If you work in construction, architecture, or building materials, you're probably familiar with the frustrating white stains that appear on cement and masonry surfaces. This phenomenon, known as efflorescence, is more than just an eyesore-it can compromise the appearance, durability, and long-term performance of building projects.
We have discovered that Polyaluminium Chloride (PAC)-a material commonly used in water treatment-can effectively inhibit efflorescence in cement mortar while even improving its long-term strength .
Studies show that adding just 5% PAC to cement mortar provides remarkable protection against efflorescence, maintaining the material's visual stability for extended periods. Here's a closer look at the problem, our solution, and why this matters for your projects.
What Is Efflorescence and Why Is It a Problem?
The Science Behind the White Stains
Efflorescence occurs when soluble salts-primarily calcium hydroxide (Ca(OH)₂)-within cement-based materials dissolve in water and migrate to the surface. As the water evaporates, these salts react with carbon dioxide in the air, forming insoluble white deposits like calcium carbonate (CaCO₃) on the surface.
Three Key Factors Drive Efflorescence:
- Presence of soluble salts – mainly calcium hydroxide generated during cement hydration
- Water movement – moisture carries dissolved salts through capillary pores
- Environmental conditions – humidity, temperature fluctuations, and drying cycles accelerate the process
Impact on Construction Projects
While efflorescence has often been overlooked as a purely aesthetic issue, it creates serious problems:
- Aesthetic damage – white patches and streaks ruin the visual appearance of colored or decorative mortar
- Surface deterioration – crystallization pressure can cause micro-cracks, powdering, and loss of adhesion
- Reduced durability – increased porosity accelerates water and CO₂ penetration, shortening building lifespan
- Project acceptance risks – visible efflorescence can lead to failed inspections and costly rework
Traditional efflorescence inhibitors rely on physically blocking pores or chemically adsorbing salts, but these methods often have limited effectiveness, high costs, or negative impacts on material performance. Our research offers a better solution.
Our Solution: Polyaluminium Chloride (PAC)
Why PAC?
Polyaluminium Chloride (PAC) is an inorganic polymer compound widely used in water treatment for its excellent flocculation properties. However, PAC's chemical characteristics make it highly effective in cement-based systems. When added to cement mortar, PAC actively participates in hydration reactions, transforming problematic compounds into stable, harmless forms.
Key Findings
After systematic research tested different PAC concentrations (0%, 3.3%, and 5.0% of cement weight) in cement mortar specimens. The results were clear:
Specimen PAC Content 7-Day Compressive Strength 28-Day Compressive Strength
| Specimen | PAC Content | 7-Day Compressive Strength | 28-Day Compressive Strength |
|---|---|---|---|
| PD-1 | 0% | 18.57 MPa | 35.04 MPa |
| PD-2 | 3.3% | – | 37.23 MPa |
| PD-3 | 5.0% | – | Improved significantly |
- Visual Appearance: After 8 months of natural curing, specimens with 5.0% PAC showed the deepest, most stable color, indicating minimal efflorescence. Image analysis confirmed that color density values improved from 56.02 (control) to 44.65 (5.0% PAC)-lower values meaning less efflorescence.
- Strength Development: While early-age strength (7 days) decreased with high PAC content, the 28-day compressive strength recovered significantly, showing that PAC promotes later-stage hydration .
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Poly Aluminum Chloride in Water Treatment
Exploring The Production Technology Of PAC
How PAC Works: The Inhibition Mechanism
1. Reducing Alkalinity at the Source
During the early stages of cement hydration, calcium hydroxide (Ca(OH)₂) is produced in large quantities. PAC reacts with this compound, effectively consuming the primary source of soluble salts. This chemical reaction reduces the overall alkalinity of the system, leaving less free calcium available to migrate to the surface .
2. Transforming Harmful Compounds
One of the most important discoveries is PAC's ability to convert ettringite (AFt) into Friedel's salt. Ettringite is a common hydration product that can contribute to efflorescence. When chloride ions from PAC interact with the system, they promote this transformation. Friedel's salt is a stable, non-soluble compound that locks calcium in place, preventing it from being carried to the surface by water.
Analysis confirmed that as PAC content increased, the characteristic peaks for calcium hydroxide and ettringite weakened or disappeared, while new peaks for Friedel's salt appeared. EDS elemental mapping further supported this, showing reduced calcium and sulfur levels in PAC-treated specimens-clear evidence that these mobile compounds had been immobilized .
3. Physical Barrier Formation
PAC's hydrolysis produces aluminum hydroxide (Al(OH)₃) gel, which has a large specific surface area and strong adsorption capacity. This gel fills capillary pores in the mortar, physically blocking the migration pathways that salts would otherwise travel. The result is a denser, more impermeable microstructure that resists water penetration and salt movement .
4. Optimizing Microstructure for Long-Term Performance
Beyond its direct chemical effects, PAC promotes the hydration of tricalcium silicate (C₃S) and dicalcium silicate (C₂S)-the primary strength-giving compounds in cement. This acceleration of later-stage hydration creates a more refined, compact microstructure that continues to develop strength over time.
Thermogravimetric analysis confirmed the presence of Friedel's salt through characteristic decomposition peaks at approximately 275°C and 450°C. This stable compound not only prevents efflorescence but also contributes to the overall durability of the mortar .
Practical Implications for the Construction Industry
For Building Projects
PAC offers a practical, cost-effective solution for preventing efflorescence in cement-based materials. Whether you're working on decorative facades, paving stones, architectural blocks, or colored mortars, PAC can help maintain the intended appearance and extend the service life of your projects.
Key Advantages
Long-lasting protection – 8-month outdoor exposure tests confirmed continued effectiveness
Minimal visual impact – PAC-treated specimens maintained color stability significantly better than untreated specimens
Improved long-term strength – despite temporary early-age strength reduction, final strength meets or exceeds standard performance
Simple integration – PAC is added as a dry powder mixed directly with cement and sand before water addition
Usage Recommendations
Studies show that:
Optimal dosage: 5.0% of cement weight provides the best balance of efflorescence control and performance
Mixing method: Pre-mix PAC powder with cement and sand before adding water
Extended mixing: Increase mixing time by 1–2 minutes for thorough dispersion
Water-to-cement ratio: Maintain between 0.5–0.6 for best results
Conclusion
Polyaluminium Chloride is a highly effective inhibitor of efflorescence in cement mortar. By addressing the problem at multiple levels-chemically consuming free calcium, transforming mobile compounds into stable forms, and physically blocking migration pathways- PAC provides comprehensive, long-lasting protection.
Studies show that, PAC's ability to promote later-stage hydration and optimize microstructure contributes to improved compressive strength and durability. While early-age strength development may be slightly affected at higher dosages, the long-term performance is enhanced.