Antiwashout admixtures

These are cohesion-inducing admixtures that render concrete cohesive enough to allow limited exposure to water with little loss of cement. Such admixtures allow placement of concrete imder water without the use of conventional tremies. The active ingredient in such admixtures is a water-soluble cellulose ether or water-soluble acrylic t5q)e pol5mier. Other auxiliary agents are also added. 

---

Fig. 6.8 Ready-to-use water-soluble packages of antiwashout admixture (courtesy Fritz Admixtures, Texas, USA).

Table 8.2 Properties of Antiwashout Underwater Concretes Using Typical Antiwashout Admixtures. ( 1991, JSCE, reprinted with permission.)... 

Property Type of Antiwashout Admixture Cellulose Type (MC) Hydroxyethyl Cellulose Type (HEC) Polyacrylamide Type... 

LMC is used in underwater concrete for both new construction and repair. The important requirements to obtain antiwashout capability, such as segregation resistance, flowability, self-leveling characteristics and lower bleeding are provided by the addition of viscosity-enhancing polymeric admixtures at polymer-cement ratios of 0.2-2.0%. These admixtures are water-soluble polymers, and classified under two groups, viz., cellulose types such as methyl cellulose and hydroxy ethyl cellulose and polyacrylamide types such as polyacrylamide and polyacrylamide-sodium acrylate [101]. 

Underwater concreting can be done by three methods the pumping of antiwashout concrete produced by the combined use of water reducing admixtures, superplasticizers and VEAs the use of tremies also using antiwashout concrete and the preplaced aggregate method discussed above. 

---