Transporting Grade 35 Concrete

Doesn't it rather depend on the distance between the batching plant and the placement site, and the road speed limit in the area, Chief?

It takes about one hour to get to the site from the batching plant. I want to know if this time and distance are allowable.

The answer to you question is contingent on what requirements you need to get from your concrete. Long time mixing of the concrete with water added to maintain the slump causes a loss of strength and other properties. Depending on temperature, materials, and job conditions, probably about three hours is a practical limit. You might have to run a trial batch to find out what you will get for strengths.

The ACI standards in US require placement with in less than 90 minutes after water is added in the plant, because any longer and to much of the cement has reacted and "set". I would specifiy a 90 minute time, and the time be checked by your onsite inspector, any batch that is not placed within the 90 minutes should be rejected and sent back to the plant. The contractor and concrete company will bitch about this when it arises, because it is a profit loss for which ever is responsible for the delays, but it is a good time to specify for a standard cement. (For rapid set cements or those with admixtures you may need to modify the specified time from water to placement).

There are retardant additives that can extend the set time, perhaps this can help.