Ready-Mix Concrete Batching, Aggregate Quarry, Sand & Gravel, Asphalt Plant and Pre-Cast Concrete HVAC Duct Guide

The respirable crystalline silica problem — start every project here

Australian aggregate quarries, ready-mix concrete batching plants, asphalt plants and pre-cast concrete factories share one occupational hazard that overshadows every other design concern: respirable crystalline silica (RCS). Safe Work Australia sets the workplace exposure standard at 0.05 mg per cubic metre as an 8-hour time-weighted average — a number that has been progressively tightened over the last decade as the silicosis disease burden in Australian quarry workers, stonemasons, batching plant operators and pre-cast finishers has become impossible for state regulators to ignore. The NSW Dust Diseases Authority register of compensable silicosis cases ran into four-digit numbers by the early 2020s and continues to grow. The iCare Dust Diseases Care scheme has paid out lifetime support to thousands of quarry, batching and pre-cast workers who developed accelerated silicosis from inadequately controlled silica dust exposure. The Australian Council of Trade Unions, the CFMEU, Master Builders Association and the Cement Concrete and Aggregates Australia have all run public campaigns on respiratory protection.

For HVAC duct engineers, this is not a peripheral compliance concern. It is the design driver. Every duct decision on these plants — fan sizing, capture velocity, hood geometry, transport velocity, filter outlet loading, operator-pulpit positive pressure differential — comes back to the RCS workplace exposure standard. If your scheme cannot demonstrate operator standby RCS exposure below 0.05 mg per cubic metre 8-hour TWA at commissioning measurement, your scheme has failed. Personal respiratory PPE is the secondary control, never the primary control. Engineering controls per AS 1668.2 mechanical ventilation and AS 3957 dust hazard standards are the primary control. Get those right and the personal monitor measurements drop below detection limits; get them wrong and the plant becomes a silicosis factory.

The other workplace exposure standards on these plants that matter for duct design are respirable inhalable dust at 10 mg per cubic metre 8-hour TWA, calcium oxide (quicklime) at 2 mg per cubic metre 8-hour TWA wherever there is lime calcination or quicklime handling, hydrogen sulphide at 10 ppm 8-hour TWA at bitumen storage and asphalt mixing, carbon monoxide at 30 ppm 8-hour TWA in workshops and weighbridges with diesel exhaust exposure, nitrogen dioxide (also from diesel exhaust) at 1 ppm 8-hour TWA, and PM10 plus PM2.5 ambient air targets at the plant boundary per AS/NZS 3580 ambient air quality method. State EPA licences typically set dust deposition at the boundary below 4 g per square metre per month and PM10 24-hour fence-line below 50 micrograms per cubic metre. The HVAC duct designer is balancing operator-station occupational protection (the silica problem) and the boundary-monitored dispersion protection (the community amenity problem) simultaneously.

The Australian heavy-materials value chain — where the duct sits

Australia's aggregate, concrete and asphalt value chain runs from the quarry face to the road surface, with five distinct industrial steps that generate HVAC duct demand: aggregate extraction and processing at the quarry, sand and gravel processing for fine aggregates, ready-mix concrete batching at the batching plant, asphalt mixing at the road-surfacing supplier, and pre-cast concrete manufacturing for structural and architectural elements. Each step has its own dust signature, its own thermal regime, its own hazardous area considerations and its own scope split between heavy welded process duct and sheet-metal comfort HVAC.

Step 1 — Aggregate quarry. Basalt, granite, limestone, sandstone, river gravel or hard rock is drilled and blasted from the quarry face, hauled by articulated dump truck to the primary crusher (typically a jaw or gyratory crusher in the 60-200 t/h range for an Australian site), screened and conveyed through secondary cone or impact crushers, screened again into product sizes, and stockpiled at the load-out yard. Dust generation peaks at the primary crusher feed (drop height plus impact fracture), the conveyor transfer points (each transfer point is a discrete dust source), the screens (vibrating screens shed fines into ambient air), the secondary and tertiary crushers, and the stockpile load-out where the bucket scoops or chute drops material into a truck. Wet method dust suppression by water spray is the primary control. Local exhaust ventilation to AS 1668.2 is the secondary control on enclosed transfer points and screens.

Step 2 — Sand and gravel processing. Sand and fine aggregate from river-dredge or hard-rock crushing is washed, classified and screened to meet Australian Standard AS 1141 aggregate testing specifications. Sand classifier extract carries moisture-laden air with entrained fines through a demister and a vented filter. Pug mill mixer (used for stabilised sand and modified aggregate blends) extracts dust plus moisture. Sand drying (where required for dry concrete or asphalt blend) goes through a small rotary dryer with its own dust extraction.

Step 3 — Ready-mix concrete batching. The batching plant takes cement (in 30-100 tonne silos), supplementary cementitious materials such as fly ash and ground granulated blast-furnace slag (in similar silos), aggregate (in compartmentalised bins or radial conveyors from stockpile), water (from town main or recycled wash water), and admixtures (in totes or dosing tanks), weighs each component into a charge, discharges into the truck mixer or central plant mixer drum, and dispatches the finished concrete to site. Each silo has a top-vent bag filter to handle pneumatic-delivery displaced air. Aggregate bins vent during fill and discharge. The mixer drum has minimal extract. The dust extract circuit is centralised through a small pulse-jet bag filter (typically 5,000-15,000 m³ per hour total) for the whole plant.

Step 4 — Asphalt plant. Hot-mix asphalt is produced by drying clean aggregate in a rotary dryer at 220-280 degrees Celsius, screening into hot bins, weighing into a charge, and mixing with hot bitumen (160-180 degrees Celsius) from heated storage tanks. The rotary dryer exhaust is the dominant emission source — heavy dust, sulphur dioxide, nitrogen oxides and volatile organic compounds, polished through a bag filter house and optionally through a regenerative thermal oxidiser. Bitumen storage tank vents and tanker loading vapour returns are the second emission source — hydrogen sulphide and polycyclic aromatic hydrocarbon vapours requiring Zone 2 hazardous area construction.

Step 5 — Pre-cast concrete. Pre-cast plants manufacture wall panels, beams, columns, hollow-core slabs, structural lintels, architectural finishes, and stair-and-balcony units in a controlled factory environment, then ship them to site for crane lift erection. The plant runs a moulding bay (form release agent application, reinforcement cage placement, concrete pour, surface finishing), a steam curing chamber (60-80 degrees Celsius, 95-100 percent RH, 4-12 hour cycle), and a finishing bay (trowel finishing, pre-stressing strand cutting, edge grinding). Each operation has its own extract and supply duct.

What unites all five steps is the silica dust source: every product flow contains silica, every transfer point generates dust, every operator standby station needs RCS exposure protection. What differs between the steps is the temperature, the hazardous-area classification, the chemistry and the duct material.

Australian operators — who is buying HVAC duct

Australia's heavy-materials sector is highly concentrated at the top, with a long tail of regional and specialist operators. For HVAC contractors, the major buying centres run as follows.

Concrete and aggregate (vertically integrated)

Boral (ASX:BLD). Sydney HQ. Australia's largest concrete and aggregate producer with over 100 batching plants and 50+ quarry operations nationally. Cement clinker production at Berrima NSW, plus Marulan limestone quarry. The Boral CleanTech Cement programme is driving alternative-fuel and lower-clinker investment that adds new comfort HVAC scope at multiple sites.

Holcim Australia. Sydney HQ, part of Holcim Group (Swiss). Major concrete, aggregate and asphalt operator with batching plants and quarries across all states. Holcim ECOPlanet low-carbon cement programme is driving cement composition and additive-handling changes.

Hanson Australia. Heidelberg Materials AU, formerly Pioneer. Strong position in NSW and QLD with concrete, aggregate and asphalt operations. Hanson Quarry Products operates a substantial quarry footprint.

Adbri (ASX:ABC). Adelaide HQ. Cement, lime and concrete producer with cement production at Birkenhead SA, lime at Galong NSW, grinding at Munster WA, plus a national batching plant network. Adbri sustainability programme is expanding alternative fuel handling at multiple sites.

