Materials: Properties, Standards, and Practical Selection
Material choices drive durability, compliance, and cost. In Australia, most structural and building materials are governed by well-defined standards and climate-specific practices.
1. Concrete (AS 3600)
Concrete offers compressive strength, durability, and versatility.
- Strength Grades: Common grades range from N20–N40 for residential/commercial slabs and beams; higher grades for transfer elements.
- Reinforcement: AS/NZS 4671 governs reinforcing steel. Maintain specified cover to reinforcement (AS 3600) for durability, especially in coastal zones.
- Workability: Slump affects placement and finish; match mix design to pumpability and finish requirements.
- Curing: Proper curing (7 days typical) reduces shrinkage and increases strength. Neglecting curing is a common cause of surface dusting and cracking.
- Joints: Control joints manage shrinkage; construction joints need proper dowels/ties and preparation for shear transfer.
2. Reinforcing & Prestressing
Rebar types include plain and deformed bars; mesh is used for slabs. Post-tensioning uses high-strength tendons to compress slabs, enabling longer spans and thinner sections—never cut or drill without scanning.
3. Structural Steel (AS 4100)
Steel provides high strength-to-weight and speed of erection.
- Sections: UB, UC, PFC, RHS/SHS. Select based on bending, axial, and torsion demands.
- Corrosion Protection: Hot-dip galvanizing (AS/NZS 4680) or paint systems per AS/NZS 2312.2. Coastal and industrial environments demand higher durability categories.
- Connections: Bolted vs welded—bolting offers speed and site flexibility; welding needs qualified procedures and inspection.
- Fire: Intumescent coatings or boxing for FRL requirements in commercial buildings.
4. Timber (AS 1684 residential framing)
Timber remains common due to availability, ease of use, and thermal performance.
- Grades: MGP10/12 pine for framing; LVL/GLULAM for long spans and lintels.
- Movement: Timber is hygroscopic—allow for shrinkage/swelling; detail control joints and tolerances.
- Termite Management: AS 3660 requires barriers or treated framing in termite-prone areas. Coordinate penetrations to maintain barrier integrity.
- BAL (Bushfire): AS 3959 defines material and detailing restrictions by BAL level. Use compliant species/finishes and ember-protective detailing.
5. Masonry (AS 3700)
Clay and concrete masonry deliver robustness and thermal mass.
- Cavity Masonry: Maintain the cavity as a drainage plane with clean-out, ties, and weep holes at compliant spacing.
- Mortar: Mix design affects bond and durability. Control joints manage shrinkage and thermal movement.
- Structural: Reinforced blockwork is common for retaining and shear walls; coordinate reinforcement, grout pours, and inspection.
6. Membranes & Waterproofing
Waterproofing failures are among the most common defect sources.
- Wet Areas: AS 3740 sets requirements for showers, bathrooms, laundries.
- External: AS 4654.2 governs membranes on roofs/terraces; ensure falls to drains and correct termination at thresholds.
7. Thermal & Acoustic Performance
Insulation and building wraps influence comfort and energy use.
- Insulation: Choose R-values appropriate to climate zone; fit without gaps and compressions.
- Sarking/Wraps: Provide water and air control; tape laps and seal penetrations for airtightness.
- Acoustics: Consider RW/STC ratings for party walls and floors; resilient mounts and sealing are critical.
8. Fire Resistance Levels (FRL)
FRL notation (e.g., 90/60/30) reflects structural adequacy / integrity / insulation. Select materials and assemblies tested to AS 1530.4 and detailed per manufacturer instructions.
Selection Guidance
- Coastal Projects: Prioritise corrosion resistance (galvanizing, marine-grade fixings, increased cover to reinforcement).
- BAL-rated Sites: Use compliant claddings, decking, and ember protection strategies.
- Termite Regions: Design continuous barriers and coordinate services penetrations to maintain protection.