[TowerTalk] concrete forms

[kr7x at comcast.net]

Adrian;

Do you really need C35 grade concrete? that is equivalent to 5000 psi concrete over here? I would think that C25 for a foundation like these would be adequate, code requirement? 

The best way to ensure bond between pours with a long duration lapse between them is to use a concrete bonding agent. You clean the surface of the old concrete with water jet to get rid of debris and latency, then apply a coat of bonding agent prior to placing the new concrete. "Weldcrete" by Larsen is one agent common in the US, in the U.K. "Nitobond EP" by Fosroc should be available.

Regards
Lonberg Design Group, Ltd.

H.S. Lonberg, P.E.,S.E. / KR7X
President
-------------- Original message -------------- 
From: Jim Lux <jimlux at earthlink.net> 

> At 08:23 AM 7/31/2006, ADRIAN REES wrote: 
> >Hi Guys 
> >Over here in the UK, I am about to "plant" 4 towers, and pour C35 Grade 
> >Concrete in the bases. Anyone know what is the setting time for this 
> >stuff, and can it poured in one or two lots ? Getting this amount of 
> >concrete onto the site is not easy. I live up a mountain, with access 
> >limited to 4 Wheel Drive vehicles, and certainly a Truck will be near 
> >impossible to get on site, let alone a Ready Mix Concrete one ! So I may 
> >have to mix on site, and pour in batches. 
> > 
> 
> You'll want to talk to your concrete supplier. 
> 
> The "set time" for the concrete can be adjusted to a certain extent (they 
> do this anyway to compensate for temperature changes.. it's a chemical 
> reaction, and if you used summer mix concrete in winter, it'll take forever 
> to cure..) Mind you, this is for "largish" jobs. The local U-kart place 
> probably doesn't do this. 
> 
> My experience (which is limited) has been that if you have a 2 or 3 hour 
> gap between batches, there's a definite non-joining, because the first pour 
> has already started to set.. it's certainly not a monolithic block. 
> 
> Obviously, a big monolithic block is better, but the real question is how 
> do you get multiple pours to join in a mechanically sound way. There might 
> be some clever way to, for instance, have interlocking grooves, or rebar 
> links, etc. 
> 
> 
> Jim, W6RMK 
> 
> 
> 
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