Ozyildirim and Sharp 1
PRESTRESSED CONCRETE PILES WITH CORROSION-FREE CARBON FIBER 1
COMPOSITE CABLE 2
3
4
5
Celik Ozyildirim, Ph.D., P.E., Corresponding Author 6
Virginia Center for Transportation Innovation and Research 7
530 Edgemont Road 8
Charlottesville, VA 22903 9
Tel: (434) 293-1977, Fax: (434) 293-1990; Email: [email protected] 10
11
Stephen R. Sharp, Ph.D., P.E. 12
Virginia Center for Transportation Innovation and Research 13
530 Edgemont Road 14
Charlottesville, VA 22903 15
Tel: (434) 293-1913, Fax: (434) 293-1990, Email: [email protected] 16
17
18
Word Count: 4,291 + 6 Tables + 5 Figures = 7,041 19
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21
22
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Submission Date: July 31, 2015 24
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Ozyildirim and Sharp 2
ABSTRACT 1
This project investigated carbon fiber composite cable (CFCC) as a replacement for traditional 2
steel strands in bridge piles. The Virginia Department of Transportation (VDOT) placed CFCC 3
in the 18 piles of the two bents of the Nimmo Parkway Bridge over the West Neck Creek in 4
Virginia Beach. Both the strands and the spirals had CFCC. These piles are considered to be a 5
corrosion-free option compared to the traditional piles. In the beginning, two test piles were cast, 6
instrumented, and driven at each of the two bents. Since the fabrication and driving operation 7
were successful, the remaining 16 piles were cast and driven. 8
VDOT now has the ability to implement the use of a corrosion-free strand in prestressed 9
elements where corrosion is a concern, such as those exposed to brackish water, saltwater, or 10
deicing salts. 11
12
13
14
15
16
Keywords: Carbon fiber composite cable, CFCC, CFRP, Reinforcement, Concrete, Corrosion 17
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Ozyildirim and Sharp 3
INTRODUCTION 1
The Virginia Department of Transportation (VDOT) now uses steel reinforcement that is alloyed 2
for corrosion- resistance in bridge deck construction, which ensures that the steel itself has 3
inherent corrosion resistance rather than relying on a barrier such as an epoxy coating or crack-4
free low-permeability concrete. This change demonstrated that one of the primary factors in 5
selecting reinforcing materials should not be initial costs (1). Instead, the important factor is the 6
up-front cost plus the future cost associated with deck maintenance operations (often-calculated 7
using life-cycle cost analysis); especially when minor changes in material costs could greatly 8
reduce maintenance costs (1). VDOT’s efforts have addressed conventional reinforcement in 9
bridge structures; however, the use of corrosion-resistant prestressed strands in bridge elements 10
has not been addressed. Strands are used in relatively small quantities in bridge structures but 11
are subjected to greater stress when compared to traditional deck reinforcement. Corrosion is 12
more critical in strands that are under high-stress conditions as compared to traditional 13
reinforcing steel bars. Wires can fracture even though section loss attributable to corrosion is 14
small because of the higher stress in each wire and the stress intensity in the area of corrosion. 15
Then, as corrosion progresses in different wires in an area and more individual wires fracture, the 16
remaining wires in the strand can become overloaded and an unexpected rapid failure of the 17
structural steel strand can result. 18
Corrosion-related damage to prestressed or post-tensioned strands has been observed in 19
the field. An example of a post-tensioned high-strength steel strand that exhibited section loss 20
attributable to corrosion is shown in Figure 1. Further, when corrosion is left unchecked, 21
complete loss of steel continuity can occur. Examples of failed external post-tensioned tendon 22
and broken strands in a prestressed beam are also shown in Figure 1. These examples have 23
created uncertainty for transportation agencies because of concern that damage might be 24
occurring in other similar bridge elements. Clearly, with a design life of 75 to100 years being 25
sought, it is important that the high-strength strands also exhibit high corrosion resistance just 26
