What is setting of Portland cement?

Answer 1

In normal usage, allowing the concrete to "set" is the same same as allowing the concrete to "cure". This process starts soon after you mix the cement and aggregate with water, and is a result of the water in the mix chemically binding with cement components. As the concrete sets or cures, the mixture gets harder. Depending on the proportions of the materials in the concrete, after a few hours the concrete will be hard enough to support the weight of the workers as they perform finishing operations (trowelling). After a couple of days, the concrete will typically be hard enough to remove formwork, as long as no loads are imparted to the concrete in doing so. Concrete in the US is typically specified as the compressive strength reached after 28 days. The term "initial set" is used informally to represent the time, after about 4 or 5 hours, where the concrete materials are beginning to bond chemically, and at which point the concrete must be undisturbed or irreparable damage to the structure will occur. All consolidation, compaction and initial floating (levelling) needs to be complete well before the concrete begins its initial set.