Journal of the Civil Engineering Forum.
January 2026, 12.
:89-103 DOI 10.
22146/jcef.
Available Online at https://jurnal.
id/v3/jcef/issue/archive Hydrated LimeAeBased Coating for Cool Pavement Technologies:
Evaluation of Durability and Thermal Performance Muhammad Khuzamy1 .
Taqia Rahman1* .
Imtiaz Ahmed2 .
Syed Bilal Ahmed Zaidi3 1 Department of Civil and Environmental Engineering.
Universitas Gadjah Mada.
Yogyakarta.
INDONESIA 2 AtkinsRyalis.
Nottingham.
UNITED KINGDOM 3 Taxila Institute of Transportation Engineering.
University of Engineering and Technology.
Taxila.
PAKISTAN *Corresponding author: taqia.
rahman@ugm.
SUBMITTED 26 August 2025 REVISED 20 October 2025 ACCEPTED 25 October 2025 ABSTRACT Heat-reflective pavement coatings are commonly employed for road cooling and to mitigate Urban Heat Island (UHI) effects by reflecting solar radiation and reducing surface temperatures.
However, their cooling efficiency diminishes over time due to abrasion, soiling.
UV exposure, and environmental aging, which degrade the reflective polymer layer.
As a cost-effective alternative, hot-rolled hydrated lime (HL) applied to pavement surfaces has emerged, forming a light-coloured mineral layer that enhances reflectivity and potentially reduces pavement temperature.
This study investigates hydrated lime (HL) as a mineral-based alternative, applied through hot-rolling to form a reflective surface layer that is compatible with conventional asphalt practices.
Its performance was evaluated through laboratory thermal simulations .
ayAenight cyclin.
and abrasion wear testing and compared with three commercial paint-based HRCs: epoxy resinAeTiOCC and acrylic emulsionAeTiOCC.
The results show that HL coatings achieved surface temperature reductions of up to 89 AC compared to uncoated asphalt, exceeding the best-performing paint-based sample (White-AE, 19.
29 AC), suggesting that HL has strong potential as an effective reflective coating.
This was achieved with a formulation of fine HL particles (No.
400 mes.
at a higher dosage .
g/mA).
In abrasion resistance tests.
HL outperformed paint-based HRCs, with lower mass losses .
6Ae1.
3 g vs.
8Ae1.
, which was attributed to stronger adhesion and particle embedment.
In addition, post-abrasion tests revealed that HL samples retained better thermal stability, with smaller temperature increases (OIT : 5.
9Ae6.
8 AC) than HRCs (OIT : 6.
3Ae7.
2 AC).
Based on these outcomes.
HL applied at 200 g/mA using fine particles (No.
400 mes.
is recommended as the optimal formulation for maximizing cooling performance and surface durability.
Overall, these findings suggest that hot-rolled HL is a durable, low-cost, and effective alternative cooling strategy to popular HRCs for UHI mitigation.
KEYWORDS Cool pavements.
Hydrated lime.
UHI mitigation.
Heat reflective coating.
Road cooling.
Asphalt.
A The Author.
This article is distributed under a Creative Commons Attribution-ShareAlike 4.
0 International license.
1 INTRODUCTION
Rapid urbanization has accelerated global land use change and urban spatial expansion (Gyneralp et al.
Rahman et al.
, 2025.
Projections indicate that by 2050, global urban land area will increase by approximately 78Ae171%, with Asia and Africa collectively contributing to nearly two-thirds of this growthAi46Ae 49% and 16Ae25%, respectively (Huang et al.
, 2.
Europe, urban areas are expected to expand by 7% by 2030 (Gyneralp et al.
, 2.
Such expansion intensifies the Urban Heat Island (UHI) effect, in which urban areas exhibit higher surface and air temperatures than their rural surroundings (Ibrahim et al.
, 2.
On average, the UHI effect elevates daily summer temperatures 5Ae0.
7 AC, and in densely developed urban cores, the increase can reach up to 3 AC (Huang et al.
, 2.
In addition to human-induced urbanization, the intensity of the UHI effect is further influenced by environmental and spatial factors such as vegetation cover .
%), seasonality .
%) and diurnal variation .
%) (Deilami et al.
, 2.
Among these, the decline in urban vegetationAidriven by massive infrastructure developmentAihas significantly contributed to elevated surface temperatures.
The conversion of vegetated areas into impervious built-up zones such as residential complexes, commercial areas, and extensive road networks has altered the thermal balance of urban landscapes (Fathan et al.
, 2025.
Mathan and Krishnaveni, 2.
One of the most critical contributors to this thermal imbalance is pavement infrastructure, which occupies approximately 30Ae40% of the total urban surface area (Cheela et al.
, 2021.
Liu et al.
, 2.
Of this, an estimated 75Ae80% comprises dark-coloured pavements, particularly asphalt, which exhibit low albedo values and high thermal absorption (Cheela et al.
, 2021.
Huang et al.
, 2.
For instance, conventional asphalt pavement typically has an albedo of approximately 0.
