Limestone is a major dry bulk cargo, with global seaborne trade of approximately 25 to 35 million tonnes per year. The cargo is principally calcium carbonate (CaCO3) used as a feedstock in cement manufacture, steelmaking flux, glass production, and lime kilns, and as construction aggregate. The IMSBC Code regulates limestone shipments under a Group C schedule with handling requirements driven by dust generation only.
Schedule structure
The IMSBC Code includes the following limestone-related schedule entries:
- Limestone: bulk crushed and screened limestone for industrial and construction use. Group C (not liquefiable, no chemical hazard).
- Calcium carbonate: a closely related entry covering finer-particle limestone products. Group C.
Both entries cover non-hazardous mineral cargoes handled under standard bulk procedures.
Cargo properties
Limestone is supplied in particle sizes ranging from quarry stone (50 to 200 millimetres) for steel flux and aggregate, through crushed grade (5 to 50 millimetres) for cement raw mix, to fine ground product (below 1 millimetre) for chemical and agricultural applications. Bulk density varies with particle size from approximately 1.4 tonnes per cubic metre for coarse stone to 1.6 tonnes per cubic metre for crushed and well-packed material. Stowage factor is approximately 0.6 to 0.7 cubic metres per tonne.
The cargo is non-toxic, non-flammable, non-self-heating, and non-reactive with steel structure. The principal handling concerns are:
- Dust generation: fine limestone dust is generated during loading and discharge, particularly from the finer crushed grades. Dust suppression is required at most modern terminals.
- Compatibility with weather: limestone is moisture-tolerant and requires no specific weather protection during loading or voyage. Wet limestone is somewhat heavier and may pack more densely in the hold.
- No chemical hazards: no special segregation, no temperature monitoring, no atmosphere monitoring required.
Major routes
Limestone seaborne trade flows include:
- Coastal Mediterranean and short-sea trade serving cement and steel industries.
- Vietnamese and Chinese export to Southeast Asian construction markets.
- Norwegian export to UK, Northern European, and African construction and steel markets.
- Caribbean export from Bahamas, Belize, and Mexico to US Atlantic and Gulf Coast cement plants.
- Egyptian export to Middle Eastern and Mediterranean markets.
Limestone is widely available globally, so most consumption is from local quarries within a hundred or two hundred kilometres of the cement or steel plant. Long-distance seaborne trade serves regions where local limestone is absent or of inferior quality.
Loading and discharge
Loading is by shore conveyor and shiploader. Loading rates of 1,500 to 4,000 tonnes per hour are typical. Hold preparation requires only standard cleanliness and bilge clearance. The cargo self-trims for crushed grades; coarse stone may require some bulldozer trimming.
Discharge is by grab-fitted shore cranes. Receiving ports are typically cement plants, steel mills, or aggregate distribution terminals.