Article

Assessment of Post-Tensioned Grout Durability by Accelerated

Robustness and Corrosion Testing
Samanbar Permeh and Kingsley Lau *

Department of Civil and Environmental Engineering, Florida International University, Miami, FL 33174, USA;
samanbar.permeh1@fiu.edu
* Correspondence: kilau@fiu.edu

Abstract: The corrosion of steel in post-tensioned tendons has been associated with deficient grout
materials containing high free sulfate ion concentrations. In a Florida bridge in 2011, tendon corrosion
failures occurred for a prepackaged thixotropic grout that had developed material segregation.
However, the available grout and corrosion testing prescribed in material specifications, such as grout
bleed water testing, was not able to identify the propensity or modality for the grout deficiencies and
the associated steel corrosion that was observed in the field. It was of interest to identify corrosion
testing methods that could prescribe grout resistance to segregation-related deficiencies that can form
by aberrations in construction. The objectives of the work presented here included (1) characterizing
the development of physical and chemical grout deficiencies due to excess mix water and water
volume displacement, (2) developing small scale test methodologies that identify deficient grout,
and (3) developing test methodologies to identify steel corrosion in deficient grout. The inverted-tee
test (INT) and a modified incline-tube (MIT) test were assessed and both were shown to be useful to
identify the robustness of grout materials to adverse mixing conditions (such as overwatering and
pre-hydration) by parameters such as sulfate content, moisture content, electrical resistance, and steel
corrosion behavior. It was shown that the different grout products have widely different propensities
for segregation and accumulation of sulfate ions but adverse grout mixing practices promoted the
development of grout deficiencies, including the accumulation of sulfate ions. Corrosion potentials
of steel < −300 mVCSE developed in the deficient grout with higher sulfate concentrations. Likewise,
the corrosion current density showed generally high values of >0.1 µA/cm2 in the deficient grouts.
The values produced from the test program here were consistent with historical data from earlier
research that indicated corrosion conditions of steel in deficient grout with >0.7 mg/g sulfate, further
Citation: Permeh, S.; Lau, K. verifying the adverse effects of elevated sulfate ion concentrations in the segregated grout.
Assessment of Post-Tensioned Grout
Durability by Accelerated Robustness Keywords: corrosion; post-tensioned (PT); grout; accelerated testing
and Corrosion Testing. Constr. Mater.
2023, 3, 449–461. https://doi.org/
10.3390/constrmater3040029

Received: 27 September 2023 1. Introduction

Revised: 30 October 2023 Prestressed concrete by post-tensioning (PT) methods has been widely used for bridge
Accepted: 17 November 2023 construction, providing greater range of design possibilities and positive material and
Published: 23 November 2023 construction characteristics to improve durability. Cementitious grout in bonded PT sys-
tems provides barrier protection from the external environment in addition to protection
afforded by the concrete element and the tendon duct material [1–3]. As the grout is typi-
cally made from Portland cement, the steel strand is further protected from corrosion by
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
the development of a passive layer due to the alkaline grout pore water solution. These
This article is an open access article
corrosion protection levels are often effective in preventing corrosion of the embedded
distributed under the terms and
steel; however, there have been several cases of premature corrosion in Florida bridges and
conditions of the Creative Commons elsewhere [4–8]. Many of those cases were related to the inadequate or degraded protection
Attribution (CC BY) license (https:// of the strand at joints where moisture and chloride ions can penetrate. Other cases were
creativecommons.org/licenses/by/ related to the development of void spaces within the tendon due to the formation of bleed
4.0/). water. In those instances, the steel strand was partially exposed in the grout voids in contact

Constr. Mater. 2023, 3, 449–461. https://doi.org/10.3390/constrmater3040029 https://www.mdpi.com/journal/constrmater

Constr. Mater. 2023, 3 450

with the bleed water lens. In part due to aggregation of chloride ions by the transport of the
bleed water, as well as possible carbonation and moisture recharge due to imperfect duct
sealing, macrocell coupling of the developed corrosion anodes at the grout–air interface
and the remaining steel (strand embedded in the grout and auxiliary steel components)
resulted in accelerated corrosion. Material specifications since the early 2000s for grout with
non-bleed characteristics were established to prevent the corrosion associated with grout
bleed water; however, by 2011, there were cases where steel strand corrosion developed
in grouts meeting the non-bleed thixotropic grout specifications [9–14]. The corrosion
was not associated with bleed water or void formation and chloride ion concentrations
were not significantly elevated in those cases. Some of these cases were associated with
physically and chemically deficient segregated grout characterized as moisture-rich and
low cement content material with high concentrations of sulfate and alkali ions [15–17]. The
accumulation of sulfate ions were apparently manifested by the grout segregation process
that occurred soon after grout placement due to the ionic mobility of the sulfate ion that
originated from the original grout material [16]. These issues have proven the importance
of having good grout quality to extend the service life of bonded post-tensioned tendons.
The extent of grout deficiency, moisture presence, aggressive ion accumulation, and grout
pore water carbonation contribute to the severity of the defect.
Grout material testing for corrosion mitigation and quality control typically focus
on minimizing the formation of bleed water that have been largely associated with
the premature corrosion of strand. Specified testing included the wick-induced bleed
tests, Schupak pressure test, and incline tube test. Building specifications also limit the
chloride content, often prescribed as a percent of chloride per cement content. Various
testing approaches for the corrosion of steel in the cementitious materials have been
considered [18–24]. Trejo et al., 2009 [21], evaluated accelerated corrosion test procedures
including the mini-macrocell test. An anodic potentiostatic polarization test was developed
in consideration of chloride penetration through damaged tendon ducts as part of a Federal
Highway Administration (FHWA) research project on the durability of bonded tendons
in post-tensioned bridge structures [25]. The FHWA post-tensioning tendon installation
and grouting manual [26] continues to refer to this test method. Schokker, 1999 [27], and
Hamilton et al., 2000 [28], further developed the test method and addressed complications
with the electrochemical polarization test parameters. Pacheco et al., 2006 [29], included
the linear polarization resistance method to provide more practical testing than the anodic
potentiostatic tests. Based on the research by Schokker and Hamilton, the post-tensioning
institute (PTI) made provisions in the PTI M55 specification for grouting of post-tensioned
structures for an accelerated corrosion test (ACT) for the assessment of grout materials [30].
The ACT gives provision for the acceptance of grout materials that exhibit a polarization
resistance corresponding to a value greater than 700 kΩ·cm2 . The polarization resistance of
steel embedded in the test grout material gives an indication as to if the grout constituent
materials allow depassivation of the steel to occur. Further provisions allow alternative
acceptance requirements by testing by an anodic potentiostatic polarization method for
the grouted specimen immersed in chloride solution and polarized to +200 mVSCE where
the time to corrosion must exceed that of a control neat grout. The polarization would
allow migration of the chloride ion through the grout and holds the steel at a large an-
odic polarization that would allow the fast detection of corrosion once chloride-induced
corrosion initiates. Current specifications in Florida and Virginia require prepackaged
grout materials to be tested according to the PTI ACT method whereby materials that
exhibit a time to corrosion exceeding 1000 h are considered satisfactory. As mentioned
earlier, this test component derived from the viewpoint of the ability of the grout to resist
chloride penetration through the grout, as can occur in scenarios where there is incomplete
protection provided by the tendon duct and reinforced concrete structural element but
which does not directly address developed grout deficiencies such as segregation.
The rapid-macrocell test was developed under the strategic highway research program
(SHRP) [31] for testing of the corrosion of steel rebar [32,33], including in standard specifica-
Constr. Mater. 2023, 3 451

