Cement: IMSBC Code Schedule and Carriage

Portland cement is classified as Group C under the IMSBC Code: not liable to liquefy, no chemical hazard in the Group B sense. Its particle size, 5 to 30 micrometres median, is what sets it apart from almost every other bulk cargo. When aerated during loading, it flows like a low-viscosity fluid. Any water contact starts irreversible hydration that can convert a hold of powder into a concrete-hard mass. Its dust is highly alkaline and a serious respiratory and eye hazard. Getting these three properties right defines cement carriage.

Cement is one of the most widely traded dry bulk commodities by volume. Global seaborne cement trade runs at approximately 60 to 80 million metric tons per year of finished cement, with a further 50 to 70 million metric tons of cement clinker moving separately as an unground intermediate. The two cargoes share a Group C classification under the IMSBC Code but differ in almost every property that governs safe carriage. This article covers finished cement only.

The IMSBC Code was adopted by IMO Resolution MSC.268(85) in 2008 and entered force on 1 January 2011 as mandatory under SOLAS Chapter VI. It lists CEMENT as a dedicated schedule entry in Appendix 1. Amendment 06-21, adopted by Resolution MSC.500(105), and Amendment 07-23, adopted by Resolution MSC.539(107) with mandatory effect from 1 January 2025, have not changed the Group C classification or the fundamental hazard profile for cement.

Cement in the global supply chain

What Portland cement is and how it is made

Portland cement is a hydraulic binder: it reacts with water to form a rigid, load-bearing solid without requiring heat or air after the mixing stage. The chemistry that produces this behaviour starts in the cement kiln. Limestone and clay (or shale) are ground together, blended to a target raw meal chemistry, and calcined at 1,400 to 1,500 degrees Celsius. The resulting nodular kiln product is cement clinker: hard dark-grey calcium silicate nodules of 5 to 25 mm. Clinker is then cooled and ground in a ball mill or vertical roller mill together with approximately 4 to 6% gypsum (calcium sulfate). The gypsum controls the rate of reaction with water by inhibiting the rapid hydration of tricalcium aluminate (C3A). The product of that grinding is Portland cement.

The fineness of grinding determines both the chemical reactivity and the physical handling properties of the cement. A typical Ordinary Portland Cement (OPC) is ground to a Blaine specific surface area of 320 to 420 m2/kg, corresponding to a median particle diameter of 10 to 20 micrometres, with the finest particles below 5 micrometres. Some higher-strength cements are ground finer: a Class G oil-well cement is ground to 270 to 360 m2/kg, while rapid-setting cements may be ground to 450 m2/kg or above. This fineness is what makes cement dust so hazardous and what makes the aeration behaviour during loading so significant.

Portland cement powder, when settled and undisturbed, has a bulk density of 1,300 to 1,500 kg/m3. When freshly aerated, the entrained air between particles reduces the effective bulk density to 900 to 1,100 kg/m3. This difference in density between aerated and settled cement is the root cause of the stability concern during loading that masters and cargo officers must understand.

Cement types carried in bulk

The IMSBC Code schedule entry for CEMENT covers calcined hydraulic binders in general, including Ordinary Portland Cement (OPC or CEM I), Portland composite cements (CEM II through CEM V in the European EN 197-1 classification), blast-furnace slag cements, pozzolanic cements, and masonry cements. All are fine grey or off-white powders with similar physical handling properties. Supplementary cementitious materials such as fly ash, ground granulated blast-furnace slag (GGBS), and silica fume are sometimes co-loaded or carried in dedicated shipments; their handling properties differ somewhat (lower fineness for slag, higher fineness for silica fume at 15,000 to 25,000 m2/kg), but they fall under the same Group C classification and the same general carriage principles.

White Portland cement, used for architectural applications, is ground to the same or greater fineness than OPC but from raw materials with low iron content. It carries identical handling hazards.

Seaborne trade routes and volumes

Cement seaborne trade flows from large-scale export producers to markets with insufficient domestic kiln capacity. The principal export regions are Eastern Asia (China, Vietnam, South Korea, Japan, Thailand, Pakistan), the Eastern Mediterranean and Middle East (Turkey, Egypt, UAE, Saudi Arabia, Iran), and South Asia. The principal import regions are West Africa, East Africa, the Pacific island states, the Caribbean, and parts of Latin America and South Asia where demand growth outpaces local production.

China’s cement export volumes fluctuate significantly with domestic policy. Chinese exports have ranged from a few million to over 20 million metric tons in recent years, depending on domestic demand, government production limits, and freight market conditions. Vietnam has become one of the largest cement exporters in the world as new kiln capacity has substantially outpaced domestic demand, particularly for exports to the Philippines, Bangladesh, and African markets. Turkey’s cement sector, operating at some of the highest furnace efficiencies in the region, exports primarily across the Mediterranean and to West Africa.

