3.1 Latex Comonomer Design
3.1.1 Comonomers hydration and performance in URHC-LMC
LMC incorporating URHC is widely used in infrastructure repairs, especially bridge
decks requiring rapid setting and early strength. Achieving a compressive strength
of ≥21 MPa within four hours is critical to minimize traffic disruptions. URHC reduces
curing time while ensuring structural integrity, and latex further enhances mechanical
performance by improving flexibility, adhesion, and environmental resistance. The
latex forms a continuous polymer film in the cement matrix, strengthening the bond
between particles and improving resistance to dynamic loads and harsh environments
(Soroushin and Spinkel, 1999).
Carboxylic acid-based comonomers AA, MAA, and IA, accelerate hydration, promoting
early strength gain. Their high heat of hydration (AA: 385 J/g, MAA: 360 J/g, IA:
345 J/g) results from strong ionic interactions with calcium hydroxide. Fig. 3 compares heat generation, showing carboxylic acids have higher exothermic profiles
than non-carboxylic counterparts. However, excessive heat release can cause thermal
cracking, requiring careful control of hydration kinetics.
Non-carboxylic comonomers like (MMA, 310 J/g) and (N-MAM, 290 J/g) generate less heat,
reducing thermal cracking risk but may delay strength development. Therefore, URHC-LMC
performance relies on balancing hydration rate and thermal effects through targeted
comonomer selection and additive optimization to ensure durability and safety in large-scale
repairs.
The heat of hydration was quantitatively evaluated using an isothermal conduction
calorimeter (TAM Air, TA Instruments, USA), operated at a constant temperature of
25±0.1°C in accordance with ASTM C1702-17, wherein cement pastes were formulated with
a water-to-cement ratio of 0.35, incorporating 90 wt.% cement and 10 wt.% styrene-butadiene
latex modified with 2 wt.% of a specific comonomer (AA, MAA, IA, MMA, or N-MAM), thoroughly
mixed under ambient laboratory conditions (22-25°C, RH 50-60 %) for a total of 2.5
minutes to ensure homogeneity, after which 5 grams of the freshly mixed paste was
carefully transferred into sealed glass ampoules and immediately placed into the calorimeter
chamber, where continuous heat flow data was recorded over a 72-hour period to capture
both initial and long-term exothermic profiles, and the total heat release (in J/g)
was subsequently calculated by integrating the resulting heat.
Fig. 3. Comparison of the Heat of Hydration for Different Comonomers Used in LMC
3.1.2 Effect of comonomers
An experiment was conducted to evaluate the polymerization stability and workability
of latex in LMC incorporating URHC, a system widely used in infrastructure repairs
such as bridge decks that require fast setting and early strength development. A key
performance target is achieving a compressive strength of at least 21 MPa within four
hours to minimize traffic disruption and enable rapid reopening. To investigate the
influence of formulation, 2 wt.% of various comonomers were added to the latex, and
their effects on polymerization stability, workability, and strength were assessed
(Buch et al., 2008).
To assess latex stability after polymerization, each sample was filtered through a
200-mesh stainless steel screen directly within the reactor to evaluate the degree
of coagulation and particle aggregation. The amount of residue retained on the mesh
was collected and dried at 150°C for 30 minutes, then weighed to determine the percentage
of aggregated solids. A lower residue value indicated higher colloidal stability.
All stability tests were conducted at a controlled pH of 11.5.
When URHC is incorporated into LMC, the early hydration behavior is strongly influenced
by the interaction among key cementitious compounds such as C3A, C3S, and CSA.
In this study, three carboxylic acid-based comonomers (AA, MAA, and IA) and two non-carboxylic
monomers (MMA and N-MAM) were evaluated. The carboxyl groups in AA, IA, and MAA react
strongly with CSA, forming calcium- carboxylate complexes that accelerate hydration
and contribute to rapid strength gain. However, this also leads to latex coagulation,
reducing fluidity and negatively affecting workability.
On the other hand, MMA and N-MAM exhibit lower reactivity with cement, allowing for
better latex dispersion and improved workability. These formulations remain fluid
longer, making them easier to handle on-site. However, their slower hydration kinetics
delay the formation of calcium silicate hydrate (C-S-H), resulting in insufficient
strength development within the required time frame. Fig. 4 illustrates these findings. These results highlight the trade-off between early strength
and workability, underscoring the importance of optimizing comonomer selection based
on project-specific performance needs.