05Ae0.
10, meaning it reflects only 5Ae10% of in- Journal of the Civil Engineering Forum coming solar radiation while absorbing 90Ae95% (Rahman et al.
, 2025.
This high absorptivity leads to substantial heat accumulation and gradual release, resulting in surface temperatures that can reach up to 59.
4 AC
under peak conditions (Boujelbene et al.
, 2.
This persistent heat retention not only intensifies the UHI effect but also contributes to premature pavement deterioration (Nugroho et al.
, 2.
, increased cooling energy demand, and elevated thermal discomfort in urban environments (Rajagopal et al.
, 2.
The impacts of the UHI phenomenon extend far beyond elevated temperatures.
They include increased energy consumption, deteriorating air quality, heightened health risks, and reduced environmental resilience (Vujovic et al.
, 2.
UHI-induced warming can increase building cooling energy demand by 10Ae120%, placing additional pressure on power generation systems (Huang et al.
, 2.
This increased energy demand often results in higher emissions of pollutants such as carbon monoxide (CO), carbon dioxide (COCC), sulphur dioxide (SOCC), nitrogen oxides (NOx ), and particulate matterAicompounds known to exacerbate respiratory and cardiovascular conditions, including bronchitis and airway irritation (Vujovic et al.
, 2.
The chain of consequences associated with UHI underscores the urgent need for effective mitigation strategies.
Among the most widely studied approaches are cool pavement technologies, which aim to lower surface temperatures by increasing reflectivity (Wong et al.
, 2.
, enhancing evaporation (Ega Fajar et al.
Rahman et al.
, 2025.
, or modifying thermal properties (Shamsaei et al.
, 2.
One widely adopted cool pavement solution is the application of heatreflective coatings (HRC.
, which are designed to increase surface albedo and reduce solar heat gain (Rahman et al.
, 2.
These coatings form a thin, highreflectivity layer on the pavement surface, enabling significant reductions in both surface and near-surface air temperatures by reflecting a larger portion of incoming solar radiation (Alhaqi et al.
, 2024.
Wang et al.
, 2.
Field and simulation studies have shown that HRCs can reduce peak pavement surface temperatures by up to 30 AC compared to uncoated asphalt, and in some cases even achieve sub-ambient surface temperatures under certain conditions (Elmagri et al.
, 2024.
Mandal et al.
However, these benefits are offset by several limitations.
Rahman et al.
reported that typical HRCs exhibit functional durability of only about one year, especially under moderate to heavy traffic loads.
Additionally.
HRCs often suffer from low abrasion resistance, high application costs, and concerns about the environmental impact of certain chemical constituents used in the coating formulation (Man et al.
, 2.
These limitations reduce their viability for long-term Vol.
12 No.
1 (January 2.
or large-scale implementation, particularly in highwear roadway segments or cost-sensitive infrastructure A promising alternative to polymer-based paint HRC is the application of hydrated lime (Ca(OH)CC) directly to the pavement surface during or immediately after compaction, followed by hot pressing.
This method forms a thin, light-coloured mineral layer that increases surface reflectivity, thereby reducing solar heat absorption and lowering surface temperatures.
When properly applied, the reflective layer is expected to remain effective for up to five years under typical field conditions (Emery et al.
, 2.
In addition to its thermal benefits, hydrated lime (HL) is cost-effective, widely available, and compatible with standard paving practices (Emery et al.
, 2014.
Mondal et al.
, 2.
A recent study by Man et al.
further demonstrated that hot-pressed hydrated lime can lower asphalt surface temperatures by approximately 10 ACAislightly less than conventional paint-based coatings but at a substantially lower cost.
Based on the above background, hydrated lime (HL) offers a potentially more cost-effective and abrasionresistant alternative to paint-based heat-reflective coatings (HRC) while providing comparable surface cooling benefits.
However, no previous studies have comprehensively evaluated its thermal and mechanical performance under varying application parameters in direct comparison with HRC.
To address this gap, the present study aims to assess the abrasion resistance and thermal performance of hot-pressed HL as a reflective surface treatment and compare it with conventional paint-based HRC.
This was conducted through laboratory experiments involving surface temperature measurements and abrasion resistance tests, incorporating variations in paint formulations for HRC and different particle sizes and spreading dosages for HL.
The information on hydrated lime (HL) as an alternative to paint-based HRC is important for assessing its impact on cooling performance, durability, and practical use in 2 RESEARCH OBJECTIVE AND APPROACH The main objective of this study is to evaluate the thermal performance and abrasion resistance of paintbased heat-reflective coatings (HRC.
and hot-pressed hydrated lime (HL) as reflective treatments for asphalt HL was selected for its potential as a more durable, cost-effective alternative, while waterbased acrylic and oil-based epoxy were used to represent commonly used polymer binders in HRCs.
In addition, the study assesses the effect of surface abrasion on the retained thermal performance of these coatings after wear.
The experimental setup is illustrated in Figure 1.
