9.2 Test Order and Parallel Timing

Order the Tests Around Concrete That Is Still Representative

The individual ASTM methods each have their own procedure, but real field work places them into a deliberate order driven by the ASTM C172 time windows. After the composite sample is obtained and remixed, the technician has only 5 minutes to begin slump, temperature, and air, and 15 minutes to begin molding cylinders. Those windows mean the most time-sensitive measurements come first and the technician cannot let slow setup or chatter eat the clock.

The standard, defensible order is:

1. Temperature — ASTM C1064. Insert the thermometer with at least 3 in. (75 mm) of concrete around the sensor for at least 2 minutes (until the reading stabilizes); read within 5 minutes of sampling.
2. Slump — ASTM C143. Fill the cone in three equal-volume layers, 25 rods per layer, strike off, lift in 5 ± 2 s, measure to the displaced original center.
3. Air content — ASTM C231 (pressure) or C173 (volumetric). Use C173 for lightweight or highly porous aggregate because pressure assumptions fail there.
4. Density and yield — ASTM C138. A known-volume measure is filled, consolidated, struck off, and weighed.
5. Strength specimens — ASTM C31. Mold cylinders within the 15-minute window.

Where Parallel Work Helps and Where It Hurts

A skilled technician overlaps compatible steps without confusing the data. Temperature can run in parallel with slump setup because the thermometer simply sits in the concrete. The air meter and density measure are often consolidated together — C231's base bowl and C138's measure both need rodding or vibration of a known volume — so the technician can plan one consolidation effort that serves both readings when the same container and procedure apply.

What parallel work must never do is blur sample identity or mix up raw numbers. The dangers are:

If the technician cannot say with certainty which reading came from which sample, the time saved is worthless because the results lose traceability.

Protect the Sample While You Work

Between steps, the remixed sample sits in a clean, damp, non-absorbent pan or wheelbarrow, and the technician shovels it again before drawing each new portion so segregation and bleeding do not bias the next test. A sample left uncovered in sun and wind loses moisture and warms, which can shift slump and air enough to fail an otherwise good batch. The technician should shade the sample and keep tools clean and pre-wetted.

The order is not a rigid script to memorize blindly; it is a logic. Time-critical, change-sensitive tests run first (slump, air). Tests that need controlled consolidation of a known volume (air by pressure, density) are grouped. Cylinders come last but inside the 15-minute window, so the technician budgets time and never lets fresh-property testing run long. Knowing why each test sits where it does lets the technician adapt — for example, doing air by volumetric C173 instead of pressure C231 when the aggregate is lightweight.

Budgeting the Two Clocks Together

The two C172 windows run concurrently from the composite sample, and the technician must budget both at once. The 5-minute window only requires each fresh test to begin in time — once slump is started inside the window, finishing it a minute later is fine. But the 15-minute cylinder window is easy to lose if fresh testing runs long, because molding three layers of multiple cylinders with proper rodding takes real time. A disciplined plan looks like this:

Adapt the Order, Keep the Logic

The sequence is a logic, not a rigid script. If lightweight aggregate is used, swap C173 volumetric for C231 pressure because the pressure method's assumption of incompressible aggregate fails on porous particles. If only fresh tests are required (no cylinders that day), the 15-minute window simply does not apply, but the 5-minute window still does. If a helper is available, temperature and slump can overlap so the air and density work starts sooner.

The technician should be able to defend the order with reasoning — time-sensitivity first, shared consolidation grouped, specimens within the window — rather than reciting a memorized list. That reasoning is exactly what lets a technician recover gracefully when a job throws an exception at them.

The sequence also protects data quality in a subtle way: each test that is time-critical and consumes a separate portion (slump, then air) is taken from freshly reshoveled material, so neither test borrows a stiffened or segregated portion from a previous one. Running slump last, after the sample has sat and lost moisture, would bias it low and could fail a perfectly good batch. Ordering by sensitivity therefore is not just about beating the clock — it keeps every reading representative of the concrete as it was discharged.