To increase the hydration reaction rate and the amount of hydration products, different types and proportions of acids were mixed into mortars. The effects of the acid type and content on the early compressive strength of cement-based materials and the strengthening mechanism were assessed via X-ray diffraction and Fourier-transform infrared spectrum analyses. The addition of acetic acid or hydrochloric acid significantly increased the compressive strength of mortars at 1 d and 3 d, and slightly increased it at 28 d. With increasing acetic acid content, the strengthening effect increased first and then decreased with the best content at 4%. With increasing hydrochloric acid content, the strengthening effect decreased gradually with the best content at 2%.
