From dirt to Clay, from dirt to (ceb)compressed earth block

Spread the Cement. You will need about three to four pounds of Portland cement for each square foot of your soil cement surface. Use a bit less for soils with a lot of sand or gravel, and a bit more for soils with more clay or organic matter.
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Which product is better—portland cement or hydrated lime—in stabilizing clay soils?

In 2003, an investigation was completed that evaluated the performance of portland cement and hydrated lime in stabilization and in improving engineering properties of several soils. Three soils were examined that had Plasticity Index (PI) values of 25, 37, and 42. The following general conclusions can be drawn based upon the investigation performed:

1. For the soil with a PI of 25, portland cement performed better than lime even at dosages as low as 3 percent. For the soils with a PI of 37 and 42, the performance increased significantly when the cement dosage was increased to 6 percent or more.

 2. The maximum dry density of all three soils stabilized with portland cement attained higher maximum dry density than the lime-stabilized soils.

3. The unconfined compressive strength (UCS) of the soil with a PI of 25 stabilized with portland cement was almost always higher than that of lime-stabilized soil.

4. Strength of cement-stabilized soil is generally higher than lime-stabilized soil at all ages.

5. California Bearing Ratios (CBR) measured for all three soils stabilized with 6 percent and 9 percent portland cement or lime, clearly indicate that cement-stabilized soils have superior load bearing capacity.

6. For all three soils, stabilized with 6 percent and 9 percent portland cement, there was a significantly higher strength than lime-stabilized soils after vacuum saturation tests.

7. The physiochemical nature of cement-stabilized soils results in better wet-dry durability.

8. Hydraulic conductivities of the soil with a PI of 25 stabilized with portland cement were significantly lower than lime-stabilized ones at all dosage levels.

9. The concentration of calcium ions in leachates from lime-stabilized soils is generally higher than those from cement-stabilized soils.

For the complete findings contained in this investigation, please see PCA publication RD125 – Comparative Performance of Portland Cement and Lime Stabilization of Moderate to High Plasticity Clay Soils.

A compressed earth block (CEB), also known as a pressed earth block or a compressed soil block, is a building material made primarily from damp soil compressed at high pressure to form blocks. Compressed earth blocks use a mechanical press to form blocks out of an appropriate mix of fairly dry inorganic subsoil, non-expansive clay and aggregate. If the blocks are stabilized with a chemical binder such as Portland cement they are called compressed stabilized earth block (CSEB) or stabilized earth block (SEB). Typically, around 3,000 psi (21 MPa) is applied in compression, and the original soil volume is reduced by about half.

Creating CEBs differs from rammed earth in that the latter uses a larger formwork into which earth is poured and manually tamped down, creating larger forms such as a whole wall or more at one time rather than building blocks. CEBs differ from mud bricks in that the latter are not compressed and solidify through chemical changes that take place as they air dry. The compression strength of properly made CEB can meet or exceed that of typical cement or mud brick. Building standards have been developed for CEB.

CEBs are assembled onto walls using standard bricklaying and masonry techniques. The mortar may be a simple slurry made of the same soil/clay mix without aggregate, spread or brushed very thinly between the blocks for bonding, or cement mortar may also be used for high strength, or when construction during freeze-thaw cycles causes stability issues. Hydraform blocks are shaped to be interlocking.Completed walls require either a reinforced bond beam or a ring beam on top or between floors and if the blocks are not stabilized, a plaster finish, usually stucco wire/stucco cement and/or lime plaster. Stabilized blocks can be left exposed with no outer plaster finish. In tropical environments, polycarbonate varnish is often used to provide an additional layer of wet-weather protection.

There are many advantages of the CEB system. On-site materials can be used, which reduces cost, minimizes shipping costs for materials, and increases efficiency and sustainability. The wait-time required to obtain materials is minimal, because after the blocks are pressed, materials are available very soon after a short drying period. The uniformity of the blocks simplifies construction, and minimizes or eliminates the need for mortar, thus reducing both the labor and materials costs. The blocks are strong, stable, water-resistant and long-lasting.

• CEB can be pressed from damp earth. Because it is not wet, the drying time is much shorter. Some soil conditions permit the blocks to go straight from the press onto the wall. A single mechanical press can produce from 800 to over 5,000 blocks per day, enough to build a 1,200 square feet (110 m²) house in one day. A high performance CEB press, of open source design, named "The Liberator", can produce from 8,000 to 17,000 or more blocks per day. The production rate is limited more by the ability to get material into the machine, than the machine itself.
• Shipping cost: Suitable soils are often available at or near the construction site. Adobe and CEB are of similar weight, but distance from a source supply gives CEB an advantage. Also, CEB can be made available in places where adobe manufacturing operations are non-existent.
• Uniformity: CEB can be manufactured to a predictable size and has true flat sides and 90-degree angle edges. This makes design and costing easier. This also provides the contractor the option of making the exteriors look like conventional stuccohouses.
• Presses allow blocks to be consistently made of uniform size, while also obtaining strengths that exceed the ASTM standard for concrete blocks (1900 psi).
• Non-toxic: materials are completely natural, non-toxic, and do not out-gas
• Sound resistant: an important feature in high-density neighborhoods, residential areas adjacent to industrial zones
• Fire resistant: earthen walls do not burn
• Insect resistant: Insects are discouraged because the walls are solid and very dense, and have no food value
• Mold resistant: there is no cellulose material - such as in wood, Oriented Strand Board or drywall - that can host mold or rot
• In India, CSEB's with cement stabilization have shown to be very beneficial. The observed compressive strength, flexural strength at 28 days of aging with 9% cement stabilization has been observed to be 3.2 MPa and 1 MPa respectively.