Title: Effects of Different Fly Ashes and Silica Fume on Selected Properties of an Expansive Grout
Author(s): L. D. Wakeley and A. D. Buck
Publication: Symposium Paper
Appears on pages(s): 1261-1278
Keywords: compressive strength; expanding agents; expansion; fly
ash; grouts; microstructure; permeability; silica; x-ray
An expansive grout, based on Class H cement, an expan- sive admixture consisting essentially of plaster of paris (calcium sulfate hemihydrate), and a Class C fly ash, was proportioned for use underground. Specimens of this grout, and of five modified versions of it, were tested to determine the effects of using two ther fly ashes, with or without silica fume, on compressive strength, volume change, phase composition, and microstructure. Properties were monitored to 960-days age. Up to 365-days age, specimens of the mixture modified with Class F fly ash had lower compressive strengths and generally more expansion than did those of the original composition. At ages of 90 days and greater, the same was true of samples prepared with a second Class C fly ash. Substitution of silica fume for 5 or 10 percent of the cement gave higher early strength, but the combination of the second Class C fly ash and 10 percent silica fume gave the lowest strengths at ages of 90 days and greater. Despite the substitutions, properties were markedly similar, compressive strength from all modifications exceeded 90 MPa at 365 days, and phase composition and microstructures became more similar with time.