Super-Absorbent Polymers Case
Internal curing was originally promoted to reduce autogenous shrinkage and autogenous shrinkage cracking [5–10]. However its potential benefits are numerous. Recent work has demonstrated benefits of internal curing for reducing drying shrinkage, drying shrinkage cracking [11, 12], reducing the likelihood of thermal cracking [13,14], and improved plastic shrinkage cracking resistance [15]. Internal curing can also improve the freeze–thaw resistance, increase the resistance to fluid absorption [5, 16, 17] and reduce ion diffusion [18] in concrete. It is becoming increasingly clear that internal curing has great potential for the concrete industry to create a longer lasting more sustainable product. Additionally, it is well known that the pozzolanic reaction of finely divided alumina-silicates with calcium hydroxide liberated as cement hydrates is dependent upon the availability of moisture. It is mean that internal curing can also be beneficial for the pozzolanic reaction by supplying enough water.
The most popular methods of internal curing for concrete are using water-saturated aggregates and super-absorbent polymers (SAPs). Unfortunately, because of strict requirements on mechanical behavior and the maximum size of aggregate, only the SAPs have been proposed to be used as an internal curing agent to mitigate the autogenous shrinkage of UHPC up to now. It has been shown that the technology also works in practice. However, SAPs may easily make the concrete heterogeneous, because it will leave voids even as big as 600 ÎĽm, equal to the maximum sand size in concrete, which might negatively influence the properties of UHPC.
In order to meet the requirement of HPC/UHPC (low porosity and permeability), different kinds of cement replacement materials are usually added to them. Silica fume is one of the most popular pozzolanas, whose addition to concrete mixtures results in lower porosity, permeability and bleeding because their oxides (SiO2) react with