Use of coupling agents for increasing passivants and cohesion ability of consolidant on limestone

Deterioration of monuments constructed of limestone could be potentially arrested by applying a combination of coupling agents with consolidants, which can prevent acid attack and mechanical weakening. Two different coupling agents including N-(2-aminoethyl)-3-aminopropyl methyl dimethoxysilane (AE-APMDMS) and diethyl phosphatoethyl triethoxysilane(DEPETES) were used to link calcite. Calcite was impregnated with these coupling agents and studied by FTIR, TG-DSC and contact angle measurement. According to these techniques, new bands, a two stage decomposition pattern appeared and a slight increase in surface hydrophobicity for AE-APMDMS and DEPETES that indicated interactions between the coupling agents and calcite. The Scotch Tape test and compressive strength test showed that the cohesion between consolidant and limestone powder improved, while the ability of consolidation decreased, which were resulted by coupling agents. Resist acid test on limestone powder coated with the coupling agents resulted in a decreased deterioration rate. Limestone treated with combined consolidant plus AE-APMDMS or DEPETES showed a significant decrease in capillarity water absorption.