Publish Time: 2026-07-20 Origin: Unionchem
Table of Contents
Self-compacting concrete is one of the most significant advances in construction technology of the past three decades. A concrete mix that flows under its own weight, fills complex formwork without vibration, passes through dense reinforcement without segregation, and still achieves the mechanical properties of conventionally vibrated concrete — the engineering and economic advantages are substantial.
But SCC is also one of the most sensitive concrete formulations in existence. The same fluidity that makes it self-compacting also makes it vulnerable to segregation — the separation of coarse aggregates from the paste — and bleeding — the upward migration of water through the mix. A mix that is slightly too fluid, or that encounters a small variation in aggregate moisture content or cement reactivity, can go from performing perfectly to segregating completely.
The solution to this sensitivity is a viscosity modifying agent (VMA) — an admixture that increases the viscosity and cohesion of the cement paste without reducing fluidity, providing the mix with robustness against small variations in constituent materials and batching conditions.
Welan gum is one of the most effective VMAs available for SCC. Its combination of high viscosity at low shear (preventing segregation at rest), strong shear-thinning behavior (maintaining flowability under the shear of placement), stability in the highly alkaline cement environment, and compatibility with the polycarboxylate superplasticizers used in SCC makes it uniquely suited to this application.
This guide is for concrete technologists, admixture formulators, and construction chemical engineers working on SCC formulations. It covers how welan gum works as a VMA, the specific stability mechanisms it provides, dosage and interaction with superplasticizers, robustness testing, troubleshooting, and how to compare welan gum with alternative VMAs.
Unionchem supplies high-performance welan gum for SCC and construction applications:Welan Gum — Unionchem Product Page
Conventional concrete requires mechanical vibration during placement to consolidate the mix, eliminate air voids, and ensure the concrete fully fills the formwork. Vibration is labor-intensive, time-sensitive, and can be difficult or impossible in congested reinforcement, restricted access areas, or large continuous pours.
SCC eliminates the need for vibration by achieving sufficient fluidity through mix design — primarily through the use of high-range water reducers (superplasticizers) and carefully controlled paste volume and aggregate content. A properly designed SCC mix:
Flows under its own weight to fill the formwork completely
Passes through gaps between reinforcing bars without blocking
Resists segregation — maintains a homogeneous distribution of aggregates throughout the flow
Self-levels to a smooth, uniform surface
These four properties — filling ability, passing ability, segregation resistance, and surface finish — define SCC performance, and they are assessed by standardized tests (slump flow, J-ring, V-funnel, sieve segregation) before every pour.
The fundamental challenge in SCC design is that fluidity and stability are in direct conflict. Increasing fluidity (by adding more superplasticizer or water) improves filling ability but reduces segregation resistance. Reducing the water-to-binder ratio improves stability but reduces fluidity.
Conventional SCC design manages this conflict through high paste volume (more cement, supplementary cementitious materials, and filler to increase the cohesion of the paste phase) and reduced coarse aggregate content (fewer large particles to segregate). These approaches work, but they increase cost and can affect mechanical properties.
A VMA offers a third approach: increase the viscosity and cohesion of the paste phase directly, without changing the water content or aggregate proportions. This allows the mix designer to achieve both high fluidity and adequate stability simultaneously — and to maintain that stability even when constituent materials vary slightly between batches.
In practice, SCC is never batched under perfectly controlled laboratory conditions. Aggregate moisture content varies. Cement reactivity varies between deliveries. Ambient temperature affects admixture dosage requirements. A VMA that provides robustness — that keeps the mix within acceptable performance limits despite these variations — is not a luxury; it is a practical necessity for reliable SCC production.
This is where welan gum's unique rheological properties become critical.
Welan gum is a microbial polysaccharide produced by fermentation of Alcaligenes sp. In aqueous solution, welan gum molecules form a rigid, extended helical structure — similar in some respects to xanthan gum, but with significantly greater thermal and chemical stability.