tions for testing of stainless steel rebar in ASTM A955 Annex 2.28. The rapid macrocell test
has also been used in research for steel strand in grouts [34,35]. The test method separates
two test cells, each comprising a steel electrode embedded in cementitious material or
immersed in a representative test solution. The two test cells are electrically coupled with a
connection wire and a shunt resistor and ionically coupled via a salt bridge (such as agar
admixed with salt). Each test cell develops net anodic behavior or net cathodic behavior
after its galvanic coupling where a net macrocell current between the cells can develop.
With these test conditions controlled, the rapid-macrocell test can be used to differentiate
corrosion conditions with small test elements and basic electronic instrumentation. In
order to assess deficient grouts, the anode component should maintain grout material
characteristics that allow for corrosion initiation such as pH, chloride concentration, sulfate
concentration, etc. [36,37].
Due to the corrosion tendon failures in a Florida bridge in 2011 [8] associated with a
prepackaged thixotropic grout that had developed material segregation, it was of interest
to identify corrosion testing methods that would account for the susceptibility of grout
materials to form physical and chemical deficiencies. It would be suggested that testing
attuned to grout segregation (such as to identify grout robustness and corrosion mitigation)
could be used to prescribe grouts resistant to aberrations in construction and provide
greater confidence in material selection [38–41]. Full scale tendon mockups such as those
required prior to bridge construction in Virginia for grout material selection may be cost
prohibitive and excessive. Tests such as a modified incline tube test were used in research
to identify grout segregation but this testing can also be costly. Furthermore, the chemistry
of complex grout mix designs can be affected by the many environmental and construction
factors including temperature, grout storage, pre-hydration, excess moisture mixing, etc.
As construction can sometimes have delays in grout casting as well as other non-ideal
construction conditions, specified grouts that are robust after adverse mixing and grouting
conditions can minimize the severity of developed grout defects.
On a related technical note, inhibitor impregnation utilizing a silicon hydrocarbon
polymer that forms a protective film was applied on tendons in a FDOT bridge (Jacksonville,
FL, USA). Field results showed that inhibitor, as part of a commercially-available system,
could be distributed along the length of the tendon via the strand interstitial spaces. The
result of laboratory trials showed that the inhibitor-impregnated specimens had reduced
corrosion by more than 90% comparing to untreated samples [42]. The procedure has since
been used on PT tendons at risk of corrosion on other bridges, buildings, and industrial
structures in Florida, Virginia, New York, Ontario, Newfoundland, and the UK. The field
case study also showed severe corrosion of galvanized steel components in the presence of
deficient grout [43,44]. The development of an accelerated corrosion test that considers the
robustness of grout materials in terms of corrosion durability ideally could disseminate the
beneficial effects of corrosion mitigation technologies such as the inhibitor impregnation as
well as performance of other metallic component such as galvanized steel.
In this paper, the development of an accelerated material test that has been lacking
in material specifications is described to identify materials that can be susceptible to
segregation where the differentiation of localized grout chemistry could allow corrosion
initiation. The outcome of the work would ideally provide information on the modality
of tendon degradation (different from conventional PT corrosion mechanisms) in the
presence of physically- and chemically-deficient grout and provide support for more
discerning material specifications. The objective of the work presented here, as part of
a larger test program, included to (1) to characterize the development of physical and
chemical grout deficiencies due to excess mix water and water volume displacement, (2) to
develop small scale test methodologies that identify deficient grout, and (3) to develop
test methodologies to identify steel corrosion in deficient grout. To address these research
goals, testing included methods that would promote the development of grout deficiencies.
This included adverse mix conditions such as overwatering and grout pre-hydration
for the grouts in vertically-deviated setups to promote water displacement. The results
Constr. Mater. 2023, 3 452

presented here for commercially available grouts do not represent material performance as
intended following accepted mixing protocols and specifications but were used rather for
illustrative purposes to develop corrosion testing protocols that can address grout physical
and chemical deficiencies.

