Q. Indirect tensile strength in water-retaining structures ?
Crack width formation is dependent on the early tensile strength of concrete. Principle of critical steel ratio also applies in this situation. Amount of reinforcement essential to control early thermal and shrinkage movement is determined by the capability of reinforcement to induce cracks on concrete structures. If an upper limit is set on early tensile strength of immature concrete, then a range of tiny cracks will be formed by failing in concrete tension. Though if the strength of reinforcement is lower than immature concrete then the subsequent yielding of reinforcement will generated isolated and wide cracks that are undesirable for water-retaining structures. Thus in order to control the formation of such wide crack widths, concrete mix is specified to have a tensile strength (generally measured by Brazilian test) at 7 days not exceeding a certain value (e.g. 2.8N/mm2 for potable water).