1 BEHAVIOR COMPARISON OF PRESTRESSED …docs.trb.org/prp/16-3991.pdf · The materials used for...

BEHAVIOR COMPARISON OF PRESTRESSED CHANNEL GIRDERS FROM HIGH 1

PERFORMANCE CONCRETE AND LOCALLY DEVELOPED ULTRA-HIGH 2

PERFORMANCE CONCRETE 3

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5

6

Mark P. Manning, Corresponding Author 7

Graduate Research Assistant 8

New Mexico State University 9

Department of Civil Engineering 10

P.O. Box 30001, Las Cruces, NM 88003 11

Tel: 505-231-2043; Email: [email protected] 12

13

Brad D. Weldon, PhD 14

Assistant Professor 15





20

Michael J. McGinnis, PhD 21

Assistant Professor 22

University of Texas at Tyler 23


3900 University Blvd., Tyler, TX 75799 25


27

David V. Jauregui, PhD, PE 28

Department Head 29





34

Craig M. Newtson, PhD, PE 35

Associate Professor 36





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Word count: 5063 + 9 x 250 words = 7313 words 43

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Submission Date: November 15, 201547

mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]

Manning, Weldon, McGinnis, Jauregui, and Newtson 2

1

ABSTRACT 2

In response to the demand for sustainable and improved bridge design practices, development of 3

emerging materials like ultra-high performance concrete (UHPC) are at the forefront of structural 4

innovation. Offering significant advantages to bridge superstructure design, UHPC provides 5

advanced mechanical and durability properties including high compressive strength and increased 6

tensile capacity. With the introduction of high strength steel fibers into mixture proportions, post-7

cracking tensile and flexural tensile capacities are increased, providing greater ductility while 8

reducing or possibly eliminating the need for mild steel reinforcement. This research investigates 9

the behavioral response of full-scale prestressed bridge girders under four-point flexural loading. 10

Two channel shaped girders were designed to provide equal design moment capacity to facilitate 11

comparative analyses of performance. The first of these girders utilized non-proprietary UHPC [20 12

ksi (138 MPa)] mixture proportions consisting primarily of local materials and mixing procedures 13

and a curing regimen developed at New Mexico State University, Las Cruces, New Mexico. The 14

second girder is designed using high performance concrete [HPC, 9.5 ksi (65 MPa)] and mild steel 15

reinforcement typical of New Mexico bridge design. Digital image correlation (DIC) was used to 16

capture deformations throughout testing, creating a full field of displacements that captures tensile 17

and compressive strain behavior in the pure moment region. This investigation demonstrates the 18

advantages and improved performance of UHPC and demonstrates the contribution of steel fiber 19

reinforcement to post-cracking strength and flexural capacity. 20

21

22

23

24

Keywords: UHPC, ultra-high performance concrete, flexural girder behavior, steel fiber 25

reinforcement, bridge girders, digital image correlation. 26 27


INTRODUCTION 1 The current deterioration of the ever aging U.S. infrastructure serves as a catalyst for innovation. 2

Increased interest and demand for durable, sustainable materials and improved bridge design 3

practices has led to the development of advanced material resources. Ultra-high performance 4

concrete (UHPC) is one of these emerging structural technologies. Offering advanced mechanical 5

and durability properties, including high compressive strength and increased environmental 6

resistance, there is potential for longer structural lifespans and a corresponding reduction in 7

lifecycle environmental and economic impact (1). Increased tensile and flexural capacity is 8

achieved with the addition of high strength steel fibers while reducing the need for mild steel 9

reinforcement. The resulting structural members are smaller and lighter, requiring less structural 10

detailing and fewer members, allowing for more rapid construction and reduced lifecycle 11

maintenance. 12

Prior to widespread application of UHPC, further research is required to afford greater 13

understanding of the material and structural behavior, and to determine efficient and economical 14

means of production. By assessing the behavioral response to various load and environmental 15

conditions, design tools and recommendations for implementation of UHPC in structural design 16

may be provided. In response, researchers at New Mexico State University (NMSU) have recently 17

developed non-proprietary UHPC mixture proportions (2). Utilizing materials typical of precast 18

production and primarily local to New Mexico, the resultant material possesses the superior 19

mechanical and durability properties characteristic of UHPC (3, 4). 20

Following development and material studies, two full-scale prestressed channel girders 21

were designed to better understand the structural behavior and with the intent of future replacement 22

of a structurally deficient local bridge superstructure. Designed to provide equal moment 23

capacities, the first girder utilizes the UHPC mixture proportions developed at NMSU, and the 24

second uses high performance concrete (HPC) typical of current New Mexico bridge design. 25

