## 9 Effect of Parameters on Performance of Cementitious Self-Healing Agents
Furthermore, the air chambers were among the accelerated environment conditions applied on the undamaged and pre-cracked beams for the flexural strength assessment. The widths of the formed pre-cracks in the samples were 270 mm and 130 mm, which were created both with and without additives. Generally, the binding of monomers via long chains leads to the formation of the polymers. A polymer net layer that heals the cracks is made after the polymer binds \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Ref.** & **Exposure Condition** & **Crack Healing** & **Findings** \\ \hline
[96] & Immersion in water & 0.2 to 0.4 mm & Enhancement in CS and TS by 13.98\% and 35\%, respectively. \\ \hline
[97] & Immersion in water & 0.86 mm & Concretes with CA revealed the maximum self-repairing rates, for the cracks of larger widths up to 0.25 mm. \\ \hline
[98] & Immersion in water & 0.4 mm & For cracks up to 0.40 mm, the corresponding ratio of healing and closing was 0.99 and 0.98 after 42 days. \\ \hline \end{tabular}
\end{table} 
Table 5: Crystalline admixtures based self-healing cementitious materials. with cement particles once they are incorporated into the concrete. The higher viscosity of the polymers enables them to fill the cracks efficiently. The effects of polymers as the autonomous healing agents in concrete have been intensively studied. For example, pellets filled with healing gel and made with polymers were incorporated into concrete to test their healing efficacy [101]. The encapsulation method was used to incorporate the polyurethane capsules into the cracks to fill them using the healing agent. The mechanical properties of the concrete sample were assessed via split tensile and three-point bending tests. An increase in the spit tensile and FS were observed in the samples after curing for a week. The super-absorbent polymers and polyurethane were combined and used as healing agents [53]. The concrete containing acrylate and acrylamide superabsorbent polymer (SAP) was mixed with polyurethane fibers. The CS of the standard concrete was found to be 18% higher than that those made using super-absorbents, thereby demonstrating that the observed improved strength was not an outcome of the polyurethane mixing. When subjected to flexural testing, the crack width in the concrete became 250 mm. The hydration process triggered the generation of calcium carbonate, wherein the swelling of the super-absorbent polymers was catalyzed via the released water inside the formed cracks. Thus, the calcium carbonate healed the cracks by filling them. A study was conducted to determine the influence of acrylate-end capped polymer precursors for healing the cracks in concrete [102]. This was induced via the entry of capsules into the concrete containing epoxy acrylate and polyester acrylate-like chemicals. Elongation caused the damage in the polymer walls when subjected to a load, which was due to the mixing of the concrete specimens with the polyester-based substances and propylene glycol. When the specimen was placed in an alkaline environment, such polymers still do not deteriorate because of their strong self-recovery capacity. The polyester-based healing agent strain limit was below 50% and the width of the formed crack was increased above 50%. The restriction of cement particles and PPG binding was observed via the visual test. In short, the potential of acrylate polymers as healing agents is significant and the type of acrylate-capped precursors determines the self-recovery procedure. Various healing adhesives contained within the microcapsules and mixed with cementitious materials is an upcoming research area [85]. The autonomous healing ability can be generated by combining the cement paste with the polystyrene-divinylbenzene (stn-DVB), diglycidyl ether of biphenyl and epoxy resin (E), and other similar types of adhesive materials. Parameters involving strength can substantially be enhanced via this mix.