Research On Properties Of Mixed Portland Cement Based On Ultra-fine Clinker

The use of fly ash,slag,limestone powder and other industrial waste as mixed material to replace part of the clinker to produce cement has remarkable technical,economic and environmental effects.Because of the low activity of the mixed material,the early strength of Portland cement hardened paste with large amount of mixed materials is not high,and the application of industrial waste residue in cement is greatly limited.Using ultra-fine clinker instead of ordinary clinker to produce large amount of mixed-material portland cement can not only improve the effective utilization rate of cement clinker,but also improve the early strength,porosity and other properties of portland cement with high content of mixed materials.In this paper,ultra-fine cement clinker?including dihydrate gypsum?and three kinds of mixed materials?fly ash,limestone powder,granulated blast furnace slag powder?were mixed with Portland cement.The particle packing density,slurry fluidity,mortar strength,hydration products and drying shrinkage properties of three kinds of Portland cement mixed with a mixture were studied.The specific content is as follows:Firstly,the packing density of ultra-fine clinker-mixed composite powders at different ratios was calculated and tested using the Aim-Goff compact packing model and the vibrating compaction method.And the correlation between the packing density and the fluidity of the ultra-fine clinker-mixed composite powder was discussed.Research indicates:?1?The theoretical calculation of the packing density of ultra-fine clinker-granulated blast furnace slag and ultra-fine clinker-fly ash composite powder is consistent with the actual measurement variation rule,and some deviation exists for the ultra-fine clinker-limestone powder composite powder.?2?The ratios relationship of the ultra-fine clinker-mixed composite powder to the maximum packing density is as follows:Ultra-fine clinker:granulated blast furnace slag=1:9,ultra-fine clinker:fly ash=2:8,and ultra-fine clinker:limestone powder=7:3.The Portland cement mixed with ultra-fine clinker-granulated blast furnace slag and ultra-fine clinker-limestone powder has the best fluidity under the maximum packing density,and the influence of the unburned carbon on silica cement mixed with ultra-fine clinker and fly ash does not conform to the above rules.Secondly,the mortar strength,hydration products and dry shrinkage properties of the ultra-fine clinker-mixed material and general fine clinker-mixed material portland cement were studied by comparative tests.The test results indicates:?1?Under the same cement composition ratio,the cement prepared with ultra-fine clinker instead of general clinker has higher mortar strength.Especially,the early strength of the mortar specimen was significantly improved,which solved the shortcomings of low early strength of the Portland cement with a large amount of mixed materials,but it also increased the early drying shrinkage.?2?The result of XRD test showed that the amount of Ca?OH?₂ crystals in the hydration products of ultra-fine clinker-limestone powdered Portland cement decreased compared with that of Portland cement mixed with general clinker,and the quantity of calcium carbonate hydrate increases.Ultra-fine clinker-fly ash portland cement and ultra-fine clinker-granulated blast furnace slag powder portland cement hydration produces more C-S-H gels.?3?Economical efficiency and practicability of ultra-fine clinker-mixed portland cement.The proportion of ultra-fine clinker-mixed materials that meet the GB175 medium strength grade 32.5 cement is as follows:Ultra-fine clinker:granulated blast furnace slag=2:8,ultra-fine clinker:limestone powder=6:4,Ultra-fine clinker-mixed material ratios that meet the GB175 medium strength grade 42.5 cement ratio is:ultra-fine clinker:Fly ash=6:4.Finally,the porosity of cement stone and the strength of cement mortar specimen with different ratios of ultra-fine clinker-mixed materials were studied.The results show:?1?Within a certain dosage range,the increase of the ultra-fine clinker content can reduce the porosity of the cement stone.?2?Under the dispersion effect of naphthalene superplasticizer.Filling compaction effect of ultra-fine clinker on ultra-fine clinker-mixed Portland cement can be more effectively demonstrated.The compressive strength of mortar specimen has been improved to a certain extent,and with the increase of age,the increase in compressive strength is greater.