Most finished cement trade moves on dedicated cement carriers rather than on conventional bulk carriers, for reasons of cargo protection and discharge efficiency that are examined in detail below. The vessel size range for dedicated cement carriers is 5,000 to 35,000 DWT, reflecting the typical lot sizes in this trade.

The IMSBC Code schedule for cement

Group classification and regulatory basis

The IMSBC Code Appendix 1 lists CEMENT as a Group C cargo in a schedule entry separate from CEMENT CLINKERS. Group C means the cargo is not liable to liquefy (no Transportable Moisture Limit testing is required) and does not present the chemical hazards that require Group B classification. There is no toxic gas evolution, no self-heating, no flammable off-gassing under normal carriage conditions.

What Group C does not say is that the cargo is hazard-free. The IMSBC Code schedule records special properties and special requirements for cement that reflect three genuine operational hazards: the aeration and free-flow behaviour of the powder during loading, the heavy alkaline dust, and the water reactivity that irreversibly destroys the cargo if moisture is present. All three are recorded in the schedule’s special requirements. None of them disappear because the Group C label appears on the cargo declaration.

IMSBC Code schedule particulars

The following table summarizes the cargo properties as recorded in the IMSBC Code schedule for CEMENT and the practical ranges from shipper declarations and industry experience:

The schedule notes that cement, when aerated during loading, behaves as a fluid and that this behaviour requires special attention during loading to allow the cargo to de-aerate and settle before further cargo is placed on top.

How cement compares with cement clinker

The most common source of confusion in cement carriage documentation is treating cement and cement clinker as interchangeable within Group C. They are not. The table below shows the differences that govern safe carriage:

The moisture sensitivity difference is the most operationally significant. A clinker cargo that absorbs water partially cakes and may require mechanical breaking at discharge, but the commercial value of the clinker as a grinding feed is diminished rather than destroyed. A cement cargo that absorbs free water sets irreversibly into a mass with the compressive strength of structural concrete. There is no remediation: the cargo is lost, and the hold requires mechanical demolition work before the next cargo.

Aeration, fluidisation, and stability during loading

Why cement fluidises

Portland cement at a median particle size of 10 to 20 micrometres has a very high specific surface area relative to its mass. When air is entrained between particles, either by pneumatic conveying from shore silos or by the turbulence of a loaded falling from a spout at height, the air cannot escape quickly. The fine particles resist gravity settlement because the viscous drag force on each particle from the surrounding air is large relative to the gravitational force. The result is a suspension that behaves macroscopically like a low-viscosity Newtonian fluid: it flows through small openings, levels to a flat free surface, and exerts hydrostatic pressure on hold walls.

This behaviour is qualitatively different from any coarse bulk cargo. Iron ore pellets dropped from a loading spout aerate slightly and settle within seconds. Cement loaded from a shore silo via pneumatic conveyor can remain fluidised for 10 to 30 minutes after loading into a hold. During that period, the cargo surface is not a fixed angle-of-repose pile but a near-horizontal fluid-like surface that responds to ship motion.

The stability implication of aerated cement

The stability concern during loading arises because a fluidised cement surface creates a free-surface effect analogous to liquid in a tank. The free-surface correction for an aerated cement surface reduces the ship’s effective metacentric height (GM) by a quantity equal to the second moment of the free surface area divided by the ship’s displacement volume. For a large hatch opening in a Handymax bulk carrier loading cement at a rate of 1,000 t/h, the free-surface correction from the aerated surface can be of the order of 0.10 to 0.30 m during the loading phase, depending on the hold geometry and the degree of aeration.

This does not routinely cause accidents, but it must be accounted for in the stability calculation. The IMSBC Code requires that a cargo that aerates during loading be treated with attention to stability during the loading operation, not only at the loaded departure condition. The loading plan should be reviewed before operations begin, and GM should be calculated at each stage of the sequence, including when large hatches are partially filled with aerated cargo.

Masters and chief officers loading cement in conventional bulk carriers for the first time should recognise that the cargo surface visible through the hatch when loading is in progress does not behave like a solid pile. Walking on an aerated cement surface is possible but the surface gives underfoot with a distinctive softness. Personnel should not enter a partially loaded hold while loading is in progress, for the same reason that one does not enter a grain hold during active pneumatic loading: the surface is not structurally reliable.

De-aeration and settling

Cement settles and de-aerates as air escapes upward between the particles. The rate of de-aeration depends on the fineness of the cement, the temperature, and the height of the cargo column. At typical loading temperatures of 15 to 35 degrees Celsius, a one-metre-deep newly loaded cement mass takes approximately 1 to 4 hours to reach close to its settled bulk density. A full hold of 10,000 tonnes loaded rapidly may continue to settle for 6 to 12 hours after loading is complete.

The practical consequence is that the draft observed immediately after loading will increase slightly over the subsequent hours as the cargo settles and the aerated air escapes. Surveyors conducting a final draft survey for quantity determination should allow adequate settling time after the last loading operation before taking the draft readings. The IMSBC Code notes the settling behaviour as relevant to the density and quantity determination.

