Applied Research Of Low-grade Metakaolin In Cement-based Materials

With the rapid development of China’s national economy,the investment in the construction industry is getting larger and larger,and the amount of cement is increasing dramatically.In order to meet the demand of the construction industry for cement,a great amount of resources and energy needs to be consumed in the process of cement production,and a great amount of greenhouse gas CO₂ is emitted in the process of production,which has a serious impact on the natural environment.In order to protect the environment,adhere to the green and sustainable development road and improve the utilization of low-grade mineral resources,this paper explores the application of low-grade kaolin in the construction industry in Fogang,Guangdong province.The main way is to calcine it into metakaolin and use it as inorganic admixture instead of some cement in cement-based materials,thus realizing the resource utilization of low-grade kaolin ore.The main research work and results of this paper are as follows:（1）Three kinds of metakaolin with different metakaolin content were ground by ball mill,and the influence of mechanical excitation on the activity of low-grade metakaolin powder was studied.The results showed that mechanical excitation had better excitation effect on the powder with high content of metakaolin.when the content of metakaolin in the powder was high,the strength of mortar test block doped with metakaolin increased with the increase of the specific surface area of the powder.When the metakaolin content in the powder used is low,the strength of mortar test block doped with metakaolin decreases with the increase of the specific surface area of the powder.（2）Taking metakaolin powder with large specific surface area as the research object,the influence of metakaolin content on the strength of mortar test block under standard curing conditions was studied.The results showed that when the content of metakaolin was 0¹9%,the flexural strength and compressive strength of rubber sand test block decreased with the increase of metakaolin content.When the content exceeds 13%,with the increase of metakaolin content,the flexural strength and compressive strength of mortar test block decrease significantly.When the content reaches 19%,the flexural strength and compressive strength of mortar test block are 82%and 88%of the standard respectively.（3）Under standard curing conditions,when metakaolin is mixed with slag powder,the flexural strength and compressive strength of mortar test block decrease with the increase of metakaolin dosage.（4）The influence of specific surface area of metakaolin powder on the strength of mortar test block under autoclaved curing condition was studied.The results showed that the strength of rubber sand test block increased with the increase of metakaolin specific surface area under thermal excitation.When the content of metakaolin with a specific surface area of 949.8 m²/kg is 10%,the compressive strength of the reference sample without metakaolin is increased by12%.（5）Under autoclaved curing conditions,when the content of metakaolin is 0¹6%,the compressive strength of rubber sand test block increases with the increase of metakaolin content.When the content of metakaolin is 16%,the compressive strength of the reference sample without metakaolin is increased by 22%.As the content of metakaolin continues to increase,the compressive strength of mortar test block tends to decline.（6）Under autoclaved curing conditions,the compressive strength of metakaolin mixed with slag powder mortar test block is lower than that of two kinds of admixtures separately mixed with mortar test block.（7）The low-grade metakaolin was applied to fiber-reinforced cement products,and the influence of metakaolin on the impact strength of fiber-reinforced cement products was studied.The results showed that under standard curing conditions,the impact strength of 16%metakaolin-doped sample reached 9.5J,which was 6.9%higher than that of unbiased kaolin reference sample.