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Title: Sulfate Resistance of Mortars With Pulverized Fuel Ash

Author(s): A. L. A. Fraay, A. Reigersman, and J De Pee

Publication: Special Publication

Volume: 100


Appears on pages(s): 2041-2058

Keywords: air entrainment; blast furnace slag; expansion; fly ash; mortars (material); porosity; portland cements; sulfate resistance; Materials Research

Date: 4/1/1987

This paper deals with sulfate attack on mortars containing fly ash. Mortars of ordinary portland cement and of blast furnace slag cement were investigated. Two different sand gradings were used as well as two different water contents. At various time intervals during the tests, the length changes were measured. The tests were performed with various concentrations of Na2SO4 solution. At several intervals the pH of the solution was restored to 7 to 8 by titration with a H2SO4 solution. Seven different fly ashes were tested. In one series, instead of the fly ash a fine graded sand was used as a replacement for cement. The specimens were stored for one month at constant relative humidity of 95 percent. After immersion for five months in the Na2SO4 solution, the bending strength, compressive strength, and the pulse velocity of the specimens were measured. The sulfate attack was controlled by the fly ash and the amount of entrapped air in the mortars. The finer fly ash gave a good sulfate resistance. The specimen with the higher air content showed a higher sulfate demand (to restore the pH) at increasing (water + air)-(cement + fly ash) ratio. The porosity factor and strength had a greater effect than the C3A content of the portland cement.