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International Concrete Abstracts Portal

Showing 1-5 of 94 Abstracts search results

Document: 

19-312

Date: 

September 1, 2020

Author(s):

Ahmed T. Omar, Mohamed M. Sadek, and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This study aims to evaluate the impact resistance and mechanical properties of a number of developed lightweight self-consolidating concrete (LWSCC) mixtures under cold temperatures. To achieve LWSCC mixtures with minimum possible density, the authors explored different replacement levels of normalweight fine or coarse aggregates by lightweight fine and coarse expanded slate aggregates. The studied parameters included testing temperature (+20°C, 0°C, and –20°C), type of lightweight aggregate (either fine or coarse expanded slate aggregates), binder content (550 and 600 kg/m3 [34.3 and 37.5 lb/ft3]), coarse-to-fine (C/F) aggregate ratio (0.7 and 1.0), and the use of polyvinyl alcohol (PVA) fibers (fibered and nonfibered mixtures). The results indicated that for all tested mixtures, decreasing the temperature of concrete below room temperature significantly improved the mechanical properties and impact resistance. Increasing the percentage of lightweight fine or coarse aggregate in the mixture showed more improvement in the mechanical properties and impact resistance under cold temperatures. However, the failure mode of all tested specimens appeared to be more brittle under subzero temperatures. It was also observed that the inclusion of PVA fibers helped to compensate for the brittleness that resulted from decreasing the temperature, and it further enhanced the impact resistance and mechanical properties under low temperatures.

DOI:

10.14359/51725975


Document: 

19-232

Date: 

May 1, 2020

Author(s):

Mohamed M. Sadek, Mohamed K. Ismail, and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This study aimed to optimize the use of fine and coarse expanded slate lightweight aggregates in developing successful semi-lightweight self-consolidating concrete (SLWSCC) mixtures with densities ranging from 1850 to 2000 kg/m3 (115.5 to 124.9 lb/ft3) and strength of at least 50 MPa (7.25 ksi). All SLWSCC mixtures were developed by replacing either the fine or coarse normal-weight aggregates with expanded slate aggregates. Two additional normal-weight self-consolidating concrete mixtures were developed for comparison. The results indicated that due to the challenge in achieving acceptable self-consolidation, a minimum binder content of at least 500 kg/m3 (31.2 lb/ft3) and a minimum water-binder ratio (w/b) of 0.4 were required to develop successful SLWSCC with expanded slate. The use of metakaolin and fly ash were also found to be necessary to develop successful mixtures with optimized strength, flowability, and stability. The results also showed that SLWSCC mixtures made with expanded slate fine aggregate required more high-range water-reducing admixture than mixtures made with expanded slate coarse aggregate. However, at a given density, mixtures developed with expanded slate fine aggregate generally exhibited better fresh properties in terms of flowability and passing ability, as well as higher strength compared to mixtures developed with expanded slate coarse aggregate.

DOI:

10.14359/51722407


Document: 

19-205

Date: 

May 1, 2020

Author(s):

Rabab Allouzi, Aya Al Qatawna, and Toqa Al-Kasasbeh

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Foamed concrete is currently studied to investigate its feasibility to be used structurally to produce a lightweight concrete mixture that is workable and has sufficient mechanical properties. This encouraged this research to design a foamed concrete mixture to be used in the construction industry. The main parameters that shall be satisfied for structural use are the workability, density less than 1900 kg/m3, and minimum cylinder compressive strength of 17 MPa (2500 ksi) based on ACI 213R. In this paper, 14 different foamed concrete mixtures are designed and tested to investigate their applicability. As fly ash quality affects foamed concrete permeability and as foamed concrete has low resistance to concentrated stresses, the proposed mixtures do not contain fly ash and are reinforced with polypropylene (PP) fibers. The effect of water-cement ratio (w/c), sand-cement ratio (s/c), PP fibers content, and the foam agent content are investigated. It is found that the compressive strength increases with the increase in density. The optimum s/c is 1:1, w/c is 0.4, and the PP fibers content is 1% by weight of cement. A relationship of splitting tensile strength relative to compressive strength is proposed.

DOI:

10.14359/51722405


Document: 

19-035

Date: 

January 1, 2020

Author(s):

Aravind Tankasala and Anton K. Schindler

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

In this project, the effect of using lightweight aggregate (expanded slate) on the early-age cracking tendency of mass concrete mixtures was evaluated. Concretes representative of mass concrete mixtures—namely, normal-weight concrete, internally cured concrete, sand-lightweight concrete, and all-lightweight concrete—at two different water-cementitious materials ratios (0.38 and 0.45) were tested in cracking frames from the time of setting until the onset of cracking. The development of early-age concrete stresses caused by autogenous and thermal shrinkage effects were measured from setting to cracking. The behavior of concretes containing lightweight aggregates was compared with normal-weight concrete placed under temperature conditions simulating fall placement in mass concrete applications. Increasing the amount of pre-wetted lightweight aggregates in concrete results in systematic decrease in density, reduced modulus of elasticity, and reduced coefficient of thermal expansion. All these factors effectively improve the concrete’s early-age cracking resistance in mass concrete applications.

DOI:

10.14359/51719082


Document: 

18-040

Date: 

November 1, 2019

Author(s):

Sherif Yehia, Sharef Farrag, and Omar Abdelghaney

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

The durability of lightweight concrete (LWC), especially in the long term, is an essential factor for its successful implementation in structural applications. The use of supplementary cementitious materials (SCMs) and/or fibers changes the interaction between concrete constituents at a microlevel, which might improve durability. In this paper, the mechanical properties and durability aspects of fiber-reinforced, self-consolidating, high-strength, lightweight concrete were evaluated. Concrete specimens were exposed to wetting-and-drying cycles for 1 year in salt water to simulate chloride attack present in the United Arab Emirates and then were compared to control specimens. Results of the compressive strength, flexural strength, and modulus of elasticity are presented and discussed. In addition, scanning electron microscope (SEM) scans and rapid chloride permeability test (RCPT) were conducted. Results showed that the inclusion of fibers alters the microstructural features of concrete; hence, a different chloride resistance mechanism is introduced. Nevertheless, inclusion of fibers did not lead to an increase in chloride permeability. At 1 year, there was an ~3% and 10% reduction in compressive strength in the exposed plain and the fiber-reinforced mixtures, respectively, compared to the non-exposed mixtures. However, fibers significantly enhanced the flexural strength of lightweight concrete (up to an ~100% increase) compared to plain mixtures. In addition, cracks were ~80% smaller in the fiber-reinforced mixtures compared to the plain mixture.

DOI:

10.14359/51716976


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