Disclosed is a composition including an amorphous calcium aluminate with a final lime:alumina molar ratio between lower and upper limits. The amorphous calcium aluminate is a combination including at least: a first amorphous calcium aluminate with a first lime to alumina molar ratio, strictly lower than the lower limit of the predetermined range; and a second amorphous calcium aluminate with a second lime to alumina molar ratio, strictly higher than the upper limit of the predetermined range. The combination includes a first amount of the first amorphous calcium aluminate and a second amount of the second amorphous calcium aluminate, the first and second amounts being determined in such a way that the final lime to alumina molar ratio of the amorphous calcium aluminate, corresponding to the average of the first and second lime to alumina molar ratios weighted by the first and second amounts, is within the predetermined range.