Concrete vs. Magnesium AZ91D

Compare Concrete vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

Mechanical	Concrete	Magnesium AZ91D
Yield strength	none (brittle)	150MPa1
Ultimate tensile strength	not sourced	230MPa1
Compressive strength	27.6MPa2	not sourced
Elongation at break	none (brittle)	3%1
Young's modulus (stiffness)	design value25.1GPa3	45GPa1
Density	2,240–2,400kg/m³4	1,810kg/m³1
Strength to weight	not sourced	82.9kN·m/kg
Stiffness to weight	10.8MN·m/kg	24.9MN·m/kg2.3x higher
Poisson's ratio	0.15–0.25	base material0.356
Shear modulus	10.7GPa	16.7GPa1.56x stiffer in shear
Bulk modulus	12.9GPa	50GPa3.88x higher
Speed of sound	3,289m/s	4,986m/s1.52x faster

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Concrete	Magnesium AZ91D
Thermal conductivity	0.9W/m·K7	72W/m·K180x more heat through a fin
Thermal expansion	8–12µm/m·K8	25µm/m·K1
100 mm part over a 50 °C swing	50µm growth2.5x less	125µm growth
Specific heat	900J/kg·K9	1,050J/kg·K117% higher
Heats up and cools (diffusivity)	0.431mm²/s	37.9mm²/s87.9x faster
Thermal shock resistance	not sourced	6,240W/m
Melting point	not sourced	melting range470–595°C1
Max service temperature	65°C5	not sourced

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources9 documents: Magnesium Elektron, National Ready Mixed Concrete Association, Federal Highway Administration, Oak Ridge National Laboratory, U.S. Department of Defense, USDA Forest Products Laboratory, National Institute of Standards and Technology

Concrete: Normal-weight portland cement concrete, strength class f'c = 4000 psi (28 MPa) per NRMCA CIP 35; density NRMCA CIP 36; thermal conductivity USDA FPL Wood Handbook; service temperature ORNL/NRC review
Magnesium AZ91D: ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.

1
Elektron Die Casting Alloys (Datasheet 475)Magnesium Elektronarchived copyMagnesium AZ91D · Yield strength: typical, 0.2% tensile yield, ambient temperatureMagnesium AZ91D · Ultimate tensile strength: typical, ambient temperatureMagnesium AZ91D · Elongation at break: typical, ambient temperatureMagnesium AZ91D · Young's modulus (stiffness): typicalMagnesium AZ91D · Density: typicalMagnesium AZ91D · Thermal conductivity: typicalMagnesium AZ91D · Thermal expansion: typical, temperature range not statedMagnesium AZ91D · Specific heat: typicalMagnesium AZ91D · Melting point: melting range
2
CIP 35: Testing Compressive Strength of ConcreteNational Ready Mixed Concrete Associationarchived copyConcrete · Compressive strength: specified compressive strength class (f'c), not a measured typical
3
LRFD Steel Girder Superstructure Bridge Design Example, Design Step 2: Concrete Deck DesignFederal Highway AdministrationConcrete · Young's modulus (stiffness): design value: AASHTO LRFD 5.4.2.4 applied by FHWA to f'c = 4.0 ksi normal-weight concrete
4
CIP 36: Structural Lightweight ConcreteNational Ready Mixed Concrete Associationarchived copyConcrete · Density: range for normalweight concrete
5
The Effect of Elevated Temperature on Concrete Materials and Structures: A Literature Review (ORNL/TM-2005/553)Oak Ridge National Laboratoryarchived copyConcrete · Poisson's ratio: general range at normal ambient conditions (overall 0.11-0.32)Concrete · Max service temperature: code long-term temperature limit (ASME Code, concrete containments)
6
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseMagnesium AZ91D · Poisson's ratio: base material: AZ91C casting (MIL-HDBK-5J handbook physical constant)
7
Wood Handbook (FPL-GTR-282), Chapter 4: Moisture Relations and Physical Properties of WoodUSDA Forest Products LaboratoryConcrete · Thermal conductivity: typical (comparative value)
8
Thermal Coefficient of Portland Cement ConcreteFederal Highway AdministrationConcrete · Thermal expansion: typical range for portland cement concrete (aggregate dependent)
9
Best Practice Guidelines for Structural Fire Resistance Design of Concrete and Steel Buildings (TN 1681)National Institute of Standards and Technologyarchived copyConcrete · Specific heat: typical (NIST guidance for thermal analysis)

Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Mechanical

Which is lighter, Concrete or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,320 kg/m³ for Concrete.

Which is stiffer, Concrete or Magnesium AZ91D?

Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 25.1 GPa for Concrete, so the same part in Magnesium AZ91D deflects less under the same load.

Which is lighter for the same job, Concrete or Magnesium AZ91D?

For the same stiffness or strength: Magnesium AZ91D is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate.

Part that must be	Concrete	Magnesium AZ91D
Stiff rod or tie (tension)	2.3x heavier	lighter
Stiff beam (bending)	1.72x heavier	lighter
Stiff panel or plate	1.56x heavier	lighter

For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).

Thermal

Which conducts heat better, Concrete or Magnesium AZ91D?

Magnesium AZ91D conducts heat better: 72 W/m·K against 0.9 W/m·K for Concrete.

Which expands less with temperature?

Concrete expands less: 10 µm/m·K against 25 µm/m·K for Magnesium AZ91D.