Mixing procedures, casting methods, and curing regimens were developed in collaboration with a 26

local precast plant to facilitate incorporation of UHPC to normal batch plant operations without 27

changes to the batching facility. After familiarizing precasters with UHPC by means of several 28

trial batches (5), both the HPC and UHPC girders were cast and transported to NMSU for testing. 29

This investigation focuses on the behavioral response of the girders to flexural loading. Due to the 30

differences in material properties and the use of high strength steel fibers, several differences arose 31

between the UHPC and HPC designs including cross-sectional geometry and mild steel 32

reinforcement requirements. 33

34

A LOCALIZED UHPC 35 The UHPC used for this research was developed over several years at NMSU and trial tested at a 36

local precast plant, evolving to provide economic feasibility without compromising the advanced 37

qualities of the material (2, 5). For purposes of research and application, the mixture proportions 38

and curing regimen were optimized for use in precast settings. The materials used for these mixture 39

proportions are primarily obtained through local distributors in the state of New Mexico. By 40

utilizing cost effective, familiar local material constituents and developing efficient mixing, 41

casting, and curing procedures, the implementation of UHPC in existing production facilities and 42

for local bridge design may be accomplished. 43

44

Mixture Proportions 45 The advantages of UHPC are achieved in large part due to the elimination of coarse aggregates, 46


resulting in a dense and nearly impermeable concrete matrix. Consisting of seven materials 1

specifically chosen to create the dense microstructure, the UHPC used for this research produces 2

the desired material and durability properties. Granular and cementitious materials include angular 3

sand passing a No. 4 sieve [0.187 in. (4.76 mm) nominal opening], Type I/II portland cement, and 4

20% supplementary cementitious materials that include silica fume and Class F fly ash at a ratio 5

of 62.5/37.5 percent by mass. A water to cementitious materials ratio of 0.14 was used, drastically 6

less than normal or high strength concretes. Thus, a high range water reducing admixture 7

(HRWRA) was used to improve workability. 8

High strength, straight monofilament steel fibers were the final constituent of these mixture 9

proportions. These fibers have a length to diameter [0.5 in. (13 mm) to 0.008 in. (0.20 mm)] aspect 10

ratio of 65 and tensile strength of 285 ksi (1965 MPa) and meet ASTM A 820 requirements (6). 11

These fibers are engaged in the tension and shear regions, bridging micro-cracks and resisting 12

crack propagation, contributing to post-cracking strength and providing confinement in 13

compression. To improve design economy a fiber content of 1.5% by volume was used, less than 14

most commercially available products. 15

16

FULL-SCALE PRESTRESSED CHANNEL GIRDERS 17

Collaborating with the New Mexico Department of Transportation (NMDOT), this research 18

provides the preliminary design for the replacement of a deteriorating local bridge superstructure 19

using UHPC developed with local materials. The bridge currently consists of two, 25 ft (7.62 m) 20

simple spans with nine channel shaped girders per span. The new structure will incorporate one 21

span with the UHPC girder design, and the second span will use the HPC design, providing the 22

potential for long-term durability and performance studies. Due to the advantages of using UHPC 23

in both the stem and the deck, the channel shape girder was adopted for the replacement design. 24

The geometry of the cross-section takes full advantage of the high compressive strength of UHPC 25

in the deck region, as well as the increased tensile capacity throughout the girder. 26

27

Design 28 Two designs were prepared in accordance with the American Association of State Highway and 29

Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design 30

Specifications (2012), one for HPC and one for UHPC (7). The HPC girder was designed following 31

AASHTO requirements with no modifications. The compressive strength, fc, met standard 32 NMDOT mixture proportion requirements for prestressed bridge girders and used a design release 33

strength of approximately 0.75fc. Design values are summarized in Table 1. Taking advantage of 34 the properties of UHPC, changes were made to the design and described in the following sections. 35

