Admixture Dose Calculator
Percentage dose to kg per m³ and per batch, with the new w/b ratio.
With the default inputs: Cement 300 kg/m³ · Fly ash 60 kg/m³ · Slag 0 kg/m³ etc.Admixture per m³ 7.20 kg/m³
Edit the inputs below to recalculate.Inputs
Result
| Total binder | 360kg/m³ |
| Dose on binder | 2.00% |
| Per 100 kg binder | 2.00kg |
| Per batch | 2.40kg |
| Water after reduction | 148.8kg/m³ |
| Original w/b | 0.486 |
| w/b after reduction | 0.413 |
The dose applies to total binder (cement + fly ash + slag + silica fume), not cement alone - counting only cement under-doses the mix once SCMs are used, which shows up as poor water reduction and fast slump loss. Batch quantities are usually a few hundred grams to a couple of kilograms, so weigh them on a 0.1 kg scale. Use the measured water reduction for that dose, never the datasheet maximum; the real dose must come from trial mixes.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Binder = cement + fly ash + slag + silica fume | not cement alone |
| Admixture = binder × dose% | per m³ |
| Water = base water × (1 − reduction) | measured reduction |
| w/b = water / binder |
How to work it out
- Total binder = cement + fly ash + slag. Admixture dosage is on total binder, not cement alone.
- Admixture per cubic metre = total binder × dosage % ÷ 100.
- Per batch = per cubic metre × batch volume. Admixture is a liquid, weighed or metered by volume at a density of about 1.05-1.20.
- Water after reduction = baseline water × (1 − reduction rate). Use a measured reduction rate; the 25% in the datasheet may not hold with your materials.
- Check the new water-binder ratio = reduced water ÷ total binder, against the design value.
Where it goes wrong
- Basing dosage on cement only — with 60 kg of fly ash and 60 kg of slag, binder is 420 kg against 300 kg of cement, so the real dose is 29% short.
- Taking the datasheet's maximum reduction — 25% is the brochure figure; with a given cement 15-18% is realistic, and assuming 25% leaves the mix short of water and low on slump.
- Not metering the admixture — dosing it with the cement or pouring in a diluted guess gives ±20% errors, which show up as retardation, bleeding or variable strength.
- Storing liquid admixture without agitation — solids settle and the tank stratifies, so the bottom dose is double the top.
Material and cost
Polycarboxylate superplasticiser runs 2,200-3,000 per tonne, which is 12-20 per m³ at 1.5-2.5% dosage. Trimming 0.3% saves little but costs slump retention and pumpability, and the pumping and labour premium far exceeds the material saved.
On site
- Always trial the admixture-cement combination; changing cement brand means re-trialling. This is the most common source of incidents.
- Raise retarder dosage in hot weather and lower it in cold; one fixed dose all year will fail somewhere.
- Agitate liquid admixture tanks daily to stop stratification.
Basis
- GB 8076-2008 Concrete admixtures (water reduction measurement and uniformity)
- GB 50119-2013 Code for application technology of concrete admixtures (dosage and compatibility testing)
- JGJ 55-2011 Specification for mix proportion design of ordinary concrete
FAQ
Why dose on total binder rather than cement?
Is a higher water reduction always better?
Two kilograms per batch is hard to weigh accurately - what to do?
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Admixture Dose Calculator. 2026-10-25. https://jianzhujisuan.com/en/concrete-additive