Large samples (up to 15cm diameter) of SYNROC D containing simulated Savannah River (SRL) waste sludge have been prepared and performance tested. Waste loadings of 60-65 wt% for the SRL composite sludge have been achieved; this corresponds to a waste concentration (volumetric) loading of approximately 2.3-2.5 g/cm3. A typical SYNROC D sample has a density of about 4.0 g/cm3 with less than 0.2% porosity. The compressive and flexural strengths of SYNROC D are 51,200 and 9,400 psi, respectively and Young's Modulus is 20.1 × 106 psi by ultrasonic measurement. The quantity of respirable fines (less than 10 μm) generated during a constant energy density impact (10J/cm3) was less than 0.16 wt%. Values for the thermal conductivity (22°C) and the thermal expansion coefficient (22–950°C) were measured to be 1.7 W/m·K and 11 × 10−6 K−1, respectively. Normalized elemental leach rates determined by 28-day MCC-1 tests (90°C) for Cs, Sr, U and Nd are 0.7, 0.3, 5×10−5 and < 8×10−3 g/m2·d respectively.