expansion gaps in concrete paths

[Nearlyman]

Around part of the perimeter of my house is a 900mm wide 'L' shaped concrete slab pathway: it extends along the entire length of the gable end and around the 90 deg corner to about half the length of the house, measured from the gable end, finishing at the paved patio immediately adjacent patio doors which open on to it.

Pitched at about 3M intervals there are 3 slots - quite deep - across the width of the pathway and which are about half inch wide: I am certain these are expansion slots/gaps.(I was an engineer not an architect :=))
Problem(?): in Nov 2004, when the house was built, these gaps/slots were filled with some kind of dense but resilient material; I've no idea what kind of substance it was neither did I know the purpose it served: clearly it was put there for some good(?) reason else the "gap" would have simply been left empty....?

It has become apparent, over time, however that this material - whatever its nature - was formulated (on the evidence) to be biodegradable, because it has now completely eroded/disappeared!

Because the gap is relatively deep it provides an ideal dirt trap and regularly fills with small pieces of debris not least; grass cuttings, bits of leaf and sundry other detritus which can occur from time to time in most gardens.

As the pathways - due to the upward sloping up nature of the site away from the house - are prone to flooding during heavy rainfall (off the raised grassed areas surrounding the property) I do have concerns that the now empty gaps are effectively directing (funnelling) the excess surface water to the base of the house and hence into the footings; the pathway directly abuts the house and there has appeared, over the time since the house was built , a crack along the entire length of the pathway at this abutment point.

I am aware that tar was once a favoured material for filling such gaps, but the path is frequently exposed to full sun since it enjoys a southerly aspect; meaning that the path can reach temperatures high enough to soften, even melt, the tar and thereby give it leave to migrate; and incidentally, attract the uninvited interest of my infant grandchildren..:=) not to mention pick-up on footwear, which could easily be carried into the house.

Question is; what - for the sake of satisfying my curiosity - might the original, now "evaporated"material, have been and what could I now use instead that would maintain the expansion capabilities of the slab and and also resist deterioration over time? I am not getting any younger, and for the record, I am not getting any richer either, i.e. paying someone else to do the work is simply 'out of the question'.

I see it important to "DIY" these task to get them "sorted" whilst I still have the physical capability: both this and my future financial resources look set to decline at about the same rate - by my latest reckoning -and now is the time to put right what I can before both the means and the capability desert me.

Any advices on how best to deal with these expansion gaps will be much appreciated - thank you.
regards
Nearlyman

[welsh brickie]

fill the gap with expanding foam,cut it back when set and use a silicone sealant to finish.The original expansion gap was made of mdf or ply.