Study On The Preparation And Properties Of Geopolymer Mortar

After long-term service,the concrete pavement may be damaged,especially the thin layer of concrete pavement often has many minor diseases including surface voids,peeling and cracks,which can affect the normal operation of road and the appearance of the pavement.To eliminate the influence of these diseases,it is necessary to repair the concrete pavement and cover a layer of new materials on the surface.Among this repair process,to bond the new material and the old material as a whole is particularly important.Although ordinary cement-based repair materials are widely used,there are some disadvantages,such as poor interface bonding performance and long maintenance period.Therefore,it is necessary to develop a repair material with early strength,fast hardening,excellent bonding performance and small shrinkage to meet the needs of rapid open traffic.The preparation and properties of metakaolin-slag geopolymer mortar have been studied in present thesis.After the experiments,it has been found the metakaolin-slag geopolymer mortar possess the characteristics of high strength in early stage,rapid hardening,high interfacial bonding strength between old and new materials and excellent durability,which can provide a reference and guidance for the rapid repair of concrete pavement.Firstly,metakaolin geopolymer has been prepared by using metakaolin as raw material,NaOH and water glass as composite activator.The influences of activator modulus,alkali equivalent,liquid-solid ratio and content of slag on the early strength and setting time of geopolymer have been studied.The experimental results show that,when the activator modulus is 1.0,the alkali equivalent is 11%and the liquid-solid ratio is 0.31,metakaolin geopolymer has the best performance and the 1d compressive strength can reach 38.4MPa.The setting time of geopolymer of metakaolin is related to the activator modulus,alkali equivalent,liquid-solid ratio and slag content.With the increase of water glass modulus and liquid-solid ratio,the setting time is prolonged;with the increase of alkali equivalent,the setting time is shortened;with the increase of slag content,the setting time is significantly shortened.Secondly,the orthogonal experiment has been designed with the variables of alkali equivalent,liquid-solid ratio and content of slag,to study the influence of these factors on the flexural strength and compressive strength of geopolymer mortar,to gain the significance,primary-secondary relationship and optimal level of these factors.The experimental results show that,when the slag content is 20%,the alkali equivalent is 13%,and the liquid-solid ratio is 0.42,the strength of metakaolin-slag composite geopolymer mortar reaches the largest value,the flexural strength is 12.7 MPa and the compressive strength is 65.0 MPa at 28d.Then,on the basis of the orthogonal experiment,the optimal mixture ratio has been adopted to study whether the bonding strength,shrinkage and durability of geopolymer mortar meet the standard requirements of pavement repair materials.The experimental results show that the repair mortar with the slag content is 20%,its bonding strength and shrinkage can meet the requirements.And its bonding strength of Id is 2.8MPa,the shrinkage rate of 28d is 0.018%.In addition,geopolymer mortar is resistant to sulfate corrosion,not resistant to hydrochloric acid corrosion.Finally,by means of XRD and SEM,the characterization of geopolymer mortar has been analyzed to explore the reactant phase and microstructure of the geopolymer mortar,reveal the mechanism of its strength enhancement.The XRD test shows that after adding slag,the metakaolin geopolymer mortar appears a new physical phase,and other physical phases are basically the same.The SEM shows that,when the slag content is 20%,the finest microstructure is the geopolymer mortar and the more thorough is the reaction of metakaolin.The conclusion of this paper can provide a basis for the geopolymer repair mortar of metakaolin,and also can provide a reference for the development of geopolymer repair materials with better performance.