The disc-bending point load test for the early strength of hardened cement paste

A circular disc specimen of finite thickness is freely bottom-supported by a tube that has diameter less than the disc diameter. The specimen is subjected to bending stresses by applying a concentrated load to the centre of its top surface, and the load is increased gradually until the disc fails. A theoretical basis for using this loading configuration as a strength test is derived. This so-called disc-bending point load test is used in this paper for testing the strength of API Class G hardened cement paste specimens of various curing ages. The measured disc-bending point load strength index (I_db) is used for computing the rupture moduli of the test specimens, and for estimating their compressive strengths. The test results are compared with data from conventional strength tests such as the uniaxial compression test, as well as the diametral and axial point load strength tests. Correlations between I_db and uniaxial compressive strength are shown for disc specimens of various thicknesses, and the effect of indentor penetration and disc thickness is investigated.