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Showing 1-5 of 124 Abstracts search results

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: 

19-137

Date: 

March 1, 2020

Author(s):

Assem A. A. Hassan

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

This study investigated the structural behavior of large-scale rubberized self-consolidating engineered cementitious composite (SCECC) beams designed to fail in shear. Specifically, the experimental program focused on the use of crumb rubber (CR) and powder rubber (PR) in SCECC as a partial replacement of silica sand at replacement levels of 0, 10, 20, and 30% (by volume). All cast SCECC, SCECC-CR, and SCECC-PR beams were compared with the performance of normal self-consolidating concrete (SCC) beam (containing coarse aggregates) at comparable compressive strength. The results obtained from this study included the fresh and mechanical properties of the developed mixtures, in addition to load-deflection curves, cracking behavior, first flexural crack load, diagonal crack load, ultimate load, ductility, and energy absorption capacity of the tested beams. The performance of some code-based equations in estimating the ultimate capacity and cracking moment of the tested beams was also evaluated. The results showed that all SCECC, SCECC-CR, and SCECC-PR beams exhibited higher performance compared to that exhibited by the normal SCC beam. However, the inclusion of either CR or PR in SCECC led to a reduction in the first crack load, diagonal crack, and ultimate load capacity of SCECC. The ductility and energy absorption capacity of SCECC was found to increase when 10% CR was introduced, while further increase in the percentage of CR decayed both the ductility and energy absorption capacity. On the other hand, the use of PR with up to 30% contributed to improving the deformability of the SCECC beam with no significant loss in its load-carrying capacity, thus providing a sustainable composite with higher ductility and energy absorption.

DOI:

10.14359/51720300


Document: 

18-193

Date: 

January 1, 2020

Author(s):

I. González-Taboada, B. González-Fonteboa, F. Martínez-Abella, and S. Seara-Paz

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

A rheograph is a plastic viscosity-yield stress diagram that systematically reveals the effects of diverse changes on the rheological behavior of the cement-based suspension. In this work, the time-dependent rheological behavior of self-consolidating recycled concrete (SCRC) and conventional self-consolidating concrete (SCC) was compared and the effect of changes in material quantities was assessed using different rheographs. The developed analysis leads to the conclusion that differences obtained depend on the quantity of water compensated in the mixing protocol to take into account the high absorption of recycled aggregates. This fact determines the region of the curves “rheological variations – effective water to cement ratio” where concretes are designed. The high slope region of these curves will be reached when high percentages of recycled aggregate are used, when SCRC is designed with a low water-cement ratio (w/c), and/or when long-term self-consolidating behavior is measured. In these cases, a different time-dependent rheological behavior is expected from an SCRC than from an SCC; otherwise, the rheological behavior over time of an SCRC will be similar to that of an SCC.

DOI:

10.14359/51720289


Document: 

18-563

Date: 

January 1, 2020

Author(s):

Hisham Qasrawi

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

Green self-consolidating concrete (SCC) is the aim of the construction industry nowadays. The accumulation of steel slag wastes causes severe environmental problems. These wastes can be recycled and replace natural aggregates, resulting in sustainable green SCC. In this research, natural aggregates in SCC are replaced, wholly or partly, by steel slag coarse aggregates (SSA) that were produced by crushing by-product boulders obtained from the steel industry. The fresh properties, (workability, stability, and bleeding), can all be attained when the suitable amount of SSA is used. SSA concrete increased the air content. Higher values are reported under hot conditions. The study shows that the 28-day compressive strength of SCC increased by approximately 10% when natural aggregate is replaced by SSA. However, adverse effects are reported when the ratio of SSA is more than 50%. Under hot weather, the strength was less and the optimum replacement ratio is 25%. The tensile strength of SCC increased by approximately 20% when natural aggregate is replaced by SSA. Adverse effects are reported when the ratio of SSA is more than 75%. Under hot weather, the same is observed but the value of the 28-day strength was lower. Special strength development mathematical relations are obtained and discussed. The modulus of elasticity increased by the increase in slag. The optimum value was at 50% for both conditions. An adverse effect is observed when the ratio of slag exceeds 75%. The drying shrinkage of concrete was lower for concrete containing SSA.

DOI:

10.14359/51719072


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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