As the figure above illustrates, cement-specific materials come in a wide variety of forms, are comprised of several different constituents, and can be mixed and placed using methods that range from pumping a fluid mixture through a hose to casting inside formwork to placement and compaction in lifts using earthwork equipment. What these materials have in common is they use hydraulic cement binders like portland and blended cements to improve the physical, chemical, and mechanical properties of the hardened matrix that results when mixed with other constituents. The figure is not intended to be used for mix design determination, but rather to show how these materials compare to each other in terms of cementitious content, water content, and method of consolidation. General definitions for each of these cement-specific materials are provided below.
A mixture of soil, portland or blended cement, and water. When first mixed, SC looks like native soil, and it is then placed and compacted in lifts using typical earthmoving equipment. However, the cement acts as a binder between the soil particles and, like CTB, the SC gains strength and durability as the cement hydrates.
A compacted mixture of pulverized in situ soil, water, and small proportions of portland or blended cement that results in an unbound or slightly bound material. The treated material is similar to a soil but has reduced plasticity and a lower susceptibility to moisture, resulting in a more workable material.
A compacted, engineered mixture of pulverized in situ soil, water, and moderate proportions of portland or blended cement (slightly more than CMS) that results in a semi-bound to bound material. The treated material has structural engineering properties similar to or better than those of a granular material.
A fully bound, compacted, engineered mixture of aggregate, water, and sufficient portland or blended cement to meet the project-specified minimum durability and strength requirements. Because of the better aggregate selection available for CTB, it typically uses about the same quantity of cement as CSS; however, CTB results in a stronger, more durable, more frost-resistant layer.
A type of CTB, FDR is a process that involves pulverizing and blending an existing distressed asphalt roadway surface and its underlying base and/or subgrade materials. Portland or blended cement is mixed with the pulverized material, compacted, and cured, resulting in a new homogenous and stabilized base. This process compares favorably to the complete removal and replacement of a distressed asphalt pavement and underlying granular base material.
A mixture of aggregates, portland or blended cement, water, and sometimes supplementary cementitious materials (SCMs) and/or chemical admixtures. Fresh RCC is stiff and has zero slump, and it is usually placed in horizontal lifts using conventional earthmoving or paving equipment and compacted using a vibratory drum roller.
A mixture of aggregates, portland or blended cement, water, and sometimes supplementary cementitious materials (SCMs), fibers, and/or chemical admixtures. When freshly mixed it is plastic enough to be placed and consolidated within formwork where it hardens and gains strength. Whether reinforced or unreinforced, CIP concrete (commonly referred to as conventional concrete) is the most widely used building material in the world.
A near-zero-slump, open-graded material consisting of portland or blended cement, coarse aggregate, little or no fine aggregate, admixtures, and water. The combination of these ingredients produces a hardened material with 15 to 25 percent voids or connected pores that allow water to pass through easily as part of a hydrologically designed system.
A construction product produced by casting concrete in a reusable mold which is then cured in a controlled environment, transported to the construction site, and maneuvered into place. Precast concrete elements can be produced from either dry mixes (vibrated or hydraulically pressed to consolidate/compact the material in molds) or from more fluid mixes to create shapes or panels.
For more information about precast concrete, refer to the National Precast Concrete Association, Precast/Prestressed Concrete Institute, and the Interlocking Concrete Pavement Institute.
Lean Concrete Base (LCB)
A base or subbase material that is composed of aggregate and portland or blended cement (sometimes includes fly ash, slag, or chemical admixtures) that is uniformly blended and mixed with water, then spread, shaped, and consolidated using conventional concrete equipment. LCB contains more cement than CTB but much less than conventional CIP concrete, with design strengths much higher than CTB but much less than CIP.
For more information about LCB, refer to the National Ready Mixed Concrete Association and the American Concrete Pavement Association.
A mixture of portland or blended cement, water, and air (created through a preformed foam) to produce a low density hardened concrete material. LCC can function as a lightweight, strong, durable, and inexpensive soil or fill replacement, can be produced at a plant or on site, and is self-leveling and self-consolidating.
Also referred to as controlled low-strength material (CLSM), controlled density fill (CDF), flowable mortar, plastic soil-cement, and soil-cement slurry, it is a self-leveling and self-consolidating concrete material. Traditional flowable fills are mixtures of portland or blended cement, water, fly ash, fine aggregate, and air, and are primarily used as a backfill material.
For more information about flowable fill, refer to the National Ready Mixed Concrete Association.