Effect of initial curing period on the behavior of mortar under sulfate attack.

• Effect of initial curing period on the behavior of mortar under sulfate attack was systematically investigated. • Relationships between compressive strength and other mechanical properties considering initial curing age are proposed. • Initial curing for 14 days can ensure the development of mechanical strength, mass growth rates and linear expansion rates. The infrastructures in the ocean and salt lake areas are usually subjected to sulfate attack shortly after casting. But the influence of early exposure is unclear yet. This study aims to evaluate the influence of early exposure on mortar properties under sulfate attack and to identify the degradation mechanism under this condition. The mortar specimens with different initial curing periods (1, 3, 7, 14 and 28 days) were immersed in 10% Na 2 SO 4 solution for equal time periods (60, 90, 150, 240 and 360 days). Evaluation of the influence of early exposure on mortar behavior under sulfate attack was based on changes in physical properties and mechanical strengths. The degradation mechanism of the mortar specimens was analyzed by X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS). The results showed that the shortening of the initial curing period led to more sulfate ions penetrating into the specimen, resulting in more serious surface spalling, higher expansion rate and mass growth rate, lower mechanical strength. Microscopic images showed that the cement matrix of the early exposed specimen was much looser. In addition, the relationships between compressive strength and other mechanical strengths considering the initial curing period were established and fitted reasonably well with other data sources. [ABSTRACT FROM AUTHOR]