International Concrete Abstracts Portal

ABOUT THE INTERNATIONAL CONCRETE ABSTRACTS PORTAL

  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal

Showing 1-10 of 484 Abstracts search results

Document: 

18-311

Date: 

July 1, 2019

Author(s):

Saif Al-Shmaisani, Ryan D. Kalina, Raissa Douglas Ferron, and Maria C. G. Juenger

Publication:

Materials Journal

Volume:

116

Issue:

4

Abstract:

With the availability of ASTM C618 Class F fly ash decreasing, fly ash suppliers are working to find materials to meet demand by beneficiating ashes that do not comply with specifications and reclaiming ponded or landfilled ashes. The performance of three beneficiated and two reclaimed fly ashes was evaluated in this study by testing: 1) workability of paste, mortar, and concrete; 2) pozzolanic activity using isothermal calorimetry, portlandite consumption, and compressive strength of mortar and concrete; and 3) the ability to suppress expansion due to alkali-silica reaction and sulfate attack. Mixtures containing the fly ashes were compared against control mixtures containing portland cement and either a “production” fly ash or an inert quartz filler. All the beneficiated and reclaimed fly ashes are able to perform similarly to a production Class F fly ash, with differences in performance generally linked to particle size and shape following grinding.

DOI:

10.14359/51716713


Document: 

18-309

Date: 

July 1, 2019

Author(s):

X. Wirth, D. Benkeser, N. N. Nortey Yeboah, C. R. Shearer, K. E. Kurtis, and S. E. Burns

Publication:

Materials Journal

Volume:

116

Issue:

4

Abstract:

Due to changes in energy production and increased emissions regulations, fly ashes that meet specifications for concrete production are becoming increasingly limited in North America. Woody biomass ash, ash from coal that has been co-fired with small amounts of biomass, and previously geologically disposed, weathered coal fly ashes are each vast and geographically distributed potential sources which could augment the limited supply of “on-spec” or ordinary fly ash. This study characterizes a range of these alternative ash sources to assess if they fulfill the physical and chemical requirements and the strength performance index in ASTM C618. Changes to ASTM C618 that address the current fly ash production environment are recommended, including broadening the definition of fly ash to allow for reclaimed weathered ashes, co-fired ashes, and blended ashes that meet prescriptive and performance specifications.

DOI:

10.14359/51716712


Document: 

18-248

Date: 

July 1, 2019

Author(s):

Yin Shen, Taiyu Song, Guoping Li, CS Walter Yang, and David W. Scott

Publication:

Structural Journal

Volume:

116

Issue:

4

Abstract:

Horizontally curved concrete girder bridges have been widely used in urban viaducts and overpasses across the world. When designing these structures, it is necessary to estimate the maximum deflections under service loads to satisfy requirements of the serviceability limit state. Because of twist due to torsion in curved concrete girders, the maximum deflection needs to take into account the effect of torsional twist, which has not been considered in previous research. Based on the concept of effective torsional stiffness, a new method is proposed for calculating post-cracking twist angles in curved concrete girders. The proposed method in combination with the effective moment of inertia method can accurately predict maximum deflections in curved concrete girders. The simplicity of the proposed method is illustrated in an example. The calculated central deflections and twist angles are compared with experimental data obtained from previous tests that cover curved box-section and solid-section non-prestressed and prestressed concrete beams. The proposed method provides satisfactory predictions in terms of twist angles until the first yielding of reinforcement. The variations between the calculated and measured twist angles and maximum deflections are within ±10% and ±20%, respectively. The results of this study indicate that deflection formulas from the ACI 318-14 Code and the AASHTO LRFD Bridge Design Specifications may produce non-conservative results for curved concrete girders under certain loading conditions.

DOI:

10.14359/51715566


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: 

18-149

Date: 

January 1, 2019

Author(s):

Ryan D. Kalina, Saif Al-Shmaisani, Raissa Douglas Ferron, and Maria C. G. Juenger

Publication:

Materials Journal

Volume:

116

Issue:

1

Abstract:

ASTM C618 is used to qualify fly ash and natural pozzolans for use in concrete and for sale to the concrete industry. This study tests the notion that ASTM C618 does not adequately qualify natural pozzolans for use in concrete, with the primary concern that ASTM C618 has the potential to provide “false positives” for inert materials. Pozzolanicity tests and the tests outlined in ASTM C618 were performed on a variety of natural materials, including those that were known to be pozzolanic or inert and those with unknown pozzolanicity. Compressive strength testing at a fixed water-cementitious materials ratio (w/cm) was also performed on the materials, and the results were compared against the results of the strength activity index (SAI) from ASTM C618, which has a variable w/cm. This study proves that inert natural minerals passed ASTM C618 for a Class N natural pozzolan for use in concrete, suggesting that the standard is inadequate.

DOI:

10.14359/51712243


Document: 

15-345

Date: 

November 1, 2018

Author(s):

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

Publication:

Structural Journal

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:

Materials Journal

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:

Structural Journal

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:

Structural Journal

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: 

18-231

Date: 

May 1, 2018

Author(s):

Chunyu Qiao, Mehdi Khanzadeh Moradllo, Hope Hall, M. Tyler Ley, and W. Jason Weiss

Publication:

Materials Journal

Volume:

116

Issue:

3

Abstract:

This paper studies the influence of air content on the electrical resistivity and formation factor of concrete as these measures are often used in specifications for acceptance and payment. Experimental measurements are conducted on 30 air-entrained concretes with three water-cement ratios (w/c = 0.40, 0.45, and 0.50) over a large range of air contents (2.5 to 9.0%). The porosity of the concrete is measured, which is comparable to the theoretical estimation from the Powers-Brownyard model. Electrical resistivity measurements are performed on saturated concrete samples, and samples submerged in simulated pore solutions. The samples submerged in a bucket of simulated pore solution achieve a degree of saturation that relates to the filling of matrix pores, (that is, the Nick Point). The degree of saturation at the Nick Point (SNK) decreases as the air content increases. A formation factor (FSAT) is calculated for the saturated concrete, as well as the apparent formation factor FNK for the samples submerged which reach Nick Point saturation (SNK) in the simulated pore solution. As the air content increases, FSAT decreases due to the increased porosity (air voids) that are filled with conductive fluid, while FNK is independent on the air content (as the air voids are filled with nonconductive air). As the w/c increases, both FSAT and FNK decrease due to the increased porosity and connectivity. For the concrete with the same w/c, the addition of a high-range water-reducing admixture (HRWRA) results in higher values of FSAT and FNK due to the refined microstructure in mixtures containing HRWRA. A saturation function is used to provide a powerful tool in quality control to back-calculate FSAT that relates to different transport properties.

DOI:

10.14359/51714506


12345...>>

Results Per Page