36

UHPC Material Characterization and Compressive Strength 37

Current AASHTO standards do not include requirements or recommendations for concretes with 38

compressive strength in excess of 15 ksi (100 MPa). It was therefore necessary to determine the 39

design modulus of elasticity using Equation 1, developed through an extensive study on 40

commercially available products and found to adequately represent the material behavior of this 41

particular UHPC (4, 8). 42

43

Ec = 46200fc (psi) (1) 44 45

The modulus of rupture is significantly influenced by the addition of steel fibers to the concrete 46


matrix. Similarly, the equation for the modulus of rupture is limited to 15 ksi (100 MPa), and thus 1

not valid for UHPC. Tests have shown the modulus of rupture to consistently reach approximately 2

1.3 ksi (9.0 MPa), thus the modulus of rupture was conservatively assumed to be 1.0 ksi (7.0 MPa) 3

for design (9). 4

Based on prior material testing, conservative estimates of UHPC compressive strength 5

were selected for the time of strand release, and subsequently agreed upon with NMDOT. These 6

values are included in Table 1. 7

8

TABLE 1 Design Parameters 9

UHPC HPC

Compressive Strength at Release, (ksi) 11.0 7.0

Compressive Strength at Design, (ksi) 20.0 9.5 Depth, d (in.) 12.5 15.0

Flange Width, bf (in.) 48.0 48.0

Flange Depth, df (in.) 4.0 4.0

Stem Width, bw (in.) 6.0 7.0

Cross-sectional Area, Ac (in2) 294 346

Strand Ultimate Strength, fpu (ksi) 270 270

Mild Steel Yield Strength, fsy (ksi) 60.0 60.0 1 ksi = 6.895 MPa, 1 in. = 25.4 mm, 1 in2 = 645.16 mm2

10

Cross-Sectional Geometry 11

Although the 25 ft (7.62 m) span length was maintained for both designs, the advanced properties 12

of UHPC allowed for a 15% reduction in cross-sectional area. Referring to Table 1, the depth and 13

stem width of the UHPC specimen were reduced by 2.5 in. (65 mm) and 1.0 in. (25.4 mm), 14

respectively, in comparison to the HPC design, resulting in a smaller section requiring less material 15

(see Figure 1). 16

17

Reinforcement Layout 18

The use of steel fiber reinforcement contributes significant post-cracking tensile strength, as well 19

as notable confining action when subjected to compression, and may facilitate the reduction or 20

elimination of mild steel reinforcement. Although a single mild steel reinforcement layout that 21

meets AASHTO requirements for HPC was provided for both girder designs, the smaller UHPC 22

section would actually require additional shear reinforcement. However, previous studies have 23

shown the contribution of steel fiber reinforcement to shear capacity, and it was determined for 24

design that steel fibers would provide adequate additional shear reinforcement (10, 11). By 25

maintaining a single reinforcement layout for both design sections, it is possible to provide a direct 26

comparison of behavior. 27

As seen in Figures 1a and 1b, each design section was prestressed with six, 270 ksi (1860 28

MPa), 0.60 in. (15 mm) low-relaxation fully-bonded prestressing strands per stem. Each strand 29

was pretensioned to 202.5 ksi (1396 MPa), providing a total jacking force of approximately 527 30

kips (2345 kN). Shear reinforcement was provided in each stem in the form of No. 3 (No. 10) 31

stirrups, placed in pairs to create hoops. After satisfying bursting reinforcement requirements, 32

shear reinforcement was placed at 6 in. (152 mm) spacing in the high shear regions [24 in. (610 33

mm) from each end], then increased to 8 in. (203 mm) spacing over the remaining length of the 34

girder. The outer bar of the hoop is bent to accommodate shear keys (not present on test specimens). 35


1 (a) 2

3 (b) 4

FIGURE 1 Reinforcement layout (a) HPC cross-section and (b) UHPC cross-section 5 6

Transverse No. 5 (No. 16) bars were spaced at 6 in. (152 mm) increments along the full length of 7

the beam in the deck and extended down into the stems. Although not typical in design, alternating 8

No. 3 (No. 10) and No. 4 (No. 13) bars provide longitudinal reinforcement in the deck (see Figures 9

