The Effect of Soil Gradation and Addition of Natural Fibres on the Mechanical Properties and Freeze-Thaw Durability of On-Site Manufactured Compressed Earth Blocks
Implementation of sustainable materials is becoming an imperative consideration in modern building because of the impact of the construction industry on climate change patterns. Building with earth is an ancient technique common in many warm regions and developing countries due to its low cost, and is garnering attention for applications in cold regions due to its favorable hygrothermal properties, ease of use, and low embodied energy. The compressed earth blocks (CEBs) in this project were manufactured on-site by an experienced builder in Cobourg, Ontario, Canada using a combination of various soil gradations and locally sourced natural fibres (Phragmites, straw, switchgrass, and rice hulls). Approximately 280 CEBs were tested in direct compression and three-point bending at ambient conditions, saturated conditions, and after being subjected to six and twelve freeze-thaw conditioning cycles. Results showed that blocks constructed with about 20% gravel particles had up to a 29.3% increase in compressive strength and up to a 71.4% increase in flexural strength than blocks constructed with soil containing only sand, silt, and clay particles. The addition of natural fibres was more beneficial for the compressive strength. In general, blocks produced with the larger quantities of fibres had significantly reduced compressive and flexural strengths than the blocks produced with lower quantities of fibres. The addition of 0.5% of Phragmites fibres resulted in a strength of 7.5 ± 0.34 MPa when added in combination with the gravel particles. The corresponding flexural strength of this block type was 1.56 ± 0.36 MPa which was 11.4% less than the flexural strength obtained using gravel particles and no fibres. Blocks produced with 0.125% straw achieved the highest compressive strength of 8.96 ± 0.71 MPa and blocks produced without fibres had the highest flexural strength of 1.34 ± 0.23 MPa of that investigation. After subjecting the CEBs to six and twelve freeze-thaw cycles, the blocks showed strength retentions of up to 140% for both the compressive and flexural strengths. The moisture absorbed by the blocks during the cycling process appeared to have allowed for additional curing of the blocks, resulting in the increased capacity of the CEBs.