Section Materials

Section 3 of Eurocode 2, dedicated to materials, is structured in the following paragraphs:

3.1 - Concrete

3.2 - Reinforcing steel. Annex C-EC2 is related to this paragraph

3.3 - Prestressing steel

C3.1.1 General

This section deals with normal weight concrete, viz. according to EN 206-1 having density greater than 2000 but not exceeding 2600 kg/m3. "Light-weight" concrete is dealt with in Sect.11-EC2.

C3.1.2 Strength

Compressive strength is defined in [3.1.2(1 )P-EC2], in accordance with EN 206-1, by the characteristic value fck (5% fractile of distribution) obtained through the elaboration of compression tests executed at 28 days on cylindrical specimens of diameter 150 mm and height 150 mm. As in many countries testing is carried out on 150 mm cubic specimens, EN 206-1 admits fck,cube compressive strength, too.

Compressive strength classes are denoted by letter C followed by two numbers that indicate the cylinder and cube characteristic strength, expressed in N/mm2, for example C30/37.

EC2 contemplates 14 classes: from C12/15 to C90/105.

Table [3.1-EC2] gives the numeric values of strength and deformation characteristics associated with strength classes and the analytic relationship expressing such values in function of fck. Average values of compressive strength fcm , of tensile strength fctm and of elasticity modulus Ecm are plotted in Fig. 3.1 in function of fck. Ecm is denoted by the inclination of the line secant of the a-£ relation between points a = 0 and a = 0,4-fcm as indicated in [Fig. 3.2-EC2].

Clause [3.1.2(6)-EC2] deals with the development of compressive strength with time. Formula [(3.2)-EC2] allows to calculate the average strength fcm at a time t (days) in function of the value at 28 days, which can be deduced from Table [3.1-EC2] and from the class of cement used. Cement classes conforming to EN 197 are:

- Class R (rapid hardening), including CEM 42,5R, CEM 52,5N and CEM 52,5R

- Class N (normal hardening) including CEM 42,5N and CEM 32,5R

- Class S (slow hardening) including CEM 32,5N.

Table 2.1 shows the development until 360 days of average strength fcm of concrete produced with cement from the three classes, where the compressive strength at 28 days for each class, fcm, equals 1.

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