concrete and temperature question

[FJ and G]

Today I built a form to make a concrete arch bridge (mass production style). I'll post photos later this week of the method I used, which allows the user to vary the length and height of the form in a matter of seconds and doesn't require any screwing.

 

Anyway, tomorrow, I wanted to pour the concrete in the form (it's too cold and dark right now). However, the temperatures have been in the low 30s and up in 40s in the afternoon. I happened to be building a concrete table and after 2 days, the struck the mold and the table top broke apart, aparently still wet and not cured. I don't want this to happen to the archway tomorrow.

 

Is there a minimum temperature for concrete? I know that cold weather takes longer. Maybe I should have just waited a few days longer before stryking the mold?

 

thanks 

[Anonymous]

You have a electric blanket you can raise temp. over the whole.

Here some info I found intersting.

http://www.precast.org/publications/mc/2005_septoct/techspeak.htm

Toad

[cabbage]

(The Boring Science bit)...

Portland cement sets by absorbing CO2 from the air. This is a chemical reaction and as in all things -the rate of reaction is proportional to the change in temperature. As a rough guide for every 10 deg Kelvin the temperature raises the reaction rate doubles, conversely for each 10 deg Kelvin fall the reaction rate halves.

If you can see if you can obtain low temperature high alumina portland cement mix -which is what we use for northern scandinavian climes. If you cannot "warm" your concrete mix then I would suggest you leave at least FOUR times as long as you would normally. The reaction will produce "some" heating that will cure your concrete mix that way.

Alternative methods of fast cure include putting black plastic sheeting over the cast and using solar heat absorbtion to warm the mass and a few "tea light" candles with the flames on the ends of the casting bars to keep it warm through out the night -thus providing both heat and CO2(!)

regards

ralph

[FJ and G]

Ralph,

<>I don't mind waiting 4 x longer; but I do mind if the ice forming in the concrete expands and weakens the mixture. I just checked on the piece that had crumbled from the first table and they are still moist and crumbly (I'm keeping track of the failed pieces and won't strike the mold on the second batch until the failed pieces have adequately set up) a good way to test when to strike!@

 

Toad,

 

The link was VERy helpful and seems to confirm my fears about cold. It got into theupper 20s last night and there's thick ice everywhere I was using the hose to mix the concrete.

 

Lesson learned. I may have to wait a while before going forward with more concrete projects and the weather forcast is notoriously bad in my area. 

<>

[rpc7271]

Obvisously the warmer the better. You can start by mixing your concrete with hot water not cold. I have kept concrete pours very warm overnight by covering them with a blue fiberglass tarp- tented. With the center higher than the rest and then placing a light with a 100 watt light bulb in it. This generates a lot of heat when comnfined. Be sure to coat your forms with some sort of mold release before you pour them. In construction whey use a special 'oil'. You probably won't want to use that. I have heard of people using WD-40 and Pam food spray. If it was me I would go with Pam as it should wash off if there is a residue after you remove the forms. Post pictures when you are finished please.

[gbbari]

Professor Ralph would you be so kind as to re-state that reaction rate formula using Fahrenheit as the units of temperature?  I looked but just cannot find a thermometer around the house that uses a Kelvin scale...

 Al

[cabbage]

Sorry...

Comming from a SI background -I forget that people still use Imperial.

For each 18 degrees Fahrenheit raise in temperature the reaction rate doubles and for each 18 degrees Fahrenheit fall in temperaure the reaction rate halves.

As I have customers who live north of the permafrost line it makes the maths a lot easier to work everything out in Kelvin!!!

Zero Kelvin is -273 deg Centigrade or -414 deg Fahrenheit.

regards

ralph

PS I have just checked with the St Paul Office and they work everything out in Kelvin too.

[FJ and G]

Here’s the base and pedestal of the bar table (for near pool table) that I was working on when the weather was warm. It’s got rebar in it and will be overlayed with tiles. The base and pedestal alone weigh about 200 pounds.



Due to the cardboard form that held the concrete, the pillar takes on the look of a giant toilet paper cardboard.



