Study On Preparation Of Ultra High Strength Concrete With High Volume Of Cementitious Materials

Since the advent of ultra high strength and high performance concrete, with excellentmechanical properties, working performance and durability, it has been widely valued andstudied. But the traditional ultra high strength concrete often has large amount of cementand tend to use expensive raw materials and complex methods of the preparation andconstruction, which have affected its extensive application in engineering.Based on the conventional preparation of concrete, with the use of mineral admixtures(silica fume, mineral powder, ferronickel powder, fly ash, etc.) mixing and aggregates ofgood particle morphology, a large amount mixing (replacement of cement by more than50%), high strength (more than120MPa), high workability (slump more than200mm),low-cost ultra high strength concrete has been successfully prepared.Through the cement paste and mortar experiment mixed with mineral admixtures, thecompressive strength and fluidity of ultra high strength cementitious materials are studied,and the related mechanism is also analyzed. Based on this, the influence factors ofcompressive strength between ordinary fine aggregate concrete and ferronickel slagconcrete are researched, and the both workability are compared, and at last, the successfulreason of preparation of ultra high strength concrete is analyzed. The results have shownthat the long-term strength of cementitious material with high volume of blendingmaterials can exceed the strength of pure cement.The cementitious material can be usedfor the preparation of ultra high strength concrete; Ferronickel slag concrete has thefluidity advantage over ordinary fine aggregate concrete. It can be densely molded at lowwater-binder ratio and achieves the higher strength.Hydration degree of cementitious materials is analyzed by measuring the chemicallycombined water content, micro performance of ultra high strength concrete is studied bymeans of XRD and SEM.The results show that the hydration degree of cementitiousmaterials with high volume of blending materials is not high at low water-binder ratio.Silica fume and mineral powder have the higher activity in early age so that they canpromote hydration, fly ash has a greater effect in promoting hydration in the later age,while the activity of ferronickel powder is weak in all times and it has no significant effecton promotion of hydration；The main mineral compositions of ferronickel slag arepyroxene and hortonolite and it does not have the hydration activity. The cement paste offerronickel slag ultra high strength concrete is tightly bound with the aggregate. Thetransition zone has no obvious Ca(OH)2crystals but was wrapped by C-S-H gel. Theinterfacial properties of ferronickel slag concrete have greatly improved as compared with the ordinary concrete.