Cement Australia. Joint venture between Holcim and Heidelberg Materials. Three integrated cement plants at Gladstone QLD, Railton TAS and Port Kembla NSW (the grinding-only station). Significant cement silo and bagging plant footprint at each site.

Wagners Holding Company (ASX:WGN). Toowoomba QLD HQ. Cement, concrete and earth-friendly concrete operator with cement plant at Pinkenba QLD and earth-friendly concrete (geopolymer cement) commercialised at scale.

Independent Cement and Lime. Largest independent supplier of blended cement in the south-east markets, drawing local clinker plus imports for blending. Blending and bagging operations generate steady comfort HVAC and extraction duct demand.

BGC Cement. Privately owned by the Buckeridge Group of Companies (Bunder Group), based in Perth WA. Integrated cement, concrete and aggregate operator with strong WA market share.

CSR Limited (ASX:CSR) Building Products. Includes Hebel autoclaved aerated concrete, Gyprock plasterboard, PGH Bricks and Viridian Glass. Hebel manufacturing in particular has process extract duct demand around the autoclave and surface finishing.

Asphalt and road surfacing

Fulton Hogan. Trans-Tasman major asphalt producer and road surfacing contractor with operations across all Australian states and New Zealand. Significant network of asphalt plants, all requiring rotary dryer exhaust, bag filter and bitumen Zone 2 ductwork. Strong contract base with state road authorities.

Downer Group (ASX:DOW) Roads. National roads and infrastructure contractor. Asphalt production and road surfacing across all states. The Roads division includes Bemax mineral sands and Reinforced Earth retained walls.

BMD Constructions. Queensland-based national infrastructure contractor with growing asphalt production capacity.

SAMI Bitumen Technologies. Polymer-modified bitumen specialist. Multiple PMB production workshops nationally, each requiring localised VOC capture and Zone 2 construction.

Boral Asphalt, Hanson Asphalt, Adbri Asphalt. The vertically integrated majors all operate asphalt production alongside their concrete and aggregate operations.

Australian Asphalt Pavement Association (AAPA). Industry body driving best practice in asphalt production, emission control and worker health.

Quarries (specialist and regional)

Mawson Group (formerly ATC). Newcastle NSW headquartered, operating multiple quarries across NSW. Aggregate, sand and gravel.

Hanson Quarry Products. Substantial national quarry footprint complementing Hanson's concrete and asphalt operations.

Boral Quarries. National network including Penrith Lakes, Peppertree NSW and major Victorian operations.

Holcim Quarries. Network of quarries supplying Holcim's concrete and asphalt plants.

Independent Quarries. Wholesaler-supplier of aggregate to the merchant batching plant market.

Hymix Australia. Specialty quarry and concrete operator with focus on architectural aggregate and decorative concrete.

Pre-cast concrete

Hollow Core. Major hollow-core slab producer with plants in Sydney and Melbourne. Continuous casting line plus traditional moulding bay.

Westkon Precast. Melbourne-based pre-cast manufacturer with structural wall panels, beams and architectural elements.

Civilex. Sunshine Coast QLD pre-cast specialist.

Strapdoor. Brisbane pre-cast door and panel manufacturer.

National Precast Concrete Association Australia (NPCAA). Industry body for pre-cast manufacturers, driving design standards, quality assurance and worker safety.

Industry bodies

The Cement Industry Federation (CIF), Cement Concrete and Aggregates Australia (CCAA), Concrete Institute of Australia (CIA) and Australian Asphalt Pavement Association (AAPA) jointly set the technical, sustainability and worker-health agenda for the sector. Their published best-practice documents are frequently referenced in EPA licence conditions and EPC project specifications, and HVAC duct designers working on these plants need to read at least the latest CCAA dust management guide and AAPA hot-mix asphalt manual before committing to a scheme.

Aggregate stockpile dust suppression and windbreaks

The aggregate stockpile yard is the outdoor frontier of the dust problem. Stockpiles of crushed rock, screened aggregate, washed sand and processed sub-base material sit in open-air rows, are continuously replenished from the screening plant and continuously withdrawn for truck dispatch. Wind erosion lifts fines off the surface of dry stockpiles; bucket scoops and chute drops generate point-source dust during withdrawal; truck-loading from elevated radial stackers creates a substantial dust plume during the second-to-fourth metre of free fall.

Engineering controls in priority order: (1) water spray bars at the radial stacker outlet and the truck-loading chute, sized for 10-20 litres per tonne of throughput, with surfactant additive in summer dry-period operation; (2) windbreaks at the boundary fence, typically 3-6 m tall steel or mesh windbreak walls on the prevailing wind side, reducing wind speed at the stockpile by 50-80 percent within 5-10 stockpile-heights downwind; (3) telescoping load-out chute (with skirt and shroud) at truck-loading to bring drop distance down from 4-6 m bucket to 0.5-1.0 m chute exit; (4) stockpile crusting agents (lignin sulphonate or polymer surfactant) on long-term stockpiles that will not be disturbed for weeks; (5) ambient PM10 monitors at the boundary with continuous logging.

None of this is sheet-metal HVAC scope. Water spray, windbreak fabrication and crusting agent dosing are mechanical and civil scope. But the dust monitoring data feeds back into the operating-area HVAC design — operator cabins on yard mobile equipment (front-end loaders, articulated dump trucks, water trucks) need pressurised filtered cabin ventilation with two-stage filtration, and that is sheet-metal duct scope from a cabin-conditioning specialist supplier rather than a building HVAC contractor.

Conveyor transfer point local exhaust ventilation

Conveyor transfer points — where material drops from one conveyor belt onto the next — are the single largest discrete dust source in any aggregate processing plant. Drop height is typically 2-5 metres, and the impact at the receiving belt generates a momentum plume that lifts fines into ambient air. A typical Australian aggregate plant has 8-20 transfer points across the conveyor circuit, depending on plant configuration. Each one needs dust control.

The engineering hierarchy: (1) enclose the transfer point with steel skirt boards and rubber dust seals along the belt edge for 3-5 metres downstream of the receiving point; (2) install a stilling box (a long enclosed plenum after the receiving point) to allow the momentum plume to decay before exiting into the conveyor gallery; (3) provide ducted local exhaust ventilation at the stilling box top, typically 2,500-7,500 m³ per hour per transfer point depending on belt width and product type; (4) duct the extract through a cyclone primary separator and a pulse-jet bag filter house, with knocked-out coarse fines returned to the conveyor belt via a rotary valve.

Trunk duct between the transfer point hoods and the bag filter house is welded heavy fabrication carbon steel 4-6 mm wall thickness, with abrasion liners (chromium carbide overlay or basalt-lined inserts) at every bend and tee. Trunk duct minimum transport velocity 18-22 m/s to keep aggregate fines suspended. Trunk duct diameter typically 400-800 mm depending on plant scale. None of this is sheet-metal HVAC scope; it is welded fabrication delivered by structural-steel and pressure-vessel shops.

What sits on the HVAC contractor's side: the bag filter house outlet duct (clean air, less than 30 mg per normal cubic metre, typically 60-90 degrees Celsius), the stack to atmosphere (carbon steel 3-5 mm wall thickness), the supply ventilation to the conveyor gallery (positive-pressure outside air to dilute any escaped dust before it reaches operator walkways), and the control room HVAC for the central control building. The supply and gallery HVAC is conventional galvanised duct on SBKJ machinery.

Crusher and screen dust extraction

Primary crushers (jaw crushers at 60-400 t/h or gyratory crushers at 300-2,000 t/h in major quarries) are the second-largest dust source. The feed-end of a jaw crusher sees rock impact-fracturing under the swing jaw; the discharge generates a pressure pulse that ejects fines into ambient air. Secondary cone crushers and impact crushers similarly generate a fine plume at the discharge. Vibrating screens spread the rock across screen panels and shake fines through — the fines exit at high concentration through the gaps between screen and feed chute.