In the cement paste of an SCC mix, welan gum creates a three-dimensional polymer network that modifies the rheology of the paste in two critical ways:
At rest — or under the very low shear rates that occur when the concrete is stationary in the formwork — welan gum's polymer network provides a measurable yield stress and high apparent viscosity. This means the paste resists flow until a threshold force is applied.
In practical terms: aggregate particles cannot sink through a paste that has a yield stress. The paste holds the aggregates in suspension, preventing segregation even during the extended period between mixing and final set.
Under the higher shear rates that occur during mixing, pumping, and flow through formwork, welan gum's network breaks down — the apparent viscosity drops dramatically, and the mix flows freely. This is the same pseudoplastic (shear-thinning) behavior that makes xanthan gum effective in food applications, but welan gum maintains this behavior at temperatures up to 150°C and in the highly alkaline (pH 12–13) cement environment where xanthan gum would degrade.
The combination of these two properties — high viscosity at rest, low viscosity under shear — is exactly what SCC requires: the mix flows during placement but holds its aggregates in suspension once it comes to rest.
The cement paste environment is chemically aggressive: pH 12–13, high calcium and alkali ion concentrations, and temperatures that can reach 60–80°C in mass concrete pours. Most organic polymers degrade rapidly under these conditions.
Welan gum's rigid helical structure is exceptionally stable in alkaline environments. It maintains its viscosity-modifying function throughout the placement and early hydration period — the critical window during which segregation must be prevented.
For a complete overview of welan gum's properties and industrial applications, see:What Is Welan Gum and What Is It Used For?
Filling ability is measured by the slump flow test — the diameter of the concrete spread after the slump cone is lifted. Typical SCC target: 550–850 mm, depending on application.
Welan gum at typical dosage levels (0.01%–0.04% by cement weight) does not significantly reduce slump flow when used in combination with an appropriate superplasticizer. The superplasticizer controls fluidity; welan gum controls viscosity and cohesion independently.
Key principle: In a well-designed SCC with welan gum, slump flow and plastic viscosity are controlled semi-independently — the superplasticizer dosage sets the flow, and the welan gum dosage sets the viscosity. This decoupling is one of the most important practical advantages of using a VMA.
Passing ability — the ability of the mix to flow through gaps in reinforcement without blocking — depends on both fluidity and the absence of aggregate bridging. Welan gum contributes to passing ability by maintaining the homogeneity of the mix: a segregated mix, where coarse aggregates have concentrated in one region, will block reinforcement gaps even if the overall fluidity is adequate.
This is the primary function of welan gum in SCC. The sieve segregation test (EN 12350-11) measures the proportion of paste that passes through a 5 mm sieve after the concrete has rested — a high result indicates that paste has separated from aggregates.
Welan gum reduces sieve segregation by holding aggregates in the paste through its yield stress and viscosity contribution. Well-formulated SCC with welan gum typically achieves sieve segregation values below 15% (the standard acceptance threshold) even with relatively high slump flows.
Bleeding — the upward migration of mix water — is a form of segregation that affects the surface quality and near-surface properties of the hardened concrete. Welan gum reduces bleeding by increasing the viscosity of the aqueous phase, slowing the upward movement of water through the paste.
Welan gum is highly efficient — effective at very low concentrations. Typical dosage in SCC:
Application | Welan Gum Dosage (% by cement weight) | Notes |
Standard SCC (w/b 0.38–0.45) | 0.010% – 0.025% | Most common range for general SCC |
High-fluidity SCC (slump flow >750 mm) | 0.020% – 0.040% | Higher VMA needed for very fluid mixes |
SCC with high aggregate content | 0.020% – 0.035% | More aggregate requires more cohesion |
SCC in hot weather (>30°C) | 0.025% – 0.045% | Higher temperature reduces viscosity effect |
Underwater concrete / tremie concrete | 0.030% – 0.060% | Anti-washout requirement |
Oil well cement slurry | 0.020% – 0.050% | High temperature, high pressure conditions |
Grout and repair mortar | 0.010% – 0.030% | Fine aggregate systems |
Starting point for most SCC applications: 0.015%–0.020% by cement weight.
