CTQP Grouting Technician — Questions and Answers
Question 1: What is the PRIMARY purpose of injecting cementitious grout into post-tensioning ducts after stressing is complete?
- To increase the compressive strength of the surrounding concrete sections
- To protect prestressing tendons from corrosion and develop bond between the tendon and concrete (Correct answer)
- To add structural dead load that improves the structure's stability under wind
- To seal formwork voids that remain after concrete placement
Correct answer: To protect prestressing tendons from corrosion and develop bond between the tendon and concrete
PT duct grouting serves two critical functions: it encases the prestressing steel in an alkaline cementitious environment that prevents corrosion, and for bonded systems it transfers stress from the tendon into the surrounding concrete along the tendon's full length. Failure to fully grout ducts has caused catastrophic PT bridge failures.
Question 2: Why is a low water-cementitious material (w/cm) ratio critical in post-tensioning grout design?
- Lower w/cm makes the grout more resistant to high injection pressures
- Lower w/cm reduces bleed water, which can form voids at the top of ducts that expose tendons to moisture (Correct answer)
- Lower w/cm increases the flow rate of grout through long ducts
- Lower w/cm reduces the curing temperature of the grout in summer conditions
Correct answer: Lower w/cm reduces bleed water, which can form voids at the top of ducts that expose tendons to moisture
Excess water in grout bleeds to the top as the grout sets. When that bleed water evaporates, it leaves voids at the crown of the duct — the worst possible location because moisture and chlorides can then accumulate against the bare prestressing steel, causing corrosion. FDOT and ASBI limit w/cm to control bleed water.
Question 3: The Marsh cone (flow cone) test is performed on PT grout to evaluate:
- Compressive strength of the grout at 7 and 28 days
- Bleed water percentage at 3 hours after mixing
- Consistency and flowability of the freshly mixed grout (Correct answer)
- Air content and unit weight of the grout
Correct answer: Consistency and flowability of the freshly mixed grout
The Marsh cone test measures how quickly a fixed volume of grout flows through a standard orifice, expressed in seconds. The result indicates whether grout has the right consistency to flow through PT ducts without segregation, blockage, or excessive pressure buildup. FDOT and ASBI specify acceptable flow time ranges.
Question 4: Grouting of a post-tensioning duct should begin from:
- The high point of the duct to allow gravity to assist grout flow downward
- The lowest point of the duct, injecting grout upward to displace air toward vent ports (Correct answer)
- Both ends simultaneously to cut grouting time in half
- The midpoint of the duct to equalize pressure in both directions
Correct answer: The lowest point of the duct, injecting grout upward to displace air toward vent ports
Grout is injected at the low end of the duct so it rises and displaces air upward toward vent ports at high points and the far anchorage. Starting from the high end would trap air beneath the grout with no path for escape, leaving voids around the tendons.
Question 5: Grout injection at the inlet is considered complete when:
- The injection pressure reaches the maximum allowable pump pressure
- Grout flowing from the far-end vent exhibits the same consistency as the grout being injected at the inlet (Correct answer)
- The grout temperature at the vent reaches 70°F
- Exactly one duct volume of grout has been pumped regardless of vent output
Correct answer: Grout flowing from the far-end vent exhibits the same consistency as the grout being injected at the inlet
When grout exiting the far-end vent matches the freshly mixed grout at the inlet — free of air bubbles, water pockets, and lumps — it confirms the duct is uniformly filled. Vents are then capped under pressure to retain the grout, and the inlet is sealed.
Question 6: Which certification program is recognized as a prerequisite for the FDOT CTQP Grouting Technician Level I qualification?
- ACI Concrete Field Testing Technician Grade I
- NICET Level II in Construction Materials Testing
- American Segmental Bridge Institute (ASBI) Grouting Certification (Correct answer)
- PTI Level 1 Unbonded PT Field Inspector
Correct answer: American Segmental Bridge Institute (ASBI) Grouting Certification
FDOT requires completion of the American Segmental Bridge Institute (ASBI) Grouting Certification Training Course as a prerequisite before a candidate can sit for the CTQP Grouting Technician Level I qualification. ASBI developed the industry standard grouting training curriculum used by most U.S. DOTs.
CTQP Grouting Technician
What is the PRIMARY purpose of injecting cementitious grout into post-tensioning ducts after stressing is complete?