Wet method (water spray inside the crusher enclosure, water spray on the screen feed, water spray on the conveyor receiving the screen discharge) is the primary control where product specifications allow moisture addition. End products that go into asphalt or dry concrete may have moisture limits (typically 1-3 percent for asphalt aggregate, 4-6 percent for concrete aggregate) that constrain how much water can be added at the crusher.

Where wet method is constrained or impractical (mobile crushing plant, winter operation in southern Australia with freeze risk, end-product moisture limits), dry dust extraction follows the same hierarchy as conveyor transfer points: enclosure hood over the dust source, ducted extract at 18-22 m/s transport velocity, cyclone primary separator, bag filter house. Hood capture velocity at the source face 1.0-2.5 m/s depending on plume momentum.

For a typical Australian hard-rock quarry running 150-500 t/h with 6-12 active dust sources (primary crusher, secondary crusher, tertiary crusher, two-deck screen, three-deck screen, conveyor transfers), the total dry dust extraction circuit handles 20,000-60,000 m³ per hour of air through a central pulse-jet bag filter house with 200-600 m² of filter cloth area, draining recovered fines back to the conveyor belt for re-blending into the product. None of the heavy-duty extract trunk duct is SBKJ scope; it is welded fabrication. The bag filter house outlet stack and the gallery supply HVAC are.

Sand classifier, washing and screening — moisture-laden extract

Sand classification — separating sand into fine, medium and coarse fractions for concrete and asphalt blends — uses either wet hydraulic classifiers (settling tanks, hydrocyclones, fluidised-bed classifiers) or dry pneumatic classifiers (air-swept rotor classifiers). Wet classification is dominant in Australia because of the higher moisture tolerance in the end product, and because wet classification fundamentally eliminates dust generation. Pneumatic dry classification generates dust and needs its own bag filter.

Sand washing — using water sprays to scrub clay and silt off the aggregate surface — is universal in Australia for fine aggregate destined for concrete (AS 1379 specifies maximum 4-8 percent fines passing 75 micron depending on aggregate grade). Wash plant extract is moisture-laden air rather than dry dust — extract duct handles a wet aerosol through a demister and a vent stack. Demister design follows mesh-pad or chevron-vane configurations with 50-150 mm bed depth. Wash plant vent duct is stainless 304L or galvanised with epoxy internal coating to handle condensate.

Screen washing — wet screens that scrub the aggregate surface with sprays during the screening operation — generates similar moisture-laden vent air. Pug mill stabilised aggregate mixers (used for cement-bound base courses and stabilised sub-base) also generate moisture-laden dust during the wet-mix discharge.

All of this wet-method extract is welded fabrication scope (stainless 304L for the demister housing, vent duct in 304L on the SBSF-1525 stitchwelder if SBKJ scope reaches there, or carbon steel in the welded shop). The make-up air supply to the wash plant building, the operator pulpit HVAC and the office HVAC are sheet-metal galvanised duct on SBKJ machinery.

Ready-mix concrete batching plant duct scope

A ready-mix batching plant is the most concentrated heavy-materials operation in any Australian city — there are hundreds of batching plants in metropolitan Sydney, Melbourne, Brisbane, Perth and Adelaide alone, and they sit in industrial zones next to residential boundaries. State EPA boundary monitoring per AS/NZS 3580 is the regulatory frame; operator-station RCS exposure below 0.05 mg per cubic metre is the occupational frame.

The batching plant duct scope splits into four streams.

Stream 1 — cement silo top-vent filters. Each cement and SCM silo (typically 4-8 silos at a mid-sized plant, holding 30-100 tonnes each) has a dedicated pulse-jet bag filter mounted on the silo top. The filter handles two air streams: displaced air during pneumatic tanker delivery infill (typically 1,000-3,000 m³ per hour during the 20-40 minute delivery window) and thermal venting during day-night cycles (typically 50-150 m³ per hour continuous). Filter outlet loading below 30 mg per normal cubic metre. Each filter is a DCE-style 30-100 bag pulse-jet unit. The connecting clean-air duct between the filter outlet and atmosphere is short — typically a 200-300 mm diameter 0.7-1.0 mm galvanised stub on each filter — but if the design routes outlet air through a building roof penetration, that connecting duct can extend several metres and is fabricated on an SBAL-V or SBTF.

Tanker pneumatic delivery is the largest single emission event on the plant. A 30 tonne cement tanker delivers in 20-40 minutes at typical pneumatic blow rates of 1,500-3,000 kg per minute, displacing 1,000-3,000 m³ per hour through the silo top-vent filter. Filter blow-back malfunctions during this delivery window are the largest single fugitive emission risk. Filter pressure-drop monitoring with alarms is mandatory.

Stream 2 — aggregate bin and weigh hopper extract. The aggregate bins at the top of the batching tower (typically 4-8 compartments holding different aggregate sizes) vent during fill from the feed conveyor and during discharge to the weigh hopper. Each bin has a small extract hood at the top, manifolded to a central pulse-jet bag filter (typically 5,000-15,000 m³ per hour total plant capacity). The trunk extract duct from bin hoods to the central filter is welded carbon steel; the outlet duct to atmosphere and the building supply HVAC is galvanised sheet metal.

The weigh hopper sits below the aggregate bins and receives sequential measured drops from each bin compartment. During discharge into the truck mixer or central plant mixer, the weigh hopper vents through a small extract that captures the displacement plume. Cement weighing batcher has its own small extract.

Stream 3 — mixer drum extract. Central plant mixers (twin-shaft mixers, planetary mixers, drum mixers) generate minimal extract — typically a small displacement vent at the drum top during charge and discharge. Truck-mounted mixer drums (the rotating drum on the truck) generate even less — the truck drum is essentially sealed during transit, and only the loading dock dust during discharge into the drum is a controlled emission point. Loading dock dust capture is at the drum loading hopper extract.

Stream 4 — comfort HVAC. The batching plant control room (where the batch operator runs the plant computer), weighbridge office (where the truck driver records the load), QC laboratory (where field sample cubes are prepared for crushing strength tests per AS 1289 soil testing and AS 1379 concrete supply), and amenities (lunch room, change room, toilets) are conventional sheet-metal HVAC ductwork. Galvanised G275 or G300 at 0.5-1.0 mm wall thickness fabricated to AS 4254 on the SBAL-V auto duct line, spiral round duct for trunk runs on the SBTF-1500C or SBTF-1602, TDF flange connections, Pittsburgh seam locking on the SBPC1500. Positive-pressure offset of +25 to +50 Pa relative to the surrounding plant areas, with two-stage F4 plus F7 filtration on intake to keep dust out of the office.

Total plant duct fabrication scope for a mid-sized Australian batching plant runs 200-800 m² of duct depending on building size and HVAC system complexity. Fabrication time on a single SBAL-V auto duct line is 1-3 weeks; installation time on-site is 1-2 weeks; the full HVAC programme from PO to handover is 6-12 weeks excluding any permit lead time.

Cement silo top-vent filter design detail

The cement silo top-vent filter is the most critical piece of dust control equipment on any batching plant. Failure or malfunction of the silo top-vent filter during pneumatic tanker delivery generates a visible white cement plume that triggers state EPA boundary complaints within minutes and triggers a Section 91 (or equivalent) clean-up notice within hours. Every batching plant operator has seen at least one of these events; competent HVAC and dust-extract design exists to prevent them.

The filter is a pulse-jet bag filter, typically a Donaldson Torit, Disa, Camfil, Nordfab, BMD Australia or comparable manufactured unit, mounted bolt-up on the silo top flange. Sizing follows: air volume = tanker pneumatic blow rate (m³ per hour at silo conditions) × 1.2 safety margin. Filter cloth area = air volume / target air-to-cloth ratio. For typical Australian cement deliveries, the target air-to-cloth ratio is 1.5-2.0 m³ per m² per minute for polyester membrane media or 1.0-1.5 for PTFE membrane media. A 30 tonne delivery at 2,500 m³ per hour blow rate × 1.2 = 3,000 m³ per hour design air volume, and at 1.5 air-to-cloth ratio that needs 33 m² of filter cloth, which is a 30-bag unit at typical bag dimensions.

