C12/15 vs C20/25

C20/25 is 1.1 times as stiff as C12/15. Their densities are about the same. Per unit mass C20/25 is 1.1 times as stiff. Strength: f_ck = 12 MPa for C12/15, f_ck = 20 MPa for C20/25.

C12/15 EN 1992-1-1 C20/25 EN 1992-1-1

Side by side

ratio = C20/25 / C12/15 · log scale

Property	C12/15	C20/25	Unit	Ratio
E Young's modulus	27	30	GPa	1.11×
G Shear modulus	11.25	12.5	GPa	1.11×
ν Poisson's ratio	0.2	0.2	–	1×
ρ Density	2447	2447	kg/m³	1×
γ Weight density	24	24	kN/m³	1×
α Coefficient of thermal expansion	10	10	10⁻⁶/K	1×
f_ck Characteristic cylinder strength	12	20	MPa	1.67×
f_ck,cube Characteristic cube strength	15	25	MPa	1.67×
f_cm Mean cylinder strength	20	28	MPa	1.4×
f_ctm Mean tensile strength	1.6	2.2	MPa	1.38×
f_ctk,0.05 Tensile strength, 5 % fractile	1.1	1.5	MPa	1.36×
f_ctk,0.95 Tensile strength, 95 % fractile	2	2.9	MPa	1.45×
ε_c1 Strain at peak stress	1.8	2	‰	1.11×
ε_cu1 Ultimate strain	3.5	3.5	‰	1×
ε_c2 Strain at peak, parabola–rectangle	2	2	‰	1×
ε_cu2 Ultimate strain, parabola–rectangle	3.5	3.5	‰	1×
n Exponent, parabola–rectangle	2	2	–	1×
ε_c3 Strain at peak, bilinear	1.75	1.75	‰	1×
ε_cu3 Ultimate strain, bilinear	3.5	3.5	‰	1×
E/ρ Specific stiffness E/ρ · derived	11.03	12.26	MJ/kg	1.11×
c₀ Bar wave speed √(E/ρ) · derived	3322	3501	m/s	1.05×
f/ρ Specific strength f/ρ · derived	4.903	8.172	kJ/kg	1.67×

Values at the first thickness band or product form of each material (EN 1992-1-1; EN 1992-1-1). A minimum and a characteristic value are not the same kind of number — read the ratio as a guide. Each material's page lists every band and every source.