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Calcimator

Slip Form Calculator

Calculate slip form rate of rise, concrete volume per hour, and project duration.

About this calculator

Form Exposure Time depends only on Rate of Rise and Slip Form Height -- how fast the form climbs past a fixed-height opening -- and never on Concrete Initial Set time itself, so pushing Concrete Initial Set up or down never changes Exposure Time. What it DOES change is whether that exposure time is enough: Set Time Adequate flips from 1 (safe) to 0 (rate too fast) whenever Concrete Initial Set exceeds Exposure Time, and Set Time Safety Ratio (Exposure Time as a percentage of Set Time) swings from 400% at a fast-setting 1-hour mix down to just 33% at a slow-setting 12-hour mix, at this calculator's other defaults -- crossing below 100% is exactly the point where the concrete would still be too fluid when it exits the bottom of the form.

Rate of Rise moves the same output from the other direction: pushing it up to 36 in/hr at the default 4-hour set time cuts Exposure Time to about 1.3 hours, well under the 4 hours needed, flipping Set Time Adequate to 0. Max Safe Rate is the calculator's own recommended ceiling for a given Slip Form Height and Concrete Initial Set -- staying at or below it is what keeps Set Time Safety Ratio at or above 100%.

Inputs

ft
in
ft
ft

Results

Form exposure time (hrs)

4

Set time adequate (1=yes)1
Max safe rate (in/hr)12
Volume per hour (cy)2.96
Total volume (cy)296.3
Total slip time (hrs)100
Total slip time (days)4.2
Estimated jack count23
Set Time Safety Ratio100%
How to Use This Calculator
  1. Enter the Rate of Rise in inches/hour and Slip Form Height in feet for the assembly.
  2. Enter Wall Thickness, Structure Perimeter, Total Structure Height, and Concrete Initial Set time.
  3. Review Form Exposure Time and Max Safe Rate to confirm the rise rate allows proper concrete set.
  4. Check Volume Per Hour and Total Volume in cubic yards to schedule batching plant production.
  5. Use Total Slip Time in hours and days to plan crew rotation for continuous 24-hour operations.

How the result changes with Rate of rise (in/hr)

Rate of rise (in/hr)Form exposure time (hrs)
68
95.3
182.7
301.6

What each input means

Rate of rise (in/hr)
Vertical speed of the slip form. Typical range: 6-18 inches per hour.
Slip form height (ft)
Height of the slip form assembly. Typically 4-5 feet.
Wall thickness (in)
Thickness of the concrete wall being formed.
Structure perimeter (ft)
Total perimeter of the structure (e.g., silo circumference).
Total structure height (ft)
Total height of the structure to be slip-formed.
Concrete initial set (hrs)
Time for concrete to reach initial set at the ambient temperature.

What each result means

Form exposure time (hrs)
Time concrete is inside the form before exiting the bottom.
Set time adequate (1=yes)
1 if concrete sets before leaving the form, 0 if rate is too fast.
Max safe rate (in/hr)
Maximum rate of rise that still allows concrete to set inside the form.
Volume per hour (cy)
Cubic yards of concrete placed per hour.
Total volume (cy)
Total concrete volume for the entire structure.
Total slip time (hrs)
Total duration of the continuous slip forming operation.
Total slip time (days)
Total duration in days (continuous 24-hour operation).
Estimated jack count
Approximate number of hydraulic jacks needed (one per ~3.5 ft perimeter).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Rate of rise (in/hr) = 12, Slip form height (ft) = 4, Wall thickness (in) = 12, Structure perimeter (ft) = 80 = 6 input(s) provided
  2. Calculate Form exposure time
    Form exposure time = formHeight / rateOfRiseFtHr
    4 = 4
  3. Calculate Set time adequate
    1 = 1
  4. Calculate Max safe rate
    Max safe rate = maxRateFtHr * 12
    12 = 12

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Does Concrete Initial Set time change how long the concrete is actually inside the form?

No. Form Exposure Time is set purely by Rate of Rise and Slip Form Height -- how fast the form climbs relative to its fixed height -- so Concrete Initial Set never changes that number. What it changes is whether that exposure time is enough for the concrete to set before it exits the bottom.

What does Set Time Safety Ratio actually mean?

It's Form Exposure Time expressed as a percentage of Concrete Initial Set -- 100% means the concrete sets exactly as it exits the form, with no margin. At this calculator's defaults it swings from about 400% with a fast 1-hour mix down to 33% with a slow 12-hour mix, and anything below 100% means Set Time Adequate flips to unsafe.

If I push Rate of Rise too fast, does the calculator warn me?

Yes -- Set Time Adequate flips from 1 to 0 the moment Concrete Initial Set exceeds Form Exposure Time. At the default 4-hour set time, raising Rate of Rise to 36 in/hr cuts Exposure Time to about 1.3 hours, well under what's needed, and the flag flips to unsafe immediately.

What does Max Safe Rate tell me that Set Time Adequate doesn't?

Max Safe Rate converts the same set-time constraint into a rate of rise you can dial in directly, in inches per hour, for your specific Slip Form Height and Concrete Initial Set -- rather than requiring you to guess a Rate of Rise and check whether Set Time Adequate stays at 1 afterward.

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