1a and 1b). Steel bearing plates [9 in. (230 mm)] were embedded in the stems at each end of the 10

beam at bearing locations. 11

12

Girder Production 13

Production of the full-scale girders was performed in Albuquerque, New Mexico. The first girder 14

was batched using NMDOT typical proportions for 9.5 ksi (65 MPa) minimum compressive 15

strength HPC, while the second was cast with UHPC mixture proportions according to Table 2. In 16

comparison to the 3 to 5 minutes required for batching HPC, achieving the desired consistency for 17

UHPC required mixing times of approximately 12 to 15 minutes. After batching was complete (for 18

both HPC and UHPC), concrete was transported to the casting bed using an auger delivery truck. 19

The time required for concrete placement was 20


TABLE 2 Mixture Proportions for 1 yd3 Batch of UHPC 1

Material Constituent Weight (lb)

Angular Sand 1826

Type I/II Portland Cement 1296

Silica Fume 202.5

Class F Fly Ash 121.5

Water 244.0

HRWRA 74.90

High Strength Steel Fibers 198.5 1 lb = 4.45 N

2

approximately 15 minutes. To ensure proper UHPC consolidation and steel fiber dispersion and 3

orientation, concrete was cast in layers and casting beds vibrated throughout the process. 4

Compression and modulus of rupture samples were cast with each girder and placed on the casting 5

beds to provide curing consistent with the full-scale specimens. From start to finish, UHPC 6

production time was approximately 30 minutes, only slightly longer than production time for HPC. 7

8

Curing and Detensioning 9

Previous research has demonstrated the significant contribution to UHPC compressive strength 10

provided by steam and/or dry heat curing regimens (1). Curing regimens were developed at NMSU 11

for the UHPC to take advantage of both steam and dry heat. For precast plant production, the 12

regimen was developed to accommodate the facility work schedule. The HPC girder was covered 13

with an insulated tarp and provided steam at approximately 160F (70C) for approximately 18 14 hours. Having achieved proper release compressive strength, strands were detensioned and curing 15

completed. For the UHPC specimen, the concrete was covered with an insulated tarp and the curing 16

regimen began with approximately 18 hours of propane heat at approximately 70F (22C) until 17 initial set. Steam was provided for approximately 36 hours until the end of the work week, and 18

then continued for 5 days after plant operations resumed. Due to lower than expected average 19

steam curing temperatures of 130F (55C) and scheduling issues, curing time was extended by 7 20 days, significantly longer than the normal 4 day steam heat regimen. The UHPC girder was 21

detensioned 11 days after casting, at which time full compressive strength was achieved. 22

23

24 (a) (b) 25

FIGURE 2 (a) HPC girder after curing and (b) placement of UHPC girder. 26


Due to challenges arising from the curing regimen, production methods will continue to be refined 1 for greater economy and efficiency. Investigations to determine the early-age strength development of 2

UHPC and durability properties due to various curing regimens are ongoing. 3

4

FLEXURAL TESTING 5 Experimental flexural testing was performed at the NMSU Department of Civil Engineering 6

Structural Systems and Materials Testing Laboratory (SSMTL). The testing setup and 7

instrumentation are detailed in the following sections. 8

9

Test Setup 10 The girder specimens were placed on four short reinforced concrete columns and positioned 11

beneath two, 110 kip (490 kN) capacity hydraulic actuators. Each column was provided a steel 12

column cap and 4 in. (100 mm) cylindrical steel roller support. The roller supports under one end 13

of the girder remained free to displace laterally, reducing development of axial forces. The 14

actuators were placed 24 in. (610 mm) apart, each 12 in. (305 mm) from midspan, effectively 15

creating a pure moment region. Computer controlled actuator displacement increments of 0.1 in. 16

(2.54 mm) were applied at a rate of 0.1 in./min (2.54 mm/min). Load was applied until failure and 17

recorded by load cells within the actuator loading heads. As shown in Figure 3, load was distributed 18

through steel spreader beams to 3 in. (75 mm) diameter semi-circular load points centered over 19

each stem. The load at each point was recorded with additional load cells to capture distribution 20

of loading. 21

22

Instrumentation 23 Each girder was instrumented with a range of sensors to capture the behavioral response to flexural 24

loading (see Figure 3). Electronic clinometers, also known as tiltmeters, were positioned at mid- 25

depth of the girder over each support to record beam rotation and provide a representation of the 26

