Some references to a method consisting of the testing of mortar viscosity and comparing it with the pure binder viscosity may be found in the literature. By and large, such a comparison would be a stiffening factor. However, as it has been pointed out in Anderson’s work (Anderson, 1987), not only do the filler properties affect that factor but the properties of the binder used for testing do as well. Certainly the reliability of that method is controversial.
8.3.2 Other Factors and Filler Tests
An interesting and simple method of testing fillers is that discussed in the study by Kandhal et al. (1998). Called the German Filler Test,[55] it consists of determining the amount of filler required to absorb 15 g of hydraulic oil and is carried out as follows:
1. Put 15 g of hydraulic oil into a small melting pot, add 45 g of filler, and mix them together.
2. Shape the mixture into a ball.
3. If shaping the ball is successful (i. e., it does not break down) put it into the pot again and add another 5 g of the filler.
4. Having mixed both components, shape the ball one more time and inspect its cohesion.
5. Repeat with another 5 g filler batch until the ball breaks down (lost cohesion).
It is then assumed that the 15 g of hydraulic oil have been completely absorbed by the filler air voids. The test also indicates there is a lack of free oil (similar to free binder) in the mixture that might bond the mortar together. In that case, the result shows the quantity of filler (in grams) required to achieve that condition. The results of this test show a very good correlation to results from the modified Rigden test (Kandhal et al., 1998).