Here’s procedure for pouring the top of the table:



Notice that I wish to use the larger circumference of the top of the bucket for the table top so fill with crusher fines, then place a 45 lb weight plate (smooth side up, not side that is in picture), so the surface will be level and then plastic over the weight plate so concrete won’t adhere to weight plate. Then pour concrete (you can’t see it but chicken wire is emeshed in the cement)





when I removed this “table top” it cracked last week b/c it had not properly set. On Saturday, I poured a fresh batch and am waiting longer to see what transpires. I have some broken pieces from the first batch I’m using to judge the set time.



Arch form made with wood and vinyl siding. This arch form would be placed on its side over a thin sheet of Styrofoam and walls would be wood. (I want to create a series of arch bridges for trains to traverse. I want an old, weathered look to them, with some crumbling. Incidentally, I read that in real bridge design, designers coat the rebar with zinc or epoxy or galvanize it sometimes to avoid rust expansion).



Experiment putting slate and thin rocks over concrete. Plan would be to make the concrete arch, coat with thinset, then overlay these thin stones. Sounds arduous but sort of fun. Incidentally, this piece of experimental concrete came from one of the concrete bags I'd purchased, apparently, the bag had gotten wet and part of the concrete solidified. I didn't feel like returning the bag, however, as it would have cost more in time and money returning it than what I paid ($3).



OR, I may do this procedure. Experiment putting aggregates on Styrofoam and pouring concrete over that. Considering using this for the arch bridge wall but worried water may get between aggregates, freeze and expand.



observer


(one other problem I have in my garden is that we didn’t get pears b/c of the killer snowstorm in mid-April. Now, due to the heat wave this year, the tree is full of pears that should be ripe in another month. Perhaps I need to prune?).

So many problems to contend with!

[Anonymous]

Due to the cardboard form that held the concrete, the pillar takes on the look of a giant toilet paper cardboard.



observer

As for the pillar they make a coarse stone on a handle you can buy at Home Depot and would think other stores that sands the coon creet down. Then fill in the holes if you choose to with a thin set.

Seeing how the observer is doing a great job she needs a scooby snack.

Toady

[FJ and G]

Thanks, Toad,

 

The piller and small holes will be covered with thinset then tile; I just thought it looked kinda neat. I've been collecting towell and toilet paper rolls incidentally, to model some building pillers. Maybe this will give some ideas to some of you.

The hound was bored to tears by all this so I took her rabbit hunting. That perked her up.

[Anonymous]

Santa just might bring her a stuffed rabbit for Christmas

[FJ and G]

The table is starting to take shape. Tiles still need to go on the sides of the top and bottom and of course it all needs grouting. Each tile was buttered individually. The bottom and top tiles were hand cut with wet saw. The top was bolted in place in a recessed hole and thin set was used to cover the bolt and attach the top. I struck the mold for the top after a week and it was still green but held together (slow cure b/c of cold weather outside).

Here’s my mold for doing an arch bridge. Note the stones embedded at the bottom of the mold and in the last photo, they are placed in the wet cement for the other side. To prevent possible rust expansion from Rebar, I used corner bead instead, which cannot rust according to my experiments.

This particular mold uses wood forms and the arch is covered with house siding (screws taped over so they don’t stick). The house siding should allow easy release. I may strike the mold on Thanksgiving (so I can create another mold; I need about 15 of these), but won’t move the mold until the weekend as it likely isn’t cured.

The arch is designed to have a primitive and aged look of stone and concrete, not a neat and tidy new look like you will see on other model arches. The arch will be mortared to footings.

[Anonymous]

Man that table looks heavy! I am going to have to watch you closer! Ideas, Ideas, Ideas

Toad

[FJ and G]

Thanks, Toad,

I'll provide photos of the construction as it progresses. The arch, incidentally, took 1 bag of cement so it was $3. It would have cured faster down in Texas :-)  where weather is warmer.

 

This week I'm going to begin digging an open pit mine which will feature tracks spiriling down. It has never been done in a big way  by any model railroader (just 1 or 2 levels is the most I've ever seen). I've also got a massive tunnel I'm emplacing with large diamter sewer pipe on a different part of the layout.

 

Doing stuff like this is more fun that running the trains.  

[FJ and G]

Last night I struck the mold, although it was still somewhat green (lucky it didn’t break!). In 30 minutes I mixed another batch and this weekend I’ll strike another mold. Using 1 bag of 80 lb concrete plus all the rubble inside and rocks out and reinforcing metal, each arch is probably 150 lb

[S&G Rute of the Silver River]

How do you move them, renting the local football team? Good work though.

