The rainy season inevitably brings a familiar problem to Philippine roads: potholes, cracks, depressions and pavement sections that deteriorate soon after heavy rains.

For motorists, the question is straightforward: Why does a road that was recently paved or repaired begin to fail once the rains arrive?

According to Engr. Teddy Javines of IGWT-JAV, the answer cannot be attributed to the asphalt mixture alone.

Pavement performance depends on several factors, he said, including the asphalt mix design, materials, application, traffic loading, weather, drainage and, critically, the condition of the pavement layers beneath the surface.

“Once lumambot ang sub-base, sure na magkakaroon ng cracks ang concrete,” Javines said.

He also emphasized the role of environmental conditions and drainage, citing differences between road performance in the Philippines and Singapore.

“Almost pare-pareho naman ang bitumen. Ito ang gawin mong basis: yung number one asphalt designer sa Singapore ay Pinoy, at dito sa atin siya nag-aral at nagkaroon ng experience. The same design was used in Singapore, pero mas matibay doon dahil mas maganda ang weather conditions at mas maayos at matibay ang drainage system nila,” Javines said.

The comparison underscores a basic principle of pavement engineering: a road is not simply a layer of asphalt placed over the ground.

An asphalt pavement is a layered structure. The surface course rests on base and sub-base materials that distribute traffic loads to the soil beneath. When water penetrates these layers and remains there, it can weaken the pavement structure and accelerate deterioration.

Moisture and pavement failure

Research by the U.S. Federal Highway Administration (FHWA), an agency under the United States Department of Transportation, documents the role of excess moisture in pavement deterioration. Its technical guidance notes that water can enter pavement through cracks, pavement edges and other pathways, while moisture in base and sub-base materials can reduce their strength and stiffness.

The FHWA research is based on U.S. conditions and is not a Philippine road standard. It nevertheless provides engineering context for understanding how water can contribute to pavement failure.

Moisture can also affect the asphalt mixture itself.

A 1998 FHWA publication, Tips on Identifying and Correcting Superpave Mixes Susceptible to Moisture-Induced Damage, discussed stripping, a process in which water weakens the bond between asphalt binder and aggregate. Once that bond is compromised, the mixture becomes more vulnerable to deterioration under traffic.

Research published by the National Academies of Sciences, Engineering, and Medicine has likewise examined moisture susceptibility in asphalt pavement. A 2022 report identified aggregate-binder compatibility, standing water or water under pressure within pavement layers, and construction practices as factors that can contribute to moisture-related damage.

A 2025 National Cooperative Highway Research Program publication further examined how water contributes to the deterioration of flexible and composite pavements and measures that highway agencies can use to limit water-related damage throughout a pavement's life cycle.

Together, these studies point to an important distinction: asphalt does not necessarily fail simply because it becomes wet. Rather, moisture can interact with the asphalt mixture, the bond between materials and the underlying pavement structure, while repeated traffic loading accelerates deterioration.

Javines likewise cautioned against assuming that asphalt can withstand prolonged saturation.

“Yes, walang assurance din kung talagang babad sa tubig. Kahit hindi bumigay ang asphalt, kung yung adhesive naman niya sa concrete ang bumigay dahil sa tubig, eventually matutuklap din ang asphalt,” he said.

As a result, visible pavement damage does not necessarily indicate where the failure began.

A pothole, for example, may be the final manifestation of a problem that started beneath the pavement, where water weakened supporting layers before repeated traffic caused the surface to collapse.

Asphalt as part of the pavement system

Javines said asphalt serves several functions when used as part of a pavement system.

“Maraming purpose ang asphalt. Una, protection ng concrete pavement. Kung walang asphalt, madaling pasukin ng tubig ang sub-base ng concrete. Once na lumambot ang sub-base, sure na magkakaroon ng cracks ang concrete. Pansin mo, yung mga concrete na walang asphalt, maraming cracks. Pangalawa, maintenance and safety ng mga sasakyan. Alam naman natin na once hindi smooth ang daan, madaling masira at mabilis maubos ang gulong ng mga sasakyan. Pangatlo, aesthetic din ng kalsada,” he said.

On major roads, asphalt and concrete can therefore work together as components of a pavement system.