Pulse-jet cleaning uses compressed air at 4-7 bar fired into the bag interior through a venturi at the bag top, dislodging accumulated dust which falls into the silo. Pulse interval typically 5-15 seconds during delivery, lengthening to several minutes during quiescent periods. Compressed air consumption 50-150 normal litres per pulse per bag.

Filter pressure drop monitoring uses a differential pressure transducer across the filter, with stepped alarm thresholds typically 1.0 kPa (info), 1.5 kPa (warning), 2.0 kPa (alarm — stop delivery), 2.5 kPa (trip — stop delivery, dispatch maintenance). Alarm response is immediate stop of pneumatic delivery to prevent over-pressurisation of the silo and breach of the top-vent filter into atmospheric emission.

The connecting clean-air duct from filter outlet to atmosphere is typically a 200-300 mm diameter spigot in 0.7-1.0 mm galvanised, or in stainless 304L where coastal corrosion exposure demands it. Fabricated on the SBAL-V or SBTF spiral tubeformer. If the design routes through a building roof, the penetration uses a weatherproof flashing per AS 1562 metal roofing.

Pug mill mixer, sand drying and asphalt drum dryer extract

Pug mill paddle mixers handle wet aggregate mixes — cement-treated base course, stabilised sand, cold-mix asphalt and modified aggregate blends. The pug mill discharge generates a moisture-laden dust plume (water plus fines) that needs extract at the discharge chute. Typical pug mill extract 2,000-8,000 m³ per hour through a small vent stack with a demister and a coarse bag filter. Pug mill housing is enclosed and dust-tight; extract is at slight negative pressure relative to ambient.

Sand drying (used by ready-mix plants producing dry-bagged mortar mix or specialty pre-cast concrete) goes through a small rotary or fluid-bed dryer at 100-200 degrees Celsius, with extract through a small cyclone and bag filter sized 5,000-20,000 m³ per hour depending on dryer scale.

Asphalt drum dryer is the largest single combustion exhaust on a heavy-materials site. A typical 150 t/h Australian asphalt plant runs a 1.2-1.8 m diameter rotary drum dryer 8-15 m long, fired by a propane, natural gas or diesel burner at 4-12 MW thermal duty, with aggregate feed at the cold end and hot aggregate exiting at 160-180 degrees Celsius. Exhaust gas at the feed end is 220-280 degrees Celsius after the heat exchange with cold aggregate. Exhaust gas volume 25,000-80,000 m³ per hour at actual conditions depending on dryer scale.

Asphalt dryer exhaust is dirty: aggregate dust loading 50-300 g per normal cubic metre, sulphur dioxide from sulphur in the burner fuel, nitrogen oxides from combustion, carbon monoxide if combustion is fuel-rich, and volatile organic compounds carried over from any return aggregate fines. The exhaust path follows: drum exhaust → primary cyclone (knocks out 70-80 percent coarse) → secondary cyclone or settling chamber → pulse-jet bag filter house (final dust below 50 mg per normal cubic metre) → induced draft fan → stack. Total exhaust duct length 30-80 metres of welded heavy fabrication carbon steel, 4-6 mm wall thickness, with abrasion liners at every bend.

Filter media selection is critical because the gas is hot: polyester membrane media is rated for continuous 130-150 degrees Celsius (suitable only after dilution cooling), Nomex is rated 200-220 degrees Celsius (the typical Australian asphalt plant filter media), PTFE is rated 250-260 degrees Celsius (premium choice for high-temperature streams). Ambient air mixing or evaporative cooling at the dryer exhaust dilution point drops gas temperature into the filter operating window.

None of the asphalt dryer exhaust duct is sheet-metal HVAC scope. It is welded heavy fabrication delivered by specialist mineral-processing fabrication shops. SBKJ scope on an asphalt plant is the comfort HVAC for the operator pulpit, switch room, lab, weighbridge and amenities — typically 100-400 m² of galvanised duct.

Asphalt mixing chamber and regenerative thermal oxidiser polishing

Downstream of the rotary dryer, hot aggregate at 160-180 degrees Celsius is conveyed to the asphalt mixing chamber (a twin-shaft pug mill mixer in most Australian plants) where it is mixed with hot bitumen at 160-180 degrees Celsius plus optional polymer modifier and mineral filler. The mixing chamber is enclosed and ventilated at negative pressure to capture the bitumen fume plume during mix release.

Mixing chamber off-gas is the dominant VOC and odour emission source on an asphalt plant. It contains volatile aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) from bitumen vapour, and trace hydrogen sulphide from sulphur compounds in the bitumen. Total VOC loading 50-500 mg per normal cubic metre depending on bitumen grade, mix temperature and polymer modifier. Odour threshold dilution-to-detection (D/T) values typically 1,000-10,000 at the source.

Best-available control technology is a regenerative thermal oxidiser (RTO) operating at 800-900 degrees Celsius combustion chamber temperature with 1 second residence time. The RTO uses two or three ceramic heat-exchanger beds (saddles or structured ceramic media) that switch every few minutes, recovering 95-97 percent of the combustion heat back to the inlet stream — operating fuel demand is therefore minimal once the RTO is at temperature. Inlet duct to the RTO in 304L stainless steel to handle the wet-acid corrosion risk during start-up. Outlet stack in carbon steel 3-5 mm wall thickness.

RTO sizing typically 10,000-30,000 m³ per hour for a 150 t/h Australian asphalt plant, with VOC destruction efficiency 98-99 percent. Capital cost AUD 1-3 million installed for that size class. Operating fuel demand 50-200 kW natural gas for the burner ignition and bed temperature maintenance.

Not every Australian asphalt plant has an RTO. Older plants and rural plants frequently operate with the bag filter only, achieving acceptable particulate but with limited VOC and odour control. New build and EPA compliance upgrades increasingly require RTO. Site selection — distance to nearest residential or sensitive receptor — drives the RTO requirement.

Bitumen storage tank vent and tanker loading vapour return

Bitumen storage tanks at the asphalt plant store paving-grade bitumen (typically C170 or C320 viscosity grade per AS 2008) at 160-180 degrees Celsius in vertical cylindrical insulated steel tanks of 50-300 tonne capacity. Each tank has a heating coil (steam, hot oil or electric) maintaining temperature, an internal agitator, a level gauge, a thermometer, and a top vent. The vent emits vapour during temperature swings, level changes and tanker loading displacement.

Bitumen vapour at 160-180 degrees Celsius contains hydrogen sulphide (Safe Work Australia WES 10 ppm 8-hour TWA), polycyclic aromatic hydrocarbons, and condensable bitumen fume. Storage tank breathing emission is typically 5-30 g per tonne stored per year for quiescent tanks; tanker loading is 50-200 g per tonne loaded as a discrete event. The dominant emission control is closed-loop vapour return from the tanker dome to the storage tank ullage space during loading, which captures 95-99 percent of the displacement vapour.

Vapour return duct between the tanker connection manifold and the storage tank ullage is in stainless 304L, sized to handle the tanker loading rate (typically 1,000-3,000 litres per minute liquid in, displacing equivalent vapour volume out). All flanges bonded and earthing continuity verified before each load — per AS/NZS 60079 Zone 2 hazardous area requirements. No aluminium, no anodised fittings, no painted unbonded surfaces. The vapour-return manifold has a break-flange isolation, a check valve to prevent backflow, and a vapour seal trap to drop out any liquid bitumen condensate.

Loading platform classification is Zone 2 hazardous area for the volume immediately around the loading manifold during loading (typically a 1.5-3 m radius hemispherical envelope). All electrical equipment within the zone is rated Ex e or Ex d per AS/NZS 60079.0 and AS/NZS 60079.10.1. Operator standby position is outside the Zone 2 envelope. Hydrogen sulphide personal monitors as the secondary safety check.

Tank breather vent during quiescent operation is small (typically 50-200 m³ per hour through a 100 mm diameter vent pipe). Some sites discharge directly to atmosphere; better practice is to route the breather to a small carbon canister, a thermal oxidiser, or back through the RTO inlet stream. Vent duct in stainless 304L all the way to the carbon canister or RTO. SBKJ stitchwelder SBSF-1525 (2.5 kW) is the appropriate fabrication machine for the stainless seams on this duct.

