Abstract
Abstract: Powers theory proposes calculation method for the pure volume of cement hydration products, which does not apply to calculate the volume of cementitious materials with mineral admixture. The formula of cementitious materials volume was proposed that based on the basic principles of cement and mineral admixture hydration, and the proposed method of reliability was verified by the results of Powers theoretical model and volume fraction of cement hydration products. On this basis, the factor such as water-cement ratio, the ratio of admixture and types was further researched for the volumes of cementitious materials hydration products. Mixture in test were designed 2 water-cement ratio (0.30 and 0.40, respectively), two content (20% and 60%, respectively) of mineral admixture, and 3 kinds of mineral admixture (lithium slag, fly ash and steel slag, respectively), forming paste that was stirred according with the designed ratio in 5 mL centrifuge tube in a blender and curing to 1, 7, 14, 28, 60 and 90 d in curing room (temperature was (20±1)℃, humidity was not less than 95%), and then testing reaction extent of cement and mineral admixture (such as fly ash, steel slag. lithium slag) according with the chemical bound water and HCl dissolution method. The results showed that hydration extent of lithium slag, fly ash and steel slag at 28d decreased by 46.63%, 69.56% and 74.82% (P<0.05) when mineral admixture content varied from 20% to 60% and water-cement ratio was 0.30. Hydration extent of cement at 28 d was increased by 7.25% when water-cement ratio increased from 0.30 to 0.40. When mineral admixture content varied from 20% to 60%, hydration extent of lithium slag, fly ash and steel slag at 28 d increased by 24.14% 18.56%, 17.61% and 8.84%, 12.21%, and 29.37% (P<0.05), respectively. In contrast, the influence of the mineral admixture content was bigger than water-cement ratio for the hydration extent of composite cementitious materials. In different water-cement ratio and the same mineral admixture content, the hydration extent of cement-based materials with lithium slag was maximal, followed by fly ash, steel slag was minimal, and it could be improved when curing period was extended. The calculated volume fractions of composite cementitious material, CSH, aluminates phase AF and CH in composite cementitious material were lower than cement paste, the volume fraction of unhydrated particles and pores were higher than cement slurry. The volume fraction of unhydrated particles, CSH, CH, aluminates phase AF and pores in lithium slag-cement based was 36.64%, 37.01%, 9.48%, 17.45% and 8.68%, respectively. The volume fraction of unhydrated particles, CSH, CH, aluminates phase AF and pores of fly ash and steel slag-cement based was 100.93%, 91.49%, 101.79%, 102.81%, 131.80% and 97.59%, 91.38%, 106.33%, 97.71%, 170.16% that of lithium slag-cement based. The volume of the pores and CSH gel increased because of the secondary reactions between CH in cement and SiO2 and Al2O3 in mineral admixture when lithium slag, fly ash and slag were incorporated. But the volume fraction of CSH in cement-lithium slag slurry and the volume fraction of AF in cement- fly ash slurry were larger than others, even if the water-cement ratio was from 0.30 to 0.40. Mineral admixtures was different because of chemical composition of mineral admixtures, pozzolanic activity, particle morphology and origin and processing techniques was different, therefore, the volume fraction of unhydrated particles, pores, CSH, CH and aluminates phase were affected by water-cement ratio with content and admixture species, water-cement ratio, water-cement ratio and admixture species and content, respectively. On the whole, the performance of cement-lithium slag slurry was the best, followed by cement-fly ash slurry, and cement-steel slag was the minimum. This study can provide valuble information for lithium slag, fly ash and steel slag to use in cement and concrete, and to reduce energy consumption and conserve resources.
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