Recovery and Restructuring of Fine and Coarse Soil Fractions as Earthen Construction Materials

Abstract: Excessive consumption of natural resources to meet the growing demands of building and
infrastructure projects has put enormous stress on these resources. On the other hand, a significant
quantity of soil is excavated for development activities across the globe and is usually treated as
waste material. This study explores the potential of excavated soils in the Brittany region of France
for its reuse as earthen construction materials. Characterization of soil recovered from building sites
was carried out to classify the soils and observe their suitability for earthen construction materials.
These characteristics include mainly Atterberg limits, granulometry, organic matter and optimum
moisture content. Soil samples were separated into fine and coarse particles through wet sieving.
The percentage of fines (particles smaller than 0.063 mm) in studied soil samples range from 28% to
65%. The methylene blue value (MBV) for Lorient, Bruz and Polama soils is 1, 1.2 and 1.2 g/100 g,
and French classification (Guide de terrassements des remblais et des couches de forme; GTR) of soil
samples is A1, B5 and A1, respectively. The washing of soils with lower fine content helps to recover
excellent-quality sand and gravel, which are a useful and precious resource. However, residual fine
particles are a waste material. In this study, three soil formulations were used for manufacturing earth
blocks. These formulations include raw soil, fines and restructured soil. In restructured soil, a fine
fraction of soil smaller than 0.063 mm was mixed with 15% recycled sand. Restructuring of soil fine
particles helps to improve soil matrix composition and suitability for earth bricks. Compressed-earth
blocks of 4 × 4 × 16 cm were manufactured at a laboratory scale for flexural strength testing by using
optimum molding moisture content and compaction through Proctor normal energy. Compressive
strength tests were performed on cubic blocks of size 4 × 4 × 4 cm. Mechanical testing of bricks
showed that bricks with raw soil had higher resistance with a maximum of 3.4 MPa for Lorient soil.
Removal of coarse particles from soil decreased the strength of bricks considerably. Restructuring of
fines with recycled sand improves their granular skeleton and increases the compressive strength
and durability of bricks.