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How Polycarboxylate Superplasticizer Dosage Affects Concrete Performance in Plateau Regions

Plateau construction projects face unique environmental challenges: large day-night temperature differences, special local aggregates, and unstable fresh concrete workability. Polycarboxylate superplasticizer is a vital high-performance admixture widely used in high-altitude infrastructure. Improper PCE dosage either leads to insufficient flow for pumping or severe segregation that damages the concrete’s long-term mechanical strength.

Most existing PCE research focuses on plain lowland concrete, while targeted testing data for plateau environments remains scarce. This paper conducts a controlled variable laboratory test using three PCE dosage levels (1.0%, 3.0%, and 4.3%) based on local Tibetan raw materials. It evaluates fresh concrete slump, spread, and compressive strength at 7 d, 28 d, and 56 d, identifying the optimal admixture proportion balancing construction workability and long-term structural strength for plateau engineering.

Test Raw Materials & Mix Proportion Design

Raw Material Specifications

Cement: P·O 42.5 ordinary Portland cement from Tibet Gaozheng Cement Plant. Initial setting time 189 min, final setting time 226 min; 28d compressive strength 57.1 MPa. Main chemical composition: CaO 62.02%, SiO₂ 27.07%.
PCE Superplasticizer: Local commercial polycarboxylate admixture, solid content 21.20%, water reduction rate 33%.
Fine aggregate: Manufactured sand with water content 6%; Coarse aggregate: 5–20 mm continuous graded crushed stone. Sand ratio fixed at 40%.
Mineral admixture: Fly ash, blended with cement as a composite binder.

Three Test Groups (Fixed Water-Cement Ratio=0.4)

All groups maintain identical cement, fly ash, sand, stone, and water dosage; only the PCE proportion is adjusted based on the total binder mass:

Group C-1: PCE dosage = 1.0%
Group C-2: PCE dosage = 3.0%
Group C-3: PCE dosage = 4.3%

Fixed mix per cubic meter: Cement 340 kg, fly ash 100 kg, sand 760 kg, stone 1140 kg, water 175 kg.

Test Standards & Procedures

Fresh concrete test: Follow GB/T 50080-2016 to measure slump and spread immediately after mixing.
Compressive strength test: 150 mm cubic specimens, standard curing for 7 d, 28 d, 56 d, tested per GB/T 50081-2019.
Mixing sequence: Coarse aggregate → binder → fine aggregate → water → PCE, total mixing time 3 minutes; vibrate compaction after casting, demold after 24 hours for continuous curing.

Test Results & Performance Analysis

Effect of PCE Dosage on Fresh Concrete Workability

Group	PCE Dosage	Slump (mm)	Spread (mm)	Workability Evaluation
C-1	1.0%	160	260	Poor flow, hard pumping
C-2	3.0%	208	535	Balanced flow, no segregation
C-3	4.3%	230	600	Excessive fluidity, segregation risk

Low dosage (1.0%): Insufficient dispersion leads to low slump and spread. The stiff mixture cannot meet normal pumping and pouring requirements for plateau construction.
Medium dosage (3.0%) achieves ideal workability: Sufficient flow without bleeding or aggregate separation, perfectly suitable for on-site construction.
Overdose (4.3%) greatly boosts fluidity but creates ultra-large spread values. Excessive free water separates the mortar from the coarse aggregate, destroying uniformity and damaging volume stability.

Compressive Strength at Different Curing Ages

Group	7d Strength (MPa)	28d Strength (MPa)	56d Strength (MPa)
C-1	34.38	40.24	50.71
C-2	40.52	44.09	56.48
C-3	25.14	30.03	39.78

Group C-2 (3.0% PCE) delivers maximum strength across all ages. Its 56-day compressive strength reaches 56.48 MPa, with a 39.4% strength increase from 7 d to the late curing stage. Uniform internal microstructure and full cement hydration drive outstanding mechanical performance.
Group C-1 (1.0% PCE) suffers from low compactness due to poor flow. Internal pores and voids reduce early and long-term compressive strength compared to the optimal dosage group.
Group C-3 (4.3% PCE) shows severe strength degradation at every age. Overdosage causes mortar segregation, uneven aggregate distribution, and abundant internal voids, permanently weakening concrete load-bearing capacity.

Determination of Optimal PCE Dosage for Plateau Concrete

Under this test’s raw material and mix design conditions, 3.0% of total binder mass is the optimal polycarboxylate superplasticizer dosage for plateau concrete.

Below 3.0%: Insufficient fluidity restricts concrete compaction and reduces strength development.
Above 3.0%: Excessive admixture triggers segregation, destroying internal structure and lowering long-term mechanical properties.
At 3.0%: The mixture balances pumpable workability and maximum compressive strength at all curing ages, fully adapting to high-altitude construction conditions.

Core Research Conclusions

PCE dosage significantly regulates plateau concrete fluidity. Raising the dosage from 1.0% to 3.0% greatly improves slump and spread to meet construction standards; a further increase to 4.3% leads to an over-fluid mix with a high segregation risk.
The 3.0% PCE group achieves the highest compressive strength at 7 d, 28 d, and 56 d (56.48 MPa). Low dosage limits compactness, while excessive admixture causes segregation and obvious strength loss.
A comprehensive performance comparison confirms 3.0% PCE as the ideal proportion for plateau concrete, addressing both insufficient flow and segregation defects to achieve coordinated construction performance and long-term structural strength.

Practical Engineering Guidance for Highland Construction

Plateau road, bridge and building projects using local Tibetan cement and aggregate: Set polycarboxylate superplasticizer dosage at 3.0% of total binder mass for standard C30–C40 structural concrete.
Avoid low dosage (<1.0%) for mass pouring or long-distance pumping, as stiff mixtures easily cause construction blockages and porous hardened concrete.
Strictly control maximum PCE dosage below 4.3% without special viscosity-modifying compounding; overdose segregation permanently weakens structural bearing capacity and durability in high-altitude cold environments.
Conduct small-scale trial mixing before formal batching if raw material sources change across different plateau zones and adjust the admixture proportion slightly based on local sand, stone and cement activity.

Conclusion-How Polycarboxylate Superplasticizer Dosage Affects Concrete Performance in Plateau Regions

High-altitude plateau environments impose unique demands on the control of polycarboxylate superplasticizer dosage. The 1.0% dosage results in stiff, hard-to-pour concrete with low compactness, while 4.3% overdosage triggers severe segregation and irreversible strength decline. Laboratory testing with local Tibetan materials verifies that 3.0% PCE addition delivers balanced fresh workability and peak long-term compressive strength at all curing ages.

Construction technicians and admixture engineers working on plateau infrastructure can reference this optimal dosage to optimize concrete mix design, ensure smooth on-site pouring, and guarantee reliable long-term structural safety in high-altitude, harsh environments.