TECHNOTE Construction of Field-Cast 

Ultra-High Performance 

Concrete Connections

FHWA Publication No: FHWA-HRT-12-038

FHWA Contact: Ben Graybeal, HRDI-40, (202) 493-3122, 

benjamin.graybeal@dot.gov.

Introduction

Ultra-high performance concrete (UHPC) is an emerging 

construction material that has been demonstrated to 

advance the state of the art for construction of prefabricated

bridge elements and systems (PBES). Specifically, UHPC 

allows for significant simplifications in the design of the 

component connections, while simultaneously affording 

enhanced durability and simplified construction practices. As 

of early 2012, 18 bridges in the United States and Canada 

have been constructed using field-cast UHPC connections, 

and figure 1 and figure 2 show two of those bridges. The 

bridge shown in figure 1 is the first in the United States to 

use field-cast UHPC connections. Eight simple span deckbulb-tee girders were joined with non-contact lap splice 

deck-level connections. The bridge in figure 2 has precast 

concrete deck panels and field-cast UHPC connections. 

However, as with any new technology, initial deployments 

of field-cast UHPC technology face hurdles relating to 

inevitable construction process changes. This TechNote 

provides an introduction to many of the topics that should 

be considered when deploying UHPC connections.

Definition

UHPC is a cementitious composite material composed of 

an optimized gradation of granular constituents, a waterto-cementitious materials ratio less than 0.25, and a high 

percentage of discontinuous internal fiber reinforcement. The 

mechanical properties of UHPC include compressive strength 

greater than 21.7 ksi (150 MPa) and sustained post-cracking 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov/research/
2

tensile strength greater than 0.72 ksi (5 MPa).1

UHPC has a discontinuous pore structure that 

reduces liquid ingress, significantly enhancing

durability compared to conventional concrete.

Ultra-High Performance Concrete and Material 

Property Characterization of Ultra-High Performance Concrete provide further background 

on UHPC-class materials.(1,2) At present, UHPC 

is typically acquired from a supplier in three 

separate components, specifically a pre-bagged 

cementitious powder, a steel fiber reinforcement, and chemical admixtures. Water is 

supplied onsite. As with other pre-bagged 

grouts, UHPC is mixed onsite and then 

placed into the formwork through the use of 

conventional construction equipment.

Design

The design of field-cast UHPC connections is 

critical to the overall performance of the structural system. As opposed to conventional 

grouts, UHPC is frequently engaged to shorten 

development lengths of embedded connectors 

and, at times, is designed to inherently carry 

tensile and shear loads as a critical element 

within the structure. A few specific connection 

details, such as those discussed in Behavior 

of Field-Cast Ultra-High Performance Concrete 

Bridge Deck Connections Under Cyclic and 

Static Structural Loading and Development of 

a Field-Cast Ultra-High Performance Concrete 

Composite Connection Detail for Precast Concrete Bridge Decks, have been rigorously tested 

at service and ultimate performance limits.

(3,4) The design concepts demonstrated within 

these tested connections are directly applicable

and may be conservatively extended as new 

designs are considered. A variety of other 

connection designs have also been demonstrated to perform through field applications 

on bridges in the United States and Canada.

The design of UHPC connections must consider

both service and ultimate limit states, as well 

as the practicality of construction and the 

long-term durability of the deployed system. 

Topics such as cyclic and static stress levels 

in the UHPC, tensile stress ranges in steel 

connectors, and bond strength of UHPC to 

conventional concrete in relation to tensile 

demand must all be considered. Designers 

and owners must recognize that a UHPC 

connection is necessarily connecting two or 

more other structural components. The UHPC 

connection should be designed for appropriate 

load-carrying capacity and long-term durability 

but should not be expected to address inherent shortcomings within the bodies of the 

connected conventional components.

Figure 1. Route 31 bridge in Lyons, NY. Figure 2. Route 23 bridge in Oneonta, NY.

 1The tensile behavior of UHPC is generally defined as “strain-hardening,” which is a broad term defining concretes wherein 

the sustained post-cracking strength provided by the fiber reinforcement is greater than the cementitious matrix cracking 

strength. However, the definitional dependence on cementitious matrix cracking strength may inappropriately include some 

concretes that exhibit low first-cracking strengths. Note that the post-cracking tensile strength and strain capacity of UHPC is 

highly dependent on the type, quantity, dispersion, and orientation of the internal fiber reinforcement.
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Prefabricated Component 

Preparation

Prior to completing the connections between 

PBES components, the components must be 

fabricated, transported, and assembled on the 

bridge. These activities must be completed 

according to the design. In particular, the 

discrete connectors that emanate from the 

prefabricated components into the connection 

void space must match the design geometry. 

