Invloed van vloeibare kuringsmetodes op plastiese krimpkrake van beton

Visagie, Jurie Wynand (2020-04)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

AFRIKAANSE OPSOMMING: Die kraak van beton is ‘n algemene probleem wat kan lei tot verlies aan duursaamheid, dienslewe en estetiese waarde. Tog is daar verskeie beskikbare maniere om die ontwikkeling van krake te verhoed of te beperk met onder meer die gebruik van verskeie kuringsmetodes en -materiale. Die mees gebruikte metodes onder die verskeie beskikbare kuringsmetodes, is die bespuiting en bevogting van beton met water. Hierdie is egter slegs twee van vele beskikbare metodes gemik op die kuring van vars en verharde beton. Die vorming van krake gedurende die vars staduim staan bekend as plastiese krake aangesien hierdie krake gedurende die plastiese na semi-plastiese fase van beton vorm. Die gevaar van plastiese krake word veral gevind in elemente met groot oppervlakareas wat aan omgewings met hoë verdampingstempo blootgestel is. Die studie ondersoek die invloed van vloeibare kuringsmiddels op plastiese beton. Dit word algemeen aanvaar dat faktore soos krimp, versakking en kapillêre druk die kraak van beton beïnvloed aangesien die faktore oorwegend plaasvind gedurende die stolling van beton. Dit is gedurende die plastiese fase dat dié faktore die meeste deur kuring beïnvloed word. Dit word algemeen aanvaar dat oppervlakkuring die gevaar van plastiese krake verminder indien die middels op die regte tyd, plek en wyse toegepas word. In hierdie studie word beide enkel en veelvuldige toepassings, sowel as drie kuringsmiddels, gebruik om die invloed van kuring op plastiese kraakontwikkeling en die gedrag daarvan te ondersoek. Enkeltoepassing van waterkuring is toegepas op kritieke tye gedurende die ontwikkeling van plastiese krake, naamlik vóór die opbou van kapillêre druk, begin van beduidende krimp, vóór en op die eerste sigbare haarlynkraak, sowel as gedurende die vinnige kraakgroeiperiode. Veelvuldige toepassings van waterkuring is toegepas om die krimp van beton in te perk en sodoende die kraak van beton te verminder of selfs te voorkom. Die gedrag van waterkuring is ook vergelyk met die gedrag van drie kuringsmiddels wat tans in die praktyk beskikbaar is, naamlik ‘n wasemulsie, petroleumharsemulsie en ‘n akrielemulsie. Die kuringsmiddels is toegepas soos voorgeskryf deur die verskaffer. Die studie het bevind dat enige toepassing van kuring die ontwikkeling van potensiële plastiese krake verlig. In hierdie studie is daar bevind dat die kuring net vóór die beduidende groei van krimp optimaal was. Hierdie is bevestig deur die veelvuldige toepassings van kuring wat daarop gemik was om die krimp van beton te beperk. Die veelvuldige kuringstoepassings, gemik daarop om die krimp van beton na 5% van die ongekuurde monster se finale krimpwaarde in te perk, bewys dat oppervlakkrake voorkombaar is. Oor die algemeen is dit bevind dat waterkuring wat té vroeg of té laat na die ontwikkeling van plastiese krake toegepas word, oneffektief is. Al die kuringsmiddels het die kraakarea’s verlaag, terwyl die petroleumemulsie selfs oppervlakkrake voorkom het. Ten slotte, ‘n enkeltoepassing van waterkuring in uiterste omstandighede met hoë verdamping, is nie genoeg om plastiese krake te voorkom nie, veral as die toepassing nie op die regte tyd toegepas word nie. Tog was die veelvuldige toepassing van waterkuring meer suksesvol en is oppervlakkrake voorkom. Die studie wys dat kuring, veral die enkeltoepassing van waterkuring net vóór beduidende krimp, sowel as die veelvuldige toepassing van kuring gemik op die beperking van krimp, moontlik krake kan voorkom in minder ernstige toestande.

ENGLISH ABSTRACT: The cracking of concrete is a common issue which may cause durability, service life and aesthetic concerns. Different means can be implemented to combat the formation of cracks, including various means of curing. The two most commonly used curing is the spraying and/or misting of concrete using water. These, however, are but two of many methods available which can be applied to fresh and hardened concrete. The cracks that occur during the fresh state of concrete are referred to as plastic cracks since these cracks form while the concrete is still in a plastic to semi-plastic state. These plastic cracks occur especially in concrete elements with large surface areas which are exposed to harsh environment conditions with high evaporation rates. This study investigates the influence of liquid curing measures on the cracking of plastic concrete. It is well known that factors such as shrinkage, settlement and capillary pressure affects the cracking of concrete and that these factors predominantly occur during the setting of concrete. It is within the plastic phase that these factors are the most influential and most likely to be altered by curing. It is known that surface curing of concrete mitigates plastic shrinkage cracking when applied correctly and at the appropriate time. In this research both single and multiple water application, as well as three curing compounds, were used to investigate the effect of curing on plastic shrinkage cracking. Single application water curing was spray applied at critical times during the development of typical plastic cracking such as: before the start of capillary pressure buildup, start of significant shrinkage, before and on the first visible surface crack, and during rapid crack growth. Multiple application water curing was spray applied to limit the shrinkage of concrete, aiming to limit or prevent cracking from occurring. Water curing performance was also compared to a wax emulsion, petroleum-based resin and water-based acrylic emulsion curing compounds, all applied at the supplier specified times. The findings of this research showed that any application of curing helps to relieve the associated potential plastic shrinkage cracking of concrete. Optimal water curing application, based on the response of the various mechanisms of plastic shrinkage cracking was found to be just after the start of shrinkage and before any shrinkage-related damage occured. This was confirmed by the limiting the shrinkage using multiple applications. The multiple curing application proved to prevent surface cracking when limiting the shrinkage of concrete to approximately 5%, while even the 5% growth step limitation proved to lower the crack area significantly. In general, water curing done either too early or after plastic cracks have formed, is ineffective. All curing compounds applied, reduced the crack area, with only the petroleum resin-based curing compound resulting in no surface crack formation. Finally, once-off application of water curing in extreme environmental conditions with high evaporation, is not enough to prevent plastic cracking, especially if the application timing is not optimal. Whereas multiple curing application proved to be far more successful and could prevent surface cracking. This research shows that curing, especially single application curing at the start of shrinkage and multiple application curing aimed to limit shrinkage, can prevent cracking in less severe environmental conditions.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108248
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