For this purpose, asphalt slabs measuring 306 y 306 y 50 mm were compacted and subsequently cut Vol.
12 No.
1 (January 2.
into four smaller specimens .
y 15 y 5 c.
This specimen size is commonly used in laboratory thermal asphalt tests, as reported by previous studies (Anting et al.
, 2017.
Pan et al.
, 2.
Three types of HRCs were applied to the asphalt surface: epoxy resin .
hite and blue variant.
, acrylic emulsion, and a commercial reflective paint (BeCoo.
For HL, two particle sizes (No.
200 Ae 75 m and No.
400 Ae 38 .
were tested across four spreading dosages .
, 100, 150, and 200 g/mA) (Alhaqi et al.
, 2024.
Emery et al.
, 2014.
Man et al.
, 2.
Coatings were applied by dry spreading (HRC.
and hot pressing (HL) onto clean, uncontaminated slab surfaces at room temperature .
AC).
To measure internal temperature responses under heating and cooling simulations, thermocouples were 5 cm below the surface (Figure .
, with thermal grease used to ensure proper contact.
Samples were then exposed to tungsten iodine lamps .
y 500 W) inside an insulated heating box .
cm heigh.
to simulate maximum solar radiation .
0 W/mA) and record surface temperature under controlled indoor These lamps were selected because their spectral distribution closely resembles natural sunlight in the infrared range, and their combined power output effectively replicates typical solar intensity, making them suitable for accelerated laboratory thermal testing (Zheng et al.
, 2.
To assess mechanical durability, all coated samples were tested for abrasion resistance using a wet track abrasion machine operated in a dry configuration.
After abrasion testing, specimens were re-tested for thermal performance under the same heating conditions to determine the effect of surface Results were analysed to understand how coating durability influences cooling effectiveness, with the aim of identifying practical strategies for enhancing the lifespan and performance of cool pavement technologies.
Journal of the Civil Engineering Forum Table 1.
Properties of asphalt pen 60/70 used in this research (Nugroho et al.
, 2.
Binder Properties Result Mass loss after TFOT (%) Penetration at 25 AC .
1 m.
Ductility at 25 AC .
>140 Kinematic viscosity at 135 AC .
Softening point (AC) Flash point (AC) Specific gravity Solubility in Trichloroethylene (%) 2 Aggregate The andesite aggregate used in this study for asphalt mixtures exhibited moderate abrasion resistance .
2%), low fine particle content, strong bitumen adhesion (Ou 95%), and high angularity .
4%), indicating good interlocking capacity.
Key mechanical propertiesAiincluding abrasion, surface texture, elongation, and soundnessAiare summarized in Table 2.
Table 2.
Properties of aggregates used in this research
Aggregate Properties Result
Abrasion
Crushed particles in coarse aggregates 95/90 Flat and elongated aggregates Soundness Aggregate adhesiveness to bitumen
>95%
3 MATERIALS AND METHODS
Sand equivalent 1 Materials Angularity Clay lumps and friable particles 1 Asphalt Binders In this study, an unmodified asphalt binder with a 60/70 penetration grade was selected for preparing the asphalt mixtures.
The binderAos essential physical characteristicsAiincluding its kinematic viscosity at 135 AC, penetration at 25 AC, softening point, and ductilityAiare summarized in Table 1 (Nugroho et al.
This binder was used to produce asphalt slabs that served as the substrate for the application of surface reflective treatments.
3 Asphalt Mixtures This study utilized asphalt mixtures with the gradation illustrated in Figure 2, following the mixture gradation for asphalt concrete wearing course and aligned with Indonesian road construction standards (Kementerian PUPR, 2.
Sieve analysis was conducted using ASTM E11 specifications, with the maximum aggregate size of 19 mm .
/4 inc.
To determine the optimal binder content, the Marshall mix design procedure was followed (ASTM, 2020.
The mixing process began by heating 1200 g of aggregate to 160 AC and bitumen to the same temperature before mixing.
The mixture was Journal of the Civil Engineering Forum Vol.
12 No.
1 (January 2.
Figure 1 Experimental setup of the research.
homogenized and placed into a mold, then compacted at 140 AC using a Marshall hammer delivering 75 blows per face.
The target air void content was set to 4 to From the test, the optimum asphalt binder content was determined to be 5.
At this content, the asphalt mixtures exhibited an average air void in total mix (VITM) of 4.
Figure 2 Aggregate gradation for asphalt mixture.
4 Hydrated Lime Hydrated lime (HL), or calcium hydroxide (Ca(OH)CC), used in this study is an inorganic compound produced by slaking quicklime (CaO) with water.
It is a white, strongly alkaline powder known for its chemical reactivity and ability to form strong bonds with asphalt Its portlandite structureAicharacterized by its hexagonal symmetry and layered arrangementAi underpins its high reflectivity, making it suitable for cooling applications (Iizuka et al.
, 2.
The HL used was in the form of fine, heterogeneous granules of varying sizes, applied in No.
and No.
mesh particle sizes to evaluate their effects on thermal performance and abrasion resistance.