like the corrosion- resistant reinforcement in the decks. 27
Repairs to elements with strands are costly and difficult since they are generally load-28
carrying members under the deck. In many cases, traffic must be interrupted, causing 29
inconvenience and safety concerns related to work zones. In many structures, the costs of traffic 30
control and repairs can easily approach a large percentage of building a new structure. 31
32
33
FIGURE 1 Corrosive attack on structural strand showing section loss in steel strand (left), failed post-34
tensioned tendon (middle), and corroding strands in beams because of leaking joints (right). 35 36
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Ozyildirim and Sharp 4
As a progression of the corrosion-resistant reinforcement studies, research at the Virginia 1
Center for Transportation Innovation and Research (VCTIR) focused on the high-strength strand 2
materials. Work by others with high-strength carbon fiber composite cable (CFCC) in 3
prestressed elements has shown promising results (2-6). Corrosion-free (i.e., CFCC) strand in 4
bridge piles is expected to result in large savings by eliminating the widespread costly corrosion 5
problem in prestressed elements, such as those exposed to brackish water, saltwater, or deicing 6
salts. Some concern exists because CFCC typically has a higher initial cost than traditional steel 7
strand. However, CFCC can be cost-effective compared to traditional steel because of its 8
corrosion-free performance (7). 9
10
PURPOSE AND SCOPE 11
The purpose of this study was to validate that CFCC in prestressed elements can be technically 12
and cost-effectively employed for bridge structures at high risk for corrosion. The study focused 13
on ensuring VDOT’s successful implementation of CFCC strand as a replacement material for 14
traditional steel strand. 15
This work involved the fabrication and driving of bridge piles for the Nimmo Parkway 16
Bridge over the West Neck Creek in Virginia Beach. 17
18
METHODS 19
20
Overview 21
VDOT placed CFCC in the 18 piles of the two bents of the Nimmo Parkway Bridge over the 22
West Neck Creek in Virginia Beach. The strands and spiral materials were CFCC. Initially, two 23
test piles were cast at the producer’s Plant 1 and driven. During driving, the test piles were 24
instrumented and the dynamic response was compared to that of the conventional piles with steel 25
strands. One year later, the 16 production piles were cast by the same producer, but at a different 26
facility, known as Plant 2. 27
The design information for the conventional steel strand piles and the CFCC piles are 28
summarized in Table 1. 29
30
TABLE 1 Design Information for Conventional and Carbon Fiber Composite Cable (CFCC) Piles 31 32
Property Conventional Steel Strand Piles CFCC Piles Pile size (location) 24 in square (in all Bents except
in 12 and 13) 24 in square (in Bents 12 and 13)
No. of strands 16 16 Strand diameter 0.5 in 0.6 in Strand pattern Square Circle Spiral Galvanized W3.5 (0.211-in
diameter) CFCC (0.225-in diameter)
Initial tension per strand 31 kips 34 kips Minimum ultimate strength 270 ksi (low relaxation) 270 ksi (low relaxation) Area of strand 0.196 in
2 0.2827 in2
Initial prestress per strand 31/0.196 = 158 ksi 34/0.2827 = 120 ksi Initial prestress/Fu 58.5% 44.5%
Fu = ultimate strength 33
Ozyildirim and Sharp 5
CFCC Properties 1
The manufacturer indicated that the CFCC would meet the properties listed in Table 2 (8). It is 2
important to note that the total elongation does not meet the requirements of ASTM A416, i.e., a 3
minimum value of 3.5%. 4
5
TABLE 2 Manufacturer's Specifications for Carbon Fiber Composite Cable 6 7
Property Limit Value
Guaranteed tensile capacity (Pu)a Greater than 2.33 kN/mm
2 (338 ksi)
Tensile modulusa Greater than 155 kN/mm
2 (22,481 ksi)
Elongation at break Equal to 1.7%
Specific gravity Equal to 1.6
Relaxationb Less than 1.3%
Creep strainc Less than 0.07 x 10
-3
Coefficient of linear expansiond Less than 0.6 x10
-6 /
oC (0.333 x 10
-6 /
oF)
Specific resistance Equal to 3000 cm (1,181in)
Creep failure load ratioe Greater than 0.85
Fatigue capacity stress rangef Greater than 780 N/mm
2 (113 ksi)
Bending stiffness Greater than 56.9 kN/cm2 (82.5 ksi)
Heat resistance Greater than 130 oC (266
oF)
