Title:
Frost Durability of Concrete Containing
Viscosity-Modifying Admixtures
Author(s):
Kamal Henri Khayat
Publication:
Materials Journal
Volume:
92
Issue:
6
Appears on pages(s):
625-633
Keywords:
admixes; air entrainment; freeze-thaw durability; scaling; vis-c
o s i t y .
DOI:
10.14359/9782
Date:
11/1/1995
Abstract:
The use of viscosity-modifying admixtures in special concrete intended for underwater placement and repair has increased in the last decade. Such admixtures have also been employed in the production of highly flowable yet cohesive concrete that can be used in a variety of land-based applica-tions. Limited information exists about the frost susceptibility of such concrete. The effect of an adding sequence of the air-entraining admixture, in relation to the viscosity-modifying admixture and the high-range water reducer on an air-void system is evaluated. The impact of two commonly used viscosity modifying admixtures, welan gum and hydroxypropyl methylcellulose, on frost durability (ASTM C 666) and scaling resistance (ASTM C 672) is determined for fluid mixes made with w/c ratios of 0.32, 0.40, and 0.45. Test results indicate that the air-entraining admixture is most effective when added after the viscosity-modifying admixture and high-range water reducer. Providing that an adequate air-void system is secured, concrete made with welan gum or hydroxypropyl methylcellulose can exhibit adequate frost durability similar to that of conventional concrete. Regardless of the presence of a viscosity-modifying admixture, concrete with a 0.45 w/ ratio and a spacing factor less than 400 um can develop a frost durability coefficient greater than 75 percent. An excellent durability coefficient can be obtained with concrete made with a w/c ratio of 0.32 or 0.40, again, independent of the viscosity-modifying admixture. Regardless of the spacing factor and the presence of a viscosity modifier, highly fluid concretes can develop poor scaling resistance that can be partially attributed to the relatively high porosity of the skin " concrete.