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The influence of different types and dosage of water reducing agent on the working performance of concrete

High-performance concrete is essential for modern municipal, residential, and infrastructure construction projects. Engineers constantly seek cost-effective ways to boost concrete flowability, durability, and compressive strength without raising material costs or compromising construction efficiency. Water reducing agents (superplasticizers) are the most widely used admixtures to optimize concrete mix performance, but two mainstream types—polycarboxylate superplasticizer and naphthalene-based superplasticizer—deliver drastically different results at identical mixing ratios.

This article shares a complete laboratory test comparing polycarboxylate superplasticizers and naphthalene superplasticizers at dosages ranging from 0% to 0.5% of cement mass. We analyze three critical performance metrics: slump (workability), electric flux (impermeability), and 28-day compressive strength. The test data reveal the superior performance of polycarboxylate superplasticizers and provide recommended optimal dosages for field concrete mix design.

Why Superplasticizer Selection Matters for Concrete Performance

Concrete mix design balances raw material costs, on-site pumpability, long-term waterproofing, and structural load capacity. Without superplasticizers, concrete mixes require more water to reach a workable slump, which creates a porous internal structure, weakens compressive strength, and reduces resistance to water and chemical penetration.

Previous research has explored fiber reinforcement, mineral admixtures, and custom synthetic superplasticizers to upgrade concrete properties. However, few studies provide a direct, side-by-side comparison of polycarboxylate and naphthalene superplasticizers across multiple dosage levels, with standardized slump, impermeability, and compression testing.

This controlled-variable test uses a fixed-base concrete mix with a polypropylene fiber additive. Two superplasticizer types are tested at 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% cement dosages. All specimens follow GB/T 50081-2023 standards for mechanical property testing, delivering actionable data for civil engineers and concrete batch plant operators.

Test Raw Materials & Experimental Scheme

Raw Material Specifications

Cement: Ordinary Portland cement, density 2.8 g/cm³, 28-day compressive strength 53.5 MPa
Coarse aggregate: Crushed stone, bulk density 2563 kg/m³
Fine aggregate: Extra-fine sand, apparent density 2486 kg/m³
Fiber additive: 6 mm polypropylene fiber
Water: Tap water for mixing
Polycarboxylate superplasticizer: 20% water reduction rate, 80% solid content
Naphthalene superplasticizer: 15% water reduction rate, 93% solid content

Base concrete mix ratio (per cubic meter): 346 kg cement, 810 kg sand, 848 kg stone, 80 kg mixing water, 170 g polypropylene fiber. Superplasticizer dosages are calculated as a percentage of cement mass.

Test Group Setup

Group A (Control): No superplasticizer added
Group B (Polycarboxylate): B1 (0.1%), B2 (0.2%), B3 (0.3%), B4 (0.4%), B5 (0.5%)
Group C (Naphthalene): C1 (0.1%), C2 (0.2%), C3 (0.3%), C4 (0.4%), C5 (0.5%)

All specimens are cast into 40 mm × 40 mm × 160 mm molds and cured under standard conditions for 28 days before testing. Three core tests are conducted: the slump flow test, the electric flux impermeability test, and the universal machine compressive strength test.

Test Results & Performance Analysis

Concrete Slump (Workability) Performance

Slump directly reflects concrete pumpability and on-site construction workability. The control group (A) without superplasticizer recorded a slump value of 184 mm.

Polycarboxylate Superplasticizer Slump Data

0.1% (B1): 191 mm
0.2% (B2): 205 mm
0.3% (B3): 213 mm
0.4% (B4): 224 mm
0.5% (B5): 246 mm

Naphthalene Superplasticizer Slump Data

0.1% (C1): 188 mm
0.2% (C2): 199 mm
0.3% (C3): 204 mm
0.4% (C4): 218 mm
0.5% (C5): 232 mm

Key findings:

The slump increases steadily with increasing superplasticizer dosage for both products. Superplasticizer molecules adsorb onto cement particle surfaces, creating electrostatic repulsion that releases trapped free water and improves flowability.
At equal dosage rates, polycarboxylate superplasticizer delivers higher slump values due to its higher 20% water reduction rate, compared to 15% for naphthalene-based agents.

Impermeability (Electric Flux) Results

Lower electric flux values indicate denser internal concrete pore structures and stronger resistance to water and ion penetration. Control group A measured 994 C.

