TECHBRIEF Compression Response 

of a Rapid-Strengthening 

Ultra-High Performance 

Concrete Formulation

FHWA Publication No.: FHWA-HRT-12-064

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

PB2012-112545.

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This document is a technical summary of the unpublished 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, Compression 

Response of a Rapid-Strengthening Ultra-High Performance 

Concrete Formulation, available through the National 

Technical Information Service at www.ntis.gov.

Objective

Ultra-high performance concrete (UHPC) has garnered interest 

from the highway infrastructure community for its ability to 

create strong, robust, field-cast connections between prefabricated structural components. The objective of this research 

was to evaluate the compressive mechanical response of a 

rapid-strengthening UHPC formulation exposed to a range 

of curing conditions. The results of the research effort are 

provided herein.

Introduction

There is a growing need for durable and resilient highway 

bridge construction/reconstruction systems that facilitate rapid 

completion of onsite activities, thus minimizing the intrusion 

forced on the traveling public. Modular components can provide high-quality, accelerated, and safe construction; however,

offsite prefabrication of bridge components necessitates an 

increased reliance on the performance of field-installed connections between these components. The mechanical and 

durability responses of the grouts used in these connections are 

critical to the overall performance of the infrastructure system.

UHPC is an advanced construction material that provides 

new opportunities for the future of highway infrastructures. 

Since 2001, the Federal Highway Administration has been 

researching the optimal uses of UHPC in highway bridge 

infrastructures through its Bridge of the Future initiative. 

Recently, the highway sector has focused on UHPC’s use as a 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov/research/
2

field-cast grout that can simultaneously afford 

simplified construction practices and enhanced 

long-term performance. One concern with 

UHPC-class materials has been their tendency 

to exhibit a dormant period after mixing and 

prior to the initiation of mechanical property

development. The accelerated achievement of 

particular mechanical response benchmarks is 

of particular interest, as it could enable the 

broader use of UHPC-class materials in accelerated bridge construction projects.

UHPC

Advances in concrete materials have led to the 

development of a new generation of cementitious materials, namely UHPC. As a class, these 

concretes tend to contain high cementitious 

materials contents, low water-cementitious 

materials ratios, compressive strengths above 

22 ksi (150 MPa), and sustained tensile strength 

resulting from internal fiber reinforcement. 

Table 1 presents a set of material properties for 

a UHPC formulation similar to that investigated 

in this study. Further details on the mechanical and durability properties of this UHPC can 

be found in Material Property Characterization 

of Ultra-High Performance Concrete.

(1) An introduction to UHPC can be found in Ultra-High 

Performance Concrete, and assistance with the 

construction of field-cast UHPC connections is 

provided in Construction of Field-Cast Ultra-High 

Performance Concrete Connections.

(2,3)

The exceptional durability of UHPC has been 

well documented. Of particular importance, 

UHPC does not exhibit early-age microcracking

that commonly occurs with conventional 

concrete. This feature, combined with the 

discontinuous pore structure in the homogeneous cementitious matrix, results in concrete 

with an extremely low permeability. 

The tensile mechanical response of UHPC also 

surpasses 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 rethink 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. 

Of particular interest, UHPC can significantly 

shorten the development length of embedded

discrete steel reinforcement, can exhibit exceptional bond when cast against previously 

cast concrete, and can display both high and 

sustained levels of tensile resistance. These 

properties facilitate the redesign of the 

modular component connection, leading to 

simplified construction and enhanced long-term 

system performance.

Testing Program

This research project focused on the assessment of compressive mechanical response of 

rapid-strengthening UHPC. Eight batches of 

this UHPC formulation were mixed and used 

to cast sets of cylinders that were 3 inches 

(76.2 mm) in diameter and 6 inches (152.4 mm) 

in nominal length. The mix design included 

the manufacturer-supplied premix, superplasticizer, and steel fiber reinforcement, along with 

potable water. The steel fiber reinforcement 

was 0.5 inches (12.7 mm) long and 0.008 inches 

(0.2 mm) in diameter and was composed of 

straight fibers included at 2 percent by volume. 

The primary mix design was used for six of 

the batches, while the remaining two batches 

also included a chemical accelerator to assess 

its ability to accelerate the attainment of compressive mechanical response benchmarks. 

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 

(7.0–10.3 MPa)

Chloride ion penetrability 

(ASTM C1202-12)(4) Very low to negligible
3

Approximately 33 cylinders were cast from each 

batch and then cured using 1 of 3 curing regimes 

until testing. The curing regimes included an 

ambient room temperature cure, an elevated 

temperature cure, and a reduced temperature 

cure. The associated temperatures were 73, 105, 

and 50 °F (23, 41, and 10 °C), respectively. The 

test specimens were subjected to the curing

condition continuously from casting until approximately 1 h before compression testing.

