Crack mitigation in concrete : superabsorbent polymers as key to success?

Cracking is a major concern in building applications. Cracks may arise from shrinkage, freeze/thawing and/or structural stresses, amongst others. Several solutions can be found but superabsorbent polymers (SAPs) seem to be interesting to counteract these problems. At an early age, the absorbed water by the SAPs may be used to mitigate autogenous and plastic shrinkage. The formed macro pores may increase the freeze/thaw resistance. The swelling upon water ingress may seal a crack from intruding fluids and may regain the overall water-tightness. The latter water may promote autogenous healing. The use of superabsorbent polymers is thus very interesting. This review paper summarizes the current research and gives a critical note towards the use of superabsorbent polymers in cementitious materials

Mechanical and self-healing properties of cementitious materials with pH-responsive semi-synthetic superabsorbent polymers

Cracks are one of the main problems in mortar and concrete leading to need of reparations and additional costs. One of the recent innovative solutions are superabsorbent polymers (SAPs). SAPs can swell up to several hundred times their own weight, can block the cracks and aid in healing them. Polysaccharides can offer a more sustainable alternative for synthetic SAPs. Functional monomers have been combined with cross-linkable methacrylated polysaccharides to incorporate them in the polysaccharide networks. These polymers have been chemically characterized in previous research by measuring among other their moisture and swelling capacity, where the pH-responsiveness leads to better control of these parameters. The current manuscript deals with the effect these polymers exhibit on the bending and compressive strength of mortar samples on the one hand and on the crack closure and self-healing of cracks on the other hand. The obtained results have been benchmarked with commercial SAPs and indicated that methacrylated alginate combined with acrylic acid, both with high as well as low degree of substitution gave rise to a strong self-healing capacity. They did induce a substantially lower effect on the compressive strength of mortars compared to commercial SAPs. Methacrylated chitosan combined with dimethylaminopropyl methacrylamide also gave very promising self-healing results, coming close to those of the best commercial SAP, although they induced a slightly more severe effect on the mortar strength than this commercial polymer

Use of methacrylated alginate for self-healing concrete

Superabsorbent polymers (SAPs) are cross-linked networks able to take up aqueous sdoialupteiorsn,s f ourp b tioo mseedveicraall phuurnpdorseeds taimnde sa gthrieciur lotuwranl wuseeig. hRt.e Tcehnetyly a, rteh euys headv neo fwouandda yths einir way in concrete-related applications. The presence of cracks endangers the durability of concrete. A possibility to stimulate self-healing of cracks is the addition of such a SAP. Upon crack formation, these SAP particles will absorb incoming water and swell, thereby closing the fracture and preventing further infiltration. When the SAP then slowly releases the absorbed water to the surrounding cement particles, it will aid the autogenous healing. One of the major issues is the negative impact these SAPs have on the compressive strength of mortar. The present work reports on the development and the characterization of SAPs based on a polysaccharide (i.e. methacrylated alginate, algMOD) combined with acrylic monomers acrylamide (AM) and/or acrylic acid (AA), with a variation of the degree of methacrylation of the algMOD applied. This is useful to study the effect of the density of the cross-linked network when incorporated in mortar. The resulting materials were characterized in depth using ATR-FTIR spectroscopy, high resolution magic angle spinning (HR-MAS) 1H-NMR spectroscopy, dynamic vapour sorption (DVS) experiments (to assess moisture uptake capacity) and optical microscopy. The influence on the mortar mixtures was examined by flexural and compressive tests. Finally, the effect on the self-sealing and -healing efficiency was tested. The SAPs showed a swelling capacity up to 600 times their own weight. Especially algMOD–AA does not significantly reduce the compressive strength (even upon addition of 1 wt% of this SAP versus cement weight). AlgMOD–AA also shows a very promising self-sealing and -healing behaviour and can be considered a very interesting and relatively cheap solution to seal and heal cracks in concrete

Bio-based pH-responsive superabsorbent polymers for self-healing cracks in concrete

Cracks endanger the durability of concrete. Introducing a superabsorbent polymer (SAP) during concrete mixing can create a self-sealing and -healing construction. SAPs are able to take up aqueous solutions up to several hundred times their own weight. Bio-based SAPs starting from polysaccharides have gained increasing interest in recent years due to their biocompatibility, non-toxicity and low price. The use of pH-responsive SAPs can also be extremely useful as they should only swell more upon crack formation and less during mixing of the SAPs in the concrete. The present work describes the development and the characterization of SAPs based on methacrylated polysaccharides (alginate and chitosan) combined with pH-responsive monomers dimethylaminoethyl methacrylate (DMAEMA) and dimethylaminopropyl methacrylamide (DMAPMA). The materials exhibited a high moisture uptake capacity up to 120% of their original weight with a negligible hysteresis. The pHresponsive swelling behavior was studied in aqueous and cement filtrate solutions with a varying pH. Chitosan combined with DMAEMA or DMAPMA showed the targeted pHresponsive swelling. Chitosan combined with DMAPMA also showed a limited compression strength reduction and a promising self-sealing and -healing behavior and could thus be considered as a very interesting future solution to seal and heal cracks in concrete

The contribution of elastic wave NDT to the characterization of modern cementitious media

To mitigate autogenous shrinkage in cementitious materials and simultaneously preserve the material’s mechanical performance, superabsorbent polymers and nanosilica are included in the mixture design. The use of the specific additives influences both the hydration process and the hardened microstructure, while autogenous healing of cracks can be stimulated. These three stages are monitored by means of non-destructive testing, showing the sensitivity of elastic waves to the occurring phenomena. Whereas the action of the superabsorbent polymers was evidenced by acoustic emission, the use of ultrasound revealed the differences in the developed microstructure and the self-healing of cracks by a comparison with more commonly performed mechanical tests. The ability of NDT to determine these various features renders it a promising measuring method for future characterization of innovative cementitious materials

Effect of the drying technique on the sorption properties in cementitious materials

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INDUÇÃO DE OVULAÇÃO COM SWAB VAGINAL EM GATAS DOMÉSTICAS E SEUS EFEITOS SOBRE A MORFOLOGIA UTERINA

A ovulação em gatas é induzida por um reflexo neuroendócrino atribuído à estimulação mecânica dos receptores sensoriais durante o coito. Esta estimulação pode ser simulada com auxílio do swab vaginal, desencadeando a pseudogestação. Objetivou-se verificar a eficiência da indução de ovulação com swab, a fim de estabelecer um tratamento contraceptivo natural para felinos domésticos, bem como os efeitos sobre o útero do uso repetido dessa técnica. Na primeira fase do trabalho, foram avaliados 12 animais em três ciclos estrais consecutivos. No primeiro ciclo (T1), houve estimulação vaginal com swab. No segundo ciclo (T2), foi utilizado macho vasectomizado para cópula. No último ciclo (T3), a ovulação foi acompanhada sem estímulo (controle). Na segunda etapa do trabalho, 13 gatas foram submetidas a sucessivos estados de pseudogestação com intuito de verificar os efeitos da estimulação mecânica sobre o útero. A confirmação da ovulação em todas as etapas do trabalho foi realizada por meio da mensuração dos níveis de progesterona. A estimulação vaginal com swab apresentou resposta similar à obtida por monta natural (P>0,05). Algumas gatas apresentaram modificações uterinas discretas; no entanto, nenhum desses achados foi considerado de relevância patológica. Desta forma, a indução de ovulação com swab mostrou-se segura e sem efeitos colaterais expressivos.Palavras-chave: contraceptivo; estro; felinos; ovulação

Role of the surface chemistry of the adsorbent on the initialization step of the water sorption process

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