Grouting training Q&A

The time limits, referenced in ASBI/PTI Specification for Multistrand and Grouted Post- tensioning M50.3-19 Table 11.1, are after installation (i.e., placement of strand into the duct).

Vapor Phase Corrosion Inhibitor powders are the most commonly used corrosion protection measure for strands that won’t be grouted for some time after installation. Ideally, strands are grouted immediately or within a few days of installation and tensioning.

The air test should be performed after the strands are stressed and prior to grouting. This is required by the PTI M55.1 Section 5.5.4. Testing prior to concrete placement is not typically required. However, in some special cases may be helpful and/or required.

Not really, flushing will just add more water to the system and if there was water in the ducts to start with, flushing will just add more as it’s likely there is no way to eliminate the water from the ducts. The prevention to this situation is to use drains at all low points and keep them open until you are ready to grout. The thixotropic grouts will do a decent (but not perfect) job of driving the accumulated water out of the ducts – the best solution would be to continue pumping grout (I know, that’s a lot of extra grout) until the density readings improve – and they will as the grout pushed more water out of the duct.

There is a table in the back of the student manual that clarifies which tests are Laboratory Tests, Field Trial Tests and/or Production Tests per the PTI M-55 Specifications. Your project specifications may differ.

A resource on vertical tendons (and excellent resource for many other items as well) is the FHWA Post-tensioning Tendon Installation and Grouting Manual, May 2013, FHWA-NHI-13- 026. Sections 4.3.7 and 4.5.10 and 4.5-11 address vertical tendons. It can be downloaded here:

One of the first considerations in a plan for vertical tendons is to ensure the particular grout to be used is rated for the vertical head/pressure that will be encountered. The pressure should be considered for the equipment as well. In addition, some strategies for grouting vertical tendons may include one or more of the following, especially for tall tendons: breaking the tendon grouting up into stages/lifts, grouting the top portion of the tendon as a separate operation, adding a reservoir/standpipe at the top of the tendon.

Yes, the discharge points should always be above the duct level. By keeping the vents and discharge points above the duct level, it helps minimize potential for trapped air pockets. Guidance on the vent locations is provided in ASBI/PTI Specification for Multistrand and Grouted Post-tensioning M50.3-19 Section 9.9.

Theoretically it shouldn’t take any longer to install PL3 than PL2. PL3 just adds the ability to monitor the in-service tendon. In practice, PL3 does require a few additional components such as half-shells used to isolate tendon ducts from the supporting reinforcing bars so it would take a little more time to do a PL3 installation.

The location and timing of using the backup grout plant should be included in the plan as one of the troubleshooting items. Typically, this is not demonstrated or mocked up, but practicing this would not be a bad idea, especially if access is a challenge.

ASBI has a form found on the website for applicants to provide their work history. Your suggestion for maintaining records is excellent! ASBI does not require someone to “sign off” on the experience record however this is required for the companion PTI certifications.

If grouting must be done “months” after stressing there are a few steps that should be taken, assuming this is allowed by project specifications. The tendon should be capped and sealed as much as possible. Corrosion inhibitor should be used as the presentation mentioned. Use of a vacuum is something I have never considered. Chances are you would never be able to seal the tendon well enough to keep a vacuum in the tendon. Very rarely can we get the tendons sealed that well. Plus, with corrugated duct, we have seen that water gets caught in the duct and is very difficult to get all of the water out. The best solution is to not allow moisture inside.

After the full speed mixing, you transfer it to the second (agitator tank). In that tank it just needs to keep moving so it doesn’t gel up from the antibleed admixture. So, lowest speed on paddle in the second tank is good.

Strand should be protected from corrosion at all costs prior to installation. It should never be stored unprotected and should never be left exposed to the elements. Any rust identified on strand prior to use should be closely examined. If any sign of section loss or pitting is identified, then the strand should be immediately removed from the project. If there is any question as to the severity of the rust, then rejection of the strand should be strongly considered. This is something that should go beyond just documentation if there is a question as to material integrity. All strand should be tracked as far as coil numbers and heat numbers when installed, and this is something that is typically part of a PT stressing worksheet. The contractor is ultimately responsible for the condition of the material used, but this is an issue that the owner will want to have input and know exactly the condition of the material and if it is cleaned, should be carefully inspected.

Yes, correct follow the ASTM standards for all of the tests.

Yes, during post-grout inspection any voids that are found, or vents that are low, should be filled. The same grout should be used.

