When it comes to constructing long-lasting roads, highways, and foundations, soil stabilization is critical. One of the most effective methods for improving the strength and durability of clay soils is lime stabilization. But how do engineers determine the right amount of lime needed for a specific area of soil? That’s where a Lime Series Test—also known as an Eades-Grim test or pH series test—comes in. This essential laboratory procedure helps ensure that lime-treated soil achieves the optimal pH for stabilization, leading to long-term strength and durability.
The success of lime stabilization in aviation infrastructure dates back over 80 years to the United States Army Corps of Engineers’ (USACE) use of the method at Bergstrom Airforce Base—now Austin-Bergstrom International Airport. Since then, lime stabilization has been widely adopted in airport construction across Texas and beyond, delivering outstanding results in mitigating soil expansion and improving long-term pavement performance.
What Is a Lime Series Test?
A Lime Series Test is a laboratory test used to determine the amount of lime required to modify and stabilize a clay-based soil. When lime is added to soil, several chemical reactions take place, influencing its workability and strength. The test helps identify the lime demand—the percentage amount needed to achieve a stable, long-lasting subgrade.
The Science Behind Lime Stabilization
Clay soils are naturally high in silica and alumina, which are not highly soluble at neutral pH levels (around 7). However, when lime is added, the pH rises above 10, increasing the solubility of these compounds. This allows pozzolanic reactions to occur, forming cementitious compounds that permanently alter the soil’s structure, making it more stable and load-bearing.
Key moments in the lime stabilization process include:
Initial Drying
When lime is added to clay soil, it begins drying out almost immediately.
Modification Phase
Once the soil’s pH reaches 10, its plasticity index starts to break down, leading to visible texture changes.
Stabilization Zone
The ideal pH range for stabilization is between 10.5 and 12.4. When lime is applied correctly, the pH is raised to 12.4, ensuring long-term soil strength. Studies show that once stabilized, the pH will remain above 10.
How the Lime Series Test Works
To determine the lime demand for a specific soil, technicians conduct a series of pH tests at different lime concentrations. The process follows these steps:
- Soil Sample Preparation: A 50-pound soil sample is collected from the site and broken down into 30-gram sub-samples.
- Mixing with Distilled Water: Each sub-sample is mixed with 140 grams of distilled water.
- Stirring and Waiting: The mixture is stirred every 15 minutes for an hour to ensure even distribution.
- pH Measurement: The pH is measured at different lime increments to determine the percentage of lime needed to reach 12.4 pH.
- Final Analysis: The results help engineers decide how much lime is required to stabilize the entire soil section.
The process typically takes about three days, and for large-scale projects, multiple tests are necessary since soil composition can vary across the site. Because not all clay soils behave the same way, assuming a one-size-fits-all approach to lime application can lead to suboptimal stabilization.
Why Lime Series Tests Matter
Properly executed Lime Series Tests ensure that pavements, highways, and foundations remain durable for decades. Without these tests, insufficient lime application can result in:
- Inadequate soil strength and failure over time
- Increased construction costs due to rework
- Reduced performance of roads and structures
By accurately determining the lime demand, engineers and contractors can create a stronger, more resilient foundation—one that withstands moisture, traffic loads, and environmental changes over time.
Learn More About Lime’s Capabilities
