Durability of unstabilized rammed earth in temperate climates: A long term study

This paper describes a 16-year study on the weathering behavior of unstabilized rammed earth constructed in the temperate climate of the Northeastern United States with an average annual precipitation of 1,174 mm. A freestanding experimental rammed earth wall utilizing natural clay binders was constructed on the campus of the Massachusetts Institute of Technology in 2005 to evaluate its durability over time. The research documents the erosion of the 450 mm thick wall and identifies the environmental factors responsible for the observed deterioration. While erosion levels are highly dependent on localized environmental factors, results show that regions of the test wall with high levels of environmental exposure have an erosion rate of 3.5 mm/year, regions with medium exposure have an erosion rate of 1.5 mm/year, and regions with low exposure have an erosion rate of 0.5 mm/year. The estimated lifespan of the freestanding unstabilized rammed earth wall with minimal protection from natural climatic conditions in a temperate climate is between 37 and 75 years before repairs are required to preserve structural integrity. This lifespan is comparable to the typical service life of structures in North America built with more carbon-intensive materials such as concrete. The results presented, which are specific to the minimally protected test wall, can be considered conservative. Historic structures provide ample evidence that when adequately protected, unstabilized rammed earth can last nearly indefinitely, suggesting that this low impact material could be used to replace more carbon intensive construction materials with significant environmental benefits.