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International Concrete Abstracts Portal

Showing 1-5 of 126 Abstracts search results

Document: 

19-158

Date: 

September 1, 2020

Author(s):

Faez Sayahi, Mats Emborg, Hans Hedlund, and Andrzej Cwirzen

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This research studies the effect of retarder, accelerator, stabilizer, air-entraining agent, and shrinkage-reducing admixture (SRA) on plastic shrinkage cracking in self-consolidating concrete (SCC). The main objective is to identify the dominant cracking cause—that is, plastic settlement or plastic shrinkage—in an SCC containing a particular admixture. During experimentation, crack-free concretes were achieved by adding air-entraining agent and SRA, while accelerator and retarder increased the crack area. The impact of admixtures on the cracking mechanism was identified by comparing the respective vertical and horizontal deformations. It was observed that the crack-free concretes had moderate settlement and horizontal shrinkage, while the cracked specimens exhibited significant deformation either vertically or horizontally.

DOI:

10.14359/51724623


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: 

19-137

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: 

18-563

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


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