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International Concrete Abstracts Portal

Showing 1-5 of 478 Abstracts search results

Document: 

15-345

Date: 

November 1, 2018

Author(s):

André R. Barbosa, David Trejo, and Drew R. Nielson

Publication:

Volume:

115

Issue:

6

Abstract:

There is interest in using high-strength steel (HSS) reinforcing bars in many concrete design applications. HSS reinforcement has the potential to decrease construction costs and reinforcement congestion. However, the design value of HSS reinforcing bars for concrete-concrete shear-friction interfaces is currently limited to a nominal yield strength of 60 ksi (420 MPa) in both bridge and building code provisions. In part, this is due to the limited information on the performance of HSS reinforcing bars in concrete shear interfaces. This paper presents new data on the performance of shear-friction interfaces containing Grade 80 (550) HSS reinforcing bars. The results of five push-off test specimens constructed using reinforcing steel meeting ASTM A706 Grade 80 (550) specifications and five push off test specimens using reinforcing steel meeting ASTM A706 Grade 60 (420) specifications are presented. All specimens were reinforced with No. 5 (No. 16M) reinforcing bars across the shear interface and designed according to current AASHTO design equations. Results indicate that the specimens containing the HSS reinforcing bars across the interface exhibited higher peak forces and higher post-peak sustained interface shear forces. Results indicate that as long as the reinforcing bars yield, Grade 80 (550) HSS may be used at its full design yield stress in shear-friction applications.

DOI:

10.14359/51710885


Document: 

17-442

Date: 

September 1, 2018

Author(s):

Xuhao Wang, Peter Taylor, Ezgi Yurdakul, and Xin Wang

Publication:

Volume:

115

Issue:

5

Abstract:

Slipform paving is a road construction process where concrete is extruded by a paver that forms the stiff, fresh concrete into the desired slab shape. Slipform paving is especially suitable for time-sensitive projects requiring high productivity, as it allows placement of 65 to 100 m3 (85 to 130 yds) of concrete per hour. Mixture proportioning for slipform paving applications has often been based on recipes or previous mixtures rather than based on developing proportions for the specific needs of the project using local material. Therefore, a performance-based mixture proportioning approach is needed to balance the target performance requirements for workability, strength, durability, and cost effectiveness for a given project specification. The aim of this study was to develop an innovative performance based mixture proportioning method by analyzing the relationships between the selected mixture characteristics and their corresponding effects on concrete performance. The proposed method provides step-by-step instructions to guide the selection of required aggregate and paste systems based on the performance requirements of slipform pavements.

DOI:

10.14359/51702351


Document: 

17-352

Date: 

September 1, 2018

Author(s):

Vasileios Papadopoulos, Juan Murcia-Delso, and P. Benson Shing

Publication:

Volume:

115

Issue:

5

Abstract:

This paper presents results of an investigation on the development of headed bars extending from a column into the slab of a reinforced concrete slab bridge. Three full-scale slab-column specimens were tested under quasi-static cyclic lateral loading to determine the minimum embedment length required for the headed bars to develop their full tensile capacity, and the reinforcement details needed in the slab-column joint region to prevent premature anchorage failure, when a plastic hinge forms at the top of the column. The experimental results showed that for 5000 psi (34.5 MPa) concrete and Grade 60 steel, a development length equal to 11 times the bar diameter is adequate for headed bars in slab-column joints designed according to Caltrans specifications with a minimum of 2 in. (50.8 mm) of clear concrete cover. Specimens with shorter embedment lengths were able to develop the moment capacity of the columns and showed significant ductility, but exhibited moderate to severe punching cracks in the cover concrete of the slabs. Finite element analyses of slab-column assemblies showed that punching damage can be eliminated by increasing the concrete cover above the bar heads.

DOI:

10.14359/51702247


Document: 

16-348

Date: 

July 1, 2018

Author(s):

Caitlin M. Tibbetts, Michael C. Perry, Christopher C. Ferraro, and H. R. (Trey) Hamilton

Publication:

Volume:

115

Issue:

4

Abstract:

The structural design of concrete is typically based on service limit states and uses the modulus of elasticity as a design parameter. However, the modulus of elasticity of concrete used for the design of structures is typically determined indirectly using specified compressive strength. This research investigated the differences between the physical and empirically based relationships of the modulus of elasticity and compressive strength of concrete. Concrete incorporating various types of coarse aggregate was evaluated with particular emphasis on limestone from Florida formations, better known as limerock. The goal of this research was to establish the accuracy of coarse aggregate correction factors used for predicting the modulus of elasticity of concrete. It was found that a value of 1.0, rather than 0.9, was appropriate for the correction factor for Florida limerock; the current structural design guidelines used by the Florida Department of Transportation have revised the specifications to reflect this finding.

DOI:

10.14359/51701914


Document: 

16-372

Date: 

May 1, 2018

Author(s):

Jun Ki Lee

Publication:

Volume:

115

Issue:

3

Abstract:

This study investigates the transfer length of 0.6 in. (15.4 mm) Grade 350 (2400 MPa) strand in 11.6 ksi (80 MPa) pretensioned concrete members. The test specimens were fabricated considering an accelerated construction scheme including gradual releasing and strand debonding, along with steam curing to achieve three initial concrete compressive strengths (fci′) of 5.8, 8.7, and 11.6 ksi (40, 60, and 80 MPa). At the release, the longitudinal strain profiles of both strand and concrete were measured using a series of electrical resistance strain gauges (ERSGs) to determine the transfer length. The strain profiles of the strands were in good agreement to those of the concrete and clearly presented the prestress bond transfer from the strand to the concrete. The experimental results indicate that the transfer length of high-strength concrete pretensioned members with Grade 350 strands is well-correlated to the initial compressive strength of concrete (fci′). Also, the transfer length is conservatively predicted using the design provisions in the ACI 318 and AASHTO specifications.

DOI:

10.14359/51701295


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