# Slump Test Calculator

More slump is not better — 40 mm separates a pumpable mix from a bleeding one.

- Page: https://jianzhujisuan.com/en/slump-test
- Category: Concrete (https://jianzhujisuan.com/en/c/concrete)
- Chinese version: https://jianzhujisuan.com/zh/slump-test.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Target slump 120 mm, Maximum aggregate size 20 mm, Air entrainment Non air-entrained, Sand fineness modulus fm 2.6): **Water demand 200 kg/m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Target slump | number | 120 | mm |  |
| Maximum aggregate size | select | 20 mm | — |  |
| Air entrainment | select | Non air-entrained | — |  |
| Sand fineness modulus fm | number | 2.6 | — |  |

## Formula

- **Base water**: ACI 211.1 Table 6.3.3 by maximum size: 207 at 10 mm, 190 at 20 mm, 166 at 40 mm
- **Slump correction**: w = wbase × [1 + 0.03(slump − 75)/25]
- **Sand correction**: about ±2% per 0.1 of fineness modulus (empirical)
- **Air entrainment**: air-entrained mixes use ×0.89 (ACI Table 6.3.3 air column)
- **Slump class**: EN 206 / GB/T 14902: S1 10-40, S2 50-90, S3 100-150, S4 160-210, S5 ≥220 mm

## Worked example

120 mm target slump, 20 mm aggregate, non air-entrained, fm 2.6: base water 190 kg/m³, a 5% slump correction, 200 kg/m³ actual, EN 206 class S3, suitable for pumping, and about 400 kg/m³ of binder at a 0.50 water-binder ratio.

## Questions

### What slump is acceptable?

It depends on use and code. EN 206 has five classes: S1 at 10 to 40 mm for foundations and mass pours, S2 at 50 to 90 mm for ordinary beams and slabs, S3 at 100 to 150 mm for congested reinforcement or pumping, S4 at 160 to 210 mm for high-rise pumping and S5 above 220 mm for self-compacting. GB/T 14902 uses the same S1-S5 classes, and pumped work in practice sits at S3-S4, that is 120 to 180 mm. What matters most is consistency: scatter beyond 30 mm points to batching or moisture control problems.

### Why is adding water on site not allowed?

Because it raises the water-binder ratio directly and strength falls with it — about 1.5 to 2 MPa per 0.01 of w/b. Twenty kilograms into an 8 m³ truck takes w/b from 0.50 to 0.51 and loses roughly 2 MPa, turning C30 into something that may fail as C28. Adding water also improves slump without improving cohesion, so the mix bleeds, segregates and blocks the pump more readily. The right move is a superplasticiser slurry at the same mix proportions, or reject the load.

### How does spread differ from slump?

Slump measures vertical deformation, spread measures lateral flow, which is what matters in highly fluid mixes. Ordinary concrete at 100 mm slump spreads to about 350 mm; beyond 220 mm slump the cone test itself stops discriminating because the mix collapses as a mass, so spread takes over — typically 550 to 650 mm for SF1 and 660 to 750 mm for SF2. Self-compacting concrete also needs T500 (2 to 5 seconds) and a V-funnel time.

### What slump does pumping need?

100 to 200 mm is stable, with 120 to 180 mm the sweet spot. Below 100 mm line resistance grows and blocks appear at bends and vertical runs; above 200 mm the aggregate settles, paste rises, mortar runs ahead at bends and the aggregate arches — which blocks more often, not less. So “wetter pumps better” is backwards. What actually matters is cohesion and water retention, which fly ash, slag or a viscosity modifier improve far better than water ever will.

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