## 5 Conclusions  
Several mortar compositions, compatible with the original mortars and designed to be sustainable and resist the severe marine environment, were selected, using different binder mixes and aggregates, and their main physical and mechanical characteristics were analysed in laboratory conditions and compared at 28, 90, and 180 days. This work showed that all specimens have, in general, good appearance, without cracking in laboratory conditions during the curing age. The exception are the lime mortars with nanosilica (A+NS), that evidenced significant cracking. In general, all the mortars present relatively low mechanical strengths, moderate values of modulus of elasticity, and high rates of water absorption at 28 days, but they also showed improved behaviour with increasing curing age. In general, the slaked air lime mortar (A) shows some potential of improvement in the real environmental conditions of the Fort with salty water spray and thermal variation, due to its pore network with large pores and high connectivity, which allows fast drying and good performance to salt attack. However, its low mechanical characteristics and high rate of water absorption can compromise its durability due to the severe real environmental conditions, with strong winds that could cause erosion on the mortar surface. With the aim to approach the original formulation and increase the mechanical strengths of the lime mortar (A), quicklime with 10% and 30% by volume of lime was added (A+Q10% and A+Q30%). The obtained results showed an improvement of the behaviour with moderate but higher strengths at later ages and lower water absorption rates, ascribed to a reduction in the volume and diameter of large capillary pores, namely with an addition of 30%. A general detrimental strength development was detected in lime mortars with nanosilica (A+NS), namely with the addition of large amounts of NS (5% wt) in the lime mortar. Moreover, the addition of NS leads to an increase in porosity and high rates of water absorption. This behaviour was ascribed to the microcracking occurrence in these mortars and/or to the poor stability of the hydrated phases generated, which eventually impaired the strengths at latter ages. These results advise against its use for cultural heritage sites since they are more vulnerable to degradation and their behaviour is less stable. The slaked air lime with white cement mortar (C:A) also shows mechanical strength improvements, namely at early ages, ascribed to the presence of hydrated compounds. However, probably due to its large volume of capillary porosity, this composition presents higher values of water absorption, as well as its drying occurring slower than that of lime mortars. Therefore, the compositions A+Q30% and C:A seem to generally improve the mortar behaviour in comparison to the A mortar, increasing the mechanical strengths and, in some cases, reducing the water absorption. Hence, a fine-tuning of these compositions by substitution of part of the siliceous sand by different percentages of limestone aggregate were made. The results show increases in the mortars' mechanical strength and reductions in the rate of water absorption by capillarity, namely with 30% of substitution, due to their well-packed system. However, for all compositions, the drying occurs slower, which could compromise the durability of these mortars, such as the appearance of microorganisms in a very humid environment, if a good balance is not achieved. The NHL mortars had a lower w/b ratio and consequently lower porosity than the air lime-based mortars. Therefore, besides the highest mechanical strengths and lowest capillary water absorption, they present a slower drying process and a possible trend to early degradation due to the salt crystallization.