For each particle size, four application rates were used, 50, 100, 150, and 200 g/mA (Table .
Due to its hygroscopic nature.
HL readily absorbs moisture from the air, and its ultrafine particles tend to clump when exposed to ambient humidity (Abu-Halimeh, 2.
To address this, particle size separation was carried out in accordance with ASTM C110 (ASTM, 2020.
The procedure involved spreading HL evenly on an iron tray and drying it in an oven at 105 AC for 2Ae3 hours until a constant weight was reached.
The dried material was then sieved using No.
No.
200, and No.
400 mesh sieves on a mechanical sieve shaker for 30 minutes.
After sieving, the Vol.
12 No.
1 (January 2.
Journal of the Civil Engineering Forum Table 3.
Paint-based heat-reflective coating (HRC) samples and designations Samples (Designatio.
a Binder / Organic Polymers Filler.
TiO2 Other additivesb White-ER White-AE White-BC Proprietary (BeCoo.
Ae Ae a ER = Epoxy Resin.
AE = Acrylic Emulsion.
BC = BeCool reflective paint.
b Additives include hardener/coalescing agents, dispersant, and defoamer.
separated particles were stored in sealed containers in a dry environment to prevent moisture uptake and agglomeration.
In addition to the laboratory-prepared coatings, a commercial paint.
BeCool, was also used.
It is a two-layer reflective coating system incorporating nano microspheres as the reflective component, with a solar reflectance of 0.
77 and thermal emittance of 0.
BeCool is commonly applied to roofs and is intended to reduce heat transfer in hot-humid climates.
5 Paint-Based Heat reflective Coatings (HRC) In this study, three paint-based heat-reflective coatings (HRC.
were evaluated: two laboratory-formulated coatings and a commercially available product.
Painbased HRCs incorporate a blend of organic binders and inorganic reflective materials to achieve solar reflectance (Rahman et al.
, 2024.
Xie et al.
, 2.
In such formulations, organic polymers serve as the adhesive matrix, securing the components in place, while inorganic fillers enhance the surfaceAos ability to reflect solar In this study, two types of polymer bases were employed: water-based acrylic emulsion and oil-based epoxy resin, as they are commonly used binders in HRCs.
Both types were combined with titanium dioxide (TiOCC), a well-known reflective white pigment, without the addition of color pigments.
To refine the coating properties, various functional additives were incorporated.
These include hardeners to promote epoxy curing, coalescing agents to ensure film formation, dispersants to stabilize the mixture, defoamers to eliminate entrapped air, and matting agents to reduce surface gloss.
The detailed component breakdown for both coating types is presented in Table 3.
Formulation ratios were adapted from prior studies by Li and Xie .
Xie et al.
to ensure compatibility and effectiveness.
6 Specimen Preparation To create the specimen for testing, slab-shaped asphalt mixtures measuring 306 mm y 306 mm y 50 mm were fabricated using an asphalt mixing machine and a rut sample forming machine, in accordance with ASTM D8079Ae23 standards (ASTM, 2.
The preparation process began with drying the aggregates at 160 AC, followed by heating the asphalt binder to the required mixing temperature.
Both components were then thoroughly blended at 145 AC using the asphalt mixer.
The hot mixture was poured into a slab mold and compacted using a rut sample forming machine through 40 loading After compaction, the mixtureAialong with the mouldAiwas allowed to cool naturally to ambient temperature .
pproximately 25 AC).
Once cooled, the compacted slab was removed from the mold and precisely cut using a stone cutter into four equal sections, each measuring approximately 150 mm y 150 mm y 50 mm with a 3 mm blade thickness (Figure 1.
A total of 24 asphalt slab specimens (Figure .
were prepared, including uncoated controls, three paint-based heat-reflective coatings (BeCool, epoxy, and acryli.
, and eight hydrated lime (HL) surface treatments using Table 4.
Hydrated lime (HL) samples and designations Particle Size No.
No.
Surface application rate
50 g/m2 100 g/m2 150 g/m2 200 g/m2 H2-50
H4-50
H2-100
H4-100
H2-150
H4-150
H2-200
H4-200
Designation Rule: H = Hydrated Lime.
2 = Particle size No.
4 = Particle size No.
last number = spreading dosage .
/m2 ).
Journal of the Civil Engineering Forum Vol.
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Figure 3 Asphalt slab specimens: .
uncoated control, .
white-BC (BeCool formulatio.
, .
white-EP .
poxy pain.
, .
white-AE .
crylic pain.
, .
Ae.
hydrated lime (H.
at 50, 100, 150, and 200 g/mA, and .
Ae.
hydrated lime (H.
at the same Each specimen is 30 y 30 cm and prepared in duplicate.
two formulations (H2 and H.
applied at four dosage levels .
Ae200 g/mA) .
s listed in Table 3 and Table .
Each variation was prepared in duplicate.
Different application techniques were employed depending on the coating material.
For HL, application was conducted .
while the asphalt was still hot, since HL lacks strong adhesion to cooled asphalt surfaces (Zhang et al.
