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These 10 free CSTT questions are organized by exam domain, so you can see how each part of the Concrete Strength Testing Technician blueprint is tested. Reveal the answer and explanation under each question.
The top ends of freshly molded cylinders are ready for capping: settlement has stopped, and free water and laitance have been removed. Which material is specified for this procedure?
Correct answer: A - Neat portland cement paste
During sulfur capping, the hood stops exhausting air outdoors. The pot remains at 138°C, and an odor noticed earlier is no longer detectable. Which response is appropriate?
Correct answer: D - Stop capping until effective exhaust to outdoors has been restored.
During daily quality control, a cylinder tests at 62 MPa. Twelve randomly selected, fully debonded pieces from across its top cap have an average thickness of 2.8 mm and a maximum thickness of 5.4 mm. The cap material had adequate strength, and other capping checks passed. Which thickness assessment is correct?
Correct answer: D - Noncompliant, because the local thickness exceeds the 5 mm maximum.
A project specifies 60 MPa for final acceptance, but the cylinders now being tested are for a separate 20 MPa formwork-release requirement. Compliant nominal 50 Shore A neoprene pads are available, with acceptable condition and recorded use counts. Which pad-selection decision is supported?
Correct answer: D - Use nominal 50 pads without qualification; the 20 MPa release requirement controls this test.
Nominal 60 Shore A neoprene pads have 72 recorded uses and are due to test cylinders for a specified strength of 30 MPa. Inspection finds superficial perimeter scuffing, no reduction in perimeter thickness, and satisfactory dimensions and specimen ends. What does this inspection support?
Correct answer: A - Continue using the pads, monitoring condition and tracking the applicable 100-reuse limit.
A corner fragment breaks away during compression testing with unbonded caps, but the indicated load continues to rise. The specimen remains aligned and the retainers show no displacement. What should the technician do at this point?
Correct answer: C - Continue the prescribed loading until ultimate capacity is established.
Two compression-machine ranges have current force verifications: 150-1500 kN and 25-250 kN. A cylinder is expected to fail between 80 and 120 kN. Which setup is appropriate?
Correct answer: B - Use the lower range, which covers the anticipated failure load.
An undamaged core from a specified 35 MPa, normal-density concrete mixture has a prepared length of 160.0 mm and perpendicular midheight diameters of 100.0 and 100.5 mm. Its maximum compression load is 300 kN. For length-to-diameter correction, use 0.96 at L/D = 1.50 and 0.98 at L/D = 1.75, interpolating between them. What compressive strength should be reported?
Correct answer: C - 36.8 MPa
With a beam seated at 4% of its estimated ultimate load, a 0.25 mm contact gap extends 35 mm beneath one loading block. The proposed leather shim is uniformly 6 mm thick, measures 40 mm along the span, and extends across the full beam width. How does this treatment compare with ASTM C78?
Correct answer: B - It is permitted; the gap and shim dimensions meet the requirements.
A laboratory investigates an unexpected drop in flexural strength. Companion compression results remain consistent with earlier batches, and machine verification is satisfactory. Which change would most plausibly bias the beam results downward?
Correct answer: C - Leaving moist-cured beams uncovered until their surfaces visibly dry.
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