Study On The Hydration Activity And Rheological Properties Of Cement-based Materials Modified By Calcined Attapulgite

Attapulgite has the property of dehydration under high temperature,and heat treatment is also a common means to improve the performance of attapulgite.However,in the research of cement-based materials,the systematic theoretical analysis of the change of the reaction activity of attapulgite after calcination is still lacking.By studying the change of physical and chemical properties of attapulgite calcined at different temperatures,and the influence on the rheological properties,hydration process and mechanical properties of portland cement composite system,the optimal calcination temperature of attapulgite was obtained.It provides necessary theoretical research for the application of calcined attapulgite in cement-based materials.The reaction activity was excited by calcining attapulgite at 200??800?,the change of physicochemical properties of calcined attapulgite was analyzed,and the hydration activity and rheological properties of cement-based materials modified by calcined attapulgite were studied.?1?The effects of calcination temperature on physical and chemical properties of attapulgite were studied.The particle size distribution,dehydration degree and mineral composition of calcined attapulgite were studied by means of laser particle size analysis,TG-DSC and X-ray diffraction.?2?The rheological properties of cement-based materials modified by calcined attapulgite were studied,including water absorption and thixotropy.?3?The hydration activity of attapulgite modified cement-based materials calcined at different temperatures was analyzed by measuring the content of active Si O₂ in attapulgite,chemical combined water and mechanical strength,and the optimal calcination temperature of attapulgite was obtained.?4?XRD,FT-IR and mechanical strength were used to further analyze the reaction activity of attapulgite calcined at the optimal temperature,and the impermeability of modified cement-based materials was studied by mercury intrusion method.The main conclusions of this paper are as follows:?1?Calcination can increase the dispersion of particle size distribution of attapulgite;the degree of dehydration of attapulgite increases with the increase of temperature,and the dehydration process is basically completed at about 500?,at this time,palygorskite completely decomposes and amorphous substances increase.?2?The water absorption of attapulgite decreased with the increase of temperature,and the thixotropy of cement paste is improved by adding attapulgite calcined at 200??500?.?3?Calcination can improve the reactivity of attapulgite,and calcination at 500?is the best.With the increase of calcination temperature,the content of active Si O₂ in attapulgite increases gradually,the chemical binding water content in cement paste and the reaction degree of attapulgite increase gradually,and both reach the optimum at 500?;when the calcination temperature exceeds 500?,the reaction activity of attapulgite decreases,and the hydration activity of modified cement-based materials also decreases.The mechanical strength of cement-based materials modified by calcined attapulgite can meet the strength requirements,and the splitting tensile strength is improved.?4?Attapulgite calcined at 500?has enough reactivity.The mechanical properties and pore structure of cement-based materials modified by attapulgite calcined at 500?were improved.At the age of 28 days,the compressive strength and splitting tensile strength of cement-based materials modified by attapulgite calcined at 500?increased by 6.6%and 45.7%respectively.The porosity of hardened cement paste was reduced,the proportion of harmless pores was increased,and the pore structure was improved.The results of XRD and FT-IR show that attapulgite calcined at 500?can quickly produce hydrated products such as calcium silicate hydrate with Ca?OH?₂,and the reaction activity is strong.