Study On Organic/Inorganic Compound Modification Of Natural Hydraulic Lime For The Restoration Of Historic Bulidings

Due to the superiority of natural hydraulic lime(NHL)in the field of historic building restoration,it has been widely studied and applied in recent years.However,as an effective restoration material for historic buildings,the durability of NHL still has a large space to improve.So,it has great significance in improving the service performance and prolonging the service life of NHL.In this study,two kinds of organic modifiers,such as isobutyltriethoxysilane and silicone acrylic latex,and inorganic silica fume were used for the compound modification of NHL.The effect of compound modification on the properties of NHL was evaluated,and the modification mechanism was expounded.The results showed that,the hydration and hardening process of NHL was retarded by solely using two kinds of organic modifiers,resulting in degradation of some properties.The use of organic-inorganic compound modification with certain formula overcame the defects of the use of organic modification alone.The hydration and hardening process of NHL was accelerated,the shrinkage decreased as much as 73.64%,the water absorption and capillary water absorption decreased as much as 96.38%and 99.31%respectively,the flexural strength,compressive strength and bond strength increased as much as 533.33%,650.21%and 500.43%respectively,the compressive strength loss rate decreased as much as 96.67%and 62.35%respectively after freeze-thaw cycle and acid corrosion,and the damage time exposed to salt corrosion was greatly prolonged.The main reason for the improvement was attributed to the following:the pozzolanic reaction between silica fume and Ca(OH)2 increased the content of hydration products,isobutyltriethoxysilane played bridging coupling role between different matrix components of the cementitious system,the formation of crosslinking network between silicone acrylic latex and cementitious matrix through Ca,and the filling effect of silica fume.The properties of the modified NHL-based repair materials were compared with those of several frequently used repair materials.Compared with non silicate traditional lime-based,high modulus potassium silicate(PS)based repair materials and silicate fired hydraulic lime repair material,the modified NHL-based repair material had better hardening speed,mechanical properties,shrinkage resistance and durability.The compatibility between the modified NHL-based restoration material and the repaired matrix was evaluated by using the orthogonal experiment and the fuzzy comprehensive theory.The restoration material with the best compatibility was applied to the site reinforcement test of the earthern site represented by the M2 Tomb of Dingtao in Shandong and the brick site represented by the Wanping city wall of Beijing.After a long time of preservation,the interface between the repair material and the repaired matrix did not crack or separate,the interfacial bonding performance and compatibility were good.There were no weathering and falling off to the repaired part of the matrix,the durability was good.The methods of material modification,compatibility evaluation and the beneficial results obtained in this study provided reference for the optimal selection of restoration materials for other similar earthen or brick sites.