1. Introduction
In modern cementitious systems, cellulose ethers such as HPMC play a crucial role in adjusting rheology, improving water retention, and enhancing interface bonding. However, the viscosity of the HPMC used significantly affects concrete’s fresh-state behavior and long-term performance. This study aims to quantify and interpret the effects of varying HPMC viscosities in concrete formulations, with practical guidance on material selection.
2. Materials and Methods
2.1 Raw Materials
Cement: 54.2 MPa 28-day compressive strength (P.O 42.5).
Supplementary Cementitious Materials (SCMs): Class F fly ash and ground granulated blast furnace slag (GGBFS).
Aggregates:
Coarse: Crushed gravel (5–31.5 mm).
Fine: Manufactured sand (fineness modulus = 2.8).
Cellulose Ether (HPMC):
Low Viscosity (~30,000 mPa·s): HPMC-3W, corresponding to Celopro® MK20M
Medium Viscosity (~100,000 mPa·s): HPMC-10W, corresponding to Celopro® MK50M
High Viscosity (~200,000 mPa·s): HPMC-20W, corresponding to Celopro® MK70M
These commercial grades (Celopro® MK20M, MK50M, MK70M) are manufactured by Celotech Chemical Co., Ltd., optimized for use in cement-based systems where controlled rheology, water retention, and mechanical performance are required.
2.2 Concrete Mix Design
| Component | Content (kg/m³) |
|---|---|
| Cement | 180 |
| Fly Ash | 105 |
| Mineral Powder | 40 |
| Sand | 846 |
| Gravel | 1033 |
| Water | 161 |
| Superplasticizer | 4.2 |
2.3 Test Standards
Workability: GB/T 50080-2016
Mechanical Strength: GB/T 50081-2002
Water Retention: JGJ/T 70-2009
Water retention tests excluded particles >2.36 mm through square-hole sieving.
3. Results and Discussion
3.1 Slump and Expansion Behavior
As viscosity increases, HPMC enhances paste cohesion and internal friction, resulting in:
HPMC-3W: At low dosages, air-entrainment dominates, increasing slump. At higher levels, viscosity overrides, reducing slump and expansion.
HPMC-10W: Balanced response—moderate cohesion and entrainment yield stable flow at low dosage, but reduce slump at higher usage.
HPMC-20W: Consistently reduces workability, with strong viscosity dominating bubble effects.
Interpretation: High-viscosity HPMC significantly inhibits flowability. Optimal slump is achieved by balancing dosage and viscosity to retain entrainment effects without over-thickening the matrix.
3.2 Compressive Strength Development
At ~0.0025% HPMC dosage (by weight of cement), all grades show a strength peak at 3 and 28 days.
Excessive dosage increases porosity due to entrapped air and disrupted hydration kinetics.
HPMC-3W and 10W: Follow similar strength patterns—initial gain followed by strength plateau or decline.
HPMC-20W: Shows a steady decline in strength with increasing dosage, attributed to higher polymer film formation and internal voids.
Conclusion: The higher the viscosity, the more careful the dosage control required to maintain compressive strength targets.
3.3 Water Retention Efficiency
All HPMC types significantly reduce water loss in fresh concrete:
HPMC-3W: Limited effect below 0.005%; sharp improvement above that.
HPMC-10W: Water retention improves steadily with dosage—ideal for applications requiring stable moisture control.
HPMC-20W: Offers highest water retention efficiency at low dosage, but shows diminishing returns at higher levels due to gel saturation.
4. Practical Recommendations for Product Selection
| Application Area | Recommended HPMC Grades |
|---|---|
| Block Laying Adhesives | Celopro® MK40M FP, Celopro® MK70M FP, Celopro® MT4016 |
| Cement Tile Adhesives | Celopro® MK40M FP, Celopro® MK70M FP, Celopro® MT4016 |
| Self-Leveling Compounds | Celopro® MK400 FP, Celopro® MT1004 |
| Structural Concrete with Tailored Rheology | Celopro® MK20M, MK50M, MK70M (as tested in this study) |
Each application demands a different balance between flowability, strength development, and moisture retention. Medium-viscosity HPMC grades (e.g., MK50M or MK40M FP) often strike the most effective compromise.
5. Conclusion
Workability: Low-viscosity HPMC (30K) improves slump at limited dosage; higher viscosities reduce slump more significantly.
Strength: Optimum compressive strength occurs at ~0.0025% HPMC. Beyond this, strength declines due to increased porosity and retarded hydration.
Water Retention: High-viscosity HPMC (200K) offers superior retention but may require precise dosage control.
Recommendation: Select HPMC grade based on application priority—low viscosity for workability, medium for balance, high for retention-critical formulations.