27

28 FIGURE 3 Flexural testing setup and instrumentation plan (UHPC girder shown). 29


symmetry of load application. String potentiometers were placed along the longitudinal length of 1

the span on either side of the girder to measure deflection. Placement locations included quarter 2

points, midspan, and offset midspan to avoid loss of data should the primary instrument be lost 3

due to cracking at the application point. Linear variable displacement transducers (LVDTs) were 4

applied at midspan to the vertical face as well as directly below each stem to record extreme tensile 5

strain. The two LVDTs applied to the vertical face were positioned above and below the uncracked, 6

transformed neutral axis, measuring induced compression and tension through the depth of the 7

girder, making it possible to track the depth and behavior of the neutral axis in response to loading. 8

All instrumentation was connected to a data acquisition system, facilitating real time monitoring 9

and data collection throughout testing. 10

11

Digital Image Correlation 12 The presence of high strength steel fibers in UHPC creates a unique dynamic between the concrete 13

and reinforcement interface. As tensile strain is developed, steel fibers are engaged, first bridging 14

micro-cracks throughout the specimen and distributing tensile stress, then slowing the propagation 15

of macro-cracks prior to fiber pullout. Conventional instrumentation used to capture strain and 16

curvature, such as strain gauges or LVDTs, only capture strain at the point of application or are 17

otherwise limited by gauge lengths. However, advancements in digital image technology provide 18

alternative methods for capturing a range of parameters during structural testing. This is 19

particularly useful for application to UHPC containing steel fibers, as digital image correlation 20

(DIC) may be applied to capture a larger field of strain deformation, deflections, and track the 21

progression of crack development. 22

23

24 (a) (b) 25

FIGURE 4 UHPC beam with DIC stochastic grid pattern (a) prior to testing and (b) 26

deflecting under load. 27 28

Through the application of photogrammetric location principles and image correlation techniques, 29

DIC provides a comprehensive strain profile (12). Two high resolution cameras are placed such 30

that their position and orientation with respect to one another is fixed and known. A stochastic grid 31

pattern with adequate contrast is marked on the surface of the specimen (see Figure 4) allowing 32

for thousands of unique correlation areas, referred to as facets, to be defined across the imaging 33

area. These facets are tracked through each sequential pair of images as the specimen deforms 34

under load. Before and after every load step, the three-dimensional location of each facet is 35


calculated and a full field of displacements is derived, with greatest accuracy being achieved for 1

in-plane locations. During the tests, DIC was applied to capture behavior of the full-scale girders 2

in and around the pure moment region. 3

4

RESULTS 5 6

HPC Specimen 7 Through early loading, the HPC specimen exhibited a linear load-deflection relationship (see 8

Figure 5a) up to a load of 37.8 kips (168 kN) and deflection of 0.85 in. (22 mm) where initial 9

cracking occurred. At this point, hairline cracks began to propagate along each stem, first within 10

the constant moment region then up to approximately 3 ft (1 m) outside this area. The girder 11

continued to carry load as stiffness continued to decline and plastic deformation occurred. 12

Eventually, an ultimate load of 76 kips (338 kN) was achieved at a deflection of 6.70 in. (170 mm). 13

14

15

16 (a) (b) 17

18 (c) (d) 19

FIGURE 5 Load versus deflection and Moment versus Curvature behavior for (a, b) HPC 20

and (c, d) UHPC. 21

22


The disparity between the east and west curves for moment-curvature of the HPC girder 1

(Figure 5b) can be attributed to the propagation of large cracks outside the gauge length of the 2

LVDTs, impeding the data gathered by the sensor. The moment corresponding to initial cracking 3

was identified as 202 kip-ft (274 kN-m), and the girder reached an ultimate moment of 419 kip-ft 4

(568 kN-m). 5

6

UHPC Specimen 7 Load-deflection and moment-curvature data of the UHPC specimen is presented in Figures 5c and 8

5d. The linear region of the UHPC load-deflection curve exhibits nearly identical stiffness to that 9

of the HPC girder (Figure 5a). Initial cracking occurred at approximately 50 kips (224 kN) at a 10

deflection of 1.2 in. (30 mm), corresponding to an approximate moment of 270 kip-ft (365 kN-m). 11

