Chlorures et concrete : cement et armatures

In Dakhla, salt is in the air your structures breathe. Direct answer: chlorides — sea spray, marine air, salts — penetrate concrete and depassivate the rebars even in alkaline media, triggering pitting corrosion, the most violent there is. The defences: a tight mix (W/C ≤ 0.45), increased cover in marine zones, careful curing — and for demanding coastal works, a CPJ 55.

Where chlorides come from

Three origins dominate. The marine environment: direct spray, salt-laden air, saline soils — the default exposure in Dakhla and along the whole Atlantic coast. Materials: insufficiently washed marine aggregates, non-potable mixing water, off-spec admixtures. History: some legacy chloride-based set accelerators — now banned in reinforced concrete.

The critical threshold

Corrosion starts when the free chloride content at the steel surface exceeds a threshold — on the order of 0.4 % of the cement mass as chlorides for common reinforced concrete (concrete-code exposure classes frame these limits per structure). The nuance matters: only the free fraction counts, the one dissolved in pore water; part of the chlorides binds to hydrates and stays inert.

How they advance

Chlorides do not flow: they diffuse through pore water, rise by capillarity in alternately wet and dry zones, and enter with water absorbed during rain and spray. The wetting-drying cycles of a marine facade work like a pump: each cycle deposits a little salt a little deeper.

Defence in layers

• Tight mix: W/C ≤ 0.45 in marine exposure, substantial cement content, careful compaction — density slows everything.
• Increased cover: steel depth is travel time; design codes raise it in coastal zones.
• 7 days of curing: a dense skin in the first week closes the surface expressway.
• CPJ 55 for demanding coastal works: 55 MPa at 28 days, Blaine fineness ≥ 380 m²/kg — the class recommended for the coastline.
• Barriers: coatings, protection mortars, surface water-repellents — as a complement, never a substitute for density.

Warning signs on a structure

Localised rust stains in facets, spalling along the rebars (rust swells until the cover pops), hollow sounds under the hammer. At the first signs: diagnosis (chloride profiling by coring at depth) then treatment — waiting only accelerates.

For your seaside works, CPJ 55 is formulated for that level of demand; CPJ 45 covers everyday work. Free quote within 24 h, delivered in Dakhla City.