Cement clinker is a major dry bulk cargo intermediate between raw cement materials and finished cement powder, with global seaborne trade of approximately 50 to 70 million tonnes per year. Clinker moves principally from regions with abundant limestone and energy resources to regions with cement grinding and packaging facilities but limited raw material supply, allowing the cement industry to optimise its capital-intensive clinker kilns separately from the lower-capital grinding operations. The IMSBC Code regulates clinker shipments under a Group C schedule with specific provisions for hot-loading and dust handling.
Schedule structure
The IMSBC Code includes a single schedule entry for cement clinker:
- Cement clinker: Group C (not liquefiable, no chemical hazard). Subject to handling provisions for elevated cargo temperature and dust generation.
The schedule applies to ordinary Portland cement clinker and to similar calcium silicate clinkers. Specialty clinkers such as calcium aluminate clinkers, sulphate-resistant clinkers, and white cement clinker are handled under the same schedule provisions.
Cargo properties
Cement clinker is the unmilled product of the cement kiln: nodules of fused calcium silicates and aluminates produced at temperatures of 1,400 to 1,500 degrees Celsius and then cooled. The product comprises hard granular nodules of approximately 5 to 50 millimetres in diameter, with a small fraction of fines from breakage. Bulk density is approximately 1.3 to 1.5 tonnes per cubic metre, similar to finished cement.
Distinctive properties affecting marine carriage:
- Hot-loading risk: clinker may be loaded directly from kiln coolers at temperatures of 80 to 150 degrees Celsius, particularly in continuous-production facilities where clinker is loaded directly to ship without intermediate cooling. Hot-loaded clinker can damage cargo hold paint coatings, accelerate corrosion of unprotected steelwork, and pose burn hazards to crew. The IMSBC Code requires the shipper to declare cargo temperature at loading and the master may decline excessively hot consignments.
- Dust generation: clinker dust is generated by mechanical breakage during loading, voyage motion, and discharge. The dust is fine, alkaline, and a respiratory hazard. Dust suppression is required at loading and discharge operations.
- Hardness: clinker is significantly harder than most bulk cargoes and accelerates wear of grabs, conveyors, and hold paint coatings.
- Insensitive to moisture: unlike finished cement, clinker is relatively insensitive to moisture exposure. Some surface hydration occurs over long voyages in humid conditions but the bulk of the cargo remains usable. This difference reflects the unmilled state of the product; only after grinding does the clinker exhibit the rapid moisture-reactivity of finished cement.
Hot-loading procedures
Where clinker is loaded above approximately 80 degrees Celsius, additional precautions apply:
- Crew should not enter cargo holds during or immediately after loading without enclosed-space safety procedures and temperature checks.
- Hatch covers and sealing surfaces should be inspected for thermal expansion and clearance.
- Ventilation should be increased during loading to dissipate heat and water vapour.
- Cargo cools to ambient over a few days; bulk temperatures of 50 degrees Celsius or below are typically achieved by the second or third day of voyage.
Bulk carriers carrying hot clinker should have certified hold paint systems rated for elevated temperatures or recent inspection of paint condition. Some cement majors have ship vetting procedures that exclude vessels with damaged or non-rated paint systems from clinker carriage.
Major routes
Cement clinker seaborne trade flows include:
- China and Vietnam (export of large surplus clinker production) to Africa, Bangladesh, the Philippines, and South America.
- Türkiye and Greece (Mediterranean export) to North Africa and West Africa.
- UAE and Saudi Arabia (export of large desert kiln capacity) to East Africa and South Asia.
- Iran (significant export despite sanctions, principally to Pakistan, the UAE, and East Africa).
Receiving ports for clinker are typically grinding terminals adjacent to cement distribution networks. The clinker is unloaded into shore silos and then milled with gypsum to produce finished cement for the local market.
Loading and discharge
Clinker loading is by shore conveyor and shiploader, similar to other bulk cargoes. Loading rates depend on shore equipment but are typically 1,000 to 3,000 tonnes per hour at major export terminals. Trimming with bulldozers may be needed for hatch closure.
Discharge is by grab-fitted shore cranes at receiving ports. Some receiving terminals have continuous unloaders with large bucket elevators or pneumatic systems, but grab discharge is the most common method. Discharge rates of 500 to 1,500 tonnes per hour per grab are typical.
Comparable cargoes
Clinker is one of the larger-particle Group C bulk cargoes, sharing handling characteristics with limestone, gypsum, and certain aggregates. Compared to finished cement, clinker is less moisture-sensitive but more abrasive and more prone to hot-loading issues. Compared to coal, clinker is non-self-heating, non-flammable, and lower-hazard, but generates similar dust loads.