Dead sand - Characteristics

[TheVictorianCobbleCo]

Hi - read thro the detailed info section, can't find definitive answer, hoping for clarity here. Having come back from xmas break, first week of production, and seem to have been lumbered with "dead sand". (making slabs and pavers a la Marshalls etc). Its as if the cement will not bind with the sand. (I suspect its been scraped up from wind blown residue in the quarry) Is there a common description for this sand? Am I on the right track? Given that normal casts are completely trouble free, this weeks slabs show fine hole porosity along the sides and top, the surface can be easily rubbed off after 3 days curing, weak cross section, powdery surface. Any coments appreciated.

[nick65]

My only experience with dodgy sand, was when it has been scraped up from the floor in the quarry. It was useless because it was contaminated with oil and diesel from the plant that used the track.
This was not delierate as there had been some flooding and the water had run down from the track to the quarry floor.
Its worth checking to see if the sand was contaminated at source in a simillar way or by some water via a dirty bucket or the like onsite.
I have know idea if sand is dug up like this.
Tecnical helpline .Aggregate Industries (charcon) 01335 372222

[lutonlagerlout]

i had a batch of ballast like this a while back,haunched a load of kerbs ,but it just seemed to fall apart once it had gone off
dont know what the reason was i blamed the labourer at the time but he swore it was gauged correctly?
LLL

[Tony McC]

Could it be salt contamination? Lot of salt around at this time of year and a brine will result in a weaker concrete.

[TheVictorianCobbleCo]

It seems I'm the victim of the scrapings of the quarry closing for Christmas, and I received their tidy up stuff, very fine, and contaminated by who knows what. The great pity is I now have a weeks supply of pool copings that must be downgraded to being used as stair treads. Really made my day!!!

[Big Phil]

if you bought the sand direct from the quarry they should have a description (hopefully a EN Standard too), as there are many different grades of sands and each react differently. The description should match the sand you ordered, but it seems strange you are unsure of the name of the sand you need. It may have been the wrong type supplied/ordered in error. Sands can be dry screened or wet processed and generally between 0/1, 0/2 & 0/4mm in size, with a Fine, Medium or Coarse grade. The benefit of the EN Standard descriptions is that it specifies the 'end use', i.e. Concrete Sand, Building Sand etc.

Contamination & scrape-ups may have been unprocessed sand (lagoon extraction, fill sand etc), which has it's uses in construction, and not really seen as 'waste'. However, loading from this stockpile in error will cause you some issues!

Obtain the delivery ticket information and see if it matches previous deliveries. If you bought through a merchant, their source may have changed.

[TheVictorianCobbleCo]

I'm still stumped on this one. 1) I pretty much know the sand was cr*p, but on checking and changing it, still no resolution. Have altered the cement content, cleaned the moulds superclean, tried a different release oil, checked theres no oil in the water, polished the mould with Ramwax prior to casting, all to no avail. I use 3 types of mould, ABS, Fibreglass, and our own special rubber. The product comes out perfectly in the rubber mould, with some blemishes (30%) to the SIDES of the ABS moulds, and with about 70 - 90% blemishes to the sides of the fibreglass moulds. I've tried to find out if the release oil has a "used by" date, but no response yet. Also altered the vibration rate/time to no effect. The blemish is as if the surface of the slab loses its colour (yet I colour right thro the product) with tiny pinholes on the sides of the product. the product is a 300 x 300 x 38 coping stone with a rivenstone surface finish, one side bullnose, and this is where the defect is most noticable. The bullnose face is also the only supersmooth surface of the coping, so I wonder if its not the fibreglass mould. I have new and old FG moulds, the problems the same. Puzzling, to say the least. ???

[TheVictorianCobbleCo]

Eureka, as they say in the movies - apart from the poor sand, hace discovered the porosity of the fibreglass is far less than that of the rubber or ABS moulds, so in effect the release oil had nowhere to go so combines with the surface of the slab to give an altered composition. Am now fine spraying on the release agent (much less) onto the mould, which solves the problem. A word of advice tho - fibreglass moulds are NOT ideal for REPEATED castings - don't waste the money. ABS and rubber - upwards of 3000 castings - FG struggling after 200 - 300.

[David Sarti]

I suspected the dust suppressant chemical which many quarries use. Symptoms as you described.



Edited By David Sarti on 1236170705

[Big Phil]

I suspected the dust suppressant chemical which many quarries use. Symptoms as you described.

what chemical is that then? H2O?

can't think of many sand quarries that would use dust suppression if wet processed, and even on a dry process there's not a great deal of mess with piano wire screening.

[lutonlagerlout]

well as they say bill "when you have eliminated the impossible,whatever is left,no matter how improbable is possible"

nice one,

LLL