Sustainable conservation of salt-damaged bricks using multi-functional lime mortar with bio-based and waste admixtures

In historic masonry structures, rising damp is the main source of moisture and salt-related deterioration, which is often augmented by archaeological excavations. This study investigates the conservation of salt-damaged fired bricks from the Roman period from the Sagalassos archaeological site through desalination using a sacrificial rendering mortar incorporating bamboo biochar and textile waste as novel admixtures. Brick samples were first desalinated, then exposed to controlled sodium sulfate contamination before applying the rendering mortar. Half of the samples were left untreated, while the other half was subjected to rising damp conditions by placing them in 1 cm of water. This procedure was repeated three times with salt concentrations measured at different depths after each cycle. The properties and desalination efficiency of biochar- and textile waste-modified mortars were analyzed using ion chromatography, polarized optical microscopy, particle size analyzer, SEM-EDS, XRF and MIP. Carbonation degree and strength development were evaluated via TGA/DSC, XRD and mortar testing, while durability was tested with 72 freezing-thawing cycles. Results suggest that sacrificial rendering mortars with textile waste (by 91% dry, 82% dry+wet) and biochar (by 90% dry, 86% dry+wet) effectively extract salts from archaeological bricks, while the biochar-modified mortars offer superior durability with higher carbonation (82%) and strength (1.4 MPa). These findings highlight the potential of sustainable admixtures in the conservation of salt-damaged archaeological bricks. • Biochar and textile waste were used for the first time for salt extraction in a sacrificial mortar • Desalination with mortars having biochar and textile waste is more effective under dry conditions • Salt mitigation efficiency slightly decreases with capillary water uptake; however, it remains superior to the control mortar. • Bamboo biochar advances lime mortar carbonation due to CO2 sequestration and provides strength and durability