Polymer-modified bitumen (PMB) workshop HVAC

Polymer-modified bitumen (PMB) is bitumen with added polymer (typically styrene-butadiene-styrene SBS, ethylene-vinyl-acetate EVA, recycled crumb rubber, or specialty polymer blends) to improve high-temperature deformation resistance and low-temperature crack resistance. SAMI Bitumen Technologies, Boral, Fulton Hogan and a number of specialty suppliers operate PMB production workshops nationally.

PMB production runs at 180-200 degrees Celsius with shear mixing under high-power agitators. Polymer addition generates a localised VOC plume — styrene and butadiene from SBS, vinyl acetate from EVA, sulphur compounds from crumb rubber. Localised VOC capture at the polymer addition hopper plus general workshop extract at 8-10 air changes per hour are the engineering controls.

Workshop hazardous area classification — typically Zone 2 across the production floor, escalating to Zone 1 inside vessels and immediately around the polymer addition point. All electrical equipment Ex-rated per AS/NZS 60079.

Duct material is stainless 304L throughout the production zone (vapour capture, transfer ducts, RTO inlet ducting). Comfort HVAC for the workshop control room and offices is conventional galvanised on SBKJ machinery. The PMB workshop is a moderate-scale HVAC scope — typically 300-1,500 m² of duct depending on workshop size and process complexity.

Pre-cast concrete moulding bay HVAC

Pre-cast concrete plants manufacture structural and architectural elements in a controlled factory environment, then ship them to site by truck for crane lift erection. National Precast Concrete Association Australia (NPCAA) is the industry body. Major producers include Hollow Core, Westkon Precast, Civilex, Strapdoor and a number of regional specialists.

The moulding bay is the main production floor. Steel forms (matched-pair moulds for the desired element shape) are cleaned, treated with release agent, fitted with reinforcement cage and pre-stressing strand, charged with fresh concrete from the central mixer, vibrated to consolidate, and screeded smooth. The release agent application is the dominant VOC emission point during normal operation. Release agents are typically light hydrocarbon solvent-based products (mineral spirits, kerosene blends) or water-based emulsions (newer-generation products).

For solvent-based release agents, VOC emission during spray application is significant — typically 100-300 mg per cubic metre at the operator standby position without local exhaust. Engineering control is a spray application booth with downdraft ventilation, paper or activated-carbon exhaust filter, and integrated worker platform. Operator-station VOC kept below the relevant WES (toluene 50 ppm, xylene 80 ppm, or the specific solvent listed on the SDS).

General bay extract at 6-10 air changes per hour to handle ambient VOC, concrete dust and admixture release. Bay supply through high-level diffusers in conventional galvanised duct on SBKJ machinery. Bay exhaust through low-level grilles to capture the heavier-than-air solvent VOC. AS 1668.2 mechanical ventilation is the governing code.

Concrete pour and vibration generates aerosolised concrete fines and admixture VOC at the form top. Operator-station capture is by mobile hood on flexible arm, manifolded to the bay general extract trunk. Form vibration also generates significant low-frequency noise — sound absorption ducting and acoustic louvres at the bay supply and extract penetrations are common, addressed in the acoustic guide.

Steam curing chamber design

After casting, the pre-cast element cures inside a steam curing chamber (often called a curing kiln or curing tunnel) at 60-80 degrees Celsius and 95-100 percent relative humidity for 4-12 hours per cycle. Saturated steam is injected from a boiler plant; the chamber walls are insulated metal panels; the element is loaded on a wheeled trolley and indexed through the chamber.

Chamber vent at end of cycle releases the moist hot air to atmosphere through a vent stack. Vent duct in stainless 304L to handle the saturated condensate that drops out during cooling. Insulated externally with trace heating in cold-climate plants (Tasmania, Victorian Alps, NSW Snowy Mountains regions) to prevent condensate freeze and vent blockage.

Vent fan typically 5,000-20,000 m³ per hour at chamber temperature, sized for 5-minute purge of the chamber air volume at end of cycle. Vent stack discharge above the eaves of the building to disperse the moisture plume away from operator walkways.

Make-up air to the chamber during cycle is typically a small leak path (chamber is not maintained at positive pressure). Steam injection rate matches the loss through the leak path plus the heat-up demand at start of cycle.

SBSF-1525 stitchwelder fabricates the 304L vent duct. Carbon steel chamber wall panels are fabricated separately by specialist insulated-panel suppliers.

Trowel finishing, pre-stressing strand cutting and grinding

After the cure cycle, the element is demoulded and moved to the finishing bay. Trowel finishing — manual or mechanical surface preparation — generates fine concrete dust and surface admixture aerosol. Pre-stressing strand cutting (cutting the high-tensile prestressing strands once concrete has cured to specified strength) generates minimal extract — a small particulate hood at the cut point captures the cut-off debris.

Concrete sawing and grinding (for edge finishing, surface texture creation, or rectification of defects) is the highest single RCS risk task in the pre-cast plant. AS 3957 dust hazard standard requires wet method as the primary control — water-fed saws with bonded vacuum collection, water-fed grinders with shroud and vacuum. Personal monitor measurements during wet-method sawing typically below 0.01 mg per cubic metre RCS. Dry sawing (where unavoidable) requires dust collection vacuum at the cutting head plus respiratory PPE; RCS exposure on dry sawing routinely exceeds the WES.

Vacuum collection trunk lines route to a central HEPA vacuum or to a small pulse-jet bag filter. Discharge to atmosphere after HEPA filtration or back to a settling tank for wet collection. Duct material galvanised or stainless depending on chemistry; fabricated on SBKJ machinery for the clean side.

Form release agent spray booth

Where the pre-cast plant uses solvent-based release agents, a dedicated spray application booth is the engineering control. Booth design follows AS 1668.2 mechanical ventilation principles:

• Downdraft ventilation with vertical airflow from booth ceiling to floor grilles, ensuring solvent vapour moves away from the operator's breathing zone.
• Booth face velocity 0.5-1.0 m/s at the open booth front to prevent VOC escape into the surrounding bay.
• Filter exhaust through paper or activated-carbon filters to remove overspray and VOC before atmospheric discharge.
• Hazardous area zoning per AS/NZS 60079 — the booth interior is typically Zone 1 or Zone 2 depending on solvent flash point and spray rate.
• Make-up air supply tempered and filtered to AS 1668.2 indoor air quality limits.

Booth exhaust duct in galvanised or stainless depending on solvent chemistry; fabricated on the SBAL-V or SBSF-1525. Stack discharge above the workshop roof eaves.

Lab QC, workshop garage and office HVAC

Every aggregate, batching, asphalt and pre-cast plant has a quality control laboratory testing aggregate gradation per AS 1141, concrete cube strength per AS 1379, asphalt mix design per AS 2008 and AS 2009, and miscellaneous performance testing. The lab is a low-dust, temperature-controlled environment with conventional comfort HVAC: 7.5-10 litres per second per person fresh air, +25 to +50 Pa positive pressure relative to plant areas, two-stage F4 plus F7 filtration on intake.

Workshop garage (where plant maintenance is performed on mobile equipment, conveyors and processing machinery) is a higher-extract environment. Diesel engine exhaust during maintenance starts is the dominant air quality concern. Engineering controls: ducted exhaust extraction reels on overhead trolleys, connecting to the engine exhaust tailpipe during workshop run-up; under-floor trench ventilation in the workshop floor; ceiling-mounted general extract at 6-10 air changes per hour. Carbon monoxide WES 30 ppm and nitrogen dioxide WES 1 ppm are the target indoor air quality.

Office area (administration, weighbridge, dispatch office) conventional comfort HVAC per AS 1668.2. Positive pressure relative to plant areas. Standard galvanised sheet-metal duct on the SBAL-V.

