Title: Influence of Condensed Silica Fume and Sand/Cement Ratio on Pore Structure and Frost Resistance of Portland Cement Mortars

Author(s): R. F. Feldman

Publication: Symposium Paper

Volume: 91

Issue:

Appears on pages(s): 973-990

Keywords: cements; freeze-thaw durability; mortars (material); porosity; portland cements; sands; silica.

DOI: 10.14359/10107

Date: 2/1/1986

Abstract:
Pore structure changes in silica fume-portland cement blend mortars fabricated with 0, 10 and 30% silica fume at a water/binder ratio of 0.60 and a sand/cement ratio of 2.25 have been monitored by mercury porosimetry while being cured for 1 to 180 days. The threshold value for pore intrusion increases with pore size and becomes less abrupt with silica fume addition; it is in the 0.5 to 20 x l03 nm region. Mortars were also made with and without 10% silica fume at a water/cement ratio of 0.60 and sand/cement ratios of 0, 1.0, 1.5, 1.8, 2.0, 2.25 and 3.0; the sand passed ASTM C109. Mercury intrusion measurements were carried out after 14 days of curing. In the presence of silica fume pore volume in the 0.5 to 20 x 103 nm pore diameter range increased with sand/cement ratio. Mortar prisms were subjected to freezing and thawing cycles (two cycles in 24 h) according to ASTM standard test method C 666, Procedure B. Freezing and thawing resistance was monitored by measuring changes in residual length and weight. Results indicate that if the sand/cement ratio is 2.25 or over, expansion is less than 0.02% after 500 cyles. At lower sand/cement ratios 10% silica fume gives little protection.