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How Two PCE Superplasticizers Perform in High Mineral Blended Low Carbon Binder Systems
Blog How Two PCE Superpla
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The sediment dredged from rivers and lakes contains ultrafine particles and an extremely high natural moisture content. Without proper solidification treatment, the original silt cannot be directly used for embankment reinforcement, slope protection, land reclamation, and road subgrade filling. The traditional solidified soil formula improves mechanical strength by adding a cement binder, but a higher cement dosage greatly reduces the mixture’s fluidity and hinders pumping during construction.
Superplasticizer (water reducing agent) is a widely used concrete additive that improves workability. Adding them to cement-stabilized sludge effectively balances the strength and fluidity of pumpable structures. Two mainstream high-efficiency water reducing agents, calcium lignosulfonate (CLS) and polycarboxylate superplasticizer, exhibit vastly different performance in high-clay marine dredging sludge.
This article decomposes the experimental research on marine silt in the Huaihe River channel, compares the flowability improvement effects of CLS and polycarboxylate superplasticizer at different dosages, explains the adsorption mechanism of clay minerals that limits the performance of polycarboxylate, and provides practical guidance for selecting additives for dredging mud solidification engineering.
Dredging and disposing of silt has become a key environmental and geotechnical engineering challenge on a global scale. Storing untreated sludge occupies a large amount of land, causing secondary soil and water pollution, and requires 3-5 years of natural dewatering before it can be reused. Cement solidification is the most mature and large-scale technology for sludge resource recycling, providing a stable carrying capacity for infrastructure filling.
Pumping is the most effective construction method for on-site solidification of sludge. However, there is a core engineering contradiction:
Low cement dosage: The solidified soil has sufficient fluidity, but low compressive strength;
High cement usage: mechanical strength is improved, but fluidity is poor, brittleness is high, and pipeline pumping is blocked.
Previous studies have confirmed that high-efficiency water-reducing agents are effective composite additives for stabilizing soil. Existing research has confirmed that calcium lignosulfonate has a threshold dose that affects the flowability of mud-solidified soil. However, few papers systematically compare CLS and polycarboxylate superplasticizers and elucidate the mechanisms underlying performance differences driven by clay mineral composition in natural soil.
This experiment selected some dredging silt samples for flowability tests at dosages of 0%- 4% for high-efficiency water-reducing agents, clarifying the applicable scenarios for the two water-reducing agents to support on-site solidification engineering design.
Testing soil samples
Basic physical indicators: liquid limit of 55%, plastic limit of 24%, natural moisture content of 61%, specific gravity of 2.67. Particle composition: 3.94% sand, 48.31% silt, 48.20% clay.
Mineral composition of soil samples (key factors affecting the performance of high-efficiency water reducing agents): montmorillonite 20%, illite 73%, chlorite 2%, kaolinite 5%. Montmorillonite has a strong adsorption capacity for polycarboxylate molecules.
Adhesives and superplasticizers
The cement is ordinary Portland cement, which fully complies with the national standard GB 175-2020. The cement-to-soil mix ratio for all test groups is fixed at 15%.
Polycarboxylate superplasticizer: gray-white powder, active ingredient ≥ 90%, bulk density 650-850g/L.
Lignosulfonate calcium (CLS) has an analytical purity of 98% and is a dark brown powder with a slight aromatic odor.
There is no unified national standard for testing the flowability of solidified soil. This experiment uses internationally recognized 80 mm × 80 mm cylindrical organic glass molds (with equal diameter and height), in accordance with Japanese standard JHS A313-1992, to provide stable, reproducible flowability data for high-water-content mud mixtures.
Test steps:
Adjust the experimental soil to a moisture content equal to 2.5 times the liquid limit (138%) and set the cement dosage to 15%. Two types of superplasticizers were tested for mass dosage (relative to cement mass): 0%, 0.6%, 0.8%, 1.0%, 2%, 3%, and 4%.
The baseline flowability of the solidified soil without adding any high-efficiency water-reducing agent is 9.07 cm. Once the dosage exceeds 1%, the performance gap between CLS and polycarboxylate superplasticizer will significantly widen.