Air escaping from a settling cement surface in an enclosed hold creates a dusty atmosphere within the hold. Hatch covers should not be entered during the settling period without respiratory protection. The dust is not only a nuisance: it is alkaline and at concentrations that can exceed occupational exposure limits in a poorly ventilated space.

Dust: caustic, fine, and respiratory hazard

The chemical basis of cement dust hazard

Portland cement dust is not simply an inert nuisance dust. It is alkaline, with a pH above 12 when wetted, because of the calcium hydroxide (Ca(OH)2) and calcium oxide (CaO) content in the powder. Calcium oxide reacts with moisture on skin or mucous membranes to form calcium hydroxide, an exothermic reaction that causes progressive alkali burns. Unlike acid burns, which cause immediate pain on contact, alkali burns penetrate tissue gradually as the strongly basic solution saponifies cell membranes. The delay in pain onset means that moderate exposures are often not recognised until significant tissue damage has already occurred.

The particle size that matters most for health is the respirable fraction, conventionally defined as particles below 10 micrometres aerodynamic diameter. Portland cement contains a substantial respirable fraction: particles below 10 micrometres typically represent 20 to 40% of the mass of a finely ground OPC. These particles penetrate into the alveolar region of the lung. Prolonged occupational exposure to Portland cement dust is associated with chronic obstructive pulmonary disease, occupational asthma, and, at high exposures over many years, pneumoconiosis. The alkaline chemistry adds chemical irritation to the mechanical particle loading.

The eye is the most sensitive target organ for cement dust exposure. Calcium hydroxide solution causes liquefactive necrosis of the cornea, more aggressive than the coagulative necrosis from acid exposures at comparable pH, because the OH- ion penetrates tissue without self-limitation. A single unprotected exposure to an eye-level dust cloud during loading or discharge can cause permanent corneal damage within seconds of contact.

Occupational exposure limits and their relevance to marine operations

Occupational exposure limits (OELs) for Portland cement dust vary by jurisdiction. The UK Health and Safety Executive EH40 table sets 10 mg/m3 (inhalable) and 4 mg/m3 (respirable) as 8-hour time-weighted averages. The US OSHA permissible exposure limit is 15 mg/m3 (total dust) and 5 mg/m3 (respirable). The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value is 1 mg/m3 for the respirable fraction, reflecting concern about long-term lung effects at lower concentrations.

In marine loading operations, dust concentrations at the loading spout during active cement loading from a conventional shiploader can substantially exceed these limits in the absence of engineering controls. Pneumatic loading into dedicated cement carriers routes all dust to the hold interior, where it settles with the cargo: this is one of the practical advantages of enclosed systems. Grab-and-hopper loading of conventional bulk carriers generates dust at the point of cargo transfer and at the hatch, where wind dispersion across the vessel deck is common.

Personal protective equipment during cement loading and discharge operations should include, at minimum, a P2 (Europe) or N95 (US) half-face respirator and chemical splash goggles. A full-face respirator is preferred wherever dust levels are above the basic threshold, because it protects both the respiratory tract and the eyes. Gloves and skin-covering clothing are required to prevent cement contact with skin during extended exposure.

Dust suppression methods and their limits

Water spraying at cargo transfer points is the standard dust suppression method for conventional bulk carrier cement operations. The principle is to bind the fine particles into agglomerates too heavy to become airborne. Effective water spray reduces respirable dust concentrations by 60 to 80% in operational tests. The critical constraint is that water application must be controlled to avoid wetting the cargo mass itself: cement dust suppression requires wetting the airborne fines, not the bulk.

Enclosed loading systems are more effective and avoid the tension between dust suppression and cargo protection. Telescoping loading spouts with internal dust filtration systems capture dust at the point of generation and return it to the cargo stream or discharge it to a bag filter. Shore shiploaders at modern cement export terminals use this approach as standard.

Ventilation of the cargo area during loading is counterproductive if the goal is dust suppression: increased air movement increases dust suspension. During loading, hatches not actively receiving cargo should be closed to prevent cross-contamination of the hold atmosphere.

Water reactivity: the absolute imperative to keep cement dry

The chemistry of cement hydration

Portland cement reacts with water through a series of chemical reactions collectively called hydration. The four main clinker minerals react at different rates. Tricalcium aluminate (C3A) reacts almost immediately with water; the gypsum added during grinding controls this reaction by forming ettringite, which slows the C3A hydration to an hours-scale timescale. Tricalcium silicate (alite, C3S) hydrates over hours to days, forming calcium silicate hydrate (CSH) gel, which is the primary strength-giving product, and calcium hydroxide. Dicalcium silicate (belite, C2S) hydrates much more slowly, over weeks to months. Tetracalcium aluminoferrite (C4AF) hydrates over days, contributing to early colour but little strength.