2. Materials and Methods

Four grout products and a neat grout were used. Table 1 lists its chemical makeup
determined by X-ray fluorescence testing. From previous research, it was identified that
deficient grout can form at the upper elevation of vertically-deviated tendons due to the
displacement of water-rich materials during the pumping stage of the grout installation.
Table 2 details the conditions for grout material specimens. A replication of test specimens
for each material condition is shown in Table 2. An excess of mix water, 10% above the
manufacturers’ recommended limit, was added. Previous research [14] used up to 15%
excess water to create adverse conditions in attempts to reproduce the grout deficiencies
in the field. However, the research here sought to provide fewer extreme conditions for
practical implementation of testing to real world conditions but was aggressive enough to
assess grout robustness with the earlier noted caveats.

Table 1. Grout chemical makeup analyzed by XRF.

Mass (%) Grout A Grout B Grout C Grout D Neat Grout

Sodium (Na) - - 0.3, 0.3 0.03, - -
Potassium (K) 0.3, 0.6 0, 0.01 1.1, 1.2 0.1, 0.1 0.2, 0.4
Calcium (Ca) 24.3, 45.1 30.5, 42.2 42.3, 46.5 33.9, 36.2 31.7, 47.6
Silicon (Si) 3.5, 6.6 4.3, 5.4 14.4,16.4 4.1, 4.2 4.1, 5.8
Sulfur (S) 0.6, 0.8 0.5, 0.7 1.5, 1.8 1.0, 1.1 0.6, 1.6
Chloride (Cl) - - - - -

Table 2. INT and MIT grout material specimens.

Test Setup Material Number of Samples Grout Condition

Grout A 2 As Received and 10% extra mix water
Grout B 2 As Received and 10% extra mix water
2 As Received and 10% extra mix water
INT Grout C
2 Expired and 10% extra mix water
Grout D 2 Expired and 10% extra mix water
Neat Grout 2 0.45 w/c
Grout A 6 As Received and 10% extra mix water
MIT
Grout B 6 As Received and 10% extra mix water
Grout A was used for horizontal PT applications and Grout B was used for vertical applications.

The inverted T-test (INT) was proposed where a dramatic change in the vertical axial
cross-section of the test specimen was introduced, allowing for localized accumulation of
deficient grout materials. For example, if grout segregation were to occur in a 1 mm layer
at the widest area of the Tee body, an equivalent volume of that material transported to the
upper levels of the Tee header would be 2.89 cm in height. A schematic of the INT is shown
in Figure 1. INT testing is benchtop in scale and significantly reduces material wastage
and fabrication costs compared to MIT and full-scale mockup testing; however, the grout
placement and dimensions are not representative of field grout pumping conditions. INT
specimens were cast without (Figure 1a) and with steel (Figure 1b) for grout material and
corrosion testing, respectively. The grout was mixed using an electric mixer and filled in the
Constr. Mater. 2023, 4, FOR PEER REVIEW 5

wastage and fabrication costs compared to MIT and full-scale mockup testing; however,
Constr. Mater. 2023, 3 the grout placement and dimensions are not representative of field grout pumping condi-453
tions. INT specimens were cast without (Figure 1a) and with steel (Figure 1b) for grout
material and corrosion testing, respectively. The grout was mixed using an electric mixer
and
moldfilled
by a in the mold
manual pump.by aAfter
manual pump.
28 days After 28
of curing daysthe
within of curing
INT mold,within the INT
sections mold,
of the mold
sections of the mold were made for the material and corrosion testing. For material
were made for the material and corrosion testing. For material testing, the tee header was testing,
the tee header
partitioned intowas partitioned
three into three
sections [0”–2”, sections
12”–14”, [0”–2”,(0–5.1,
24”–28”, 12”–14”, 24”–28”,
30.5–35.6, (0–5.1,
61–71.1 30.5–
cm)]. For
35.6, 61–71.1 cm)]. For corrosion testing, the tee header was partitioned into 9-inch
corrosion testing, the tee header was partitioned into 9-inch length sections. The segments length
sections.
were cut The
andsegments
demolded. were cut and demolded.
A 1/8-inch (3.2 mm) hole A 1/8-inch (3.2 mm)
was drilled hole
at the topwas drilled
of the at
exposed
the top of the exposed steel cross-section of each specimen and a steel screw was
steel cross-section of each specimen and a steel screw was inserted so that a hard electrical inserted
so that a was
contact hardmade.
electrical contactcopper
Insulted was made.wireInsulted copper to
was soldered wire
thewas soldered
steel to thethe
stud. Both steel
top
stud. Both the top and bottom of each specimen were coated with
and bottom of each specimen were coated with an epoxy to mask the exposed steel an epoxy to mask the
bar
exposed steel and
cross-section bar cross-section
the electricaland the electrical connection.
connection.
½” Φ
steel bar

a. b. Epoxy collar 1”length

24˝-28˝
1” PVC pipe
1” PVC pipe

Two 9-in. TEST SPECIMEN

TEST SPECIMEN (TEE HEADER)
9”

2”x1” PVC
2”x1” PVC
reducer bushing
reducer bushing
29” 9” 29”
3”x2” PVC tee
12˝-14˝

3”x2” PVC tee

3”x2” PVC flush bushing
3”x2” PVC flush bushing
2”x1” PVC 9”
2”x1” PVC
reducer bushing
reducer bushing
0˝-2˝

1” PVC ball valve

1” PVC ball valve
6”
TEE BODY

6” 6”
6”

TO GROUT
TO GROUT
MIXER
MIXER
1” PVC pipe 3” PVC cap 1” PVC pipe 3” PVC cap

Figure 1.
Figure INT–testschematic:
1. INT–test schematic:(a)
(a)grout
groutmaterial
materialtesting
testingand
and(b)
(b)corrosion
corrosiontesting.
testing.

