Adding reinforcing "starter" bars to concrete
G.W. Walker
I'm about to lay some concrete next to an existing garage
base, to extend it, and some one suggested adding some steel
reinforcing to it. Sounds good, I thought. They also suggested
drilling the existing base and inserting the reinforcing
bars into the existing concrete to help tie the two sections
together.
Sounds plausible, I thought -- but how to "fix" the bars
into the existing concrete? Some form of resin maybe?
Any ideas welcome!
Gavin
David Simpson
<g...@eng.cam.ac.uk> writes
bigger than the diameter of the bolt, clean out any dust( if using an
electric drill disturb the smooth side of the hole by opening up a few
depressions in the sides so the resin can get a key), pour the resin in
and push the bar in and leave it too set.
--
David Simpson
G.W. Walker
David Simpson <david....@chapelhouse.demon.co.uk> wrote:
>In article <8pomlj$mjn$1...@pegasus.csx.cam.ac.uk>, G.W. Walker
><g...@eng.cam.ac.uk> writes
>>
>>into the existing concrete? Some form of resin maybe?
>>
>
>bigger than the diameter of the bolt, clean out any dust( if using an
>electric drill disturb the smooth side of the hole by opening up a few
>depressions in the sides so the resin can get a key), pour the resin in
>and push the bar in and leave it too set.
Sounds exactly like what I'm after. Ta!
Gavin
mlv
>
> I'm about to lay some concrete next to an existing garage
> base, to extend it, and some one suggested adding some steel
> reinforcing to it. Sounds good, I thought. They also suggested
> drilling the existing base and inserting the reinforcing
> bars into the existing concrete to help tie the two sections
> together.
>
> into the existing concrete? Some form of resin maybe?
>
Big lump hammer (club hammer). That's what I use for fixing starter bars.
I generally use standard nominal 1/2" re-bar (which has the embossed
'diamond' pattern on it). I scrounged some off a building site about 15
years ago and have been using it ever since.
Cut the re-bar into straight lengths - allow something like 120-150mm to go
into the existing concrete slab and maybe 200-300mm into your new slab.
File/grind a neat taper onto the end that will be driven into the existing
concrete slab. You can do this with a disc cutter, if you have one. Also,
use a wire brush to remove any loose rust.
Get a good SDS hammer drill and drill suitable holes into the mating edge of
your existing concrete slab. Start with a 12mm dia drill and increase to a
13mm (1/2") diameter if necessary. It's important to get the hole size
correct to give a good interference fit (from memory, I use 13mm dia.) Drill
a trial hole first.
Don't bother to clean the concrete dust out of the hole, it will build up in
the cavities of the re-bar pattern as you hammer the re-bar home and assist
in retaining the bar.
If you get the hole size correct, the re-bar will drive solidly into the
hole with a dull metallic ring and you will feel it bottom out. Done
properly, you will never pull the re-bar out again.
Whether you hammer your re-bar in or use an adhesive, you should (IMO) adopt
the principle of skew-nailing. For example, as you drill for the re-bar
along the edge of the existing concrete slab, drill the first hole at an
angle running from left-to-right at around 30 degrees to the perpendicular.
Drill the next hole straight (perpendicular). Drill the third hole at an
angle running from right-to-left at around 30 degrees to the perpendicular.
Repeat this pattern as you move along the edge of the slab. The opposing
angled re-bars will resist any attempt by the new concrete slab to move away
from the existing concrete slab.
After you have fixed the re-bars in their holes, you can bend the protruding
ends of the angled ones back to perpendicular if you wish. If you've used an
interference fit and a big hammer, you can dress and bend the bars straight
away (slip a piece of metal tube (i.e. conduit), over the re-bar if you need
extra leverage to bend it). If you're faffing around with adhesive, you will
have to wait until it has fully hardened.
Four other tips:
1. You might consider digging for a distance of something like100-200mm
(and a similar depth) back under the mating edge of your existing concrete
slab (especially if your new slab will be thicker) so that the new slab
underpins the existing slab.
2. If you're using a steel mesh in your new concrete slab, wire it (or weld
it) to your starter bars. Don't let the edges of the mesh get too near the
free edges of your new concrete slab or there will be a corrosion risk. A
'mesh-free' border of 100-150mm should be maintained all round. Also make
sure that the steel mesh lies roughly in the centre of the new concrete slab
and doesn't sink to the bottom or get too near the top. The mesh can be held
up by several small pieces of brick or concrete block, which then become
incorporated into the new concrete slab.
3. Thoroughly clean the mating edge of the existing concrete slab to remove
all roots, soil etc. and knock off any insecure stones/pieces of concrete,
etc. A good wire-brushing or high-pressure hosing will clean it well, but
don't flood your new foundations, particularly if you have a clay soil.