These are guidance ranges. Actual dosage must be determined by trial mixes in your specific system, with your specific cement, aggregates, and superplasticizer.
For a typical SCC with 400 kg/m³ cement content:
0.015% × 400 kg = 60 g/m³ of welan gum
0.025% × 400 kg = 100 g/m³ of welan gum
At these quantities, welan gum is one of the lowest-dosage admixtures in the SCC system — but its effect on mix stability is disproportionate to its quantity.
The most important compatibility question in SCC admixture design is the interaction between the VMA and the superplasticizer. In a poorly designed system, the VMA and superplasticizer can interact in ways that reduce the effectiveness of both.
PCE superplasticizers are the standard choice for SCC. They provide high water reduction at low dosage and have a relatively flat slump loss profile over time.
Welan gum is compatible with PCE superplasticizers — they do not interact adversely, and their effects on rheology are largely additive and independent. The PCE controls the yield stress reduction (fluidity), and the welan gum controls the plastic viscosity (cohesion). This independence is what allows the semi-independent control of flow and stability described above.
Practical implication: When adjusting SCC mix design, the superplasticizer dosage and welan gum dosage can be adjusted independently to hit the target slump flow and target viscosity simultaneously. This is a significant advantage over VMA approaches that are more strongly coupled to the superplasticizer system.
Older-generation superplasticizers (naphthalene sulfonate, melamine sulfonate) are less commonly used in SCC but are still encountered in some markets. Welan gum is generally compatible with these superplasticizers, but the interaction may be less clean than with PCE — some adjustment of dosages may be required.
The order of addition of admixtures affects performance. The recommended sequence for welan gum in SCC:
Add welan gum to the mix water before adding to the dry materials — this ensures full hydration of the welan gum before it contacts the cement
Alternatively, add welan gum as a pre-dissolved solution (0.1%–0.5% in water) — this is the most reliable approach for consistent dosing
Add superplasticizer after the welan gum solution has been incorporated into the mix
Pre-dissolving welan gum in water before addition to the concrete mixer is strongly recommended for consistent performance. Dry addition of welan gum powder directly to the concrete mixer can result in incomplete hydration and inconsistent viscosity development.
Several VMA types are used in SCC. Understanding how welan gum compares with the alternatives helps in making the right selection for your specific application and market.
Property | Welan Gum | Xanthan Gum | HEC | Starch-Based VMA | Cellulose Ether (HPMC) |
Alkaline stability (pH 12–13) | Excellent | Poor | Good | Moderate | Good |
Thermal stability (>60°C) | Excellent | Poor | Moderate | Poor | Moderate |
Shear-thinning behavior | Excellent | Excellent | Moderate | Moderate | Moderate |
Segregation resistance | Excellent | Good (if stable) | Good | Moderate | Good |
Effective dosage | Very low (0.01%–0.04%) | Low | Moderate | Moderate–high | Moderate |
PCE compatibility | Excellent | Good | Good | Variable | Good |
Robustness to material variation | Excellent | Moderate | Moderate | Low | Moderate |
Cost per unit weight | Higher | Moderate | Moderate | Lower | Moderate |
Cost-in-use | Competitive (very low dosage) | N/A (not stable in cement) | Moderate | Moderate | Moderate |
Xanthan gum has excellent shear-thinning behavior and is widely used as a VMA in drilling fluids. However, it is not suitable for SCC because it degrades rapidly in the alkaline cement environment (pH 12–13). Within hours of contact with cement paste, xanthan gum loses its viscosity-modifying function — precisely when segregation resistance is most needed.
