a powered rotary screed has a plurality of interchangeable modules of different lengths so that the power screed can accommodate a range of job applications . additionally , the rotary screed comprises a centrally located expansion member that can be adjusted to cause an upper ridge member of the rotary screed to expand outward , thus raising a medial portion of the roller screeds so that they may be adjusted to maintain horizontal alignment . the screed is propelled by two drive tubes that are supported by drive modules and powered by hydraulic motors . the screed further comprises a two - section strike tube which is likewise powered by a hydraulic motor . an operator rides in an operator &# 39 ; s station and controls the speed and direction of the rotary screed .