These connectors are critically important to 

the performance of the bridge system. UHPC 

affords the opportunity to reduce or eliminate field fit-up issues. As a result, designers

should ensure that the constructability advantages provided by UHPC are engaged. Field 

assembly of components should proceed 

quickly, and field modification of discrete 

connectors should not be necessary.

The preparation of the bonding surfaces where 

the precast component meets the field-cast 

UHPC can also be of critical importance to the 

long-term performance of the bridge system. 

UHPC can bond exceptionally well to conventional concrete at these connection interfaces. However, the bond strength is highly 

dependent on the surface of the precast concrete. As with other cementitious grouts, 

UHPC is not likely to form a strong bond with 

smooth, dry, precast concrete. On the other 

end of the spectrum, UHPC cast against 

a concrete element with an exposed aggregate surface finish has been demonstrated to 

provide enhanced bond. Prewetting of a 

precast concrete interface to a saturated 

surface dry condition immediately before 

UHPC casting is generally beneficial because 

it eliminates the dehydrating effect that can 

occur when dry concrete extracts water 

from the mating UHPC. Field-applied epoxy 

bonding agents and concrete form liners are 

other options for enhancing the bond.

Formwork

The formwork required to contain UHPC 

placed into a connection requires somewhat 

tighter control than the formwork commonly 

deployed in field-cast concrete applications. 

Rheologically, UHPC is a self-consolidating

concrete that contains little or no coarse 

aggregate. As such, UHPC exhibits higher 

formwork pressure than conventional concrete and can easily leak between formwork 

that is not appropriately sealed. As opposed 

to conventional concrete, the lack of blocking

elements (i.e., coarse aggregate) within UHPC 

results in formwork leaks that continue to 

flow and expand unless immediate firm 

action is taken to stop a leak.

Success or failure of formwork on past projects 

has been directly attributed to contractor attentiveness to the need to ensure that formwork 

is sealed and capable of resisting the hyrdostatic pressure that UHPC imparts. Contractors 

who expect UHPC to behave like conventional 

concrete have been proven wrong, while 

contractors who recognize the differences and 

prepare appropriately have achieved success. 

Some contractors have gone so far as to 

temporarily fill connection forms with water 

to ensure leak tightness and pressure resistance. Although not necessary, this activity can 

prove beneficial.

Forms for field-cast UHPC should be designed 

to allow for either slight overfilling or slight 

overpressure as the pour is completed. Small 

amounts of air trapped both in UHPC and in the 

connection spaces can result in UHPC initially 

appearing to fill the void space but later exhibiting slight subsidence as the air escapes. For 

deck-level connections, wood or foam strips are 

frequently installed on either side of the connection to allow it to be overfilled. Additionally, 

the formwork is frequently designed to allow 

for UHPC to be enclosed (i.e., top-formed) 

immediately after the placement in one area is 

completed. In nearly all cases, formwork is 

designed to allow for a UHPC “chimney” to be 

cast, thus providing extra UHPC which can 

fill subsided areas. This “chimney” is akin to 

the sprue in the metal and plastic component 

casting industries. It allows for a slight overpressure on the field-cast UHPC which assists in 

ensuring that the connection space is fully filled.
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It can be advantageous to include portions of 

formwork on prefabricated components, thus 

lessening the demand for field-installed formwork. For instance, adding formwork to prefabricated components, such as concrete lips at 

deck panel connections, can simplify the field 

construction activities. However, it should be 

recognized that the field benefits afforded 

through these sorts of modifications can 

increase the cost and complexity of the prefabrication activities.

Mixing and Placing

As with any pre-bagged cementitious composite, UHPC must be mixed according to the supplier’s specifications. These specifications frequently provide information on the constituent 

volumes to be mixed and the order of constituent addition to a particular mixer. UHPC is sensitive to mixing deviations, so mix proportions 

and timings must be followed. The addition of 

water or chemical admixtures beyond those 

specified can cause detrimental impacts on the 

early and long-term performance of the fieldcast UHPC.