[FJ and G]

thanks! I do a lot of deadlifts in the gym. It is a painful hobby (weightlifting) compared with the leisures of garden railroading. Also at times rely on a dolly or homemade ramp.

[FJ and G]

The completed table.



Arch bridges completed. Next will be to design some curved arch bridges. Bit more of a challenge.

 

below, one arch is darker b/c it is still green (wet)!

 

[Anonymous]

Hope you got a way to stake them down, hate for BB to be crushed by one that fell over on her! Would be bad, it would crush something.

But good news its your hired for down here in Spring time.

Hoping to get another shop built ASAP but my way of building is different than these slack jokers I been speaking with. Even Morgan buildings don't pass. I am looking for quality and it seems not many around to do a job and yes I am helping in the building to (have construction back ground).

[FJ and G]

bridges will be mortared down to concrete pilings and to each other. Right now, pretty hard to push them over (depending on terrain they are sitting on); but good point.

shoddy construction yes!

I used screws to build basement but builders used nails upstairs and nail pops are everywhere. Also, the 2 air condition units on the ground tilted and started creeping downhill; also burst pipes and so on and not tamping front concrete porch, which is good for BB b/c small animals burrow there and BB the beagle gets happy when she smells them

[FJ and G]

Here’s my first try at a curved arch. Unfortunately, the weather is still cold (in the 40s F so people are complaining about the severe winter chill) and the casting is still “green” meaning it’ll take a few more days of curing before it can be moved.

Step 1

We start out with the same casting box, which in this case is some thrown away pieces of drawer wood and my homemade arch with vinyl siding for the curved portion so it can easily be demolded later on. The box is held together with those handy dandy clamps which you can barely see. In cold weather, you need a week or more before striking the mold.

Notice the earth in the box built up on each side in a curve. This is no ordinary earth. It is crusher fines (also called slurry or quarter minus). They are chipped stone found in quarries and garden centers. Commonly used as sewer pipe cushioning stone when burying pipes. You can buy a ton for around $15. It’s also used for track ballast. I chose the crusher fines b/c it interlocks and holds its shape. For added adhesion, I wetted the crusher fines.



Step 2

Next, I arranged rocks on the bottom and on the crusher fines.



Step 3

Then I poured quikrete over the stones about 1.5 inches and layed rebar inside. For rebar, I don’t use steel or stuff that will rust but something that is galvanized or stainless steel. This is important b/c concrete is permeable and water will eventually rust the steel and cause it to expand up to 3 times its volume (according to an engineering book I read) and crack your project. This happens to bridges so some engineers coat the rebar with epoxy.

Step 4

Then I lay another 1.5 inches of quikrete over the rebar and add rocks. I want an old looking bridge with a bit of concrete covering the rocks. If you want all of the rocks to show up nice and shiny, then about 2 or 3 hours after pouring the mold, lightly mist the rock face and using a soft bristle brush, scrib away the concrete film.

Incidentally, the curve of the arch caused the concrete to sag a bit using my hand (latex glove), I pushed it back and it settled OK. If I wanted a steeper angle, I would have covered the top with flexible material (like siding) and stuck rocks on it so the concrete would be weighted down and retain its shape.



Step 5

After 4 days, I struck the mold. You can see the crusher fines underneath and notice the curve to the arch. It is still too fragile to stand up. I use the fingernail test. Since I can push my fingernail into the concrete, I know it is too soft.

Incidentally the far end is a bit too thin so when it cures, I’m going to place the box back around the arch and coat the end with concrete bonding adhesive, then simply add more concrete and aggregate (I’ll post photos later).



Here’s fully cured concrete arches. I tested them by jumping up and down on them. I then used my handy dandy mini tripod (last photo) to self-snap a photo of part of me and the hound. I fed the hound a good hefty meal prior to the photo to add some extra weight.

[Anonymous]

And I thought I'd seen alot when I was a Peace Officer!!!!!

Just jump, go ahead and jump!

Toad

[Capt Bob Johnson]

I know several concrete contractors and they will not pour if temp is forecast to go below 40 deg F within 24 hours of pour!