MIT testing
MIT testingisisbased
basedononthethe incline-tube
incline-tube testtest
whichwhich
waswas previously
previously developed
developed by in-by
industry groups to assess grout durability and includes dimensions
dustry groups to assess grout durability and includes dimensions and grout placement and grout placement
methods better
methods betterrepresentative
representativeofofactual
actualconstruction.
construction.BasedBasedononpositive
positive research
research outcomes
outcomes
to identify grout segregation in previous research, the MIT was revisited. Grout A A
to identify grout segregation in previous research, the MIT was revisited. Grout andand BB
with 10% excess water were cast according to Florida Standard Specification
with 10% excess water were cast according to Florida Standard Specification Section 938. Section 938.
The test
The test setup
setup generally
generallyconsists
consistsofofpumping
pumpinggrout groutin in
a 3-inch (7.6(7.6
a 3-inch cm)cm)diameter pipe,pipe,
diameter along
a 15-foot
along (4.6 m)
a 15-foot length
(4.6 at a 30
m) length at degree incline.
a 30 degree A schematic
incline. A schematic of the
of specimen
the specimen assembly
assembly used
in this research is shown in Figure 2. Testing was conducted in ambient
used in this research is shown in Figure 2. Testing was conducted in ambient South Florida South Florida
outdoor conditions.
outdoor conditions.AA15-foot
15-foot(4.6
(4.6m) m)0.5-inch
0.5-inch(1.3(1.3cm)
cm)diameter
diametersteel steel
barbar was
was placed
placed inin
the MIT for additional corrosion testing. A manual grout pump
the MIT for additional corrosion testing. A manual grout pump was used to inject the was used to inject the
grout into the MIT assembly. After ~365 days of hydration, for the corrosion testing, at the at
grout into the MIT assembly. After ~365 days of hydration, for the corrosion testing,
the base
base of each
of each tendon,
tendon, the the embedded
embedded steel
steel barbarwaswas exposed
exposed forfor electrical
electrical contact
contact forfor
thethe
electrochemical testing. Six portals [4 × 3 inch (10.2 × 7.6 cm)]) along
electrochemical testing. Six portals [4 × 3 inch (10.2 × 7.6 cm)]) along the length of the MIT the length of the
MIT specimen
specimen werewere
mademade to expose
to expose the grout
the grout within
within the the
ductduct
by by cutting
cutting andand removing
removing thethe6
Constr. Mater. 2023, 4, FOR PEER REVIEW
PVC cover. Grout was sampled from each of the MIT specimens within
PVC cover. Grout was sampled from each of the MIT specimens within the top and bottom the top and bottom
66 inches
inches ofof the
theduct.
duct.

Figure2.2.MIT–test
Figure MIT–testset
setup.
up.Left:
Left:tendon
tendonschematic.
schematic.Right:
Right:outdoor
outdoortest
testsetup.
setup.

The INT test segments were placed in saturated calcium hydroxide solution (pH 12.6)
made from deionized water. A stainless steel rod, placed adjacent to the test segment in
the test solution, was used as a counter electrode. A saturated calomel electrode (SCE) was
used as a reference electrode. For the MIT test setup, at the base of each tendon, the em-
bedded steel bar was exposed so that electrical contact can be made for the electrochemical
Constr. Mater. 2023, 3 454

The INT test segments were placed in saturated calcium hydroxide solution (pH 12.6)
made from deionized water. A stainless steel rod, placed adjacent to the test segment in the
test solution, was used as a counter electrode. A saturated calomel electrode (SCE) was used
as a reference electrode. For the MIT test setup, at the base of each tendon, the embedded
steel bar was exposed so that electrical contact can be made for the electrochemical testing.
A counter electrode made out of activated titanium mesh (4 × 3 inch) inserted between
two wet sponges was affixed to exposed grout surface at openings made in the duct. A pen
copper/copper-sulfate reference electrode (CSE) was placed at the center of the fixture.
The open-circuit potential (OCP) and linear polarization resistance (LPR) measure-
ments were made using an SCE (for INT specimens) and CSE (for MIT specimens). The LPR
testing was made from the OCP and a cathodicaly polarized 25 mV at 0.05 or 0.1 mV/s scan
rate. Electrochemical impedance spectroscopy (EIS) was conducted at the OCP condition
using a 10 mV AC perturbation in the frequency range of 100 kHz to 1 kHz, sampling
10 data points per decade. The solution resistance, Rs, was determined as the high fre-
quency limit by fitting the impedance spectrum to the Randles equivalent circuit analog
and was used to correct for the measured polarization resistance by LPR (Rp’) following
the equation Rp = Rp’ − Rs.

3. Results and Discussion

3.1. Material Characteristic
The INT specimens allowed for the physical separation of grout materials from the tee
header and tee body. The results of the moisture content are shown in Figure 3. There was
strong differentiation in moisture content between the tee header and body for Grout C and
expired Grout C and D. Grouts C and D appeared to have higher contents of fine materials
such as silica- and calcium-bearing components that may have contributions to the physical
separation of material. Pre-hydration of the material may also allow development of non-
binding filler components that may be susceptible to differential transport. Differences
Constr. Mater. 2023, 4, FOR PEER REVIEW 7
in moisture content of the grout from the tee header and body were less apparent for
Grouts A and B.

40

35

30
Moisture Content (%)

25

20

15

10

0
2"-4"

14"-16"

26"-28"

2–4” 14–16” 26–28”

2"-4"

14"-16"

26"-28"

2"-4"

14"-16"

26"-28"

2"-4"

14"-16"

26"-28"

2–4” 14–16” 26–28”

2"-4"

14"-16"

26"-28"

2"-4"

14"-16"

26"-28"
INT Body

INT Body

INT Body

INT Body

INT Body

INT Body

2–4” 14–16” 26–28” 2–4” 14–16” 26–28” 2–4” 14–16” 26–28” 2–4” 14–16” 26–28”
INT Header INT Header INT Header INT Header INT Header INT Header

Grout A Grout B Grout C Expired Grout C Expired Grout D Neat Grout

Figure
Figure3.3.Moisture
Moisturecontent
contentofofgrout
groutcast
castininINT
INTwith
with10%
10%extra
extramix
mixwater.
water.Values
Valuesfor
forgrout
groutininthe
thetee
tee
body and at various elevations of the tee header given.
body and at various elevations of the tee header given.