The weather conditions surrounding the UHPC 

prior to and during mixing can impact the fresh 

properties of the concrete. The temperature 

of the UHPC will increase during mixing, and 

some mix water will be lost due to evaporation. Mixing UHPC under cool temperatures and 

away from direct exposure to sun and wind 

is advantageous. Maintaining a reduced temperature on the pre-bagged UHPC powders and 

the mix water is advantageous. The fluidity 

of UHPC can become reduced, and the likelihood of surface dehydration can increase if the 

temperature of UHPC at the conclusion of 

mixing exceeds 80 °F (26.7 °C). Cubed ice has 

been demonstrated to be a viable replacement 

for some or all of the mix water when mixing 

in warm conditions.

UHPC can be mixed in most concrete or grout 

mixers. UHPC mixing requires a significant 

energy input in order to disperse the liquids 

uniformly within the powder matrix. Higher 

energy mixers will complete the mixing 

process more quickly. Both tow-behind pan 

mixers and conventional concrete ready-mix 

trucks have been used to mix UHPC. As a ruleof-thumb, the volume of UHPC that can be 

mixed in one of these mixers is approximately 

half of the volume of conventional concrete 

that could be mixed in the same mixer. Figure 3

shows a portable concrete pan mixer preparing 

UHPC for placement during the construction 

of the field-cast connections on the Keg Creek 

Bridge in Council Bluffs, IA.

The choice of mixer should be determined 

based on the rate of UHPC delivery required 

at the construction site. Frequently, a fieldcast connection between bridge components 

may require more UHPC than can be quickly 

delivered. As such, the connection needs to 

be divided into smaller sections so that the 

placement rate allows the UHPC to quickly fill 

the divided connection space. This requirement is based on the fact that, like conventional 

concrete, UHPC is susceptible to surface 

dehydration, which can lead to the appearance 

Figure 3. Portable concrete pan mixer preparing 

UHPC for placement during the construction of the 

field-cast connections.
5

of a false set in a thin layer on the concrete 

surface. Subdivision of connection spaces is 

most critical for deck-level connections between 

precast concrete elements. These connections 

are fully exposed to the weather during casting, 

possibly leading the exposed surface of the 

UHPC to desiccate and crack prior to the form 

being filled. Methods of estimating conventional concrete surface dehydration rates are 

available and should be engaged to assist in 

coordinating construction activities.(5)

Traditionally, the placement of UHPC into fieldcast connections has been completed through 

the use of motorized or non-motorized wheelbarrows, with connection spaces being filled 

consecutively. Figure 4 shows UHPC placement 

on a bridge in Lyons, NY. It is also possible to 

pump, augur, or chute UHPC; however, these 

methods may result in temporarily stagnant 

UHPC exhibiting poor rheological performance 

when placed in the connection.

UHPC should always be placed into connection spaces so that successive placements are 

poured into previously placed UHPC. UHPC is a 

steel-fiber reinforced concrete and, depending

on the structural design of the connection, may 

rely on the tensile capacity afforded by those 

fibers. When two “heads” of adjacent UHPC 

pours meet one another, an interface is formed 

wherein there is limited interface crossing by 

the fiber reinforcement. This situation can be 

avoided by pouring fresh UHPC into UHPC 

which was recently cast and remains fluid.

UHPC is self-leveling, and this fact must be 

considered when designing formwork and 

placing UHPC. UHPC is commonly placed 

beginning at the lowest point within any 

formwork pour area and moving toward the 

highest point. Filled areas of lower elevation 

need to be top-formed (i.e., closed) in order to 

stop UHPC from overflowing the connection. 

For deck-level connections, this top-forming can 

be accomplished through the use of plywood 

strips, which are placed over the field-cast 

UHPC and are fastened in place. The placement 

concludes at the “chimney.”

Traditional concrete finishing techniques are 

not normally employed on field-cast UHPC. The 

high supplementary cementitious materials 

content and the low water content restrict the 

ability to draw water-rich paste to the surface 

of the concrete. As such, alternate techniques 

must be employed to ensure an appropriate 

concrete surface is delivered. Most commonly, 

UHPC is either cast in a closed form, or the form 

is closed immediately after casting. The closed 

form should be designed to allow full filling of 

the connection space without the trapping of 

air. UHPC should be in contact with the top 

formwork, minimizing the surface dehydration 

that can occur on exposed surfaces of fresh-cast 

UHPC. On horizontal surfaces that will eventually

be exposed to the public, the connection is 

frequently overfilled. This allows the UHPC 

surface to be ground to match the adjacent 

pre-fabricated surfaces.