Boundary monitoring and EPA licensing

State EPA licences for aggregate quarries, batching plants, asphalt plants and pre-cast plants specify boundary monitoring obligations under AS/NZS 3580 ambient air quality method. Typical state EPA conditions in NSW (Environment Protection Authority), VIC (EPA Victoria), QLD (Department of Environment Science and Innovation), SA (EPA South Australia), WA (Department of Water and Environmental Regulation), TAS (EPA Tasmania) and NT (EPA NT) include:

• Dust deposition at the boundary below 4 g per square metre per month (deposition gauge method per AS/NZS 3580.10).
• PM10 24-hour average at the boundary below 50 micrograms per cubic metre (continuous tape monitor or TEOM method per AS/NZS 3580.9).
• PM2.5 24-hour average at the boundary below 25 micrograms per cubic metre (continuous monitoring per AS/NZS 3580.9.10).
• Noise typically 65 dBA daytime, 55 dBA evening, 45 dBA night, 1 m beyond boundary at the nearest receptor.
• Odour threshold dilution-to-detection (D/T) typically below 2-7 at the boundary for asphalt plants and PMB workshops.

Continuous boundary monitoring with automatic alarms is required at all sensitive-receptor sites. Data feeds into EPA reporting (annual emissions summary) and to community complaint response. Boundary exceedance triggers a Section 91 (or state equivalent) clean-up notice with statutory response timeframes.

Hazardous area classification — bitumen, propane, dust

Hazardous area classification on heavy-materials sites covers three sources: flammable liquid vapour (bitumen storage and PMB workshop), flammable gas (propane LPG and natural gas for burner fuel), and combustible dust (cement, aggregate fines, polymer dust at PMB workshops). AS/NZS 60079 hazardous area classification is the governing standard.

Bitumen vapour Zone 2. The bitumen storage tank vent envelope and the tanker loading manifold envelope are typically Zone 2 — a place in which an explosive gas atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only. Zone 2 envelope dimensions typically 1.5-3 m hemispherical radius from the vent or loading point. All electrical equipment within Zone 2 must be rated Ex e (increased safety), Ex d (flameproof), Ex i (intrinsic safety) or Ex n (non-sparking) per AS/NZS 60079.0.

Propane LPG Zone 2. Burner fuel trains for asphalt dryers, pre-cast curing boilers and aggregate dryers fired on propane LPG are Zone 2 around the regulator skid, the fuel manifold and the burner approach. Installation per AS 5601 LPG installations.

Natural gas Zone 2. Natural gas-fired burners similarly. The Zone 2 envelope around the fuel train follows AS/NZS 60079.10.1.

Combustible dust Zone 22. Cement, aggregate fines, polymer dust and recycled crumb rubber dust at PMB workshops can be classified Zone 22 (dust atmosphere) under AS/NZS 60079.10.2. Zone 22 is the dust equivalent of Zone 2. Bag filter house interiors are routinely Zone 22 unless explosion venting per EN 14491 demonstrates exclusion. NFPA 654 combustible dust standard and NFPA 660 combustible dust unified standard inform the U.S. equivalent classification — Australian plants frequently cross-reference NFPA documents in EPC specifications.

For the HVAC duct designer, hazardous area classification dictates: duct material (no aluminium in Zone 2 vapour, no painted unbonded surfaces, all flanges bonded with continuous earth), duct construction (earthing studs at every flange, continuity test before commissioning), ductwork support (no isolated metallic supports without earth bonding), and equipment selection (Ex-rated motors, dampers and instruments).

Fire-rated duct, fire dampers and smoke control

Fire-rated duct construction follows AS 1530.4 fire test methods for elements of building construction. Duct passing through a fire-rated wall must be either fire-rated duct (AS 1530.4 tested assembly with calcium silicate or vermiculite insulation board) or fitted with a fire damper at the penetration. Fire damper installation, commissioning and maintenance follow AS 1851 routine service of fire protection systems and equipment.

On heavy-materials sites, fire-rated duct applies in three locations: through fire-separated MCC and electrical room walls (typical 1-hour or 2-hour rating), through fire-separated chemical storage walls (admixture stores at the batching plant, polymer stores at the PMB workshop), and through fire-separated office-to-plant area divides.

Smoke control duct in MCC rooms (smoke extract on fire alarm) per AS 1668.1 fire and smoke control in buildings is welded carbon steel or fire-rated galvanised duct with rated dampers at penetrations. Battery rooms (for backup power UPS) similarly.

Duct material selection — galvanised, stainless, coated, mild steel

Material selection by application area runs as follows.

• Galvanised steel G275 or G300 (0.5-1.5 mm). The default workhorse for sheet-metal HVAC duct on these plants — batching plant control room, weighbridge office, lab, MCC, amenities, asphalt operator pulpit, pre-cast office, cement silo top-vent clean-air duct. Fabricated to AS 4254 on the SBAL-V auto duct line for rectangular duct or the SBTF spiral tubeformer for round duct.
• Stainless steel 304L (0.6-2.0 mm). The default for vapour-return and humidity-laden duct — asphalt bitumen vapour return between tanker loading and storage tank, asphalt RTO inlet, steam-curing chamber vent at pre-cast plants, sand-washing demister and vent duct. Fabricated on the SBSF-1525 stitchwelder (2.5 kW) for longitudinal seams; the SBAL-V handles 304L coil with sheet-metal forming if coil is pre-pickled.
• Stainless steel 316L (0.8-2.0 mm). Used where coastal corrosion exposure adds chloride attack on top of standard vapour service — asphalt plants within 5 km of the coast (Newcastle, Botany, Port Melbourne, Geraldton, Port Adelaide all common). Same fabrication machinery as 304L; just upgraded coil.
• Spark-resistant construction (earthed stainless, no aluminium, bonded flanges). Mandatory for Zone 2 bitumen vapour and Zone 2 LPG service. Construction discipline is more important than material choice — 304L with bonded flanges is the standard solution.
• Carbon steel 3-6 mm (welded heavy fabrication). The default for heavy process extract duct — crusher and conveyor transfer point trunk duct, asphalt dryer exhaust, cement silo trunk extract, cyclone hopper and bag filter house casing. This is welded heavy fabrication scope handled by structural-steel and pressure-vessel shops. SBKJ scope reaches only where SBKJ supplies stitchwelder machinery (SBSF-1525) for the sheet-metal seams on the cyclone hopper cone and bag filter housing — SBKJ does supply that machinery, and several Australian fabricators run SBKJ stitchwelders for cyclone fab.
• Fluoropolymer-coated steel (PVDF, ETFE). Used where galvanised coating is attacked by chemistry — admixture storage room supply HVAC at batching plants with aggressive admixture chemistry, accelerator and retarder dosing rooms. Niche scope.
• Concrete-lined or basalt-lined steel. Used at high-abrasion zones on aggregate dust trunk lines — bend outer walls, tee impingement targets. Heavy fabrication scope.

Duct velocity, hood capture velocity and minimum transport velocity

The three velocity numbers every duct designer on these plants needs to memorise:

• Hood capture velocity at the dust source face — 1.0-2.5 m/s. The face velocity that pulls the dust plume into the hood. Lower end for low-momentum sources (slow conveyor transfer, weigh-hopper discharge); upper end for high-momentum sources (crusher discharge, screen drop). AS 1668.2 sets the principles.
• Trunk duct minimum transport velocity — 18-22 m/s. The velocity required to keep aggregate fines and cement dust suspended in dilute-phase pneumatic flow. Below 18 m/s the duct chokes with deposited fines; above 22 m/s the duct erodes at bends.
• Plenum and dust collector inlet velocity — 8-12 m/s. The reduced velocity inside a cyclone or bag filter inlet plenum that allows coarse fines to drop out of suspension into the hopper. Transition from 20 m/s trunk to 10 m/s plenum is through a 15-20° expansion taper.
• Comfort HVAC supply velocity — 5-8 m/s. The standard sheet-metal HVAC supply duct velocity per AS 1668.2 and AS 4254. Higher velocity in trunk mains (8-12 m/s) drops to lower velocity at branch and outlet (3-6 m/s) for noise control.