Polycarboxylate Electric Flux

B1 (0.1%): 765 C | B2 (0.2%): 731 C | B3 (0.3%): 711 C | B4 (0.4%): 682 C | B5 (0.5%): 631 C

Naphthalene Electric Flux

C1 (0.1%): 884 C | C2 (0.2%): 810 C | C3 (0.3%): 775 C | C4 (0.4%): 730 C | C5 (0.5%): 701 C

As the superplasticizer dosage increases, the water-cement ratio decreases, refining the pore-size distribution and densifying the transition zone between the cement paste and aggregate. Polycarboxylate creates far lower electric flux at identical dosages, making it the better choice for waterproof structures, underground projects, and bridge decks.

28-Day Compressive Strength Test

Control group A compressive strength: 50.6 MPa.

Polycarboxylate Compressive Strength

B1 (0.1%): 53.2 MPa | B2 (0.2%): 54.6 MPa | B3 (0.3%): 55.8 MPa | B4 (0.4%): 56.1 MPa | B5 (0.5%): 57.8 MPa

Naphthalene Compressive Strength

C1 (0.1%): 51.5 MPa | C2 (0.2%): 52.8 MPa | C3 (0.3%): 54.5 MPa | C4 (0.4%): 55.2 MPa | C5 (0.5%): 55.9 MPa

Critical conclusions:

Higher superplasticizer dosage reduces water demand, accelerates full cement hydration, and forms a tighter hardened cement network, raising compressive strength.
Polycarboxylate at a 0.3% dosage increases concrete strength to C55 grade; naphthalene requires a 0.4% dosage to achieve the same C55 strength level. Superplasticizer addition can upgrade concrete strength by one full grade.
Across all matching dosages, polycarboxylate superplasticizer outperforms naphthalene in compressive strength gain.

Core Test Conclusions

Both polycarboxylate and naphthalene superplasticizers effectively raise concrete slump and improve construction workability. Flowability rises proportionally with increased admixture dosage.
Increasing the superplasticizer dosage reduces the concrete’s electrical conductivity, enhancing impermeability and long-term durability against water damage and corrosion.
Compressive strength continuously improves with higher superplasticizer content, with the potential to upgrade concrete strength by one grade.
At identical mixing dosages, polycarboxylate superplasticizer achieves superior slump, impermeability, and compressive strength compared to naphthalene-based superplasticizer.
Recommended optimal field dosages:

Polycarboxylate superplasticizer: 0.3% of cement mass
Naphthalene superplasticizer: 0.4% of cement mass

Engineering Application Guidance

High-performance concrete, waterproof structures, and high-strength projects should prioritize polycarboxylate superplasticizer at 0.3% dosage for balanced cost and performance.
Low-budget general construction may use a naphthalene superplasticizer at 0.4% dosage to achieve the target strength and workability.
Avoid overdosing superplasticizer beyond 0.5% to prevent excessive bleeding, segregation, and extra material costs without proportional performance gains.
Pre-production trial mixes are recommended when adjusting superplasticizer dosage to match local aggregate quality and on-site pumping requirements.

FAQ

Q1: Why is polycarboxylate superplasticizer better than naphthalene for concrete?

A: Polycarboxylate features a higher water reduction rate (20% vs 15%), better dispersion of cement particles, denser internal concrete microstructure, and greater improvements in flowability, impermeability, and compressive strength at the same dosage.

Q2: What is the minimum superplasticizer dosage to boost the concrete strength grade?

A: 0.3% polycarboxylate or 0.4% naphthalene superplasticizer can upgrade concrete to the next strength grade in standard mixes with polypropylene fiber additives.

Q3: Does more superplasticizer always improve concrete performance?

A: Performance gains slow significantly above 0.5% dosage. Excess superplasticizer causes concrete segregation, bleeding, and unnecessary material expense with minimal additional strength or durability benefits.

Conclusion

Superplasticizer type and mixing dosage are two decisive variables that control concrete workability, waterproof durability, and structural compressive strength. Direct lab testing confirms that the polycarboxylate superplasticizer delivers superior overall performance compared to a traditional naphthalene superplasticizer at equal dosages.

Civil engineers and concrete producers can follow the recommended 0.3% polycarboxylate or 0.4% naphthalene dosage to design economical, high-performance concrete mixes for residential, municipal, and infrastructure construction projects. Matching the correct superplasticizer type and optimal dosage reduces water demand, strengthens internal concrete structure, and extends the service life of finished concrete structures.