To roadbase or not to roadbase

[Smiley Guy]

I am manually excavating part of my back yard to get ready to pave about 70-80 sqm.

I am tossing up whether I should lay roasbase or not (under the sand).

The soil is a red dirt - so I am assuming lots of clay underneath but it is hard and crumbly, not soft. (if you go down far enough you will find a lot of clay - did this digging up front yard). If I use roadbase I really want to lay only 50mm (too much work man!). The area will be used for pedestrian traffic only - no cars at all. A couple of people coming to do quotes say they may not need to use roadbase.

ANY IDEA AS TO WHETHER OR NOT I NEED TO USE ROADBASE?

Also - does the thickness of the pavers have anything to do with this decision? I am using 2nd hand Austral clay pavers in excellent condition - they are 65mm thick (& 110mm x 225mm - heavy b*&^%s). They were previously used in a car parking area.

[Tool-Horder]

First up to answer a question with a question, how long do you want the area to last? Since it will only see pedestrian traffik the main consideration with the roadbase question would be how well drained the area is. If it is an area which gets boggy after rain I would definatly use road base. If the 'moisture level' in the area is fairly stable, I would still use the road base but you might get away without it. For pedestrian areas I prefer to lay paving on what is commonly sold up here as packing sand (crushed bluemetal). The best way to describe it is very fine agregate (2 -> 3mm) and fine dust. After wetting down and compaction it sets like concrete. Only way to dig up again is to scrape across it. If you still need to touch up levels after compaction only use a thin layer of sand. The recomended thickness of roadbase sub layer for paving is 100mm. The purpose of the layer is to provide a stable layer which is not affected by moisture. If you have a clay base it will swell/shrink with changes in moisture levels. Around here the clay is very reactive. With a big dry spell exposed clay surfaces will show cracks up to 75mm wide. Another point to remember is that if a low spot forms in the area , water will lay there, soak through the joints in the pavers and over time will only make the sunken area worse.

So in closing, a bit more work/expense now could save a lot of time/sweat/nagging from the missus later on when you have to re-level the area.

[ernknot]

I agree with Tool-horder, use the road base, compact and top off with sand to keep your levels when laying the pavers. Do this and it will last a long time and add value to your property. Besides it will look real spiffy.

[Doughboy]

For a good job definitely go with road base as both ernknot and toolhorder have eluded to. If it is your first time paying pavers take your time with the road base and sand to make sure you get the correct fall and levels, once these have been taken care of the pavers will go down more easily and the finished job will look better also it will last longer.

Pete

[Smiley Guy]

I want it to last FOREVER!

Thanks - I think I'm leaning towards the roadbase for sure. I have found because of the slight slope in my land I won't have to dig as much (I am levelling it out a bit - but yes I am still leaving some slope).

Does anybody else have comments about this CRUSHED BLUE METAL? Sounds like a good idea. Is it more expensive?

I have 6 bags of cement left over from another job (although I am not a tradie - just like diy). If I use regular roadbase can I just throw in some of this cement with the roadbase? It is starting to go a little hard because I left it on the garage floor. It's still not too bad - I'm going to move it. Need to get rid of it!

[Smiley Guy]

Tool Horder said:

The purpose of the layer is to provide a stable layer which is not affected by moisture. If you have a clay base it will swell/shrink with changes in moisture levels.

When water gets to the clay and the clay reacts - wopn't that just push arouns the roadbase and whatever's on top anyway? or does the water not get through the roadbase?

[Tool-Horder]

Tool Horder said:

The purpose of the layer is to provide a stable layer which is not affected by moisture. If you have a clay base it will swell/shrink with changes in moisture levels.

When water gets to the clay and the clay reacts - wopn't that just push arouns the roadbase and whatever's on top anyway? or does the water not get through the roadbase?

There is really 2 thins that come into play her, both related to each other. Road base actually uses clay content as a bonding agent for the agregate. However the clay is of a non reactive type, so it is stable. The roadbase provides a layer which is relativly impervious to water and rigid. As for the clay base reaction lets have a quick look at footting design and the reasons as to why they work the way they do. On a site with reactive clay the a deeper footing depth will give you a much more stable surface than a larger surface area footing. The reason they work is in the ammount of time it takes for the water to reach the bottom of the footing. Minimise the change in moisture level and you minimise the amount of swelling/shrinking in the clay. Simple as that. The road base layer forms a rigid layer which will float on top of the clay/soil base evening out movements. Take a small patch of clay, wet it well and push you hand/foot on one side and where does the clay move to .... opposite side (and between your toes). Compact a layer of road base over this and do the same thing .... does not move as much. The big secret with the base is compaction, compaction and then a little more compaction and just to be safe compact again.