Welan gum's superior alkaline stability is the primary reason it is preferred over xanthan gum for cementitious applications.
Hydroxyethyl Cellulose (HEC) is stable in alkaline environments and is used as a VMA in some grout and mortar applications. However, in SCC:
HEC provides less shear-thinning than welan gum — the viscosity reduction under shear is less pronounced, which can affect flowability
HEC requires higher dosages to achieve equivalent segregation resistance
HEC's performance is more sensitive to temperature variation
For more on HEC and its industrial applications, see:What Is Hydroxyethyl Cellulose (HEC) and What Is It Used For?
Diutan gum is another microbial polysaccharide used as a VMA in SCC. It has similar alkaline stability to welan gum and comparable shear-thinning behavior. The choice between welan gum and diutan gum is primarily one of availability, cost, and specific performance characteristics in your cement system — both are effective VMAs for SCC. Welan gum is more widely available globally and is the more established product in the market.
SCC mix design with a VMA is best understood through the concept of two-point rheology: the mix has two key rheological parameters that must both be within target ranges:
Yield stress (or slump flow): must be low enough for the mix to flow and fill the formwork
Plastic viscosity (or T500 time): must be high enough to prevent segregation and bleeding
In a conventional SCC without VMA, these two parameters are strongly coupled — reducing yield stress (increasing fluidity) also reduces plastic viscosity (reducing stability). With welan gum, they can be adjusted semi-independently:
Adjust slump flow → change superplasticizer dosage
Adjust plastic viscosity / stability → change welan gum dosage
This decoupling is the fundamental practical advantage of the VMA approach and is what makes SCC with welan gum more robust than SCC without VMA.
Parameter | Typical Range for SCC with Welan Gum |
Water-to-binder ratio (w/b) | 0.35 – 0.45 |
Paste volume | 330 – 380 L/m³ |
Coarse aggregate (max 16–20 mm) | 280 – 360 kg/m³ |
Fine aggregate | 800 – 950 kg/m³ |
Cement + SCM (fly ash, slag, silica fume) | 380 – 480 kg/m³ |
PCE superplasticizer | 0.2% – 0.8% by binder weight |
Welan gum | 0.010% – 0.040% by cement weight |
Target slump flow | 600 – 750 mm |
Target T500 | 2 – 5 seconds |
Target sieve segregation | < 15% |
Before finalizing an SCC mix design with welan gum, robustness testing is essential. This involves deliberately varying key parameters within the range of expected production variation and verifying that the mix remains within acceptance criteria:
Water content variation: ±5 L/m³ from target
Aggregate moisture variation: ±0.5% from target
Superplasticizer dosage variation: ±10% from target
Cement content variation: ±10 kg/m³ from target
Temperature variation: test at minimum and maximum expected ambient temperature
A robust SCC mix with welan gum should remain within slump flow and segregation acceptance criteria across all of these variations. If the mix fails robustness testing, increase the welan gum dosage and retest.
Beyond SCC, welan gum is also used as a rheology modifier in oil well cement slurries — the cement systems pumped into the annular space between the casing and the wellbore to provide zonal isolation and structural support.
Oil well cementing presents even more extreme conditions than SCC:
Temperatures up to 150°C+ in deep wells
Pressures up to several hundred bar
High salinity brine environments
Highly alkaline cement slurry (pH 12–13)
Welan gum maintains its viscosity-modifying function under all of these conditions. In oil well cement slurries, it:
Prevents settling of weighting materials (barite, hematite) during placement
Controls free water (bleeding) in the set cement
Provides rheology modification for pumpability optimization
Maintains stability in high-temperature, high-salinity environments where most organic polymers fail
Typical dosage in oil well cement: 0.02%–0.05% by cement weight.