Load continued to increase to an ultimate value of approximately 84 kips (374 kN) and maximum 12

deflection of 6.40 in. (163 kN). Similar to the HPC data, a crack formed outside the gauge length 13

of the LVDTs at midspan on the east side of the UHPC girder, thus limiting the curvature captured 14

by sensors. The ultimate moment achieved by the UHPC specimen was 463 kip-ft (628 kN-m). 15

16

Performance Comparison 17

The improved performance of the UHPC specimen is immediately clear when comparing the 18

curves of Figure 5. Despite the reduced cross-section, the UHPC specimen displayed the same 19

stiffness and linear behavior as that of HPC, and remained linear up to 34% greater deflection prior 20

to cracking. The initial cracking load of the UHPC specimen was approximately 28% greater than 21

HPC. At the ultimate load of the HPC girder, 76 kips (338 kN), the UHPC girder exhibits a 22

deflection of 3.2 in. (81 mm), less than half of the ultimate deflection of the HPC specimen. The 23

ultimate load achieved by the UHPC specimen was 10% greater than that of HPC. 24

Tiltmeter data was recorded to provide beam rotation relative to each support as seen in 25

Figures 6a and 6b. For HPC and UHPC, applied load produced nearly symmetrical rotation at each 26

support. Prior to initial cracking, the similarity of the linear region of each specimen is clear. 27

Cracking of the HPC girder occurred at a rotation of just 0.47 degrees. The UHPC girder 28

experienced initial cracking at a rotation of approximately 0.67 degrees, at which point the 29

corresponding HPC rotation is in excess of 0.85 degrees, a difference of almost 25%. As the girder 30

begins to soften, the slope of the HPC rotation exhibits a much faster decline due to increased 31

deformation and loss of stiffness. At the ultimate state of HPC, the difference in curvature has 32

increased dramatically to greater than 60%, indicative of the increased post-yield stiffness of the 33

UHPC girder. Even at failure, the UHPC girder carried 10% greater loads with slightly less rotation 34

than the HPC specimen. 35

36

Digital Image Correlation Results 37

Analysis of DIC data provides a more strikingly visible representation of the difference in behavior 38

of the two girders. Figure 7 presents a progression of load stages and corresponding deflections 39

for both the HPC and UHPC tests. The figure utilizes the color spectrum to characterize strain 40

development and distribution as the specimen deforms. The first set of images, Figure 7a and 7b, 41

represent the HPC (left) and UHPC (right) girders under zero load. The second set of images (7c 42

and 7d) correspond to the loads at which first cracking occurred for each specimen. The appearance 43

of green and yellow is indicative of the minute strain development as micro-cracking begins. As 44

the load stages progress, the disparity in performance of the girders becomes increasingly apparent. 45

46


1 (a) (b) 2

FIGURE 6 Load versus rotation behavior for (a) HPC and (b) UHPC. 3

4

5

6

(a) (b)

(c) (d)

(e) (f)

(g) (h)

(i) (j)

FIGURE 7 DIC photos for HPC (left) and UHPC (right) for (a, b) zero load, (c, d) initial 7

cracking, (e, f) 60 kips [265 kN], (g, h) 70 kips [310 kN], and (i, j) failure. 8

9

10


In Figures 7e and 7f, flexural tensile stress has caused cracks to open along the stem of the 1

HPC girder, represented by the areas in red, in which tension has exceeded the capacity of the 2

concrete. At this stage there is already a deflection difference of 1 in. (25.4 mm) between the 3

girders. At 60 kips (265 kN), HPC crack propagation has extended past mid-depth and deflection 4

continues. Although cracking of the UHPC specimen has occurred, propagation is substantially 5

impeded by fiber engagement, effectively distributing tensile stress even at increasing loads. At 70 6

kips (310 kN), deflection of the UHPC specimen is approximately half that of HPC. The last set 7

of images (7i and 7j) shows each specimen at ultimate load and deflection. Whereas cracking 8

occurred along the entire stem of the HPC specimen, cracking of the UHPC specimen was limited 9

to only the areas of greatest tensile strain development where fiber pullout was achieved. It is 10

important to note the difference in ultimate load of the specimens, significantly increased for 11

UHPC, and the fact that intermediate load stages between the 70 kip (310 kN) stage leading to 12

failure are not shown here. 13

14

CONCLUSIONS 15

The findings of this investigation provide evidentiary support of the improved flexural behavior 16

of locally developed UHPC. Analyses of the behavior of two full-scale prestressed channel girders, 17

designed to provide equal capacities, demonstrated the advantages of UPHC characteristics and 18

the contribution of steel fiber reinforcement in comparison to the performance of HPC. 19

