C12/15 vs C25/30

C25/30 is 1.1 times as stiff as C12/15. Their densities are about the same. Per unit mass C25/30 is 1.1 times as stiff. Strength: f_ck = 12 MPa for C12/15, f_ck = 25 MPa for C25/30.

C12/15 EN 1992-1-1 C25/30 EN 1992-1-1

Side by side

ratio = C25/30 / C12/15 · log scale

Property	C12/15	C25/30	Unit	Ratio
E Young's modulus	27	31	GPa	1.15×
G Shear modulus	11.25	12.92	GPa	1.15×
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	25	MPa	2.08×
f_ck,cube Characteristic cube strength	15	30	MPa	2×
f_cm Mean cylinder strength	20	33	MPa	1.65×
f_ctm Mean tensile strength	1.6	2.6	MPa	1.62×
f_ctk,0.05 Tensile strength, 5 % fractile	1.1	1.8	MPa	1.64×
f_ctk,0.95 Tensile strength, 95 % fractile	2	3.3	MPa	1.65×
ε_c1 Strain at peak stress	1.8	2.1	‰	1.17×
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	12.67	MJ/kg	1.15×
c₀ Bar wave speed √(E/ρ) · derived	3322	3559	m/s	1.07×
f/ρ Specific strength f/ρ · derived	4.903	10.22	kJ/kg	2.08×

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.