The
Thegrout
groutfrom
fromthetheINT
INTand andMIT
MITspecimens
specimenswas wasfurther
furthertested
testedfollowing
followingthetheupdated
updated
FMFM 5-618 method [45] to assess the effects of poor construction on the extenttotowhich
5-618 method [45] to assess the effects of poor construction on the extent which
sulfate
sulfateions
ionscan
canaccumulate
accumulateincluding
includingoverwatering
overwateringand andprehydration
prehydration(Figure
(Figure4).
4).Different
Different
grout
groutproducts
productshad haddifferent
differentyields
yieldsofofleached
leachedsulfate
sulfateions
ionsininthe
theINT
INTheader.
header.AsAsshown
shown
ininFigure
Figure4,4,higher
highersulfate
sulfatelevels
levels(apparently
(apparentlyalready
alreadydissolved
dissolvedininthethepore
porewater)
water)were
were
generally
generallyobserved
observedininthe thetee
teeheader
headerthan
thanthe
thetee
teebody,
body,likely
likelyrelating
relatingtotothe
thedisplacement
displacement
ofofwater
watertotothe
thetop
topofofthe
thespecimen.
specimen.Comparisons
Comparisonsofofthe theaverage
averagesulfate
sulfateconcentrations
concentrationsinin
MIT
MITspecimens
specimensdo doindicate
indicate differentiation the sulfate
differentiation of the sulfatecontent
contentininthe
thegrout
groutfrom
fromthe
theupper
up-
andand
per lower
lowerelevations
elevations ofof
thetheducts.
ducts.For
Forboth
bothGrout
GroutA A and
and B, the average
averagesulfate
sulfatecontent
content
in the grout from the top of the specimen was higher than the average sulfate content from
the bottom of the specimen. It was anticipated that MIT testing of the other grout materials
would produce differentiation in sulfate content between the top and bottom elevations
as well.
 sulfate ions can accumulate including overwatering and prehydration (Figure 4). Different
grout products had different yields of leached sulfate ions in the INT header. As shown
in Figure 4, higher sulfate levels (apparently already dissolved in the pore water) were
generally observed in the tee header than the tee body, likely relating to the displacement
Constr. Mater. 2023, 3 of water to the top of the specimen. Comparisons of the average sulfate concentrations 455 in
MIT specimens do indicate differentiation of the sulfate content in the grout from the up-
per and lower elevations of the ducts. For both Grout A and B, the average sulfate content
in
inthe
thegrout
groutfrom
fromthe toptop
the of the specimen
of the waswas
specimen higher thanthan
higher the average sulfate
the average content
sulfate from
content
the bottom of the specimen. It was anticipated that MIT testing of the other grout
from the bottom of the specimen. It was anticipated that MIT testing of the other grout materials
would produce
materials woulddifferentiation in sulfate content
produce differentiation between
in sulfate content the top andthe
between bottom elevations
top and bottom
as well.
elevations as well.
100

Grout Sulfate Concentration (mg/g) 10

1 Max
Max Max
Max
Min
Min Min

0.1 Min

0.01

0.001
0–2” 12–14” 24–26” 24–26” 24–26” 0–2” 12–14” 24–26”

Top

Bottom

Top

Bottom
0"-2"

12"-14"

24"-26"

0"-2"

12"-14"

24"-26"

24"-26"

24"-26"

24"-26"

0"-2"

12"-14"

24"-26"
0–2” 12–14” 24–26” 24–26”
INT BODY

INT BODY

INT BODY

INT BODY

INT BODY

INT BODY
INT Header INT Header INT INT INT INT Header
Header Header Header

Grout A (INT) Grout B (INT) Grout C(INT) Exp. Grout C Exp. Grout D Neat Grout (INT) Grout A Grout B
(INT) (INT) (MIT) (MIT)

Figure
Figure4.4.Comparison
Comparisonof ofsulfate
sulfateion
ionconcentrations
concentrationsiningrout
groutfrom
fromINT
INTand
andMIT.
MIT.Values
Valuesfor
forgrout
groutin
in
the tee body and at various elevations of the tee header given.
the tee body and at various elevations of the tee header given.

3.2.Electrochemical
3.2. ElectrochemicalCharacteristic
Characteristic
As shown
As shownin in Figures
Figures 55 and
and 6,
6, the
the steel
steel embedded
embedded in in Grout
Grout A A and
and BB all
all developed
developed
passive potentials in the range of − 100 < OCP < − 200 mV . Some of the
passive potentials in the range of −100 < OCP < −200 mVSCE. Some of the specimens cast
SCE specimens cast
with neat grout developed similar passive potentials. However, specimens
with neat grout developed similar passive potentials. However, specimens cast with cast with Grout
C and C
Grout expired Grout C
and expired and D
Grout C developed more electronegative
and D developed potentials
more electronegative at levels at
potentials that may
levels
be interpreted as active corrosion (as negative as − 450
that may be interpreted as active corrosion (as negative asSCE mV ) according to ASTM C876
−450 mVSCE) according to ASTM [46].
This observation was coincident with the physical grout deficiencies described
C876 [46]. This observation was coincident with the physical grout deficiencies described earlier [47];
however,
earlier since
[47]; the specimens
however, since thewere immersed
specimens wereinimmersed
saturated calcium hydroxide
in saturated calcium solution prior
hydroxide
Constr. Mater. 2023, 4, FOR PEER to
REVIEW testing and were tested in chloride-free saturate calcium hydroxide solution,
solution prior to testing and were tested in chloride-free saturate calcium hydroxide solu-88 corrosion
Constr. Mater. 2023, 4, FOR PEER REVIEW
activation
tion, wasactivation
corrosion not expected. Testing
was not of theTesting
expected. grout of
pore
thewater
groutfor chemical
pore water for deficiencies
chemical
(Figure 4) showed higher sulfate accumulation in Grout C and expired grout C and D.
deficiencies (Figure 4) showed higher sulfate accumulation in Grout C and expired grout
C and100 D.
100
*1: Limit for Corrosion Risk ( ASTM C876)
*1: Limit for Corrosion Risk ( ASTM C876)
*2: Limit for Severe Corrosion (ASTM C876)
0 *2: Limit for Severe Corrosion (ASTM C876)
0