, 2.
The asphalt surface temperature was carefully maintained at 120 AC, monitored continuously using a noncontact infrared heat gun to ensure uniformity and .
Figure 4 Specimen preparation and testing: .
compacted HL, .
spreading HRC, .
heatingAecooling simulation, .
drytrack abrasion test.
Vol.
12 No.
1 (January 2.
accurate temperature control throughout the process.
Once the asphalt reached the target temperature.
HL was distributed according to the dosage level and compacted with a rubber roller wrapped in soft tape to enhance surface bonding (Abu-Halimeh, 2.
(Figure 4.
Water was lightly applied during rolling to facilitate HL penetration into the surface pores.
In contrast, paint-based coatings were applied on cooled asphalt slabs using a paintbrush at a dosage 6 kg/mA (Yi et al.
, 2.
(Figure 4.
To ensure uniform application and prevent clumping, the coating mixtures were prepared using a high-shear mixer equipped with a variable-speed blade.
Each mixture was blended in a 7 cm y 7 cm cylindrical container placed under the mixer blade.
For the water-based acrylic formulation, matting agents, dispersants, and defoamers were first mixed for 10 minutes at 150 rpm, followed by the addition of acrylic and TiOCC for another 10 minutes, and finally, coalescing agents were blended in for 10 more minutes.
The epoxy resin variant involved mixing the resin with coalescing agents at 1000 rpm for 10 minutes, then incorporating TiOCC along with dispersants and defoamers, and continuing the mixing for an additional 15 minutes, followed by a final 10-minute mixing step with coalescing agents.
Once the optimal formulation was achieved, coatings were brushed onto asphalt slabs with a uniform thickness of 0.
1cm and cured at 25 AC for 24 hours.
For the BeCool reflective paint system, the manufacturerAos instructions were followed: the primer layer was applied and allowed to dry for 20Ae30 minutes, followed by the application of the top coating without dilution at 0.
kg/mA.
After curing, each specimen was drilled vertically from the top to a depth of 7.
5 cm .
easured from the 2.
cm top surfac.
to insert a thermocouple (Figure 1.
Thermal grease was added to fill the borehole, ensuring efficient heat conduction and eliminating air voids.
restrict heat loss to only the top surface, all lateral sides of the slabs were insulated using polystyrene foam (Alhaqi et al.
, 2.
2 Methods 1 Abrasion Test Abrasion resistance testing was performed to assess the durability of surface coatings applied to asphalt mixtures.
The test utilized a wet track abrasion tester (Figure 1.
), equipped with a loaded wheel applying a total force of 2.
5 kg.
While this setup does not fully replicate actual traffic loads, it provides a reliable means to evaluate the relative abrasion resistance of the coatings (Han et al.
, 2.
The test was conducted using a dry methodAiwithout waterAito simplify the conditions and assess the coatingsAo initial resistance to wear (Figure 3.
Journal of the Civil Engineering Forum The procedure began with recording the initial weight of each sample.
Specimens were then subjected to 2000 abrasion cycles in the testing machine, following the approach described by Momber et al.
After completion, the final weight of each sample was measured.
Additionally, the worn surface area was recorded to determine the extent of surface degradation.
Performance indicators, including the mass loss (ML) and abrasion coefficient (AC) were calculated using Equation .
and Equation .
, as outlined by Rahman et al.
ML =
m1 Oe m0 y 100% .
m1 Oe m0
AC =
where m0 is the mass of the sample before abrasion.
m1 is the mass after abrasion.
Ab is the abraded surface area of the sample.
2 Heating-Cooling Simulation Test To replicate the effects of solar heating in a controlled setting, an indoor simulation Figure 1.
was conducted using a pair of 500 W iodine tungsten lamps, yielding a combined simulated solar irradiance of approximately 1000 W/mA, as verified using a pyranometer (Alhaqi et al.
, 2.
These lamps served as artificial sunlight sources, replicating thermal exposure conditions similar to natural daytime radiation (Pan et al.
, 2.
The lamps were operated for 12 hours to represent daytime heating and turned off for another 12 hours to simulate nighttime conditions.
To ensure uniform thermal conditions and minimize environmental disturbances, the entire setup was housed in a thermally controlled enclosure constructed from wood and lined with reflective aluminum foil, as shown in (Figure 4.
The lamps were suspended 75 cm above the asphalt specimens, which were centrally placed within the enclosure.
addition, wind speed and humidity were measured during the test to ensure consistent conditions.
To minimize lateral heat losses, polystyrene insulation was installed around the specimen edges (Figure 4.
This setup is consistent with previous experimental protocols reported by Pan et al.
and Chen et al.
After 24 hours of testingAicomprising a full simulated diurnal cycleAitemperature data were recorded and evaluated to capture the thermal behavior of each surface treatment configuration.
Journal of the Civil Engineering Forum
4 RESULTS AND DISCUSSION
1 Initial Thermal Performance Figure 5 presents the simulated temperature responses of asphalt slabs subjected to 12-hour heating and 12hour cooling cycles.
