Novel Methodology to Assess Salt Movement Between Mortar and Stones from Heritage in Spain

The development of sustainable cementitious materials is crucial to reducing the environmental footprint of the construction industry, particularly due to the high CO₂ emissions associated with Portland cement production. Alkali-activated materials (AAMs), derived from industrial by-products such as phosphogypsum (PG) and ground granulated blast furnace slag (GGBFS), have emerged as promising alternatives. However, their compatibility with natural stone in heritage structures remains poorly understood, especially regarding salt migration and potential damage. This study presents a novel methodology for assessing salt movement in solid materials between two types of stones—Boñar and Silos—and two types of binders: blended Portland cement (BPC) and an AAM composed of 70 wt% ground granulated blast furnace slag (GGBFS) and 30 wt% phosphogypsum (PG). The samples underwent capillarity and immersion tests to evaluate water absorption, salt transport, and efflorescence behavior. Conductivity mapping and XRD analysis revealed that AAM-based mortars exhibit a significantly higher release of salts, primarily sodium sulfate, which may pose a risk to adjacent porous stones. In contrast, BPC showed lower salt mobility and different salt compositions. These findings highlight the critical importance of evaluating the compatibility between alternative binders and heritage stones. The use of AAMs, while environmentally beneficial, may pose significant risks due to their tendency to release soluble salts. A thorough understanding of salt transport mechanisms is therefore essential to ensure that sustainable restoration materials do not inadvertently accelerate the deterioration of structures, and this process becomes more serious when the deterioration affects heritage monuments.

POLLET Linde;  ANTOLÍN-RODRÍGUEZ Andrea;  GISBERT-AGUILAR Josep;  BÚRDALO-SALCEDO Gabriel;  JUAN-VALDÉS Andrés;  GARCÍA-ÁLVAREZ César;  RAGA-MARTÍN Angel;  SCHROEYERS Wouter;  CALVO Víctor;  FERNÁNDEZ-RAGA María; 

2025-07-18

MDPI

JRC142774

1996-1944 (online),   

https://www.mdpi.com/1996-1944/18/14/3340,    https://publications.jrc.ec.europa.eu/repository/handle/JRC142774,   

10.3390/ma18143340 (online),