The mechanical characteristics of on-site manufactured compressed earth blocks: the effects of water repellent and other additives

Abstract

The compressed earth block (CEB) is a form of masonry unit comprised of mechanically compacted earth with a natural clay binder. CEBs typically experience a 50% reduction in compressive strength when saturated. As a result, CEBs are typically stabilised with Portland cement, hydrated lime, or metakaolin. More recently, a commercial silane/siloxane water-repellent admixture with the tradename Plasticure, specifically designed for earth construction, has become available. This paper is an experimental investigation of the influence of Plasticure on the dry and wet strengths of CEBs stabilised with Portland cement, hydrated lime, and metakaolin. Prisms were tested wet and dry with three repetitions each. In total, 106 specimens were tested. The wet specimens were soaked in water for 24 h before compressive testing. Typical CEBs without Plasticure absorbed water equal to 7 to 9% of their original weight. This resulted in reductions of compressive strengths from the dry condition by 40 to 50%. For CEBs that are only stabilised with cement, the addition of Plasticure reduces the amount of water absorbed by 61 to 81% and also reduces moisture-based strength loss by 34 to 71% after 24 h of submersion; this reduces the strength range between dry and wet CEBs drastically. Long-term submersion of cement-stabilised Plasticure specimens (40 days) results in a water absorption of 60% of the absorption measured for CEBs without Plasticure. However, the wet strength is similar to the wet strength of CEBs without Plasticure that are submerged for 24 h. Despite the reduction in strength, all the measured wet compressive strengths exceeded the requirements outlined by Australian, New Mexican and ICC design standards.

Keywords:

• Compressed earth blocks
• compressive strength
• water absorption
• Plasticure

Acknowledgements

The authors would like to acknowledge the in-kind support provided by Henry Wiersma.

Additional information

Funding

This work was supported by the Natural Sciences and Engineering Research Council (NSERC), Canada [grant number RGPIN/249728-2012].