[FJ and G]

We had our first snow yesterday. I took the day off to clean my basement but found time to walk the hound (rabbit chasing) through the woods that are within sight of where I live along the Broad Run River. I have a few more tips and experiments. I’ll continue this series later with wall installation, ties, rails, and so on, using techniques you’ve never seen before that may or may not work. You will notice that I brought the arches inside that I’m working on as the cure time outside is unacceptable and the cold will prevent a good bonding.



The curved archway was much too thin on both ends (as a rule, I measure once, cut twice)



So I added Concrete Bonding Adhesive to the arch and coated with cement and stones (the coated portion is wet and darker in color). In real life, stonework is often patched like this. It should be ready to demold this weekend.



Instead of bringing crusher fines inside to form the curved archway, I used a technique indoor modelers use to make mountains, cutting Styrofoam into wedding cake form and adjoining with heavy duty construction adhesive. The white beads are annoying. I used a shop vac to vacuum them up and then used a propane torch to lightly melt the beads on the finished form.



There’s a weir, probably built by farmers to provide water for cattle, I imagine well over 100 years ago. This weir is what inspired me to do the arch. I took these photos while out with the hound yesterday, chasing squirrels and rabbits. See how the ancient concrete sort of blends with the stone. Concrete has worn away exposing them. Also, moss is growing with profusion.



Here’s the upper portion of the weir. Normally, water is lapping all the way to the ends but we’ve been in a severe drought this year.



Here’s some nearby scenery.



Can you find the hound in the next 2 photos? Last year, we had a severe ice glaze on the steep terrain near the river and the hound lost her footing and ski’d about 150 feet from the top all the way to the river, landing on a miniature iceberg in the river. Fortunate for me that I didn’t have to wade out to retrieve her.







This particular river near my house is close to Bull Run and Manassas. Civil War soldiers skirmished here during the two famous battles. About 4 years ago I was out in these parts with a metal detector. It was cold and about this time of year. Suddenly a bull came out from the woods and chased me up a tree. A whole herd of cows followed the bull and they surrounded the tree.

I had a light jacket on and as evening approached it started getting cold but the bull and cows maintained their vigil around my tree. The bull stared up at me with red in its eyes and started pushing on the tree. I swung down to a lower limb and kicked the bull in the head, hoping to send it away. I also threw dead tree limbs at it. But these tactics just made it angrier.

To make a long story short, as darkness set in, I swung down from the tree and screamed at the top of my lungs. This confused the bull for just 2 seconds, which gave me enough time to race to the river. I jumped in, broke the ice and somehow got across to the other side with the bull standing on the bank bellowing.

I was so full of adrenalin that I didn’t even feel cold (maybe numb). As I scooted for home, I could still hear that bull bellowing.

[Anonymous]

This particular river near my house is close to Bull Run and Manassas. Civil War soldiers skirmished here during the two famous battles. About 4 years ago I was out in these parts with a metal detector. It was cold and about this time of year. Suddenly a bull came out from the woods and chased me up a tree. A whole herd of cows followed the bull and they surrounded the tree.

I had a light jacket on and as evening approached it started getting cold but the bull and cows maintained their vigil around my tree. The bull stared up at me with red in its eyes and started pushing on the tree. I swung down to a lower limb and kicked the bull in the head, hoping to send it away. I also threw dead tree limbs at it. But these tactics just made it angrier.

To make a long story short, as darkness set in, I swung down from the tree and screamed at the top of my lungs. This confused the bull for just 2 seconds, which gave me enough time to race to the river. I jumped in, broke the ice and somehow got across to the other side with the bull standing on the bank bellowing.

I was so full of adrenalin that I didn’t even feel cold (maybe numb). As I scooted for home, I could still hear that bull bellowing.

About metal detectoring lay out a grid. Works best in this type of event.

As far as a bull, well he just thought you wanted his hurd.....LOL What my grandmother (which she was not) told me to do was break a 2x4 over/above his nose area. Well I did have cows at that time and yeah the bull ran me and my mother around when feeding time was upon. A storm came up and broke a nice size cedar stick down I used from then on as a walking stick in the mud and happen to be one cold day bull got pushy and he went to his knees (front). I was just glade I was not hurt because I was not backing down any more, mom had better time after that also with the bull. JFI

 

[concretelackey]

You are doing some fine concrete work there!