a Calculated by effective cross section. 8
b 0.7 * Pu, 1,000 hr (20 ± 2
oC)
c 0.6 * Pu, 1 000 hr (20 ± 2
oC). 9
d 20
oC to 200
oC
e At 1 million hours 10
f 2 x 10
6 cycles at 0.75 * Pu 11
12
Test Piles 13
14
Concrete Properties 15
The mixture proportions given in Table 3 were used in the fabrication of both the CFCC and 16
conventional test piles at Plant 1. A commercially available air-entraining admixture, a retarding 17
admixture, and a high-range water-reducing admixture were also added. The specified 28-day 18
compressive strength was 5,000 psi, and the release strength was 3,500 psi. The specified air 19
content was 3% to 7%. Because of the addition of a high-range water-reducing admixture, the 20
maximum slump of 9 in was permitted provided there was no visible segregation. 21
22
TABLE 3 Mixture Proportions of Concretes for Piles (lb/yd3) 23
24
Ingredient Plant 1 Plant 2
Type III portland cement 511 494
Type F fly ash 171 211
Coarse aggregate (No. 67) 1683 1683
Fine aggregate (natural sand) 1355 1292
Water 238 235
Maximum water–cementitious material ratio 0.35 0.33
Calcium nitrite (gal/yd3) 2 2
25
Concrete properties of the piles at the fresh and hardened states were determined. Table 26
4 lists the tests conducted at the fresh and hardened states and the specification that governed 27
each test. 28
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Ozyildirim and Sharp 6
TABLE 4 Concrete Properties and Related Specifications 1 2
Test Specification
Fresh concrete
Slump ASTM C143
Air content ASTM C173
Temperature ASTM C1064
Unit weight (density) ASTM C138
Hardened concrete
Compressive strength ASTM C39
Elastic modulus ASTM C469
Permeability ASTM C1202
3
Casting of Piles 4
The fabrication of the piles including the end preparation of strands, prestressing, concrete 5
placement, steam curing, and detensioning was documented. 6
7
Driving Operation 8
The driving of a pile is a physical process, as the repetitive blows to the pile head drive the pile 9
into the ground. Therefore, piles were visually inspected for cracked or damaged concrete prior 10
to and after placement. The piles were instrumented in order to determine the dynamic response 11
for comparison to that of the conventional piles with steel strands. 12
13
RESULTS AND DISCUSSION 14
15
Test Piles 16
Two 24-in- square test piles with CFCC were cast at the same bed. The prestressing bed was 17
180 ft 8 in long to accommodate the piles; one of the piles, P1, was 76 ft long, and the other pile, 18
P2, was 82 ft long. The CFCC in spools, couplers, and material for the preparation of the ends of 19
the CFCC were shipped from the manufacturer’s facility in Japan. One interesting side note is 20
that since CFCC is not a ferrous material, Buy America requirements do not apply. CFCC is 21
currently produced in Japan, so additional shipping time is required. The producer has indicated 22
interest in establishing a CFCC fabrication facility in the USA in early 2016. 23
24
Strand Handling 25
The CFCC was unspooled, placed on the plywood surface, and cut to length. Cutting was done 26
by a saw with a carbide blade. The CFCC was handled with care to avoid rubbing and cutting, 27
but a damaged strand was detected (Figure 2). The gouge could have been caused by rubbing or 28
by a sharp or heavy object. The damaged length was discarded. There was no other visible 29
damage in the remaining strands, however, it is important to remain attentive when handling the 30
strands and watch for damaged areas. 31
The strands were placed in the forms treated with release agent. Paper was placed along 32
the bottom of the form to create a barrier between the CFCC and the release agent to avoid 33
contamination of the strand. In addition, while the strands were placed through the metal head 34
plates, plastic bushings were used to prevent any scraping or damaging of the CFCC during the 35
placement and stretching of the CFCC. 36
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Ozyildirim and Sharp 7
1 2
FIGURE 2 Gouge detected on carbon fiber composite cable prior to tensioning. 3 4
Strand End Preparation 5
To prestress concrete using CFCC, the CFCC was attached to the steel strand through the use of 6
a coupler (this method is sometimes referred to as “double chucking”) and the steel was pulled 7