The tests were completed through a modified 

version of ASTM C39-11, “Standard Test Method 

for Compressive Strength of Cylindrical Concrete 

Specimens,” and ASTM C469-10, “Standard Test 

Method for Static Modulus of Elasticity and 

Poisson’s Ratio of Concrete in Compression.”(5,6)

According to the ASTM C39-11 test method, 

the two modifications were that the load rate 

increased and that the axial strain was captured 

during the test. The specified loading rate of 

35 psi/s (0.24 MPa/s) was changed to 150 psi/s 

(1.0 MPa/s) due to the high compressive strength 

of UHPC and the duration of the test, which 

resulted from the slower load rate. The axial 

strain was measured through the use of a parallel ring compressometer. This device is similar to 

the traditional compressometer described in 

ASTM C469-10, except that it holds three 

measurement transducers and does not use a 

hinge to multiply the deformations. Aside from 

the increased load rate, the tests completed in 

this study followed the alternative given in 

section 6.5 of ASTM C469-10, which allows 

for the simultaneous collection of both compressive strength and modulus of elasticity.(6)

The variables considered within this study 

included the effect of using a chemical accelerator and the effect of curing temperature on the 

compressive mechanical response. Additionally, 

specimens were cast from two different premix deliveries, thus allowing for assessment of 

the effect of premix age after blending. Batches 

were mixed with premix ages ranging from 2.5 

to 6 months.

Performance indicators focused on the axial 

compressive stress and strain response of 

the UHPC. Compressive strength, modulus of 

elasticity, strain at compressive strength, and 

overall stress-strain response were captured 

and analyzed.

Results

This study provided a clear indication of the 

compressive mechanical response of this UHPC 

formulation as influenced by a range of curing 

temperatures. The compressive strength gain as 

a function of time and curing temperature is of 

greatest practical interest to the everyday use 

of this UHPC. Figure 1 shows the compressive 

strength gain from 0 to 56 days after casting 

for the three curing conditions. Two independent 

Figure 1. Compressive strength gain results. Compressive Strength (ksi)

Compressive Strength (MPa)

Batch Data

Curve Fit

Curing Regime

105 °F (41 °C)

0

25

20

15

10

5

0

172.4

137.9

103.4

68.9

34.5

73 °F (23 °C)

50 °F (10 °C)

0 1 2 3 4 5 6 7 8 14 28 56

Days After Mix Initiation
4

batches were tested for each curing condition. 

An approximate response curve is shown for 

each curing condition. Note the clear impact 

that the curing temperature had on the time 

to strength gain initiation and on the rate of 

strength gain. In all cases, the strength surpassed 21.7 ksi (150 MPa) by 56 days after mixing.

A relationship between the constant curing 

temperature and the time to start of rapid strength 

gain was developed. This simple relationship is 

provided in figure 2.

Where:

tstart = Time of initiation of rapid strength gain in 

days.

T = Curing temperature in degrees Celsius.

A curve fitting analysis was conducted on the 

strength gain results. The result of this analysis 

is shown in figure 3. The strength of the UHPC 

can be determined based on the 28-day strength 

and the time after the start of mixing. Table 2 

provides the appropriate curve-fitting parameters for the three curing regimes.

Where:

f ‘c,28d = Compressive strength at 28 days (ksi).

f ‘c,t = Compressive strength at time t in days 

after mix initiation (ksi).

a = Fitting parameter in days.

b = Dimensionless fitting parameter.

The relationship between the compressive 

strength and the modulus of elasticity was 

also evaluated. Figure 4 provides the results 

from the six batches of UHPC at three curing 

temperatures. A best-fit analysis of the compressive strength results between 14 and 26 ksi 

(97 and 179 MPa) indicates that the equation 

in figure 5 provides an appropriate fit over this 

strength range. 

 f ‘c,t = f ‘c,28d (1- e

-

(t - tstart)

b

 a )

Figure 3. Relationship between time after mix 

initiation and compressive strength as a function of 

curing temperature.

tstart = 2.8

 √T

Figure 2. Relationship between curing temperature 

and initiation of rapid compressive strength gain 

from 50 to 105 °F (10 to 41 °C).

Figure 4. Modulus of elasticity as a function of compressive strength.

Table 2. Parameters relevant to function presented 

in figure 3.

