Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Water-cement ratio in type V concrete

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Mr. Long:

See My Responses Below:

Arvel L.Williams, P.E.

LtTang wrote:

Hello all,

With the recent talk about Type V concrete, I would like to post the following
questions for our panel.

1.  How important is the water cement ratio in mixing Type V concrete?

As with most cementitious materials the water cement ratio controls the strength and durability of the concrete.   At a minimum ACI guidelines should be adhered too.   I prefer to see no mix with W/C greater than 0.50 in any case, regardless of cement type.  The higher the water cement ratio the less durable and poorer the performance of the concrete.  Specifically,

Increasing W/C ratios give:

    Lower Compressive Strengths
    Lower Durability
    Higher Shrinkage and More Shrinkage Cracks
    More Permeable Concrete (Reduces resistance to chemical attack)
   .

2.  Does higher ratio (greater than 0.45 per UBC) in anyway diminish concrete
     strength or reduce concrete capacity in protecting foundations from
sulfate deterioration.
See Above response.
3.  Since the UBC specify the 0.45 ratio, how can this be maintained in the
field?   I've seen on numerous occasions pumping contractors hosing water to keepthe
     concrete from hardening.
The best way is to have an inspector in the batch plant and a second at the job site.

Typical job specs (ASTM C94) will allow for a single retempering.  This water should be added in the ready-mix truck and thoroughly mixed into the concrete.  The driver should note this additional water on the ticket.  I would consider any other method of adding water suspect   If you have an inspector he should be monitoring this and not allowing the contractor to excessively retemper the mix.
 

4.  Will your standard slump test determine what ratio the concrete is at when
it's ready for pumping?
The slump test measure only one thing - slump.  This can be used as an indication of the consistency between batches and the workability of the concrete nothing more.  W/C should be determined by measuring the batch quantities and calculating.

If the inspector is concerned about the concrete, I would cast a set of cylinders after the retempering to measure compressive strengthI consider compressive strength to be a good indicator of concrete quality.

5.  Should engineers begin an observation program to check for this ratio?

The reason why I am asking this is that there is a recent lawsuit, still
pending, that involves this.  The lawyers are speculating that since the party
involved does not specify the 0.45 ratio on plans, he/she should be held
liable for complete foundation repair cost.  From the mix tickets, the water
cement ratio was noted to be 0.6 when the trucks left the mixing plant.  They
contended that because of the high ratio, concrete is more poruos which allows
sulfate to seep into the concrete faster, damaging it before adequate strength
was reached.  It's interesting how lawyers can dig through anything to build
their case.  Anyway, your reply would be greatly appreciated.
 

Two questions I'd ask myself are

1.  Did the EOR review and approve the mix design or request this in the project specifications?

2.  If yes, was the approved mix design actually used in the construction?

My 2 cents.

Arvel L. Williams, P.E.