mineral / Cementitious / Concrete Masonry Unit
Interlocking concrete block, 390x190x190mm (190mm wall thickness)
Mortarless interlocking 390x190x190 mm CMU system. Minimum compressive strength 10–20 MPa, dry density >1800 kg/m³, FRL up to 180/180/180 (grouted system). Faster installation than mortared blockwork; reduced skill requirement; approximately $4–8 per block ($40–90/m² supply) with lower labour costs than conventional CMU.
Atlas code
MIN-CEM-CMU-006
At-a-glance signals
Mortarless interlocking 390x190x190 mm CMU system. Minimum compressive strength 10–20 MPa, dry density >1800 kg/m³, FRL up to 180/180/180 (grouted system). Faster installation than mortared blockwork; reduced skill requirement; approximately $4–8 per block ($40–90/m² supply) with lower labour costs than conventional CMU.
Overview
Executive summary
Interlocking dry-stack concrete masonry units (CMU) use a mechanical tongue-and-groove or surface-key interlock that aligns courses without conventional 10 mm mortar beds above the first course. The standard unit is nominally 390 x 190 x 190 mm (work size), corresponding to a face dimension of 400 x 200 mm on a 10 mm module. Matching half, end, corner and lintel units complete the system. Manufactured to AS/NZS 4455.1 and tested to AS/NZS 4456, the block achieves a minimum unit compressive strength of 10–20 MPa and a dry density above 1800 kg/m³. Australian suppliers include Adbri Masonry (Versaloc 200 series) and Austral Masonry. The system suits retaining walls, loadbearing residential walling, boundary walls, garden structures and fire pits. Cores may be grouted and reinforced to AS 3700 for structural applications.
Best when…
- Mortarless dry-stack above first course — eliminates mortar mixing, reduces waste and speeds construction by 30–50 % compared with conventional CMU.
- Reduced skill requirement: semi-skilled crew can achieve acceptable alignment and plumb without experienced blocklayers.
- Self-aligning tongue-and-groove profile reduces the risk of course creep and provides consistent joint geometry.
- Minimum unit compressive strength 10–20 MPa (system dependent); grouted system characteristic compressive strength 10.2 MPa per AS 3700.
- FRL up to 180/180/180 (fully grouted system); integrity/insulation up to 240 min when fully corefilled.
- High thermal mass (190 mm grouted wall ~350 kg/m²) supports passive solar design and reduces peak cooling loads.
- Acoustic performance Rw 56+ suitable for party walls and boundary applications.
- Non-combustible, inert — zero VOC, no off-gassing in service.
- Long service life (50–100+ years) with minimal maintenance.
- Readily available from national suppliers (Adbri, Austral Masonry); supply lead time 1–2 weeks.
Top advantages
- 01 Mortarless dry-stack above first course — eliminates mortar mixing, reduces waste and speeds construction by 30–50 % compared with conventional CMU.
- 02 Reduced skill requirement: semi-skilled crew can achieve acceptable alignment and plumb without experienced blocklayers.
- 03 Self-aligning tongue-and-groove profile reduces the risk of course creep and provides consistent joint geometry.
- 04 Minimum unit compressive strength 10–20 MPa (system dependent); grouted system characteristic compressive strength 10.2 MPa per AS 3700.
- 05 FRL up to 180/180/180 (fully grouted system); integrity/insulation up to 240 min when fully corefilled.
Top limitations
- 01 First course must be set in levelling screed or mortar to establish true datum — any error propagates through all courses.
- 02 Dimensional tolerance ±2 mm means minor face misalignment between courses; not suitable where flush fair-face finish is critical without grinding.
- 03 Core percentage >30 % reduces net section area; grouting is required for all structural and fire-rated applications.
- 04 FRL structural adequacy data is system-specific — consult manufacturer's Fire and Sound brochure; generic values do not apply.
- 05 Heavier individual unit (~15.6 kg) than lightweight CMU alternatives; manual handling limits productivity for single-person crews.
