Testing - Concrete Mix Design, Quality Control and Specification - page 145

Table 7.1 Cube and cylinder strength conversion

Compressive strength at 28 days MPa (N/mm)
Cylinders (150 mm dia. × 300 mm)

Concrete grade Cubes (150 mm × 150 mm)

C 2/2.5 2 2.5

C 4/5 4 5

C 6/7.5 6 7.5

C 8/10 8 10

C 10/12.5 10 12.5

C 12/15 12 15

C 16/20 16 20

C 20/25 20 25

C 25/30 25 30

C 30/35 30 35

C 35/40 35 40

C 40/45 40 45

C 45/50 45 50

C 50/55 50 55

7.4 MATURITY/EQUIVALENT AGE CONCEPT

Concrete gains strength with age. It also gains strength more rapidly the
higher the temperature. It is desirable to establish a relationship between
strength, time, and temperature so that the strength of a particular concrete
after any particular time and temperature cycle can be established from
a knowledge of its strength after any other time and temperature cycle.
There have been two attempts to achieve this and both are detailed in
ASTM C 1074. Although the two terms maturity and equivalent age are
sometimes used in a qualitative way as interchangeable, they each have a
precise meaning in numerical terms.

Maturity is the age of a particular concrete expressed as degree hours,
that is, as the area under a temperature-time graph.
Equivalent age is the age at which a particular concrete would have
developed its current strength if maintained at a nominated standard
temperature.

Both of these definitions are incomplete in that the base temperature in the
case of maturity, and the standard temperature and an “activation energy”
in the case of equivalent age remain to be nominated.
The maturity (or TTF, time temperature function) concept was developed
in the United Kingdom in the 1950s and is generally attributed to Saul
(1951) or Nurse (1949). The base temperature should theoretically be that