Concrete screws - smaller stainless screws tested
- Thread starter IanWalker
- Start date
Bob Mehew
Well-known member
Neat piece of work. I should add that the standards are quite unclear about the number of tests one needs to do and thus the value for strength that one deduces from such work. So frankly, a single result means little. (Especially as we found some anchors had metallurgical defects which seriously undermined their strength.) Another point which was revealed by Simon's work is that the behaviour of limestone varies quite dramatically between naturally eroded exposures and exposures created by quarrying. (Blasting in quarries does create micro factures so that the bed rock has a much lower strength.) So the spread of results was quite large for testing done in quarries, reducing the overall deduced strength.
For what it is worth, BCA has an anchor puller with a 50 kN load cell. It normally is used for axial pulls, but using the approach devised by Simon Wilson it could be adapted for radial testing using a suitably sized concrete step.
PM me if you want more detail. It's a long story.
For what it is worth, BCA has an anchor puller with a 50 kN load cell. It normally is used for axial pulls, but using the approach devised by Simon Wilson it could be adapted for radial testing using a suitably sized concrete step.
PM me if you want more detail. It's a long story.
I have assumed that the manufacturer has appropriate quality control to produce a consistent product. The tests were to see if they suit my application.
I don't intend to place them in a quarry. But yes, rock variability is a potential issue (as it is with an anchor placed in the rock). Cheers
I don't intend to place them in a quarry. But yes, rock variability is a potential issue (as it is with an anchor placed in the rock). Cheers
Chris Curry
New member
This is excellent, thanks Ian. I've been using 100x7mm (also with Raumer Minox 8mm hangers) which are probably overkill if you're getting 20kn out of 75x6mm. Good work 
AKuhlmann
Member
A little late to the thread, but thank you for producing some recorded data on the topic! I’ve seen the Fischer 8mm (10mm with threads) x 70mm pull tested and the modern hangers broke first which was very reassuring.
Consequently, now all my exploration is on screws so I can remove them and re drill the hole for resins
Consequently, now all my exploration is on screws so I can remove them and re drill the hole for resins
Wayland Smith
Active member
Not starting a flame, (although no doubt someone will!)
Just a question, when you remove screws do you re-use them?
I didn't set out to test re-use of screws, or re-use of holes. The manufacturer of these do not state they are suitable for re-use, in which case I think it is sensible to suggest they are tested and warranted for single use only. They are cheap enough to use once.
From a practical point of view, if they look okay, it seems likely they will be okay to re-use. The risk would be your own if not following the manufacturers guidance in this way - but then if installing in a substrate not tested and approved, you are presumably happy with this. You could undertake some testing - say, install a sample screw five times and see what it looks like. Bear in mind that if you are leaving them in-situ, other cavers may expect they have been installed competently and in accordance with the instructions (and not re-used multiple times by a cheapskate who didn't bother to check if it would work).
If you are not happy re-using single-use screws, then re-usable concrete screws are available, the manufacturers for which provide gauges for testing they are not unduly worn. Presumably they are a go/nogo on the cutting thread outer diameter.
Here is an example gauge:-
eshop.wurth.co.uk
From a practical point of view, if they look okay, it seems likely they will be okay to re-use. The risk would be your own if not following the manufacturers guidance in this way - but then if installing in a substrate not tested and approved, you are presumably happy with this. You could undertake some testing - say, install a sample screw five times and see what it looks like. Bear in mind that if you are leaving them in-situ, other cavers may expect they have been installed competently and in accordance with the instructions (and not re-used multiple times by a cheapskate who didn't bother to check if it would work).
If you are not happy re-using single-use screws, then re-usable concrete screws are available, the manufacturers for which provide gauges for testing they are not unduly worn. Presumably they are a go/nogo on the cutting thread outer diameter.
Here is an example gauge:-
Buy Test gauge concrete screw for temporary fixings online
Only with Würth: Buy Concrete screw sleeve gauge W-BS, For checking the wear of concrete screw if used multiple times for temporary fixing of construction equipment easily and securely online ▶ Your specialist for trade and industry » Find the perfect product ✓Over 125,000 products ✓Purchase on...
eshop.wurth.co.uk
Babyhagrid
Well-known member
The smaller concrete screws work well for digging I've found. For quickly drilling and hauling boulders out of the way
pwhole
Well-known member
I use Excalibur 8mm screws and have generally been happy with them. Last week I pulled some out of a bolt-climb and reinstalled them higher up, but they'd only been in a week, and not in very hard rock, so I figured they'd be OK. I always use a nylon washer between the screw and the hanger as the screw will rust eventually at the contact point if left in the wet - with the nylon washer they don't.
AKuhlmann
Member
I tend not too but often it can be in harder rock which will blunt the screws (igneous rocks). If it were softer rock (slates) I might but tbh they’re really cheap so why pinch the pennies when it’s your life?
I would say more but Ian’s just said above all I would have to add