the concrete samples that are to be kept on site after the pour will need to be kept under cool and wet conditions, as their stregnth will be measured later and will be compared to project specifications. an important point not to forget here is that to keep the actual concrete poured on site cured. you either need to use sealing compound or keep the surface of the concrete wet in order to have complete hydration of cement and concrete gaining its deisgn strength. otherwise the actual concrete poured in the field will not be the same as the specimen taken whose strength is measured