An alkali such as wet Portland cement can stay on your skin for several hours before you feel the chemical burn. Acidity and alkalinity are measured on a pH scale. Adding an acid to an alkali tends to neutralize its pH. Adding vinegar to cement water can drop the pH from 12 to 8. But it also generates heat. Buffers may be a better choice than vinegar.
Buffers neutralize both acids and alkalies and generate less heat.
Commercial products are marketed for neutralizing the pH of Portland cement products on the skin. Neutralite is a buffering solution. Mason's Hand Rinse is an acidic rinse. In theory, either product or another similar product could be helpful if it neutralizes cement residue on the skin surface. Wear gloves and practice good hygiene.