How do you prevent cold joints in a single placement?

• A. Use bonding agents or roughening
• B. Stop placing during cold weather
• C. Increase slump
• D. Place concrete continuously or minimize cold intervals

Answer: (D)

Cold joints happen when a new batch is placed after the previous one has started to stiffen, creating a weak plane where bonding between layers is limited. The best way to prevent that in a single placement is to place concrete continuously and minimize any pause between pours. Keeping the pour uninterrupted helps the new concrete bond with the old, forming a single, monolithic structure with consistent strength. If a pause is unavoidable, the interval should be kept as short as possible and the area planned for a joint, but continuous placement is the most effective preventive measure. Bonding agents or roughening are useful if a joint must exist, but they don’t prevent a cold joint as effectively as eliminating the interval between placements. Stopping during cold weather and increasing slump don’t directly address the bonding issue caused by a pause in placement.