Preparation Of Alkali-excited Metakaolin-based Mortar And Study On Its Impermeability And Dry Shrinkage Properties

Urban underground pipe network is one of the important infrastructures of a city.Concrete pipes are widely used in the construction of underground pipe network because of their advantages of adapting to various complex environments.However,the structural and functional defects of the existing concrete pipelines in our country are becoming more and more serious due to the long-term disrepair.Therefore,it is extremely urgent to repair and strengthen the existing drainage pipelines.At present,the widely used repair mortars are mostly cement-based repair materials,which have problems such as high cost and poor durability.Geopolymer,as a new type of inorganic non-metallic cementitious material,has many properties similar to cement.Compared with ordinary Portland cement(OPC),it has a series of advantages such as high early strength,short setting time,low thermal conductivity,strong corrosion resistance and high durability.Therefore,geopolymer has the potential to become a new type of repair material,and the research and development of geopolymer as a repair mortar has important engineering value.In this paper,metakaolin,sodium sodium silicate and sodium hydroxide as the main test raw materials,through the alkaline excitation process to prepare metakaolin based mortar.The orthogonal test and single factor test are used to study the alkali equivalent,fly ash content and water-solid ratio.The influence of geopolymer mortar properties,and the modification test of metakaolin-based mortar by adding basalt fiber and calcium oxide to obtain the effect of basalt fiber and calcium oxide on the properties of metakaolin-based mortar.The main research results of this paper are as follows:(1)For the 7d and 28 d compressive strength of metakaolin based mortar,the most significant factor is alkali equivalent,followed by the content of fly ash,and the smallest factor is water-solid ratio.When the alkali equivalent is 18%,the content of fly ash is 10% and the water-solid ratio is 0.41,the 7d and 28 d compressive strength of metakaolin based mortar achieve the best value.For the flexural strength of metakaolin based mortar,the 7d flexural strength test results show that the watersolid ratio has the most significant effect,followed by the alkali equivalent,and the smallest effect is the fly ash content.The 28 d flexural strength test results show that the water-solid ratio has the most significant effect,followed by the fly ash content,and the alkali equivalent has the least effect.When the water-solid ratio is 0.41,the fly ash content is 0%,and the alkali equivalent is 18%,the 7d and 28 d strength of metakaolin based mortar achieves the best value.(2)By adding calcium oxide,the setting time of metakaolin based mortar can be significantly shortened,and the bonding property of mortar can be improved.In the meantime,it will have a negative impact on the fluidity,impermeability,compression and flexural strength of mortar.The addition of basalt fiber can improve the flexural strength and bonding strength of mortar and improve the dry shrinkage performance of mortar,but it will have a certain negative effect on the compressive strength,impermeability and fluidity of mortar.