with the hydraulic jack. The end of the CFCC was prepared so that wedges do not damage it 8
during stressing. First, a mesh sheet made of layers of metal and plastic were wrapped around 9
the end portion of CFCC. The end preparation of these two test piles were performed by the 10
manufacturer’s technicians, who flew in from Japan. The couplers were within the pile forms, 11
and the technicians worked in the tight form space. Second, a braided grip was put on the mesh 12
sheet (Figure 3), which is made of stainless steel. The prepared end was held by the four-part 13
wedges in a chuck barrel. A tool was used to ensure equal spacing between the wedges, and the 14
wedges were pushed into the chuck barrel evenly. A specially designed apparatus with a 15
hydraulic jack was used to push the wedges into the barrel. A mark on the wedge indicated how 16
far to push. 17
FIGURE 3 End preparation of carbon fiber composite cable with mesh sheet and braided grip (left) so that 18
4-part wedges are evenly pushed into the barrel (right). 19 20
After completing the end preparation of each CFCC strand, the chuck holding the CFCC 21
was placed on one end of the coupler as shown in Figure 4. The steel strand was then placed in 22
the other end of the coupler, and a traditional chuck was used to secure it. After all couplers 23
were assembled, they were staggered and a preload of 5 kips was applied with the jack. 24
Ozyildirim and Sharp 8
1 2
FIGURE 4 Carbon fiber composite cable and steel couplers joined (left), and couplers staggered and 3
tensioned (right). 4 5
Prestressing 6
After applying a preload of 5 kips, the jack was used to increase the load in increments of 10 kips 7
until the maximum tension of 34 kips was achieved. Normally for steel, continuous and rapid 8
loading is done by completing prestressing within 30 sec; however, with CFCC, longer 9
prestressing is desired, about 2.5 to 3 min. At each preload and then at maximum load, the 10
extension of the CFCC was measured. There was no noticeable slippage, and the expected 11
elongation occurred. 12
For safety reasons regarding the use of a new strand material at this facility, the CFCC 13
was kept prestressed overnight. On the following day, spirals that were already in the bed 14
(placed before the strands) were tied to the CFCC with plastic ties. The CFCC spiral was light 15
and could be carried easily by one person. There were no sags in the CFCC tendons after 16
placement of the CFCC spiral; sagging would be normal with the conventional steel 17
reinforcement because of the heavy weight of the steel. For each pile, two lifting devices were 18
placed. The lifting was accomplished by inserted threaded rods. The rods were placed in 19
cardboard tubes to avoid contact with the CFCC and the spiral. Later, the bolts and the 20
cardboard were removed and the hole was grouted. The pile forms were then blown clean and 21
ready for concrete. The spiral and lifting device are shown in Figure 5. Figure 5 also displays 22
corrugated plastic at the head of the pile where the dowels are placed for connection to the pile 23
bent. The use of the plastic was to prevent contact between the conventional steel reinforcement 24
and the CFCC to prevent a galvanic cell between the two that could cause corrosion of the 25
reinforcing steel since the CFCC is a more noble material. Although the CFCC wires are coated 26
with a plastic material that should prevent such activity, the use of the plastic pipe avoided the 27
possibility of contact due to damaged coating on the CFCC fibers. 28
29
Concrete Properties 30
Concrete was batched in a central plant and delivered in trucks with augers carrying 5 yd3
each. 31
The first (B1) and fourth (B2) of the five loads were sampled for fresh and hardened concrete 32
tests. These specimens were steam cured in the bed overnight and then brought to the VCTIR 33
laboratory, where they were kept in a moist room until testing. The fresh concrete properties are 34
given in Table 5. Workable concretes with proper air contents were achieved. 35
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Ozyildirim and Sharp 9
FIGURE 5 Spiral tied to carbon fiber composite cable with plastic ties (left) and lifting device placed (right).
