Effect of Slag Fineness on the Development of Concrete Strength and Microstructure
N. Nakamura, M. Saki, and R. N. Swamy
Appears on pages(s):
blast furnace slag; compressive strength; heat of hydration; high-strength concretes; microstructure; scanning electron microscope; permeability; slags; Materials Research
Presents the test data on the development of the microstructural properties of concrete containing 50 percent replacement of cement by ground granulated blast furnace slag of varying fineness. The concrete mixtures were proportioned for a 28-day compressive strength of 60 to 120 MPa; the ground granulated blast furnace slag was obtained by pulverizing and classifying ordinary ground slag of 453 m¦/kg of surface area by air permeability. Three degrees of fineness, namely, 453, 786, and 1160 m¦/kg, were used to replace portland cement. The water-binder ratio was kept low at 0.30 and 0.40, and a high-range water-reducing admixture (HRWR) was used to give concrete slumps of 160 to 200 mm. The following microstructural characteristics and properties were investigated: pore structure by mercury intrusion, hydration and rate of heat evolution, microstructure by scanning electron microscopy, and water permeability. The data obtained from these tests are analyzed and correlated, where appropriate, to strength development. It is shown that the use of very fine slag of about 1200 m¦/kg specific surface area results in accelerated hydration, high early strength of 30 to 50 MPa at 3 days, high 28-day cylinder compressive strength of 100 to 110 MPa, very low total pore volume and fine pore sizes, a highly densified microstructure, and very low water permeability diffusion coefficient.