The results are shown for three surface treatments: .
paint-based heat-reflective coatings, .
hydrated lime with No.
200 mesh size, and .
hydrated lime with No.
400 mesh size.
Each subfigure compares coated and uncoated samples over a full 24-hour cycle.
As illustrated in Figure 5, there is a clear temperature distinction between coated .
sing HRC and HL) and uncoated samples.
The horizontal axis represents time in hours, while the vertical axis shows surface temperature in degrees Celsius.
During the heating period, all samples exhibited a steady temperature rise, reaching their peak between the 10th and 12th hour.
The uncoated sample reached the highest temperature at the end of the heating phase, surpassing 80 AC, reflecting its high heat absorption and low solar reflectivity (Chen et al.
, 2019b.
Wang et al.
, 2.
In the paint-based HRC group (Figure 5.
), noticeable surface temperature reductions were observed, with the acrylic-based formulation (White-AE) performing best, followed by the epoxy-based (White-EP) and the commercial BeCool (White-BC).
This suggests the polymer type and composition significantly influence heat reflectance efficiency.
For hydrated lime surface treatments, both No.
mesh (Figure 5.
), and No.
400 mesh (Figure 5.
), groups demonstrated that higher dosages led to better cooling performance.
The H2-200 g/mA and H4-200 g/mA samples recorded the lowest peak temperatures in their respective groups, with the latter showing a Vol.
12 No.
1 (January 2.
marginally superior cooling effect.
This indicates that finer hydrated lime particles may enhance surface reflectivity due to increased coverage and bonding and Mie scattering (Man et al.
, 2.
The observed temperature reductions of the coatings suggest the potential to lower pavement temperatures and extend pavement life by slowing material degradation.
Broader application could help mitigate urban heat island effects, though long-term field validation under real traffic and environmental conditions is still needed.
Following the heating phase, all samples cooled to approximately 31 AC over a 12-hour period with the halogen lamp switched off, simulating nighttime conditions .
ooling phas.
During the cooling phase .
Ae24 hour.
, all samples showed a gradual temperature decline as external heat sources were removed.
Coated specimensAiwhether with paint-based HRC (Figure 5.
) or HL treatments (Figure 5.
)Aimaintained lower surface temperatures than the uncoated sample throughout this period.
This behaviour suggests that these coatings not only reduce heat accumulation during the day but also limit thermal re-radiation at night, which may help mitigate nocturnal ambient temperatures and UHI effects.
By the end of each 24-hour cycle, both coated and uncoated surfaces tended to reach similar temperatures, suggesting that the starting temperature on the following day is nearly the same.
This is important for UHI mitigation (Han et al.
, 2.
For a comprehensive comparison between paint-based HRC and HL treatments, the surface temperature reductions after 12 hours of heatingAitermed the cooling effectAiare presented in Figure 6.
These temperature differences reflect the effectiveness of each surface treatment in mitigating heat accumulation.
The paintbased group (HRC) exhibited strong performance: the Figure 5 Average temperature of each sample under heating and cooling: .
paintable HRC, .
hot-pressed HL .
, .
hot-pressed HL .
Vol.
12 No.
1 (January 2.
Journal of the Civil Engineering Forum Figure 6 Temperature differences at the end of the heating phase compared to uncoated samples.
acrylic-based coating (White-AE) reduced the surface temperature by 19.
29 AC, followed by the epoxy-based (White-EP) and BeCool commercial paint (White-BC).
These results confirm the effectiveness of paint-based coatings in minimizing solar heat absorption due to their high reflectivity and film-forming capability.
Meanwhile, the HL-coated samples also performed competitively, with thermal reductions largely influenced by both particle size and dosage.
The No.
400 HL
particles (H.
consistently outperformed the coarser No.
200 group (H.
, likely due to enhanced coverage and light scattering from finer particles.
At the lowest dosage .
g/mA).
H4 achieved a 10.
66 AC reduction, while H2 only achieved 5.
27 AC.
When the dosage increased to 100 g/mA and 150 g/mA.
H4 showed reductions of 15.
92 AC and 18.
03 AC respectively, with diminishing returns above 150 g/mA.
The highest dosage of 200 g/mA resulted in the best performance across both groups: 19.
67 AC for H2 and 21.
89 AC
for H4, which was the greatest reduction among all These findings suggest that, when applied optimally.
HL coatingsAiparticularly with finer gradation and higher dosageAican match or even outperform commercial and lab-formulated HRCs in surface temperature mitigation.
A one-way ANOVA test .
< 0.
was used to examine differences in cooling performance among paint-based HRCs .
34Ae19.
29 AC) and HL coatings .
27Ae21.
89 AC).
The results indicate that higher-dosage HL coatings, particularly H4-200 .
89 AC) and H2-200 .
67 AC),
provided greater cooling than paint-based HRCs .
poxy and commercia.
, while acrylic HRC .
29 AC) showed comparable performance to H2-200.
Lower-dosage HL coatings exhibited similar cooling to paint-based coatings, suggesting that application rate strongly influences performance.
