If your ordering the concrete from the batch plant chances are you are paying for it. Therefore you are liable for it even in circumstances when the concrete pump blocks, breaks down, or is late to site. Its important to have positive communication with the concrete pumping company and your concrete batch plant at all times.   Make sure there is a back up plan in place for emergencies and delays. Most experienced concrete pumping firms have access to other concrete pumps in times of need, but it may be prudent to consider "what if" before your pour, as opposed to during it. Especially if you are pouring at 7am and all the other concrete pumps are busy, or in situations where you are miles from another concrete pumping yard.