Concrete Superplasticizer is the core material of modern concrete technology, which can significantly improve the workability, strength and durability of concrete. Among the many superplasticizers, polycarboxylate superplasticizer (PCE) and naphthalene superplasticizer (FDN) are the two most widely used types.
However, many engineers face some questions when choosing superplasticizers:
- What is the difference between polycarboxylate superplasticizer and naphthalene superplasticizer?
- Which one is more suitable for high-strength concrete, precast components or pumping construction?
- How to choose the most economical solution according to engineering needs?
Below, we will deeply analyze the performance differences between the two through chemical structure, scientific comparison, experimental data, engineering cases, etc. And then provide a selection decision guide to help you optimize the concrete mix design.
Comparison of the chemical structure and action mechanism of PCE and SNF
Chemical structure and action mechanism of PCE
The molecular structure of polycarboxylate superplasticizer is based on polycarboxylic acid as the main chain, and the side chain contains polyether groups. The molecular weight is usually between 20,000 and 50,000 Daltons, and its functional groups mainly include carboxylic acid groups and sulfonic acid groups. This structure enables PCE to disperse cement particles through the dual effects of electrostatic repulsion and steric hindrance. Among them, the physical barrier formed by the long side chain can effectively prevent particle agglomeration, and some ester PCEs also have sustained release properties and can continuously release active ingredients.
Chemical structure and action mechanism of SNF
In contrast, the molecular structure of naphthalene superplasticizer is based on naphthalene sulfonate formaldehyde condensate, with a low molecular weight (1,000 to 3,000 Daltons), and mainly relies on the electrostatic repulsion generated by the sulfonic acid group to disperse cement particles. Due to its short and rigid molecular structure, FDN is prone to failure in high temperature environments and lacks steric hindrance.
Comparison of key performance indicators
In terms of water reduction rate, polycarboxylate water reducer can usually reach 20% to 40%, and some high-performance products even exceed 35%. The water reduction rate of naphthalene-based water reducers is generally between 15% and 25%, and a higher dosage is required to achieve similar effects. For example, under the same water-cement ratio (0.4), adding 0.8% PCE can achieve a water reduction rate of 28%, and the 28-day compressive strength reaches 72.5 MPa. Adding 1.2% FDN can only achieve an 18% water reduction rate, and the 28-day strength is 65.3 MPa.
Slump retention is another important indicator. The slump loss of PCE concrete within 2 hours is usually less than 10%, which is very suitable for long-distance transportation or high-temperature environment construction. The slump loss rate of FDN concrete is often as high as 30% to 50%, and a retarder (sodium gluconate) must be compounded to meet construction requirements. For example, in a project at 30℃, the slump of FDN concrete dropped from 220 mm to 150 mm within 1 hour, while PCE concrete only dropped to 205 mm.
Comparison of adaptability with cement
PCE shows significant advantages for high C3A content cement. Its steric hindrance effect can effectively resist the adsorption of C3A on water reducer molecules, while FDN needs to increase the dosage by 30% to achieve the same effect under this environment.
PCE has better tolerance in the face of high-alkali cement (Na2O content exceeds 0.6%), while FDN is prone to rapid setting. When the mud content of aggregate exceeds 3%, ordinary PCE may fail, but the special anti-mud PCE can still play a role, while FDN basically loses its effectiveness under this condition.
Comparison of engineering applicability
In super-high-rise pumped concrete projects, PCE’s ultra-high water reduction rate can reduce the pumping pressure by 30%, while SNF is only suitable for projects with a height of less than 100 meters.
The use of early-strength PCE in the production of prefabricated components can shorten the demoulding time by 50%, while the use of FDN requires a compound early-strength agent.
Self-compacting concrete (SCC) requires an expansion of more than 700 mm, which is an indicator that FDN cannot achieve.
For marine anticorrosive concrete, PCE can reduce the chloride ion diffusion coefficient by 50%, while FDN requires additional rust inhibitors.
In emerging fields such as 3D printing concrete, PCE can precisely control rheological properties, while FDN is completely inapplicable.
However, PCE is sensitive to certain clay minerals (such as montmorillonite) and its price is usually 30% to 50% higher than FDN. FDN can’t meet the needs of modern high-performance concrete and is slightly less environmentally friendly, while the production process contains formaldehyde release).
Economic Analysis
From the perspective of unit price, PCE prices are usually between 1,100 and 1,500 USD per ton, while FDN is 700 to 1,000 USD per ton. In terms of typical dosage, PCE is 0.8% to 1.2%, and FDN is 1.0% to 1.5%. This makes the cost of PCE in a cubic meter of concrete reach 8 to 20 USD, and FDN is 7 to 15 USD.
However, considering the cost of the entire life cycle, PCE can save 15% to 25% of cement, reduce pumping energy consumption by 40%, and significantly extend the life of the structure.
Selection Recommendations
PCE should be given priority for high-strength (above C50), self-compacting concrete, high temperature or long-distance transportation construction, severe corrosive environment, and green building certification projects.
In non-important structures with low-grade concrete (below C30), short-term construction without durability requirements, and extremely limited budgets, FDN can be considered.
With the decline in PCE prices and the improvement of environmental protection requirements, the market share of PCE is gradually increasing.