Cementitious and geo-polymeric mortars compared with the same mechanical strength class

In the perspective of using environmentally friendly materials for the rehabilitation and restoration of ancient buildings, the behaviour of geo-polymeric mortars was studied. The research was developed into two main aspects: substitution of Portland cement with an alternative binder and recycling of industrial by-products. The experimentation was carried out comparing the performances of cementitious and geo-polymeric mortars with the same mechanical strength class (R1≥ 10 MPa, R2 ≥ 15 MPa, R3 ≥ 25 MPa, R4 ≥ 45 MPa), according to the European Standard. In particular, four geo-polymeric mixtures were prepared with a sodium silicate/sodium hydroxide proportion of 1:1 with different concentration of NaOH and a sand/fly ash proportion of 2.7:1. Four cementitious mortars were prepared with water/cement equal to 0.5, 0.65, 0.9 and 1.1 by weight, respectively. Different properties both in fresh and hardened state were evaluated and compared. The adherence with brick was reduced when geo-polymeric mortars were used. However, best results were obtained by geo-polymeric mortars with respect to cement ones for vapour permeability, capillarity water absorption, elastic modulus and resistance to salt crystallization.