Fig. 4. Comparison of Latex Stability, Workability, and Compressive Strength Based
on Different Comonomers. (a) Latex Stability and Workability, (b) Compressive Strength
3.1.3 Enhancing latex stability and strength in URHC-LMC system
To enhance polymer stability and early-age performance in URHC-LMC, this study investigated
the effect of increasing total comonomer content to 3 wt.% relative to the primary
monomers. Formulations combined 1 wt.% of carboxylic acid-based comonomers (AA, MAA,
IA) with 2 wt.% of N-MAM to evaluate their synergistic effects on latex dispersion,
workability, and early compressive strength. Carboxylic acids introduced negatively
charged carboxyl groups into the polymer matrix, enhancing colloidal stability through
electrostatic repulsion. Among them, AA showed the highest ionization, promoting rapid
ionic interaction with calcium ions and superior early strength. IA and MAA also improved
stability but were less effective due to their bulkier structures and lower ionization.
N-MAM further improved polymer flexibility and film formation; however, its hydrophilic
amide groups increased the risk of latex coagulation at higher concentrations by promoting
water absorption and chain entanglement. Fig. 5(a) illustrates the impact of each comonomer combination on stability and workability.
The AA-N-MAM blend offered the strongest initial stabilization, while IA and MAA combinations
better preserved workability over time. Excess N-MAM (>2 wt.%) negatively affected
stability, highlighting the importance of dosage control.
Workability and early strength were also assessed based on comonomer reactivity. As
shown in Fig. 5(b), AA accelerated hydration and achieved the highest early strength but reduced workability
due to rapid stiffening. IA offered the best balance, providing extended working time
and satisfactory strength. MAA allowed moderate hydration control, while MMA and N-MAM
improved workability through reduced ionic interaction but delayed strength gain.
Notably, N-MAM contributed to long-term dispersion and durability, though excessive
use impaired storage stability and field performance. Overall, increasing comonomer
content to 3 wt.%, particularly through optimized combinations of AA or IA with N-MAM,
significantly improved latex stability, early strength, and workability in URHC-LMC
systems, provided that N-MAM dosage is carefully controlled.
Fig. 5. Effects of Combining Carboxylic Acid (1 wt.%) and N-MAM (2 wt.%) Comonomers
on (a) Latex Stability and Workability, (b) Compressive Strength
3.1.4 Enhancing URHC-LMC flexibility and durability in bridges
To enhance the performance of URHC-LMC, this study addressed key vulnerabilities such
as aggregate microcracking and environmental stressors including chloride ingress
and freeze-thaw cycles. Specific polymer modifications were made namely, increasing
BD content, reducing ST content, optimizing the Tg to 0-10°C, and decreasing latex
particle size. These adjustments aimed to improve flexural strength, permeability
resistance, and surface scaling durability (Su et al., 2024).
Fig. 6(a) shows the relationship between Tg, particle size, and flexural strength. Crushed
stone aggregates often develop internal microcracks during processing, which act as
stress concentrators and weaken the concrete’s flexural capacity under dynamic loads.
Increasing BD content improves the flexibility and elasticity of the latex film, enabling
it to bridge microcracks and fill microvoids, thereby enhancing stress distribution
and crack resistance throughout the matrix.
Fig. 6(b) illustrates the correlation between Tg, particle size, and permeability. Bridge decks
exposed to marine environments or de-icing salts suffer from chloride-induced corrosion
and freeze-thaw damage. Chloride ingress leads to steel corrosion, while freeze-thaw
cycles cause internal expansion, resulting in cracking and surface degradation. By
maintaining Tg within 0-10°C, the latex film remains flexible under thermal stress,
accommodating volume changes during freeze-thaw events. Reducing particle size enhances
film density, effectively sealing microvoids and limiting water and ion penetration.
This improves barrier performance, protects reinforcement, and reduces corrosion rates.