-100
-100
(mVSCE )
SCE)

-200
OCP(mV

-200 *1
*1
OCP

-300
-300
*2
-400 *2
-400

-500
-500 25–34” 7–16” 25–34” 7–16” 25–34” 7–16” 25–34” 7–16” 25–34” 7–16” 25–34” 7–16”
25"-34"
25–34” 7"-16"
7–16” 25"-34"
25–34” 7"-16"
7–16” 25"-34"
25–34” 7"-16"
7–16” 25"-34"
25–34” 7"-16"
7–16” 25"-34"
25–34” 7"-16"
7–16” 25"-34"
25–34” 7"-16"
7–16”
25"-34"
Top 7"-16"
Bottom 25"-34"
Top 7"-16"
Bottom 25"-34"
Top 7"-16"
Bottom 25"-34"
Top 7"-16"
Bottom 25"-34"
Top 7"-16"
Bottom 25"-34"
Top 7"-16"
Bottom
(Head Top)
Top (Head-Bot)
INT Header Bottom (Head Top)
Top (Head-Bot)
INT Header Bottom (Head Top)
Top (Head-Bot)
INT Header Bottom (Head Top)
Top (Head-Bot)
INT Header Bottom (HeadTopTop) (Head-Bot)
INT Header Bottom (Head Top)
Top (Head-Bot)
INT Header Bottom
(Head Top) (Head-Bot) (Head Top)
INT Header (Head-Bot) (Head Top)
INT Header (Head-Bot) (Head Top)
INT Header (Head-Bot) (Head Top)
INT Header (Head-Bot) (Head Top)
INT Header (Head-Bot)
INT Header
Grout A Grout B Grout C Expired Grout C Expired Grout D Neat Grout
Grout A Grout B Grout C Expired Grout C Expired Grout D Neat Grout

Figure
Figure5.
Figure 5.Open–circuit
5. Open–circuitpotential
Open–circuit potentialfor
potential forINT
for INTtesting.
INT testing.Values
testing. Valuesfor
Values forgrout
for groutat
grout atvarious
at variouselevations
various elevationsof
elevations ofthe
of thetee
the tee
tee
header
headergiven.
given.
header given.

-100 -100
-100 -100
CSE)
CSE)

-150 -150
(mVvsvsCSE)
(mvvsvsCSE)

-150 -150

-200
-200 -200
-200
OCP(mv

OCP(mV
OCP

OCP

-250
-250 -250
-250

-300
-300 -300
0 5 10 15 -300
0 5 10 15 0 5 10 15
0 5 10 15
Distance from Bottom (ft) Distance from Bottom (ft)
Distance from Bottom (ft) Distance from Bottom (ft)

Figure 6. Open–circuit potential of steel in MIT specimens. Left: Grout A. Right: Grout B.
Figure
Figure6.
6.Open–circuit
Open–circuitpotential
potentialof
ofsteel
steelin
inMIT
MITspecimens.
specimens.Left:
Left:Grout
GroutA.
A.Right:
Right:Grout
GroutB.
B.

Consistent
Consistent with
with the
the OCP
OCP measurements,
measurements, thethe specimens
specimens cast
cast with
with Grout
Grout CC and
and ex-
ex-
pired grout C and D had much lower Rp (Figure 7). The OCP for the steel
pired grout C and D had much lower Rp (Figure 7). The OCP for the steel in the MIT in the MIT
specimens
specimens is
is shown
shown in
in Figure
Figure 6.
6. The
The OCP
OCP of
of the
the steel
steel showed
showed aa modest
modest decrease
decrease to
to more
more
 Constr. Mater. 2023, 3 456

Consistent with the OCP measurements, the specimens cast with Grout C and expired
grout C and D had much lower Rp (Figure 7). The OCP for the steel in the MIT specimens is
shown in Figure 6. The OCP of the steel showed a modest decrease to more electronegative
potentials at the upper 5 feet (1.5 m) of the tendons. However, the potentials overall were
generally indicative of passive conditions. Indeed, the resolved Rp shown in Figure 7 did
not show strong indication for elevated corrosion rates for the steel at the upper elevations.
The greater corrosion activity of steel in the grout with elevated sulfate concentrations
was due to the ability of sulfate ions that are made present at the steel surface early on in
the grout placement to destabilize the passive oxide film. The sulfate ions may be able to
adsorb onto the steel surface and compete with favorable oxides and hydroxides to hinder
the development of the passive film [48–52].
Figure 8 shows the resolved solution resistance for both INT and MIT setups. Generally,
the specimens showed similar solution resistance except for Grout C which showed the
highest solution resistance. For the MIT specimens, the resolved solution resistance of the
grout, however, was generally differentiated between locations from the top and bottom
of the tendon, indicating differentiation in the grout and moisture content by elevation
(Figure 8). The lower solution resistance in the deficient grout that develops at higher
elevations would allow more efficient coupling of local anodes and steel cathodes to
support greater corrosion activity. The lower solution resistance was resolved for grout at
the top of the tendon than at the lower elevations, further supporting the use of the MIT
as a means to test grout performance. It was noted that greater differentiation in solution
resistance between tendon elevations as well as lower values were obtained for Grout
A compared to Grout B. Indeed, Grout B had better performance as it was designed for
vertical PT applications and Grout A has been accepted for only horizontal PT applications.
FOR PEER REVIEW The sulfate content in Grout B was better differentiated between the high point elevation
9
(~0.48 mg/g) and the low point elevation (~0.13 mg/g) than for Grout A but Grout A
showed as much as ~0.6 mg/g sulfate at high and low point elevations.

