Band 25, Heft 2

Studies have shown that rheology of asphalt mastic plays an important role in pavement performance, specifically for the case of recycled asphalt pavement (RAP) mastics which contains mostly aged binder. This study determines the rheological properties of RAP mastics and a comparison is conducted with the no-RAP binder. Influence of RAP fines on rutting and cracking performances is also studied. A performance grade PG 70-22 binder is mixed with varying percentages (10, 20, and 40 %) of crushed stone (no-RAP) and RAP fines to prepare mastics. Dynamic Shear Rheometer testing is conducted to measure the complex shear modulus G*, and phase angle δ of these mastics at high and intermediate temperatures through frequency sweep. Bending Beam Rheometer test is conducted at low temperatures (-10, -16, and -22 °C) to measure the stiffness S and relaxation (m-value). Direct Tension Test is conducted to compute the failure strain at -22 °C. Results show an improvement in rutting with the addition of RAP fines (increase in G*/sinδ), a decline in low-temperature cracking resistance (increase in S). Addition of RAP fines up to 20 % does not affect the fatigue resistance of the mastics adversely. However, fatigue cracking of 40 % RAP mastic is shown to be high (increase in G*sinδ). 40 % RAP mastic shows a smaller failure strain than the virgin binder and 40% no-RAP mastic, which indicates that mastics containing RAP are more susceptible to low-temperature cracking. To characterize the viscoelastic properties of the RAP mastics, the G* master curve is constructed at 22 °C reference temperature. RAP mastics’ master curves follow the sigmoidal function irrespective of %RAP in mastics. However master curves do not show any significant difference between RAP mastics and no-RAP mastics.

As a fundamental rheological property, shear yield stress is used to assess the flowability of suspensions. Slump test is a cheap and quick experiment which is commonly used to estimate shear yield stress on-site. It has been generally believed that, cylinder height to diameter ratio and lifting velocity has no effect on the slump test results. In this work, the sensitivity of the slump test to the height to diameter ratio and lifting velocity of cylinder was investigated. Projections on the top surface of suspension column after the slump test were also analyzed. Results indicated that, the effect of cylinder height to diameter ratio is negligible in the low range of shear yield stress, while it is remarkable in the high range. It was deduced that, using a cylinder with dimension ratio in the range of 0.83 to 1.15 is more reliable. Furthermore, it is shown that the lifting velocity of cylinder has a significant effect on the results. A high lifting velocity could introduce a great error in estimation particularly in a large height to diameter ratio.

Viscosity reduction of aqueous kaolin suspensions by conventional additives (deflocculation) is studied, using standard viscosity measurements. Apparent viscosity at 100 s-1, and flow behavior index n give complex information about changes of viscosity and flow character of deflocculated suspensions. Several widely used deflocculants - electrolytes and polyelectrolytes - are tested in a wide range of concentrations. The optimum concentrations of these deflocculants, which result in minimum apparent viscosity of suspension, are found. Sedimentation stability of deflocculated suspensions is monitored. Inorganic electrolytes are found to be more effective in viscosity reduction. On the other hand, low-molecular-weight polyelectrolytes produce more stable final suspensions.

The core of activated sludge monitoring lies in the biological analyses. Anyway, the knowledge of sludge physical characteristics is crucial for a proper management of WWTPs (Waste Water Treatment Plants). One of these physical features is viscosity that, notwithstanding its valuable role has not yet become a routine analysis. This study examined the evolution of rheological properties of two sludges alongside the “purification route” (from the biological reactor up to the sludge treatments). It could been shown that sludges behaved like non-Newtonian fluids and dry solids content strongly affected viscosity values, which reached relatively high values. Microscopic observation of flocs was carried out. Both the sludges revealed similar features, in particular an over-proliferation of filamentous bacteria. This work showed how rheological measurements can be a tool to obtain information on microbiological composition of activated sludge and how it could be related to settleability properties.

Maximizing oil recovery from current reserves is becoming more important as global usage continues to rise. In this paper, we present the development of two microfluidic sandstone devices of high complexity and differing permeability capable of quickly and inexpensively testing the oil recovery performance of fluids with different rheological properties. Our initial baseline experiments were performed by displacing oil with water over a wide range of flow rates. Next, a commercially available fluid thickener, Flopaam 3630, was tested. Flopaam is both shear thinning and viscoelastic and was found, due primarily to its large viscosity, to recover more oil than the water and increase the oil recovery substantially in both the larger and smaller permeability microfluidic sandstone devices. Finally, a shear-thickening nanoparticle solution was studied. The shear-thickening solution was designed to thicken at a shear rate of about 10 s -1 , a typical shear rate in the oil reservoirs. These shearthickening fluids were found to be an excellent enhanced oil recovery fluid, especially when the shear rates within the microfluidic sandstone devices closely matched the shear rates associated with the shear-thickening regime. For the high permeability sandstone devices tested, when the appropriate choice of shear-rate-dependent viscosity was used to define a capillary number, the oil recovery obtained from both the Newtonian and non-Newtonian fluids were found to collapse quite well onto a single master curve. This, however, was not the case for the lowest permeability sandstone devices where the increased complexity was found to negatively affect the performance of the viscoelastic fluid when compared to either the Newtonian or the shear-thickening fluid. Finally, it was shown that these oil recovery results are insensitive to whether a single-stage recovery process or a more complex two-stage recovery process that starts with an initial water flood followed by a flood with a secondary fluid were used.