The behavior of cement-based materials is manipulated by chemical and physical processes at the nanolevel. Therefore, the application of nanomaterials in civil engineering to develop nano-modified cement-based materials is a promising research. In recent decades, a large number of researchers have tried to improve the properties of cement-based materials by employing various nanomaterials and to characterize the mechanism of nano-strengthening. In this study, the state of the art progress of nano-modified cement-based materials is systematically reviewed and summarized. First, this study reviews the basic properties and dispersion methods of nanomaterials commonly used in cement-based materials, including carbon nanotubes, carbon nanofibers, graphene, graphene oxide, nano-silica, nano-calcium carbonate, nano-calcium silicate hydrate, etc. Then the research progress on nano-engineered cementitious composites is reviewed from the view of accelerating cement hydration, reinforcing mechanical properties, and improving durability. In addition, the market and applications of nanomaterials for cement-based materials are briefly discussed, and the cost is creatively summarized through market survey. Finally, this study also summarizes the existing problems in current research and provides future perspectives accordingly.

Cracking caused by shrinkage deformation of cement-based materials at early age is a major problem leading to material failure in restrained conditions. Carbon nanotubes (CNTs) are incorporated into cement-based materials, and the autogenous shrinkage and crack resistance of the new composite materials obtained by linear shrinkage and ring tests are studied to solve the destruction of the materials caused by the shrinkage of cement-based materials. The results showed that addition of CNTs significantly inhibited the autogenous shrinkage of cement-based materials with maximum reduction rate above 40%. CNTs also significantly improved the cracking resistance of cement-based materials. The optimal effect was noticed at CNTs content of 0.1 wt%. The incorporation of CNTs not only inhibits the autogenous shrinkage of cement-based materials, but also inhibits the drying shrinkage of cement-based materials to some extent. Therefore, carbon nanotubes have the potential to solve the destruction of materials caused by shrinkage of cement-based materials.

Tensile creep is an important factor affecting the early cracking resistance of concrete. The tensile creep model can effectively predict the development of tensile creep. In order to establish an appropriate tensile creep model, a temperature–stress testing machine (TSTM) was employed to test the development of temperature, deformation and restraint stress of benchmark concrete and concrete mixed with the MgO under different temperature curing modes. The development law of early age stress, strain and creep was analyzed via the test data of the TSTM. The early age tensile creep of concrete was predicted with the existing Kelvin creep model. The effect of variable temperature on creep was considered in this study, and an improved Kelvin creep model was proposed. The prediction accuracy of the two models was compared and analyzed. The results indicate that MgO has little influence on the creep and specific creep of concrete. The early age cracking resistance of MgO concrete is better than benchmark concrete. The improved Kelvin model based on the microprestress-solidification (MPS) theory predicts the early tensile creep of concrete more accurately in variable temperature conditions. These are significantly helpful for the application of the MgO expansion agent in dam engineering.

Concrete face rockfill dam (CFRD) is a commonly used and cost-effective type of dams. However, random cracks are often seen in the face slab concrete (FSC) of a CFRD during construction, largely due to the shrinkage caused by concrete temperature gradients, drying, and cementitious hydration. This study aims to improve the cracking resistance of FSC by using shrinkage compensating and cracking control materials. In this study, 5.0% by weight MgO-type expansive agent (MEA) or 0.1% by weight carbon nanotube (CNT) was added to a reference FSC (FSC-REF) selected from a CFRD. Fresh and hardened state properties of the developed concrete were tested. Different properties such as hydration heat, capillary pressure, mechanical properties at various ages, drying and autogenous shrinkage, thermal expansion coefficient (CTE), pore structure, and cracking resistance at early age of the FSC mixes (FSC-REF, FSC-MgO, and FSC-CNT) were determined. The results showed that the CNT addition lowered the capillary pressure and reduced the risk of plastic shrinkage cracking, while it also reduced drying and autogenous shrinkage of FSC. The addition of both CNT and MgO had little influence on the heat of hydration of FSC, but these slightly improved the axial tensile properties of FSC. CNT reduced the thermal expansion coefficient of FSC, whereas MgO increased it. Both CNT and MgO decreased the total porosity of the FSC, and the CNT addition significantly reduced the number of mesopores. The temperature-stress test results showed that MgO/CNT improved the cracking resistance of the FSC at early age under both temperature matching curing mode and constant temperature curing mode. Based on measured properties, CNT can be considered a promising additive for cracking control of FSC.

The creep of face-slab concrete in a rockfill dam is critical for determining the restrained stress and cracking resistance of the concrete at an early age. In this article, the mix proportion of the face-slab concrete for a rockfill dam under construction without any cracking resistance additive was taken as the reference concrete (called JC) mix proportion. The carbon nanotubes (CNTs) and magnesium oxide expansion agent (MEA) were incorporated into JC to prepare face-slab concretes called NC and PC, respectively. The temperature–stress tests under temperature matching curing (TMC) and constant temperature curing (CTC) modes were conducted on these three kinds of concretes to investigate the effects of CNTs and MEA on the early-age creep properties of the face-slab concrete under variable stress conditions. The results showed that the creep performance of NC concrete under CTC mode was lower than that under TMC mode. Combined with mercury intrusion porosimetry test results, the mechanism of the effect of CNTs and MEA on creep was analyzed. The results showed that the temperature change may lead to the CNTs debonding from the cementitious matrix or matrix cracking for the NC concrete. The incorporation of CNTs can increase the early-age creep and improve the cracking resistance of concrete.