TECHBRIEF Field-Cast UHPC Connections

for Modular Bridge Deck

Elements

FHWA Publication No: FHWA-HRT-11-022

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

benjamin.graybeal@dot.gov

This document is a technical summary of the unpublished Federal Highway Administration (FHWA) report 

Behavior of Field-Cast Ultra-High Performance Concrete 

Bridge Deck Connections Under Cyclic and Static Structural 

Loading, which is available through the National Technical 

Information Service (NTIS), www.ntis.gov.

NTIS Accession No. of the report covered in this TechBrief: 

PB2011-101995

Objective

This TechBrief highlights the results of a study aimed 

at evaluating the performance of field-cast ultra-high 

performance concrete (UHPC) connections linking precast 

concrete bridge deck components. 

Introduction

The use of modular bridge deck components has the 

potential to produce higher quality, more durable bridge 

decks. However, the required connections often prove 

lacking, resulting in less than desirable overall system 

performance. Advanced cementitious composite materials, 

whose mechanical and durability properties far exceed 

those of conventional concretes, present an opportunity 

to significantly enhance the performance of field-cast 

connections, thus facilitating the wider use of modular 

bridge deck systems. UHPC represents a class of such 

advanced cementitious composite materials. Of particular 

interest here, UHPCs can significantly shorten the development length of embedded discrete steel reinforcement and 

can exhibit exceptional bond when cast against previously 

cast concrete. These properties allow for a redesign of the 

modular component connection to facilitate accelerated 

construction and enhanced long-term system performance.

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov
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Field-Cast UHPC Connection 

Details

The concept of using the advanced properties 

of UHPC to significantly modify the design 

of connections between precast concrete 

components is not new. In fact, research 

and deployments in this area date back to 

at least 1995.(1) At that time, two projects 

were completed at Aalborg University in 

Denmark wherein a commercially available 

UHPC was used as a closure fill material in 

the connection of slab elements in a building. 

In association with these projects, a series of 

studies on the bonding performance between 

UHPC and straight lengths of mild steel 

reinforcement were completed at Chalmers 

University in Sweden.

More recently, the concept of using the properties of UHPC to redesign the connections 

between modular bridge components has 

been recognized in North America. By late 

2010, field-cast UHPC connections between 

prefabricated bridge components had been 

implemented in nine bridges in Canada 

and two in the United States. These bridges 

use a range of details to connect a variety 

of different precast concrete modular 

bridge components, including adjacent 

box beams, full-depth precast deck panels, 

and deck-bulb-tee girders. The connection 

designs deployed to date have tended to 

mimic non-contact lap splice connections 

with a female-female shear key profile. 

Figure 1 shows the casting of UHPC into 

the longitudinal connection between the 

top flanges of deck-bulb-tee girders. This 

bridge, constructed by the New York State 

Department of Transportation (NYSDOT), 

opened to traffic in 2009.

The two fundamental differences between 

the field-cast UHPC connection concept 

and conventional modular component 

connection concepts are simplicity and 

performance. The UHPC connection concept 

allows for small, simple connections without 

requiring post-tensioning or large volumes 

of field-cast concrete. The performance 

of the connection exceeds that normally 

anticipated from a field-cast connection, 

thus allowing the joined components 

to emulate or surpass the behavior of 

monolithic construction. 

UHPC

Advances in the science of concrete materials 

led to the development of the next generation of cementitious materials, namely 

UHPC. As a class, these concretes tend 

to contain high cementitious materials 

contents, very low water-to-cementitious 

materials ratios, compressive strengths 

above 22 ksi (150  MPa), and sustained 

tensile strength resulting from internal 

fiber reinforcement. Table  1 presents a 

select set of material properties for the type 

of UHPC investigated in this study. Further 

details on the mechanical and durability 

properties of this UHPC can be found in 

previous FHWA reports.(2)

The exceptional durability of UHPC has been 

well documented. Of particular importance, 

UHPC contains no coarse aggregate, so 

Figure 1. Placement of UHPC into longitudinal 

connection between deck-bulb-tee girders.

Photo courtesy of NYSDOT
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it does not exhibit the early-age microcracking common to conventional concrete. 

This, combined with the discontinuous pore 

structure in the homogeneous cementitious matrix, results in a concrete with an 

extremely low permeability. 

Tensile behavior of UHPC also stands in contrast to that of conventional concrete. The 

discrete steel fiber reinforcement included 

in UHPC components allows the concrete 

to maintain tensile capacity beyond cracking of the cementitious matrix. The inelastic 

straining of the component is resisted by 

fiber reinforcement that bridges the tight, 

closely spaced cracks. 

