Study On Key Material System For Rock Reinforcement Of Grottoes Based On The Degradation Of Cemented Structure

This paper focuses on the key scientific and technical issues of grottoes protection and establishes a detailed multidisciplinary comprehensive investigation and research system.Aiming at the complex of rock cultural relics with long-term and complex evolution process,the deterioration process and influencing factors of rock materials in grottoes under the influence of environment are analyzed and studied by using fine geological technology.The purpose is to reveal the inherent law of the deterioration of the material properties of cultural relics in the process of environmental change and historical process,so as to guide the research and development of the protection and reinforcement technology.On this basis,a key material system for the protection and reinforcement of the cultural relics in grottoes is formed.On the basis of probing the inherent law of the decline of rock material properties.Taking"Inorganic Mineral Polymerization"as the starting point for research.Aim to enhance the durability of materials under the influence of environmental factors.Verify the technical inference of"improving the durability of protective materials through inorganic mineral polymerization".The important value of meicaolin as active silicon-aluminous material in material cementation structure design and rock cultural relic restoration was found.On this basis,further exploration was conducted to study the feasibility of activated metakaolin for improving the durability of other protective materials.Extend it to the current material system commonly used for the protection of grotto cultural relics and the improvement of rock structure.The effect of improving the durability of the existing material system and its microscopic mechanism were studied.Based on the experimental verification,the suitable reinforcement ratio system was applied in the field.Formed a kind of grottoes cultural relic protection reinforcement key technical measures.The main research conclusions are as follows:（1）The results of geological survey and non-destructive testing show that the construction of Liujiaxia Reservoir,Huangyanghe Reservoir and water seepage from the roof of the grottoes have a significant impact on the safety of the grottoes.Due to the influence of Huangyanghe Reservoir,the water in Tiantishan Grottoes is mainly supplied to the grottoes by fractures and pore structures of rock mass under the action of osmotic pressure.The rock mass of Matisi grottoes is mainly supplied by the melting water of snow mountain,and the closer the cave is to the top of the mountain,the higher the water content of the rock mass is.The seasonal changes of the Binglingsi Grottoes under the influence of the Liujiaxia Reservoir are obvious,and the rock mass is still mainly affected by water seepage in the mountain during the dry season.The North Grottoes is mainly affected by the role of fissure water and water seepage between layers.The monitoring results of the environmental factors that lead to the deterioration of rock materials in the grottoes further indicate that the rock mass is in the state of alternating wet and dry cycles due to continuous water replenishment.The rock material,especially the shallow surface,is badly deteriorated.Therefore,studying the repeated cycling of water and rocks can help reveal the mechanism of material degradation.（2）By designing saturation-drying cycle tests,indoor acid-alkali erosion cycle test and electrochemical accelerated erosion experiments for sandstone materials with different characteristics.The common and individual characteristics of rock material deterioration are revealed.As the number of dry and wet cycles increases,the contents of Fe and Ca elements in the main cementitious substances were significantly reduced.The fracture of cementitious material and the deterioration of cementitious structure can be observed through the microstructure experiment.Macroscopically,the cohesive force c of the shear strength parameter is significantly reduced and the internal friction angleΦdoes not change much.Both simulated acid-alkali solution erosion and electrochemical accelerated erosion show that the increase of measures conducive to ion migration in rock samples can accelerate the deterioration of rock materials.Different failure modes are also related to the microstructure of rock materials.When the cementing materials and the cementing structure are different,the samples of Binglingsi Grottoes and Matisi grottoes,both of which are red sandstone,show different performance degradation rules.It is concluded that the weakening process of intercrystalline bond will be affected by the different components,the structural relationship between the components and the interface type.It is proved that the influence of the internal microstructure and mechanical interface strength reduction on the durability of rock materials is very important.Therefore,for the reinforcement of rock materials,strengthening the bond of the cement and leading to the formation of new mineral phases and rearrangement of the internal microstructure are important ideas for the development of reinforcing materials.（3）Reasonable use of reaction mechanism of inorganic mineral polymerization.Using metakaolin and limestone powder as important raw materials,and the feasibility of repairing and strengthening the rock materials with the reactants was studied.Through the localization improvement and correction of the classical polymerization theory parameters,matching design of materials was realized by the reaction regulation technology of"hydration+polymerization".The test results show that the reinforcement material system can be compatible with the rock material in the aspects of physical and mechanical properties,working performance and durability.Before the reaction,the aluminum phase of meicaolin raw material was dominated by six,five and four coordination existed simultaneously.After the reaction,part of the aluminum phase was converted to the quaternary coordination,and part of the SiO₄group in the Si-O-Si chain was replaced by the A1O₄ group.Metakaolin participates in the reaction to form a network polymerization structure.Therefore,it was found that metakaolin is an important value for the restoration of rock artefacts as active silica-alumina material.In the process of reaction,the polymerization degree of reactants can be reasonably adjusted by adjusting the reaction degree of"polymerization+hydration",to form a stone body structure more matching with stone cultural relic materials.The optimized cementation structure enables the material to have better durability,so as to meet the needs of cultural relics protection and reinforcement.（4）It is found that active metakaolin is of great value in the cementing structure and durability design of rock cultural relic materials.The active meicaolin was applied to improve the physical and mechanical properties and microstructural properties of the hydraulic lime cementitious material system used in the present grotto protection.The test results prove that it has obvious effects:Introduction of metakaolin into hydraulic lime mortar can reduce the shrinkage rate of materials and improve the volume stability.When the content of metakaolin is5%,10%,15%,20%and 25%,the 28d shrinkage rate of the composite material is1.2%,1.0%,0.9%,0.8%and 0.6%,respectively.Compared with the hydrated lime mortar,it decreases by 20.0%,33.3%,40.0%,46.7 and 60%,respectively.The introduction of metakaolin into hydraulic lime mortar can effectively improve the mechanical properties of the material.When the content of metakaolin is 5%,10%,15%,20%and 25%,the compressive strength of 56d is increased by 46.5%,88.4%,153.5%,213.9%and 244.2%,respectively.The flexural strength of 56d is increased by 72.0%,92.0%,116.0%,140.0%and 152.0%,respectively.It is reflected from the side that the microstructure performance of the system has been improved and strengthened.The phase analysis of hydration products showed that the introduction of metakaolin in the hydraulic lime system would increase the content of gelling substances in the curing reaction product and improve its microstructure.Thereby significantly improving the physical and mechanical properties and durability of the material.（5）By adopting active metakaolin,the cement material system for emergency reinforcement of rock mass in grottoes was reasonably modified.It can design and produce structural reinforcement materials with stable strength development law,good workability and high durability.The test results show that:by mixing ordinary Portland cement and sulphoaluminate cement at 7.5:2.5,and 10%metakaolin is added to prepare a reinforcement material with high bonding strength.After adding metakaolin,it can improve the interface accumulation morphology of sulphoaluminate cement hydration product phase.It also can be well combined with the existing hardened mortar to meet the requirements of repair and reinforcement.This material system also has the following advantages for structural repair and reinforcement:high fluidity,stable development of strength,and no shrinkage of strength in later period.The addition of metakaolin improves the sulfate erosion resistance and frost resistance of sulphoaluminate cement and ordinary Portland cement composite mortar,and enhances the durability of repairing and reinforcing materials.The gradient design of material strength and setting time for structural repair can be carried out by referring to the method of ratio design,so as to meet the needs of practical reinforcement engineering.