2 Abrasion Resistance of Surface Coatings Following the thermal performance evaluation, the coated asphalt samples underwent abrasion testing to assess their resistance to mechanical wear.
As shown in Figure 7, the test revealed marked differences in abrasion resistance between the paint-based HRC and the HL treatments.
The top graph (Figure 7.
) illustrates the coating mass loss, while the bottom graph (Figure 7.
) presents the corresponding abrasion coefficient values.
Quantitatively, mass loss ranged from 0.
6 g to 1.
across all samples.
The highest loss was observed in H2-150 .
, indicating weaker surface bonding, while H4-100 recorded the lowest .
, reflecting superior durability.
Similarly, higher abrasion coefficient values indicated lower wear resistance.
Among paint-based coatings (HRC.
, most exhibited moderate to poor abrasion resistanceAiexcept for the BeCool (BC) sample, which performed comparatively well with a mass loss of 0.
8 g and an abrasion coefficient of 109.
g/mA.
In general.
HL coatings showed variable wear resistance depending on particle size and dosage.
While some HL specimens, particularly those with finer particles (No.
400 mes.
and higher dosages .
Ae200 g/mA), achieved lower mass losses .
6Ae0.
and abrasion coefficients .
Ae92 g/mA) than paint-based HRCs, others performed similarly or slightly lower.
This indicates that HL does not consistently outperform HRCs but can provide superior abrasion resistance when optimized for particle size and application rate.
Two key factorsAiparticle size and dosageAistrongly influenced HL coating performance.
Regrading dosage, the fluctuations observed at 50 g/mA and 150 g/mA for both mesh sizes are likely influenced by both material behaviour and variability during application.
At 50 g/mA, limited surface coverage reduces mechanical in97 Journal of the Civil Engineering Forum Vol.
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Figure 7 The abrasion resistance test result.
terlock, while 100 g/mA provides more effective bonding and higher resistance.
The drop in performance at 150 g/mA is likely due to uneven distribution or agglomeration that weakens bonding efficiency, whereas at 200 g/mA, the greater material quantity likely restores surface continuity and improves abrasion resistance.
This non-linear trend suggests that abrasion performance depends on dosage, particle packing, and application quality.
In terms of particle size, samples with No.
200 mesh particles (H2 grou.
demonstrated moderate resistance, with mass losses ranging from 0.
8Ae1.
3 g and abrasion coefficients of 98.
39Ae148.
74 g/mA.
Meanwhile, the No.
400 particle group (H.
outperformed H2, showing mass losses between 0.
6Ae0.
9 g and abrasion coefficients of 72.
17Ae126.
30 g/mA.
The superior performance of finer particles is likely attributed to their greater surface area, allowing better penetration into micro-pores and promoting stronger physical and chemical bonding with the asphalt binder (Lebedev et al.
, 2.
Additionally, higher dosages generally produced better results, with lower application rates .
, 50 g/mA) resulting in weaker abrasion resistance.
Visual observations from Figure 8 reinforce these HL-coated specimens with finer particles .
H4-.
retained more material post-abrasion compared to their coarser counterparts .
H2-.
, supporting the claim that particle fineness enhances durability.
Interestingly, the paint-based coatings presented differing abrasion patterns: although White-AE .
crylic emulsio.
recorded higher abrasion losses, it exhibited more uniform surface wear, whereas WhiteEP .
poxy resi.
showed localized and patchy abra- sion, which may suggest premature failure in isolated zones under field conditions.
This contrast highlights the importance of not only measuring total loss but also considering failure patterns when evaluating longterm surface integrity.
In conclusion, both the measurement data and surface observations confirm that HL coatingsAiparticularly those using 400-mesh particles at higher dosagesAioutperform paint-based alternatives in abrasion resistance.
3 Thermal Performance After Abrasion Following abrasion testing, the coated samples were re-evaluated to determine the effect of surface wear on thermal performance.
The analysis focused on the relative temperature changeAidefined as the difference between pre-abrasion and post-abrasion surface temperatures.
This metric indicates the extent of thermal degradation caused by abrasion: a higher value reflects greater loss in cooling performance.
As shown in Figure 9, abrasion led to a noticeable decline in thermal performance during both the heating and cooling In the heating phase (Figure 9.
), temperature differences ranged from 5.
8 AC to 8.
0 AC, with the smallest change observed in H4-100, indicating its superior retention of thermal reflectivity.
In contrast, the greatest performance loss was recorded in H2-50, highlighting its vulnerability to abrasion.
During the cooling phase (Figure 9.
), the relative temperature changes were smaller, ranging between 5 AC and 2.
9 AC, suggesting that while abrasion weakened heat dissipation, the effect was less severe than during heat absorption.
Overall, the HL coatingsAi Vol.
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Journal of the Civil Engineering Forum .
Epoxy Resin TiO2 (WhiteAeEP) .
Acrylic Emulsion TiO2 (WhiteAeAE) .
