The reactivity of lime refers to how quickly it reacts with water
Specifically, it can also be said that within 10 minutes under standard atmospheric pressure, the number of milliliters of 4N HCI solution consumed by 50 grams of lime in water at a constant temperature of 40 degrees Celsius is defined as the reactivity value of lime

The reactivity of lime depends on its structure, and the structure of lime is closely related to the burning temperature and burning time.
The structures that affect lime reactivity include bulk density, porosity, specific surface area, and crystal grain size of CaO minerals. The smaller the crystal grains, the larger the specific surface area, and the higher the porosity, the higher the lime reactivity and the stronger the chemical reaction ability.
At present, the average value of lime reactivity can generally exceed 300 ml/4N-HCI. The reactivity value of quicklime has major effects on the lime hydration process and final quality of hyated lime.

The difference between active lime and ordinary lime is that it has a large internal specific surface area and a stable bulk density. The internal specific surface area is large, mainly because the crystal grains of CaO are small, 0.2-0.6 microns, and the crystal grains of ordinary lime are 10 microns. The volume density is stable, that is, during the decomposition process of limestone, after releasing about 40% of the total weight of CO2, the volume does not change, while the volume density of ordinary lime shrinks

Determination of lime reactivity
Lime activity is generally determined by acid-base titration
Lime reactivity is an index used to express the hydration reaction rate of quicklime, that is, within a sufficient time, expressed in milliliters of 4mol/L hydrochloric acid consumed to neutralize the Ca(OH)2 produced during the hydration reaction of quicklime.