Chargement…
Chargement…
by Dakhla Aménagement Team
Alkali-aggregate reaction (AAR) is the sneakiest of concrete pathologies. Direct answer: it requires three conditions together — alkalis from the cement, reactive aggregates and moisture — to form a swelling gel that cracks the structure years later. Prevention happens before pouring: controlled aggregates and a suitable mix design.
Some aggregates contain amorphous silica (opal, chert, certain basalts and sandstones). The concrete's pore solution, rich in sodium and potassium alkalis from the cement, attacks this silica and forms an alkali-silica gel. The gel absorbs moisture and swells; the internal pressure cracks the paste around the aggregates, then the whole member. Remove any one of the three actors — reactive aggregate, alkalis, moisture — and the reaction stops cold.
The signature is visual: map cracking (polygonal pattern) on exposed faces, often with whitish gummy exudations in the cracks, relative displacements between elements, measurable swelling over time. AAR progresses over 5 to 20 years — a structure sound at 2 may declare its pathology at 10.
AAR is rare — the vast majority of commercial aggregates are stable — but when it occurs it is severe and irreversible: you treat the symptoms (injections, cuts, waterproofing to cut the moisture), you do not 'cure' the structure. It is a laboratory and quality-control pathology: it belongs to the cement maker who documents his alkalis and to the aggregate supplier who certifies his resource.
The literature places the maximum risk in hot, humid climates; the Atlantic coast combines moisture and salts. That does not make AAR a daily threat — aggregate reactivity remains the rare condition — but it is one more reason to demand material certificates on high-stakes works, and not to neglect the waterproofing of exposed parts.
Our CPJ 45 and CPJ 55, compliant with NM 10.1.004 and EN 197-1, come with 2, 7 and 28-day strength tests and a per-lot certificate — the traceability that feeds your material file. Free quote within 24 h, delivered in Dakhla City.
Quarry origin, petrographic analyses, reactivity tests: material documentation is the first barrier.
Amorphous silica (opal, chert, certain basalts): in doubt about the resource, the test decides before pouring.
Binders with contained content or pozzolanic additions: the mix can trap alkalis in stable hydrates.
Waterproofing, drainage, sound roofs: dry concrete does not swell — miss the third condition and AAR stops.
Crack mapping, exudations, swelling records: AAR declares itself over 5-20 years — patient monitoring pays.
An admixture added at batching, mass water-repellent cuts capillary absorption by 70 to 90 %. Dosage (1-2 L/m³), mechanisms, price (80-150 DH/L) — and its honest limits.
Read article
Post-combustion, oxy-fuel, mineralisation: where CO₂ capture in cement really stands, the energy locks, and what it changes (nothing) for your site.
Read articleWood, agricultural residues, RDF: substituting fossil fuel in the clinker kiln. The kiln's assets, the fuels' watch-points — and why nothing changes in the bag.
Read articleOur team responds within 24h. CPJ 45 on request, CPJ 55 on request. Delivery within Dakhla included.