Ovalbumin as natural organic binder for stabilizing unfired earth bricks: Understanding vernacular techniques to inspire modern constructions

Abstract

Cement and hydrated lime are usually effective for stabilizing unfired earth but they lead to a significant CO2 footprint. In the search for sustainable, efficient alternatives, old and vernacular techniques may provide ways of replacing such mineral binders. The example of the use of chicken egg white protein (ovalbumin) to improve earth construction materials is addressed in the present case study. It was used to stabilize two soils with different mineralogical compositions. Addition of 2 wt% and 4 wt% ovalbumin strongly increased both the dry and wet compressive strengths (water resistance) of the soils. For these properties, ovalbumin was a more efficient stabilizer than cement or hydrated lime. Concerning hygrothermal properties, the thermal conductivity of the soils did not change with stabilization, while the moisture buffer value decreased slightly but remained at least “good” according to the Nordtest criterion. Microstructural analysis can explain the efficiency of earth stabilization using ovalbumin by the formation of a gel that fills the microcracks in the soil and strengthens it by gluing them up.