mineral / Cementitious / Concrete
Structural Concrete Slab
Standard reinforced concrete floor and roof slab, 100–250 mm thick, 20–50 MPa characteristic strength — the single most widely used structural element in Australian construction, compliant with AS 3600 and NCC Volume One.
Atlas code
MIN-CEM-CC-004
At-a-glance signals
Standard reinforced concrete floor and roof slab, 100–250 mm thick, 20–50 MPa characteristic strength — the single most widely used structural element in Australian construction, compliant with AS 3600 and NCC Volume One.
Overview
Executive summary
Structural concrete slabs are the most ubiquitous load-bearing elements in Australian construction, forming the floors and roofs of virtually every multi-storey building, carpark, warehouse, and residential project in the country. Composed of Portland cement (or blended cement incorporating supplementary cementitious materials such as fly ash or ground granulated blast-furnace slag), fine and coarse aggregate, water, and chemical admixtures, the matrix is reinforced with deformed steel bar to AS/NZS 4671 or welded wire mesh to AS/NZS 4671. Slab thicknesses of 100–250 mm correspond to concrete grades N20 through N50 (20–50 MPa characteristic compressive strength at 28 days), with the reinforcement ratio and cover designed to AS 3600 exposure class requirements. Formwork to AS 3610 supports fresh concrete during placement and the critical early curing period. Concrete is delivered by agitator truck, pumped or conveyed to location, vibrated to consolidate around reinforcement, screeded level, finished as required (float, trowel, broom, or exposed aggregate), then moisture-cured for a minimum of 7 days. Full design strength develops at 28 days; structural stripping of soffit formwork typically occurs at 14–21 days depending on strength testing. In the Australian context, slabs must satisfy AS 3600 detailing for the applicable exposure class (A1 through U), fire resistance level, and deflection limits, with particular attention to long-term creep and shrinkage movements in the variable humidity conditions found from tropical Queensland to alpine Victoria.
Best when…
- Exceptional compressive strength: 20–50 MPa providing load-carrying capacity for any building type
- Excellent fire resistance: non-combustible, FRL up to -/240/240 achievable per AS 3600 Table 5.3.2 at 200 mm
- High thermal mass: 2,400 kg/m³ × 840 J/kg·K reduces diurnal temperature swing by 8–12°C in Australian climates
- Long service life: 50–100+ years per AS 3600 design life with appropriate exposure class selection
- Unlimited span adaptability: one-way, two-way, flat plate, post-tensioned and banded configurations to 15 m span
- Readily available: all capital cities and most regional centres have multiple ready-mix suppliers within 45 min haul
- Universal compatibility: all finishes applicable — tiles, carpet, polished concrete, coatings, raised floor, screed
- 100% recyclable: crushed concrete aggregate (CCA) suitable for sub-base, drainage layers and new concrete (≤30% replacement)
- Reduced storey heights vs. beam-and-slab: flat plate construction saves 200–400 mm per floor in high-rise
- Cost certainty: competitive tendering environment and standardised mix designs give reliable AUD 200–350/m³ supply pricing
Top advantages
- 01 Exceptional compressive strength: 20–50 MPa providing load-carrying capacity for any building type
- 02 Excellent fire resistance: non-combustible, FRL up to -/240/240 achievable per AS 3600 Table 5.3.2 at 200 mm
- 03 High thermal mass: 2,400 kg/m³ × 840 J/kg·K reduces diurnal temperature swing by 8–12°C in Australian climates
- 04 Long service life: 50–100+ years per AS 3600 design life with appropriate exposure class selection
- 05 Unlimited span adaptability: one-way, two-way, flat plate, post-tensioned and banded configurations to 15 m span
Top limitations
- 01 High embodied carbon: 0.10–0.18 kgCO₂e/kg, or ~240–430 kgCO₂e/m³ for a 200 mm slab
- 02 Long curing cycle: 28 days to design strength; soffit formwork cannot strip before ~14–21 days
- 03 Heavy self-weight (2,400 kg/m³) increases foundation and column loads significantly
- 04 Shrinkage cracking: drying shrinkage 400–800 microstrain requires control joints every 4–6 m
- 05 Skilled formwork and concrete placement crews required; defects difficult to remediate once set
Technical
Physical ·9
- Density
- 2400 kg/m3 AS 3600 Clause 3.1.3 — normal-weight concrete design assumption.
- Specific gravity
- 2.4 Derived from density 2400 kg/m³.
- Porosity
- 8-14 % Well-compacted structural concrete; lower bound with w/c ≤ 0.45.
- Water absorption
- 3-6 % AS 1012.21 — typical range for structural concrete w/c 0.40–0.55.
- Hardness
- 5-7 Mohs Hardened cement paste and aggregate surface hardness approximately 5–7 Mohs.
- UV resistance
- excellent No UV degradation of hardened concrete matrix; surface carbonation minor long-term effect.
- Chemical resistance
- good Good resistance to neutral and alkaline solutions; moderate to dilute acids; poor to sulphates without sulphate-resisting cement.
- pH tolerance
- 12.5-13.5 pH Fresh concrete pore solution pH 12.5–13.5; drops with carbonation over time.
- Surface roughness
- 5-200 μm As-struck formwork finish; power-trowelled finish 2–5 μm; broom finish 50–200 μm.
Mechanical ·7
- Tensile strength
- 2.2-4.2 MPa AS 3600 Clause 3.1.1.3 — characteristic flexural tensile strength f'ctf = 0.60√f'c.