Fig. 6. Effects of Glass Transition Temperature (Tg) and Particle Size on Flexural
Strength and Permeability of LMC
Furthermore, reducing latex particle size (from 190 nm to 160 nm) significantly enhances
the latex’s film-forming ability and impermeability after drying. Smaller particles
create a thinner but more uniformly distributed polymer film, increasing the specific
surface area of coverage and allowing the latex to more effectively fill and bridge
capillary pores and microvoids within the cementitious matrix. This results in denser
film formation and reduced porosity, which in turn improves chloride penetration resistance
by physically blocking ion transport pathways. In addition, finer particles contribute
to a more cohesive and continuous hydrophobic surface layer, which further limits
moisture ingress and protects embedded steel reinforcement from corrosion. These mechanisms
are consistent with barrier theory, where smaller particle size enhances tortuosity
and reduces permeability through denser packing and more efficient void filling.
These improvements significantly reduce surface scaling, chloride-induced corrosion,
and microcrack propagation, thereby strengthening the URHC-LMC system against both
mechanical and environmental deterioration. The optimized latex formulation is thus
highly suitable for demanding bridge deck applications exposed to aggressive conditions.
3.1.5 Effect of preservatives
Maintaining latex stability at high pH (>11) is critical, as degradation under alkaline
conditions significantly reduces the workability of LMC. This study evaluated the
effectiveness of three preservatives (CMIT, MIT, and BIT) in preserving latex under
conditions typical of cementitious environments (Shang et al., 2022). Latex is also vulnerable to microbial degradation during storage, especially in
hot and humid climates. Previous studies identified Pannonibacter phragmitetus and
Halomonas hamiltonii as key degraders in alkaline settings, producing acidic by-products
that lower pH and disrupt polymer structure, leading to impaired latex performance.
Initial compatibility tests were conducted at pH 11 using each preservative at 400
ppm. After 10 minutes of vigorous stirring and filtration through a 200-mesh screen,
coagulum content was measured to assess stability. As summarized in Table 6, CMIT caused significant coagulation (>4,500 ppm), reflecting poor stability at high
pH. In contrast, MIT and BIT showed excellent compatibility with minimal coagulum
formation (<1 ppm).
Further analysis evaluated preservative durability over seven days at pH 11 and 65°C,
as shown in Fig. 7. MIT degraded rapidly, with over 70 % loss of concentration, while BIT retained over
88 % of its original level, indicating superior chemical resilience. This stability
is attributed to BIT’s aromatic benzene ring and robust sulfur-nitrogen (S-N) bonds,
which resist hydrolysis and oxidative degradation. In contrast, MIT’s structure is
prone to breakdown in alkaline media.
BIT also interacts with latex particles via hydrogen bonding and van der Waals forces,
forming a stable film that enhances microbial resistance and colloidal stability,
even in environments rich in multivalent cations (e.g., Ca2⁺, Al3⁺). When combined
with N-MAM, BIT’s stabilizing effect is amplified, as N-MAM forms hydrated steric
barriers that minimize ionic interactions and coagulation (Tamira et al., 2020).
BIT’s antimicrobial efficacy is multifaceted, involving membrane disruption, metabolic
inhibition, and ROS generation. It provides long-term protection at low concentrations
(400 ppm) without compromising safety. BIT complies with global safety standards (REACH,
OSHA), and its safe handling is ensured through PPE and exposure guidelines. By preserving
latex integrity during storage and use, BIT supports consistent flowability, mechanical
strength, and cement compatibility, making it a highly effective and practical preservative
for URHC-LMC systems.
Fig. 7. Degradation Behavior of (a) MIT and (b) BIT Preservatives Over Time at pH
11 and 65°C
Table 6. Evaluating Preservatives Impact on Latex Stability at pH 11
Preservatives
|
CMIT
|
MIT
|
BIT
|
Coagulum amount (ppm)
|
4,580
|
< 1
|
< 1
|
3.1.6 Effect of gel content and TDDM optimization on mechanical stability and field
performance of latex in LMC
This study investigated the influence of latex gel content, adjusted via tert-dodecyl
mercaptan (TDDM), on mechanical stability and workability of LMC incorporating URHC.
Initial lab-scale evaluations, as shown in Fig. 8(a), tested slump and slump loss across formulations with gel content ranging from 30.7
% to 88.9 %. An optimal gel content of 50.3 % exhibited the lowest slump loss (24.2
%), effectively balancing flowability and structural cohesion under static conditions.
