Document: 

21-138

Date: 

March 1, 2022

Author(s):

Antoine E. Naaman and Surendra P. Shah

Publication:

Materials Journal

Volume:

119

Issue:

2

Abstract:

The maximum post-cracking tensile strength (σpc) recorded in numerous investigations of ultra-high-performance fiber-reinforced concrete (UHP-FRC) remains mostly below 15 MPa, and the corresponding strain (εpc) below 4/1000. Both values are significantly reduced when the specimen size increases, as is needed for real structural applications. Test data on σpc and εpc from close to 100 series of direct tensile tests carried out in more than 20 investigations are analyzed. Factors influencing the strain capacity are identified. However, independently of the numerous parameters encountered, two observations emerged beyond all others: 1) the higher the post-cracking tensile strength (whichever way it is achieved), the higher the corresponding tensile strain; and 2) fibers mechanically deformed and/or with slip-hardening bond characteristics lead to an increase in strain capacity. A rational explanation for these observations is provided. The authors believe that achieving a large strain (εpc) at maximum stress is paramount for the successful applications of ultra-high-performance concrete in concrete structures not only for strength but, more critically, for ductility and energy absorption capacity improvements.

DOI:

10.14359/51734357


Document: 

21-161

Date: 

March 1, 2022

Author(s):

Alessandro P. Fantilli and Farmehr M. Dehkordi

Publication:

Materials Journal

Volume:

119

Issue:

2

Abstract:

Experimental research performed on fiber-reinforced cement-based composites made with polymeric aggregate and reinforced with recycled steel fibers is presented in this paper. In total, 18 concrete prisms were cast with a two-stage procedure: first, the fibers from end-of-life tires were put in the molds and, subsequently, they were covered by a cementitious grout containing fine (recycled or virgin) aggregate. The two-stage composites showed more than one crack and a deflection-hardening behavior in the post-cracking regime by performing three-point bending tests. Moreover, both flexural and compressive strength increased with the fiber volume fraction. Thus, if the content of recycled materials is suitably selected, the ecological and mechanical performances of the two-stage composites improve and become similar to those of one-stage fiber-reinforced concrete made with only virgin components.

DOI:

10.14359/51734300


Document: 

21-106

Date: 

March 1, 2022

Author(s):

Ahmed T. Omar and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

119

Issue:

2

Abstract:

This paper investigates the structural performance of large-scale lightweight self-consolidating concrete (LWSCC) and lightweight vibrated concrete (LWVC) beams made with expanded slate coarse aggregates (ESCAs) and expanded slate fine aggregates (ESFAs) under flexural loads. Nine large-scale concrete beams were cast with different types of lightweight aggregate (either ESCA or ESFA), coarse-to-fine aggregate ratios (0.5 to 1.5), and total binder contents (550 and 600 kg/m3 [34.3 and 37.5 lb/ft3]). The structural performance of the tested beams was assessed based on the characteristics of the load-deflection response, cracking pattern, displacement ductility, energy absorption, cracking moment, and ultimate flexural strength. The reliability of code-based expressions in predicting the cracking and ultimate moment capacity of the tested beams was also investigated in this study. The results indicated that using ESFA better improved the beam’s cracking moment capacity, deformability, ductility, and energy absorption capacity compared to using ESCA. Although LWSCC exhibited a lower modulus of elasticity than normal-weight SCC, the deflection values observed in the LWSCC beams under service loads were well within the allowable limit provided by BS 8110. The measured crack widths at the service loads for all tested beams ranged from 0.20 to 0.26 mm (0.008 to 0.01 in.), satisfying the limits proposed by ACI 318, CSA A23.3, and BS 8110 design codes for durability aspects.

DOI:

10.14359/51734200


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: 

21-239

Date: 

January 1, 2022

Author(s):

Osama Al-Qassag, Ryan Brettmann, David Darwin, Matthew O’Reilly, and Rouzbeh Khajehdehi

Publication:

Materials Journal

Volume:

119

Issue:

1

Abstract:

A test procedure was developed to evaluate the effect of different techniques to limit settlement cracking over reinforcing steel with low concrete cover. Various specimen configurations and methods of finishing and curing were investigated. It was found that a clear cover of 1-1/8 in. (29 mm) over a No. 6 (No. 19) bar and covering the specimens after placement with sloped hard plastic enclosed in plastic sheeting provided a suitable method for obtaining clearly visible settlement cracks for concrete with slumps ranging from under 2 in. (50 mm) to over 8 in. (205 mm). The test specimen was then used to evaluate the effectiveness of a rheology-modifying admixture and four types of synthetic fibers on settlement cracking. Eighty-eight concrete batches were tested for mixtures with a cement paste (cement and water) content of 27 percent by volume and a water-cement ratio (w/c) of 0.45. The results show that the addition of the rheology-modifying admixture or fibers greatly reduces settlement cracking over reinforcing steel with low concrete cover.

DOI:

10.14359/51734302


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