Asphalt can provide a smoother riding surface while also protecting concrete pavement from water intrusion. But the durability of the system still depends on the condition of the underlying layers and the road's ability to manage water.

What ARA can—and cannot—do

Another issue raised in the discussion was the use of ARA, or Anti-Rutting Additive, in asphalt mixtures.

ARA is not a generic term for every asphalt additive. In the context of Philippine road specifications and the product discussed by Javines, it refers to an additive incorporated into hot-mix asphalt to improve resistance to rutting.

The Department of Public Works and Highways (DPWH) formally recognized ARA in Department Order No. 11, Series of 2019, which established specifications for Item 310(12), or Bituminous Concrete Surface Course, Hot-Laid with Anti-Rutting Additive (ARA).

The DPWH described ARA as an additive intended to increase the strength and durability of adhesion between aggregates. The specification set the ARA proportion at 0.3 percent by weight of the asphalt mixture and identified high-density polyethylene and other polymeric materials among the permitted types.

The order also stated that the ARA specification was recommended for asphalt overlay projects carrying fewer than 2,000 vehicles per day.

Javines explained the additive's purpose in simpler terms.

“May ARA kasi sa mixture natin. Additive ito sa asphalt na medyo mahal per kilo, pero gumaganda ang elasticity niya,” he said.

The performance of anti-rutting additives has also been examined in published research.

A 2016 study in the Journal of Testing and Evaluation examined asphalt-concrete mixtures modified with styrene-butadiene-styrene and an anti-rutting additive. The researchers found that the combined modification improved high-temperature performance and reduced permanent deformation, while noting that other characteristics, including low-temperature performance and moisture susceptibility, also required consideration.

A 2022 study published in Construction and Building Materials likewise reported improved performance from an ARA-modified asphalt mixture, including at high temperatures, while examining its effects on water stability and cracking resistance.

The Japanese manufacturer of the ARA product referenced in Philippine materials, TAC Corporation, describes the additive as a product developed to prevent rutting at high temperatures. The company says it uses polymeric materials and auxiliary agents intended to improve bonding between asphalt and aggregates and resistance to flow at elevated temperatures.

The Philippine distributor similarly identifies ARA as an anti-rutting additive developed by TAC in Japan. Those descriptions are manufacturer and distributor claims, rather than independent assessments of the product's performance.

That distinction is important. An additive designed to improve resistance to rutting does not eliminate every potential cause of pavement failure.

Rutting, moisture damage, cracking and structural failure are different pavement problems, although they can interact.

A road can have a highly rut-resistant asphalt mixture and still deteriorate if water penetrates the pavement and weakens its foundation.

Thickness, construction and drainage

Pavement thickness, construction quality and drainage therefore remain critical.

For government road projects, DPWH specifications govern the materials and procedures used in construction. The agency has also issued requirements concerning asphalt overlay thickness.

Under DPWH Department Order No. 39, Series of 2009, the department mandated a minimum design thickness of 50 millimeters, or two inches, for asphalt overlay projects. The order cited field observations and empirical studies indicating that thinner overlays were more susceptible to premature cracking, potholes, peeling and other defects.

This does not mean that every pothole is evidence of a failure to comply with a particular specification.

Rather, pavement deterioration typically results from several interacting factors.

The asphalt mixture matters.

The aggregate and binder matter.

Pavement thickness matters.

Compaction matters.

The condition of the base and sub-base matters.

Traffic loading matters.

And in a tropical country, water management can be particularly important.

For motorists, the problem becomes visible only when pavement begins to crack, deform or break apart.

By then, however, the underlying problem may have been developing for months or even years.

The rainy season may simply expose weaknesses that already existed within the pavement system.

That is why complaints about potholes and damaged roads should prompt more than a question about how much asphalt was placed on the surface.

The more important questions are whether the pavement was designed for the traffic it carries, whether the appropriate mixture and materials were used, whether the pavement was properly compacted, whether the required thickness was achieved, whether the underlying layers were adequately prepared, and whether drainage was sufficient.

For motorists, the result is measured in a smoother ride—or the jarring impact of a pothole.

For engineers, however, the real story may be several layers below the asphalt.

When the rains come, that hidden part of the road can determine whether the pavement survives the season or becomes another damaged section requiring repair.