Technical
Physical ·9
- Density
- >1800 kg/m3 Versaloc 200 series datasheet lists dry density >1800 kg/m³. Normal-weight concrete aggregate; typical range 2000–2200 kg/m³ for solid concrete; effective wall density lower due to >30 % core voids. Grouted 190 mm wall approximately 1900–2050 kg/m³ equivalent.
- Specific gravity
- 2.0–2.2 (solid material) Normal-weight concrete: specific gravity approximately 2.0–2.2. Block web material specific gravity ~2.0–2.2; effective specific gravity of hollow block (including voids) is lower, approximately 1.3–1.6.
- Porosity
- 12–18 % Normal-weight concrete CMU: total porosity approximately 10–18 % by volume in the block web material. Core voids >30 % of gross block volume per AS/NZS 4456. Capillary porosity of the concrete matrix is lower than lightweight CMU, typically 12–16 %.
- Water absorption
- 6–10 % AS/NZS 4456.14 absorption test: typical CMU 5–12 % by mass. Interlocking CMU manufactured to AS/NZS 4455.1 must meet absorption limits specified in the standard. Versaloc series: not published in available data sheets; typical for normal-weight CMU is 6–10 %. Lower absorption than lightweight CMU improves durability in exposed applications.
- Hardness
- 5–7 Mohs Hardened concrete surface: approximately 5–7 on the Mohs scale. Aggregate particles (quartz, basalt) dominate surface hardness. Not a standard specification parameter for CMU.
- UV resistance
- Excellent Excellent UV resistance — Portland cement binder and mineral aggregate are inherently UV-stable. Colour pigments may fade slightly over decades in direct UV exposure but structural integrity is unaffected. No protective coating required for UV resistance.
- Chemical resistance
- Good (alkali/water); Moderate (mild acid); Poor (strong acid, sulfate soils) Good resistance to dilute alkalis, sea water and carbonation. Moderate resistance to dilute acid (pH > 5). Susceptible to sulfate attack in soils with high sulfate content (Type SR or SL cement required per AS 3600). Resistant to most common construction chemicals. Calcium chloride deicing salts can accelerate reinforcement corrosion if grout cover is inadequate.
- pH tolerance
- 6–14 (service); pH 12.5–13.5 fresh pH Fresh concrete pore water pH approximately 12.5–13.5 (highly alkaline). Carbonation reduces surface pH over decades. The material is resistant to mild acids above pH 6 and is stable in alkaline environments. Not suitable for prolonged exposure to pH < 4 (acid soils, chemical splash) without protective coating.
- Surface roughness
- 50–200 um As-manufactured face: medium-rough texture from steel mould, Ra approximately 50–200 µm depending on aggregate size. The interlocking surfaces (tongues and keys) have tighter tolerance faces. Visible aggregate size 5–10 mm gives a characteristic textured appearance.
Mechanical ·7
- Tensile strength
- 0.1–0.3 (unreinforced); reinforcement required for tensile loads MPa Concrete masonry in direct tension: approximately 0.1–0.3 MPa (characteristic flexural tensile strength per AS 3700 Table 3.1: f'mt = 0.2 MPa for hollow block, 0.36 MPa for grouted). Reinforcement must be provided for any tensile load path. Dry-stack joints have negligible tensile capacity perpendicular to bed joint without grout.
- Compressive strength
- 10–20 MPa AS/NZS 4455.1 specifies minimum unit compressive strength. Versaloc 200 series: characteristic unconfined compressive strength of unit 20 MPa; characteristic compressive strength of grouted masonry 10.2 MPa. Generic interlocking CMU to AS/NZS 4455.1 Class 2: minimum 10 MPa. Class 3: minimum 15 MPa. Design compressive strength of masonry wall (f'm) per AS 3700 Table 3.1.
- Flexural strength
- 0.20–0.36 MPa Characteristic flexural tensile strength of masonry (AS 3700 Table 3.1): f'mt = 0.20 MPa (hollow ungrouted) to 0.36 MPa (fully grouted). Flexural capacity of wall section depends on reinforcement and core fill. Slender walls (H/t > 30) require engineering design for lateral loads including wind per AS 4055 and seismic per AS 1170.4.
