Title:
Effects of Antiwashout Admixtures on Fresh Concrete
Properties
Author(s):
Kamal Henri Khayat
Publication:
Materials Journal
Volume:
92
Issue:
2
Appears on pages(s):
164-171
Keywords:
admixtures; air entrainment; bleeding (concrete); repairs;
segregation; setting (hardening); underwater construction; viscosity;
water.
DOI:
10.14359/9767
Date:
3/1/1995
Abstract:
Most antiwashout admixtures are water-soluble polymers that modify the rheological properties of fresh concrete. Such admixtures have been incor-porated into concrete intended for underwater placements and repairs, and implemented in production of extremely workable and flowing concrete. They have also been used to enhance resistance to sagging of shotcrete and produce bleed-free cement grouts for filling post-tensioning ducts. This paper presents results from a study aimed at better understanding of the effects of antiwashout admixtures on concrete properties. It will highlight benefits and limitations of employing such admixtures in concrete. Fresh properties of low-, medium-, and high-strength concretes made using two types of antiwashout admixtures, a microbial polysaccharide and cellulose derivative, were evaluated. Fresh properties are compared with those of similar concretes made without antiwashout admixtures. Among the parameters evaluated are fluidity, bleeding, water dilution, segregation, setting time, and air content. Test results show that incorporation of an antiwashout admixture can greatly reduce external bleeding and significantly enhance resistance of concrete to water dilution and segregation. However; there is a signijcant increase in water demand, and a high-range water-reducing admixture (HRWRA) is needed to maintain a desired level of fluidity without excess addition of water. The combined additions of an antiwashout admixture and HRWRA delay setting time, especially at high concentrations of HRWRA. Viscous concretes containing antiwashout admixtures show a greater demand for air-entraining admixture. However; once enough air is entrained, proper air-void parameters needed to insure good freeze-thaw resistance can be obtained.