[en] High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The low frequency specifications required for heavy-ion acceleration typically result in large dimensions of the structure. By appropriate choice of the resonant structure for the Rare Isotope Accelerator (RIA) driver RFQ we have achieved moderate transverse dimensions of the cavity and high quality accelerating-focusing fields required for simultaneous acceleration of multiple-charge-state ion beams. In our application the RFQ must provide stable operation over a wide range of RF power levels to allow acceleration of masses from protons up to uranium. To demonstrate the technology and high-power operation we have built an engineering prototype of one-segment of the 57-MHz RFQ structure. The RFQ is designed as a 100% OFE copper structure and fabricated with a two-step furnace brazing process. The errors in the tip-to-tip distances of the vanes average less than 50 microns. The RF measurements show excellent electrical properties of the resonator with a measured intrinsic Q equal to 94% of the simulated value. In this paper we report final results of high-power tests.