The durability and sustained tensile capacity 

of UHPC present opportunities to reimagine 

common concepts in reinforced concrete 

structural design. For example, the tensile 

capacity of UHPC could eliminate the 

need for discrete mild steel reinforcement in some structural members, and the 

durability could reduce the cover required 

for any remaining reinforcement.(3) Of particular interest, the mechanical properties 

of UHPC allow for the full development

of discrete embedded reinforcements in 

exceptionally short distances. This behavior 

allows for the redesign of closure pours 

and other field-cast connections between 

modular components.

Physical Testing Program

Through its Structural Concrete Research 

Program, the FHWA recently completed 

an experimental study focused on the performance of field-cast UHPC deck-level 

connections between precast modular 

bridge components. This study was part 

of Transportation Pooled Fund Project 

No.  TPF-5(217), which is being completed 

in partnership with NYSDOT and the Iowa 

Department of Transportation.

Bridge deck components simulating both 

longitudinal and transverse connections 

were fabricated and tested under both cyclic 

and static wheel patch loadings. Four transversely connected specimens simulated the 

connections between precast deck panels. 

These specimens were identical aside from 

the different discrete reinforcing details, 

which included straight lapped bars, headed 

bars, and intersecting hoop bars. The two 

longitudinally connected specimens simulated the connections between the top 

flanges of deck-bulb-tee girders. These two 

specimens were identical aside from the 

inclusion of two different discrete reinforcing 

details, namely straight lapped bars and 

lapped headed bars. Figure 2 provides details 

on the longitudinally connected specimen 

that included a straight bar non-contact lap 

splice connection.

The tested components simulated a 

94.5-by-84.7-inch (2.4-by-2.152-m) portion 

of a bridge deck that included a 6-inch 

(152-mm)-wide field-cast UHPC connection. 

The specimens were loaded on a simple 

span, with the load applied through a simulated wheel patch placed adjacent to the 

connection near midspan. Cyclic loads were 

applied first, with the test program including at least 2  million cycles to a load just 

below the cracking strength of the specimen 

followed by at least 5  million  cycles to a 

load larger than the cracking strength of the 

Table 1. Field-cast UHPC material properties.

Property Value

Unit weight

158 lb/ft3

(2,535 kg/m3)

Modulus of elasticity

7,500–8,500 ksi 

(52–59 GPa)

Compressive strength

25–32 ksi 

(170–220 MPa)

Post-cracking 

tensile strength

1.0–1.5 ksi 

(7.0 to 10.3 MPa)

Chloride ion penetrability 

(ASTM C1202) Very low to negligible
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specimen. After the completion of the cyclic 

testing, each test specimen was statically 

loaded to failure. Figure 3 shows one of the 

longitudinal connection specimens during 

cyclic loading.

The loading program was designed to allow 

for the assessment of three critical behaviors. 

First, the cyclic loading below the cracking 

load allowed for the assessment of the cracking performance of the field-cast UHPC and 

Figure 2. UHPC longitudinal connection specimen with non-contact lap splice detail.
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the bonding performance of the UHPC to 

precast concrete interface. Second, the cyclic 

loading that generated stresses above the 

static cracking stress of the specimen allowed 

for the assessment of the cracking performance of the system, including whether there 

was any uncontrolled, progressive cracking or 

any interface debonding. Finally, the loading 

program allowed for the assessment of the 

static overload performance of the system, 

thus providing an indication of whether the 

system effectively emulated the performance 

anticipated from a monolithic concrete deck.

Due to the support and loading conditions 

applied to the subcomponent specimens, 

the cyclic loads generated stresses more 

severe than would traditionally be observed 

in a concrete bridge deck under similar 

magnitude wheel loads. A simple analytical 

study of the behavior of the transversely 

connected specimens suggests that the first 

phase of the cyclic testing with loads peaking at 16  kips (71  kN) generated stresses 

that are similar to the stresses that might 

be observed in a conventional concrete 

deck spanning 10  ft (3  m) between adjacent girders and loaded to a peak wheel 

patch load of 28 kips (125 kN). Subsequent 

cyclic testing with loads peaking at 21.3 kips 

(95 kN) generated even higher stresses and 

structural cracking of the decks.

Conclusions

The results of the test program, in combination 

with experience gained through deployments 

of field-cast UHPC-filled connections, have 

demonstrated the viability of this connection 

system. In terms of transverse deck connections, the structural behavior of the tested 

UHPC-filled connections emulated or surpassed the behaviors that would be anticipated 

from a monolithically cast concrete bridge deck. 

The cyclic responses demonstrated favorable 

cracking behavior with no interface debonding. 

The static loadings to failure resulted in global 

flexural failure of the simply-supported panels, 

with behaviors progressing through cracking, 

rebar yielding, and eventual concrete crushing.

The study also demonstrated that the discrete 

reinforcement in the transverse and longitudinal UHPC-filled connections is not susceptible to debonding from the UHPC under 

conditions such as applied in this test program. 