However, when scaled to a field test, this same formulation exhibited severe coagulation
during pumping, particularly at mechanical components such as rotating shafts, as
illustrated in Fig. 8(b). These issues were attributed to insufficient structural integrity under dynamic
shear forces and elevated temperatures, conditions not fully replicated in laboratory
settings.
To address this, additional field trials were conducted by increasing the gel content
above 85 % through precise TDDM adjustment. A formulation containing 0.24 wt.% TDDM
achieved a gel content of 85.1 %, significantly reducing coagulation and maintaining
an acceptable slump loss of 29.5 %, as shown in Fig. 8(b). Conversely, higher TDDM levels (0.58 wt.%) led to reduced gel content due to excessive
chain transfer, resulting in instability.
Mechanical components remained clean post-application, as shown in Fig. 8(c), and the modified LMC was successfully placed without flow interruptions. These findings
demonstrate that, while lower gel contents may enhance workability under controlled
conditions, a higher gel content (>85 %) is essential to ensure mechanical stability
in real-world field applications. Therefore, optimizing TDDM dosage is critical for
maintaining both pumpability and performance of latex-modified LMC in bridge deck
repairs.
Fig. 8. (a) Effects of Latex Gel Content on Slump and Slump Loss, (b) Coagulation
Observed on a Pump Shaft during Field Test, (c) Clean Pump Shaft after Optimizing
Gel Content
3.1.7 Freeze-thaw stability
Latex, which contains over 50 % water, is highly vulnerable to coalescence and particle
agglomeration during freeze-thaw cycles, leading to performance degradation. Fig. 9 illustrates the significant improvement in freeze-thaw stability achieved by incorporating
hydrophilic N-MAM as a comonomer. This enhancement is driven by several interconnected
physicochemical mechanisms.
N-MAM, a water-soluble monomer, increases steric stabilization by introducing hydrophilic
groups on latex particle surfaces. These groups form a hydrated barrier that enhances
repulsive forces and prevents particle aggregation under freeze-thaw stress. Through
hydrogen bonding, N-MAM also interacts with surrounding water molecules, limiting
ice crystal formation and reducing mechanical damage.
In addition, the modified latex exhibits a more porous particle morphology, which
acts as a buffer against internal pressure during freezing. This structure helps absorb
expansion stress, reducing coalescence risk. Upon thawing, the hydrated layer facilitates
particle mobility and re-dispersion, preventing permanent agglomeration.
Furthermore, N-MAM promotes a more uniform distribution of hydrophilic domains within
the latex matrix, minimizing weak zones susceptible to destabilization. Together,
these effects contribute to significantly enhanced freeze-thaw resilience of the latex
system.
Fig. 9. Influence of N-MAM Concentration on the Freeze-thaw Stability of Latex
3.2 Application of URHC-LMC on-site pavement
During the repair of an aging highway bridge, 10 tons of latex were produced and applied
on-site using URHC-LMC. The entire pavement process had to be completed within 10
h to minimize traffic disruption and ensure timely reopening. Fig. 10 illustrates the systematic procedure for bridge deck repair using URHC-LMC. The process
begins with traffic control implementation to ensure work zone safety (a). Damaged
pavement is then removed through mechanical cutting (b), followed by high-pressure
water jetting to eliminate deteriorated material while preserving structural integrity
(c). Precise edge cutting is conducted to define the repair boundaries (d), and vacuum
cleaning is performed to remove debris and moisture from the surface (e). The URHC-LMC
is placed using a mechanized system designed for rapid application and strength development
(f). Surface tinting and finishing are then completed to enhance durability and bonding
(g), and the repaired section is reopened to traffic after safety verification (h).
This process enables efficient, long-lasting rehabilitation of bridge decks with minimal
disruption.
This project demonstrates the high performance and durability of LMC made possible
through seeded polymerization. Incorporating 2 wt.% N-MAM enhanced latex stability
and workability while maintaining storage performance. The optimized formulation addressed
latex degradation under moisture-rich and alkaline conditions through elevated pH
control and the use of BIT, which proved effective as a high-pH preservative. Furthermore,
improved freeze-thaw resistance was achieved by increasing hydrophilic monomer content,
ensuring colloidal stability under environmental stress.
The successful field application validated laboratory findings and highlighted the
practical value of the optimized LMC formulation. This bridge project underscores
the potential of advanced latex technology to overcome long-standing challenges in
concrete repair, particularly under harsh service conditions.
