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International Concrete Abstracts Portal

Showing 1-5 of 327 Abstracts search results

Document: 

19-354

Date: 

September 1, 2020

Author(s):

Edward G. Moffatt, Michael D. A. Thomas, Andrew Fahim, and Robert D. Moser

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This paper presents the durability performance of ultra-high-performance concrete (UHPC) exposed to a marine environment for up to 21 years. Concrete specimens (152 x 152 x 533 mm [6 x 6 x 21 in.]) were cast using a water-cementitious materials ratio (w/cm) in the range of 0.09 to 0.19, various types and lengths of steel fibers, and the presence of conventional steel reinforcement bars in select mixtures. Laboratory testing included taking cores from each block and determining the existing chloride profile, compressive strength, electrochemical corrosion monitoring, and microstructural evaluation. Regardless of curing treatment and w/cm, the results revealed that UHPC exhibits significantly enhanced durability performance compared with typical high-performance concrete (HPC) and normal concretes. UHPC prisms exhibited minimal surface damage after being exposed to a harsh marine environment for up to 21 years. Chloride profiles revealed penetration to a depth of approximately 10 mm (0.39 in.) regardless of exposure duration. Electrochemical corrosion monitoring also showed passivity for reinforcement at a cover depth of 25 mm (1 in.) following 20 years.

DOI:

10.14359/51727022


Document: 

19-504

Date: 

September 1, 2020

Author(s):

C. Gunasekera, W. Lokuge, M. Keskic, N. Raj, D. W. Law, and S. Setunge

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

So far, alkali-activated concrete has primarily focused on the effect of source material properties and ratio of mixture proportions on the compressive strength development. A little research has focused on developing a standard mixture design procedure for alkali-activated concrete for a range of compressive strength grades. This study developed a standard mixture design procedure for alkali-activated slag-fly ash (low-calcium, Class F) blended concrete using two machine learning techniques: artificial neural networks (ANN) and multivariate adaptive regression spline (MARS). The algorithm for the predictive model for concrete mixture design was developed using MATLAB programming environment by considering the five key input parameters: water/solid ratio, alkaline activator/ binder ratio, Na-Silicate/NaOH ratio, fly ash/slag ratio, and NaOH molarity. The targeted compressive strengths ranging from 25 to 45 MPa (3.63 to 6.53 ksi) at 28 days were achieved with laboratory testing using the proposed machine learning mixture design procedure. Thus, this tool has the capability to provide a novel approach for the design of slag-fly ash blended alkali-activated concrete grades matching to the requirements of in-place field constructions.

DOI:

10.14359/51727019


Document: 

19-451

Date: 

September 1, 2020

Author(s):

Chengjun Yue, Hongfa Yu, Haiyan Ma, Qiquan Mei, Jinhua Zhang, and Yadong Zhang

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The objective of this paper is to study the mechanical properties of coral aggregate seawater concrete (CASC) and sisal fiber coral aggregate seawater concrete (SFCASC) under monotonic load. Based on the theory of rich slurry concrete, the authors prepared a CASC with compressive strength greater than 70 MPa. Uniaxial compression testing was carried out by using an electro-hydraulic servo device. The results showed that the brittleness of CASC was greater than that of ordinary portland concrete (OPC). Sisal fiber can improve its brittleness obviously, while the increase in compressive strength is not significant—SFCASC is only 4.6% higher than CASC. The mechanism of CASC interface enhancement was analyzed from the microscopic perspective. A mathematical model composed of piecewise curvilinear functions was formulated to describe the mechanical properties of CASC. The experimental results validated the model, and showed that the model can better describe the monotonic stress-strain relationship of CASC.

DOI:

10.14359/51726999


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: 

18-339

Date: 

September 1, 2020

Author(s):

Morteza Khatibmasjedi, Sivakumar Ramanathan, Prannoy Suraneni, and Antonio Nanni

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The use of seawater as mixing water in reinforced concrete (RC) is currently prohibited by most building codes due to potential corrosion of conventional steel reinforcement. The issue of corrosion can be addressed by using noncorrosive reinforcement, such as glass fiber-reinforced polymer (GFRP). However, the long-term strength development of seawater-mixed concrete in different environments is not clear and needs to be addressed. This study reports the results of an investigation on the effect of different environments (curing regimes) on the compressive strength development of seawater-mixed concrete. Fresh properties of seawater-mixed concrete and concrete mixed with potable water were comparable, except for set times, which were accelerated in seawater-mixed concrete. Concrete cylinders were cast and exposed to subtropical environment (outdoor exposure), tidal zone (wet-dry cycles), moist curing (in a fog room), and seawater at 60°C (140°F) (submerged in a tank). Under these conditions, seawater-mixed concrete showed similar or better performance when compared to reference concrete. Specifically, when exposed to seawater at 60°C (140°F), seawater-mixed concrete shows higher compressive strength development than reference concrete, with values at 24 months being 14% higher. To explain strength development of such mixtures, further detailed testing was done. In this curing regime, the seawater-mixed concrete had 33% higher electrical resistivity than the reference concrete. In addition, the reference concrete showed calcium hydroxide leaching, with 30% difference in calcium hydroxide values between bulk and surface. Reference concrete absorbed more fluid and had a lower dry density, presumably due to greater seawater absorption. Seawater-mixed concrete performed better than reference concrete due to lower leaching because of a reduction in ionic gradients between the pore solution and curing solution. These results suggest that seawater-mixed concrete can potentially show better performance when compared to reference concrete for marine and submerged applications.

DOI:

10.14359/51725973


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