Effect Of Minerals Composition And Content In Clay Powder On Cement Hydration And Concrete Properties

As the main raw material of concrete,the quality of sand and gravel plays a vital role in all aspects of concrete performance,and mud concent is a key factor affecting the quality of sand and gravel.Mud is a complex substance with more components.There are many studies on the effect of mud concent on the performance of mortar and concrete mixed with polycarboxylate superplasticizer,but there are few cases about the experimental research on the composition of the clay minerals contained in mud.And there is no clear limit on the amount of mud in manufactured sand.Therefore,it is necessary to deeply study the influence of different mineral composition and content in clay powder on cement hydration and concrete performance,which has certain reference value for the control of mud content in manufactured sand in the future.The study adopted three pure clay powders containing only single-component clay mineral such as montmorillonite,kaolin,and illite,and four mixed clay powders containing multi-component clay minerals prepared on the basis of these three pure clay powders,which were used to comprehensively analyze the influence of clay powders with different clay mineral composition and content on the working performance of cement paste,cement hydration process and hydration products,and in-depth analysis of its influence on concrete working performance,mechanical properties,durability and microstructure.The result are as follows:（1）Compared with cement particles,three pure mud powders and four mixed mud powders have stronger adsorption capacity for polycarboxylate superplasticizer.Among them,montmorillonite and montmorillonite-based mixed clay powder have the strongest capacity to absorb it.Its absorption value is much higher than kaolin,illite and other mixed mud powders with similar adsorption capacity.（2）Through the influence of mineral composition and content in clay powders on the fluidity and of cement paste,test block strength and cement hydration,it is concluded that when the amount of clay powder is small,it is conducive to the development of the strength of the cement paste test block.But with the increase of the clay powder content,its adverse effect on the fluidity of the cement paste and the strength of the test block increases.Among them,montmorillonite and M₄K₁I₁ mud powder mainly composed of montmorillonite have the most adverse effects,followed by kaolin and M₁K₄I₁mud powder,and illite and M₁K₁I₄ mud powder have relatively small effects.XRD and thermal analysis results show that the addition of clay powder with different clay mineral composition will not affect the formation of hydration products,but has a certain effect on the hydration rate,progress and the amount of hydration products generated.（3）The influence of mineral composition and content in clay powders on concrete compressive strength,drying shrinkage,penetration height and carbonation depth is similar to that of cement paste.When the content of clay powder is small,the impact of clay powder is small,which has a positive effect on the development of concrete strength and internal structure.When the content of clay powder increases,the existence of clay powder is not conducive to the development of various aspects of concrete performance.The results of mercury intrusion test and SEM scanning electron microscope show that addition of 4%clay powder is beneficial to improve the internal structure of concrete,and the overall structure is relatively dense.