[Alan]

I've poured my footing, and a small "pier block" on top of it. The footing is 2'x2'x12" and the pier block on top of it is 10" x 10" x 10".


If this point is supporting a point on a 4x10 beam that is holding up the center bearing point of the exterior 2nd floor wall, what amount of time should I let the concrete cure before I put that load onto it?


Thanks in advance


Edit : I'm wondering if when I put my post in if I should make it a little longer to account for compression when the weight drops onto it? If so, how much longer?

 

[Underdog]

I've poured my footing, and a small "pier block" on top of it. The footing is 2'x2'x12" and the pier block on top of it is 10" x 10" x 10".


If this point is supporting a point on a 4x10 beam that is holding up the center bearing point of the exterior 2nd floor wall, what amount of time should I let the concrete cure before I put that load onto it?


Thanks in advance


Edit : I'm wondering if when I put my post in if I should make it a little longer to account for compression when the weight drops onto it? If so, how much longer?

What type of concrete did you use? Also, what has the weather been like since pouring the concrete?

 

[jagans]

Hi Alan,

How much space is there between the footer and the beam? The pier block should be filled with concrete if you want it to carry any sort of load. I would use a min 1/4 inch metal plate between the Girder and the filled block.

Concrete= Keep it wet, 28 days if you can afford to wait that long.

The weak link in your chain will be the compressive strength of the wood girder. You have to solve for the point load over the bearing area.

 

[concretemasonry]

No need to wait more than a few days. Since the footing is so very thick in comparison to the width, there is very little stress on it that would cause cracking and the 70% you will get then under reasonable conditions. In many areas, reinforcement may not be required if it is that thick.

The 28 days is really a falicy and only relates to one of the standard curing times for testing cylinders under standard conditions in a laboratory. There are other periods (3 day, 7 day, 14 day and 60 day) that are frequently used to measure strength gain. The 28 day period is the period used to identify most mix designs and provide a guide to determine if the proper mix performance is being met. Using a pre-proportioned bagged mix there may not be too much of an over-shot of the advertised strength.

In reality, a concrete mix from a R/M supplier very rarely is as low as the 28 day strength. It is based on economics and the cost of cement is much less than the delivery cost or the cost of a problem. Here it is common to see 4000 psi concrete on standard mixes and some suppliers will refuse to sell concrete for an exposed slab, sidewalk or driveway unless it is 4000psi or 4500 psi.

Dick

 

[Underdog]

To answer your other question: No, you shouldn't plan for any deflection of the concrete. However, you should expect some shrinkage of the concrete, but this can be minimized by keeping the concrete wet during the first few days of curing. Keep in mind that concrete shrinkage rates diminish quickly with time.

Without knowing the specifics of your concrete, I would recommend at least 7 days. This is based on ACI general construction standards. If it has been cold where you live, I would wait even longer.

ACI charges for their manuals, but here is a link that describes their (and others') standards for concrete curing times.

http://www.fhwa.dot.gov/pavement/pccp/pubs/02099/chapt5.cfm

 

[Canarywood1]

I've poured my footing, and a small "pier block" on top of it. The footing is 2'x2'x12" and the pier block on top of it is 10" x 10" x 10".


If this point is supporting a point on a 4x10 beam that is holding up the center bearing point of the exterior 2nd floor wall, what amount of time should I let the concrete cure before I put that load onto it?


Thanks in advance


Edit : I'm wondering if when I put my post in if I should make it a little longer to account for compression when the weight drops onto it? If so, how much longer?

When we supplied concrete for high rise decks,we poured a floor a week,so 7 days cure is plenty for what your doing.

 

[Alan]

@ loftezy :

I used the sakrete high strength concrete mix. The weather has been mid 30's in the early morning and night, and 40's to 50's in the daytime.

I wasn't so much worried about deflection of the concrete as I was with compression of the post that I'm planning to install.

Thanks for the link

@ jagans : I poured my own block on top of the footing, and embedded a bracket into it. I haven't measured, but there's somewhere between 8 and 10" between the "pier block" and the 4x10 beam.

~

I poured the footing last weekend, so it has been sitting for well over a week, but I put the block on top of it saturday morning. I am hoping to get the post set before this weekend so that I can work on cleanup saturday and move on to something else. Lots of tools laying under there, lol.

At this point it's been more than 72 hours, and it's late so I'm not planning on doing it tonight. Tomorrow will be 4 and a half days.

 

[jagans]

I guess what I was trying to get across is why put in a post at all? If you mean wood. I think I would have thrown in a few no 4 rebar in the footing and use sonotube to come up to the girder with concrete, and set a bracket and an anchor bolt in the crete. Vapor barrier between crete and wood.

 

[concretemasonry]

The footing concrete system you used will be many times stronger that the wood above it and gain strength as it ages/cures while the wood only goes downhill when exposed to the real world. - I other words , the wood cannot transfer enough load to crack the concrete structurally.

Rebar is only for minimum code standards, if they exist or are in effect, since it is used to increase the tensile strength concrete system.

Dick

 

[Alan]

Well, apparently my patience was too thin.


I tried to pull the jacks out last night, and the 10x10 block I poured crumbled into dust. :furious: 4.5 days was not long enough. :jester:


Oh well. I guess I get to try again this weekend.


Option #2 would be to cut off the vertical rebar that I have and try some kind of bracket that bolts to the concrete footing instead. Only problem is that I wouldn't be able to put all of the dirt back, but I guess there's nothing wrong with taking it out from under the house...

If I have the wood sitting directly on the concrete footing, what distance above the dirt does the wood post have to be?

