Base stabilization is a valuable pavement technique roadway engineers can employ when designing new pavement structures or rehabilitating their existing pavements. It refers to a process that amends base aggregate material, through the incorporation of a stabilizing additive, producing a homogeneous base layer with enhanced characteristics for strength, stability, and durability. Improvements to strength and stability translate into improved performance of supported pavement structures. Base stabilization can improve the pavement structure in many ways as shown below:
Over the years, significant improvements have been made in base stabilization practices that include design specifications and methodology, equipment for distribution and uniform blending of additives, and stabilizer additives. In the rehabilitation of existing pavements, base stabilization has performed as good as or better than reconstruction at a reduced cost.
Base stabilization results in a bound structural pavement layer with measurable elastic and strength characteristics. Increased structural capacity from a base layer can result in an equivalent surfacing layer that is thinner (but not excessively thin) and more economical. The overall performance of a pavement structure is largely dependent upon its load-bearing capacity.
The base stabilization construction process involves four main stages:
- Aggregate base product: Aggregate material type and gradation influence stabilization recommendations for additive type and amount to be incorporated. A reclaiming machine is typically used to blend additive with a new aggregate product. Reclaiming can also pulverize an existing pavement to a predetermined depth, blend material and incorporate additive; a process referred to as Stabilized Full Depth Reclamation (SFDR). New aggregates can also be added to the in-place reclaimed material to obtain a desired gradation for the final product.
- Additive: Base stabilizer that is blended with the aggregate product. Bituminous and liquid chemical additives are typically injected into the aggregate blend. Dry chemical products (i.e., cement, fly-ash, etc. …) are mechanically spread over the aggregate product and blended.
- Compaction: Compaction usually starts with a vibratory pad foot roller and continues with a pneumatic roller and finishes with vibratory or static smooth drum.
- Application of an overlay: The new stabilized base layer is covered with either a bituminous or concrete surface. In some low volume applications, a thin surface treatment, such as chip seal, otta seal, or microsurfacing, may be used as a final surfacing.
Achieving stabilization with chemical additives
Base stabilization additives are divided into two broad categories: chemical stabilization and bituminous stabilization. With chemical stabilization, strength gain is achieved by creating a matrix that binds the aggregate particles together. Chemical stabilizers react chemically with the material being stabilized (e.g., lime reacts with clay) or react on their own to form cementing compounds (e.g., cement). Chemical additives should be incorporated in a range that produces increased strength and stability without creating a rigid brittle blend that can induce cracking of the overlying pavement surface. An insufficient amount of stabilizing agent will not provide adequate binding within the matrix and too much stabilizing agent can increase the rigidity of the base layer with the potential to induce cracking. Primary chemical stabilization additives are as follows: cement, lime, fly ash, cement kiln dust (CKD), and lime kiln dust (LKD).
Road stabilization with bituminous materials
With bituminous stabilization, strength gain is achieved by coating aggregate particles and development of adhesive bonding. Bituminous is a viscoelastic material that also waterproofs aggregates by coating them. Bituminous does not react chemically and its strength properties are dependent on temperature and rate of loading. Additive should be incorporated in a range that waterproofs the aggregate with enough asphalt to increase strength without the matrix becoming unstable. Bituminous stabilization is usually done in the forms of either asphalt emulsion or foamed asphalt and require a mix design to be performed. The mix design generally addresses strength and resistance to thermal cracking. Performance tests vary between stabilization processes and additives.
Many products exist to stabilize base materials for roadway construction, but it is not always clear which product is the right one to use. The selection of a stabilization additive depends heavily on the project specifications including the properties and uniformity of the aggregate material (gradation, plasticity, etc.), past experience, and economics. It is strongly recommended that a laboratory mix design be performed to verify an appropriate stabilizing additive and application rate range for the desired improvement. Also, field confirmation testing is recommended to assure material as placed meets laboratory mix design characteristics translating to improved pavement performance and expectations.
The Braun Intertec pavement team can provide technical support for performing a successful base stabilization project. Our laboratory has special expertise in stabilization mix designs. Our highly trained technicians use standard equipment and procedures to provide our clients with fast turn-around time and high-quality mix designs. On the construction side, to assure the quality of stabilized product (QC/QA testing), we can provide technicians that are MnDOT certified in each specialized field. Our pool of certified employees allows us to be responsive to any stabilization project needs.
For more information on this topic and better approaches to achieving prolonged pavement performance, join our October 14th webinar, “The Road to Success for Pavement Performance” with pavement specialists Amy Grothaus, PE, and Dan Wegman, PE.