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Preparation And Properties Of EPEG Based Hydrophobically Modified Polycarboxylate Superplasticizer

High-strength and ultra-high-performance concretes (e.g., C80) typically require low water-to-binder (w/b) ratios. While polycarboxylate superplasticizers (PCEs) enable excellent water reduction, a persistent problem remains: excessively high viscosity of the fresh concrete. This leads to:

Slow pumping and placement
Poor flowability in densely reinforced sections
Increased labor and equipment wear

Traditional solutions include adding air-entraining agents (AEA) or large amounts of fly ash, but these often reduce strength or are not always available. Another approach uses ester-type PCEs, which have limitations.

This study presents a novel EPEG based hydrophobically modified polycarboxylate superplasticizer by introducing vinyl benzoic acid (VBA) – a hydrophobic aromatic monomer. The modification creates a micro-air-entraining effect with smaller, more stable bubbles that reduce viscosity without compromising later-age strength.

EPEG Based Hydrophobically Modified Polycarboxylate Superplasticizer Synthesis & Molecular Design

Raw Materials

Component	Role	Details
EPEG (Mw 3000)	Polyether macromonomer	Vinyl-terminated
Acrylic acid (AA)	Carboxyl monomer	Adsorption
Vinyl benzoic acid (VBA)	Hydrophobic functional monomer	Benzene ring + carboxyl
H₂O₂, Vc, 2-ME	Redox initiator + chain transfer	35 °C polymerization
NaOH	Neutralization	pH 6–7

FTIR Confirmation

The FTIR spectra (Fig. 2 in the paper) show:

1674 cm⁻¹ – C=O stretch (enhanced with VBA)
785 cm⁻¹ – C–H out-of-plane bending of benzene ring
These peaks increase with VBA content, confirming successful incorporation of the aromatic structure.

Effect of VBA on Polymerization Kinetics

VBA has a much higher reactivity ratio than EPEG, meaning it preferentially reacts with AA early in the polymerization. This significantly slows down EPEG conversion.

Sample	15 min EPEG conversion	30 min EPEG conversion
CPCE	10.64%	27.73%
VPCE-1	5.88%	20.56%
VPCE-2	3.05%	15.74%
VPCE-3	0.05%	5.37% (80% lower than CPCE)

Final conversion differences are smaller, but early-stage kinetics strongly affect molecular weight development. Weight-average molecular weight (Mw) decreases as VBA content increases:

Sample	Final Mw (kDa)
CPCE	29.26
VPCE-1	27.44
VPCE-2	26.59
VPCE-3	25.83

Takeaway: VBA modifies the copolymer structure and reduces its molecular weight, thereby influencing adsorption and dispersion behavior.

Practical Recommendations

Use EPEG Based Hydrophobically Modified Polycarboxylate Superplasticizer for Low w/b Ratio Concretes (C60–C100)

Start with the optimal molar ratio: EPEG:AA:VBA = 1:4:0.4.
Expect improved pumpability and faster placement.

Monitor Slump Retention

EPEG based hydrophobically modified polycarboxylate superplasticizer shows faster fluidity loss than conventional PCE. For long transport times (>30 min), consider blending with a retarder or a conventional PCE.

Air Content Control

EPEG based hydrophobically modified PCE increases air content by ~0.5–0.7% compared to CPCE at the same dosage. This is usually beneficial for reducing viscosity, but ensure the total air content does not exceed project specifications (typically <5% for high-strength concrete).

Strength Testing

The study confirms that there is no negative impact on 3d, 7D, or 28D strength (all ~82 MPa). However, always verify with local materials.

Compatible Materials

Tested with P·II 52.5 cement, silica fume, fly ash, and common aggregates. The EPEG based hydrophobically modified PCE synthesis uses 35 °C, which is energy–efficient.

Conclusion

This study successfully designed and synthesized a series of EPEG based hydrophobically modified polycarboxylate superplasticizers by introducing vinyl benzoic acid (VBA). The key findings are:

Polymerization kinetics: VBA slows EPEG conversion (up to 80% reduction at 30 min) and reduces final Mw.
Dispersion & adsorption: EPEG based hydrophobically modified PCE shows higher initial adsorption and better initial fluidity, but faster slump loss.
Micro-air entraining: EPEG based hydrophobically modified PCE generates smaller, more stable bubbles (<100 μm) than conventional PCE, lowering surface tension.
Viscosity reduction: In mortar and C80 concrete, VPCE-2 reduces inverted slump time from 22.0 s to 13.0 s and increases initial spread to 65 cm.
Strength preservation: Despite higher air content (3.4% vs. 2.8%), 28‑day strength remains unchanged (~82 MPa).
Optimal formulation: $n (EPEG) : n (AA) : n (VBA) = 1 : 4 : 0.4$

For ready-mix and precast producers working with high-strength concrete (C60–C100) and facing pumping or placement difficulties, VPCE offers a promising one-component solution that reduces viscosity, improves flow, and maintains long-term strength.