In the most severe test, a longitudinally 

connected specimen was subjected to a 

large static overload and then 11.5  million 

subsequent cycles of structural loading at 

increasing load levels. Figure  4 shows the 

crack pattern observed on the underside of 

this specimen immediately after the overload. 

This crack pattern did not change throughout the subsequent cycling. The overload 

and subsequent cycling were not observed to 

cause any debonding of the straight lengths of 

rebar that were lapped across the connection. 

The development length of straight, uncoated 

No. 5 (16M) mild steel reinforcing bars in this 

test program was demonstrated to be equal to 

or less than 5.9 inches (150 mm) in a non-contact lap splice configuration within a field-cast 

UHPC-filled connection when subjected to 

flexural tensile loads. The cyclic loading demonstrated that when sufficiently large amplitude cyclic loads are applied, the stress range 

in the rebar can be sufficient to force the rebar 

to fail via metal fatigue. Figure  5 shows the 

Figure 3. Field-cast UHPC longitudinal connection 

cyclic test setup.
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Figure 5. Fatigue failure of rebar near lap splice connection.

Figure 4. Cracking on underside of longitudinal connection specimen immediately after 70 kip (311 kN) overload 

and through completion of cyclic loading.
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Figure 6. Flexure cracking across precast panels and a UHPC connection.

cross section of the longitudinally connected 

specimen that failed due to progressive metal 

fatigue failure of the individual rebar crossing 

the connection interface. Each rebar labeled 

“Pounded” failed during the cyclic loading, 

resulting in repeated impact of mating surfaces. The other rebar failed as the specimen 

was being separated for posttest autopsy.

Structural cracks oriented perpendicular to a 

field-cast UHPC-filled connection tended to 

follow straight across the connection and did 

not turn to run along the concrete-to-UHPC 

interface. Additionally, when encountering 

the UHPC connection, single structural cracks 

in conventional concrete precast panels 

tended to become multiple, tightly spaced 

cracks in the field-cast UHPC. In the tests 

simulating transverse connections between 

precast components, the structural loads 

caused flexural tensile cracking perpendicular to the connection along midspan on 

the tensile face of each of the specimens. 

Crack widths were commensurate with the 

cracking behavior of the parent materials. In 

a general sense, an individual conventional 

concrete panel crack of a given width will 

lead into a set of approximately 10 cracks 

in the UHPC connection, each of which are 

on the order of 10 times narrower than the 

adjacent conventional concrete crack. This 

behavior can be observed in figure 6, which 

shows the cracking at midspan of a transversely connected specimen. 

Finally, although a field-cast connection fill 

material that bonds well to precast components will alleviate one potential source of 

leakage, it cannot guarantee a leak-free deck. 

The favorable bond performance observed 

between the precast panels and the field-cast 

UHPC in transverse connection tests indicates 

that this bridge decking system is not likely 

to leak along this connection interface under 

cyclic service loads or static overloads. The 

longitudinal connection test results were 
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Researchers—This study was completed by Ben Graybeal at FHWA’s Turner-Fairbank Highway 

Research Center. Additional information can be gained by contacting him at 202-493-3122 or in 

the FHWA Office of Infrastructure Research and Development located at 6300 Georgetown Pike, 

McLean, VA 22101.

Distribution—The unpublished report covered in this TechBrief is being distributed through the 

National Technical Information Service, www.ntis.gov.

Availability—The report will be available in December 2010 and may be obtained from the 

National Technical Information Service, www.ntis.gov.

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

Accelerated construction, Durable infrastructure systems, Field-cast lap splice, Precast deck 

panel connection, Adjacent decked-girder connection, Cyclic testing.

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 

TechBrief only because they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration provides high-quality 

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.

November 2010 FHWA-HRT-11-022

HRDI-40/11-10(500)E

less clear, indicating that the connection 

interface may or may not crack under large 

structural loads that approach or surpass the 

one-way bending flexural cracking capacity 

of the panel. Any structural cracking in a 

concrete bridge deck, whether monolithic or 

modular, provides a pathway of ingress for 

contaminants, which can lead to accelerated 

degradation of the deck system. Although 

these longitudinal connections are not 

necessarily leak-proof, their behaviors are 

likely to mimic or surpass the behaviors of 

a monolithic deck subjected to similar loads.

References

1. Hansen, L., and Jensen, B. (1999). “A New 

Building System Using Joints of Ultra 

High-Strength Fibre Reinforced Concrete,” 

Innovation in Concrete Structures: Design 

and Construction: Proceedings of the 

International Conference on Creating with 

Concrete, University of Dundee, Scotland, 

pp.543–552. 

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

Characterization of Ultra-High Performance 

Concrete, Report No. FHWA-HRT-06-103, 

Federal Highway Administration, McLean, VA.

3. Graybeal, B. (2006). Structural Behavior of 

Ultra-High Performance Concrete Prestressed 

I-Girders, Report No. FHWA-HRT-06-115, 

Federal Highway Administration, McLean, VA.