100

10
Rp (kohm)

3.19 3.60
2.81 2.77

0.1
Bottom

Bottom
Bottom

Bottom

Bottom

Bottom
(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)

Top

Top
Bottom

Bottom
Head Top)

Head Top)

Head Top)

Head Top)

Head Top)

Head Top)
Top

Top
Top

Top

Top

Top

25"-34"(25–34”

25"-34"(25–34”
25"-34"(25–34”

25"-34"(25–34”

25"-34"(25–34”

25"-34"(25–34”

7–16”

7–16”
7–16”

7–16”

7–16”

7–16”
7"-16"

7"-16"

7"-16"

7"-16"

7"-16"

7"-16"

INT INT INT INT INT INT

Header Header Header Header Header Header

Grout A (INT) Grout B (INT) Grout C (INT) Expired Grout Expired Grout Neat Grout Grout A (MIT) Grout B (MIT)
C (INT) D (INT) (INT)

Figure 7. Measured polarization resistance

Figure 7. Measured grout resistance
polarization from MIT andfrom
grout INTMIT
specimens. Values for
and INT specimens. grout
Values forat
grout at
various elevations of the INTelevations
various tee header orINT
of the MIT teeduct location
header given.
or MIT duct location given.

1000

100
Rs (ohm)

10
 25"-3

25"-3

25"-3

25"-3

25"-3

25"-3
INT INT INT INT INT INT

7"-

7"-

7"-

7"-

7"-

7"-
Header Header Header Header Header Header

Grout A (INT) Grout B (INT) Grout C (INT) Expired Grout Expired Grout Neat Grout Grout A (MIT) Grout B (MIT)
C (INT) D (INT) (INT)

Constr. Mater.
Figure 3
2023,7.
Measured polarization resistance grout from MIT and INT specimens. Values for grout at 457

various elevations of the INT tee header or MIT duct location given.

1000

100
Rs (ohm)

10
3.25 3.71
3.09 2.98

1
Bottom

Bottom

Bottom

Bottom

Bottom

Bottom

Bottom

Bottom
Head Top)

Head Top)

Head Top)

Head Top)

Head Top)

Head Top)

Top

Top
(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)

(Head-Bot)
Top

Top

Top

Top

Top

Top
25–34”

25–34”

25–34”

25–34”

25–34”

25–34”
7–16”

7–16”

7–16”

7–16”

7–16”

7–16”
25"-34"(

25"-34"(

25"-34"(

25"-34"(

25"-34"(

25"-34"(
7"-16"

7"-16"

7"-16"

7"-16"

7"-16"

7"-16"
INT INT INT INT INT INT
Header Header Header Header Header Header
Grout A (INT) Grout B (INT) Grout C (INT) Expired Grout C Expired Grout D Neat Grout Grout A (MIT) Grout B (MIT)
(INT) (INT) (INT)

Figure 8. Solution resistance of grout

Figure 8. Solution from MIT
resistance andfrom
of grout INTMITspecimens. Values for
and INT specimens. grout
Values forat various
grout at various
elevations of the INTelevations
tee header or INT
of the MITteeduct location
header or MIT given.
duct location given.

3.3. Risk Assessment Based on the Sulfate Limit

3.3. Risk Assessment Based on the Sulfate Limit
The corrosion potentials and corrosion current densities for the steel embedded in
The corrosionthe potentials and corrosion
MIT specimens and the INTcurrent
specimens densities for the
show general steel embedded
correlation to the grout in
sulfate
the MIT specimens and the INT specimens show general correlation to the grout sulfatemore
content (Figures 9 and 10). As shown in Figure 9, the corrosion potential decreases to
content (Figures 9 and electronegative valuesin
10). As shown at Figure
the higher
9, sulfate concentrations.
the corrosion Likewise,
potential the corrosion
decreases to morecurrent
density showed a general increasing trend with the higher sulfate levels and indications
electronegative values at the higher sulfate concentrations. Likewise, the corrosion current
for some critical threshold value with elevated rates above a sulfate concentration for
density showed a generaldeficient increasing trend with the
grouts with characteristic higher
pH and sulfate
electrical levels (Figure
resistance and indications
10). The values
for some critical threshold
produced value with
from the testelevated rateswere
program here above a sulfate
consistent concentration
with historical data for de-
from earlier
ficient grouts with characteristic pH and electrical resistance (Figure 10). 2The values pro- was
Constr. Mater. 2023, 4, FOR PEER research
REVIEW [8,14,17,36,48] where an estimated critical sulfate concentration of 0.7 mg/g 10
observed (where the OCP was <−300 mV and icorr > 0.1 µA/cm [48]), further verifying
duced from the test program here were consistent CSE with historical data from earlier re-
the adverse effects of elevated sulfate ion concentrations in the segregated grout.
search [8, 14, 17, 36, 48] where an estimated critical sulfate concentration of 0.7 mg/g was
observed (where the OCP 0 was <−300 mVCSE and icorr > 0.1 µA/cm2 [48]), further verifying
-50
the adverse effects of elevated sulfate ion concentrations in the segregated grout.
Corrosion Potential (mVSCE)

-100
-150
-200
-250
-300
-350
-400
-450
-500
0.0001 0.001 0.01 0.1
Sulfate Concentration (g/g)

Figure 9.
Figure Correlation of
9. Correlation of steel
steel corrosion
corrosionpotential
potentialand
andgrout
groutsulfate
sulfatecontent. Circle:
content. Grout
Circle: A.A.
Grout Tri-
Triangle:
angle: Grout B. Square: Grout C. Diamond: Grout D. Cross: Neat Grout. Filled: Expired Grout.
Grout B. Square: Grout C. Diamond: Grout D. Cross: Neat Grout. Filled: Expired Grout. Blue: MIT.
Blue: MIT.
Black: INT.Black: INT.

