Blog

Study On Storage Stability Of PCE Mother Liquor

PCE mother liquor is the core raw material for preparing high-performance concrete admixtures, widely used in ready-mix plants, precast factories and infrastructure construction. However, liquid PCE products face prominent storage problems during long-term stockpiling and transportation, especially mildew contamination under hot, humid, sun-exposed environments. Severe mildew consumes active polymer ingredients in PCE mother liquor, weakening the water-reducing and slump-retaining capacity, leading to unqualified fresh concrete and hidden structural safety hazards.

This paper reports a 14-month storage test on two commercial PCE mother liquors under two distinct storage environments. It records visual changes (discoloration, mildew colony growth) in the PCE liquid, tests cement paste fluidity and C3 concrete workability/compressive strength of mildewed samples, and summarizes standardized storage measures to prevent mildew and stabilize PCE performance for batching plants and admixture manufacturers.

Test Raw Materials & Experimental Scheme

Raw Material List

PCE Mother Liquors
PCE-1: 50% solid content, pH 5.4, transparent liquid
PCE-2: 50% solid content, pH 5.1, transparent liquid

Compound Auxiliaries: Food-grade sugar retarder H1, sodium gluconate H2 (30% solid), air-entraining agent YQ (35% solid)

Cement: Runfeng P·O 42.5

Aggregate: Zone 2 medium river sand, 5–20 mm continuous graded crushed stone

Mixing water: Local tap water
Standard compound formula for finished admixture (mass ratio): 56.95% PCE mother liquor + 40% water + 2% H2 + 1% H1 + 0.05% YQ.
C30 concrete mix per cubic meter: Cement 360 kg, sand 980 kg, stone 865 kg, water 175 kg.

Two Storage Environments

All PCE samples were sealed in clean, dry bottles for continuous observation from June 2023 to August 2024 (14 months).

Environment A (Uncontrolled General Indoor): Natural sunlight exposure, temperature 18.5–34.3 ℃, relative humidity 68%–84%
Environment B (Controlled Standard Storage): Full light shielding, sealed warehouse, temperature below 30 ℃, RH ≤70%

Testing Standards

Cement paste fluidity: GB/T 8077-2012
Fresh concrete slump & spread & 1h slump loss: GB/T 50080-2016
Hardened concrete compressive strength: Standard cube specimens

Long-Term Storage Visual Changes of PCE Mother Liquor

Discoloration and Mildew Growth Rule

Environment A (sunny, high humidity)

150 days storage: PCE-1 turns pale yellow without mildew
300 days storage: PCE-1 deepens to yellow; PCE-2 shows slight discoloration
390 days storage (summer high temp): Tiny mildew colonies appear on the PCE-1 surface
Over 450 days: Massive mildew multiplies rapidly under high temperature and humidity

Environment B (shaded, cool, low humidity)

PCE-1 was only slightly pale yellow after 360 days; zero mildew colony formation for both PCE-1 and PCE-2 throughout the whole test cycle.

Key cause analysis: Rich organic retarders (gluconate, sugar) in compounded PCE provide nutrients for microbes. Sunlight accelerates polymer aging, while summer high temperatures and high humidity accelerate microbial growth, triggering discoloration and mildew. Cool, shaded, sealed storage effectively inhibits microbial activity.

Paste Performance of Discolored Non-Mildewed PCE

For PCE samples that turn yellow without mildew colonies, cement paste fluidity shows no obvious difference compared with newly produced PCE. Simple discoloration caused by light oxidation does not consume effective water-reducing polymers and will not affect normal concrete mixing.

Influence of Mildewed PCE on Concrete Performance

Tests divided mildew degrees into two levels: initial mildew (small colonies) and severe mildew (massive microbial growth).

Fresh Concrete Workability

Group 1: Slightly mildewed PCE-1

Sample	Initial Slump/Spread (mm)	0.5h Slump/Spread (mm)	1h Slump/Spread (mm)
Fresh PCE	210 / 520	210 / 470	195 / 395
Mild mildew PCE	210 / 515	210 / 455	190 / 385
Slight mildew only causes tiny slump loss, with negligible impact on on-site pouring.

Group 2: Severely mildewed PCE-1

Sample	Initial Slump/Spread (mm)	0.5h Slump/Spread (mm)	1h Slump/Spread (mm)
Fresh PCE	220 / 545	210 / 485	200 / 425
Severe mildew PCE	215 / 505	205 / 425	185 / 370
Severe mildew significantly accelerates slump loss after 30 and 60 minutes, reducing pumpability and workable time windows for transit concrete.

Compressive Strength Impact

Initial mildew has little effect on concrete compressive strength. Heavy mildew consumes large amounts of active PCE polymers, weakening cement dispersion and uniformity of hydration, leading to reduced compactness and a significant decline in long-term mechanical strength.

Mildew Damage Mechanism

Microbes consume organic functional components in PCE mother liquor, cutting water-reducing and slump-retention efficacy;
High temperature accelerates thermal degradation of PCE macromolecular chains, breaking polymer structures and losing dispersion capacity simultaneously with mildew.

Effective PCE Storage Anti-Mildew Guidelines

Based on test data, four core storage standards to extend PCE shelf life:

Storage Environment: Adopt fully shaded, sealed warehouses; strictly avoid direct sunlight, control temperature below 30 ℃ and relative humidity under 70%.
Container Management: Use airtight plastic barrels; prevent rainwater, dust and external microbial contamination during transportation and stockpiling.
Regular Inspection: Monthly visual check for liquid discoloration, floating mildew film or peculiar odor; stop using once heavy mildew occurs.
Add Preservative: Mix compatible bacteriostatic agents into the PCE compound formula to help restrain microbial growth during hot seasons.

Core Research Conclusions

Light-induced discoloration of PCE mother liquor under typical indoor storage conditions does not impair water-reducing performance and can still be used normally without loss of performance.
Summer high temperatures and high humidity greatly accelerate microbial growth, leading to mildew on the PCE compound. As mildew aggravates, effective active ingredients are consumed, leading to severe concrete slump loss and reduced compressive strength.
Shaded, low-temperature, sealed storage effectively avoids mildew growth of PCE mother liquor, maintaining stable performance during long-term storage.
Concrete producers must inspect the PCE admixture before batching and discard products that are heavily mildewed to eliminate the risk of unqualified structural concrete.

Conclusion-Study On Storage Stability Of PCE Mother Liquor

The storage environment directly determines the stability of the polycarboxylate superplasticizer mother liquor. Sunlight only causes harmless liquid discoloration, while combined high temperature and high humidity trigger mildew contamination that permanently degrades PCE’s core water-reducing and slump-retaining functions, damaging fresh concrete workability and long-term mechanical properties.

Admixture manufacturers and ready-mix concrete plants should implement standardized, shaded, sealed, low-humidity storage protocols, conduct periodic visual inspections, and deploy bacteriostatic additives for summer stock to maintain consistent PCE performance and ensure the quality of all cast-in-place and precast concrete projects.