Synopsis Apparatus was designed for the strain measurement of unsealed cylindrical concrete specimens under transient thermal states. This subject has received in sufficient attention to date arld is of interest io prestressed concrete nuclear reactor pressure vessel and fire applications. To simplify analysis of results, the imposed conditions includean arrangement for applying constant uniaxial compressive load and an automatic temperature control system which ensures as linear a rate of heating as possible and minimizes axial temperature differentials along the specimen. A strain measuring device was designed which produced accurate results under transient thermal states.