Hydrated lime mesh size 200Ae100 g/m2 (H2Ae.
Hydrated lime mesh size 400Ae100 g/m2 (H4Ae.
Figure 8 Specimens before and after abrasion tests with paint-based HRC and HL at different particle sizes and application especially those with No.
400 mesh particlesAiexhibited better thermal stability after abrasion compared to paint-based coatings, with H4 variants showing the most consistent performance.
In the paint-based HRC group.
BeCool (White-BC) exhibited the greatest increase in surface temperature after abrasion .
2 AC), indicating the highest thermal White-AE and White-ER showed similar, moderate increases .
3 AC).
Although White-AE expe- Figure 9 Relative temperature change (OIT = Tinitial -Taf ter ) of coated samples following abrasion: .
heating phase .
th hou.
, .
cooling phase .
th hou.
A higher value indicates greater thermal performance degradation due to surface Journal of the Civil Engineering Forum rienced greater mass loss, it displayed more uniform abrasion, which may help preserve reflectivity better than the patchier wear observed on White-ER.
Abrasion significantly compromises the thermal effectiveness of both coating types.
However, hydrated lime (HL) treatmentsAiparticularly those using finer particles (No.
Aidemonstrated greater thermal stability after abrasion compared to paint-based HRC Several HL coatings, however, particularly those with larger particle sizes (No.
and lower dosages, showed lower performance than HRCs.
Notably, for both HRC and HL, all coated samples maintained substantially lower surface temperatures than the uncoated control even after 2000 abrasion cycles, indicating that residual cooling effects remain effective.
Overall.
HL presents a promising and cost-effective alternative to conventional HRCs.
It offers comparable or superior cooling performance, better abrasion resistance, and more consistent post-wear thermal behaviour.
The enhanced abrasion resistance of HLAi especially with finer particlesAiis primarily due to its greater surface area, which allows better penetration into asphalt micro-pores, creating stronger mechanical Additionally.
HLAos inherent hardness and potential for surface hardening through carbonation further improve its durability under mechanical stress.
Unlike paint-based HRCs that rely on polymer binders prone to peeling or softening.
HLAos simpler composition leads to better wear retention and lower degradation under repeated abrasion.
Given its affordability and potential lower environmental impact.
HL surface treatments appear well-suited as sustainable alternatives for pavement applications.
However, long-term studies are needed to assess their durability, skid resistance, and performance under varying environmental Lastly, it is important to note that the abrasion tests in this study were conducted under controlled laboratory conditions, which may not fully replicate the complex loading and environmental factors present in actual pavement service.
Water immersion effects during abrasion testing were also not examined, even though they could significantly affect coating durability in the In addition, the thermal simulation was limited to a 12-hour on/off heating cycle, which does not represent long-term exposure.
Future studies should incorporate extended exposure durations, cyclic environmental conditions, and water immersion testing to provide a more comprehensive understanding of coating performance under real-world conditions.
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5 SUMMARY AND CONCLUSION This study investigated the thermal and abrasion performance of paint-based heat-reflective coatings (HRC) and hot-rolled hydrated lime (HL) surface treatments for asphalt pavements, aimed at reducing surface temperatures and mitigating Urban Heat Island (UHI) effects.
The main findings are as follows:
Both HRC and HL coatings significantly lowered surface temperatures under heating conditions, achieving reductions between 5.
27 AC and 21.
AC.
The best performance was recorded by HL with 200 g/mA dosage and 400-mesh particle size (H4-.
, while the White-AE .
HRC also showed strong cooling effect .
29 AC).
The effectiveness of HL is attributed to its enhanced solar reflectivity and diffuse light scattering, particularly in fine-particle formulations that offer better surface coverage and microstructural interaction.
In abrasion resistance tests.
HL coatings outperformed paint-based HRCs, with mass loss ranging 6 to 1.
3 g.
Finer HL particles (No.
400 mes.
offered greater resistance through higher surface area, micro-pore penetration, and stronger mechanical interlock, while paint-based HRCs generally exhibited weaker surface bonding.
After abrasion, all coated surfaces showed temperature increases of 5.
8Ae8.
0 AC during heating 5Ae2.
9 AC during cooling.
HL coatingsAi particularly with finer particlesAidemonstrated better post-abrasion thermal stability than HRCs, indicating more consistent performance after surface wear even though HRCs showed slightly lower absolute increases.
Overall.
HL surface treatments offer a promising, cost-effective, and environmentally friendly alternative to conventional paint-based HRCs.
When optimized in particle size and dosage.
HL delivers competitive or superior thermal performance, better abrasion resistance, and more stable residual cooling.
Further long-term studies are recommended to assess their durability, skid resistance, and performance under various environmental and traffic conditions.
DISCLAIMER
The authors declare no conflict of interest.
ACKNOWLEDGMENTS
The authors gratefully acknowledge PT Diwangkara Wihaya Nusantara (Driy.
, the manufacturer of the BeCool reflective coating, for providing the commercial materials used in this study.
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REFERENCES