In a maritime context, the critical fact is the timescale. Cement paste (cement mixed with water) sets to initial stiffness at approximately 45 to 90 minutes from water contact at 20 degrees Celsius. It reaches final set at 3 to 6 hours. Compressive strength development continues for weeks, but by 24 hours a cement paste has reached 10 to 30 MPa compressive strength. Structural concrete is typically designed around the 28-day strength of 25 to 50 MPa.

A hold of cement that absorbs free water from a hatch seal failure or hold bilge flooding will, over the course of a multi-day voyage, develop compressive strength in the wetted zones. The cargo does not become uniformly concrete: the reaction occurs where free water is present, and dry zones within the hold remain as powder. But the wetted zones near the hatch coaming, bilge, or water ingress point set into a mass that cannot be discharged by grab or pneumatic means.

How wetting occurs in practice

The most common cause of cement wetting during a voyage is failure of the hatch cover rubber seals. Cement carrier hatch covers are subject to the same fatigue, UV degradation, and compression-set effects as on any bulk carrier, but the consequence of a small hatch leak is far more severe than for most cargoes. A small gap in the hatch seal through which 5 to 10 litres of seawater per hour can enter over a 15-day voyage deposits 1,800 to 3,600 litres of water into the cargo, which is enough to set a zone of cement weighing hundreds of tonnes.

Condensation is a secondary but real source of moisture. Hold atmosphere in a loaded cement hold contains elevated humidity from the moisture released during de-aeration of freshly loaded cement. If the hold is cooled by low ambient temperatures at sea while the hold atmosphere temperature remains above the dew point, condensation forms on the inside of the hatch covers and the upper hold structure, dripping onto the cargo surface. The IMSBC Code schedule notes that cement must not be wetted and that the cargo is moisture-sensitive.

Bilge leakage is a third source. Cement fines that migrate into the bilge well during loading (which they do readily, through any gap in the bilge strainer cover) begin to hydrate in contact with bilge water. As the hydrated cement paste accumulates in the bilge, it blocks the bilge suction, making further bilge pumping impossible. The blocked bilge then accumulates water from hull weeping or condensation, and this water gradually seeps back into the cargo from below through the bilge drainage system.

Consequences of wetting: cargo loss and hold damage

A moderate wetting event that affects 500 to 2,000 tonnes of a 15,000-tonne cement cargo sets the wetted zone into a mass that cannot be discharged by the ship’s pneumatic system or by grab. The discharge must be interrupted while the set cement is broken mechanically, requiring excavator-type equipment lowered into the hold or hydraulic impact hammers working from the hatch opening. This operation takes days rather than hours, causes significant port delay, and generates a commercial dispute about who bears the cost and the liability for the cargo loss.

A severe wetting event that affects the majority of the hold volume converts the entire hold into a condition indistinguishable from a reinforced concrete structure, except without the reinforcement. Documented cases exist in P&I club records of holds that required full mechanical demolition before the vessel could resume trading. The hold plating can be intact but the hold interior is filled with set concrete that must be broken up and removed in pieces.

Beyond the cargo loss, set cement in the bilge well and bilge system requires specialist cleaning. Calcium silicate hydrate that sets in bilge pipework fills the pipe bore and cannot be cleared by chemical means. Physical replacement of bilge sections may be required.

Dedicated cement carriers: vessel design and pneumatic discharge

Why a dedicated carrier exists

The two hazards of cement, moisture sensitivity and dust, are both addressed more completely by a dedicated enclosed vessel design than by any modification to a conventional bulk carrier. The dedicated cement carrier was developed over the second half of the 20th century specifically for this cargo, and the design has been refined to the point that virtually all major cement export terminals are matched to dedicated carrier discharge systems.

A dedicated cement carrier is a fully enclosed vessel with no open hatch covers in the conventional bulk carrier sense. Cargo hatches are sealed and weather-tight to a standard exceeding conventional bulk carrier requirements, because the consequence of any ingress is immediate cargo loss. The holds are fitted with aerating pads, also called fluidising panels or aeroslides, on the tank top (the inner bottom plating). These pads are permeable to air but not to cement powder: compressed air injected from below lifts the fine particles into a fluidised state, allowing the cargo to flow by gravity along a sloped tank top toward the discharge point.

The discharge system connects the hold via aerated pipes to a rotary compressor and discharge blower, which drives the fluidised cement pneumatically from the ship’s hold discharge manifold through a flexible hose to the shore silo inlet. No open handling occurs: the cement travels from the ship’s hold through an enclosed pipe to the shore silo without any contact with open air, rain, or humidity.

Vessel size range and fleet characteristics

Dedicated cement carriers range from small coasters of 1,000 to 3,000 DWT used in coastal and island distribution trades to ocean-going vessels of 20,000 to 35,000 DWT used in deep-sea trades from Asia to Africa and the Americas. The bulk of the fleet sits in the 5,000 to 15,000 DWT range, reflecting the typical lot sizes in the cement trade: a 10,000-tonne shipment is a large order for a receiving market, and the smaller vessels can access shallower ports in developing-country markets.