4. Just before you pour your new slab, paint the mating edge of the
existing concrete slab with a thin coat of neat OPC (Ordinary Portland
Cement) which has been mixed with water to the consistency of single-cream.
Have fun!
--
Mike
Please remove 'SAFETYCATCH' from E-mail address before firing off your reply
G.W. Walker
mlv <mike.v...@jetSAFETYCATCH.uk> wrote:
[big snip!]
Thanks for that -- I hadn't thought of skewing the
bars for starters! Looks like I've got no excuse
for (a) not getting on with it at the weekend
(b) the new slab floating off down the garden
after a week or two ;-)
Cheers for such a great reply,
Gavin
John Schmitt
[starter bars in concrete]
>Sounds plausible, I thought -- but how to "fix" the bars
>into the existing concrete? Some form of resin maybe?
The ideal situation would be to have the bars set in the slab from the word go.
Obviously this is not an option here. I understand that site practise is simply
to place the bars dry in predrilled holes, and trust that during the placing
process, some of the fines in the concrete will grout the bars in. As the
application is not /per se/ load bearing, this will be a reasonable approach.
Eventually some differential movement will occur, and a small crack will
probably appear at the join. This is not the end of the world, or even of the
structure. Many, many buildings have movement cracks and have done for decades,
and have not fallen down.
John Schmitt
--
It's half and half. Sometimes they're lying, sometimes they don't know what's
happening. - Vladimir Urban on the Russian submarine 'Kursk' crisis.
I've got a disclaimer, and I ain't afraid to use it.
David Simpson
>base, to extend it, and some one suggested adding some steel
>reinforcing to it. Sounds good, I thought. They also suggested
>drilling the existing base and inserting the reinforcing
>bars into the existing concrete to help tie the two sections
>together.
>
>into the existing concrete? Some form of resin maybe?
>
>Gavin
Having read the other replies Gavin, I thought I would just make a point
about the "interference fit method" this will be fine as long as you're
not expecting any great performance from the bars. In tests, hammering
the bar in gives no pull out strength at all, it does not even register
on the gauge, whereas a good chemical anchor gives apprx 3 tonnes per
inch of embedment (ignoring the first 2 inches). Hammering starter bars
in is not an accepted form of practice and is probably only used on DIY
jobs, no civil engineer would accept it.
If you just want to prevent vertical movement you should use dowel bars
with one end fixed and the other end free, this allows lateral movement
so the two slabs can move "in and out" but hold the slabs in the
vertical plane (within reason!).
BTW polyester resin sets in 40 minutes normal grade 20 minutes winter
grade, plan it right and the resins setting while you are doing other
things, you can get quicker fixings but that will involve spinning the
bar.
--
David Simpson
mlv
>
>Having read the other replies Gavin, I thought I would just make a point
>about the "interference fit method" this will be fine as long as you're
>not expecting any great performance from the bars. In tests, hammering
>the bar in gives no pull out strength at all, it does not even register
>on the gauge, whereas a good chemical anchor gives apprx 3 tonnes per
>inch of embedment (ignoring the first 2 inches). Hammering starter bars
>in is not an accepted form of practice and is probably only used on DIY
>jobs, no civil engineer would accept it.
>
>If you just want to prevent vertical movement you should use dowel bars
>with one end fixed and the other end free, this allows lateral movement
>so the two slabs can move "in and out" but hold the slabs in the
>vertical plane (within reason!).
>
Agreed hammered in starter bars would not be acceptable for a specified
steel reinforced concrete construction. However, this is a simple supported
ground floor slab in a DIY domestic installation where your average builder
wouldn't use any starter bars at all.
Mostly these starter bars will be resisting shear forces, which, IMO, the
hammered in bars will do quite adequately.
The opposed skewing of alternate starter bars will also resist lateral
movement.
I once tried to remove one of my interference fit starter bars. I didn't
succeed and ended up cutting it off flush. It seems that during the
hammering in, there is some deformation of the pattern ribs on the bar and
pieces of concrete/stone break off and wedge themselves between the sides of
the drilled hole and edges of the re-bar pattern. IME, if the interference
fit is good (which it has to be), then the re-bar is very secure.
I suppose Gavin could go 'belt & braces' and dip his re-bars in resin before
hammering them in :-)
Ian White
>
>2. If you're using a steel mesh in your new concrete slab, wire it (or weld
>it) to your starter bars. Don't let the edges of the mesh get too near the
>free edges of your new concrete slab or there will be a corrosion risk. A
>'mesh-free' border of 100-150mm should be maintained all round. Also make
>sure that the steel mesh lies roughly in the centre of the new concrete slab
>and doesn't sink to the bottom or get too near the top. The mesh can be held
>up by several small pieces of brick or concrete block, which then become
>incorporated into the new concrete slab.
