How about improving the lime-hemp concrete properties using bio-based polymer additives?

The construction sector's high energy use and CO 2 emissions drive the search for sustainable materials such as bio-aggregate concrete. Hemp concrete, composed of hemp shiv and lime, offers benefits including a negative carbon footprint, thermal and acoustic insulation, and moisture regulation but suffers from low strength and durability. Literature studies have shown that bio-based polymers can improve the properties of lime-based materials. This study aims to evaluate the potential of using biopolymers to improve the comprehensive properties of lime-based hemp concrete. Investigated the effect of three bio-based polymers (casein, κ-carrageenan, and hydroxypropyl methylcellulose (HPMC)) on the hygrothermal properties (thermal conductivity, WVP, and MBV), mechanical strength, and capillary water absorption. Additionally, mineralogical and microstructural analyses were conducted using XRD, TG, and SEM. Results showed that within 0.5–5 % of contents, three bio-based polymers had little effect on the hygrothermal performance of hemp concrete but significantly affected mechanical strength and capillary water absorption. Adding casein hindered binder hydration and carbonation, reducing compressive strength and increasing water absorption, despite improving hygrothermal properties. Incorporating 0.5 % κ-carrageenan slightly increased compressive strength, but higher contents resulted in strength loss and higher capillary water absorption. Adding HPMC offered the most balanced performance, with 5 % content increasing strength by 155 %, reducing water absorption by 29 %, while preserving thermal conductivity and moisture buffering close to the reference group. These effects were attributed to enhanced interface bonding and the matrix itself due to HPMC's physicochemical effect. The findings contribute to developing enhanced bio-aggregate-based concrete, advancing their applicability in sustainable construction. • Lime-cement hemp concrete was modified using three bio-based polymers: casein, κ-carrageenan, and HPMC. • Biopolymers significantly altered strength and water absorption but had limited impact on hygrothermal properties. • HPMC provided the best compromise, increasing compressive strength by 155 % and lowering water absorption by 29 %. • Microstructural and mineralogical analyses elucidated the interaction mechanisms between biopolymers and hemp concrete.