As the core material of modern construction, the performance of concrete is directly related to the quality and durability of the project. However, traditional concrete often faces the problem of insufficient fluidity during construction, which leads to difficulties in pouring, uneven structure and even reduced strength. Concrete water reducer is a concrete additive developed to solve this problem. It has become an indispensable component of modern high-performance concrete.
First of all, we need to understand: What is water reducer?
Water reducer is a chemical admixture that can significantly reduce the amount of water used in concrete mixing and improve fluidity and strength. According to the different water reducing capacity, it can be divided into:
Ordinary water reducer (water reduction rate 5%~10%): Common ones are Sodium Lignosulfonate SLS and calcium lignosulfonate CLS.
High-efficiency water reducer (water reduction rate 10%~20%): Naphthalene-based water reducers such as sodium naphthalene sulfonate SNF.
High-performance water reducer (water reduction rate>20%): such as polycarboxylic acid-based water reducer.
2. What are the main functions of water reducer?
- Reduce water consumption and improve concrete strength.
- Improve workability, easy to pump and pour.
- Reduce cement consumption and save costs.
- Reduce the risk of shrinkage and cracking.
3. How does water reducer improve concrete fluidity?
(1) Dispersion: Breaking the flocculation structure of cement particles
Due to the surface charge, cement particles in fresh concrete will adsorb to each other to form a flocculation structure, encapsulating a large amount of free water. This water can’t participate in the lubrication effect, resulting in reduced concrete fluidity.
The main component of water reducer is surfactant, and its molecular structure includes:
Hydrophilic groups (such as sulfonic acid groups and carboxylic acid groups) can combine with water.
Hydrophobic groups (such as long-chain alkyl groups) are adsorbed on the surface of cement particles.
When water reducer is added to concrete:
Hydrophobic groups are adsorbed on the surface of cement particles to form a charged protective film.
The hydrophilic groups extend outward, causing the cement particles to carry the same negative charge, generating electrostatic repulsion.
The flocculation structure between cement particles is broken, releasing the encapsulated free water, thereby improving fluidity.
(2). Lubrication: Reduce friction between particles
In addition to electrostatic repulsion, the hydrophilic group of the water reducer can also form a hydration film on the surface of cement particles, which plays a lubricating role, further reducing friction resistance and making concrete easier to flow.
(3). Unique steric hindrance effect of polycarboxylic acid water reducer
Unlike ordinary water reducers and naphthalene water reducers, polycarboxylic acid water reducers have longer molecular chains and can form a steric hindrance effect.
The main chain of the molecule is adsorbed on the surface of cement particles, and the side chain extends into the solution to form a three-dimensional barrier.
In this way, the electrostatic repulsion is weakened due to the increase in ion concentration, and the steric hindrance can still effectively prevent the cement particles from re-flocculating.
This makes PCE water reducer more dispersible and durable, especially suitable for high-strength, self-compacting concrete.
4. Key factors affecting the effect of concrete water reducer
(1). Cement composition and mineral composition
C3A (tricalcium aluminate) content. C3A is the fastest hydrating mineral phase in cement and has strong adsorption to water reducer molecules. High C3A cement will consume a large amount of water reducer, resulting in a decrease in dispersion effect. If the C3A content in cement is too high (such as 12%), it may be necessary to use a slow-release polycarboxylate water reducer instead.
Sulfate (SO₃) content. Sulfate can inhibit the rapid hydration of C3A, but excessive SO₃ will compete with the water reducer for adsorption and reduce dispersibility. When using high-sulfate cement, it is recommended to choose a naphthalene-based water reducer with a higher degree of sulfonation.
Alkali content (Na₂Oeq). High-alkali cement (Na₂Oeq＞0.6%) will accelerate cement hydration, causing the water reducer molecules to be quickly wrapped and ineffective. For this type of cement, mineral powder needs to be added to reduce alkali activity. Alternatively, choose an alkali-resistant PCE superplasticizer.
(2). Aggregate characteristics
Mud content. Clay particles have a large specific surface area and will absorb water-reducing agent molecules, significantly reducing the effective dosage. When the mud content is greater than 3%, the efficiency of the water-reducing agent will decrease by 20%~40%. It is necessary to pre-clean the aggregate or increase the water-reducing agent dosage by 0.2%~0.5%.
Water absorption rate. Porous aggregates have a high water absorption rate and will compete for mixing water, resulting in faster slump loss. Soak the aggregates to a saturated surface dry state before use. Use a slump-retaining water-reducing agent (such as PCE).
(3). Environmental conditions
Temperature
High temperatures greater than 30℃ will accelerate cement hydration, water-reducing agent molecules will be quickly consumed, and the slump loss rate will increase by more than 50%.
