Self-Consolidating High Performance Concrete – SCC – Self-Compacting & Highly Flowable Concrete

The preliminary study on the feasibility of applying this viscometer to SCC was conducted in two steps. In the first step, the properties of SCC pastes made with the same w/c and different contents of superplasticizer (SP) and viscosity-modifying-admixtures (VMA) contents were studied. In the second step, the research was carried out on SCC mortars made with various sand contents but the same paste matrix.

An example of the falling ball viscometer measurement for paste of w/c=0.35 with a VMA dosage of 0.15% (by mass of water) is shown in Fig. 4. An obvious shear-thinning phenomenon can be observed since the drag force is not linearly related to the ball velocity. This hints that the falling ball viscometer is very sensitive to the rheological behavior of the measured liquid. For all the cement pastes made with VMA, the plastic viscosity was calculated by using linear regression of the upper portion of the D - V curve (

(Fig. 4). Both the plastic viscosity and the yield stress are plotted as a function of VMA dosage in Fig. 5. As expected, an increase of the viscosity is obtained when the VMA content is increased. It should be noted that the use of this particular polysaccharide-based VMA increased both the yield stress and the plastic viscosity of the cement paste.

(a) Plastic Viscosity

(b) Yield Stress

Fig. 5 Sensitivity of the falling ball

viscometer to VMA dosages

Mortar samples with various sand contents (10%-50% by the volume of the total mortar mixture) were measured using a steel ball with a 1.25 inch (3.175 cm) diameter. The calculated viscosities from the falling ball viscometer for each mortar are plotted in Fig. 6(a). It can be noted that the viscosity changes slightly when the sand content is less than 30% of the total volume of the mixture. When the sand content is higher than 30%, a significant increase in plastic viscosity with increase of sand content can take place. This result corresponds well to the results obtained by Ferraris et al.

It was found that the yield stresses of various batches of mortars can vary over a wide range when the mixture proportioning is kept constant. Qualitatively speaking, the mortar with a bigger flow diameter (mini-slump size: 70 mm and 100 mm for the upper inner and lower inner diameters, and 50 mm for the height) has a lower yield stress. The relationship between the slump flow diameter and yield stress was further studied. Fig. 6(b) plots the yield stress as a function of slump flow diameter for all the mortars measured. A unique relationship between the two studied parameters can be found, which is similar to the results reported by other researchers. This strong correlation confirms that the yield stress can be the dominant parameter that governs the slump flow diameter. However, the influences from other parameters, such as mass density, viscosity, surface tension, etc, should not be ignored.

(a) Plastic Viscosity

(b) Yield Stress & Slump flow

Fig. 6 Measurements on mortars with

various sand contents

The scale, the spring, and the steel balls can be easily assembled, disassembled, packed, and carried to any field that requires the in-situ measurement. The lightweight and portability of the equipment make this viscometer a field and lab friendly equipment. It is easy to clean the ball after each measurement, thus the easiness of the maintenance becomes another advantage of this equipment. The cost of the equipment is 15 to 25 times less than any existing concrete viscometer. The designed viscometer has proved to be efficient for both cement pastes and mortars. This enhances the potential of the application of this viscometer to concrete without changing the existing configuration. Directly measurement to concrete will be conducted as the next step.