The ice should be used to cool the mix mater and not added directly to the grout mix. Often a smaller intermediate container between the main water source and thegroutplantiswheretheicewouldbeadded. Thewateristhentransferredwith a submersible pump from the intermediate tank to the calibrated batch tank on the grout plant.

A tendon blockage isn’t normally something you can fix quickly or while grouting is underway that day. If there is a blockage, some degree of investigation will be needed to locate the blockage and the resulting voids. This can be fairly complicated depending on the tendon geometry. Ideally, use of a “rabbit” pulled thru the duct before inserting the strands will locate any duct restrictions and the air test just before grouting will make sure you have some flow – but maybe not enough flow for grout. Locating the blockage/voids may require a GPR or similar NDE devices. I suspect blockages are more common when you have multiple parallel ducts and there is some “communication” between the duct being grouted and an adjacent duct – this should also be caught by the air test.

Ducts with small cross section (flat ducts and PT Bars) can see high pressures occur with typical grout plants. One strategy to address this is to use a grout header to limit the pressure in those cases. Alternatively, a smaller grout plant or different type of grout plant may be an option (especially air operated plants as compared to hydraulic or electric which can be somewhat easier to throttle down to low flows/pressures).

I do not know if there is a minimum length. Generally, details like this will determined by the design engineer or the construction engineer developing the PT system. Individual systems are developed by the manufacturer and are used for each project based on the use and characteristics of the project.

In the PTI M-50 Specification you will find 11.5 Acceptance Criteria to determine acceptable strand condition. This references Fig. 11.1 that provides photos of strand before and after cleaning and which conditions are acceptable and which are not. Pictures 1, 2 & 3 are acceptable – all the others would be rejected.

The Acid Soluble Chloride test can be used on either the dry powder or from powder taken from the hardened grout. ASTM C1152

Yes, temporary corrosion protection oils will affect bond, more information on specific oils is found under the following: “Temporary Corrosion Protection Coatings for Strand” and can be found on the ASBI website here:

Although the diameter may vary based on the size of the pump and other variables, 1” diameter grout hoses are typical for most operations. The use of a grout header and recirculation line may be helpful in controlling excessive grout pressures, especially in small tendons such as flat duct tendons.

For a minor crack, generally yes, continue grouting. If a leak was noted, post-grout inspection looking for any voids is recommended. Attempt to plug the leak during grouting and revisit the location of the leak during post-grout inspection.

If an air leak is noticed before grouting, determine the source of the leak and repair it. Once the repair is complete retest and ensure it is resolved. This may entail a vent repair, tightening a grout cap, or even a concrete repair. In the cases of two ducts that are communicating with a leak between them, it may be prudent to grout those ducts together.

If the duct was separated and blocked with concrete, it would probably require a substantial concrete removal and repair unless it can be reached from either end. In some cases, may be able to install strands in adjacent tendons or add tendons to make up for the issue.

Softgroutisagroutthathasnothardenedovertimeintheduct. Thiscanbecaused by the bagged grout being too old or past the expiration date or stored in weather or condition that are too hot.

The M-55 Specification, ‘4.4.4 Grout Strength’ spells out the requirements but they are a minimum required strength of 3,000 psi at 7 days and 5,000 psi at 28 days. Your project specifications may have different requirements. Pre-packaged grouts typically have no issues meeting these requirements with proper proportioning and mixing.

Testing the water temperature should be at the water supply as close to introduction to the grout plant as feasible (directly with a thermometer, or with a probe at the end of wire (thermocouple) if it is within a tank that cannot be reached by hand). For example, if the water is coming from a tank on a truck into an intermediate container (such as a 200-gal plastic tank or trough) near the grout plant before dosing, the intermediate container would be the best place. If using ice, it may also be beneficial to get several temperature readings including the water source before cooling, to help in planning of future operations.

Table 3.1 in the PTI Spec tells you which types of grout use which tests. For grouts used in bridges, you do the bleed pressure test. The test is performed a minimum of 1 per project and additional for each truck load. The sample is taken at the mixer — see PTI Section 4.7.3 of spec.

The air test is recommended after stressing, cutting the tails, and installing the grout caps are completed. In other words, just prior to grouting. The purpose of air testing is to check for leaks, cross-overs between adjacent ducts, and other issues to allow repairs to be performed and/or grouting plans to be revised prior to grouting. This is the test referred to in the PTI Specification for Grouting of Post-tensioned Structures M55.1-19 Section 5.5.4.