TABLE 5 Fresh Concrete Properties 1
2
Test Test Piles Production Piles
B1 B2 B3 B4
Slump (in) 4.5 6.75 8.3 6.8
Air content (%) 7.0 6.2 5.3 5.2
Density (lb/ft3) 138.5 139.4 144.1 143.2
Concrete temperature (°F) 60 60 75 80
3
The hardened concrete properties are summarized in Table 6. The 7-day strength and 4
permeability values are the average of two specimens, and the 28-day values are the average of 5
three specimens. The compressive strengths exceeded the specified minimum 28-day strength of 6
5,000 psi at 7 days. The elastic modulus values were high. 7
8
TABLE 6 Hardened Concrete Properties 9 10
Test Age
(days)
Test Piles Production Piles
B1 B2 B3 B4
Compressive strength (psi) 7 5830 5410 5670 5910
28 7740 7530 6800 7000
Elastic modulus (106 psi) 7 4.42 --- 3.90 3.94
28 4.82 4.86 4.02 4.23
Splitting tensile strength (psi) 7 520 505 470 525
28 635 635 575 600
Permeability (C) steam cure 28 3226 4382 4224 4343
Permeability (C) accelerated
cure at 100 °F 28 570 767 --- ---
--- = No data 11
12
The permeability specimens for conventional cast-in-place concretes tested at 28 days 13
require accelerated curing. They are cured the first week at room temperature and for the next 3 14
weeks at 100 °F; they are tested at 28 days. Accelerated curing enables the determination of 15
long-term permeability at an early age of 28 days. Pozzolans or slag cements in concrete show 16
their effectiveness after the hydration reactions, which take time. Steam-cured specimens are not 17
subjected to the 3 weeks of 100 °F curing because the high steam temperatures provide 18
Ozyildirim and Sharp 10
accelerated curing similar to the curing for 3 weeks at 100 °F. The permeability values for the 1
specimens were 3226 C for B1 and 4382 C for B2 at 28 days when the specimens were kept 2
moist at room temperature after the initial steam curing. These are high permeability values; for 3
prestressed elements, VDOT specifies a maximum value of 1500 C. The temperature of the 4
beam reached 135 °F; however, the specimens were near the couplers that were exposed to lower 5
temperatures (varying between 79 °F and 91°F) to prevent slippage. Two of the specimens from 6
each batch were also tested after curing at 100 °F for 21 days in accordance with the accelerated 7
curing. The permeability values were 570 C for B1 and 767 C for B2, which are very low values 8
indicating high resistance to the penetration of liquids. In specimens subjected to relatively low 9
steam cure temperatures overnight, the high early temperatures for permeability reduction may 10
not be attained. Small specimens do not generate as much heat as the large beams. Large beams 11
would exhibit higher temperatures than the small cylinders and may exhibit reduced permeability 12
at early ages. 13
14
Placement 15
The concrete was discharged into forms starting from one end of the bed to the other. Concrete 16
was consolidated using the internal vibrators with rubber heads to prevent damage to the CFCC. 17
During concrete placement, shifting of the spirals occurred and the spacing was altered. 18
More plastic ties and discharging of some concrete to the bottom to hold the spirals in place were 19
planned for future work, which resulted in better control of the spiral spacing. Upon completion 20
of placement, the bed was covered and the specimens were placed at one end over a rack under 21
the cover. 22
A thermocouple placed a couple of inches inside the surface monitored the pile 23
temperature during the steam curing. Another thermocouple was placed in the enclosure at each 24
end of the bed. The plant used temperature-matched curing to determine the compressive 25
strength for detensioning. Temperature-matched cure (TMC) molds have heating elements and 26
were kept in the laboratory. The wireless unit near the forms sent the temperature signals to 27
control the temperature of the TMC molds in the laboratory. The control unit matches the 28
temperature of the member to that of the TMC mold. 29
In the early afternoon, right after concrete placement, the temperature recording started 30
showing that the enclosure temperature was about 55 °F and increased to 80 °F in 5 hours. The 31
temperature of the concrete in the pile based on the thermocouple was about 88 °F when the 80 32
°F enclosure temperature was reached. Then the enclosure temperature varied between 79 °F 33
and 91 °F; the concrete temperature in the pile increased up to a maximum temperature of 135 °F 34
at about 5 A.M. on the morning of November 16, about 18 hours after the addition of water to 35
the first batch; the steam was terminated. The thermocouples measuring the enclosure 36
temperature were where the couplers were; at this location, it is critical that the temperature does 37
not exceed 122 °F so that slipping of the strand in the coupler is prevented. A maximum 38
temperature of 190 °F is specified for the concrete containing the strand, which is much higher 39
than the 135 °F reached. After the termination of the steam curing, specimens representing the 40
live and dead ends for release strength were tested at about 6 A.M. The average of two TMC 41
cylinders for the south end (dead end) obtained from the first load was 4,200 psi and for the 42
north end (live end) obtained from the fourth load was 4,080 psi. Thus, the specified release 43
strength of 3,500 psi was achieved and the piles were ready for detensioning and removal from 44
the bed. 45
46
Ozyildirim and Sharp 11
As shown in Figure 6, the steel strands at both ends of the bed were cut using a torch, 1
which was done in a manner similar to that in conventional detensioning operations using a 2
sequence. Then, the CFCC between the two piles was cut using a grinder with an abrasive blade. 3
The piles were then lifted and stored next to the forms. There were no unusual large visible 4
defects on the piles, and only bug holes were evident on the formed side surfaces. 5
6
7
FIGURE 6 Torch was used to cut the steel strands at the ends (left), and the demolded beam show some tiny 8
bug holes but no large voids (right). 9
10
Driving Operation 11
Two CFCC-reinforced piles were driven as test piles along with numerous other traditional steel 12
reinforced piles during the construction of the Nimmo Parkway Bridge, which is shown in Figure 13
7. The CFCC-reinforced piles were driven using an open-end diesel hammer that had a ram 14
weight of 10,141 lb and a stroke that was 5.7 to 9.2 ft. The initial test pile drive started at the 10-15
ft mark on the pile, and the driving operation proceeded until one of the piles reached the 46.0-ft 16
mark and the other pile reached 57.5 ft. After one week, piles were driven again; one of the piles 17
to the 61.0-ft. mark, and the other pile was driven to the 61.1-ft mark. The dynamic analysis 18
indicated that there were no differences in the driving response between these piles and the 19
conventional piles with steel strands. 20
The 16 production piles were driven with no problems. In August 2014 the bridge was 21
opened to traffic. 22
23
Ozyildirim and Sharp 12
FIGURE 7 Driving of test piles (left) for the Nimmo Parkway Bridge, and instrumenting pile
before driving (right).