Bend, tee and reducer geometry on dust-laden duct

Bend abrasion on dust-laden duct is the largest single maintenance burden after filter media changeout. Centripetal acceleration at a 90° bend on a 20 m/s dust stream is around 270 g for a 1.5 m duct diameter — particles strike the outer bend wall at 15-90° impact angles, eroding the wall at typical rates 2-10 mm per million tonnes of throughput depending on aggregate hardness.

Engineering controls in priority order: (1) maximise bend radius — long-radius elbows at R/D = 1.5-2.5 are preferred over short-radius at R/D = 1.0; (2) line the outer bend wall with abrasion liner — chromium carbide overlay plate (Bisalloy 80, Hardox 450, Quard 500), basalt-lined inserts, ceramic tile inserts, or sacrificial wear plates that are bolted on and replaced every shutdown; (3) install change-over impingement targets at tee connections; (4) use eccentric reducers (flat-on-top) rather than concentric reducers on horizontal dust-laden duct to prevent particle accumulation on the lower wall.

Tee connections are the second-worst abrasion source. The branch line tee always sees impingement on the opposite wall of the run. Engineers install sacrificial wear targets, change the tee to a 45° lateral, or add a deflector plate. Reducer geometry similarly.

All of this is welded heavy fabrication scope. SBKJ does not supply abrasion-resistant overlay plate; SBKJ supplies the sheet-metal duct machinery on the comfort HVAC side. But understanding the welded-fabrication discipline is important context for the HVAC contractor scope discussion.

Dust filter media selection

Filter media selection on these plants follows temperature and chemistry.

• Polyester (PET) needle felt. The lowest-cost mainstream filter media. Rated continuous 130-150 degrees Celsius, peak 160-180 degrees Celsius. Suitable for ambient and low-temperature aggregate dust, cement silo top-vent filters, batching plant central extract, and asphalt dryer exhaust after dilution cooling. Air-to-cloth ratio 1.5-2.5 m³ per m² per minute.
• Polyester with PTFE membrane. Premium filter media with a PTFE membrane laminated to the polyester base. Lower outlet emission (under 5 mg per normal cubic metre achievable), longer service life on sticky or hygroscopic dust. Standard choice for cement silo top-vent filters where outlet emission compliance is tight. Air-to-cloth ratio 1.0-1.5.
• Nomex (meta-aramid). Higher-temperature filter media rated continuous 200-220 degrees Celsius. The typical Australian asphalt dryer filter media because it handles the dryer exhaust without dilution cooling.
• PTFE (Teflon) needle felt. Premium high-temperature filter media rated continuous 250-260 degrees Celsius. Used at high-temperature streams (asphalt dryer with limited dilution cooling, sand drying exhaust) and where chemical resistance is required.
• Glass fibre with PTFE finish. Used at the highest-temperature streams (peak 280 degrees Celsius continuous) where PTFE needle felt is at its limit.

Filter media is supplied by Donaldson Torit, Camfil, BWF, Hi-tech Filter, GORE and a number of Australian distributors. SBKJ does not supply filter media; SBKJ supplies the duct machinery that connects filter inlet and outlet to the rest of the plant.

SBKJ machinery scope for HVAC contractors

For HVAC contractors fabricating comfort HVAC and clean-air duct on concrete batching plants, aggregate quarries, asphalt plants and pre-cast facilities, the standard SBKJ machine package is built around several core machines.

SBAL-V Auto Duct Production Line. The flagship SBKJ auto duct line — 16 m/min line speed, 87 kW total installed power, processing 0.5-1.5 mm coil thickness, 1500 mm coil width. Coil-to-finished-duct in a single integrated line: decoiler, levelling rolls, notching station, beading, TDF flange forming, longitudinal seam locking, and cut-off. Single-shift output 10,000-15,000 m² per month for the SBAL-V configuration. The right machine for high-volume comfort HVAC fabrication across all the plants in this guide — batching plant control rooms, asphalt operator pulpits, pre-cast offices, lab and amenities. See the full SBAL-V product page and the broader SBKJ machine range.

SBAL-III Auto Duct Production Line. Mid-range auto duct line — 14 m/min line speed, 15.7 kW installed power. The right machine for HVAC contractors with moderate volume requirements or workshops with tight power supply.

SBAL-II Auto Duct Production Line. Entry-level auto duct line — 18 m/min line speed, 5.5 kW installed power. The right starting machine for new HVAC workshops or for shop-side overflow capacity behind an SBAL-V.

SBTF-1500C / SBTF-1602 / SBTF-2020 Spiral Tubeformer. Round galvanised duct from coil — diameters 80-1,500 mm typical (1500C), with larger sizes available on the 1602 and 2020 models. Wall thickness 0.5-1.5 mm. Spiral duct is preferred for trunk supply runs in control rooms and laboratories because of its strength and lower pressure drop. The right machine for clean-air outlet duct from cement silo top-vent filters and bag filter house outlet stacks.

SBSF-1525 Stitchwelder (2.5 kW). Resistance seam welding machine for stainless 304L and 316L sheet-metal duct fabrication. The right machine for asphalt vapour return duct, steam-curing chamber vent duct, pre-cast moulding bay 304L extract duct, and cyclone hopper cone seams on the welded fabrication side. The SBSF-1525 sits between the sheet-metal HVAC side and the welded heavy fabrication side of the scope — many Australian HVAC contractors run an SBSF-1525 alongside an SBAL-V to cover both galvanised and stainless work in the same workshop.

SBFB-1500 Flat Bar Bender (7.5 kW, 1.20 m/min). The right machine for spiral duct stiffener rings — flat bar bent into circles and welded onto spiral duct exit to add hoop stiffness on large-diameter low-pressure duct. Common on bag filter house outlet stack and asphalt RTO inlet duct.

SBPC1500 Pittsburgh Seam Lock Machine. Standard sheet-metal HVAC accessory for longitudinal seam locking on rectangular duct. Bolt-on to an SBAL-V auto line or stand-alone for retrofit workshops.

SBLR-600 / SBLR-600A Lockformer. Round elbow lockformer for HVAC fittings — gored elbows on the comfort HVAC side. Speed 7.6 m/min.

SBEM-1250 Plasma Cutter. Plasma cutting for HVAC fittings and reducer development from sheet. The right machine for low-volume fitting fabrication alongside the auto line.

SBTF-1500C / 1602 / 2020 (alternative read). The spiral series scales up to handle high-volume spiral runs for trunk extract and supply duct on large plant projects.

SBHF Hydraulic Folding Machine. Hydraulic folder for sheet-metal HVAC fittings and short-run components.

What the SBKJ standard machinery package does not address is heavy-gauge welded process extract duct fabrication. Crusher dust trunk duct, conveyor transfer point trunk duct, asphalt rotary dryer exhaust, cement silo trunk extract, and bag filter house casing in 4-6 mm carbon steel with abrasion liners are welded heavy fabrication delivered by structural-steel and pressure-vessel shops. That scope sits outside SBKJ machinery range — but SBKJ does supply the SBSF-1525 stitchwelder for sheet-metal welded seams on cyclone hopper cones and bag filter housings, which is a partial overlap zone where SBKJ machinery handles the lighter welded fabrication.

For comparison and cross-industry context, see our related guides on HVAC ductwork for cement plants, HVAC ductwork for mining mineral processing and smelters, HVAC ductwork for mining ventilation and HVAC ductwork for tile, brick and ceramic manufacturing. SBKJ Australia operates from Box Hill North VIC; see SBKJ Australia regional support for English-language commissioning, training and after-sales.

Project programme — fabrication and installation timing

Aggregate quarries, ready-mix batching plants, asphalt plants and pre-cast facilities have different operational rhythms that drive different HVAC installation programme constraints.

Aggregate quarries typically run six days a week 10-12 hours per day during the construction season (year-round in northern Australia, October-May in southern Australia). Major shutdowns happen during the wet season or during regulatory production caps. HVAC installation programmes around these natural shutdown windows.

Ready-mix batching plants run five-and-a-half days per week 12-14 hours per day, with peak demand on weekday mornings (pre-pour delivery) and slack on Saturday afternoons. HVAC installation typically happens Saturday afternoon to Sunday evening windows, working around the daily production cycle.

