Effects of Various Chemical Agents on Mechanical Characteristics of Weak Lime Mortar

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Lime water treatment on a specific lime mortar was tested and evaluated for effectiveness, showing that after a sufficiently high number of applications (160 cycles, 54–80 days of a permanent consolidation treatment) some of the poor mechanical characteristics (compression and surface cohesion) were substantially improved. The lime water treatment was also compared with some other less labour-intensive technologies. The most efficient agents were dispersions of calcium hydroxide in alcohols, which are marketed under the trade name CaLoSiL by the German producer IBZ Freiberg. The major advantage with these agents is that they can be applied much more rapidly than tens to hundreds of lime water cycles and they deliver a higher amount of lime in each cycle. While lime water contains only small calcium ions, sized about 0.1 nm, calcium hydroxide particles in CaLoSiL are considerably larger (50–200 nm). This property makes the use of these nanolime dispersions limited to structural consolidation of porous material with a sufficiently large pore diameter. Nanolime dispersions applied to mortar where the majority of pores are around 100 µm in diameter is efficient enough to allow for a one-day application of CaLoSiL E15 (7 cycles), to reach significant strengthening. It appears from the results that lower concentrations of CaLoSiL (E 15) create a better distribution of the new binder and therefore lead to higher compression strength than the more concentrated CaLoSiL (IP 25). Diluted, 8% silicic acid ester, applied in two cycles, showed the same consolidation effect as CaLoSiL E 15 applied in 7 cycles. Surface cohesion of mortar was improved following most of the consolidation treatments tested, including multiple applications of ammonium oxalate and barium water. Addition of metakaolin to lime water did not provide any added strengthening benefit. However, the combination of silicic acid ester with nano-lime product (CaLoSiL IP 25) was shown to be effective.