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Published: Benefits of Asphalt Paving

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Published: How an Asphalt Roadway Is Created

I published “How an Asphalt Roadway Is Created” on @Medium

Exploring the Different Asphalt Mixes for Paving Projects

 With an annual production value of around $30 billion, the asphalt industry supports the construction of durable, seamless surfaces for driveways, parking lots, roads, and other infrastructure. Asphalt makers alter gravel, sand, cement, and other components to produce different pavement types.

Hot-mix asphalt (HMA), or bitumen, is a typical pavement mix. Asphalt producers heat aggregates, such as crushed stone and gravel, at 300–350 degrees Fahrenheit to remove moisture. They then thoroughly mix the aggregates with a heated asphalt binder for uniformity. After this step, the producers transport the hot mix to a paving site. Transporting it at this temperature allows for easier application. Due to HMA’s durability under heavy loads and its ability to maintain its shape, developers use it for paving high-traffic surfaces, such as runways and interstates.

Like HMA, warm mix asphalt (WMA) also requires heating aggregates and binders. However, manufacturers use water-based or chemical additives to produce WMA at lower temperatures, typically 20-40 degrees Fahrenheit lower than HMA. One benefit of WMA is its broader installation temperature range, allowing long-range transportation and later placement in even cooler weather. Typical WMA applications include residential roads, commercial parking lots, and other surfaces tolerant of lighter traffic loads.

Unlike HMA and WMA, cold mix asphalt (CMA), which comprises oils and additives, requires no heating during production. Asphalt producers create CMA by coating aggregate with a bitumen emulsion. Although production techniques have improved, CMA remains less durable and weaker than HMA and WMA. Consequently, contractors often use it for temporary repairs such as maintenance and pothole patching.

Stone matrix asphalt (SMA), a variant of HMA, constitutes coarse stone aggregate, a high percentage of asphalt cement, and stabilizing agents. Engineered for durability, SMA exhibits enhanced resistance to surface deformation and wear over time. It retains its shape under heavy loads, making it ideal for high-traffic roads, truck routes, and intersections. Its composition also helps reduce vehicle noise.

Dense-graded hot mix asphalt is another HMA variant commonly used for highway surfaces, repairs, and other pavement layers due to its durability and imperviousness to the elements. It comes in two options: fine-graded and coarse-graded. The main difference between them is the size and distribution of the aggregate particles used in the mix. However, both create a dense aggregate structure that locks tightly to itself when compacted.

Unlike dense-graded HMA, a porous asphalt mix is designed to let water infiltrate pavement rather than run off. Composed of aggregates such as gravel or crushed stone and a binder (asphalt cement), its mix balances the desired permeability with load-bearing needs. Ideal for stormwater management in rainy areas, porous asphalt appeals to real estate developers wanting to integrate sustainable practices in managing drainage in certain projects.

Perpetual pavement is a durable type of road designed by layering asphalt mixes. Contractors first lay a granular base for foundation strength. On top of the base, they add a permanent binder layer for extra strength and flexibility. Then, they apply a durable wearing surface on top of the binder layer to allow the mixture to withstand traffic wear and tear. One benefit of perpetual pavement is that it only needs repair to the top layer, since the underlying mixes remain intact. Subsequently, it reduces the need for frequent and costly reconstruction or rehabilitation.

Reclaimed asphalt pavement (RAP) is a more sustainable and economical pavement material produced by grinding and crushing old asphalt pavement. RAP recycling incorporates reclaimed aggregate and binder into new mixes, reducing the need for new materials for pavement construction. When making new mixes, vital considerations include moisture content, bitumen quality and content, and particle sizes.