9.1 Field Sample to Report Workflow

From One Composite Sample to a Set of Results

ACI Field Testing Grade I is not seven isolated procedures memorized for a performance exam. The credential describes a technician who can take one representative sample and convert it into a set of accurate, traceable results before the concrete changes. Everything in this chapter flows from a single fact: fresh concrete is perishable. Slump loss, air loss, bleeding, temperature rise, and stiffening all begin the moment the sample leaves the truck, so the workflow is built around fixed time windows rather than personal preference.

The controlling document is ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed Concrete. A composite sample is obtained by taking two or more portions at regularly spaced intervals from the middle of the batch, never from the first or last 10 percent of the load. For strength-test sampling the composite must be at least 1 ft³ (28 L). The portions are combined and remixed with a shovel to make the material uniform before any test is run.

The C172 Time Windows Drive Everything

Two time limits from C172 govern the whole sequence and are heavily tested:

• Within 5 minutes of obtaining the final portion of the composite sample, begin the tests for slump (C143), temperature (C1064 may be done first), and air content (C231 or C173).
• Within 15 minutes of fabricating the composite sample, begin molding strength specimens (C31).
• The elapsed time between obtaining the first and last portions of the composite should not exceed 15 minutes.

These windows force the technician to stage equipment, calibrate beforehand, and work without wasted motion. A correct slump value measured 20 minutes late is still an invalid result because the concrete is no longer what it was at sampling.

Why This Order Is the Default

Temperature (C1064) is taken first or in parallel because the thermometer can sit in the concrete while other tools are readied, and temperature drives later interpretation. Slump (C143) comes early because it is the most slump-loss-sensitive reading and uses a fresh, unconsolidated portion. Air (C231 pressure for normalweight, C173 volumetric for lightweight or porous aggregate) and density (C138) often share the same measure or base because both fill and consolidate a known-volume container.

Cylinders (C31) come last but still must start within the 15-minute window, so the technician must not let fresh-property testing consume the entire window.

Throughout, sample identity is preserved: the technician records the truck number, the delivery ticket number, batch time, sample time, placement location, and the specific test methods. A reading with no traceability cannot support acceptance, troubleshooting, or later strength interpretation. The Grade I technician's job is to produce measured facts, not acceptance decisions, unless the project specifically assigns that authority.

Stage the Job Before the Truck Arrives

Because the clock starts at sampling, the integrated workflow really begins before any concrete arrives. A technician who is still calibrating an air meter or hunting for a tamping rod when the truck backs in will burn the 5-minute window and produce invalid data. Pre-arrival staging covers four areas:

• Equipment: a verified-calibration air meter (C231) or volumetric meter (C173), slump cone and 5/8 in. rod, scoop, strike-off bar, C1064 thermometer, a clean damp sample pan or wheelbarrow, cylinder molds, scale, and the C138 measure of known mass and volume.
• Forms: the field report and a place to record the C94 delivery ticket data, plus permanent markers for specimen labels.
• Sample location and access: a clean, level, shaded spot near the point of discharge.
• Communication: the name and number of the testing-agency supervisor, QC contact, and engineer's representative.

A Worked Example of the Window

Suppose the truck discharges at 9:00. The technician draws the first portion at 9:02 and the last at 9:05 (within the 15-minute first-to-last limit). The 5-minute clock starts at 9:05, so slump, temperature, and air must all begin by 9:10. The 15-minute cylinder clock also runs from the composite, so molding must begin by 9:20. If slump and air take until 9:12 and the technician then searches for molds, the cylinders may slip past 9:20 and the strength specimens become questionable. Staging eliminates that scramble.

The same sample-control discipline that C172 demands — remix before each draw, keep the pan clean and damp, shade it from sun and wind — is what lets all five methods run cleanly off one representative sample.

Field-workflow quick recap

• Run temperature, slump, and air within the C172 time windows (slump and air begun within 5 minutes of the final composite portion).
• Mold strength cylinders within 15 minutes of fabricating the composite sample.
• Record results on the delivery ticket/field report with the time, location, and sample identification for traceability.