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International Concrete Abstracts Portal

Showing 1-5 of 32 Abstracts search results

Document: 

19-358

Date: 

September 1, 2020

Author(s):

Christoph Mahrenholtz and Akanshu Sharma

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

The world becomes ever smaller and thus the global construction industry moves closer together. For this reason, civil engineers are looking for possibilities to harmonize design—for example, in the field of reinforced concrete structures. The streamlining would ease working in an international context and could offer opportunities for optimization: harmonization allows the identification of the technically best and most economical solution. This also holds for the provisions to calculate the development length of deformed reinforcing bars which, to date, differ notably from code to code. It is not reasonable that local codes define different development lengths for identical situations in terms of geometry and material used. This paper analyzes the provisions for the calculation of the development lengths according to internationally selected national codes as a basis for this discussion.

DOI:

10.14359/51725782


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


Document: 

18-319

Date: 

September 1, 2019

Author(s):

Jose Pacheco

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

The presence of uncontrolled or unexpected nonstructural cracking in reinforced concrete structures generally leads to conflict and disputes. The current industry practice aims to prevent or mitigate the presence of cracking at early ages (that is, plastic shrinkage, thermally induced cracking) or due to volumetric changes (restrained or drying shrinkage). However, cracking of concrete can still occur and lead to questioning the durability of concrete with prolonged service life expectations such as bridge decks, piers, or waterfront structures, to name a few. The effect of cracks on chloride penetration has been thoroughly studied, and evidence of the effect of cracks on accelerated ingress of chlorides is well established. Structural codes and guides, on the other hand, consider that the integrity of the concrete element is not significantly affected as long as the crack width does not exceed a recommended limit based on exposure conditions. Similarly, service life predictions based on chloride ingress modeling disregard the effect of cracks. Because crack-free concrete cannot be guaranteed, service life predictions that neglect the effect of cracks can be significantly inaccurate. A simplified approach is presented in this paper, where a correction to the chloride diffusion coefficient of concrete is performed to account for the effect of cracks. This correction is similar, in principle, to the so-called aging or decay coefficient in concrete. Results of Monte Carlo simulations on chloride ingress and estimations of the time-to-corrosion initiation are presented and discussed. Results indicate that a decrease of the reliability index (β), or an increase in the probability of failure (pf), can be calculated when accounting for the effect of cracks.

DOI:

10.14359/51716835


Document: 

18-235

Date: 

May 1, 2019

Author(s):

Nabila Zemour, Alireza Asadian, Ehab A. Ahmed, Brahim Benmokrane, and Kamal H. Khayat

Publication:

Materials Journal

Volume:

116

Issue:

3

Abstract:

This study investigated the effect of several parameters on the bond behavior of spliced glass fiber-reinforced polymer (GFRP) reinforcing bars in self-consolidating concrete (SCC) and normal concrete (NC). A total of 21 full-scale reinforced concrete (RC) beams were tested under four-point bending up to failure. Six influential design Code parameters were investigated, specifically concrete type, casting position, casting height, splice length, beam height, and longitudinal reinforcement type. The experimental results and observations reveal that the SCC and NC beams behaved similarly in terms of failure load, crack pattern, failure mode, and load-deflection response. The bond strength of the spliced bars in the SCC beams was slightly lower than that of the NC. The SCC beams exhibited lower reductions in bond strength than the NC beams due to the casting-position effect. In addition, the experimental findings confirm that the top-bar factor of 1.3, recommended in current design codes, can provide adequate safety margins for GFRP-reinforced NC and SCC beams with a splice length of 40db. Furthermore, the threshold depth of 305 mm (12 in.) provided in current design codes and guidelines appears to be reasonably safe.

DOI:

10.14359/51714459


Document: 

18-144

Date: 

March 1, 2019

Author(s):

Yail J. Kim and Jun Wang

Publication:

Materials Journal

Volume:

116

Issue:

2

Abstract:

This paper presents the development of cost-effective ultra-high performance concrete (UHPC) using various silica admixtures. With the aim of achieving a specified compressive strength of 138 MPa (20 ksi), a UHPC mixture is formulated. The research program consists of three phases: 1) suitable constituents are identified based on the reproduction tests of nine existing UHPC mixtures selected from literature; 2) a prototype mixture design is developed; and 3) the performance of the prototype UHPC is assessed through an experimental parametric study. The implications of various constituent types are examined with an emphasis on silica compounds (silica fume, silica powder, silica sand, finer silica sand, pyrogenic silica, and precipitated silica), including steel and polypropylene fibers. The distribution of granular particles is characterized by digital microscopy alongside an image processing technique. Benchmark tests employing the nine mixtures demonstrate that silica sand and finer silica sand perform better than silica powder from a strength perspective, and the inclusion of steel fibers rather than polypropylene fibers is recommendable. Although heat curing increases concrete strength, the prototype UHPC is designed with conventional moisture curing because of practicality in the field. The steel fibers increase the flexural capacity of the UHPC more than 60% relative to the UHPC mixed without fibers, and result in a gradual failure mode. The bulk density of silica fume influences the strength gain of the UHPC at 7 days, beyond which its effect becomes insignificant. The use of pyrogenic silica and precipitated silica is not suggested. The applicability of the modulus of rupture equations specified in published specifications and codes is assessed, and new equations are proposed for the developed UHPC mixture using randomly generated statistical data. Cost analysis shows that the prototype UHPC is up to 74% less expensive than commercial products.

DOI:

10.14359/51714450


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