Self-discharging cement carriers with integral pneumatic systems are the majority of the dedicated fleet. Some operators use purpose-built vessels with twin screws and high maneuverability to access confined berths in ports with limited facilities. Others operate vessels with a small conventional cargo crane alongside the pneumatic system, providing flexibility for ports where shore connections for pneumatic discharge are not available.

Pneumatic discharge rates and operational parameters

Pneumatic discharge rates on a dedicated cement carrier depend on the compressor capacity, the pipe diameter, the cargo distance from hold to shore silo, and the cement’s fluidisation characteristics. Typical rates at modern cement terminals are 200 to 500 t/h per discharge line. Large vessels with multiple discharge points operating simultaneously can achieve 600 to 800 t/h total ship output. These rates are lower than the grab discharge rate for coal or iron ore, but the advantage is the complete absence of dust emission and the direct delivery to shore silos without intermediate handling.

The aerating pads on the tank top must be maintained in clean condition. Cement dust that penetrates the pad membrane reduces airflow and eventually blocks the pad, requiring replacement. After each voyage, the tank top pads are backflushed with compressed air to clear any accumulated fines from the inside face of the membrane. Pad replacement is a planned maintenance item, typically every 3 to 5 years on an active cement carrier.

Residue after pneumatic discharge is typically 0.1 to 0.3% of cargo weight in a well-maintained system with clean, dry cement in good condition. This compares very favorably with grab discharge from a conventional bulk carrier, where 1 to 2% residue per hold is common. The low residue figure is one of the commercial advantages that makes dedicated carriers preferred by cement shippers who value delivered quantity accuracy.

Conventional bulk carrier cement carriage

Conventional bulk carriers carry cement on routes and in lot sizes where dedicated carriers are not commercially available or where the receiving port lacks pneumatic discharge infrastructure. West African and Pacific island trades include routes where conventional bulk carriers loaded with cement are the only practical option.

Conventional carrier loading uses enclosed shiploaders with telescoping spouts and dust filtration. The cargo is loaded into the holds through the hatches, and the same aeration and stability considerations that apply to dedicated carrier loading apply here, plus the additional risk of the open hatch during loading. Discharge from a conventional bulk carrier uses shore grab cranes with enclosed hoppers connected to covered conveyors, or, where available, portable pneumatic discharge machines (ship unloaders) that can be connected to the vessel’s cargo hold.

The commercial limitations of conventional carrier cement carriage are significant. Grab discharge is slower than pneumatic, generates more dust, and leaves a higher residue fraction. Cargo insurance premiums are higher because hatch cover integrity on a conventional bulk carrier is a greater risk than on a dedicated carrier with its superior sealing standards. Some cement shippers refuse to load their product on conventional bulk carriers or impose strict hatch cover water test and hold inspection requirements before accepting the vessel.

Hold preparation and pre-loading requirements

The dryness standard for cement holds

The hold preparation standard for cement is absolute: the hold must be completely dry before any cement is loaded. There is no acceptable level of residual moisture because any free water will initiate hydration at the point of contact. This is a stricter standard than for any other Group C cargo and stricter than for most Group B cargoes, which can tolerate some residual moisture without immediate chemical consequence.

Cargo hold preparation standards for cement require that all hold surfaces, including the tank top, frames, web frames, hatch coaming, and hatch covers, be visually dry. The bilge well must be pumped completely dry, the bilge strainer cover must be intact and in good condition, and the bilge high-level alarm must be tested and confirmed operational. Hold ventilators must be secured and sealed against rain or spray ingress.

Prior cargo residues must be completely absent. Cement is chemically sensitive to contamination. Coal or petroleum coke residues introduce sulphur and carbon compounds that react during cement hydration to produce sulfoaluminate phases associated with concrete durability problems. Salt contamination introduces chloride ions that accelerate steel reinforcement corrosion in concrete applications. A hold that previously carried fertilizer may contain nitrogen, phosphorus, or potassium compounds that are unacceptable as trace contaminants in a cement product sold for structural concrete.

Hatch cover water testing

The hatch cover water test is not optional for cement loading; it is a fundamental requirement. The standard procedure is to hose water under pressure around the entire hatch perimeter with the hatch cover closed, while observers inside the hold with torches look for any drips, weeps, or water penetration. Both the top of the hatch from outside and the interior coaming face are checked. Any point of ingress must be repaired before loading begins.

The hatch cover seals are the highest-risk component. Rubber seals degrade with time, UV exposure, and compression cycling. Cross-joints at the corners of hatch panels are the most common failure points, because the rubber cannot conform precisely to a three-dimensional corner junction. The mate’s receipt should record the date and result of the water test, and the certificate should be retained as a voyage document in case cargo claims arise at discharge.

