Selection of Sustainable Repair Mortars for Heritage Structures: A Hybrid MCDM Approach

In the present study, the selection of suitable alternative mortars for the repair of heritage structures is approached as a multi-criteria decision-making problem. The study considers various physical, mechanical, durable and sustainable factors as attributes for selection. The study compares lime with and without natural pozzolanic materials with various lime–GGBS-based mortars with/without organic addition as alternatives. To select the optimal repair mortar, the study adopts a hybrid MCDM approach that combines the analytic hierarchy process (AHP) with technique for order of preference by similarity to ideal solution (TOPSIS) and PROMETHEE-II methods. AHP is used to determine the relative importance of the attributes, and TOPSIS and PROMETHEE-II are used to rank and evaluate the alternatives. The study finds that organic lime–GGBS-based mortars with 66% replacement of lime with GGBS for 1:3 and 1:1 binder:sand mortar proportions (LG66AO and LG66BO), respectively, attained the highest relative closeness coefficients and highest net outranking flow values. Therefore, these mortars are recommended for the repair of heritage structures. The study highlights the importance of considering various physical, mechanical, durable and sustainable factors for the selection of repair mortars for heritage structures. It also demonstrates the effectiveness of the hybrid MCDM approach for optimal selection of repair mortars.