For more on welan gum in oilfield applications, see:Welan Gum: The High-Performance Biopolymer for Oilfield and Construction Applications
Likely causes:
Welan gum dosage too low for the fluidity level of the mix
Welan gum not fully hydrated before addition to mixer (dry powder added directly)
Superplasticizer dosage too high relative to VMA dosage
Aggregate content or maximum aggregate size outside appropriate range for SCC
Solutions:
Increase welan gum dosage by 0.005%–0.010% increments and retest
Pre-dissolve welan gum in mix water before addition; allow full hydration (minimum 30 minutes at room temperature)
Reduce superplasticizer dosage slightly and retest
Review aggregate grading — ensure coarse aggregate content is within SCC-appropriate range
Likely causes:
Welan gum dosage too high
Superplasticizer dosage insufficient for the VMA level used
Welan gum overdosed due to inaccurate weighing at low dosage levels
Solutions:
Reduce welan gum dosage by 0.005% increments
Increase superplasticizer dosage to restore target slump flow
Verify weighing accuracy — at dosages of 60–100 g/m³, small absolute errors represent large percentage errors; use a precision balance
Likely causes:
Variation in welan gum dissolution — inconsistent pre-dissolution procedure
Variation in aggregate moisture content between batches
Variation in cement reactivity between deliveries
Temperature variation affecting admixture performance
Solutions:
Standardize pre-dissolution procedure: fixed concentration (e.g., 0.2% solution), fixed mixing time, fixed temperature
Measure aggregate moisture content before each batch and adjust mix water accordingly
Conduct robustness testing across the range of expected material and temperature variation
Request COA per batch from welan gum supplier; verify viscosity consistency
Likely causes:
Powder added to water too quickly — surface hydration before full dispersion
Water temperature too low — slow hydration
Insufficient agitation during dissolution
Solutions:
Add welan gum powder to water slowly with continuous agitation — not the reverse
Use water at 20–40°C for faster hydration
Use a high-shear mixer or recirculation pump for dissolution; allow minimum 30–60 minutes contact time
Consider using a pre-wetted dispersion (welan gum pre-dispersed in a small amount of glycol or alcohol) for easier addition
For procurement teams and admixture formulators sourcing welan gum for SCC and construction applications, the following parameters are the most important to specify and verify:
Parameter | Why It Matters | Typical Specification |
Viscosity (1% solution, 25°C) | Primary performance indicator | ≥ 800 mPa·s (Brookfield, 12 rpm) |
Viscosity retention at high pH | Confirms alkaline stability | ≥ 80% retention at pH 12–13 |
Viscosity retention at temperature | Confirms thermal stability | ≥ 70% retention at 80°C |
Moisture content | Affects effective concentration | ≤ 15% |
Ash content | Purity indicator | ≤ 15% |
pH (1% solution) | Baseline characterization | 6.0 – 8.0 |
Particle size (mesh) | Affects dissolution rate | 80 mesh standard |
Heavy metals | Industrial safety requirement | Per applicable standard |
Always request:
Certificate of Analysis (COA) per batch — including viscosity, moisture, and pH
Technical Data Sheet (TDS) with SCC application guidance and dosage recommendations
Free samples for trial mix testing before committing to bulk supply
Alkaline stability data — viscosity retention in cement paste or NaOH solution at pH 12–13
Unionchem supplies high-performance welan gum for SCC, oil well cementing, drilling fluids, and industrial suspension applications, with consistent quality, full technical documentation, and reliable global bulk supply from China.