For the air test, a valve should be installed at the end of the air hose. This valve is closed after the required pressure is reached (typically 30psi).

The pressure gauge should be in line between that valve and the tendon inlet. A manifold with a valve relieve the air, the shut off valve to the air hose, gauge, and fitting connection may all be preassembled and hooked up in line.

It makes sure you can correct the batch going forward plus allows documentation of tendons that may need to be further inspected after grouting.

For vertical grouting, the vents are placed ahead of time (during duct placement). Approximately 3-foot between outlet of the first stage and inlet of the second stage is a practical distance to allow for shut off. The grout would be setup and hardened between stages.

If you are not replacing a port or inlet before grouting you wait for the grout to harden. We would not recommend tapping a tendon that has fresh grout in it as it may create a bigger issue by bleeding down the liquid grout. This then would require further drilling and investigation. With the vacuum injection we can effectively fill voids most voids with hardened grout in the tendon.

The approach for repairs will depend on the situation, and often can be quite different. A specific tailored plan for each location and situation is recommended, however some various considerations with respect to new ports are listed below:

  • The key is to have an idea of where the tendon should be and work carefully. It is recommended the work be performed by someone experienced in similar types of repairs. It is good practice to first layout the anticipated duct location by measurements from plan locations, use of Ground Penetrating Radar (GPR) and/or other methods. The approximate expected depth should also be determined before drilling.
  • Closely monitor the depth of the drill holes until the duct is reached then carefully measure the distance to the duct and set the drill depth to just penetrate the duct to avoid contacting the strand. Marking the drill bit or wrapping a piece of tape around the drill bit at the estimated depth to help in monitoring the depth of the hole may also be used. Drilling at the high point is often the best place to start since the strands will be in the bottom of the duct at high points and less chance of strand damage. It may be possible to drill two holes near the high point, one serving as the inlet, one as the outlet.
  • It may be prudent to consider different approaches for drilling into concrete and the duct. Typically, a larger, stronger drill and bit are used to drill the concrete but those might be too robust around the tendon steel. Suggest stopping about 1/2” away from the anticipated duct location then using a smaller drill to find the actual duct. Slow is the key and using a drill with a variable clutch that will stop if the drilling gets too hard may be helpful. As mentioned above, the strand location within the duct should be considered and avoid drilling where the strands may be located. In some cases, it might be necessary, or worth considering, to excavate a larger area of concrete to expose the duct without drilling right down on top of the duct.
  • One approach assuming the original outlet is still functional is as follows. Connect air at about 30 psi air pressure on the void area. Then probe with a 1⁄4” roto-hammer bit and air will escape as soon as the duct is pierced. Often this must be done multiple times to determine the extent of the void and to pierce the duct in a place that has no strand against the wall of the duct. Then use a larger bit with the depth to the duct marked on it. Stopping just short of this, chip the remaining concrete out and open the wall of the duct by hand. Then insert a new grout port and secure with epoxy.
  • There is generally a balance that must be maintained in providing adequate access for repair and inspection, but also avoiding doing too much damage by drilling excess holes or chipping more concrete than necessary.
  • Vacuum grouting is a procedure that can be employed as well, but still requires at least one useable grout port.

Typically, the temp is taken from the mixer prior to pumping. You’re right that it can gain heat during flow through the duct. Because excessive heat can cause you pumping problems, you may want to take the outlet temp on the first tendon just to inform you on the next tendons (it will keep your pumping pressure down so it’s worth it even if the spec refers to the inlet).

Field and trial batch test data should go either to the owner or the inspection firms — most of the time they’ll witness this testing.

A team with expired or missing certifications could certainly be rejected by the owner/inspection agency. It could also be possible that an owner/inspection agency could reject the grouting team for either poor performance or for failure to follow the project specifications. I’ve never heard of it happening yet – but it could, just as for any construction operation.

Possibly, if they have some experience with the various products. The references in the back of the M55 Spec (30 & 31) are a good source for most of the oils that are likely to be “approved” by an owner/engineer. Note that these have to be applied before inserting the strands so prior approval is required.

A very good document which includes information on thixotropic grout is Development of High-Performance Grouts for Bonded Post-tensioned Structures (1999). The document can be downloaded here:

In addition, the following article includes some information on promising developments in the use of an in-line density meter that can be used on jobsites to monitor and record the quality parameters of the grout in real time. The article can be downloaded here: AToolForContinousOnSiteMonitoring.

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