Asphalt plants run seasonal — typically March to November in southern Australia (cold-mix only in winter), and year-round in northern Australia with weather windows. The winter shutdown in southern Australia is the standard window for major HVAC change-outs and equipment overhauls.

Pre-cast concrete plants run five to six days per week single shift typically, with shutdown windows during Christmas-January and Easter. HVAC installation programmes around shift change-overs.

A typical mid-sized batching plant comfort HVAC scope (200-500 m² of duct, single building) runs 1-3 weeks fabrication and 1-2 weeks installation. A major asphalt plant comfort HVAC and 304L vapour-return scope (500-1,500 m² of duct, multiple buildings) runs 3-6 weeks fabrication and 2-4 weeks installation. A new-build pre-cast plant HVAC scope (1,000-3,000 m² of duct, multiple buildings) runs 6-12 weeks fabrication and 4-8 weeks installation. None of these are heavy process duct programmes (which run 12-26 weeks for welded heavy fabrication).

Decarbonisation pathways and the duct scope shift

The Australian aggregate, concrete and asphalt sector is committed to decarbonisation across multiple pathways, each with HVAC implications.

Lower-clinker cement and supplementary cementitious materials. Boral, Holcim, Hanson, Adbri and Cement Australia all run lower-clinker cement product programmes — increased blending of fly ash, ground granulated blast-furnace slag, calcined clay and limestone filler reduces clinker demand and therefore reduces emissions. At the batching plant level, this means more SCM silos, more weighing equipment, more dust control on additional materials handling. New silo top-vent filters and additional aggregate bin extract duct.

Recycled concrete aggregate (RCA). Crushed demolition concrete returned to the aggregate cycle reduces virgin aggregate demand. RCA processing plants add a new processing flow — crushing, screening, sometimes washing — each with its own dust control. New comfort HVAC for RCA plant operator rooms.

Warm-mix asphalt and cold-mix asphalt. Asphalt plants are progressively shifting to warm-mix (130-150 degrees Celsius mix temperature versus 160-180 for hot-mix) and cold-mix (ambient temperature) products to reduce burner fuel demand and emissions. Warm-mix reduces the rotary dryer exhaust temperature and VOC loading; cold-mix eliminates the rotary dryer entirely. Duct scope on warm-mix is similar to hot-mix; cold-mix dramatically reduces the duct scope.

Recycled asphalt pavement (RAP). Reclaimed asphalt from milling and resurfacing operations is fed back into the asphalt plant as part of the new mix. RAP feed adds a new dust extraction circuit at the RAP storage and feed point, plus increased bitumen vapour loading at the mixing chamber (because RAP carries its own bitumen content).

Geopolymer concrete and earth-friendly concrete. Wagners Holding Company has commercialised geopolymer concrete (alkali-activated aluminosilicate cement) at scale, eliminating the high-temperature kiln entirely. Geopolymer plant HVAC is fundamentally different — no kiln exhaust, no clinker mill, but new chemistry around silicate solution storage, alkali activator dosing, and curing temperature management.

Electric asphalt plants and pre-cast curing. Electric heating of bitumen storage, electric burners on small asphalt plants, electric steam generation for pre-cast curing — all reduce on-site fossil fuel combustion and therefore reduce combustion exhaust emissions. Duct scope on electric heating is dramatically smaller than fuel-fired.

What all decarbonisation pathways have in common from an HVAC contractor's perspective: comfort HVAC scope continues largely unchanged or expanded (new buildings, new operator stations); process duct scope changes significantly in chemistry, materials and sizing. SBKJ machinery scope sits inside the comfort HVAC envelope and remains relevant across the decarbonisation transition.

FAQ

What is the silica dust exposure limit for Australian aggregate quarries and concrete batching plants?

Safe Work Australia sets the respirable crystalline silica (RCS) workplace exposure standard at 0.05 mg per cubic metre 8-hour TWA. This is the killer figure — silicosis is notifiable through state Dust Diseases Authority registers and the NSW iCare scheme. Every duct design starts and ends with operator-station RCS exposure below this limit. Engineering controls per AS 1668.2 and AS 3957 are the primary control; respiratory PPE is secondary.

What duct materials are used for asphalt rotary dryer and bitumen vapour service?

Rotary dryer exhaust (220-280 degrees Celsius) is welded heavy fabrication carbon steel 4-6 mm with abrasion liners. Bitumen vapour return at storage tanks and tanker loading is stainless 304L (or 316L for coastal sites), earthed and bonded per AS/NZS 60079 Zone 2. No aluminium, no unbonded surfaces. Comfort HVAC is galvanised G275 on SBAL-V auto duct line to AS 4254.

Which Australian operators are major HVAC duct buyers in this sector?

Boral (ASX:BLD), Holcim Australia, Hanson Australia, Adbri (ASX:ABC), Cement Australia, Wagners (ASX:WGN), Independent Cement and Lime, BGC Cement, CSR Limited Building Products, Fulton Hogan, Downer Group Roads (ASX:DOW), BMD Constructions, SAMI Bitumen Technologies, Mawson Group, Hollow Core, Westkon Precast, Civilex and Strapdoor. Industry bodies: Cement Industry Federation, Cement Concrete and Aggregates Australia, Concrete Institute of Australia, Australian Asphalt Pavement Association.

How is dust controlled at crushers, conveyor transfer points and screens in a quarry?

Wet method (water spray bars) is the primary control. Where wet method is impractical, dry dust extraction: enclosure hood, ducted extract at 18-22 m/s transport velocity, cyclone primary separator (per AS 3957), pulse-jet bag filter (NFPA 654 and NFPA 660 compliance for combustible dust). Outlet loading below 30 mg per normal cubic metre. The heavy extract trunk duct is welded fabrication; the bag filter outlet and gallery comfort HVAC is sheet-metal on SBKJ machinery.

What standards govern Australian asphalt plant emissions?

State EPA licences typically specify total dust 50-80 mg per normal cubic metre at the dryer stack, NOx 300-500 mg per normal cubic metre, SO2 100-300 mg per normal cubic metre. VOC controlled through RTO at 800-900 degrees Celsius. Boundary monitoring per AS/NZS 3580 ambient air method with PM10 24-hour fence-line below 50 micrograms per cubic metre. Storage flammable per AS 1940. Hazardous area per AS/NZS 60079. LPG installations per AS 5601.

What is the SBKJ machinery scope for these projects?

Comfort HVAC and clean-air ductwork — control rooms, weighbridge offices, labs, MCC rooms, dispatch offices, operator pulpits and amenities. Fabricated on SBAL-V (16 m/min, 87 kW, 0.5-1.5 mm, 1500 mm), SBAL-III, SBAL-II auto duct lines, SBTF-1500C/1602/2020 spiral tubeformers, SBSF-1525 stitchwelder for stainless 304L work, SBPC1500 Pittsburgh, SBLR-600 lockformer, SBFB-1500 flat bar bender, SBEM-1250 plasma cutter, SBHF hydraulic folder. Heavy welded process extract duct is outside standard scope.

How is bitumen vapour at tanker loading controlled?

Closed-loop vapour return from the tanker dome to the storage tank ullage space during loading captures 95-99 percent of displacement vapour. Stainless 304L duct, all flanges bonded, earthing continuity verified before every load per AS/NZS 60079 Zone 2. Loading platform classification Zone 2 hemispherical 1.5-3 m radius. Hydrogen sulphide WES 10 ppm is the design point. RTO polishing on breather vents.

What is required for pre-cast moulding bay and curing chamber HVAC?

Moulding bay general extract 6-10 air changes per hour to handle release agent VOC, concrete dust and admixture release. Spray booth with downdraft and filter exhaust at release agent application. Steam curing chamber vent in 304L stainless to handle condensate; vent fan 5,000-20,000 m³ per hour. Trowel finishing extract at operator face. Wet-method sawing and grinding per AS 3957 for RCS control. SBAL-V galvanised for general extract; SBSF-1525 304L for steam vent.

Talk to an SBKJ engineer about your concrete, aggregate, asphalt or pre-cast HVAC duct fabrication scope →