Slag Driveway Pros and Cons

Whether building a driveway or repaving an old one, selecting suitable materials is crucial.  The driveway serves as an entryway to your home or the garage and the parking space. Slag is one of the options to choose from. It binds well on hard surfaces and is usually used in driveways, parking lots and landscaping backyards. So what are the factors to consider?

Slag has a great appearance, and it is a low-cost alternative that also conserves the environment. A slag driveway has higher strength and better adhesion which makes it more durable than most materials. On the other hand, the limitations of slag are; that it’s expensive to acquire, it can be toxic and has a high swelling potential.

What is a slag driveway?

A slag driveway is paved with slag, and it leads to the parking or garage. Slag is an artificial product that is a better substitute for natural resources like gravel and limestone.  

Slag is the leftover after a metal has been separated from its metal ore. It contains crushed particles that are hard and dense. The particles are also angular, which provides stability for the vehicles using the driveway. Steel slag is the ideal option for the driveway that is not high maintenance. 

 A slag driveway is durable and provides a low maintenance option. It provides resistance to fatigue, abrasion, cracking and permeability. 

The driveway is an essential part of a home that determines its appearance. Apart from the driveway, slag can be used on roads, industrial roads and parking.

Is slag good for driveways?

Slag is a good material for the driveway and even pavements. The use of slag in the driveway enhances its stability, resilience, and tensile strength. 

Slag also increases the driveway’s resistance to moisture damage and resistance to deformation. It also drains well and does not keep duster dirt. A slag driveway feels like concrete but is cheaper.

A driveway needs to be functional to support the vehicles getting into the home. Although slag is not a very popular driveway material, it serves this purpose. 

Slag is also considered non-hazardous according to the EPA. It is the best material for environmental sustainability. Steel slag is produced as a by-product of smelting in the steel mills. It is composed of leftover elements of this process, such as silicon dioxide, elemental metals, metal oxides and metal sulfide. Afterwards, it is crushed into different sizes for different applications. 

Pros and Cons of slag for driveways

Pros of Slag driveways

A slag driveway has multiple practical and environmental benefits compared to natural materials such as concrete, gravel, or crushed stone.

 Here is why slag is a better option.

Great and Aesthetics

When you surface the driveway with slag it gives it an impressive appearance. An attractive and functional driveway increases the value of the home. 

The appearance of a slag driveway is unique and makes it stand out. 

Low Cost and Maintenance

Due to the stability and durability of slag on the driveway, it rarely exhibits signs of wear. It will not require frequent maintenance like other materials such as gravel.

Slag is also inexpensive compared to other driveway materials like asphalt. A tonne of slag retails at approximately $35. This amount can cover a cubic yard of the driveway.

Unlike other driveway materials like gravel, slag does not need ongoing maintenance. It is also cheaper to install than concrete or asphalt.

High Strength

Slag has high strength because of its rough texture. It hardens well enabling, a thinner layer of pavement than what can be achieved by virgin natural stones. Slag is considered hardy due to its resistance to weather and wear.

Slag has a MOHS hardness value of 6 compared to granite 4 and limestone 3. Its hardness makes it more durable.

Slag offers a driveway with fatigue resistance, deformation resistance and binder compatibility.

Better adhesion

Slag has more excellent resistance to wear compared to natural rocks. It is best for a driveway that is in regular use with vehicles. The tires are able to grip its surface.

Other materials become slippery and polished with time, but slag is rougher and grippier. Because of the slag’s high traction, the driveway is not as slippery as stone or concrete driveways. This is important in wet and icy conditions, even for pedestrians.

A slag driveway will have a longer lifetime and less wear.

Greater Durability and Stability

Slag is harder and more compact than natural gravel. It has a higher particle density and a large weight per unit volume. Because of this, it has more stability and load-bearing capacity than those materials. Due to its stability, driveways and roads made from slag have less particulate pollution.

Resource and Energy Conservation

Slag is regarded as a recycled material. It enables the conservation of resources by reducing the use of gravel, and crushed stone. It, therefore, reduces the impact of mining activities on the environment.

If slag is used instead of natural stones, the need for a landfill is reduced. The amount of quarried rocks is reduced hence preserving the natural resources.

 Slag is considered a waste material. It is generated as a by-product when purifying, casting and alloying. Its use in making the driveway helps alleviate its disposal because it is used in large quantities.

Cons of Slag driveways

While a slag driveway has numerous benefits, it also comes with some drawbacks. Here are some factors to consider.

It Contains Toxic Substances

Steel slag is composed of non-toxic products like calcium, silicon, and iron. However, slag also contains toxic ingredients like Strontium, Chromium, Cadmium and Nickel. These substances are pollutants for the environment and also for human health. 

Additionally, Calcium Oxide in the slag is a potential pollutant that causes emissions in the air that can cause air pollution in the form of dust and gases.

It is Expensive

Slag is more expensive than other driveway materials like gravel and asphalt. Additionally, because it’s heavier than the natural rocks, it’s more costly to transport it. 

Using slag without a barrier or stabilization will result in problems if the driveway is used by heavy vehicles such as trucks, cars and motorcycles. When the driveway is used in this condition, the slag spreads, resulting in ruts. The driveway will need constant maintenance if a barrier is not used.

To counter this problem, stabilize the slag with permeable pavers. These provide a layer of stabilization that can withstand weight and friction.

High Swelling Potential and Alkalinity

Steel slag has the potential to expand because of the presence of free lime and magnesium oxides. In humid environments, the expansion causes heaving pavements and rough, cracked surfaces.

It can leach into the soil increasing the soil alkalinity which could risk the biosphere.

How long does a slag driveway last?

Slag is hard and durable and lives up to several decades. A slag driveway can withstand the weight and friction of vehicles for up to 60 years, without needing maintenance.

 It is hard and more durable than even the hardest metals. Slag is also more durable than natural stones like gravel.

It has a relatively long lifespan with the proper care and maintenance. Slag lives longer than other driveway materials like concrete and asphalt.

A driveway is subjected to dynamic forces over the years, including harsh environments. Because it is dense and heavy, a slag driveway can resist rain, freezing and thawing. 

The physical and mechanical properties of slag enable it to last for many years. Slag is also a high-class material that does not experience cracking or permanent deformation like other natural aggregates.

3 best slag rocks for driveways

The slag used in the driveway is made from the by-products of metal processing of steel or iron. After manufacturing, the slag is stockpiled to allow hydration and expansion. Slag is typically classified according to the type of the furnace, air cooling process and valorization.

  • Air-Cooled Blast Furnace Slag-  Air-cooled blast furnace is granular, roughly cubical and has textures. It is cooled slowly by natural cooling and by spraying it with water. 

The cooling results in crystallized rock-like slag. There can be variability in the size of the slag depending on the iron production process. The water absorption can be as high as 6% but lower than that of pelletized blast furnace slag.

  • Granulated  Blast Furnace Slag- This slag has glassy, granular particles. These granulated particles are sand-sized grains. The slag is cooled rapidly by jets of pressurized water, giving it a granulated look. Because of its properties, it has high hydraulic properties.
  • Expanded or Foamy Slag- This type of slag is cooled by controlled quantities of water or steam. The result is more porous slag with a smaller volume than air-cooled slag.


  1. US Department of Transportation|Federal Highway Administration; Use of Waste and Byproduct Materials in Pavement

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