Delayed-Expansion MgO in mass concrete for Thermal-Stress control in arch dams: A comprehensive review and roadmap for Vietnam

Tóm tắt

Temperature cracking poses a major challenge in arch dams and other massive concrete structures. During cement hydration, heat accumulation followed by cooling creates tensile stresses that may exceed the material’s tensile strength, leading to cracking and structural weakening. For arch dams, where compressive integrity is essential to transfer loads to abutments, even small thermal cracks can endanger global stability. Magnesium oxide (MgO) has been proven over decades to be an effective internal expansive agent for controlling thermal stress in mass concrete. Its delayed hydration to magnesium hydroxide [Mg(OH)₂] generates gradual expansion that compensates for thermal contraction during cooling. This review summarizes mechanisms, laboratory results, field experiences, and modeling of MgO expansion, emphasizing its application in arch dams. Studies from projects such as Baishan, Qingxi, and Three Gorges show that 3-6% MgO can reduce peak thermal stress by up to 40% and crack density by about 50%. Microstructural analyses confirm a denser matrix and improved durability, while numerical models indicate lower tensile stress and higher stability. For Vietnam’s hydropower projects, this paper proposes applying MgO-based temperature-stress control through optimized dosage, particle-size refinement, and long-term validation to develop future TCVN standards for mass concrete in arch dams.