Tongsheng Zhang;Peng Gao;Ruifeng Luo;Jiangxiong Wei;Qijun Yu;
<正>To increase the initial packing density of cement paste,The authors proposed a gap-graded particle size distribution(PSD) based on close packing theory.High performance gap-graded blended cements can be prepared by arranging supplementary cementitious materials(SCMs) with high activity,cement clinker and SCMs with low activity or inert fillers in the fine,middle and coarse fractions,respectively.However, the preparation procedures of the gap-graded blended cements are too complex for industrial production.Commercial Portland cements usually present relative narrow PSD,therefore gap-graded blended cements were prepared by adding fine and coarse SCMs fractions into commercial Portland cement.Fundamental properties of gap-graded blended cements and blended cements prepared by intergrinding were compared in the present study. The results show that blended cements prepared by intergrinding had lower amounts of both fine and coarse particles than those of Fuller distribution,while the PSD of gap-graded blended cements was much closer to the Fuller distribution.As a result, gap-graded blended cement pastes presented a higher maximum solid volume concentration than that of blended cements prepared by intergrinding.The setting times of gap-graded blended cements were decreased significantly,both early and late strengths of gap-graded blended cements increased remarkably,which can be attributed to significant hydration of fine GBFS particles. Originality The present study evaluated the feasibility of preparation of gap-graded blended cements by adding fine and coarse SCMs fractions into commercial Portland cement. Blended cements were also prepared by intergrinding the mixture of cement clinker, SCMs and gypsum as references.Compared with blended cements prepared by intergrinding,gap-graded blended cements presented decreased setting times and much higher flexural and compressive strengths,as the microstructure of gap-graded blended cement paste was denser than that of blended cement paste,which can be attributed to high initial packing density of cement paste and significant hydration of fine GBFS particles.The results will be very useful to preparation of high performance blended cement and more efficiently utilization of Portland cement clinker and SCMs in cement manufacture and concrete making.
Blended cement;;Preparation method;;Particle size distribution;;Compressive strength;;Microstructure
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