Hydrated Lime Treatment of Pozzolanic Mortars: Mechanical Performance and Accelerated Carbonation

The growing demand for eco-efficient cementitious materials has increased the use of high levels of pozzolanic additions, which, despite their environmental benefits, may adversely affect durability, particularly resistance to carbonation. This study investigates the influence of hydrated lime (HL) on the performance of pozzolanic cementitious mortars, with emphasis on carbonation resistance. HL was incorporated into the mortar composition and into the curing solution. A total of 45 mixtures combining cement, fly ash (FA), metakaolin (MK) and HL were produced with different water-to-binder (W/B) ratios. Workability, compressive strength and resistance to accelerated carbonation were experimentally assessed. The results show that workability is primarily governed by the W/B ratio and decreases at high HL contents. Although FA and MK improve mechanical performance, they increase carbonation susceptibility due to reduced alkaline reserve. For the mixtures investigated, moderate HL incorporation into the mortar composition mitigates carbonation, reducing carbonation depth by up to 30–50% relative to the reference mixture. Curing in lime-saturated water does not provide additional benefits under the conditions investigated when compared with conventional water curing.