The mechanism of frost action in concrete - theory and practical implications

Experiments indicate that the chain of events leading to deterioration of concrete in freezing and thawing cycles originate by the inability of water absorbed on the surface, or held in the smaller pores of concrete, to freeze due to the interaction between the substrate and water. Because the vapor pressure of the supercooled unfrozen water in the pores is greater than that of bulk ice in the surroundings, water migrates from the interior of the concrete to locations, such as large pores or outer surface, where it can freeze. This process results in partial desiccation of the pore in addition to ice lensing and accumulation of water on the surface. Cracking is the result of melting and freezing of the ice lenses or a condition in which redistribution of the water cannot take place. This theory has been utilized for the development of test methods for the assessment of frost resistance of porous materials. Based on these findings, it became possible to develop a novel admixture for the protection of concrete from damages of freezing and thawing. In place of current air entraining admixture, particulate matters with well defined pore structure are added to the plastic mix. The proposed method relies on the action of pre-formed air-voids instead of the formation of air-bubbles in the mixing process. By doing so, the principal cause for the limited reliability of air entrainment by conventional admixture is eliminated.Les exp\ue9riences r\ue9v\ue8lent que la s\ue9quence de faits menant \ue0 la d\ue9t\ue9rioration du b\ue9ton lors des cycles de gel et de d\ue9gel a pour cause l'incapacit\ue9 de l'eau absorb\ue9e en surface, ou contenue dans les petits pores du b\ue9ton, de geler en raison de l'interaction du substrat et de l'eau. La pression de vapeur de l'eau non gel\ue9e continue dans les pores, tr\ue8s froide, \ue9tant plus \ue9lev\ue9e que celle de la glace se trouvant aux alentours, cette eau migrevers des endroits, comme les gros pores ou la surface ext\ue9rieure, o\uf9 elle peut geler. Ce processus entra\ueene, outre la formation de lentilles de glace et l'accumulation d'eau en surface, la dessiccation partielle du pore. La fissuration r\ue9sulte de la fonte et du gel des lentilles de glace ou d'une condition dans laquelle la redistribution de l'eau ne peut se produire. On a utilis\ue9 cette th\ue9orie pour mettre au point des m\ue9thodes d'essai permettant d'\ue9valuer la r\ue9sistance au gel des mat\ue9riaux poreux. Il a \ue9t\ue9 possible, gr\ue2ce \ue0 ces r\ue9sultats, de mettre au point un adjuvant servant \ue0 prot\ue9ger le b\ue9ton contre les dommages du gel et du d\ue9gel. On ajoute au m\ue9lange plastique, au lieu de l'entra\ueeneur d'air utilis\ue9 couramment, des mati\ue8res particulaires ayant une structure de pores bien d\ue9finie. La m\ue9thode envisag\ue9e est bas\ue9e sur l'action devides d'air pr\ue9form\ue9s plut\uf4t que sur la formation de bulles d'air lors du malaxage. Ce faisant, on supprime la principale cause de fiabilit\ue9 limit\ue9e de l'entra\ueenement d'air au moyen d'un adjuvant de type classique.Peer reviewed: YesNRC publication: Ye