Using Non Shrink Precision Grout for Precast Concrete

[Falck]

I am going to use Quickcrete's Cement based Non Shrink Precision Grout for a Pre-Cast Communications Vault and Lid I am making. The vault is 4x6x4. 3" thick Side Walls. I am adding 25#'s of 3/8" Pea Rock to each 60#pound bag of Grout per the instructions to keep its High Strength Properties. The reason I want to use this is because 9500#PSI 65.5 MPa 3 day Strength and its flow-ability. I will be adding 1/2 fiberglass rebar to the precast for strength as well. I talked to Quickcrete and they said it could be done. Let me know your thoughts.

 

[BridgeSmith]

Have you contacted a precast concrete supplier to see what they have or could cast for you? Sounds like a fairly standard item for most precasters. No reason to reinvent the wheel if you don't have to. Most likely, it would be quite a bit less expensive than casting it yourself, especially using grout.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Falck]

We have typically use Hubble/Quazite polymer vaults and previous to that I used a company call Tunnel Mill. The lead time on the Quazite vaults have gone from a 3-6 week lead time to a 36 week lead time and doubled in price in the last 18 months and Tunnel Mill went out of business. I was supposed to have a order of vaults here by now but they have been delayed another 12 weeks. I have a customer who has to have this vault and lid set 10/24. That is why I am doing this and so far I am below my cost even with building the Precast forms. Do you know of any issues a might have using this product? Cause it is the most reasonably priced pre-maid Grout/Concrete mix out there with a 12500-14000PSI rating and I like the fast cure and workabilty for my application.

 

[BridgeSmith]

Hmm...ok. It seems casting them yourself is the preferred option in your situation.

With that out of the way, on to my next question. Why do you need high strength concrete/grout for this?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Falck]

To cut down the weight for transportation and handling. Instead of the sidewall having to be 4 1/2 thick I can go down to 2 1/2 thick.

 

[BridgeSmith]

For a box that size, surely your shear isn't high enough to require such a high concrete strength, is it?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Falck]

I guess I don't know I am just using a product that has the same strength as the vaults I usually get. Although they use a Polymer based concrete.

 

[BridgeSmith]

All the precast concrete we see around here is 5000 to 6000 psi.

The difference between handling a 4000lb box and a 7000lb box would not seem to be that significant, but I guess if it matters, it matters.

Btw, the capacity of the walls and the slabs for bending is barely changes for different concrete strengths. I hope you're not reducing the wall thickness based on the use of higher strength concrete; it doesn't really work that way. Reducing the wall thickness requires increasing the reinforcing to maintain the bending strength, but that only goes so far; you also need enough concrete over the reinforcing to protect it from corrosion. The inch or so of cover you get with a 2 1/2" thick wall won't be enough to keep the steel from rusting for very long.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Falck]

I need to stay under 3000# because shipping and handling and I could go up to 4" thick and still be under 3000#. So with that being said and understood. What would you use for a concrete mix? I would prefer to use Pre-made mix for quality control reasons.

 

[BridgeSmith]

I need to stay under 3000# because shipping and handling and I could go up to 4" thick and still be under 3000#.

What's the 'wet' density of the grout you're planning on using? At 4" thick and 145pcf (typical for concrete), I calculate about 4800 lbs for just sides and bottom slab.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Falck]

There is no bottom and the top is a separate piece.

 

[BridgeSmith]

In that case, have looked into precast culvert sections?

Btw, by my math, you're still over 3800 lbs, with a 4" wall.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[GC_Hopi]

Why not change manufacturers to find something that is available and can be express shipped? It does not sound like you are a manufacturer business so you are taking on a lot of risk by making a prototype and installing it.

 

[Falck]

my calculations where as follows: 4x6x.33x2 + 4x4x.33 = 26.37. So essentially 1 yard. Than the grout covers.45 Cubic Feet per bag and I am adding 25#'s of 3/8 minus Pea rock per bag and I figured the 25 pounds pea rock would cover.25 cubic feet. So I took 27 divided by .7 and came up with 38.57 bags of mix giving me a total of 2925#'s. I see I forgot to add the water weight.I figure I will need 4 to 4.5 quarts of water per bag so I guess that will add 10#'s per bag so that brings the total to 3315#'s. Is that correct?

 

[Falck]

I tried another MFG and they can not meet the deadline. So that puts me here. I have the inside portion of the form completed and once i determine the product I am using I can get the depth of concrete and do the outside. Is the Non Shrink High performance a bad idea?

 

[GC_Hopi]

I wish you the best of luck. It sounds like a tough challenge.

 

[BridgeSmith]

my calculations where as follows: 4x6x.33x2 + 4x4x.33 = 26.37.

Ok, hold up a second...your "box" only has 3 sides? That would change everything. That makes two of the sides unsupported cantilevers (according to your calculations, the 2 6' long sides), and that's a recipe for failure if it's going in the ground and will be subjected to soil loads.

Have you looked into plastic boxes?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[DoubleStud]

You need to do a test mix and do a 1 day break (for stripping and handling) and 28 days. How could you be so sure it will have that high of strength? You need to test it.

 

[Falck]

it's 4 sided I just forgot to put the 2 in he equation. In addition I will be adding a Smart Rock Sensor(

https://www.giatecscientific.com/products/concrete-sensors/smartrock-maturity-meter/)

to the concrete that will give me the PSI rating.

 

[MotorCity]

Falck - without stepping back and putting in a little due diligence, I would not recommend using grout instead of concrete. I'm not saying it can't be done, I'm just saying you should make sure it can be done. The essence of basic concrete design is based on various combinations of specific components (cement, water, fine and coarse aggregate). As I am sure you are aware, the components and relative proportions are different for grout than that of concrete. The design of concrete is more than just getting "the PSI rating". To support my statements above, ACI has very specific requirements and procedures for accepting mix designs. Some of those requirements include historical data of the proposed mix, number of samples and breaks, and the strength required when you don't have historical data. There is a reason for such data...it provides a minimum degree of reliability and a precedence that the particular combination and proportion of ingredients will result in the desired performance. I would be surprised if you are able to find historical data for the success of using grout instead of concrete. It may be worth contacting ACI to get their opinion.