Expansive stress induced by dedolomitization of dolostone-particle compacts in NaOH solution: Implications for expansion due to alkali-carbonate reaction in concrete

Alkali-carbonate reaction (ACR) in carbonate aggregates can impair concrete durability, but whether dedolomitization itself can generate expansion remains controversial. This study investigated dedolomitization-induced expansive stress using dolostone-particle compacts exposed to 1 mol/L NaOH solution at 60 °C under an initial axial pressure of 5 MPa. Stress evolution in the NaOH-cured compacts exhibited a dormant period followed by rapid growth, reaching 113.9 MPa at 250 days, while the water-cured compact showed no measurable stress growth, indicating that stress development was associated with dedolomitization under alkaline curing. XRD and FTIR confirmed progressive dedolomitization and the formation of brucite and calcite, and the degree of dedolomitization reached 97.2% at 250 days. SEM and pore-structure measurements showed that the products formed polycrystalline aggregates with abundant intercrystalline pores. Quantitative analysis indicated that although dedolomitization caused a stoichiometric decrease in absolute solid volume, the newly formed pore-bearing product skeleton volume was about 17.5% greater than that of the reacted dolomite. The porosity of the product zone was approximately 18.6%, with pore size mainly ranging from 3 to 60 nm. The absence of measurable stress during rewetting ruled out water-uptake swelling of the products as the primary cause. Combined with the confined reaction environment, pore-bearing product structure, and continued stress development, the results support crystallization pressure as the most plausible explanation for the stress generation in compacts. The results also support a four-stage mechanism involving early accommodation in packing voids, progressive loss of accommodation space, crystallization-pressure generation in confined regions, and stress transfer through increasingly connected products. These findings show that dedolomitization under restraint can independently generate expansive stress in dolostone-particle compacts and provide mechanistic insight relevant to ACR-related deterioration in concrete. • Dolostone-particle compacts developed expansive stress up to 113.9 MPa in NaOH. • Stress evolution showed a clear dormant-then-rising pattern in the compacts. • The product skeleton volume exceeded the dolomite volume by 17.5%. • Crystallization pressure is the most plausible source of expansive stress. • A four-stage mechanism is proposed for stress development in compacts.