NOTE This Standard distinguishes two treatment goals that are frequently conflated in the field, and the distinction governs almost every downstream requirement. "Modification" treats soil to reduce plasticity index, suppress swell/shrink, and improve workability and trafficability, with no structural strength target. "Stabilization" treats soil to develop a measured unconfined compressive strength so the layer carries structural load as part of the pavement or foundation section. A single project may call for both, and the binder type, application rate, compaction basis, and acceptance criteria differ between them. (1.2.1)

NOTE This Standard does not cover: unimproved earthwork, mass grading, or cut/fill balancing (Earthwork); aggregate base course over the stabilized layer (Aggregate Base Course); geosynthetic reinforcement or separation layers (Geosynthetics); asphalt or concrete surface and base courses (Asphalt Paving); full-depth reclamation or cold in-place recycling of existing pavement (Pavement Rehabilitation); final subgrade grading tolerances and surface drainage (Site Rough Grading); special inspections and compaction acceptance testing of the completed layer (Special Inspections And Testing); or deep soil or void treatment by compaction grouting, permeation grouting, or pressure injection of binders (geotechnical specialty work). (1.3)

NOTE ASTM D1633 is scheduled for withdrawal in 2026; where it is withdrawn at the time of use, the unconfined compressive strength test method designated by the governing agency or its issued replacement shall apply. ASTM D2901 (cement content of fresh soil-cement) was withdrawn in 2006; cement content of hardened material shall be verified by ASTM D806. (2.2.1)

NOTE Action submittals establish what the Contractor proposes to furnish and shall be reviewed before any binder is delivered to the site. (3.1)

NOTE Informational submittals document conditions and means that affect treatment quality but are not themselves design selections. (3.2)

NOTE Closeout submittals confirm the placed work meets acceptance criteria. (3.3)

NOTE A laboratory mix design is the foundation of every chemical treatment, and a single rate applied across the whole site is one of the most common and most damaging errors. Clay mineralogy and plasticity vary across a site; montmorillonite-rich and kaolinite-rich soils respond very differently to the same binder. The mix design sets the binder type and rate for each distinct soil so that the treatment actually achieves its goal rather than merely looking compacted. (4.1)

NOTE Soluble sulfates in the soil can react with lime and water to form ettringite, an expansive mineral that can heave a treated subgrade dramatically after paving. Screening sulfate content before specifying lime is the single most important precaution in lime treatment, and the threshold values are tabulated in the binder-selection section below. (4.2.1)

NOTE Organic matter consumes the calcium that lime and cement reactions depend on, so high-organic soil can absorb binder without gaining strength. (4.3.1)

NOTE Density testing of the finished treated layer measures the treated material, not the soil beneath it; an unstable zone below the treated lift will pass the surface density test yet still fail under load. Proof-rolling before treatment is the only reliable way to find those soft spots. (4.4.1)

NOTE Temperature controls whether the binder reaction proceeds at all. The pozzolanic and cementitious reactions that develop strength slow sharply in cold soil and effectively stop near freezing, so a layer treated and compacted below the minimum temperature can look finished while gaining no strength. (5.1)

NOTE Cement-stabilized layers lose surface strength and crack if they dry before the reaction completes; a curing membrane or continuous moist curing protects the surface until an overlying course is placed. (5.2.1)

NOTE Binder type is selected from soil classification, plasticity index, sulfate content, and treatment goal. Lime is the workhorse for high-plasticity clays because the calcium ion exchange that reduces plasticity is exactly what lime drives; portland cement suits granular and low-plasticity soils where strength gain is the goal; fly ash extends or replaces these binders; and blended treatments address soils that no single binder handles. The selections below set the binder; the rate is confirmed by the mix design. (6.1)

NOTE Lime is the default binder for high-plasticity clay modification. Hydrated lime (calcium hydroxide) is preferred over quicklime where handling safety governs; quicklime is more reactive per unit but generates heat and dust on contact with moisture. (6.2)

NOTE Portland cement is the default binder for granular to low-plasticity soils where strength gain is the goal. Cement alone cannot reduce the plasticity of a high-PI clay before mixing, so such soils require lime pre-treatment first, then cement. (6.3)

NOTE Fly ash is used standalone (Class C, which is self-cementing) or as a Class F plus lime blend (Class F is not self-cementing and must be activated by lime). Class F plus lime blends shall be designed in the laboratory because the proportions are not fixed. (6.4)

NOTE Cement kiln dust and lime kiln dust are byproduct binders that can reduce cost on low-plasticity soils; their variable composition makes a project-specific mix design essential. (6.5)

NOTE Soil soluble sulfate content governs whether lime treatment is permitted without ettringite-heave mitigation. The thresholds below are screening values; a soil near or above the upper threshold requires an engineering evaluation before any lime is specified. (6.6)

NOTE The compaction standard depends on the treatment goal. Modification layers are typically compacted to a percentage of Standard Proctor (ASTM D698); structural stabilization layers under heavy pavement are compacted to a percentage of Modified Proctor (ASTM D1557). In both cases the Proctor must be run on the treated mixture. (7.1)

NOTE A maximum time limit from binder spreading to completion of compaction is required for cement-treated soil because cement begins to set in the windrow; compaction completed after initial set destroys the bond and the density. (7.2)

NOTE The mixing method is selected for the project size, soil condition, and whether mixing is performed in place or at a central plant. In-place pulverization with a rotary mixer/reclaimer is the most common method; plant mixing in a pugmill is used where off-site mixing and haul are advantageous. (8.1)

NOTE Lift thickness is limited by the depth a single mixing pass can treat uniformly. A single lift is typically 6 to 12 in.; treatment deeper than the single-pass capacity shall be performed in two lifts. (8.2)

NOTE The mellowing period for lime treatment allows calcium ion exchange to reduce plasticity before final mixing and compaction; compressing this period is a frequent source of RFIs and weak results. (8.3)

NOTE Cement-stabilized soil develops shrinkage cracks as it cures, and a brief delay before paving lets the crack pattern stabilize so it does not propagate through the overlying course. (9.3)

NOTE Acceptance testing confirms that the placed layer meets the density, moisture, strength, and (for lime) pH criteria. Testing frequency is set per area or per lot so that a defective area is caught before it is covered. (10.1)

NOTE A freshly mixed lime-soil that reaches a pH of at least 12.4 confirms that enough lime is present and uniformly distributed; the field pH check is a fast, direct verification of lime adequacy. (10.2)

NOTE Unconfined compressive strength confirms strength gain where stabilization is the goal; the target depends on the binder and the application. The values below are the project acceptance targets confirmed by the mix design. (10.3)

NOTE Durability testing is required where the treated layer is exposed to wet-dry or freeze-thaw cycling as part of the design life. (10.4)

NOTE Cementitious binders lose reactivity when exposed to moisture, so protected delivery and storage preserve the design rate. (11.1)

NOTE The binder type, rate, and treatment depth originate in the geotechnical report and must flow consistently into the earthwork, stabilization, and aggregate-base specifications. A break in that chain, where the geotechnical engineer of record specifies one rate and the civil documents carry another, is a recurring source of field conflict. (12.1)