Balancing Strength and Hygrothermal Performance in Sodium Alginate-Stabilized Earth Materials

Earthen construction methods, such as cob, provide considerable benefits both technically and environmentally, offering enhanced thermal comfort while maintaining low embodied energy. Nevertheless, the structural use of cob remains constrained by its limited mechanical strength and high moisture sensitivity. This study explores the incorporation of sodium alginate (SA), a renewable biopolymer, at concentrations ranging from 0.5 to 2.0% by soil mass, to enhance the mechanical performance, hygrothermal behavior, and durability of cob. The results indicate that the compressive strength increased from 1.64 MPa to 4.79 MPa, representing a 192% improvement, while the flexural strength increased from 0.45 MPa to 0.94 MPa, representing a 109% improvement in the SA1.5 stabilized cob compared with the unstabilized cob (SA0). The geelong erosion test demonstrated excellent surface durability, with a maximum erosion depth of only 1.5 mm, confirming the improved water resistance and surface stability of the alginate-stabilized cob. Furthermore, the moisture buffering value (MBV) results classified alginate-stabilized cob as an excellent hygroscopic material, capable of moderating indoor humidity, while a 37% reduction in thermal conductivity (0.143 W/m^.K) was observed at SA1.5. Overall, sodium alginate effectively enhanced the strength, moisture resistance, and breathability of cob. These findings highlight biopolymer stabilization as a promising, sustainable approach for developing durable, comfortable, and low-carbon earthen construction materials.