Yahya Ghasemi Print III pdf

6.3.2. Water requirement of mixtures
As mentioned before, it is possible to estimate the amount of water requirement of a mixture 
based on the concept of water layer theory which is calculated by utilizing SSA and 
assumption of certain thickness of the water layer. However, an empirical test should be 
conducted in order to find the actual water requirement that puts a mixture on the onset of 
flow for the sake of comparing calculation to actual laboratory data. This can be achieved by 
using the Marquardt test or other commonly used tests developed for the purpose of 
measuring water demand such as spread-flow test, Puntke or Vicat needle test.
Marquardt test characterizes the water demand as the percentage of water, adhesively bound 
on particle surface (Hunger & Brouwers, 2009). The test can be performed on powders, 
mortar or the entire concrete mixture. According to the test, the amount of water can be 
determined by monitoring the power consumption of a mixer while water is being added to 
the mixture in small amounts. A dry powder has a low shear resistance and therefore requires 
less power for stirring the mix, as the water is being added to the mixture, agglomeration of 
individual particles takes place which results in more consumption of power. Finally, the 

---

41
Discussion and conclusions
power consumption reaches its maximum which reflects a point where all particles are wetted 
and the particle themselves are connected via water films. Figure 6.2. shows a scheme of 
development of power consumption in Marquardt test. 
Figure 6.2. Schematic development of power consumption in Marquardt test. (Hunger & Brouwers, 
2009).
Assuming the water layer thickness is constant for all of the particles, and in case calculated 
layer thickness is acceptably close to the measured one, Marquardt test can be used as an 
approximate test for measuring SSA.
Once the amount of water that is required to put a mix on the onset of flow is known, the data 
can be used further for starting point of a mix design approach.

---

42
References