Wischers, G. “Initial Calculation of the Compression Strength of Concrete from the Compression Strength of Normalized Cement Mortar, According to DIN 1 164 E (ISO Test Method)”. Materiales De Construcción, vol. 20, no. 137, Mar. 1970, pp. 88-92, doi:10.3989/mc.1970.v20.i137.1570.