Asphalt Still Soft: What Could Be the Possible Reasons?

Asphalt is one of the most widely used materials for construction projects involving driveways, parking lots, and roads. Its use is prevalent because of its excellent surface and durability. However, newly laid asphalt may take a shorter time to lay, but still be soft and sticky sometimes. Even though the newly laid asphalt should not be soft at all, there are some explanations for this.

Insufficient Compaction

Inadequate compaction is one of the main reasons new asphalt remains soft, which is why it is essential to perform compaction control and ensure that the layers are correctly compacted. Compaction is the process of using force to reduce the void content within the pavement structure making it denser and is an essential step in constructing asphalt concrete pavements. It helps compact all the asphalt components and eliminate the bubbles of trapped air. Inefficient compaction will result in weak asphalt with a soft feel to the touch.

There are a few reasons why the compaction may have been inadequate:

– Inadequate compaction – Failure to use the right tool, such as a heavy pneumatic tire roller, to exert the necessary weight and vibration pressure on the surface.

– There are not enough passes with the compactor. – The paving crew may have been too hasty while rolling and not have ensured adequate passes by the compactor.

– Compacting at the wrong time or stage –If the pavement is compacted outside the correct time range or stage, the compaction will have not been performed properly and it may be soft.

Insufficient Curing Time

Asphalt requires time to harden so that all the components can set well to ensure it conforms to its intended specification. If vehicles, equipment, or even people have treaded upon the surface before it has set, it will remain soft and distorted.

Asphalt cures gradually, and it may take a week to several weeks, depending on the weather conditions, mix proportion, and the thickness of the pavement. Temperature has a direct impact on the rate of curing. Hot temperatures, for instance, have a way of hastening a curing process, while cold temperatures slow the process. Curing time is another common cause of soft asphalt that is easily identifiable by an experienced professional.

Subgrade Issues

When paving and compaction are done well, there still could be issues in the subsurface layers that may lead to soft asphalt.

Some potential subgrade issues include:

– Water penetration and accumulation in some parts of the road due to poor drainage form a moisture base for the asphalt.

– Lack of adequate compaction of the aggregate base layers can result in a weak sub-grade on which to put the asphalt.

– Movement or improper settling of the soil or aggregate base over time, can result in cracks and depressions on the surface.

These subgrade problems lead to a lack of support and instability of the asphalt surface, which is undesirable. Over problematic areas, deformation begins and slowly transforms into a soft material.

Asphalt Mix Issues

Sometimes, the problem is contained in the asphalt mix; in other cases, the problem lies with the overlay.

Some examples include:

– The excessive content of asphalt binder or liquid asphalt tends to make the mixture soft and sticky. This is known as a ‘rich’ mix.

– Adding too many fine aggregates, such as sand, yields a softer mix than those containing coarser crushed stones.

– Variability in the mixes is an undesirable sign indicating that the quality control during asphalt production was poorly done. Some loads of aggregates might be made with too much binder.

– With overheating the liquid asphalt during production, the liquid asphalt becomes less dense or thicker, leading to a softer mix.

In similar situations, even efficient work on paving and compaction will not eliminate problems with the flexibility of the cement-asphalt mixture.

How to address soft asphalt:

First, it is crucial to understand that it is not a mere inconsequential issue that can quickly be dealt with in the blink of an eye.

If you’re still under warranty or workmanship guarantee from the paving company, ask them to check and rectify any soft asphalt area. Ideally, they should be able to determine whether it is the quality of the mix, the effort put in compaction, or something else.

If the warranty has expired, perhaps the owner may have to engage the services of an asphalt contractor or a paving firm to address the issue.

Here are some options they may recommend:

Add Additional Compaction

Where compaction was insufficient, more localized rolling and compaction may be sufficient to increase the rigidity of the surface. This involves using a torch or an infrared heater to warm up the soft areas so that they can be compacted at a specific temperature.

Mill Out and Repave

Some roads, especially those with highly soft or deformed sections, may require milling or grinding to be overlaid with new hot mix asphalt that can meet the specifications. This ensures that areas compromised due to weak soils are repaired and filled with well-compacted material, including the right asphalt.

Apply a Sealcoat

Applying an asphalt sealcoat entails putting a liquid material on the bound asphalt to protect it from various elements. It seals pores to prevent further penetration and “welds” the surface. If the binder is slightly soft or oxidized, a sealcoat can increase the stiffness of the resultant mixture. Keep in mind, however, that it may not sufficiently treat very soft or distorted regions.

There are several steps in the construction of asphalt surfaces; it is crucial to be accurate during all of them to produce a long-lasting, high-quality surface. New asphalt softness can be expected if there is low compaction, slow setting time, poor subgrade support, and poor mix design. Policies that tackle such matters lead to the best results as soon as possible. Other issues, such as depressions and cracks, may arise in the future if the soft asphalt areas are not fixed.