Mud Brick and Stabilised Earth: Strength by Mix, and the Least Cement or Lime That Does the Work
Year: 2026
Type: article
Abstract: Earth dug on site is the cheapest wall material available in much of the world, and also the least predictable, because two soils that look alike can differ by a factor of two in strength and by far more once rain reaches them. This paper originates a mix rule that predicts, from a soil's clay fraction alone, its unstabilised dry and wet compressive strength, its erosion rate under a stated spray test, and the least dose of cement or of lime — scanned in half-percent steps up to a stated practical cap of 8.0% by dry mass — that brings it past stated thresholds for one-storey walls (1.50 MPa dry, 0.65 MPa wet) and for two-storey walls (2.80 MPa dry, 1.10 MPa wet). The study is simulated, not measured, and no wall or brick described here has been load-tested. Under the stated assumption curves, drawn from published ranges for earth bricks, wet strength rather than dry strength decides almost every dose: unstabilised mixes with 0.8% straw fibre reach 0.96–1.92 MPa dry yet retain only a tenth of that when wet, 0.10–0.19 MPa. Cement is the cheaper stabiliser in sandy and loamy soils, needing 3.0% for two-storey loam against 5.5% for lime, while lime closes much of the gap in clay soils, needing 4.0% in clay loam against 3.0% for cement there. One soil class fails outright: expansive heavy clay at a clay fraction of 0.60 reaches only 2.30 MPa dry with cement and 2.57 MPa dry with lime at the 8.0% cap, below the 2.80 MPa two-storey threshold under either stabiliser, although it passes the one-storey thresholds at 3.5%. A second, quieter finding is that the dose which satisfies strength usually leaves the wall face eroding too fast for exposed use: loam at its two-storey cement dose of 3.0% still erodes at 23.6 mm per hour against a stated exposed-wall limit of 20 mm per hour, so strength and surface protection must be specified separately.
Author: Aldred, William Alexander
Language: English
Subfield: Building and Construction
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225737386
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