Slump Loss Calculator

Calculator

Units

Choose one unit and stay consistent.

Initial slump (mm)

Slump at batching or first test.

Measured slump now (mm)

Slump at arrival or before placement.

Elapsed time since initial (min)

Minutes between the two slump readings.

Forecast additional time (min)

Extra delay you want to plan for.

Expected base rate (optional, mm/min)

Use when you have a known loss rate from trials.

Ambient temperature (°C)

Higher temperatures often increase slump loss.

Temperature coefficient (per °C)

Multiplier: 1 + k·(T−20). Typical estimate 0.01–0.03.

Admixture factor

Retarder < 1.00, accelerator > 1.00, none = 1.00.

Minimum slump target (optional, mm)

Checks forecast slump against a workability minimum.

Maximum loss target (optional, mm)

Checks measured loss against a quality limit.

Site notes (optional)

Stored into export for traceability.

Reset CSV PDF

Example data table

Scenario	Initial slump (mm)	Measured slump (mm)	Elapsed (min)	Loss (mm)	Loss rate (mm/min)
Morning pour, short haul	200	180	35	20	0.571
Hot day, traffic delay	210	160	60	50	0.833
Pumped placement, steady flow	190	170	45	20	0.444

Values are illustrative for planning and training.

Formula used

Measured slump loss

Loss = Initial − Measured
Percent loss = (Loss / Initial) × 100
Measured rate = Loss / Elapsed time

Forecast model (linear)

Temp multiplier = 1 + k × (T − 20)
Forecast rate = Base rate × Temp × Admixture
Forecast slump = Initial − Forecast rate × Total time

Use a known base rate when available; otherwise the measured rate is used.

How to use this calculator

Test slump at batching or the first on-site check.
Test again at arrival, discharge, or right before placement.
Enter both slump readings and the minutes between them.
Add a future delay to plan the remaining workable time.
If you have trial data, enter an expected base loss rate.
Adjust temperature and admixture factor to match conditions.
Set targets to flag low forecast slump or high measured loss.
Export CSV or PDF for daily quality records and reporting.

Professional article

1) Why slump loss matters

Slump loss describes the drop in measured workability between batching and placement. On site, it affects pumping pressure, consolidation, finishing time, and surface quality. Tracking it per load helps prevent rejected deliveries, cold joints, and unplanned water additions that can weaken strength or increase shrinkage. On congested sites, small losses compound as trucks queue and pumps pause.

2) Typical field observations

For many structural mixes, crews may observe a gradual decline over 30–90 minutes, accelerated by heat and evaporation. A fast early drop can signal high absorption aggregates, low paste volume, or overdrying. Stable slump with acceptable air content usually indicates balanced moisture control, correct mixing energy, and consistent dosing.

3) Time and temperature influence

Hydration and evaporation increase with temperature, so the same haul time can behave very differently across seasons. This calculator uses a temperature multiplier referenced to 20°C to scale a base loss rate. Use site thermometers, record wind and sun exposure, and keep sampling times consistent to make comparisons meaningful.

4) Transport and mixing practices

Continuous agitation, correct drum speed, and avoiding long static waits reduce segregation and maintain uniformity. Record dispatch time, arrival time, and any queuing at gates. If the truck is stopped, re-mix before sampling and note the action so future trends remain interpretable.

5) Admixture and water management

Water reducers and retarders can preserve workability without pushing the water–cement ratio upward. Treat the admixture factor as a practical adjustment: values below 1.00 slow loss, while values above 1.00 represent accelerated setting. Always verify dosage against approved mix submittals and local temperature limits.

6) Placement, pumping, and finishing

Pumped concrete may show additional apparent loss from line friction, shear, and filtration at bends. Plan priming, hose length, and crew readiness to minimize interruptions. If a forecast indicates slump may fall below a minimum target, adjust sequencing, shorten the line, or request a revised mix before discharge.

7) Quality documentation and targets

Set a minimum slump target that matches placement method and reinforcement density, and a maximum loss target that protects consistency across loads. Exporting CSV or PDF creates a simple audit trail for QA/QC, including weather notes and any corrective actions taken. Review exports weekly to spot variation and refine dispatch spacing for upcoming critical pours.

8) Using forecasts responsibly

The forecast assumes a linear trend, which works well for short planning horizons. Some mixes lose slump nonlinearly after admixture exhaustion, extended waiting, or additional water demand from dry aggregates. Use the forecast to stay conservative, then update the model with fresh field readings to tighten predictions and reduce rework.

FAQs

Q1. What is slump loss in practical terms?
It is the decrease in measured slump from batching to placement. It reflects reduced workability caused by hydration, evaporation, absorption, and handling conditions.

Q2. How do I choose a base rate?
Use a trial-based loss rate for the same mix and haul pattern. If you do not have one, leave it blank and the calculator will use the measured rate from your readings.

Q3. Why include temperature and a coefficient?
Temperature changes hydration speed and evaporation. The coefficient lets you scale a base rate relative to 20°C; use a modest value such as 0.01–0.03 and calibrate with field data.

Q4. What should I enter for admixture factor?
Use 1.00 for no adjustment. Enter below 1.00 for workability retention effects and above 1.00 for faster setting behavior. Keep it conservative unless you have dosage and performance records.

Q5. Can I use inches instead of millimeters?
Yes. Switch units to inches and enter all slump and target values in inches. The calculator converts internally to keep calculations consistent.

Q6. Is the forecast always accurate?
No. It assumes a linear trend and cannot capture sudden changes after long waiting or admixture exhaustion. Re-test slump when delays occur and update inputs for better decisions.

Q7. What should I document with exports?
Record mix ID, batch and arrival times, weather, queue delays, and any remixing or adjustments. Attach CSV or PDF to daily QA/QC logs for traceability.