This study investigated the frost-induced deterioration of C-S-H gel and pore structure in young cement paste by TGA, FTIR, ²⁹Si-NMR, MIP, and nanoindentation, and analyzed the changes in C-S-H gel and pore structure of frost-damaged paste. For C-S-H gel, frost attack causes the loss of C-S-H gel to be as high as 36.3%, decreases the formation of LD C-S-H, and inhibits the transformation from LD C-S-H to HD C-S-H. It also decreases the mean chain length (MCL) and the degree of polymerization (n_c) of C-S-H gel due to the breakage of Q² silicate chain. Even after re-curing at 20 °C, the mass loss from C-S-H gel still exceeds 15%, and C-S-H gel also has lower MCL and n_c values. For pore structure, after suffering from frost attack, pore size distribution curve significantly moves toward the direction of increasing pore diameter. Gel pore and mesopore are decreased due to the packing of large amounts of unhydrated cement particles and few C-S-H gels formed, while capillary pore and macropore are increased owing to the freezing-induced expansion and ice crystal growth. After re-curing at 20 °C, gel pore, mesopore, and macropore approach the unfrozen level, but capillary pore is still higher than the unfrozen level.

Temperature stress cracking in low-heat cement concrete is a critical issue in hydraulic engineering due to uneven restraints and complex curing conditions in massive structures. This study investigates the early-age thermomechanical behavior of low-heat cement concrete under varying restraint levels (0%, 50%, 75%, and 100%) and curing-cooling regimes by utilizing Temperature Stress Testing Machine. Results show that higher restraint amplifies compressive stress by restricting thermal expansion but reduces cracking stress via stress localization. Cracking temperature difference decreases with increasing restraint but increases with curing age due to microstructural densification and delayed stress relaxation. The ability of concrete to resist cracking is weakened by increased confinement. Under different curing modes, the characteristic parameters of temperature stress under various restraints are not significantly different. The variation in the equivalent thermal expansion coefficient and elastic modulus of concrete is primarily influenced by internal stresses, microstructural changes, and the degree of restraint during curing. Future research should integrate multiple external factors such as ambient temperature, relative humidity, and wind speed, and investigate their synergistic impact with restraints on interlayer properties of dam concrete to refine crack prediction and enhance durability in mass low heat cement concrete.

In this study, 1 mm-thick disk samples of hardened cement paste were carbonated under 60% relative humidity (RH) and a 1.0% CO₂ concentration. Uncarbonated and carbonated samples were impregnated with 2-propanol (IPA) and analyzed by ¹H Nuclear Magnetic Resonance (NMR) relaxometry to quantify the full-scale microstructure changes in hardened cement paste during carbonation process. Pore structure changes during drying and carbonation were discussed based on the mineral composition changes, as determined by X-ray diffraction/Rietveld analysis, and volume changes as measured by length and volume change measurements. Furthermore, this water and IPA ¹H NMR technique enabled the evaluation of volume fraction changes in hardened cement pastes during drying and carbonation, combined with changes in pore structure. In the drying process under 60% RH, gel pore water evaporated, increasing the coarse pore volume, and drying shrinkage was induced. During the carbonation process, calcium carbonates precipitated in coarse pores, thereby increasing the solid volume of cement minerals and decreasing the total pore volume. As C-(A)-S-H gel was decomposed due to carbonation, the volume fraction of C-(A)-S-H and silica gel agglomeration decreased, resulting in the macroscopic carbonation shrinkage in hardened cement paste.

Concrete industry is responsible for approximately 7% of total CO₂ emissions around the globe making it a critical target for decarbonization. This review study evaluates carbon capture, utilization, and storage (CCUS) technologies applicability in concrete industry with a focus on direct air capture (DAC), CO₂ curing, mineral carbonation, and incorporation of carbonated recycled aggregates and alternative binders. Emphasis is placed on the mechanisms of various CCUS technologies, economic feasibility, environmental benefits, mechanical performance, and current challenges in their application and scalability aiming to optimize the structural efficiency, carbon uptake, and cost of concrete structures. Case studies from industrial implementations, such as CarbonCure and Solidia, are analyzed in terms of performance metrics and scale-up potential. Key barriers—such as capture costs, CO₂ transport infrastructure, and durability uncertainties are identified. The study concludes by outlining research gaps and recommending pathways to advance CCUS adoption in concrete through material innovations, standardization, and policy integration in future.