Utilizing reduced cross-sectional geometry and less mild steel shear reinforcement than 20

required by AASHTO standards, the UHPC specimen exhibited prolonged elastic behavior and 21

improved post-cracking behavior. At first cracking, the UHPC girder recorded a load of 50 kips 22

(224 kN), an increase of 28% compared to HPC, while the deflection of 1.2 in. (30 mm) is 28% 23

less than HPC at the same load. Post-cracking, the ability of steel fibers to bridge-micro cracks 24

and distribute tensile stresses delayed strain development, effectively mitigating crack 25

propagation. At the ultimate load of the HPC specimen, UHPC girder rotations were reduced by 26

more than 60% and exhibited less than half the corresponding HPC deflection. The ultimate UHPC 27

load and deflection, 84 kips (374 kN) and 6.40 in. (163 kN), resulted in an ultimate moment of 463 28

kip-ft (628 kN-m) and a total increase in capacity over HPC of approximately 10%. Despite a 29

smaller section and decreased moment of inertia, the channel shape allowed for the full 30

compressive strength of UHPC to be utilized in the deck, withstanding large flexural deformations 31

and eliminating the need for an additional deck in practical applications. 32

The use of DIC provided an innovative technology to better understand the behavior of 33

UHPC. Direct comparisons of deflections, strain development, crack patterns and propagations 34

was provided. Additionally, the use of DIC helped to identify failure mechanisms that can be used 35

to improve future designs with UHPC. The supporting evidence of tensile stress distribution 36

suggests increased resilience to shear crack development. Therefore, it may be possible to reduce 37

or possibly eliminate shear reinforcement from the UHPC design. 38

Further investigation of the comparative behavior of UHPC and HPC will continue, 39

including shear and transverse flexural testing, as well as studying the effects of significantly 40

reduced mild steel reinforcement in a prestressed UHPC channel girder. Results of current and 41

future testing will help to develop analytical models and estimation procedures for predicting 42

UHPC behavior and provide recommendations and design tools for implementation of UHPC in 43

local design standards. Furthermore, this research has demonstrated the successful batching, 44

casting, and curing of a prestressed UHPC girder using local materials without any changes to the 45

precast facility. The procedures for UHPC production and fabrication will continue to be improved 46


for greater efficiency and economy, helping to implement UHPC into widespread structural 1

applications. 2

3

ACKNOWLEDGMENTS 4

This research was funded in part by the New Mexico Department of Transportation. Special thanks 5

to Keli Daniell, NMDOT Research Bureau, Project Manager, and Diego Gomez, NMDOT Project 6

Advocate. Additional thanks to Ben Najera and Ray Trujillo, New Mexico Bridge Design Bureau, 7

for their assistance in modeling and design recommendations. The authors would like to further 8

acknowledge the support of individuals including: Shannon Burl Applegate, Bill Lujan, and 9

everyone at Coreslab Structures (Albuquerque) Inc. who contributed to this project; and Cory 10

Powell and Ruben Diaz for their time and indispensable laboratory assistance. Additional 11

assistance and materials were provided by Darren Jewell of BASF and Mona Gomez of El Paso 12

Machine and Steel. Any and all opinions, findings, conclusions, and/or recommendations 13

expressed herein are those of the author(s) and do not necessarily reflect the views of the 14

individuals or organizations listed above. 15

16

REFERENCES 17

1. Ahlborn, T.M., Harris, D.K., Misson, D.L., and E.J. Peuse. Strength and Durability 18 Characterization of Ultra-High Performance Concrete Under Variable Curing Conditions. 19

Presented at 90th Annual Meeting of the Transportation Research Board, Washington, DC, 20

2011. 21

2. Weldon B.D., Jauregui D.V., Newtson C., Taylor C.W., Montoya K.F., Allena S., Muro J., 22 Tahat M., Lyell E., and Visage E.T. Feasibility Analysis of Ultra High Performance Concrete 23

for Prestressed Concrete Bridge Applications. Final Report NM09MCS-01. New Mexico 24

Department of Transportation, June 2012. 25

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