[Bleedin Thumb]

Road base actually uses clay content as a bonding agent for the agregate. .

Sorry Tool Horder I cant agree with that. Roadbase is not bound with clay to create its strength. It gets its strength from compaction due to its "gap gradient particle size." You can use cement (or lime) stabilised road base if you need to increase the bearing capacity (CBR) however there is no need to stablize roadbase unless you will be having a high pavement traffic value say over 100,000 ESA's(Equivelant Standard Axils)[Assuming your using recomended 150mm of DGB 20 roadbase compacted to 98% Standard Compaction sitting over.........................

ZZZZZZIIIIIIIPPPPPPPPP - thats the sound of the needle being dragged across the record.

Sorry for the technical crap.
Smiley Guy,
As others say - use RB, I'd go recycled RB but ask for equivelent to RGB 20. make it 75mm thick and compact it to 50mm ( better still go 100 down to 75mm if you can excavate another 25mm)
Crushed Bluemetal (Crusher dust) is OK as a substitute for yor paving sand but not for the RB as it doesnt have the full scale gap gradient particle sizes. IE all different sizes that fit together and compact well.ie beach sand doesnt compact because the grains are all the same size. Crusherdust is about 5mm minus.
All the above is for pedestian traffic only.
Good luck

[Tool-Horder]

Sorry Tool Horder I cant agree with that. Roadbase is not bound with clay to create its strength. It gets its strength from compaction due to its "gap gradient particle size." You can use cement (or lime) stabilised road base if you need to increase the bearing capacity (CBR) however there is no need to stablize roadbase unless you will be having a high pavement traffic value say over 100,000 ESA's(Equivelant Standard Axils)[Assuming your using recomended 150mm of DGB 20 roadbase compacted to 98% Standard Compaction sitting over.........................

ZZZZZZIIIIIIIPPPPPPPPP - thats the sound of the needle being dragged across the record.
Good luck

From the tech crap it sounds like you're in the game. I have used two types of road base. Dont ask me the tech crap I only go by what the supplier tells me, but I found the one with clay content held in place much better than the one I currently have in driveway which relies on particle size for compaction. Clay based one in top drive has been in place for approx 5 years with very little washout and loose surface. It was only compacted by driving over with 2 ton vehicle. Bottom driveway has been done for approx 2 years with "gap gradient particle size." roadbase, compacted with vibrating roller. Held in place well for about six months, but since then washouts are always a prob with lots of loose agg on surface, poor traction on slopes. Both drives are of approx the same gradient with about the same amount of water run off and both see about the same ammount of trafic. I will be re-dressing the bot drive in the near future and am trying to source the roadbase I used on top drive for the job. It will be interesting to how well it holds up next time round, or if there is some other 'hidden' factor that is affecting the bot driveway performance.

Either way, washout will not be an issue when covered with paving.

[Chopstick]

I am by no means an expert (but I would go with the crushed rock - compacted) but I followed the info from this site when I did our small entertaining area and I must admit it is fantastic in going through all the details you need to worry about, in a simple concise manner.

http://www.pavingexpert.com/home.htm

[Bleedin Thumb]

Hi TH,
I cant comment on the clay stabilized stuff but if that was infact what was used to stabilize it it would have a similar chemical effect as lime.
Having said that when I have laid paving on slopes before and not stabilized the sand you always get the washout at the bottom of the slope because by the time the water has got down there it is more concentrated and is larger in volume, so maybe its just this effect that your experiencing.
The reason I prefer recycled roadbase (besides being cheaper) is that I find that the crushed concrete dust when wetted down and compacted seems to reset creating a more stable base that traditional DGB20. I doubt that this stands up to scientific scrutiny - but from experience it seems that way.

[Smiley Guy]

Thanks for the tips guys - the paver I have given the job too said he wants to use crushed blue metal.

While we're at it - I have 6 bags of cement starting to go hard but isn't completely ruined - a builder friend told me (I left them on my garage floor (concrete) - no water got in the garage but apparently I was supposed to keep them off the ground).

Anyway - I was thinking I might as well mix the cement in with the roadbase. Is this a good idea? Do I just throw it on top or mix it in? This is as long as the paver guy doesn't mind me doing this.

[Tool-Horder]

Ceratinly won't do any harm to add it. Spread it as you would a fertalizer, Throw in a handfoll at a time while shoveling base material. It is of no use in lumps so spread/rake it in well.