Sea Sand Washing
Treating abundant marine sand so it meets concrete and plaster specifications.
Sea sand (offshore or marine sand) is abundant, well graded and free of organic contaminants, but its shell and chloride content make the construction industry reluctant to use it. CFlo wet processing plants apply wet sizing, attrition scrubbing, classification and washing to reduce chlorides to desirable levels, producing concrete and plaster sand to BS 882:1992.
Sea sand as a construction resource
Sea sand has found application in coastal areas of many countries. In Asia, where coastal areas are rich in sea sand, it is already widely used in local concrete construction. These sands, however, carry excess chlorides from deposition in saline water and need treatment before use. They are generally suitable for base and sub-base concrete, and tests have shown that even reinforced concrete can be made from them, yet the construction industry remains extremely reluctant to accept sea sand.
Its natural advantages are considerable:
- More rounded or cubical, like river sand
- Generally good and consistent grading, being a natural deposit
- No organic contaminants or silt
- Abundantly available
- Can be mined at low cost
The two barriers: shells and chloride
Shell content has no adverse effect on concrete strength as such, but it reduces workability. Investigations show shells above 5 mm affect workability to some extent, while those below 5 mm cause no significant reduction, so shell content alone does not make sea sand prohibitive for concrete.
Chloride is the more serious issue. Views and standards differ considerably on permissible chloride levels, but it is certain that chloride attacks and corrodes reinforcement, affecting the durability of concrete structures, and causes efflorescence as salts ooze out of the concrete. Chloride in concrete can come from cement, aggregates, water and even admixtures; it is the overall effect that matters, and chloride content must be controlled within limits.
How CFlo treats sea sand
CFlo wet processing systems use wet sizing, attrition scrubbing, classification and washing to reduce chloride content to desirable levels. The range of sea sand washing plants can treat sea sand to produce both concrete sand and plaster sand, depending on feed gradation, to BS 882:1992 specification.
Water recovery in the system is lower than usual, as a good part of the water must be rejected due to chloride build-up. Chloride-rich silt obtained after washing can be bagged and used as an eco-friendly fertiliser, and wastewater can be processed through reverse osmosis before release. The related CFlo platform for sea sand duty is the Combo all-in-one washing system.
Frequently asked questions
Can sea sand be used to make concrete?
Yes, once treated. Untreated sea sand is generally suitable for base and sub-base concrete, and tests have shown even reinforced concrete can be made from it. CFlo washing plants reduce the chloride and shell content so the sand meets BS 882:1992 for concrete sand and plaster sand.
How is chloride removed from sea sand?
Through wet sizing, attrition scrubbing, classification and washing, which together bring chloride down to desirable levels. Because chloride builds up in the circuit, a good part of the process water is rejected rather than recycled, and that wastewater can be treated by reverse osmosis before release.
Do sea shells affect concrete quality?
Shell content has no adverse effect on concrete strength as such, but it reduces workability. Shells above 5 mm affect workability to some extent; those below 5 mm show no significant reduction. CFlo processing rejects sea shells during washing, removing the issue altogether.
Why does chloride content matter in concrete?
Chloride corrodes the steel reinforcement in concrete, undermining the durability of the structure, and causes efflorescence as salts ooze out of the surface. Since chloride can enter concrete from cement, aggregates, water and admixtures, the fine aggregate's contribution must be controlled within limits.
What happens to the silt and wash water from a sea sand plant?
The chloride-rich silt recovered after washing can be bagged and used as an eco-friendly fertiliser. Wastewater, which cannot all be recycled because of chloride build-up, can be processed through reverse osmosis before its release, keeping the operation environmentally responsible.
What products can a sea sand washing plant make?
Depending on feed gradation, CFlo sea sand washing plants produce both concrete sand and plaster sand to BS 882:1992 specification. The advantages of the raw material, consistent natural grading, rounded particles and low cost, carry through to the finished construction sand.
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