Words of advice from many years in precast concrete.... DO NOT USE EPOXY COATED STEEL REINFORCEMENT!!!!!! Yes, while the rebar or mesh is exposed to the elements the epoxy coating keeps it looking new but as soon as it is encased in concrete the epoxy coating will cause increased rusting to the rebar over a greater area if there is any damage to the epoxy. Stated differently, if you have a scratched peice of epoxy coated rebar in the concrete any mosture that contacts the steel begins the oxidation process. This oxidation is now channeled BETWEEN the epoxy and steel and will continue along its length. The reason is that the epoxy is only a surface applied coating. Galvanized steel on the other hand relys on a chemical bond that resists corrosion much better. As long as you keep your steel at least 1 1/2" from any exterior surface you will be fine even if you use plain steel rebar. Also, because of the glossy surface of the epoxy there is little to none chemical or mechanical bonding occurring between the concrete and the epoxy. To test this on your next pour take to peices of rebar about 6" in length (one being uncoated and the other epoxy coated [or apply several liberal coats of high gloss spray paint and let it dry for a day or 2 to acheive the same effect]) and fill 2 small containers (styrofoam cups will work) with your concrete. Place the end of the rebar in the concrete (one in each container) and store in a warm room for a few days. After it is very hard to the point where you fingernail will not damage the surface at all take a hammer to the the concrete. The uncoated steel (assuming there was no oil or other residue on it) will have plenty of concrete adhereing to it will the painted steel will be much cleaner.

As for the curing process, all that I'll add to what has been stated is that if the concrete freezes before a substantial set has occurred (minimum of a week for bagged concrete if mixed, poured and cured at average temps of 45 or less) then I would suggest you tear it apart and start over. The freeze will have shattered any chemical and mechanical bonds normally created and any further bonding will be to those fractured sections.

Stay away from any calcium choride "curing agents". While they will accelerate the concrete cure they will also accelerate the degradation of the concrete by causing rust.

You may be able to obtain "form oil" from a local precast plant or flatwork concrete contractor. The form oil contains a wax emulsion that forms on the mold after the solvent has evaporated. Almost all current form oils produced and sold are VOC compliant and are less detremental to the enviroment then their forefathers. You can either brush, roll or spray it using an inexpensive garden sprayer. The only down side may be cost. The precast plant I work in pays about $5.50 a gallon and will consume about 1000 gallons a month, most of that is due to the large surface area we most cover. Even so, as long as the oil is kept about 65 degrees or warmer it will apply easily and a gallon should be able to last you about 24 mold of the size shown in your pics.

I'll add more after I read this thread again.

Any questions.....just ask.

Ken

[FJ and G]

Thanks, Ken, I'm learning new stuff!

I've moved my processing indoors, where new batches are curing nicely.

For those wishing to do a similar project, I'd suggest making a small wood box form and doing a test. Prior to building the arches, I made a brick-sized test and was pleased with the results. 

 

 

[Anonymous]

For those wishing to do a similar project, I'd suggest making a small wood box form and doing a test. Prior to building the arches, I made a brick-sized test and was pleased with the results. 

That is what Mythbusters do/es, make small then go big. But then they have a larger $$$$ in there pocket. Is that a train in your pocket?

[concretelackey]

In an earlier post you mentioned concern about moisture penetration and freeze shearing (water gets in and freezes and things go bad quickly type thing). If you do some research (mainly phone calls) you should be able to locate a retailer fairly close to you that offers a REAL concrete sealer. While Thompsons and the other water sealers are decent I recommend trying to find either a SIKA (pronounced see-ka) material or a MASTER BUILDERS material to protect your investment. Both offer sealers that when cured give a desired look from a wet sheen to invisible (invisible for the sealer, it won't make the concrete disappear). Pay close attention to the instructions though, some require only a 3 day wait after the concrete sets, others 30 days. Don't try and shortcut the waiting time! It will look like crap.

I have applied this stuff using a brush and a paint sprayer. If using a paint sprayer have several ready to coat at one time to offset the clean up time.

If you PM me with the nearest large town/city to you I can try and locate some retailers near you. It may take a week or so until I get with my local contacts and they research with their contacts, etc....

Ken

[FJ and G]

Hi Ken,

 

Manassas, Va. Will these sealers also work for concrete lakes and streams (I've built a couple)?

 

Thanks