Please tell us of any problems and hazards you are aware of in using ice in concrete during hot weather.
We are not sure we have a complete list of problems by any means but we can give a few. One is the logistics of getting the required amount of crushed ice into the mixer in as short a time as possible. Introducing the ice tends to increase the length of time from beginning of batching until delivery and also reduces the total daily output of the ready mixed concrete plant. Another problem is controlling the slump. Slump cannot be measured properly until all the ice is melted. Ideally the ice should just finish melting at the time the concrete is to be discharged at the jobsite, but the rates of melting and transporting may not coincide. Consequently there may be a delay before the slump measurement can be made. It may be necessary to vary the amount of ice used per batch, using less in the morning and more as the day grows warmer. This added variation in batching and mixing increases the difficulty of control. The use of ice does effectively accomplish the purpose of cooling the mix in hot weather and is far more effective than cold water. One rule of thumb for determining how much ice to use is that the concrete temperature can be reduced one degree F for each two percent of total water replaced by ice.