title: Development of Eco-friendly and High-Strength Lime-Hemp Concrete (LHC)
Creators: name: Mahmud, Chowdhury Kaiser
Publisher: name: Graduate Studies
Year: 2025
Subjects: subject: Eco-friendly
subject: High-Strength
subject: Lime-Hemp Concrete
subject: Education--Sciences

description: There is a growing demand for eco-friendly alternatives to Portland cement (PC) in the construction industry, primarily driven by the global push to achieve net-zero carbon emissions by 2050. Lime-hemp concrete (LHC), or hempcrete, presents a promising solution to replace traditional, carbon-intensive Portland cement (PC) based construction materials. However, its adoption has been constrained by its limited mechanical strength, with compressive strength ranging from approximately 0.4 to 3.2 MPa and flexural strength ranging from 0.06-1.2 MPa depending on dry density, as reported in several studies. Despite its impressive net carbon-negative potential (around -135 kg CO₂/m³) and other remarkable properties, this limitation has hindered its widespread appeal within the construction industry. This study focuses on developing LHC, with improved mechanical strength while maintaining its advantageous properties, including breathability, insulation, and hygrothermal performance. By incorporating Polyvinyl Acetate (PVAc) adhesive into the LHC system, we developed a mix with a weight ratio of 1:0.3:0.3:0.6 of lime, hemp stalk particles (SP), PVAc, and water. This resulted in a relatively high 28-day compressive strength of 9.9 ± 0.31 MPa and a flexural strength of 5.0 ± 0.25 MPa, demonstrating promising potential for further improvement to make it suitable for load-bearing applications in the future. The optimized LHC has a dry density of 841.61±5.22 kg/m³, dry thermal conductivity of 0.061±0.0006 W/mK, dry specific heat capacity of 1883.38 J/kgK, vapor permeability of 47.83 perm-inch, and a Moisture Buffer Value (MBV) of 1.50 g/m²%RH. Later, a composite wall block was designed based on this mix for further improvement of thermal and hygrothermal properties, which achieved a vapor permeability of 60.65 perm-inch, thermal conductivity of 0.050±0.00145 W/mK, and an MBV of 1.35 g/m²%RH. In the second phase of this project, calcined tailings from the Tailing Solvent Recovery Unit (CTSRU) were used as a lime replacement material (LRM), replacing 30 wt.% of the lime. This approach could reduce the carbon footprint, cost and environmental impact of the developed LHC further by replacing a significant portion of lime with waste calcined tailings. The substitution not only mitigated the environmental impact associated with the replaced lime production and tailings management but also preserved comparable mechanical performance, attaining a compressive strength of 9.3 ± 0.85 MPa at a dry density of 939.44 ± 11.20 kg/m³. This indicates that the material retained its mechanical performance despite the use of waste materials as LRM component. According to our study, X-ray diffraction (XRD) and differential thermogravimetric (DTG) analyses showed no significant pozzolanic activity in CTSRU, as no pozzolanic reaction products were observed in XRD or increased portlandite consumption by DTG analysis. Therefore, it is considered an LRM rather than a supplementary cementitious material (SCM), which requires notable pozzolanic or hydraulic activity. The comparable strength in the presence of 30 wt% CTSRU was attributed to pore refinement, evidenced by reduced porosity, a denser microstructure, a change in pore types, reduced microcracking, and enhanced interfacial adhesion between lime-hemp particles, as confirmed by X-ray computed tomography (X-CT) and scanning electron microscopy-energy dispersive X-ray (SEM-EDS) analyses. The composite wall block made from LHC core with CTSRU achieved a dry thermal conductivity of 0.052±0.000124 W/mK, vapor permeability of 44.38 perm-inch, and an MBV of 1.28 g/m²%RH. X-CT imaging revealed around 50% porosity in the composite, while SEM-EDS analysis confirmed a denser microstructure with CTSRU. This research highlights the potential of LHC as a high-strength material with improved mechanical and hygrothermal performance, offering an eco-friendly alternative for Portland cement-based wall blocks in the future, especially as load-bearing wall applications.