Initial and Final Curing

The formulations of UHPC-class materials tend 

to result in concretes that exhibit long dwell 

times prior to the initiation of setting behaviors. However, once setting begins, strength gain 

rapidly occurs. The initial setting behaviors are 

dependent on the temperature of the UHPC. 

Although cooler temperatures are beneficial for 

mixing and placing UHPC, warmer temperatures 

Figure 4. Longitudinal connections cast between 

deck-bulb-tee girders on the Route 31 bridge in 

Lyons, NY.

Photo from New York State Department of Transportation.
6

are beneficial for the rapid setting of the concrete. Supplemental heat can be supplied to 

the UHPC and the surrounding prefabricated 

elements in order to accelerate the initial 

setting. This heat can be supplied externally 

(e.g., ground heating mats) or internally (e.g., 

resistance heating wires) but should not be 

applied via forced air heat against exposed 

UHPC surfaces. The application of supplement 

heat can be especially important for accelerated 

bridge construction projects and for projects 

that are being completed in cold weather. In 

order to reduce the risk of surface dehydration, 

the UHPC should remain sealed from exposure 

to the external environment prior the completion of initial curing. Also, UHPC should not 

freeze during initial curing.

After the attainment of sufficient strength, 

the formwork may be stripped, and UHPC 

may be exposed to the environment. The 

cementitious reactions inherent in the UHPC 

formulation will continue to occur as the full 

complement of mechanical and durability properties are achieved. UHPC may be, but does 

not need to be, kept moist during the final 

curing phase. The structure may be subjected to 

construction and/or traffic live loads during 

the later phases of the UHPC strength gain; 

however, care must be taken not to overstress 

the connections prior to the attainment of the 

design strength.

Surface Profiling

Horizontal field-cast UHPC surfaces, such as the 

exposed surface on the top of a deck-level connection, must be dressed to provide appropriate 

rideability. Frequently, both the UHPC and the 

top face of the precast concrete deck component 

are designed with a sacrificial surface that can 

be removed after the connections are cast and 

the UHPC has gained a portion of its design 

strength. Grinding the entire surface of the deck 

eases the construction requirements pertaining 

to the profile of the bridge deck and simplifies 

the creation of a consistent driving surface.

Both grinding and grooving operations of 

field-cast UHPC connections (and surrounding

precast component decks) have been conducted on the previously completed projects. 

Some contractors have reported that grinding/

grooving UHPC is easier if completed prior 

it reaching its full design strength. The ease 

with which these operations can be completed 

depends on the UHPC strength, the UHPC formulation, and the type of grinding/grooving equipment deployed. UHPC formulations designed 

to exhibit exceptional abrasion resistance 

will be more difficult to dress than traditional 

UHPC formulations.

Material Testing

In general, well-established testing procedures 

for conventional concrete are applicable to 

UHPC. However, in some instances, procedures 

may need to be modified in order to appropriately capture the true behaviors of UHPC. 

Compression testing and flow testing are 

prime examples.

Flow Testing

The rheological properties of UHPC are 

traditionally captured through the use of the 

ASTM C1437 test (see figure 5).(6) This test, which 

is basically a miniature version of the traditional slump test, measures the flow of hydraulic cement mortars. Both an initial flow reading 

and a dynamic flow reading are recorded. 

Frequently, this test is completed immediately 

after mixing in order to assess consistency 

between mixes and appropriateness for casting.

Compression Testing

As with conventional concrete, compressive

strength is an oft used indicator of the 

mechanical properties of UHPC. Research has 

demonstrated that standard concrete compression testing methods (i.e., ASTM C39 

and ASTM C109) are applicable to UHPC.(7,8)

However, these test methods may benefit 

from slight modification to facilitate efficient 

use. Most notably, a loading rate of 150 psi/s 

(1 MPa/s) has been demonstrated to be 
7

acceptable, allowing individual tests to be 

completed in a reasonable timeframe.(9)

It has also been demonstrated that at the highstrength levels achieved with UHPC, both 

reduced-size cylinders and reduced-size cube 

compressive test specimens are an appropriate substitute for full-size cylinders. Companion 

cylinder and cube strength results tend to be 

within 5 percent of one another, allowing for 

direct substitution of results.(10)

If cylinder tests are used for specimens at 

strength levels above those appropriate for 

capping methods, both cylinder ends must 

be ground planar to within the ASTM C39 

specification of 0.5 degrees.(7) It is also important to recognize that the high compressive 

strengths of UHPC may necessitate the use 

of higher capacity compression testing 

platens and machines.

