The Relationship Between The Pore Fillability Of Hydrating Cementitious Materials And Mechanical Property Of Blended Portland Cement

Efficient utilization of supplementary cementitious materials(SCMs) to produce blendedcement, being not only beneficial to energy saving, emission reducing, resources conservationand environment protection but also to improvement of workability, corrosion resistance anddurability of cement, is considered as one of the development directions of cement industry.At present, many attempts were presented to improve the mixing amount of SCMs in blendedcements based on improvement of hydration activity of SCMs. Yu proposed that theoptimized matching of cement clinker and SCMs is one of the best ways to produce highperformance blended cements with low cement clinker. But common Optimized matchingmethod is based on hydration process, strength contribution ratio and particle size ofcementitious materials lacking of quantitative matching basis. In this thesis, the solid volumeexpansion during hydrating was proposed to measure the pore fillability of cementitiousmaterials. The relational model for initial paste composition, porosity and strength of cementpaste as the quantitative matching basis was established based on the initial porosity ofcement paste and pore fillability of hydrating cementitious materials. The researchsignificances are described in detail as follows:The model for predicting strength was established. The pore fillability was representedbasing on chemical shrinkage and non-evaporable water. Then, the relational model of “initialpaste composition-porosity-strength” was presented combing with initial solid solidconcentration.The pore fillability of cement clinker, blast furnace slag and fly ashwas investigated. 60 days, the pore fillability of fine cement clinker(D50=2.5μm) is 0.79, blast furnace slag is 0.60 and fly ash is 0.20; In the middle size fraction(D50=15.1μm), the pore fillability of cementclinker is 0.64, blast furnace slag is 0.35 and fly ash is 0.10; In the coarse fraction(D50=29.9μm), the pore fillability of cement clinker is 0.39, which is blast furnace slag is 0.22 and fly ash is 0.08; For fully hydrated fine cement clinker(D50=2.5 μm),the pore fillability is0.79,but the coarse fractions(D50=29.9 μm) cement clinker is 0.41, the latter is only 52% ofthe former.The porosity of hardened blended Portland cement predicted combining initial porosityand pore fillability of hydrating cenmet paste had a relational model to compressive strength.The pore fillability of hydrating cement paste accumulatively calculated by cementitiousmaterials of different particle size fractions. Then the porosity of hardened blended Portlandcement got.The correlation of model between predicted porosity and measured compressivestrength is very good. The cement powder packing density,which obtained by measuring themaximum soild volume concentration of cement pastes was defined as initial packing constantin order to improve the porosity-strength model. The improved model was more accuratelyand had a wider adaptability. The 3d and 28 d strength which was predicted by the model isabout ±3MPa different from measured.The method for optimization of the composition of blended cement was studied and theoptimized principle was proposed. The relationship model for composition, porosity andstrength of cement paste,which related to the pore fillability of cementitious materials couldguide the optimized design of blended cment. In this thesis, the optimized design method andprinciple for blended cement was established as follows:(1)The supplementary cementitiousmaterials with excellent pore fillability, such as blast furnace slag, could fully substitute forfine cement clinker(<8 μm), the best addition is about 35%. Furthermore,the fly ash andquartz sand which also could be used as fine cementitious materials,the best addition is about10% and 5% respectively.(2)The middle size fraction( 8~30μm) should completely usecement clinker.(3)The coarse cement clinker(>30 μm) could be replaced with low porefillability supplementary cementitious materials,such as fly ash and quartz sand,the bestaddition of those was about 35% and 20% respectively.The results could be used as the quantitative matching basis for optimized matchingprinciple and provide theoretical foundation and technical support for the preparation of highperformance blended cements with larger amount of industrial wastes. By this method, hugenatural resources and energy can be saved, and significant CO2 emissions can also be reduced,resulting in numerous economic, social and environmental benefits.