- Compressive strength
- 20-50 MPa Characteristic compressive strength f'c per AS 1012.9 — 28-day cylinder test.
- Flexural strength
- 2.7-5.1 MPa Flexural tensile strength per AS 3600; increases with concrete grade.
- Shear strength
- 0.8-3.5 MPa Punching and beam shear capacity per AS 3600; unreinforced section ~0.17√f'c.
- Poisson's ratio
- 0.2 AS 3600 Clause 3.1.5.
- Impact resistance
- moderate Moderate impact resistance; brittle fracture mode without fibre reinforcement.
- Creep resistance
- moderate Long-term creep coefficient φcc = 1.5–3.0 per AS 3600 Clause 3.1.8; critical for deflection design.
Sustainability & Health
Embodied carbon & energy ·7
- Embodied carbon
- 0.10-0.18 kgCO₂e/kg Typical range per CCAA and EPD Australasia data 2022–2024. OPC-dominant mix (N32): ~0.18 kgCO₂e/kg. 30% fly ash blend (N32ECOPact): ~0.13 kgCO₂e/kg. 50% GGBFS blend: ~0.10 kgCO₂e/kg. Per m³ at 2400 kg/m³: 240–430 kgCO₂e/m³.
- Carbon footprint
- 36-80 kgCO₂e/m² Carbon footprint for 150 mm slab (360 kg/m²): OPC mix ~65 kgCO₂e/m²; high-SCM mix ~36 kgCO₂e/m².
- Embodied energy
- 0.8-1.5 MJ/kg Primary energy demand per Australian EPD data; OPC-dominant mix higher end.
- Water footprint
- 150-300 L/kg Water consumption in concrete production including curing; approximate LCA figure.
- Recycled content
- 0-50 % Standard mix: fly ash (0–30%) and GGBFS (0–50%) are industrial by-products qualifying as recycled content. Recycled concrete aggregate (RCA) can replace up to 30% coarse aggregate in non-structural slabs per AS 3600 Appendix B. High-SCM mixes readily available from all major Australian suppliers.
- Renewable content
- 0 % No renewable biological content in standard concrete.
- Circular score
- 6 /10 High recyclability (crushed as aggregate) scores well; high embodied carbon and energy in virgin production moderate the score.
Compliance & Fire
Fire performance ·6
- Combustibility class
- Non-combustible — AS 1530.1 Group 1 AS 1530.1 — confirmed non-combustible. NCC Group 1 construction material. Suitable for all building types including Type A (fire-rated) construction.
- Fire resistance level
- 60/60/60 to 240/240/240 depending on thickness and support conditions minutes AS 3600:2018 Table 5.3.2 — FRL for simply supported one-way slabs (Structural/Integrity/Insulation): 100mm = -/60/60; 150mm = -/120/120; 200mm = -/180/180; 250mm = -/240/240. Continuous or two-way slabs achieve higher FRL at same thickness. Cover to reinforcement critical variable.
- Ignition temp
- N/A °C Does not ignite. AS 1530.3 Ignitability Index = 0.
- Flame spread index
- 0 AS 1530.3 Spread of Flame Index = 0. Concrete does not support flame spread.
- Smoke dev. index
- 0 AS 1530.3 Smoke Developed Index = 0.
- Heat release rate
- 0 kW/m² AS 1530.3 Index: Heat Evolved = 0. Non-combustible material releases zero heat.
Cost & Lifecycle
Capex & lead time ·6
- Material cost (range)
- 200-350 AUD/m³ Supply only, delivered to site, Australian market 2024–2025. N25 mix AUD 200–250/m³; N32 AUD 220–280/m³; N40 AUD 250–320/m³; N50 AUD 280–350/m³. Regional premium 10–30%. Source: Holcim, Boral, Hanson published schedules.
- Material cost (per unit)
- 36-70 AUD/m² Approximate material cost per m² for 150 mm slab (0.15 m³ × AUD 240–280/m³ = AUD 36–42/m²); 200 mm = AUD 48–56/m².
- Lead time
- 1-7 days Ready-mixed concrete from metropolitan batching plants typically 24–72 hours notice; regional areas 3–7 days. Formwork procurement and set-up on critical path.
- Lifecycle cost
- 50-120 AUD/m² 50-year NPV life cycle cost for internal slab (no finishes): minimal maintenance, inspection only. External slabs or carparks: allow coatings renewal every 10–15 years.
- Annual maintenance
- 0.5-2 AUD/m²/year Internal structural slab essentially maintenance-free. Allow periodic inspection costs only; coatings on carpark decks every 10–15 years adds AUD 2–5/m²/year averaged.
- Market availability
- excellent Universally available across Australia. All capital cities and major regional centres have multiple competing suppliers. Standard mixes ex-stock; high-SCM or special mixes require 2–5 days notice.
Service life & durability ·3
- Expected lifespan
- 50-100+ years AS 3600:2018 Clause 4.2 — design service life categories; standard structures 50 years, infrastructure and significant buildings 100 years.
- Maintenance interval
- 5-10 years Routine structural inspection cycle per asset management practice; no consumable maintenance on internal slabs.
- Warranty period
- 1-2 years Defects liability period under standard Australian construction contracts (AS 4000, AS 4300).
Layer D
Where it's used
Suspended residential and apartment floors
Commercial office and retail floors
Multi-storey carpark decks
Ground-supported slab-on-ground
Industrial warehouse and logistics floor
Transfer slabs and podium structures
Roof slabs and green roof bases
Basement floors and raft foundations
Bushfire-resistant construction
Educational, health, and public buildings