Wetting of Construction Joints 9

[Kramer]

I have designed a wet well for a pump station (water only) with 18" thick walls on a 24" thick base slab. I have shown a 3 1/2" wide by 1 1/2" deep keyway in the top of the base slab at the center of the wall with a bentonite water stop in the keyway. Both ACI 318 and 350, Sections 6.4.2 call for construction joints to be wetted prior to the pour and all standing water removed. The walls are over 20'-0" tall. I am concerned that if the top of the base slab is wetted, there is not a practical way for the water to be removed from the keyway. I am also concerned the water may activate the swelling properties of the waterstop prematurely. Any thoughts on this?

 

[BridgeSmith]

"...so you don't rely on the concept of "shear friction"?"

We don't rely on the shear capacity of concrete at joints with epoxy bonding compound. If we require substantial shear capacity at a joint, we provide either a keyed joint or a rough construction joint with reinforcing crossing the joint that is developed on both sides. For a shear-resisting construction joint, we check the shear friction capacity per AASHTO. We would not use the bonding compound for such a joint - it would be wetted as I described earlier.

 

[hokie66]

Like reinforcement and jointing of slabs on ground, there are lots of ideas about how to make joints in walls. I doubt there will ever be a definitive answer, or at least one that everyone can agree on.

 

[Ingenuity]

I have followed OG and his repeated quest that 'bone-dry substrate is best' for some time. As a guy who get lots of cement paste under my fingernails, along with direct hands-on experience with pre-bagged cementitious concrete and field-batched concrete, alike (mainly for concrete repairs and deck overlays), and somewhat uniquely, with bond testing of said products and procedures, my n=1 experience is: substrate to be ALWAYS SSD.

ACI's Concrete International magazine in 2018 had a recent article on this and related factors:

Effect of Common Surface Pretreatments on Shear Strength of Bonded Concrete Overlays by Andrew S. Pultorak and Frederick R. Rutz Article available here: ==> Link​

They looked at various substrate pretreatments:

With some informative results, that I highlighted:

OG's position is (was?) a common one, based upon research at the time by Felt from 1956:

Felt investigated substrate moisture content and the use of bonding agents. He concluded that a “dry” substrate was preferable to a “damp” one and that a cement or cement-sand slurry bonding agent produced a superior bond.

However, the Bureau of Reclamation research disputed Felt's findings:

However, some studies contradict Felt’s 1956 conclusions regarding moisture content of the substrate. Wall and Shrive found that some moisture in the substrate was beneficial to bond strength. In a report for the Bureau of Reclamation, Bissonnette et al. found that optimum moisture content in the
substrate surface lies somewhere between 55 and 90% of saturation, though they state that “…fundamental issues remain unsolved with regard to moisture conditioning of the concrete substrate…”.

Anyway, the article is a good read. Form you own opinion. I shall continue to do what I have been doing for decades - substrate is SSD.

And finally, as a contractor I hate epoxy-based bonding agents, so therefore as an engineer, I similarly hate them! Office-based engineers need to listen to their experienced field contractors when it comes to bonding agents, and don't always listen to the manufacturer's rep on the 'magic' they sell.

 

[BridgeSmith]

"And finally, as a contractor I hate epoxy-based bonding agents, so therefore as an engineer, I similarly hate them!"

As one of those "office engineers" (I have some field experience, just not much with concrete pours), I have to ask, why do you hate them? Is it because they are difficult to use or because they don't perform well?

 

[oldestguy]

No argument from OG. Now that's the way to prove or disprove your arguments. Thanks. We need more of these types of statements backing up opinions. I'm adding my star.

 

[epoxybot]

Using an epoxy bonding agent inside of form work isn't something you want to do unless a dual function of the bonding agent is desired, e.g., as a waterstop. Greater requirements for reinforcement in seismic zones, post Loma Preita, have pretty much rendered this application defunct anyway.

Back in the day, we would spray the epoxy from the end of a 6 ft. spray bar. There are not many contractors that have the equipment or capability to do so. It is definitely a specialty contractor job.

Epoxies are still great for bonding a topping slab, subject to a lot of traffic or slab-to-slab repairs. You just have to pick the right formula. It should have an potlife for a gallon mass of at least an hour and an open-time (time to place concrete) of 2 to 4 hours. Epoxy formulas based on Polysulfides, Amidoamines or Amidoamine/Aliphatic Amine blends work best. Something like MasterEmaco ADH 326 (formerly: Concresive Liquid LPL) or Chemco Systems Liquid-LWL, is what to look for.

 

[Ingenuity]

As one of those "office engineers" (I have some field experience, just not much with concrete pours), I have to ask, why do you hate them? Is it because they are difficult to use or because they don't perform well?

Sorry, HotRod10, upon re-reading my reference to 'office-based engineers' may have come across as derogatory - if it did, I apologize.

To answer your question, it is as hokie66 repeatedly states in these type of discussions over the years - in way-too-many occasions, they become de-bonders.

On concrete placement day (somewhat regardless of how small or large the placement is) the most experienced concrete contractor has a very dynamic scope of work to undertake - manpower, equipment, materials delivery, weather, etc. etc., so add-in an epoxy bonding agent and it is another item that needs to be accommodated flawlessly. Based upon the post-installed field bond testing I have done, those projects that used epoxy-based bonding agents have a higher proportion of failure at the bond-line on the NEW 'wet' concrete side, indicative of epoxy set issues.

No argument from OG. Now that's the way to prove or disprove your arguments. Thanks. We need more of these types of statements backing up opinions. I'm adding my star.

Thank you.

Epoxies are still great for bonding a topping slab, subject to a lot of traffic or slab-to-slab repairs. You just have to pick the right formula. It should have an potlife for a gallon mass of at least an hour and an open-time (time to place concrete) of 2 to 4 hours. Epoxy formulas based on Polysulfides, Amidoamines or Amidoamine/Aliphatic Amine blends work best. Something like MasterEmaco ADH 326 (formerly: Concresive Liquid LPL) or Chemco Systems Liquid-LWL, is what to look for.

Absolutely, and all the manufacturer names you have dropped are great products - especially and notably, IMO, Chemco (small team, great resins and technology).

Unfortunately, those tasked with writing specifications on such uses are often engineers/specifiers who do not have direct/relevant experience with such products for the given application and the relevant field variables.

 

[BridgeSmith]

Thanks for the explanation, Ingenuity. I definitely see the point you guys are making. Hopefully, our field guys are holding the contractors to what we specify in our notes so that we don't have those issues. Given the nature and location of the work where we employ the epoxy bonding material, I'm not confident we'd do any better attempting to reach an SSD condition at the interface, and it might be more difficult to identify whether the condition actually exists.