To systematically compare laboratory and field conditions, a trial placement was carried
out on an actual bridge deck section. The initial slump measured in the field was
180 mm, indicating excellent workability and suitability for rapid construction. The
air content was measured at 4.5 %. Throughout the placement process, the mixture maintained
stable consistency, and the surface finish was uniform and free of visible defects.
Notably, the compressive strength reached 22.9 MPa at 4 hours after placement, successfully
exceeding the early strength requirements necessary for traffic reopening in time-
constrained bridge deck repair scenarios. Furthermore, the strength continued to develop,
reaching 39.8 MPa at 28 days, demonstrating excellent long-term mechanical performance
suitable for durable infrastructure applications.
These field results were highly consistent with laboratory findings, confirming that
the optimized SB latex formulation preserved its mechanical performance, workability,
and adhesion even under demanding on-site construction conditions. Although further
large-scale field validations are recommended, the initial results strongly support
the practical feasibility of applying the proposed system to real-world bridge rehabilitation
projects.
In large-scale bridge deck applications, managing thermal cracking is a critical challenge
due to the high exothermic nature of URHC systems. Rapid hydration, especially under
conservative construction timelines, leads to a steep internal temperature gradient
between the core and surface of the concrete, which induces tensile stress and increases
the risk of early-age cracking. This is particularly problematic when drying occurs
too rapidly, either due to elevated ambient temperatures or insufficient moisture
retention at the surface.
To mitigate thermal cracking in such settings, a multi-pronged strategy is essential.
First, controlled drying is crucial to moderate the evaporation rate of surface moisture.
This can be achieved by applying curing compounds immediately after finishing, which
help retain internal moisture and reduce thermal shrinkage. In addition, the use of
wet-curing methods, such as covering the surface with water-saturated non-woven fabric,
provides continuous hydration while preventing thermal gradients from forming too
sharply. These fabrics act as both thermal and moisture buffers, promoting uniform
temperature distribution and reducing drying-induced tensile stress.
Moreover, planning construction during favorable weather conditions, minimizing direct
exposure to sunlight and wind, and staging pours to limit thermal buildup in massive
sections can further alleviate internal stress accumulation. The optimized SB latex
system itself contributes to mitigation by forming a flexible polymer network that
can accommodate minor volumetric changes, thereby helping to bridge microcracks before
they propagate.
Together, these strategies address both material-level and process-level risks associated
with thermal cracking in URHC-LMC systems, ensuring mechanical integrity and long-term
performance in large-scale bridge deck rehabilitation projects.
During the field application of the URHC-LMC system for bridge deck rehabilitation,
certain practical limitations were encountered that warrant further consideration.
One of the most critical constraints arises from the strict time imposed during bridge
maintenance, where traffic control allows only a very short working period between
lane closure and reopening. As a result, construction teams often attempt to accelerate
drying and finishing processes, sometimes excessively, to meet operational deadlines.
However, this rapid drying approach can lead to non-uniform surface formation and
inconsistent film development, particularly when environmental conditions vary across
the deck. Uneven drying not only affects the appearance and surface integrity but
can also introduce localized stress points and reduce overall durability. In particular,
the formation of the SB latex film may be compromised if the evaporation rate exceeds
the polymer coalescence rate, leading to poor film continuity and weaker protective
performance.
To mitigate this limitation, it is important to balance speed with uniformity during
application. Rather than pushing for the fastest possible drying, procedures should
aim for a controlled, slightly extended drying period that ensures consistent film
formation across the entire surface. This can be achieved through the use of temporary
shading, wind barriers, or misting systems during curing, and by training workers
to prioritize uniform spreading and consolidation techniques even under time constraints.
Ultimately, optimizing field procedures to maintain short yet controlled curing conditions
is essential to achieving the desired mechanical and environmental performance of
URHC-LMC systems in real-world applications.
Fig. 10. Field Application of URHC-LMC in Bridge Deck Repair. (a) Traffic Control,
(b) Cutting of Existing Surface, (c) Removal of Deteriorated Concrete Using Water
Jet, (d) Precision Cutting, (e) Vacuum Cleaning, (f) URHC-LMC Placement, (g) Surface
Finishing, (h) Reopening to Traffic