Naphthalene Based Superplasticizer: Dosage Recommendations for Concrete Mixes

Introduction  

Naphthalene based superplasticizers (NBS) are real workhorses in modern concrete construction. They boost concrete workability without adding extra water—something that’s make-or-break for how well the concrete performs. If you’re on a construction crew, you probably rely on NBS to hit project needs: high-strength beams, pumpable foundation mixes, you name it. But here’s the catch: get the NBS dosage wrong, and you’ll run into trouble—strength drops, durability issues, even total failures. This piece breaks down clear dosage guidelines, explains what affects those numbers, and shares tips you can actually use on site.  

How Naphthalene Based Superplasticizers Work in Concrete  

You might wonder how NBS actually do their job. They disperse cement particles in the mix, which cuts down on friction between those particles. That’s what makes the concrete flow better—way better than standard water reducers. In fact, NBS can reduce water use by up to 30% when you get it right. They also keep the slump (that measure of workability) steady over time, which matters a lot for long construction days. Most NBS come as liquid solutions, so mixing them into batches is pretty straightforward. Engineers often pick NBS when they need both easy workability and concrete that gains strength fast.  

What Changes the Right NBS Dosage for Concrete?  

There’s no one-size-fits-all NBS dose. A bunch of things affect how much you need, and skipping these can ruin your mix. Let’s break down the most important factors:  

1. The Type of Cement You’re Using  

Not all cements play nice with NBS the same way. Portland cement with lots of C3A (tricalcium aluminate) usually needs more NBS. Why? Those C3A particles soak up superplasticizer molecules, leaving less to do the dispersing work. Low-alkali cement, on the other hand, typically needs less NBS than high-alkali kinds. Always test how your cement and NBS work together first—this gives you a baseline to start from.  

2. What Your Aggregates Are Like  

Aggregates (the rocks and sand in concrete) have a big say in NBS needs. Fine aggregates—like sand that’s extra fine—need more NBS. If your aggregates have over 3% clay, that clay will soak up NBS too, so you’ll need to add more. But well-graded aggregates (the ones with a good mix of sizes) cut down on internal friction. That means you can use less NBS. Always check your aggregate samples before locking in a dosage.  

3. How Strong the Concrete Needs to Be  

High-strength concrete (C60 and above) uses more cement, so it needs more NBS. All those extra cement particles need more dispersing to stay workable. Medium-strength mixes (C30 to C50) use a middle ground—0.8 to 1.2% NBS. Low-strength concrete (below C30) needs less; too much NBS here will make the mix separate. Your dosage has to match the strength you’re aiming for.  

4. The Weather on Site  

Hot days (over 30°C) speed up cement hydration, which makes slump drop fast. On those days, you’ll probably need to add 0.1 to 0.2% more NBS. Cold days (below 10°C) slow hydration down, so you can use a little less. Tweaking dosage based on daily temps keeps your concrete consistent.  

 5. What the Construction Job Requires  

If you need to pump concrete, it needs more workability—so add 0.1 to 0.3% extra NBS to avoid pipe clogs. Precast concrete might use less NBS because it needs to set faster. Mass concrete (like for dams or big foundations) uses moderate NBS to keep hydration heat low. Match the dose to what the job actually needs, and you’ll avoid gaps in performance.  

General NBS Dosage Tips by Concrete Type  

All these numbers are percentages of NBS compared to the total mass of cementitious materials (that’s cement plus things like fly ash).  

 1. Ordinary Plastic Concrete (C15–C25)  

This is the stuff you use for walkways or low-load walls. You’ll want 0.5 to 0.8% NBS here. It’s enough to make the concrete easy to work with without making it separate. After adding NBS, check the slump—if it’s below 100mm, adjust a little.  

2. Medium-Strength Concrete (C30–C50)  

For residential beams, columns, or slabs, go with 0.8 to 1.2% NBS. This balance keeps the mix workable and helps it gain strength properly. Test the 28-day compressive strength to make sure the dose is right.  

3. High-Strength Concrete (C60+)  

High-strength mixes need 1.2 to 2.0% NBS. All that extra cement needs more dispersing to stay pumpable. Aim for a slump of 180mm or more here. Check the 7-day strength too—this lets you fine-tune the dose early.  

 4. Pumpable Concrete (Any Strength Grade)  

Add 0.1 to 0.3% extra NBS if you’re pumping. This stops pipes from clogging while you’re moving the concrete. You want slump loss to be less than 50mm in the first hour. If pumping pressure goes up suddenly, adjust the dose.  

5. Mass Concrete (Dams, Foundations)  

Mass concrete uses 0.6 to 1.0% NBS. Lower doses help control hydration heat, which prevents cracking. Mix NBS with mineral admixtures (like slag) to get even better thermal performance. Keep an eye on temperature gradients while the concrete cures.  

Tips for Getting NBS Dosage Right on the Job  

Lab numbers give you a start, but site conditions always need tweaks. Here’s what works in real life:  

 1. Test Small Batches First  

Don’t jump into full loads—start with 50-liter batches. This lets you catch compatibility issues early. Write down slump, setting time, and strength for each test. Pick the lowest dose that works—this saves money too.  

2. Check Slump Nonstop  

While you’re placing concrete, check slump every 30 minutes. If it drops below your target, adjust NBS a little. Never add extra water—use NBS to get workability back. Keep a log of these checks for future jobs.  

3. Mix NBS the Right Way  

Add NBS after water and aggregates—this makes sure it spreads evenly. Don’t pour it directly on dry cement; that causes clumps. Follow your mixer’s guidelines—usually 3 to 5 minutes of mixing is enough.  

 4. Talk to Your NBS Supplier  

Share your mix details with the supplier. They know their product best and can give tailored tips. Ask for reports on how well the NBS works with your cement. If you switch aggregate sources, let them know—they might adjust their advice.  

What Happens If You Get NBS Dosage Wrong? (And How to Fix It)  

Bad dosage leads to expensive mistakes. Knowing these risks helps you avoid them:  

1. Underdosing Issues  

Underdose, and you’ll get concrete that’s hard to place—it just won’t flow. You’ll end up needing more water, which weakens the concrete long-term. Poor dispersion also creates weak spots. This usually means delays because the mix is too stiff to work with.  

2. Overdosing Problems  

Overdose, and the concrete will separate—aggregates sink to the bottom. You’ll get too much bleeding (water rising to the top), which leaves voids. Those voids make the concrete less durable—water and chemicals can seep in. Setting time also slows down, which holds up the next steps of the job.  

 3. How to Fix These Issues  

Use calibrated pumps to add NBS accurately—no guesswork. Train your crew to spot separation or stiff mixes early. Keep backup NBS batches with small concentration adjustments. Do weekly strength tests to make sure your dose is still on track.  

Wrapping Up  

NBS can make or break your concrete—but only if you dose them right. The perfect amount depends on your cement, aggregates, strength goals, weather, and job needs. The guidelines here give you a solid start, but nothing beats on-site tests and constant checks. Get NBS dosage right, and you’ll have concrete that meets performance, safety, and durability standards. That’s not just about following numbers—it’s about building structures that last.