Mechanical and durability properties and life cycle assessment of cement mortars incorporating agricultural waste ashes

Türkiye is a leading producer of hazelnuts and sugar beets, generating large amounts of biomass residues. This thesis evaluates the use of hazelnut shell ash (HSA) and sugar beet pulp ash (SBPA) as supplementary cementitious materials (SCMs). The ashes were characterized by TGA-DTG, XRD, XRF, FT-IR, SEM, specific gravity, laser particle size analysis, Blaine and BET surface area, and a novel R3 bound water test. Mixtures with 5%, 10%, and 15% biomass ash replacement (water-to-binder = 0.5) were tested for setting time, soundness, workability, water absorption, strength, mass-length change, rapid alkali-silica reaction, ultrasound pulse velocity, dynamic modulus, electrical resistivity, freeze–thaw durability, and SEM images. Environmental impacts were assessed by life cycle analysis (LCA). SBPA contained higher SiO₂, MgO, and SO₃, while both ashes were rich in CaO and K₂O. HSA had a larger median particle size (57.65 μm), resulting in lower workability and higher water absorption. Increasing ash content generally reduced workability. SBPA delayed final setting (up to 374 min), whereas HSA accelerated setting (as low as 115 min). 28-day compressive strength decrease is ranging from 33% to 52% due to HSA replacement. At 5% replacement rate, SBPA only caused a 9% reduction. 90-day compressive strength reduction is ranging from 14% to 27% with SBPA replacement. Specimens incorporating SBPA outperformed those incorporating HSA in flexural strength. Water absorption increased with replacement, especially for HSA. Alkali-silica expansion was higher for SBPA. Electrical resistivity peaked at 5% replacement both for HSA and SBPA, but decreased at higher replacement rates. LCA showed significant reductions in environmental impacts compared to reference mixtures (up to 18.85% lower CO2-eq). The findings suggest that while these biomass ashes can serve as SCMs, their limitations must be addressed. However, their environmental benefits highlight their potential as eco-friendly alternatives in cementitious composites.