Study On Modification Effect And Mechanism Of Calcined Red Clay On Red Lime Cementitious Materials Of Ancient Buildings

In the traditional building construction,red lime is widely used as the Jia-long lime of yellow glazed tile and the plastering of red wall,which mainly plays the role of reinforcement and waterproof.However,the poor mechanical properties and durability of red lime limit its application in the restoration of ancient buildings.In this study,the red clay was calcined at600 °C and 800 °C for 2 h,respectively,and two calcined red clay was prepared.Three kinds of red lime samples were made from red clay,calcined red clay at 600 °C and calcined red clay at 800 °C respectively.The modification effect of calcined red clay on red lime cementitious materials was explored through physical and mechanical properties tests and durability tests.The mechanism of calcined red clay in modified cementitious materials was investigated by microstructure characterization method,such as X-ray diffraction,infrared spectroscopy and scanning electron microscopy.Based on the above work,the main conclusions are as follows:(1)Compared with the red clay,the addition of calcined red clay in the lime can effectively improve the physical and mechanical properties of the red lime paste samples.With the increase of calcined red clay content,the volume stability,compactness and mechanical properties of the sample are enhanced.The modified effect of calcined red clay at 800 °C is the best.The red lime paste sample with calcined red clay at 800 °C has fast hardening speed and high strength at the early stage of curing,and its volume stability,compactness and compressive strength are better than those of the sample.(2)After the calcination of red clay,kaolinite transforms into metakaolinite,aluminum hydroxyl and silicon hydroxyl are destroyed to form new reaction sites.The reactivity of red clay is enhanced significantly.The reactivity of calcined red clay at 800 ℃ is higher than that of calcined red clay at 600 °C.Calcined red clay reacted with calcium hydroxide to form aluminate hydrate and hydrated calcium silicate which can be filled in the pores to optimize the microstructure of the samples and improve the mechanical properties and durability of the samples.(3)Calcined red clay modified red lime cementitious material can significantly improve the physical and mechanical properties of mortar samples.When the binder-sand ratio is L:S = 1:3,the mortar sample with calcined red clay has superior durability,and the freeze-thaw resistance is significantly improved.For mortar specimens with red clay,the structure is completely damaged after four freeze-thaw cycles.For the mortar samples with 600 °C calcined red clay and 800 °C calcined red clay,after 20freeze-thaw cycles,the damage form is that the surface shell is separated from the sample body,but the overall structure can be maintained relatively intact.(4)Compared with the mortar adding red clay,the mortar adding calcined red clay at 800 ℃ can be closely combined with the matrix and glaze layer of glazed tile,which has a good effect of ridge clamping.The interface between red lime mortar with calcined red clay at 800 °C and glazed tile is less likely to be damaged,and the durability of the specimen is better.