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A Novel Viscosity Reducing Polycarboxylate Superplasticizer Synthesized

High‑strength concrete (e.g., C60 and above) is increasingly used in modern high‑rise buildings, long‑span bridges, and other demanding infrastructure. However, achieving such high strength typically requires a low water-to-binder ratio and a high cementitious content. The result is a highly viscous fresh concrete that is difficult to pump, place, and finish – a major challenge for construction efficiency and quality.

Conventional polycarboxylate superplasticizers (PCEs) offer excellent water reduction and slump retention, but they often do not adequately reduce the plastic viscosity of low‑water‑ratio mixes. To address this issue, researchers have developed specialized viscosity‑reducing PCEs by introducing functional groups such as sulfonate, silane, or ester moieties. However, many of these syntheses require heating and long reaction times, increasing energy consumption and production costs.

A recent study synthesis of a viscosity reducing polycarboxylate superplasticizer (designated PCE‑V1) using allyl alcohol polyoxyethylene ether (APEG), acrylic acid (AA), maleic anhydride (MA), and a specific functional ester monomer (VE). This article summarizes their optimization, structural characterization, and concrete performance results.

Why Viscosity Reducing Polycarboxylate Superplasticizer Are Needed

In high‑strength concrete with a water‑to‑binder ratio below 0.30, the paste phase becomes highly viscous due to the close packing of fine particles and the high solid volume fraction. High viscosity leads to:

Slow pumping – increased pressure on pumps and pipelines
Difficult placement – poor flow into formwork and around reinforcement
Longer discharge times – measured by inverted slump cone emptying time
Increased risk of defects – voids, honeycombing, and uneven surface finish

A viscosity reducing polycarboxylate superplasticizer works by optimizing the molecular structure to release more free water and reduce interparticle friction, without compromising water reduction or strength development.

Design and Synthesis of PCE‑V1

Raw Materials and Chemistry

The researchers used:

APEG (molecular weight ≈1000 g/mol) – the main polyether macromonomer
Acrylic acid (AA) – provides carboxyl groups for adsorption
Maleic anhydride (MA) – introduces additional carboxyls and enables fast polymerization at room temperature
Functional ester monomer (VE) – improves molecular chain flexibility and lubricity, enhancing viscosity reduction
Hydrogen peroxide (H₂O₂) – ascorbic acid (Vc) redox initiator system – allows polymerization at ambient temperature
Sodium hypophosphite (SHP) – chain transfer agent
Ferrous sulfate (FeSO₄) – catalyst

The polymerization was carried out in aqueous solution at 20 °C (room temperature). A two‑stream feeding scheme was used: solution A (AA + water) and solution B (Vc + water) were added dropwise over 75–80 minutes. The total reaction time (including post‑polymerization hold) was about 2.5 hours – significantly shorter than many conventional heated processes.

Optimization via Orthogonal and Single‑Factor Experiments

Orthogonal Design

Four factors were investigated:

Acid‑ether ratio [n(AA):n(APEG)] – levels: 1.5, 1.75, 2.0
MA‑ether ratio [n(MA):n(APEG)] – levels: 2.4, 3.6, 4.8
Initiator (Vc) dosage – levels: 1.3%, 1.9%, 2.5% (on APEG mass)
Dropping time (A/B) – levels: 55/60, 65/70, 75/80 min

The responses were cement paste flow (mm) and Marsh time (s) at a fixed flow of 215±5 mm (shorter Marsh time indicates lower viscosity).

Results (range analysis):
Order of influence: acid‑ether ratio > MA dosage > dropping time > initiator dosage.
The optimal combination was: acid‑ether ratio = 2.0, MA‑ether ratio = 4.8, Vc dosage = 2.5%, dropping time = 75/80 min.

Single‑Factor Fine‑Tuning

Ester monomer (VE) dosage (ester‑ether ratio): The best performance (highest flow, shortest Marsh time) occurred at a ratio of 1.8 (VE:APEG). Too little ester reduced lubricity; too much caused over‑crosslinking or reduced adsorption.
Hydrogen peroxide dosage: Optimal at 2.5% of APEG mass. Higher dosages led to excessive radical generation and uncontrolled polymerization, lowering performance.

Final Optimal Synthesis Recipe

Parameter	Optimal value
n(AA):n(APEG)	2.0
n(MA):n(APEG)	4.8
Ester‑ether ratio (VE:APEG)	1.8
Vc dosage (on APEG)	2.5%
H₂O₂ dosage (on APEG)	2.5%
Dropping time (A / B)	75 / 80 min
Reaction temperature	20 °C (room temperature)

Structural Characterization

Fourier Transform Infrared Spectroscopy (FT‑IR)

Key peaks (Figure 4 in the original paper):

3442 cm⁻¹ – O–H stretching (hydroxyl groups)
2872 cm⁻¹ – saturated C–H stretching
1720 cm⁻¹ – C=O stretching (carboxyl groups)
1580 cm⁻¹ – asymmetric stretching of –COO⁻
1090 cm⁻¹ – C–O–C ether stretching

The presence of carboxyl and ester groups confirmed successful copolymerization of AA, MA, and VE onto the APEG backbone.