On a dedicated cement carrier, hatch sealing standards are higher than on a conventional bulk carrier because the vessel operator’s liability for cargo condition is the same as for any carrier, and the consequence of a failure is an entire hold of set concrete. Some dedicated carrier operators install inflatable hatch seals (bladder seals that are pressurised before the vessel sails) in addition to standard rubber compression seals, providing a redundant weathertight barrier.

Bilge well preparation and management

The bilge well is the most significant hidden risk in cement hold preparation. Cement fines, which are extremely mobile due to their fine particle size, migrate through any gap in the bilge strainer cover and accumulate in the bilge well. Once in the bilge well in contact with bilge water, the fines hydrate. Initial hydration produces a slurry that can still be pumped if cleared promptly; extended hydration produces a paste and then a solid mass that blocks the bilge pump suction pipe.

The standard approach is to ensure bilge strainer covers are intact before loading, clear and dry the bilge well completely before the first cement is loaded, and monitor the bilge level daily during the voyage. If the bilge level rises during a cement voyage, the bilge should be pumped immediately, and the source of the ingress (water from condensation, hatch leak, or hull weeping) must be investigated. Cement fines in the pumped bilge water will foul the bilge pump impeller and discharge check valve; these must be flushed with fresh water after each cement voyage.

If bilge cement paste is allowed to set, it requires mechanical removal. Pneumatic hammer work inside the bilge well is confined-space work with significant hazard from the strongly alkaline paste and the enclosed-space atmosphere. The bilge section may need to be cut out and replaced if the obstruction cannot be cleared mechanically. This repair takes the vessel off-hire for several days and is entirely preventable with bilge well discipline during loading and voyage.

Loading operations

Shore terminal and loading system requirements

Cement export terminals are purpose-designed for enclosed loading. The shore silo stores cement after production or receipt from the mill. The loading conveyor, which may be a belt conveyor in a fully enclosed tube, a screw conveyor, or a pneumatic pipe, transfers cement from the silo to the shiploader. The shiploader boom extends over the vessel and routes the cargo through a telescoping loading spout that passes into the hatch opening and delivers the cargo inside the hold, below hatch level, to reduce free-fall height and dust generation.

Telescoping spouts at modern terminals include a concentric outer sleeve through which suction-ventilated air is drawn upward through the annular gap between the spout and the inner fall, capturing dust before it exits the hatch. The captured dust is returned to the hold or discharged to a filter unit. At terminals with this equipment, visual dust emission at the hatch during loading is minimal. At older terminals with open spout designs, the dust plume from a loaded hatch during active loading is visible from considerable distance and requires greater reliance on PPE for vessel crew.

Loading rates at large export terminals are 1,000 to 2,000 t/h per spout. Some terminals with multiple spouts can load at 3,000 to 4,000 t/h total when two hatches are loaded simultaneously. These rates are similar to iron ore loading rates on a per-spout basis.

Managing aeration during loading

The master and chief officer must monitor cargo aeration during loading and plan the sequence to allow adequate settling time. A loading plan that fills one hold completely before moving to the next allows each hold to begin de-aerating before additional weight is added. A loading plan that partially loads all holds simultaneously with aerated cement in each hold creates the maximum combined free-surface correction and the lowest GM condition during the operation.

Hold trim during loading of cement requires attention to the spout position. Because aerated cement flows like a fluid, the cargo surface in a hold being loaded will be nearly horizontal regardless of where the spout directs the flow. Unlike iron ore or grain, it is not necessary to move the spout around the hold to achieve a level surface during the loading operation: the cargo self-levels. However, when loading is paused and the cement begins to de-aerate, it will settle to a surface profile that reflects where the mass was greatest. The final trimming pass, after the main loading is complete, should aim to achieve a level settled surface consistent with the hold geometry.

Pre-departure hold condition check

After loading is complete and hatch covers are closed, the master should verify that all hatch covers are properly dogged and sealed, that hold ventilators are closed against rain ingress, and that bilge well levels are checked and recorded. The vessel should not depart if any hatch cover is known to be defective, because a single hatch seal failure on a cement cargo represents the loss of all cement in that hold.

The load-line survey requirement for watertight integrity of hatch covers is especially pertinent for cement vessels. A vessel that carries coal or grain with a leaking hatch cover may have a cargo claim; a vessel that carries cement with a leaking hatch cover has a cargo loss and a hold full of set concrete.

Voyage handling

Hold ventilation during a cement voyage

The IMSBC Code does not require active ventilation for cement holds during the voyage in the same way as it does for some Group B cargoes. However, the decision on whether to open hold ventilators during the voyage deserves consideration.

The fresh cement in a newly loaded hold releases moisture as the aerated bulk de-aerates, raising the hold relative humidity. If the hold atmosphere is significantly warmer than the outside air, condensation can form on the inside of the hatch cover and the upper hold steel structure, and this condensate will drip onto the cargo surface. The standard guidance for most bulk cargoes is to ventilate when the outside dew point is below the hold dew point, to remove the moist hold atmosphere before it condenses. For cement, this guidance must be balanced against the risk that any malfunction in the ventilation system, or any rain that enters through an open ventilator, would wet the cargo.