CLS steadily improves the flowability of solidified soil within all dosage ranges:
0% → 1% dose: flowability increased from 9.07cm to 9.47cm, with a growth rate of 4% and slight improvement;
1% → 4% dose: The fluidity increases sharply to 12.44cm. After the 1% threshold, the growth rate accelerates sharply;
3% to 4% CLS dosage: single-stage fluidity increased by 11%.
The working principle of CLS: CLS molecules are directionally adsorbed on the surface of cement particles, generating the same negative charge and generating electrostatic repulsion between cement particles. The flocculated cement mass ruptures, releasing encapsulated free water, thereby enhancing the mixture’s fluidity. At low doses, limited adsorption sites limit fluidity; when the dosage exceeds 1%, abundant free CLS molecules fully disperse the cement aggregate, significantly improving flowability.
Polycarboxylate, as a highly efficient water-reducing agent, exhibits extremely weak fluidity enhancement in clay-rich marine solidified soil:
0% → 1% dose: increased fluidity by 4% (9.07cm to 9.41cm), consistent with CLS performance;
1% → 4% dose: The fluidity only slowly increases from 9.41 cm to 9.77 cm, and the single-stage growth rate remains below 1%.
The core limiting factor is the strong adsorption of clay minerals (especially montmorillonite) in the soil matrix. Montmorillonite preferentially absorbs polycarboxylate polymer chains, occupying the majority of additive molecules before they attach to cement particles. The reduction in polycarboxylate adsorption on cement particles will weaken electrostatic dispersion, and even with higher superplasticizers, it will seriously inhibit the improvement in fluidity.
Dosage ≤ 1%: CLS and polycarboxylate salts have almost the same fluidity-promoting effect;
Dose>1%: As the dose increases, the performance of CLS becomes increasingly better than that of polycarboxylates;
At a 4% equivalence, CLS improved the flowability of solidified soil by approximately 27% compared to polycarboxylate superplasticizers.
Both calcium lignosulfonate and polycarboxylate superplasticizer can improve the flowability of solidified dredged sludge with increasing dosage. When the mixing ratio is less than 1%, their liquidity enhancement effect is equivalent.
Clay minerals (especially montmorillonite) strongly adsorb polycarboxylate polymers, reducing the amount of superplasticizer adsorbed on cement particles and weakening their dispersibility. When the dosage exceeds 1%, the fluidity of calcium lignosulfonate is further enhanced, and compared with polycarboxylates, the promotion effect at 4% is 27% higher.
The composition of clay minerals in dredged silt varies widely across regions, leading to inconsistent superplasticizer performance. Laboratory fluidity testing is mandatory to select the optimal type and dosage of water-reducing agent for on-site curing projects.
Solidification of high-clay marine dredging mud: When the dosage of high-efficiency water reducing agent needs to exceed 1% to meet the requirements of pumping fluidity, calcium lignosulfonate should be prioritized for use;
Low clay silt or river dredging silt: 1% dosage of polycarboxylate superplasticizer can be used to balance fluidity and long-term strength;
New dredging and solidification project: Conduct pre-laboratory flowability tests to confirm soil clay mineral content, identify the type and economic dosage of high-efficiency water reducing agents;
Pump-stabilized soil construction: Control the CLS dosage between 3% and 4% to achieve sufficient fluidity without incurring excessive additive costs.
The selection of high-efficiency water reducing agents directly determines the pumping efficiency of cement-solidified dredging sludge.Polycarboxylate superplasticizer is widely regarded as an efficient additive for concrete, but due to adsorption by montmorillonite, it has lost its advantage in clay-rich marine sludge. Calcium lignosulfonate exhibits excellent flowability enhancement performance at high mixing ratios, making it an economically efficient additive choice for large-scale river dredging and solidification projects.
All geotechnical engineers and construction contractors should analyze the local soil mineral composition and conduct targeted flowability testing to select the appropriate type and dosage of superplasticizer, balance construction workability and solidified soil strength, and minimize project costs.
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