>
job, fortunately), on the instructions of the surveyor they used large
mesh, with the protruding ends glued directly into holes drilled in the
existing slab.
Ian White
Abingdon, England
David Simpson
CH.uk> writes
<snip my diatribe>
>Agreed hammered in starter bars would not be acceptable for a specified
>steel reinforced concrete construction. However, this is a simple supported
>ground floor slab in a DIY domestic installation where your average builder
>wouldn't use any starter bars at all.
>
>Mostly these starter bars will be resisting shear forces, which, IMO, the
>hammered in bars will do quite adequately.
>
>The opposed skewing of alternate starter bars will also resist lateral
>movement.
>
>I once tried to remove one of my interference fit starter bars. I didn't
>succeed and ended up cutting it off flush. It seems that during the
>hammering in, there is some deformation of the pattern ribs on the bar and
>pieces of concrete/stone break off and wedge themselves between the sides of
>the drilled hole and edges of the re-bar pattern. IME, if the interference
>fit is good (which it has to be), then the re-bar is very secure.
The way I test pulled bars was with a hollow ram jack and hydraulic
pump, our aim was to produce anchors which would always be stronger the
concrete. If we got it right the bar failed, the load is a function of
diameter, small bars snap at a few tonnes but obviously larger diameter
and special steel, i.e. macalloy, bars go a lot higher, from memory the
highest reading I had was 67 tonnes before it broke. The company I
worked for then also produced resin anchors for holding down
lighthouses, they were big beasties about 30' long.
--
David Simpson
cormaic
<david....@chapelhouse.demon.co.uk> enriched all our lives with
these words:
> Hammering starter bars
>in is not an accepted form of practice and is probably only used on DIY
>jobs, no civil engineer would accept it.
Any contractor even considering it will be thrown off the job.
Usual spec is for Lokset P40 or similar anchor grout with bar
penetration of at least 150mm into existing.
--
cormaic - paving pages at http://www.tmac.clara.co.uk/paving/
Culcheth - Last Updated on Sep 7th 2000
cormaic CAN BE FOUND AT tmac DOT clara DOT co DOT uk
Andy Woodward
>Obviously this is not an option here. I understand that site practise is simply
>to place the bars dry in predrilled holes, and trust that during the placing
>process, some of the fines in the concrete will grout the bars in. As the
>application is not /per se/ load bearing, this will be a reasonable approach.
>Eventually some differential movement will occur, and a small crack will
>probably appear at the join. This is not the end of the world, or even of the
>structure. Many, many buildings have movement cracks and have done for decades,
>and have not fallen down.
Presumably the bars will rust and expand into place with time anyway?
Jon Rouse
>Having read the other replies Gavin, I thought I would just make a point
>about the "interference fit method" this will be fine as long as you're
>not expecting any great performance from the bars. In tests, hammering
>the bar in gives no pull out strength at all, it does not even register
>on the gauge, whereas a good chemical anchor gives apprx 3 tonnes per
>inch of embedment (ignoring the first 2 inches). Hammering starter bars
>in is not an accepted form of practice and is probably only used on DIY
>jobs, no civil engineer would accept it.
Curiously '999' the other night showed the construction of large concrete
storage tanks where the contractors did indeed seem to be hammering
reinforcing bars into the previously cast concrete.
--
The views expressed are my own, and may not necessarily reflect those of my
employer.
G.W. Walker
Jon Rouse <jon....@nospampostoffice.co.uk (omit nospam to reply)> wrote:
>
>Curiously '999' the other night showed the construction of large concrete
>storage tanks where the contractors did indeed seem to be hammering
>reinforcing bars into the previously cast concrete.
Hmm -- I hope that the feature on '999' wasn't directly
related to the contractors hammering in starter-bars...
;-)
G.
mlv
>
><snip>
>
> .... The company I worked for then also produced resin
> anchors for holding down lighthouses, they were big
> beasties about 30' long.
>
Some while ago there was a TV documentary about the various designs of
lighthouse constructed on a certain rock over the centuries (can't remember
which rock, unfortunately).
One method used to fix the lighthouse down was to drill holes into the rock
and then open them out so that they tapered (large diameter at the bottom,
smaller at the top).
A steel support was then placed into the hole and the hole filled with
molten lead to secure it.
IIRC, this was a wooden lighthouse which was eventually destroyed by fire.
The lead anchors never failed and proved to be very serviceable.