The safer practice for most cement voyages, particularly in the tropics and in monsoon or frontal weather, is to keep hold ventilators closed and accept the slightly elevated hold humidity. The risk of condensation-derived moisture damage on a calm tropical voyage is smaller than the risk of rain ingress through a ventilator that is open during a squall. On cooler, drier routes (North Atlantic in winter, for example), surface ventilation when weather permits is reasonable.

Monitoring cargo condition

Cargo condition can be checked by visual inspection through hatch inspection ports, which most bulk carriers and dedicated cement carriers are fitted with. A functioning inspection port allows the officer to observe the cargo surface without opening the hatch. The surfaces to look for are the same as for cement clinker water damage: white deposits (calcium hydroxide precipitates), dark-wet patches, or visible surface hardening. Any of these observations should be logged, investigated for the water source, and reported to the operator.

Bilge level monitoring during the voyage is as important as pre-departure checks. A rising bilge level in a cement-loaded hold indicates water ingress. The source should be traced: check hatch cover condition, check the hold ventilator status, and check hull survey records for the bilge section condition. If bilge level continues rising and pumping does not clear it, this may indicate a blocked bilge pump suction from early cement hydration in the well.

Discharge operations

Pneumatic discharge from a dedicated cement carrier

Discharge on a dedicated cement carrier begins with connecting the ship’s discharge manifold to the shore silo inlet via a flexible hose. The ship’s rotary compressor is started and begins pressurising the hold via the aerating pads. Cement in the aerated state flows downward by gravity along the sloped tank top toward the discharge sump, where the pneumatic blower picks it up and drives it through the discharge line. The discharge rate is controlled by adjusting the blower speed and the aerating air pressure.

The hold temperature rises slightly during pneumatic discharge due to the compression of the aerating air. This is a normal operational effect and does not affect cargo quality. Discharge personnel monitor the discharge line pressure and temperature to detect blockages: a pressure spike in the discharge line without a corresponding flow rate indicates a cargo plug, which must be cleared by depressurising and manually breaking the blockage at the pipe access point.

Residue after pneumatic discharge, as noted above, is typically 0.1 to 0.3% of cargo weight. The residue is cleared by hand-shoveling to the sump after the hold aerating pads are used to fluidise the last of the cargo. Hold cleaning after cement discharge on a dedicated carrier is simpler than for most bulk cargoes because the enclosed hold design minimises the scatter of cargo material onto frames and upper structure.

Grab discharge from a conventional bulk carrier

Grab discharge of cement from a conventional bulk carrier is slower, dustier, and leaves higher residue than pneumatic discharge. It is used where the receiving port has no pneumatic discharge capability and the cement trade requires it. Enclosed grab systems and covered hoppers are the best available dust control for this operation.

Shore crane grabs selected for cement discharge should have solid-shell construction without gaps in the grab shell, because cement flows through small openings readily. The grab is lowered into the settled cargo, closes around a volume of cement, and lifts to the hopper. During lifting through the hold atmosphere, some cement spills through imperfections in the grab closure, contributing to hold dust levels and in-hold losses.

Discharge rates by grab on cement are typically 300 to 800 t/h per crane, lower than for iron ore or clinker because the grab must be handled carefully to minimise spill. The operating team should wet-spray the cargo surface between grab cycles to reduce airborne dust. This water application must be carefully controlled: the objective is to bind surface fines, not to wet the bulk, and excessive water application wets the cargo and starts hydration.

Residue after grab discharge is 1 to 3% of hold volume, concentrated in the bilge area and hold corners. The residue must be shoveled manually to a collection point and discharged. If any cargo has set due to bilge leakage during the voyage, the set zones must be identified before residue clearing begins, because shovels cannot break set cement and the set zones must be excluded from any manual clearing attempt and treated with mechanical equipment.

Post-discharge hold cleaning

After cement discharge, the hold cleaning priority is the bilge well and bilge system. Any cement paste in the bilge must be removed before it sets further. High-pressure fresh water hosing of the bilge well immediately after hold access is established after discharge is the correct response. Cement paste that is still hydrating responds to flushing; cement paste that has set fully does not.

The hold frame faces, hatch coaming, and hatch cover undersurface should be washed with fresh water to remove cement deposits. These deposits are alkaline and continue to react slowly with atmospheric moisture if not removed, creating calcium carbonate crusts that block drainage channels and are harder to remove over time than freshly hydrated cement.

A cargo hold cleaning certificate from a surveyor or a chief officer’s declaration of hold cleanliness, with photographic records, is the standard documentation after cement discharge and before loading the next cargo. If the next cargo is another cement shipment, the hold must be re-dried after washing.

