There are three important definitions about strength  Cubic compressive strength of concrete  Assurance factor of concrete  Standard cubic compressive strength of concrete §4.4.3 Definition of strength

The compressive strength of 150  150  150mm cube cured in standard age of 28days. Tep=20 ℃ ±3 ℃， RH ﹥ 90% cured in standard condition Instruments of strength test are shown in Fig Cubic compressive strength of concrete － f cu

Fig Instruments of strength test

Assurance factor of concrete-P% Assurance factor of concrete-P% refers to the probability of the strength beyond the designed strength in strength ensemble. Fig Sketch Map of Assurance Factor of Concrete -P% P （ t ）＝ 90% t 0t ψ(l)

Standard cubic compressive strength of concrete refers to cubic compressive strength of concrete with 95% assurance factor. f cu P=95% f cu,k Standard cubic compressive strength f cu,k of concrete － f cu,k

f cu,k is the strength to design structures f cu,k is used in quality control f cu,k is used in engineering acceptance check For example ≥1.15 fcu,k, f cu,min ≥0.95 fcu,k is average value of strength Notes Standard cubic compressive strength f cu,k of concrete － f cu,k