Ian White
concrete.
If the rebar is not well covered in concrete, so that cracks can
penetrate down from the surface, then water, oxygen and other dissolved
nasties (especially chloride from salt) can get at the steel. *Then* it
will rust like crazy and the expansion splits the concrete off - look at
an old sea wall to see what happens.
Ian White
Abingdon, England
Chris French
CH.uk> writes
>David Simpson wrote:
>>
>><snip>
>>
>> .... The company I worked for then also produced resin
>> anchors for holding down lighthouses, they were big
>> beasties about 30' long.
>>
>
>Some while ago there was a TV documentary about the various designs of
>lighthouse constructed on a certain rock over the centuries
>IIRC, this was a wooden lighthouse which was eventually destroyed by fire.
>The lead anchors never failed and proved to be very serviceable.
Bishops Rock maybe?
--
Chris French, Leeds
mlv
>
> Bishops Rock maybe?
>
Could be - I'm not sure.
The name doesn't ring a bell (or flash a light :-))
Anthony Frost
Chris French <news...@spennithorne.demon.co.uk> wrote:
> Bishops Rock maybe?
More likely to be the Eddystone. That's had 5 towers on it, the first
three of which were wooden and at least one of those went up in flames.
Winstanley I IIRC. Winstanley II got washed away in a storm with the man
himself inside, I forget what number 3 was called or how it got broken,
Smeatons tower got relocated to Plymouth Hoe and number 5 (Douglas
Tower) is still out there.
Anthony
--
| 99% of accidents occur in the home.... |
| |
| ...Stay safe, go out lots. |
John Schmitt
[on concrete slabs]
> Presumably the bars will rust and expand into place with time anyway?
Only over a very, very, long timescale. The free lime suppresses the
corrosion of the steel, and the carbonation of the lime is slow,
typically 1/2" in 30 years. The rate of carbonation decreases with the
depth of its penetration, and as there is no really old OPC based
concrete about it is possible that there is a point at which carbonation
comes to an effective halt.
John Schmitt
John Schmitt
[not sure what a lighthouse thread is doing here but...]
> More likely to be the Eddystone.
Indeed. I'll try to dig out my book about this.
> Smeatons tower got relocated to Plymouth Hoe and number 5 (Douglas
> Tower) is still out there.
I am 99% certain that Smeaton was the man who invented iron rods bonded
into the rock with lead. I think that boiling tallow was poured in
before the lead to dissipate the water, and prevent the lead being blown
violently out of the hole by steam.
John Schmitt
John Schmitt
> I am 99% certain that Smeaton was the man who invented iron rods bonded
> into the rock with lead.
It was, in fact, Rudyeard, the constructor of the previous tower which
succumbed to fire. This is according to a biography of Smeaton, written
by A W Skempton, himself an eminent civil engineer.
John Schmitt
Ian Johnston
: In article <8q58ne$alb$1...@soap.pipex.net>, mlv <mike.vincent@jetSAFETYCAT
: CH.uk> writes
:>IIRC, this was a wooden lighthouse which was eventually destroyed by fire.
:>The lead anchors never failed and proved to be very serviceable.
: Bishops Rock maybe?
The Bell Rock in the Forth had a lighthouse detroyed by fire. For many years
the Royal Scottish Museum in Edinburgh had on display a large lump of lead
removed from the stomach of one of the keepers, who was injudicious enough
to look up - with his mouth open - as the flames reached the lead covered
roof.
Ian
Roger Chapman
from "mlv" <mike.v...@jetSAFETYCATCH.uk> contains these words:
> > Bishops Rock maybe?
> >
> Could be - I'm not sure.
> The name doesn't ring a bell (or flash a light :-))
Eddystone?
Roger
Anthony Frost
John Schmitt <joh...@nw.mdx.ac.uk> wrote:
That's the man! My dad had a nice book about the Eddystone lights which
no reposes in my mums attic. I must try and remember to "aquire" it next
time I visit... :-)
mlv
>
> I am 99% certain that Smeaton was the man who
> invented iron rods bonded into the rock with lead.
> lead to dissipate the water, and prevent the lead
> being blown violently out of the hole by steam.
>
Yes, you're right about the tallow.
I'd forgotten that aspect of the lead pouring procedure.
Simon Avery
Hello John
>> Smeatons tower got relocated to Plymouth Hoe and number 5
>> (Douglas Tower) is still out there.
JS> I am 99% certain that Smeaton was the man who invented iron
JS> rods bonded into the rock with lead.
The iron part, maybe - but the Romans were using molten lead as a
waterproofing and bonding agent a bit before him. :)
--
Simon Avery, Devon, UK