| Table 1. Mix designs for the mortars tested using BML and IBB rheometers. The coarse aggregate concentration was varied (see Fig. 2) | ||||
|---|---|---|---|---|
| Mix designation for Fig. 2 | Rheometer used |
Water/Cement Mass fraction |
Sand/Cement Mass fraction | Air Entrainer (mL/100 kg of cement) |
| IBB #1 | IBB | 0.50 | 1.98 | none |
| IBB #2 | IBB | 0.50 | 1.98 | 26.0 |
| IBB #3 | IBB | 0.50 | 1.98 | 65.2 |
| BML #1a | BML | 0.38 | 2.00 | none |
| BML #2a | BML | 0.38 | 2.00 | none |
| a The same dosage (26 mL/100kg) of two different high range water reducers was used in these two mixes. | ||||
− A vane rheometer (IBB [9]) in which three concrete mixes were prepared with different air contents (Table 1) and different coarse aggregate concentrations.
− A computer simulation (see description below) in which three types of spherical aggregate gradation were used. The distributions used are shown in Fig. 1.
− A parallel plate rheometer designed for cement paste and mortar in which various concentrations of monosized glass beads were added to cement paste.
The detailed description of the BML and IBB rheometers can be found in various publications [8,9]. These were two of the rheometers used in the international round-robin tests [1]. Table 1 shows the composition of the mixes used. It should be noted that the plastic viscosity measured with the IBB is not given in fundamental units of Pa s but in Nm s. Therefore, it is impossible to directly compare the results from rheometers. Nevertheless, an empirical correlation function was determined for each pair of rheometers described in Ref. [1]. Several simulations of hard sphere systems imbedded in an isothermal Newtonian fluid, were carried out where the size distribution of the spheres consistent with those shown in Fig. 1. The number spheres varied from about 200 to 500 depending solid fraction. By applying a constant strain to system a shear flow developed. Sphere movements sphere interaction were modeled using a method on dissipative particle dynamics (DPD) [12]. The viscosity was then determined from calculation averaged stresses for a given strain rate [12]. The paste measurements were conducted using parallel plate rheometer used for cement paste [13]. rheometer was modified from the description [13] to accommodate mortar. The plates were 60 diameter (instead of the 35 mm diameter usually for cement paste) and a confinement ring was This ring has an internal diameter of 62 mm height of about 20 mm. The gap between the two was 10 mm for both the cement paste and mortar mixtures. The cement paste was prepared using cement and a w/c ratio of 0.45, with no admixtures. glass beads were nominally 1 mm in diameter volume concentration was varied from 0 % to This type of aggregate was selected to provide validation data for the DPD model as they were mono-dispersed and spherical and thus straight forward simulate.
Fig. 1 Aggregate gradations used for the computer simulations shown in Fig. 2
Fig. 2. Relative plastic viscosity as a function of the particle concentration. The composition of the mixtures is given in Table 1. The three model series correspond to the three gradations used in Fig. 1. No error bars are shown because these are the results of only one set of data (no replica). The solid line is simply a guide for the eye.