Rammed earth notes, starting at the soil chemistry,
Obviously by google images Rammed Earth(RE) looks esthetically pleasing to the eye compared to concrete by far and contemporary designs are “whole wall systems” requiring no stucco or plaster. Stabilized Rammed Earth (SRE) appears to be less material cost than concrete. Locally available but is it? What is the material and labor cost differences compared to CIC (Concrete-Insulation-Concrete) construction or a gunite (Structural Concrete Insulated Panel) and proprietary motor mix shipped (aka, Gulf Concrete Tech, Gigacrete, Thermomass) or to stick light construction? What differences in thermal mass effect and bridging can we expect? SRE (insulated) is continuous except the roof cannot be cast, SCIP, Gigacrete can.
From what I gather so far of SRE, inorganic and organic materials are used to design bonds to structural foam core insulated sandwich construction. 6-10% Portland cement powder is added for compression and stabilization strength 6MPa (870 – 1450 psi) SIREWALL claims ‘anywhere in the world’, foam core 25 PSI, plus soil(SIREWALL claims a WIPO patent (not USA) at 25-43 MPa ( 3625 – 6,230 psi = soil composition and rebar/stirrup placement design is my guess); also asphalt emulsion, calcined gypsum or cactus juice, may also be used. According to SIREWALL “pozzolan” may substitute cement. Steel or fiberglass rebar for tensile/pull (see test results below) depending on if you are in a seismic zone higher than 3, a thermal bridge exist, or PE/code, liability safeguards, require it.
Ideally, non-expansive (kaolinite) clay binders are desired, clay provides adhesion bond property. Lime, bitumen, or cement negate the expansion properties of swelling clays, but by the same mechanism negate the binding and other beneficial properties of the clay. Inorganic temper soils such as silt, sand, gravel, are common: organic straw, hair, chaff (scaly plant material). Iron oxide for color or pigment.
To eliminate efflorescence admixtures such as Xypex are added, Broada or Crommelin sealant. Ramseal?
1. pozzolan is a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM C618).[1] The broad definition of a pozzolan imparts no bearing on the origin of the material, only on its capability of reacting with calcium hydroxide and water. A quantification of this capability is comprised in the term pozzolanic activity.[2]
2.China Test Report : http://www2.cemr.wvu.edu/~rliang/ihta/papers/21%20FINAL%20Bly%20Windstorm_paper_workshop.pdf
3. 1+ year old GBA thread: http://www.greenbuildingadvisor.com/community/forum/green-building-techniques/23255/calling-all-rammed-earth-experts
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