Trade routes, vessel selection, and commercial context

Major seaborne cement routes

The largest cement trade flows are from East and Southeast Asia to West Africa, East Africa, the Pacific, and the Americas. Vietnam-to-Philippines, Vietnam-to-Bangladesh, and Vietnam-to-Africa are among the highest-volume routes in the dedicated cement carrier trade. Turkish-origin cement moves primarily to West Africa, the Mediterranean basin, and occasionally to North America. Chinese cement exports, when volumes are high, move primarily to Southeast Asia and Africa on both dedicated carriers and conventional bulk carriers depending on port capability.

Dedicated cement carriers dominate on routes where the receiving port has pneumatic discharge infrastructure. Conventional bulk carriers dominate on routes to ports with only grab discharge capability. The presence or absence of a pneumatic shore connection is the primary determinant of which vessel type is commercially viable on a given route.

Charter party considerations specific to cement

Cement charter parties routinely include clauses that address the specific risks of this cargo. Hatch cover water-tightness warranties are standard: the shipowner warrants that all hatch covers are in good and weathertight condition before loading. Cargo claims arising from hatch seal failure during the voyage are at the owner’s risk under standard terms.

Cargo temperature at loading is not a charter party issue for cement in the way that it is for cement clinker, because finished cement is produced and stored at ambient temperature. However, charter parties for cement in tropical trades sometimes specify maximum ambient temperature and humidity conditions at loading, because cement loaded in a high-humidity environment absorbs moisture from the air during the loading operation.

The draft survey at discharge ports that lack shore scales is the standard quantity determination method. The low compressibility of settled cement means that draft surveys on cement shipments generally show close agreement between loaded and discharged tonnage, provided that the survey procedures are correctly applied and dock water density is accurately measured.

Soda ash and alumina: comparable fine-powder Group C cargoes

Cement shares some handling characteristics with soda ash and alumina, both Group C fine powders. The distinctions clarify the specific properties that define cement carriage.

Soda ash (sodium carbonate) is a fine white alkaline powder, also Group C, carried in bulk. Like cement, it generates alkaline dust and is moisture-sensitive (though it does not set irreversibly; it cakes and may dissolve partially, affecting product quality). Unlike cement, it does not aerate and fluidise during pneumatic loading to the same degree, and it does not set hard on wetting.

Alumina (aluminum oxide) is a fine white or off-white powder, Group C, carried in large volumes on dedicated alumina carriers with full pneumatic or auger discharge systems. Alumina is moisture-tolerant (it does not react with water chemically) and is not alkaline in the hazardous sense. It has similar aeration behaviour during loading, with the same stability implications. Unlike cement, alumina survives a wetting event without cargo destruction: damp alumina can be dried and used. Cement cannot.

The comparison makes the water reactivity of cement the defining hazard that separates it from otherwise similar fine-powder cargoes.

Limitations

This article describes the IMSBC Code schedule for CEMENT as defined through Amendment 07-23 (IMO Resolution MSC.539(107), mandatory from 1 January 2025). The IMSBC Code is amended on a two-year cycle by the IMO Maritime Safety Committee. The current schedule text should be verified against the edition published directly by the IMO, not against commercial reproductions, which may reflect prior amendment versions.

The bulk density, stowage factor, and aeration behaviour values in this article represent the range for Ordinary Portland Cement and similar hydraulic binders traded globally. Speciality cements, including oil-well cements, rapid-hardening cements, white Portland cement, and supplementary cementitious materials such as fly ash or GGBS, have different fineness values and may aerate differently during loading. The shipper’s cargo declaration is the contractual statement of properties for any specific shipment.

The stability analysis of the aeration free-surface effect in this article is qualitative. Quantitative calculation requires the actual ship’s stability booklet, the hold geometry, the loading rate, and a specific assessment of the aeration time constant for the cement being loaded. Stability calculations for cement loading should be performed using the loading computer with appropriate input from the cargo declaration.

Occupational exposure limits cited here are from the UK HSE, US OSHA, and ACGIH as of the article’s publication date. Port-state requirements may differ, and applicable exposure limits at a specific port are determined by the laws of that port state. Masters and operators should verify local requirements at ports of loading and discharge.

Pneumatic discharge system parameters (rates, residue percentages, aerating pad maintenance intervals) are from industry practice across the dedicated cement carrier fleet and represent typical values. Actual performance depends on the vessel’s installed equipment, maintenance condition, and the cement’s fluidisation characteristics.

See also

• IMSBC Code
• IMSBC Code Group C Cargoes
• Cement Clinkers: IMSBC Code Schedule and Carriage
• Limestone: IMSBC Code Schedule and Carriage
• Gypsum: IMSBC Code Schedule and Carriage
• Cargo Hold Preparation Standards
• Marine Cargo Hold Ventilation
• Free-Surface Effect
• Bulk Carrier
• Cargo Draught Survey for Bulk Carriers
• Soda Ash: IMSBC Code Schedule and Carriage
• Alumina: IMSBC Code Schedule and Carriage
• IMSBC Cement Calculator
• Cement Carrier CII
• IMSBC Group A/B/C Classification