Additive use advice: ① Compound retarder (such as sodium gluconate). ② Select PCE high-efficiency water-reducing agent with strong temperature adaptability.
Low temperatures less than 5°C will slow down hydration, delay the dispersion of the water-reducing agent, and require longer mixing time.
Humidity
Low humidity (<60% RH) will intensify water evaporation, causing the fluidity of concrete to decrease rapidly. At this time, air entraining agent (air content 3%~5%) is required.
(4). Mix design
① Water-cement ratio (W/B)
Low water-cement ratio (<0.4). The water reducer has a large dispersion resistance, so it is necessary to increase the dosage or select a high water reduction rate PCE (>25%).
High water-cement ratio (>0.5). The effect of the water reducer is easily diluted by excess water, so it is recommended to reduce the dosage of the water reducer.
② Types of cementitious materials
Fly ash and mineral powder: Spherical particles can improve fluidity and reduce the demand for water reducers. Adding 30% fly ash can reduce the dosage of water reducers by 10%~15%.
Silica ash: Ultra-high specific surface area requires an increase in the dosage of water reducers by 0.3%~0.8%.
(5). Construction process
Mixing time
Insufficient mixing time will cause uneven dispersion of the water reducer and residual local flocculation structure.
Too long mixing time may cause excessive bubbles or slump loss.
Mixing order
First dry mix aggregate and cement, mix for 30 seconds.
Add 80% water and mix for 15 seconds.
Add water reducer and remaining water and mix for 60 seconds.
Transportation and parking time
Pumped concrete: Every 30 minutes of parking will cause a slump loss of 10~20mm, and a slump retainer must be compound
5. Some suggestions for comprehensive optimization of the use of concrete water reducers
Water reducers are key materials for improving concrete performance, but they must be used scientifically to achieve the best results. The following is a comprehensive optimization plan based on material science and engineering practice:
(1). Material compatibility test
Before using a new batch of cement, a pure paste fluidity test must be carried out.
Test items:
✓ Initial fluidity.
✓ 30/60 minute fluidity retention rate.
✓ Compatibility with aggregates, observe whether there is water seepage and segregation.
(2). Dynamically adjust the dosage
Key points of control:
| Condition changes | Adjustment range of dosage | Scientific basis |
| Temperature rises by 5℃ | + 0.1%~0.2% | High temperature accelerates molecular failure |
| Aggregate mud content increases by 1% | +0.15%~0.3% | Clay absorbs effective ingredients |
| Cement C3A＞8% | +0.2%~0.5% | High C3A cement has strong adsorption |
In addition, when using polycarboxylate water reducer, it is recommended to use the post-mixing method, that is, add 80% water first, and then add water reducer.
(3). Compounding technology solution
High temperature construction: PCE (0.8%), sodium gluconate (0.03%) and air entraining agent (0.002%).
Prefabricated components: PCE (1.2%), triethanolamine (0.02%) early strength agent.
Underwater concrete: PCE (1.0%), cellulose ether (0.05%) anti-dispersant.
(4). Aggregate pretreatment
For aggregates with high mud content:
✓ High-pressure water washing until the mud content is less than 1%.
✓ Add clay inhibitors, such as cationic polymers.
For aggregates with high water absorption:
✓ Sprinkle water 24 hours in advance to moisten.
✓ Control the moisture content in the saturated surface dry state.
(5). Environmental adaptability adjustment
| Environmental conditions | Solution | Mechanism of action |
| High temperature (>30℃) | Compound retarder and sunshade construction | Delay hydration heat peak |
| Low temperature (<5℃) | Use early strength PCE and warm water (<40℃) to mix | Promote molecular diffusion |
| High wind drying | Add hydroxypropyl methylcellulose | Inhibit water evaporation |
(6). Key measures to ensure long-term performance
Avoid excessive chloride ions, prestressed structure <0.06%.
When used in marine environments, compound rust inhibitors such as calcium nitrite.
Control bubble structure, gas content 4%~6%, pore size <200μm.
(7). Intelligent management
IoT monitoring: Install sensors on mixer trucks to transmit slump data in real time.
AI proportioning system: Automatically optimize water reducer dosage based on historical data.
Blockchain traceability: Record the entire chain data of water reducer production, transportation and use.
Conclusion
Water reducer effectively breaks the cement flocculation structure and releases free water through electrostatic repulsion, lubrication and steric hindrance, thereby improving the fluidity of concrete. Selecting a suitable concrete water reducer and optimizing the mix ratio can not only improve construction performance, but also reduce costs and improve durability.