Water remains one of the biggest threats to asphalt roads, making proper road slope, drainage and regular pavement maintenance essential in preventing premature deterioration, according to an official of the Philippine Institute of Civil Engineers (PICE).

Alexander Rentegrado, president of the PICE Ilocos Norte-Laoag City Chapter, said the durability of an asphalt road should not be judged solely by the quality of the asphalt material used.

“The number one enemy of asphalt is water,” Rentegrado said in an interview.

He explained that roads are designed with a cross slope, or camber, that allows rainwater to flow toward the sides instead of remaining on the pavement.

The road surface should not be completely flat, he said. Its proper slope allows water to move toward gutters, shoulders and drainage facilities, preventing it from accumulating on the driving surface.

Rentegrado said stagnant water can eventually penetrate cracks and other weaknesses in the pavement, reaching the underlying layers and weakening the road structure.

“When water becomes stagnant, they seep through everything,” he said.

Even a small pothole or opening in the asphalt, he added, can become a bigger problem when left unrepaired because water can enter the pavement and gradually damage the layers underneath.

This makes routine road maintenance important, particularly in areas frequently exposed to heavy rainfall.

“A small hole can damage the asphalt pavement,” Rentegrado said, emphasizing that pavement defects should be addressed before they expand and allow more water to penetrate the road.

He said the road surface, drainage system and underlying pavement structure must therefore be treated as one system.

A properly sloped road will not be effective if drainage facilities are blocked or inadequate, while a well-built drainage system cannot prevent ponding if the pavement itself has low spots where water collects.

Airport-grade asphalt not practical for ordinary highways

Rentegrado also acknowledged that higher-grade asphalt materials, including those used in airport runways, can provide better pavement performance.

However, he said using such materials throughout the country’s highway network would involve significantly higher costs.

“Airport-grade asphalts are good, but they are expensive,” he said.

For ordinary highways, he said pavement specifications should instead be matched to the road’s intended use, traffic volume and environmental conditions, while ensuring proper construction, grading, drainage and maintenance.

Bridges face a different threat

Unlike roads, where water primarily threatens the pavement and its underlying layers, bridges can face a more immediate danger from strong currents attacking their foundations.

Rentegrado said bridge safety should not be assessed only by looking at the visible concrete or steel portions of a structure.

Engineers must also examine the riverbed, soil conditions and areas surrounding bridge piers and abutments, particularly during periods of extreme flooding.

One major concern is scour, in which fast-moving water removes soil and sediment around bridge foundations. As the riverbed is eroded, the soil supporting the foundation can be reduced or washed away.

The recent damage to the Aquino and Agana bridges in Tarlac City illustrates the force that swollen rivers can exert on infrastructure. Portions of the bridges were swept away after heavy rains associated with the Southwest Monsoon, or Habagat, caused strong currents.

Rentegrado said such incidents highlight the need to protect not only the bridge structure but also its foundation and surrounding river environment.

Local knowledge should be part of planning

Rentegrado also stressed the importance of consulting communities and local authorities when planning bridges, roads, slope protection and other infrastructure in areas vulnerable to flooding.

He said local residents often have firsthand knowledge of how water behaves in their communities, including areas where rivers regularly overflow, where water normally accumulates and how currents change during severe weather.

Such information, he said, can complement engineering studies during the planning stage.

A feasibility study, he noted, is conducted under specific conditions and cannot simply reproduce the actual forces and conditions experienced during an extreme calamity.

This is why engineers should consider historical flooding, local observations and the experiences of communities alongside technical studies when designing infrastructure.

For slope protection projects, he said engineers must likewise examine the actual behavior of the soil, waterways and surrounding terrain rather than relying solely on plans prepared without sufficient appreciation of local conditions.

Protect the design and foundation

Rentegrado said the original engineering design of a bridge must be followed and that protective measures around its foundations must be properly maintained.

A bridge may appear structurally sound above the water while its supporting soil beneath the river is being eroded.

This becomes particularly critical when rainfall increases the volume and velocity of water passing underneath a bridge.

Regular inspection is therefore necessary, especially for bridges located along waterways that are frequently affected by flooding.

Engineers, he said, must consider the bridge together with the river, soil, drainage and surrounding terrain when assessing infrastructure safety.

‘You cannot fight the weather’

The same principle applies to levees and flood-control structures, Rentegrado said.

“You cannot fight the weather,” he said.

Engineers can design a structure according to established standards and anticipated conditions, but every structure has a design limit.

“Regardless of how perfect the design is, if the weather brings in more than what a levee can handle, something will break,” he said.

He explained that extreme weather can produce water volumes and hydraulic forces beyond what a structure was originally designed to withstand.

For Rentegrado, engineering safety is therefore not simply about using stronger materials or building larger structures. It also involves understanding the limits of a design, maintaining infrastructure, protecting vulnerable components and continuously monitoring changing conditions.

Roads, bridges, drainage facilities, slope protection and flood-control structures should be treated as interconnected parts of an infrastructure system, he said.

For roads, this means maintaining the correct cross slope and drainage capacity while immediately repairing pavement defects that can allow water to penetrate.

For bridges, it means protecting foundations against scour and monitoring changes in riverbeds and surrounding soil.

For slope protection, it means considering actual ground and water conditions and incorporating local knowledge into the planning process.

And for levees and flood-control structures, it means recognizing the amount of water and force they were designed to withstand while preparing for conditions that may exceed those limits.

Ultimately, Rentegrado said infrastructure safety depends not only on the materials used but on how the entire system is designed, constructed, maintained and monitored.