- Shear strength
- 0.05–0.15 (ungrouted dry-stack); 0.3–0.6 (grouted reinforced) MPa Ungrouted dry-stack masonry: shear resistance limited by interlocking key geometry; characteristic shear strength of dry-stack joint approximately 0.05–0.15 MPa. Grouted and reinforced masonry: characteristic shear strength of wall section per AS 3700 Clause 8, typically 0.3–0.6 MPa for standard grout and reinforcement. Consult engineer for specific design values.
- Poisson's ratio
- 0.15–0.20 Normal-weight concrete masonry: Poisson's ratio approximately 0.15–0.20. AS 3700 does not prescribe a standard value for masonry; 0.20 is commonly used in finite-element analysis of masonry walls.
- Impact resistance
- Good (low-velocity); Moderate (hard-point impact — face spalling) Normal-weight concrete masonry has high resistance to low-velocity impact (vehicle bollard, garden edging). Face spalling can occur under hard point impact. High-impact applications (vehicle barrier, security wall) require reinforced and grouted system with engineering design. Resistance is superior to lightweight CMU and brick.
- Creep resistance
- Good — low creep at service loads Concrete masonry exhibits low long-term creep under sustained compressive load. Creep coefficient for normal-weight concrete masonry approximately 1.0–2.0 (ratio of creep to elastic strain). Negligible creep at service stress levels typical in residential construction. AS 3700 Section 5 accounts for long-term effects.
Sustainability & Health
Embodied carbon & energy ·7
- Embodied carbon
- 160 kgCO2e/m² Embodied carbon of concrete masonry: approximately 100–180 kg CO₂e/m² for a 190 mm wall including block manufacture, mortar (first course) and grout. Per-block embodied carbon approximately 8–12 kg CO₂e (Adbri EPD data). The primary driver is Portland cement clinker (clinker factor ~0.85 for standard GP cement). SCM (fly ash, slag) substitution reduces embodied carbon by 20–40 %. Green Star Materials Reduction credit available. Interlocking system reduces mortar use by ~95 % compared with conventional CMU, saving approximately 5–10 kg CO₂e/m². Per m² of 190mm interlocking concrete block wall (includes block manufacture and mortar/grout).
- Carbon footprint
- 32 Carbon footprint per m² of 190 mm wall (block manufacture + transport 50 km + first-course mortar): approximately 28–36 kg CO₂e. Reduction strategies: specify GP cement with >30 % fly ash or slag substitution (saves ~10 kg CO₂e/m²); source from local manufacturer (saves transport emissions); specify block grout with SCM content.
- Embodied energy
- 1.1 MJ/kg Embodied energy (cradle-to-gate): approximately 1.0–1.3 GJ/tonne for normal-weight concrete CMU per AusLCI database. Per block (approximately 15.6 kg): 15.6–20 MJ. Per m² of 190 mm wall: approximately 220–280 MJ.
- Water footprint
- 180 L/kg Manufacturing water consumption: approximately 150–200 litres per tonne of concrete masonry including mixing water, curing and plant wash. Per block: approximately 2–3 litres embedded water. Mortarless dry-stack system saves approximately 0.5–1 L/m² of construction water compared with conventional CMU (mortar mixing water eliminated above first course).
- Recycled content
- 15 % Recycled content: some manufacturers incorporate up to 15–20 % recycled aggregate (crushed concrete, recycled glass sand) in CMU production. Adbri states some products include recycled content. Standard grey blocks: typically 10–15 % recycled aggregate by mass. Certification varies — verify with supplier EPD.
- Renewable content
- 0 % No renewable content. Aggregates are virgin quarried materials (limestone, basalt, granite); cement is manufactured from calcined limestone. No biomass or bio-based content.
