Application of encapsulated superabsorbent polymers in cementitious materials for stimulated autogenous healing

Abstract

Superabsorbent polymers have shown potential for use in mortar and concrete as self-healing agents. The main drawback is, however, that these superabsorbent polymers also absorb mixing water during the preparation and casting of mortar or concrete, leading to a loss in workability. To avoid the absorption of mixing water, superabsorbent polymers were coated using a fluid bed spraying process. The barrier coating consisted of three successive coating layers: polyvinylbutyral as primer/wetting layer, cyclo-olefin copolymer as a barrier layer and a sol-gel derived zirconium-silicon oxide as an adhesion-promoting topcoat layer. The coated SAPs were characterized, and their swelling determined to quantify the delay in uptake of water and Ca(OH) 2 solution. The last was considered as the most important, as the SAPs will finally be applied in mortar or concrete having a pore solution with high pH. The results showed that swelling could be delayed to a large extent, but for a short time. Results showed that the selfsealing efficiency of mortars was not affected by coating the SAPs. Moreover, due to the reduced uptake of mixing water, the strength reduction, noticed when uncoated SAPs were added to the mortar, could partly be compensated.

Effect of submicron admixtures on mechanical and self‐healing properties of cement‐based composites

“…The water absorption capacity of these SAPs in DW and CS followed a similar trend as the maximum amount of water absorbed was higher in the case of DW than in the case of CS for all SAPs, a behavior which is in accordance with literature . Consequently, it is concluded that when SAPs are incorporated in cement as admixtures it is preferable for them to be directly added in cement pastes where the values of iconicity and pH are high, thus suppressing their initial swelling during mixing, as also found in literature . Nevertheless, significant differences were observed among the different SAPs .…”

“…This fact can be assigned to both the rigidity of the inorganic shell and to its uniform and solid formation. Should there have been defects in the inorganic shell, in means of cracks, it is believed that the organic core would have swollen fully outside the inorganic shell, causing the structure deterioration of the SAP particles as reported in literature . Τhe EDS analysis confirms the successful encapsulation of the polymeric core into the inorganic shell due to the presence of silicon and calcium elements in the SAPs of P(MAANa‐co‐EGDMA)@SiO 2 (Si content 6.88 wt%) and P(MAANa‐co‐EGDMA)@CaO‐SiO 2 (Si content 14.33 wt.% and Ca content 13.70 wt.%), respectively.…”

“…In cementitious materials of early age, SAPs release water they have absorbed gradually during cement setting and hardening thus mitigating autogenous shrinkage and enhancing prolonged hydration reactions which contribute to the densification of the cement microstructure and thus to the improvement of the structure durability . SAPs have also been used in cement as additives to stimulate autogenous self‐healing/sealing behavior when cracks are introduced in concrete structures . As water penetrates the formed crack, it is absorbed by SAPs which on one hand swell filling the crack volume (self‐sealing behavior) and on the other hand stimulate further hydration reactions and calcium carbonate precipitation (self‐healing behavior) according to the mechanisms that have already been explained for autogenous self‐healing/sealing in cementitious materials earlier …”

“…SAPs have also been used in cement as additives to stimulate autogenous self‐healing/sealing behavior when cracks are introduced in concrete structures . As water penetrates the formed crack, it is absorbed by SAPs which on one hand swell filling the crack volume (self‐sealing behavior) and on the other hand stimulate further hydration reactions and calcium carbonate precipitation (self‐healing behavior) according to the mechanisms that have already been explained for autogenous self‐healing/sealing in cementitious materials earlier …”

“…Nevertheless, there are still great challenges reported in literature regarding the SAPs/cement composites: (1) the process followed for their incorporation in the concrete mix as well as the decrement in the mixture's workability, (2) the preservation of their ability to absorb and release water multiple times and specifically upon crack formation so that a self‐healing/sealing event will take place, (3) the macropore formation in the produced specimens due to the absorbing/desorbing behavior of SAPs during and after the mixing procedure which leads to the degradation of their mechanical properties, and (4) the lack of adhesion between the phases of the cement matrix/SAPs interface which could result in the development of additional defects acting as stress inducers.…”