Study On The Properties And Mechanism Of Rock Wool-mortar Interface Modified By EVA

In recent years,with the improvement of people’s safety awareness in various aspects,the fire protection performance of building insulation materials has also gradually received social’s attention.Therefore,rock wool,which is a Class A fireproof material,came into being.It’s widely used in the external insulation system of building exterior wall with the advantages of good thermal insulation,low density,low thermal conductivity and excellent sound insulation.However,there are serious problems in the application process of rock wool that affect its structural safety.The main problems are the low tensile bond strength of the interface between rock wool and mortar and easily to absorb water,which leads to the phenomenon that the insulation layer expands and falls off during the service of the building,which greatly endangers the safety of the building.In this paper,the structural stability of the interface of rock wool-mortar was modified by interfacial agent-EVA.On this basis,the waterproof performance of rock wool,the effect of EVA emulsion on the hydration process of rock wool’s base mortar,the acid and alkali corrosion resistance of rock wool modified by EVA,and the life prediction of rock wool modified by EVA were discussed.The main research results obtained are as follows:（1）EVA emulsion,SAE emulsion and inorganic conposites were used to modify the interface rock wool-mortar,and obtained the optimal interfacial agent by adjusting the solid content of the two emulsions and the mix ratio of the inorganic conposites.After modification,comparing the tensile bond strength,waterproofness and workability of the interface comprehensively,the comprehensive modification effect order of the available interface treatment agent is obtained:EVA emulsion>SAE emulsion>inorganic conposites.（2）The EVA emulsion undergoes a hydrolysis reaction in an alkaline medium,and the generated CH₃COO^-reacts with free calcium ions Ca²⁺to generate Ca（CH₃COO）₂and then form（C₄H₆CaO₄·2H₂O）,which suppresses the calcium silicate hydrate gel（C-S-H）in the early generation,and delay the hydration process of cement.In the later period,C₄H₆CaO₄·2H₂O decomposes with the passage of time,resulting in an increase in the content of CaCO₃ in the mortar,which is beneficial to prevent harmful media from invading and destroying rock wool.（3）After dehydration and drying,the EVA emulsion forms a polymer film on the rock wool fiber and binds to the surface of the fiber by physical adsorption,which can improve the acid and alkali resistance of the rock wool fiber to a certain extent.But with the passage of time,the polymer film on the surface of the fiber will gradually fall off,and the rock wool fiber begin to be corroded.After corrosion in low-concentration H₂SO₄ solution,the overall structure of the rock wool fiber has not been destroyed,but a little spot attachments（CaSO₄）appear on the surface of the fiber.As the concentration of the solution increases and the corrosion time becomes longer,CaSO₄ increased continuously even covering the fiber surface completely.Eventually,excessive aggregation of CaSO₄ fall off from the fiber and forms cracks,resulting in a decrease in the strength of the rock wool.After the rock wool was corroded by NaOH solution,a large amount of pine needle-liked substance was formed on the fiber surface,and found the substance was CaCO₃ mainly by XRD and SEM-EDS analysis.（4）After modifying the rock wool with EVA and SAE emulsions,the diffusion process of water vapor in the rock wool is simulated and analyzed by ANSYS to predict its service life of the rock wool under a certain temperature and humidity.The results indicated that the service life of rock wool by modified EVA was longer than that of SAE emulsion;the existence of deformed structure greatly reduces the service life of rock wool;increasing the thickness of rock wool can effectively increase the service life.