The effects of pyrolysed spent coffee grounds and spent tea leaves on hydration, autogenous shrinkage, strength, and resistivity of mortar

The effects of spent coffee grounds (SCG) and spent tea leaves (STL) on the physicochemical and durability-related properties of mortar are evaluated. Untreated SCG and STL are unsuitable due to their high organic content and pronounced water absorption capacity, which adversely affect cement hydration. SCG and STL were subjected to pyrolysis at 350°C and 500°C, yielding biochar materials subsequently incorporated into mortar at replacement levels of 7.5% and 15% by sand volume. Both raw and pyrolysed materials were chemically characterised. The resulting mortars were assessed through isothermal calorimetry, autogenous shrinkage measurements, compressive strength testing, and electrical conductivity analysis. Mortars containing untreated SCG and STL exhibited increased electrical conductivity. In contrast, pyrolysed materials showed improved behaviour, particularly those treated at 350°C, indicating possibly enhanced microstructural development.