10

1
t Density (uA/cm2)

0.1

0.01
 -500
0.0001 0.001 0.01 0.1
Sulfate Concentration (g/g)

Figure 9. Correlation of steel corrosion potential and grout sulfate content. Circle: Grout A. Triangle:
Constr. Mater. 2023, 3 Grout B. Square: Grout C. Diamond: Grout D. Cross: Neat Grout. Filled: Expired Grout. 458 Blue: MIT.
Black: INT.

10

Current Density (uA/cm2)

0.1

0.01

0.001

0.0001
0.0001 0.001 0.01 0.1
Sulfate Concentration (g/g)

Figure 10. Correlation of steel corrosion current density and grout sulfate content. Circle: Grout A.
Figure 10. Correlation of steel corrosion current density and grout sulfate content. Circle: Grout A.
Triangle: Grout B. Square: Grout C. Diamond: Grout D. Cross: Neat Grout. Filled: Expired Grout.
Triangle: Grout B. Square: Grout C. Diamond: Grout D. Cross: Neat Grout. Filled: Expired Grout.
Blue: MIT. Black: INT.
Blue: MIT. Black: INT.
The data in Figures 9 and 10 show that there is differentiation in the corrosion behavior
Theindata
of steel groutinmaterials
Figures that
9 and 10 show
develop that there
different is differentiation
chemistries in theThe
in its pore water. corrosion
expired behav-
ior of steel
grouts in grout
developed thematerials that develop
highest sulfate differentand
ion concentrations chemistries
showed the in greatest
its poresuscepti-
water. The ex-
pired
bility grouts developed
for corrosion the highest
development. sulfate ion
The aggressive concentrations
chemistries and showed
were developed the greatest
in expired
Grouts C and D subjected to water transport associated with vertical
susceptibility for corrosion development. The aggressive chemistries were developed deviations such that in
transport can be gaged by the grout that accumulate in the vertical
expired Grouts C and D subjected to water transport associated with vertical deviations tee header in the INT
test. that
such The most electronegative
transport can be gagedpotentials
by the and greatest
grout thatcorrosion
accumulate ratesinofthe
steel developed
vertical in
tee header in
specimens from the INT tee header coincident with the highest sulfate ion concentrations.
the INT test. The most electronegative potentials and greatest corrosion rates of steel de-
Although not as sharply parced here with testing of Grout A and B, MIT specimens in other
veloped
researchin specimens
[14,15] from the
have shown INTdiscrimination
similar tee header coincident with the
for susceptible highest
grout sulfate
materials. Theion con-
centrations. Although not as sharply parced here with testing of
results imply that the simple INT test setup can be useful to identify grout segregation Grout A and B, MIT spec-
imens in other
robustness. research
Testing [14,15]degrees
with greater have shown
of groutsimilar discrimination
pre-hydration and added forwater
susceptible
levels grout
materials. The results
may be considered imply
in future that theincluding
research, simple INT test setuptocan
the possibility be useful
identify to identify
threshold levels grout
for various grout materials, but this was not within the scope of the
segregation robustness. Testing with greater degrees of grout pre-hydration and added work for the practical
evaluation
water levels of may
groutberobustness
considered for material
in futureacceptance.
research, including the possibility to identify
threshold levels for various grout materials, buttesting
The results of the testing further indicate that this wasfor corrosion
not within in the
fieldscope
structures
of the work
should include grout sampling in vertically-deviated regions of PT tendons (such as de-
for the practical evaluation of grout robustness for material acceptance.
viators, joints, and anchors) where water-rich deficient grout materials can accumulate.
The The results
testing of the testing
can include the qualityfurther indicate
of grout that testing
hydration, moisture forcontent,
corrosion in field
electrical structures
resis-
should
tance, and sulfate ion content as well as conventional testing for voids, bleed, and chloride as de-
include grout sampling in vertically-deviated regions of PT tendons (such
viators, joints, and anchors) where water-rich deficient grout materials can accumulate.
ion content.
The testing can include the quality of grout hydration, moisture content, electrical re-
4. Conclusions
sistance, and sulfate ion content as well as conventional testing for voids, bleed, and chlo-
It was
ride ion shown that the different grout products have widely different propensities for
content.
the segregation and accumulation of sulfate ions but that adverse grout mixing practices
4.such as the addition of 10% mix water above the manufacturer’s recommendation and
Conclusions
pre-hydration promoted the development of grout deficiencies, including the accumulation
of sulfate ions, even without external sulfate ion sources.
The corrosion potentials and corrosion current densities for the steel embedded in
the INT and MIT specimens were correlated with the grout sulfate content and the values
produced from the test program here were consistent with historical data from earlier
research, further verifying the adverse effects of elevated sulfate ion concentrations in the
segregated grout. The expired grouts developed the highest sulfate ion concentrations and
showed the greatest susceptibility for corrosion development. The sulfate limits expressed
as mass relative to the grout sample mass can be implemented to normalize the leaching
volume and mass size.
The sulfate content associated with severe corrosion was associated with deficient
grout materials with a high moisture content. As such, it is recommended that the sulfate
Constr. Mater. 2023, 3 459

testing is incorporated into material testing to assess the susceptibility of grout materials to
segregate. Test methods such as the modified incline tube test incorporating overwatering
in the grout mixing or alternative testing to facilitate the capturing of displaced water, such
as the inverted-tee test, should be considered for grout material sampling. In the field,
the extraction of grout materials from locations typically associated with moisture and/or
bleeding such as at high points, points of deviation, and joints should be considered.

Author Contributions: Writing—review and editing, S.P. and K.L.; Supervision, K.L. All authors
have read and agreed to the published version of the manuscript.
Funding: This research was funded by Florida Department of Transportation (FDOT), grant number
BDV29-977-44.
Data Availability Statement: All data contained within the article.
Acknowledgments: This investigation was supported by the Florida Department of Transportation
(FDOT). The opinions, findings, and conclusions expressed here are those of the authors and not
necessarily those of the FDOT or the US Department of Transportation.
Conflicts of Interest: The authors declare no conflict of interest.

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