19th April 2022 at 7:31 pm #7168Andrew_BParticipant
Hi Alan thanks for sharing your experience. A conversation with the slot cutters corresponds with what you are saying. Does concern me a bit the temperature of the bitumen being poured and the cable only rated to an operating temperature limit of 85 degrees C though presumably a short duration of a higher temperature won’t damage it, though it doesn’t spec any limits other than the operating temperature in TR2029. Not sure about BS6500/6195, not checked. Given the widespread use of bitumen direct onto the cable and the generally low failure rate then investigating this as a reason for premature loop failure probably not worth pursuing. Begs the question though, where is bitumen direct onto the cable specified as a standard installation means? Siemens have a pretty good guide on loops and the methods spec’d there are dry sand then hot pour bitumen or epoxy resin then hot pour. Many would refer to HCD G series which does specifically differentiate the encapsulant from the hot pour bitumen . I think its probably the case on a number of jobs I’ve had involvement on that the signals contractor isn’t fully communicating the requirements of the 12/5 to the slot cutters, probably assumptions are being made about what the original requirement was.20th January 2022 at 7:48 am #email@example.comParticipant
My experience is that on the Cornwall Council network the bitumen direct approach has been used for a very long time. However on the trunk road in the County
National Highways specified epoxy resin. I know this having been involved in the debate because the same company used to install loops for either party and there
would be frustration from the company at inconsistency between the two approaches. I never noticed any premature fails on the bitumen direct approach. I guess the bitumen cooling and forming around the loop cable in the slot is a robust finishing situation for the loop. We had loops that were still going after 30 years for sure using the itumen direct approach. I understand why national highways wanted epoxy maybe due to higher speeds , much more expensive TM on repairs and a vastly bigger network maybe Cheers Alan23rd November 2021 at 3:11 pm #7136Andrew_BParticipant
On a recent job I’ve questioned the lack of encapsulation for the loop cable and been told by some slot cutters that their standard practice is to pour bitumen direct onto the loop cable – ie no encapsulant such as epoxy resin first as called for in HCD G series / MCH1540 / MCH1542.
I’m concerned that it is cutting corners and could lead to premature failure due to a variety of reasons but of course it may be several years to gain evidence of this and proving cause of failure isn’t always going to be easy.
Does anyone have any experiences to share on this?
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