Method and compositions for stabilizing concrete residues

A method for stabilizing concrete residue in a ready-mix truck drum consisting essentially of the steps of:

• 1) adding water to the ready-mix truck drum to form a slurry with the concrete residue therein;
• 2) adding from 32 to 96 fluid ounces of a stabilizing agent to stabilize the concrete slurry for a period of time;
• the stabilizing agent being selected from the group consisting of a phosphonic acid derivative;
• a hydroxycarboxylic acid or salt thereof;
• a polycarboxylic acid or salt thereof;
• ascorbic acid, isoascorbic acid;
• a sulphonic acid-acrylic acid copolymer;
• a polyhydroxysilane;
• a polyacrylamide;
• a carbohydrate;
• a lignosulfonate;
• and mixtures thereof;
• 3) mixing the stabilizing agent and drum contents to form a stabilized concrete slurry;
• and
• 4) thereafter adding fresh concrete to the stabilized concrete slurry.