Welan gum for SCC — optimized grade for self-compacting concrete and cementitious systems
Welan gum for oil well cementing — high-temperature stable grade for downhole applications
Welan gum for drilling fluids — rheology modifier for water-based drilling systems
Full technical documentation: TDS, COA (viscosity, alkaline stability, moisture), SDS
Alkaline stability and thermal stability test data
Free samples for trial mix testing and formulation qualification
Technical support for SCC mix design and admixture formulation
For full product details and to request a sample or quote:Welan Gum — Unionchem Product Page
Product | Role in Construction / Oilfield | Product Page |
Welan Gum | VMA for SCC, oil well cement, drilling fluids | |
HEC | Thickener / water retention in grout, mortar, paints | |
Xanthan Gum | Viscosifier in water-based drilling fluids | |
PAC | Fluid loss control in drilling fluids | |
CMC | Fluid loss control, viscosity in drilling / HDD |
Self-compacting concrete is a formulation challenge that requires a VMA capable of doing two things simultaneously: holding aggregates in suspension at rest, and allowing the mix to flow freely under the shear of placement. Welan gum's pseudoplastic behavior in alkaline, high-temperature cementitious environments makes it one of the few admixtures that can reliably deliver both properties.
The key to using welan gum effectively in SCC is understanding the two-point rheology framework: the superplasticizer controls fluidity, and the welan gum controls stability. Adjusting these two independently — rather than trying to balance fluidity and stability through water content or aggregate proportions alone — is what makes SCC with welan gum both high-performing and robust against the material variations of real production conditions.
At dosages of 0.01%–0.04% by cement weight, welan gum is one of the lowest-dosage admixtures in the SCC system. But at those dosages, it is the ingredient that determines whether the mix segregates or stays uniform — and in SCC, that is the difference between a successful pour and a failed one.
Explore Unionchem's welan gum solutions for SCC and construction:Welan Gum — Unionchem Product Page
A VMA is an admixture that increases the viscosity and cohesion of the cement paste in SCC without reducing fluidity. It prevents segregation (separation of coarse aggregates from the paste) and bleeding (upward migration of mix water) while allowing the mix to flow freely under placement shear. Welan gum is one of the most effective VMAs for SCC due to its strong shear-thinning behavior and stability in the alkaline cement environment.
Xanthan gum has excellent shear-thinning behavior but degrades rapidly in the highly alkaline cement environment (pH 12–13). Welan gum maintains its viscosity-modifying function in alkaline conditions and at elevated temperatures — both of which are unavoidable in cement paste. This alkaline stability is the primary reason welan gum is used in SCC and xanthan gum is not.
Typical dosage is 0.010%–0.040% by cement weight, equivalent to approximately 40–160 g per m³ of concrete (for a 400 kg/m³ cement content). Start at 0.015%–0.020% and adjust based on trial mix results. Higher dosages are needed for very fluid mixes (slump flow >750 mm) or in hot weather conditions.
At typical SCC dosage levels (0.01%–0.04% by cement weight), welan gum does not significantly affect the compressive strength or other mechanical properties of the hardened concrete. Its effect is primarily on the fresh concrete rheology. Some studies have shown a marginal effect at very high dosages, but this is not relevant at practical use levels.
The recommended approach is to pre-dissolve welan gum in the mix water before adding to the concrete mixer. Prepare a dilute solution (0.1%–0.5% welan gum in water) with continuous agitation, allow at least 30–60 minutes for full dissolution, then use this solution as part of the mix water. Dry addition of welan gum powder directly to the mixer can result in incomplete hydration and inconsistent performance.
Yes. Welan gum is fully compatible with PCE superplasticizers — the most widely used superplasticizer type in SCC. The two admixtures work independently: PCE controls fluidity (yield stress), and welan gum controls stability (plastic viscosity). This semi-independent control is one of the key practical advantages of using welan gum as the VMA in PCE-based SCC systems.
Yes. Unionchem supplies welan gum with full technical documentation including COA, TDS, alkaline stability data, and dosage guidance for SCC applications. Free samples are available for trial mix testing. See: Welan Gum — Unionchem Product Page
Unionchem supplies high-performance Welan Gum for self-compacting concrete, oil well cementing, drilling fluids, and industrial suspension applications — with consistent quality, full technical documentation, and reliable global bulk supply from China.
Explore our construction and oilfield products:
Contact us:sales@unionchem.com.cnPhone: +86-13953383796 | +86-533-7220272Website:www.unionchem.com.cn
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