Both 3-inch- (76-mm)- and 4-inch- (102-mm)-

diameter cylinders are frequently used to 

assess the compression strength of UHPC 

on highway projects completed in the United 

States and Canada. If used for assessment 

of the curing behaviors of a field-cast 

connection, these cylinders should be match 

cured with the connection.

Summary

UHPC has captured the interest of bridge 

owners across the United States as they look 

for innovative solutions to facilitate rapid 

and robust construction of highway bridges. 

As with any new technology, the first round 

of implementations requires extra oversight, 

as front-line workers adjust common practices to align with new requirements. This 

TechNote is intended to provide insight into 

practical details associated with the use of 

field-cast UHPC for connections between prefabricated bridge elements. Recognition of the 

topics discussed herein should increase the 

likelihood of successful deployments of UHPC 

technology by owners across the United States.

References

1. Graybeal, B. (2011). Ultra-High Performance Concrete, Report No. FHWA-HRT11-038, Federal Highway Administration, 

Washington, DC.

2. Graybeal, B. (2006). Material Property 

Characterization of Ultra-High Performance Concrete, Report No. FHWA-HRT06-103, Federal Highway Administration, 

Washington, DC.

3. Graybeal, B. (2010). Behavior of Field-Cast 

Ultra-High Performance Concrete Bridge 

Deck Connections Under Cyclic and Static 

Structural Loading, Report No. PB2011-

101995, National Technical Information 

Service, Springfield, VA.

4. Graybeal, B. (2012). Development of a FieldCast Ultra-High Performance Concrete 

Composite Connection Detail for Precast 

Concrete Bridge Decks, Report No. PB2012-

107569, National Technical Information 

Service, Spingfield, VA.

5. ACI 305R-10. (2010). Guide to Hot-Weather 

Concreting, American Concrete Institute, 

Farmington Hills, MI.

6. ASTM Standard C1437. (2007). “Standard 

Test Method for Flow of Hydraulic Cement 

Mortar,” ASTM Book of Standards, Volume 

04.01, West Conshohocken, PA. 

Figure 5. ASTM C1437 flow test on UHPC.(6)
8

Researchers—This TechNote was developed by Ben Graybeal at the Federal Highway Administration’s 

(FHWA) Turner-Fairbank Highway Research Center. For additional information, contact him at (202) 

493-3122 or through the FHWA Office of Infrastructure Research and Development located at 6300 

Georgetown Pike, McLean, VA, 22101-2296.

Distribution—This TechNote is being distributed according to a standard distribution. Direct 

distribution is being made to the Divisions and Resource Center.

Availability—This TechNote may be obtained from the FHWA Product Distribution Center by email to 

report.center@dot.gov, fax to (301) 577-1421, phone to (301) 577-0818, or online at http://www.fhwa.dot.

gov/research.

Key Words—Ultra-high performance concrete, UHPC, Fiber-reinforced concrete, Bridge, Accelerated 

construction, Durable infrastructure system, Prefabricated bridge elements and systems, Field-cast connections, Test methods.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no liability 

for the use of the information contained in this document. The U.S. Government does not endorse 

products or manufacturers. Trademarks or manufacturers’ names appear in this report only because 

they are considered essential to the objective of the document

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides highquality information to serve Government, industry, and the public in a manner that promotes public 

understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, 

and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and 

processes to ensure continuous quality improvement.

april 2012 FHWA-HRT-12-038

HRDi-40/04-12(300)E

7. ASTM Standard C39. (2010). “Standard 

Test Method for Compressive Strength of 

Cylindrical Concrete Specimens,” ASTM 

Book of Standards, Volume 04.02, West 

Conshohocken, PA.

8. ASTM Standard C109. (2008). “Standard 

Test Method for Compressive Strength 

of Hydraulic Cement Mortars (Using 2-in. 

or [50-mm] Cube Specimens),” ASTM 

Book of Standards, Volume 04.01, West 

Conshohocken, PA.

9. Graybeal, B. (2007). “Compressive Behavior 

of Ultra-High Performance Fiber-Reinforced 

Concrete,” ACI Materials Journal, 104(2), 146–

152, Farmington Hills, MI.

10. Graybeal, B. and Davis, M. (2008). “Cylinder 

or Cube: Strength Testing of 80 to 200 MPa 

(11.6 to 29 ksi) Ultra-High-Performance 

Fiber-Reinforced Concrete,” ACI Materials 

Journal, 105(6) 603–609, Farmington 

Hills, MI.