Engineered Soil

Cement based soil-cement, also known as Engineered Soils, was first used in 1935. Since that time, Portland cement has been used to stabilize soils and aggregates for pavement applications on thousands of kilometres of roadway all over the world. After more than 85 years, collective experience has demonstrated that different kinds of engineered soil mixtures can be tailored to specific pavement applications. The basics, however, always remains the same: soil-cement is simply a hydraulic binder (Portland cement or Portland cement blended with supplementary cementing materials) blended with soil and/or aggregate, and water and compacted for use in a pavement structure. Although sharing a similar chemical process, engineered soil differs from conventional Portland cement concrete in the consistency of the material, quantity of hydraulic binder required, overall construction procedures, function and strength requirements.

Cement-treated base is aggregate and potentially native soil which is mixed with Portland cement, and water and then compacted to a high density to form a hardened material to serve as a structural layer in a pavement.  It can be mixed-in-place or mixed in a pug mill or central batch plant and transported to the job site. Properly constructed CTB mixtures have been shown to improve subgrade strength, bind gap graded material together, improve granular layer strength, provide long term durability and decrease the pavement layer thicknesses required in design.

The FDR-HRB process pulverizes the existing bituminous surfacing and blends it with underlying base, subbase, and/or subgrade materials, which are mixed with a HRB such as Portland cement to create a new stabilized base.  A new surface is then applied, providing a new roadway structure using recycled materials from the failed pavement.

The table below provides a summary of the four types of Engineered Soils including the purpose, types of material stabilized typical cementitious content ranges by dry weight and the expected unconfined compressive strength (UCS) of the treated material based on the cementitious contents noted in the table.

 Engineered Soils can be divided into four main categories:

  • Cement Modified Soils (CMS) – a material treated with a relatively small proportion of GU, GUL or blended cement in order to amend its undesirable properties so they are suitable for use in subgrade or foundation construction (i.e. drying, reducing plasticity and providing stability). Also eliminates the need for undercutting and provides solid working platform.
  • Cement stabilized subgrade (CSS) – is used to improve the engineering properties of the native in-situ subgrade soil so that it behaves similarly to or better than an enhanced, untreated aggregate base with uniform support. This type of stabilization provides all the benefits of CMS in addition to reducing moisture susceptibility, permeability, volume change potential, and plasticity, as well as, improving bearing strength of the subgrade.
  • Cement-treated base (CTB) – is aggregate and potentially native soil which is mixed with GU, GUL or blended cements, and water and then compacted to a high density to form a hardened material to serve as a structural layer in a pavement structure.  It can be mixed-in-place or mixed in a pug mill or central batch plant and transported to the job site. Properly constructed CTB mixtures have been shown to improve subgrade strength, bind gap graded material together, improve granular layer strength, provide long term durability and decrease the pavement layer thicknesses required in pavement designs.
  • Full Depth Reclamation (FDR) of asphalt pavements with Portland Cement – The FDR-PC process pulverizes the existing bituminous surfacing and blends it with underlying base, subbase, and/or subgrade materials, which are mixed with GU,GUL or blended cement to create a new stabilized base. A new surface is then applied, providing a new roadway structure using recycled materials from the failed pavement.

The Table below provides a summary of the four types of Engineered Soils including the purpose, types of material stabilized typical cementitious content ranges by dry weight and the expected unconfined compressive strength (UCS) of the treated material based on the cementitious contents noted in the table.

Summary of Engineered Soil Types Using Cement Based Binders

Source: Guide to Cement-Stabilized Subgrade Soils, May 2020

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