Understanding AC-BC Asphalt: Structure, Function, and Benefits in Road Construction

In road infrastructure development, the quality of asphalt pavement plays a critical role in ensuring durability and driving comfort. One of the key layers in flexible pavement construction is Asphalt Concrete – Binder Course (AC-BC). This article provides a concise yet complete overview of AC-BC, including its function, structure, specifications, and practical benefits.

What Is AC-BC Asphalt?

AC-BC stands for Asphalt Concrete – Binder Course. It is an intermediate layer in flexible pavement structures, placed above the base course and below the surface wearing course (AC-WC).

Although it does not come into direct contact with vehicle traffic, AC-BC plays a vital role in transferring vehicle loads to the lower layers and ensuring overall pavement stability.

Main Functions of AC-BC

1. Structural Binder
   AC-BC bonds the base layer and the surface course, creating a strong, integrated pavement structure.

2. Load Distribution
   It helps distribute vehicle loads from the surface layer to the underlying structure, preventing early deformation.

3. Road Durability
   With a homogeneous mix of asphalt and aggregate, AC-BC adds resistance to dynamic loads and extreme weather conditions.

Composition and Technical Specifications

Typical AC-BC composition includes:

• Coarse and fine aggregates

• Filler (cement, stone dust)

• Bitumen (Pen 60/70 or modified asphalt)

General technical specifications (based on Indonesian Ministry of Public Works):

Parameter Typical Value Aggregate Gradation Intermediate (between coarse & fine) Bitumen Content 4.5% – 6% Layer Thickness ± 5 cm Marshall Stability ≥ 800 kg Void in Mix (VIM) 3% – 5% Flow 2 – 4 mm

AC-BC Installation Process

1. Base Surface Preparation
   The underlying base is cleaned and coated with a tack coat (bonding agent).

2. Hot Mix Laying
   Asphalt mix is laid evenly using an asphalt finisher according to the designed thickness.

3. Compaction
   Compaction is done using a tandem roller, pneumatic roller, and finishing roller to achieve optimal density.

Key Advantages of AC-BC

• High structural stability

• Strong resistance to repeated traffic loads

• Efficient load transfer to lower layers

• Minimizes cracking and deformation risks

Safety (K3) in AC-BC Roadwork

Safety in asphalt work is non-negotiable. Key K3 measures include:

• Mandatory use of Personal Protective Equipment (PPE): helmet, reflective vest, safety shoes, heat-resistant masks

• Securing the construction site from active traffic

• Installing project safety signs and barriers

• Conducting daily safety briefings for workers

Conclusion

Asphalt AC-BC is an essential part of flexible pavement systems, serving as a load-distributing and bonding layer. When applied with correct specifications and safety standards, it contributes to strong, durable, and long-lasting roads. Combined with a solid safety culture, it ensures both construction quality and worker protection.

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