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Temperature Response Law of Multiple Admixtures Dissolution Characteristics of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizers are the primary high-performance admixture for modern high-strength concrete. However, ready-mix producers and admixture manufacturers frequently face two critical production obstacles when compounding multi-component PCE formulas: auxiliary precipitation, stratification and crystallization under variable temperatures, as well as unstable performance caused by inconsistent additive solubility.

This article conducts systematic laboratory testing on five widely used solid auxiliaries (sucrose, sodium gluconate, sodium metabisulfite, sodium thiosulfate, maltodextrin) in four PCE mother liquors at solid contents of 25%, 30%, 35%, and 40%. Full-temperature gradient tests from -5 °C to 40 °C are conducted to quantify solubility variation rules, analyze dissolution mechanisms, and build a temperature-solid content-solubility database. The research provides core data for intelligent automatic admixture batching algorithms and practical low-temperature anti-crystallization guidance for admixture factories.

Raw Materials & Experimental Program

Test Materials

PCE mother liquors: Compound water-retaining and slump-retaining polycarboxylate superplasticizer with solid contents of 25% (A1), 30% (A2), 35% (A3), and 40% (A4), mixed at a mass ratio of 7:3 for water-reducing and slump-preserving base liquids.

Solid Auxiliaries Tested:

B1: Food-grade sucrose (≥99% purity)
B2: Industrial sodium gluconate (≥98% purity)
B3: Sodium metabisulfite (≥95% purity)
B4: Sodium thiosulfate (≥99% purity)
B5: Maltodextrin (≥99% purity)

Standard Test Procedures

Prepare 100 mL of PCE mother liquor for each solid content group, and add solid auxiliaries incrementally (2 g per batch) while stirring at 600 rpm.
Maintain a constant temperature between -5 °C and 40 °C, with 5 °C increments; stir for 10 min after each addition, and observe the liquid transparency.
Terminate dosing when undissolved particles appear; filter the liquid through a 0.45 μm PES membrane; dry the filter residue at 105 °C to calculate the saturated solubility.
Seal filtrate and store 12 h at 25 °C, record stratification or crystallization phenomena to confirm an effective stable solubility threshold.
Repeat three parallel tests for each group to control the relative error below ±0.5%.

Key Observation Phenomenon

Freeze-thaw cycle tests show obvious stratification and crystal precipitation at -5 °C, and complete solidification of the PCE compound liquid at -10 °C, which will disrupt admixture uniformity and weaken concrete slump retention performance.

Test Results & Mechanism Analysis

Solubility Variation with Temperature & Solid Content

All five auxiliaries show positive temperature dependence: solubility rises steadily as temperature increases from -5 °C to 40 °C, controlled by an entropy-driven dissolution reaction. Higher PCE solid content generates stronger steric hindrance from polymer molecular chains, significantly reducing auxiliary saturated solubility. When solid content rises from 25% to 40%, the maximum solubility of sucrose (B1) drops by over 60%, showing the core inhibitory effect of concentration.er 60%.

Auxiliary solubility ranking across all temperature bands: B1 (sucrose) >> B2 (sodium gluconate) > B3 (sodium metabisulfite) > B4 ≈ , B5 (sodium thiosulfate, maltodextrin).

25% Solid Content PCE Mother Liquor

Sucrose reaches 75 g/100 mL at 40 °C, the highest solubility among all additives. Its polyhydroxy structure forms extensive hydrogen bonds with the PCE aqueous phase, resulting in a low dissolution activation energy (18.2 kJ/mol) and enabling excellent solubility even at low temperatures. B4 and B5 display nearly identical solubility below 15 °C due to the suppressed hydrophobic solvation effect.

30% Solid Content Polycarboxylate Superplasticizer

All auxiliaries show 20%–35% lower solubility than the 25% groups. Sodium gluconate (B2) exhibits anomalous solubility growth between 30–35 °C, driven by dynamic complexation between carboxylate groups and PCE side chains. Hydrophobic B4 and B5 gain faster solubility growth above 35 °C than B3. Critical dissolution temperature Tc of maltodextrin is measured at 32.5 °C.

35% Solid Polycarboxylate Superplasticizer

The steric inhibition effect intensifies sharply. At 40 °C, sucrose’s maximum solubility is only 38 g. Sodium metabisulfite dissolves faster at high temperatures due to redox-induced ion dissociation, while maltodextrin’s spiral chain structure expands at 30–35 °C to boost solubility. The solubility gap between B1 and B5 expands to 32.2 g.

40% High-Solid Polycarboxylate Superplasticizer

Dissolution inhibition becomes exponential. Sucrose solubility plateaus between 25–40 °C with only a 3 g increment. Sodium gluconate’s carboxylate ion dissociation promotes steady solubility growth, while hydrophobic thiosulfate and maltodextrin perform better at high temperatures.

Core Dissolution Mechanisms

Entropy-driven high-temperature dissolution: Higher temperature accelerates molecular thermal motion, breaks hydrogen bonds between PCE polymer chains, and releases free water to dissolve more solid additives.
Steric hindrance of high-concentration PCE: Dense PCE macromolecular chains occupy liquid space, limit free water activity, and block auxiliary diffusion paths, lowering saturated solubility.
Functional group matching differences: Polyhydroxy sucrose forms hydrogen networks easily; carboxylate gluconate dynamically complexes with PCE side chains; sulfite salts rely on ion dissociation for dissolution; hydrophobic maltodextrin dissolves sufficiently only at high temperature to unfold branched chains.

Key Engineering Conclusions

Temperature strongly regulates auxiliary solubility: Low temperature (<10 °C) restricts molecular diffusion and suppresses dissolution, easily triggering crystallization and stratification; high temperature accelerates entropy-driven dissolution for all tested solid additives.
PCE mother liquor solid content exerts an inhibitory effect on additive solubility. The higher the solid concentration, the lower the saturated dissolvable mass of sucrose, gluconate and sulfite auxiliaries.
Auxiliary performance hierarchy: Sucrose has the best low-temperature solubility; sodium gluconate balances medium-temperature compatibility; maltodextrin and thiosulfate are best suited to high-temperature compounding conditions.
The temperature-solubility-solid content dataset can be coded into intelligent PCE compounding equipment, supporting real-time dynamic adjustment of auxiliary dosage and early warning of precipitation risks.

Practical Compounding Guidance for Admixture Manufacturers

Low-temperature construction environments (<10 °C): Adopt PCE mother liquor with solid content ≤30% and prioritize sucrose as a slump-retaining auxiliary to avoid crystal precipitation.
Hot-climate production (>30 °C): 35% solid PCE is acceptable; maltodextrin and sodium thiosulfate can be added for cost control.
Winter cold storage prevention: Avoid storing 40% high-solid PCE outdoors without insulation; maintain warehouse temperature above 0 °C to prevent stratification.
Intelligent batching system upgrade: Embed the established solubility prediction model to set temperature-linked auxiliary dosing thresholds and eliminate unstable admixture quality caused by precipitation.

Conclusion

The solubility of sucrose, sodium gluconate, sulfite and maltodextrin auxiliaries in the PCE mother liquor is jointly controlled by ambient temperature and polymer solid concentration. Low temperature and high solid content synergistically reduce the additive’s dissolution capacity and cause crystallization defects, disrupting concrete slump retention and construction stability.

The established multi-temperature solubility database provides reliable parameter support for intelligent automatic admixture compounding systems. Admixture factories can select matched PCE solid content and auxiliary types according to local seasonal temperature changes to produce stable, non-stratified, anti-freezing polycarboxylate superplasticizer products.