- Circular score
- 7.5
Compliance & Fire
Fire performance ·5
- Combustibility class
- Non-combustible (AS 1530.1) Non-combustible per AS 1530.1 (non-combustibility test). NCC classification: non-combustible building material. No ignitability, heat release or smoke development in fire. Meets NCC Volume One CP8 structural adequacy through prescribed FRL.
- Fire resistance level
- FRL 180/180/180 (grouted 190 mm system); up to 240/240/240 fully corefilled minutes Versaloc 200 series (190 mm grouted): FRL 180/180/180 (structural adequacy/integrity/insulation) per AS 1530.4. Fully corefilled 200 mm wall: integrity and insulation 240 minutes. Structural adequacy and Rw + Ctr refer to manufacturer's Fire and Sound brochure for full system ratings. AS 3700 Table 4 prescribes FRL for various wall configurations. For NCC Section C fire compartment walls, FRL is selected to match required fire resistance level of building element.
- Flame spread index
- 0 Flame spread index = 0 per AS 1530.3. Non-combustible mineral material — no flame spread. Complies with NCC Specification C1.10 non-combustible material requirements without restriction.
- Smoke dev. index
- 0 Smoke development index = 0 per AS 1530.3. No smoke production from concrete masonry. Compliant with NCC Specification C1.10 without restriction.
- Heat release rate
- 0 kW/m2 Zero heat release rate — concrete masonry contributes no fuel to a fire. Classified as Group 1 (non-combustible) material under NCC. CSIRO cone calorimeter test not applicable to inorganic masonry.
Cost & Lifecycle
Capex & lead time ·6
- Material cost (range)
- $4–8 AUD per block Supply cost per block (390x190x190 mm standard unit) ex-distributor yard, 2024–2025 Australian market. Lower end: standard grey CMU, volume order. Upper end: coloured or textured units, small order. Excludes GST. Corner, half and lintel units approximately 20–40 % premium.
- Material cost (per unit)
- $40–100 AUD/m2 (supply only) Material supply cost per m² of wall face at 12.5 blocks/m² (Versaloc 200 series yield). Range: $4/block × 12.5 = $50/m² (budget grey) to $8/block × 12.5 = $100/m². Excludes grout, reinforcement, first-course mortar, accessories. Savings vs conventional CMU are on labour, not materials.
- Lead time
- 1–2 weeks (standard); 2–3 weeks (regional or specialty) Standard Versaloc 200 series or equivalent stocked by Adbri and Austral Masonry distributors in most Australian capital cities. Regional locations: 2–3 weeks. Specialty colours or units (corner, half, lintel): 2–3 weeks.
- Lifecycle cost
- $350–500 AUD/m2 (50-year LCC) 50-year life cycle cost including supply, installation, minor maintenance (sealing, repointing of first course mortar, painting if specified) and a 20 % end-of-life credit for crushed aggregate recycling. Lower than conventional CMU due to labour saving. Excludes structural grouting and reinforcement costs.
- Annual maintenance
- $0.30–1.00 AUD/m2/year Concrete masonry requires minimal ongoing maintenance. Unsealed exposed face: negligible annual cost (periodic inspection). Painted surface: repainting every 10–15 years at $8–15/m² amortised = $0.60–1.50/m²/year. Sealing with penetrating silane/siloxane: approximately $3–6/m² every 10 years = $0.30–0.60/m²/year. First-course mortar joint repointing: once in 30+ years.
- Market availability
- moderate–good (major cities); moderate (regional) Stocked by major masonry suppliers (Adbri, Austral Masonry, PGH, various independents) in VIC, NSW, QLD, SA, WA. Not available from all builders' merchants — specialist masonry supplier usually required. Regional availability moderate; interlocking system units less common than standard CMU outside capitals.
Service life & durability ·3
- Expected lifespan
- 100
- Maintenance interval
- 10
- Warranty period
- 10
Layer D
Where it's used
Residential loadbearing walls
Retaining walls
Boundary and acoustic walls
Garden walls and raised beds
Steps and stair cheek walls
Fire pits and outdoor fireplaces
Commercial and industrial walling