Study On Mechanical Properties Of Geopolymer Mortar Reinforced By Nanoparticles And Fibers At High Temperature

Geopolymer material is a kind of inorganic SiO₄,AlO₄ tetrahedron as the main composition,the structure with three dimensional frame structure of the new free calcium aluminum silica gel material,with rapid hardening,early strength,low shrinkage,low permeability,good durability,high temperature resistant and heat insulation,preparation of harmful gases such as CO₂,less in water conservancy,municipal,bridge,underground,and other fields has great application prospect,is expected to become the new green gelled material to replace cement.Using geopolymer as cementing material,quartz sand as aggregate,and adding nanomaterials and fibers,a new type of structural repair and reinforcement material with excellent mechanical properties and durability can be prepared,that is,geopolymer mortar reinforced by nano-particles and fibers.However,in addition to bearing conventional loads,the building structure and its components may also be subjected to thermal stress caused by strong dynamic load caused by explosion or high temperature environment such as fire,etc.Therefore,the high temperature resistance of geopolymer mortar reinforced by nano-particles and fibers is a subject worth studying.In this paper,the mass loss,basic mechanical properties,pore structure changes and microscopic strengthening mechanism of geopolymer mortar reinforced by nano-particles and fibers under high temperature are studied by combining macro test and micro test analysis,and the corresponding calculation model is established.The main research contents and results are as follows:?1?Through the mixture ratio design of nanoparticle and fiber co-reinforcing geopolymer mortar,the mixing ratio of 12 groups in this paper,as well as the dosage range of PVA fiber and nano-SiO₂were determined.The relationship between the mass loss rate and the macroscopic morphology and the temperature was studied by using the mass loss and the appearance change of the polymer mortar specimens after high temperature.The results showed that with the increasing temperature,the mass loss of geopolymer mortar enhanced by nano-particles and fibers increased continuously,which tended to be stable after 600?,and the remaining mass of the sample was about 80%.The appearance color of geopolymer mortar changed from blue-gray to brick-red,and the matrix became brittle.?2?By nanometer particles and fibers after high temperature synergy to geopolymer mortar specimens of cube compressive strength test,flexural strength test and the axial compression test,analysis of the dosage of PVA fiber volume content,nano-SiO₂ and heating temperature on geopolymer mortar compressive strength,flexural strength and the influence of the axial compressive strength,and fitting out of the geopolymer composite mortar strength affected by heating temperature curve,respectively set up considering the cube compressive strength-temperature and against folding strength-temperature of geopolymer composite mortar mathematical model.The results showed that when the temperature was lower than 200?,the temperature increase had a favorable effect on the compressive strength of the sample cube,and the compressive strength reached the maximum value when the content of PVA fiber volume was 0.8% and the content of nano-SiO₂ was 1.5%,respectively.When the temperature was higher than 200?,the compressive strength of the sample cube continued to decrease.When the temperature is lower than 100?,the flexural strength and axial compressive strength of the sample increase with the increase of temperature.In addition,in the range of dosage in this paper,the flexural strength of the sample increases with the increase of PVA fiber volume dosage and nano-SiO₂ dosage.?3?Through the hole structure analysis test,the geometric parameters?number,size and spacing of bubbles?of the composite geopolymer mortar samples reinforced by nano-particles and fibers at high temperature were measured,and the effects of PVA fiber volume content,nano-SiO₂ content and heating temperature on the hole structure of composite geopolymer mortar matrix were analyzed.The results show that when the temperature is lower than 200?,the pore size of geopolymer mortar is optimized.When the temperature exceeds 400?,the internal matrix is damaged seriously and the porosity increases.A certain amount of PVA fiber and nano-SiO₂ improved the pore size distribution.?4?Using micro testing methods of nano particles and fibers after high temperature synergy to geopolymer mortar specimen,the micro facies analysis,studies the PVA fiber,nano-SiO₂ and heating temperature on the influence of the microstructure of geopolymer composite mortar,failure surface of geopolymer composite mortar specimen cracking analyzed the microstructure observation,the application of the combination of macro and micro point of view,from the micro level,has proven the nano particles and fibers synergy to geopolymer mortar after the high temperature mechanical behavior affect the mechanism of action.The results show that the microstructure and compactness of geopolymer mortar are improved when the temperature is lower than 200?.When the temperature exceeds 200?,as the temperature continues to rise,the integrity of the microstructure becomes weaker and loose-like.The cracks are seriously cracked horizontally and longituinally,a large amount of water is lost,and the colloidal decomposition and sintering are serious.PVA fibers and nano-SiO₂ reinforced geopolymer mortar were subjected to high temperatures from 200?to 400?,resulting in short acicular and cluster products.