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International Concrete Abstracts Portal

Showing 1-5 of 30 Abstracts search results

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


Document: 

17-232

Date: 

May 1, 2018

Author(s):

Shahab Samad, Attaullah Shah, and Mukesh C. Limbachiya

Publication:

Materials Journal

Volume:

115

Issue:

3

Abstract:

Limited research work exists on assessment of punching shear of reinforced concrete (RC) flat slabs made with blended cement incorporating ground-granulated blast-furnace slag (GGBS). This research is aimed at analyzing the punching shear strength of RC flat slabs cast from blended cement having GGBS in different proportions as partial replacement of cement. Four flat slabs supported on the ends were tested under column load such that one flat slab was cast from normal concrete with no GGBS and the remaining three flat slabs were cast with 30, 40, and 50% replacement of cement by GGBS. Experimental punching shear, midspan deflections, strain in the steel bars, and cracking pattern of the slabs were determined. The results of punching shear of flat slabs from the tests were compared with the nominal punching shear capacities proposed by BS 8110, BS EN1992-1-1/EC2, and ACI 318. The provisions of these building codes for the punching shear were observed as safe and conservative for the RC flat slab made from blended cement incorporating GGBS.

DOI:

10.14359/51702012


Document: 

17-083

Date: 

March 1, 2018

Author(s):

Nakin Suksawang, Salam Wtaife, and Ahmed Alsabbagh

Publication:

Materials Journal

Volume:

115

Issue:

2

Abstract:

This paper determines the effect of discrete fibers on the elastic modulus of concrete and cement composites. Five types of discrete fibers consisting of steel, polypropylene, macro-polyolefin, polyvinyl alcohol (PVA), and basalt fibers were investigated. Results show that discrete fibers had little effect on elastic modulus for fiber-reinforced concrete (FRC) with coarse-to-fine aggregate ratio (C/S) greater than 1. However, for FRC with C/S smaller than 1 and fiber-reinforced cement composites (FRCCs), discrete fibers reduced the elastic modulus. Accordingly, a new elastic modulus equation is proposed to better estimate the elastic modulus of FRC with a maximum fiber volume fraction of 10%. The proposed equation was compared with existing equations from other codes, including American, Japanese, Korean, Norwegian, and European codes, as well as equations proposed by other researchers. These equations were evaluated using more than 400 data points taken from the experimental program and other literatures. The proposed equation provides the most accurate prediction for the elastic modulus of FRC and FRCC with a coefficient of variation of 15% as compared to 32% using ACI 318 equation for C/S ≤ 1.

DOI:

10.14359/51701920


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