Curing Regime

T

(°C)

f’c,28d

(ksi)

a

(days) b

105 °F (41 °C) 41 24.5 0.25 0.25

73 °F (23 °C) 23 24 1.0 0.30

50 °F (10 °C) 10 22.5 4.0 0.50

68.9

48.3

34.5

6.9

0.0

0 5 10 15 20 25 30

Compressive strength (ksi)

13.8

20.7

27.6

62.1

55.2

41.4

Elastic Modulus (GPa)

10,000

7,000

5,000

1,000

0

2,000

3,000

4,000

9,000

8,000

6,000

Elastic Modulus (ksi)

0.0 34.5 68.9 103.4 137.9 172.4 206.8

Compressive strength (MPa)

105 °F (41 °C)

73 °F (23 °C)

50 °F (10 °C)

Ec = 49,000√ f’c
5

Where:

Ec = Modulus of elasticity in psi.

f’c = Compressive strength in psi.

The overall stress-strain response of this UHPC 

was also captured through this test program. 

Both qualitative and quantitative assessments 

of the development of overall compressive 

mechanical response were completed. Figure 6

shows two stress-strain responses obtained 

at each of the three curing temperature. The 

development of the response between 2 and 

28 days after mixing is clearly displayed.

Conclusions

This research project captured the compressive 

mechanical response of a rapid-strengthening 

UHPC. The conclusions of this research project 

are as follows:

•	 The early-age compressive strength gain of 

the rapid-strengthening UHPC formulation 

is directly proportional to the curing 

temperature to which the UHPC is subjected. Using ambient room temperature 

specimens as a baseline, the cool cure specimens required significantly longer curing 

time to reach comparable strength 

levels. Similarly, specimens subjected to 

elevated curing temperatures achieved 

higher strengths more quickly. All batches, 

regardless of curing condition, reached 

56-day compressive strengths within 

approximately 2 ksi (13.8 MPa) of one 

another.

•	 The rate of compressive mechanical property attainment was not significantly 

impacted by the age of the premix at the 

time of mix initiation. Premix ages between 

2.5 and 6 months after blending were 

investigated. 

•	 The use of a chemical accelerator to 

promote rapid strength gain did not seem 

to accelerate the attainment of the desired 

mechanical properties at early ages. The 

use of accelerating admixtures should be 

investigated prior to deployment in order to 

ensure appropriate performance.

•	 The compressive strength was found to 

be predictable as a function of time based 

on the 28-day compressive strength and 

Ec = 49,000√ f’c

Figure 5. Modulus of elasticity as a function of 

compressive strength between 14 and 26 ksi 

(97 and 179 MPa).

Figure 6. Example compressive stress-strain results. Axial Stress (ksi)

0

25

20

15

10

5

30

Axial Stress (MPa)

0.0

172.4

137.9

103.4

69.0

34.5

206.9

0.0 0.002 0.004 0.006

28-day test

2-day test

105 °F (41 °C)

73 °F (23 °C)

50 °F (10 °C)

Axial Strain
6

Researchers—This study was led by Ben Graybeal at FHWA’s Turner-Fairbank Highway Research 

Center. For additional information, contact him at (202) 493-3122 or in the FHWA Office of Infrastructure 

Research and Development located at 6300 Georgetown Pike, McLean, VA, 22101-2296.

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

National Technical Information Service at www.ntis.gov.

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

report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at http://www.fhwa.dot.

gov/research.

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

construction, Durable infrastructure systems, Stress-strain, Compressive mechanical response.

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.

september 2012 FHWA-HRT-12-064

HRDI-40/09-12(300)E

the constant temperature curing regime 

to which the concrete is subjected.

•	 The modulus of elasticity of this UHPC 

formulation was found to be predictable 

as a function of the compressive strength. 

The developed relationship is applicable 

for compressive strengths from 14 to 26 ksi 

(97 to 179 MPa).

References

1. Graybeal, B. (2006). Material Property Characterization of Ultra-High Performance Concrete, Report No. FHWA-HRT-06-103, Federal 

Highway Administration, Washington, DC.

2. Graybeal, B. (2011). Ultra-High Performance Concrete, Report No. FHWAHRT-11-038, Federal Highway Administration, Washington, DC.

3. Graybeal, B. (2012). Construction of FieldCast Ultra-High Performance Concrete 

Connections, Report No. FHWA-HRT12-038, Federal Highway Administration, 

Washington, DC.

4. ASTM C1202-12. (2010). “Standard Test 

Method for Electrical Indication of Concrete’s 

Ability to Resist Chloride Ion Penetration,” 

ASTM Book of Standards Volume 04.02, 

ASTM International, West Conshohocken, PA.

5. ASTM C39-11. (2011). “Standard Test Method 

for Compressive Strength of Cylindrical 

Concrete Specimens,” ASTM Book of 

Standards Volume 04.02, ASTM International, 

West Conshohocken, PA.

6. ASTM C469-10. (2010). “Standard Test Method 

for Static Modulus of Elasticity and Poisson’s 

Ratio of Concrete in Compression,” ASTM 

Book of Standards Volume 04.02, ASTM 

International, West Conshohocken, PA.