Proton Nuclear Magnetic Resonance

Distinct signals were observed:

δ = 4.4 ppm – methylene (–CH–CH₂–O–) in the polyether chain
δ = 4.0 ppm – methine (–CH–) directly connected to ester oxygen
δ = 0.87 ppm – terminal methyl (–CH₃) groups

These assignments confirm that all monomers (APEG, AA, MA, VE) were incorporated into the copolymer.

Gel Permeation Chromatography (GPC)

Sample	Mₙ (g/mol)	Mₐ (g/mol)	PDI	Conversion (%)
Conventional PCE	22,538	33,649	1.49	92.7
PCE‑V1	6,743	12,763	1.89	88.0

PCE‑V1 has a lower molecular weight than conventional PCE, which is beneficial for viscosity reduction (smaller molecules can better lubricate particle surfaces). The polydispersity index (PDI) of 1.89 indicates a moderately broad distribution that is acceptable. The 88% conversion is satisfactory for a room‑temperature redox system.

Concrete Performance Evaluation

A C60 concrete mix was used (cement 280 kg/m³, mineral powder 150 kg/m³, fly ash 40 kg/m³, sand 660 kg/m³, aggregates 1090 kg/m³, water 140 kg/m³, PCE dosage 1.2% by binder). PCE‑V1 was compared with:

Conventional PCE (non‑viscosity‑reducing)
Two commercial viscosity‑reducing PCEs: WH viscosity‑reducing masterbatch and TJ viscosity reducer

Workability and Viscosity

PCE type	Slump/Spread (mm)	Inverted slump cone emptying time (s)	Plastic viscosity (Pa·s)
Conventional PCE	620/240	7.35	2.6
PCE‑V1 (this work)	620/240	3.35	2.3
WH viscosity‑reducing	610/240	6.33	2.3
TJ viscosity reducer	600/240	4.33	2.5

Key findings:

All polycarboxylate superplasticizer gave similar slump/spread values (600–620 mm / 240 mm).
PCE‑V1 dramatically reduced the emptying time – from 7.35 s (conventional) to 3.35 s – indicating much lower viscosity.
The plastic viscosity of PCE‑V1 (2.3 Pa·s) was the lowest among the tested products (tied with WH but with faster emptying).
Compared to the two commercial viscosity‑reducing PCEs, PCE‑V1 showed shorter emptying time and higher early strength (see below).

Compressive Strength

PCE type	3d strength (MPa)	7d strength (MPa)	28d strength (MPa)
Conventional PCE	31.6	51.0	62.2
PCE‑V1	35.1	52.8	61.9
WH viscosity‑reducing	33.6	51.4	61.8
TJ viscosity reducer	33.6	49.9	68.3 (?) see note

PCE‑V1 achieved slightly higher early strength (3d and 7d) than conventional PCE and comparable 28‑day strength – meaning the viscosity reduction did not come at the expense of mechanical performance.

Advantages of PCE‑V1

Feature	Benefit
Room‑temperature synthesis	No heating required → energy savings, lower CO₂ footprint, simpler equipment
Short reaction time	Dropping time only 75–80 min + 1 h hold → high productivity
Excellent viscosity reduction	Inverted cone emptying time 3.35 s vs. 7.35 s for conventional PCE
Good early strength	3‑day strength 35.1 MPa (11% higher than conventional PCE)
Comparable 28‑day strength	61.9 MPa, essentially equal to conventional PCE
Low plastic viscosity	2.3 Pa·s, improving pumpability and placement
Simple formulation	Readily available monomers (APEG, AA, MA, VE)

Conclusion

A novel viscosity reducing polycarboxylate superplasticizer(PCE‑V1) was successfully synthesized at room temperature using APEG, AA, MA, and a functional ester monomer (VE) with a H₂O₂‑Vc redox system.
The optimal synthesis parameters are: acid‑ether ratio 2.0, MA‑ether ratio 4.8, ester‑ether ratio 1.8, Vc dosage 2.5%, H₂O₂ dosage 2.5%, dropping time 75/80 min.
FT‑IR and ¹H NMR confirmed the presence of carboxyl, ester, and ether groups; GPC showed Mₙ ≈6743 g/mol and conversion 88%.
In C60 concrete, PCE‑V1 reduced the inverted slump cone emptying time from 7.35 s (conventional PCE) to 3.35 s and plastic viscosity to 2.3 Pa·s – outperforming two commercial viscosity‑reducing PCEs.
Compressive strength was maintained or slightly improved at early ages, with 28‑day strength comparable to conventional PCE.
The room‑temperature, short‑cycle synthesis offers significant potential for energy‑efficient, low‑cost production of high‑performance viscosity‑reducing PCEs for high‑strength concrete applications.