Title:
Effect of Superplasticizer Dosage on Mechanical Properties, Permeability, and Freeze-Thaw Durability of High-Strength Concretes With and Without Silica Fume
Author(s):
Richard Gagn, Alain Boisvert, and Michel Pigeon
Publication:
Materials Journal
Volume:
93
Issue:
2
Appears on pages(s):
111-120
Keywords:
chlorides; flexural strength; freeze-thaw durability; high-strength concretes; permeability; silica fume; superplasticizers; Materials Research
DOI:
10.14359/1407
Date:
3/1/1996
Abstract:
This paper presents the results of a study on the effects of slump and superplasticizer dosage on the compressive and flexural strength, permeability, and freezing and thawing durability of typical high-strength concretes. Two types of cement were used: a Canadian Type 10 portland cement (ASTM Type I) and a Canadian blended cement containing 7.5 ¦ 0.5 percent silica fume. A water-to-binder ratio of 0.30 was selected to produce air-entrained and non-air-entrained concretes having a compressive strength ranging between 60 and 100 MPa. The superplasticizer dosages (ranging from 0.7 to 1.6 percent, expressed as dry mass of superplasticizer per mass of cement or blend) were selected to produce concretes having slumps ranging from 70 to 240 mm. Some physical and mechanical properties of high-strength concretes made with Type 10 portland cement were found to be significantly reduced when the superplasticizer dosage approximately exceeded the saturation concentration of the cement-superplasticizer combination. Relatively high dosages of superplasticizer (> 1.1 percent; slump > 200 mm) can reduce compressive strength (1-, 28-, and 91-day) and flexural strength (28-day) by 15 to 50 percent, and increase air permeability by a factor of 3 to 5. The effect of such relatively high dosages of superplasticizer on the frost resistance (ASTM C 666, Procedure A) of concretes made with Type 10 cement appears to be of less importance, since the durability of all concretes containing at least a small volume of entrained air was not influenced by slump or superplasticizer content. Compressive strength, flexural strength, air permeability, and rapid chloride permeability of high-strength concretes made with silica fume-blended cement (HSF) were not affected by the superplasticizer dosage. Silica fume appears to be very effective in preventing strength losses and permeability increases in high- slump, high-strength concretes containing high dosages of superplasticizer.