Crystallographic, thermoelectric, and mechanical properties of polycrystalline Ba8Al16Si30-based samples with type-I clathrate structure prepared by combining arc melting and spark plasma sintering methods were investigated. The major phase of the samples was a type-I clathrate with an actual Al/Si ratio of similar to 15/31, strongly suggesting that framework deficiency was absent or was present in very low concentration in the samples. The Hall carrier concentration n of the samples was approximately 1 x 10(21) cm(-3), which is lower than the values reported so far for the Ba8Al16Si30 system. Other important material parameters of the samples were as follows: the density-of-states effective mass m* = 2.3m (0), Hall mobility mu = 7.4 cm(2) V-1 s(-1), and the lattice thermal conductivity kappa (L) = 1.2 W m(-1) K-1. The thermoelectric figure of merit ZT reached approximately 0.4 (900 K) for a sample with n = 9.7 x 10(20) cm(-3). Simulation using the experimentally determined values of material parameters showed that ZT reached values > 0.5 if the carrier concentration is optimized at about 3 x 10(20) cm(-3). Young's, shear, and bulk moduli were estimated to be approximately 98, 39, and 117 GPa, respectively, and Poisson's ratio was found to be 0.25 from the longitudinal and transverse velocities of sound, v (L) = 6038 m/s and v (T) = 3503 m/s, respectively, for a sample with ZT = 0.4. The coefficient of thermal expansion (CTE) ranged from approximately 8 x 10(-6) K-1 to 10 x 10(-6) K-1 (330-690 K), which is smaller than the values reported for Ba8Ga16Ge30 and Sr8Ga16Ge30 clathrates.