 

[Underdog]

It just crumbled to dust after four days? Are you sure you didn't forget the water :wink:

Even though I joke, it does seem odd that it crumbled after four days of curing. Based on the data sheet for the Sakrete 5000 High Strength Mix, it should be about 3,000 PSI after four days.

http://www.sakrete.com/uploads/downloads/Sakrete 5000 Plus CM Tech Data 5-121.pdf

Have you calculated the load that you are expecting this pier block to hold? Are you building this to conform to standard construction practices or is this designed by an engineer?

 

[Mort]

If it crumbled to dust, there's something wrong. It's not that you stripped the forms too early. ACI standards are to strip concrete test cylinders within 24 hours, and the only time I ever had a sample crumble was CDF (which, to be honest, is what is supposed to happen. I'm not sure why my boss had me take a CDF test cylinder in the first place).

Without knowing how it was mixed, its tough to say why it did that.

 

[Alan]

It just crumbled to dust after four days? Are you sure you didn't forget the water :wink:

Even though I joke, it does seem odd that it crumbled after four days of curing. Based on the data sheet for the Sakrete 5000 High Strength Mix, it should be about 3,000 PSI after four days.

http://www.sakrete.com/uploads/downloads/Sakrete 5000 Plus CM Tech Data 5-121.pdf

Have you calculated the load that you are expecting this pier block to hold? Are you building this to conform to standard construction practices or is this designed by an engineer?

I didn't calculate any loads. I don't really know how to go about it anyway. I figured on it being much larger and thicker than the old footing and probably overbuilt.

 

[Underdog]

I didn't calculate any loads. I don't really know how to go about it anyway. I figured on it being much larger and thicker than the old footing and probably overbuilt.

I guess I was just asking if you are expecting this pier to hold up half of your house

In my mind, there are only two reasons why the pier would behave the way it did:

1. Poor mix design/execution: Not enough water, poor mixing, contamination (dirt in the mix), not enough cure time, etc.
2. Loads exceeded design strength. I find this unlikely in residential construction unless you are doing something crazy, like having this pier support half your house. Also, the pier wouldn't just "crumble" in this scenario--it would be a catastrophic sudden (and loud!) failure.

To remove the possibility of poor concrete work, I would really like to recommend using a precast concrete pier block. However, those typically have a compressive strength of 2,000 PSI, and I can't recommend it without knowing how much weight you expect this pier to hold.

 

[Duckweather]

If night temps fall below freezing before the first set the concrete may have frozen. If you are going to do it again use hot water, mix it as stiff as you can pour, and wrap it with some kind of insulation for the night.

 

[Alan]

I guess I was just asking if you are expecting this pier to hold up half of your house

In my mind, there are only two reasons why the pier would behave the way it did:

1. Poor mix design/execution: Not enough water, poor mixing, contamination (dirt in the mix), not enough cure time, etc.
2. Loads exceeded design strength. I find this unlikely in residential construction unless you are doing something crazy, like having this pier support half your house. Also, the pier wouldn't just "crumble" in this scenario--it would be a catastrophic sudden (and loud!) failure.

To remove the possibility of poor concrete work, I would really like to recommend using a precast concrete pier block. However, those typically have a compressive strength of 2,000 PSI, and I can't recommend it without knowing how much weight you expect this pier to hold.

This Footing/Pier is supporting a point on a 4x10 beam (4x10 beam runs full length of the building under center load bearing wall) that is carrying the central bearing point for the upstairs exterior wall. I'm sure it's a sufficient amount of weight, but there's another footing within 5 feet and the other end is resting on the stem wall.


Here's a thought I had today : Is it possible that the footing sucked the water right out of the pier block? Should I have done something differently on this cold joint to prevent that from happening?

 

[kwikfishron]

Four days and turned to dust???

It's almost unbelievable, especially where you're located.

Water is a good thing (in the right amount).

 

[jagans]

Just use a sonotube Alan, and extend it right up to the girder. Jack the girder a little high, then let it set down on the pier. The only reason I said rebar is to key the pier to the footing. You can just hang an anchor bolt in the concrete from a drilled 2 x 4 till it sets up for your bracket. Tapping the tube all around will get rid of honeycombs

4 x 10 = 40 x 3400= 136,000lbs I think you are covered on the weight, assuming 3400PSI Concrete.

I agree with the others, something was definitely wrong with your mix, or it froze before set.

 

[Alan]

Just use a sonotube Alan, and extend it right up to the girder. Jack the girder a little high, then let it set down on the pier. The only reason I said rebar is to key the pier to the footing. You can just hang an anchor bolt in the concrete from a drilled 2 x 4 till it sets up for your bracket. Tapping the tube all around will get rid of honeycombs

4 x 10 = 40 x 3400= 136,000lbs I think you are covered on the weight, assuming 3400PSI Concrete.

I agree with the others, something was definitely wrong with your mix, or it froze before set.

(that's the reason I wanted the rebar in there too)

No chance that the concrete footing would have sucked the water out of the mix?

I'm just worried that if I have it so high up, I will be having major difficulties not only with having to drag even more concrete under the house, but trying to get it from my transporting device into the form.


I think I might give it one more shot the way I did it before. I'll let it sit for a week, then pull the form off to make sure the concrete is fairly solid. Then i'll give it another week just to be safe before putting a post on it.

I have a halogen light under there, so maybe i'll leave that on overnight on the first night just to ensure that freezing doesn't occur although I dont think that was the problem. I'd say we didn't get below 30* at the coldest point in the middle of the night. May not even have been quite that cold.

 

[jomama45]

I would skip the concrete pier myself and would just lay 2 block with a partial block on top. Choose w/e width you'd like, pour the cores solid around your rebar dowels, set the post bracket (now a "beam bracket") in the grout, and shim whatever gap you have left at the top with steel plate shims.........