but when the sugar content exceeds a very small threshold, often cited at around 0.2% to 1% by weight of the cement, the retardation becomes so severe that the concrete may never properly set or gain adequate strength. The sugar essentially prevents the microscopic crystals from growing and interlocking, leaving behind a weak, unusable slurry instead of the intended durable rock.
1 pound is about .5% well within the necessary amounts, and you do not need to ruin every square foot of concrete to make the structure unusable.