Modernizing Roadbed Construction: Key Updates to Alabama’s Lime Stabilization Specification

The Alabama Department of Transportation (ALDOT) has recently updated its Specification 232 for Lime Stabilized Roadbed, aiming to modernize the standard practices for modifying and stabilizing in-situ soils during roadbed construction.

The significant changes are outlined below: 

Equipment Requirements

The revised specification mandates the use of more robust equipment for lime spreading, mixing, water distribution, compaction, and scarifying. This ensures best practices, such as using a soil reclaimer instead of a disk harrow, are followed in contracted work. 

Class Definitions

The classification system has been simplified by eliminating Class 3. Now, only two classes remain:

• Class 1: Lime Stabilization
• Class 2: Lime Modification

Rapid soil drying with lime will be managed on an as-needed basis by project managers, increasing the speed and efficiency of construction projects. This approach leads to cost savings and minimizes disruptions to the traveling public.

Dual Application

While the initial proposal suggested removing the dual lime application requirement for Class 1 stabilization, the final version retains this requirement. However, the engineer now has the discretion to allow for a single pass when deemed appropriate.

Mellow Period

The mellow period for both Class 1 and Class 2 stabilization has been significantly reduced. The standard mellow period is now set at a minimum of 24 hours and not to exceed 72 hours. Contractors can propose a shorter mellow period if the requirements are met and supported by field data. 

Cure Period

A new Plasticity Index (PI)-based specification has been introduced for the cure period. This change allows for a variable cure period based on the soil’s PI and the time of year (warmer vs. cooler average temperatures). Additionally, proof rolling may be used as an indicator of adequate curing, subject to the engineer’s approval.

Payment and Reapplication Criteria

Payment terms and reapplication criteria have been clarified. Payment will only be made for lime incorporated on the same day. The previous requirement for retreatment after six hours of exposure has been removed. 

Temperature Restrictions

The previous calendar restriction prohibiting lime application between October 1st and April 1st has been replaced with a temperature-based limitation. Lime application is now only prohibited when the ambient temperature is below 40°F (5°C).

Lime Kiln Dust (LKD)

The use of Lime Kiln Dust (LKD) is now permitted in Class 2 (Soil Modification) treatments, expanding the range of materials available to contractors and the DOT.

Moisture Content Guidelines

Clearer guidelines on moisture content during mixing operations have been introduced, emphasizing the importance of maintaining optimal moisture levels for successful lime treatment.

Hydrated Lime Usage

Due to the dusty nature of hydrated lime, the revisions require written approval for its use in dry form. This change encourages the use of alternative application methods that minimize dust generation.

Soluble Sulfate Restrictions

New restrictions on soluble sulfate levels in soils treated with lime have been introduced, in alignment with recommendations from Mintek. These restrictions aim to prevent potential issues associated with high sulfate levels and calcium-based reagents like lime and cement.

These updates reflect ALDOT’s commitment to improving roadbed construction practices, ensuring durability, and optimizing the use of materials and equipment.

For more details on these updates, contact us.