Source: http://earthstructures.co.uk/physprop.htm
Timestamp: 2020-01-19 18:08:39
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Physical Properties and Compliance with UK Building Regulations
The following technical information is also available for download as a PDF file here.
Stabilised rammed earth (SRE) can successfully be used to conform to the Building Regulations (2000) for England and Wales as an acceptable alternative form of low-rise masonry construction in public and residential buildings. Recommendations for how this can be achieved are given through the case study by the Planning Department of Chesterfield Borough Council (ref: Hall, Damms & Djerbib, 2004).
At present there are no officially recognised codes of practice for rammed earth construction in the United Kingdom. The fitness of SRE materials is currently established under:
a) Tests and calculations, and
b ) Past experience
Suitability and classification of soil materials is established in accordance with:
BS 1377-2: 1990 - Soils for Civil Engineering Purposes - Part 2: Classification Tests, British Standards Institute, London
BS 1377-4: 1990 - Soils for Civil Engineering Purposes - Part 4: Compaction Related Tests, British Standards Institute, London
A series of 100mm SRE cube samples are produced in a laboratory using the prescribed mix design in accordance with the guidelines prescribed in:
Hall M and Djerbib Y, 2004b, "Rammed Earth Sample Production: Context, Recommendations and Consistency", Construction and Building Materials, 18 [4] pp.281-286. N.B. Based upon BS 1881 for concrete materials
The curing shrinkage and estimated construction tolerances are calculated based upon:
BS EN 772-16: 2000 Methods of Test for Masonry Units - Part 16: Determination of Dimensions, British Standards Institute, London
Cube samples are tested for compressive strength in accordance with the guidelines prescribed in:
Hall M and Djerbib Y, 2004b, "Rammed Earth Sample Production: Context, Recommendations and Consistency", Construction and Building Materials, 18 [4] pp.281-286. NB Based upon BS 1881 for concrete materials.
Cube samples can also be tested for other physical properties depending upon the application, e.g. moisture absorption, acoustic, thermal etc.
Approved Document A - Structural Stability
For the purpose of assessment under Part A (structural stability) of the Building Regulations, SRE walls can simply be treated as a high density mass walling element.
All SRE test specimens are characterised and produced as 100mm cube samples using the methodologies proposed by Hall M & Djerbib Y, 2004, "Rammed Earth Sample Production: Context, Recommendations and Consistency",Construction and Building Materials, 18 [4] pp.281-286.
Minimum characteristic unconfined compressive strength (f 'cu) = ≥ 3.5 N/mm2 Typical range of f 'cu =3.5 N/mm2 to 12 N/mm2.
N.B. The f 'cu can be increased by altering the soil grading, the cement content, the ramming and the curing procedures.
Typical dry density (ρd) = 2000 to 2100 kg/m3 (at 98% of Proctor compaction) Tested in accordance with BS 1377-4: 1990 - Soils for Civil Engineering Purposes - Part 4: Compaction Related Tests.
300mm Hilti C10 epoxy holds 2,000kg pull, Amdel Report No. M1034/87.
For further details of compliance please refer to:
Hall M, Damms P & Djerbib Y, 2004, "Stabilised Rammed Earth (SRE) and the Building Regulations (2000): Part A – Structural Stability", Building Engineer, 79 [6] pp. 18-21
SRE is classified as a "non-combustible material".
Fire resistance rating = 4 hours.
Tests performed by CSIRO Report No. 1839.
Approved Document C4 - Resistance to Weather and Ground Moisture
SRE walls are constructed using standard practices for DPC & DPM installation
Experimental testing has revealed that SRE easily conforms to the Building Regulations in this country;
Hall M & Djerbib Y, 2004, "Moisture Ingress in Rammed Earth: Part 2 – The Effect of Particle-Size Distribution on the Absorption of Static Pressure-Driven Water", Construction and Building Materials
Pressure-driven moisture absorption:
Initial surface absorption after 10 min (6% cement content) = 1.90 to 9.95 ml/m2 sec
Capillary absorption:
Typical Sorptivity (S) value = 0.251 to 1.631 mm min-0.5
Initial rate of suction (6% cement content) = 0.29 to 1.47 kg/m2 min (Compare with conventional materials using graph below)
Graph: adapted from Hall M & Djerbib Y, 2005, "Moisture ingress in rammed earth: Part 3 - Sorptivity, surface receptiveness and surface inflow velocity", Construction and Building Materials.
Durability of SRE materials is determined using the 'accelerated erosion test' (AET) in accordance with
Standards New Zealand, 1998, NZS 4298: 1998 Materials and Workmanship for Earth Buildings, Wellington, New Zealand
AET value for SRE = 0.0 mm/min
Tests performed by Materials Consultants Aust. Pty. Ltd. Report No. 202/87
Please note: Unstabilised rammed earth walls may not be compliant under Building Regulations. Both Regulation 7 and Approved Document C categorically state that external masonry walls on a building must:
Not transmit moisture due to rain (or snow) to another part of the building that might be damaged
In order to demonstrate compliance "laboratory values for new internal walls and floors within: dwelling-houses, flats and rooms for residential purposes, whether purpose-built or formed by material change of use" must have a minimum Rw of 40 dB (Rw = weighted sound reduction index)
Example: an SRE wall; Assuming a wall thickness of 300mm the typical Rw of the wall = 58.3 dB
SRE buildings can be assessed either using the target U-value method, the Carbon Index method or the elemental method. The walls can be constructed in 3 different Part L-compliant configurations:
1. Solid SRE wall with external insulated cladding + render
2. Solid SRE wall with internal dry lining
3. Cavity SRE wall with solid-foam cavity insulation
For a cavity SRE wall with 175mm SRE inner & outer leaves incorporating polyisocyanurate solid cavity insulation and stainless steel wall ties;
Calculated U-value = 0.335 W/m2 K (for 50mm thick insulation)
Or, = 0.245 W/m2 K (for 75mm thick insulation)
SRE walls also have very high thermal capacitance (i.e. "thermal mass")
Typical value for a 300mm wall = 1673 KL/m3K
Approximate thermal time lag = 6 - 8 hours