Production Piles 1
The test piles indicated that CFCC requires special end preparation and handling, but once cast it 2
behaves as with conventional piles. In addition, the test piles provided the lengths needed for the 3
remaining 16 production piles. 4
One year after the test piles the contractor ordered the production piles. They were cast 5
at Plant 2 with the mixture proportions given in Table 3. These values were similar to those used 6
in the test piles. A commercially available air-entraining admixture, a water-reducing and 7
retarding admixture, and a high-range water-reducing admixture were also added. The strand 8
handling, end preparation, prestressing, and concrete placement were similar to those for the test 9
piles. Four piles were cast in the bed. The preparation of the piles including strand placement, 10
end preparation, placement into the couplers, prestressing, casting of concrete, curing, and 11
detensioning required more than a 24-hour cycle. Each set of piles in a bed were completed 12
within 2 days from beginning of placement of reinforcement to removal from forms. 13
Conventional piles were prepared and detensioned in a 24-hour cycle. Studies are ongoing at 14
VCTIR to expedite the end preparation in order to achieve daily production with the CFCC piles 15
so that from placement of reinforcement to the removal from forms can be accomplished within 16
24 hours. 17
Production piles were also steam cured. The temperature in the beam reached 145 °F. 18
The specimens were kept at the end of the bed with the couplers. At this location, temperatures 19
were lower than at the remainder of the bed to ensure that slippage within the couplers did not 20
occur. The ends were prepared by plant personnel. The manufacturer’s technicians did not 21
come to prepare the ends, but the manufacturer’s engineer was there to supervise the operation. 22
A local crew fabricated the piles with no problems. 23
24
Concrete Properties 25
Two batches of concrete denoted B3 and B4 were tested; the fresh concrete properties are given 26
in Table 5, and the hardened concrete properties in Table 6. Workable concretes and specified 27
air contents were obtained. The 7-day compressive strengths had exceeded the specified 28
minimum 28-day strength of 5,000 psi. The permeability values were high. However, the values 29
were similar to the ones for the test batches without the accelerated cure. If accelerated curing 30
had been used, very low values would have been expected. 31
Ozyildirim and Sharp 13
CONCLUSIONS 1
CFCC-reinforced piles can be fabricated using a local crew. 2
CFCC should be handled with care to prevent damage to the strand. 3
The couplers should be protected from high temperature to prevent slipping. 4
Additional fabrication time is required because of the extra time needed to prepare the 5
ends, place them into the chuck, and then into the coupler. Improvements in the end preparations 6
are expected to provide daily cycles so that from the beginning with the placement of the 7
reinforcement to the removal from the forms can be accomplished within 24 hours. 8
To achieve the long-term permeability of the concrete, accelerated curing is needed if 9
the samples are not exposed to high temperatures during steam curing at the plant. 10
During driving, CFCC-reinforced piles responded in a manner similar to that of 11
conventional steel-reinforced piles. 12
13
ACKNOWLEDGMENTS 14
The authors thank the Virginia Department of Transportation and the Federal Highway 15
Administration for their support of this research, particularly VDOT’s Structure and Bridge 16
Division; VDOT’s Materials Division; and Ethan Bradshaw, William Ordel, Jonathon Tanks, 17
Mike Burton, Lew Lloyd, and Gail Moruza from the Virginia Center for Transportation 18
Innovation and Research. 19
20
REFERENCES 21
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