In cold regions, understanding the freeze-thaw behavior of air-entrained concrete is important for designing durable structures and assessing the remaining service life of existing structures. This study presents a hygro-thermo-mechanical multiphase model that describes the cyclic freeze-thaw behavior of partially saturated air-entrained concrete containing dissolved salt. An equilibrium and a non-equilibrium approach are adopted to model the ice formation, including the freeze-thaw hysteresis, inside the porous network. The model also considers the diffusive and convective transport of the dissolved salt coupled to the freeze-thaw processes. Two examples are presented to verify and highlight the capabilities of the model. The first example shows that the model is capable of reproducing the experimentally observed mechanical response of specimens containing NaC1-solutions of different concentrations. In the second example, a larger absorption of liquid from an external reservoir is obtained with an increasing salt concentration in the reservoir, which is consistent with experimental observations.

Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.

This paper presents an extension of a novel hygro-thermo-mechanical multiphase model for simulation of freezing of partially saturated air-entrained concrete on the structural scale to account for the effect of damage in the material. The model is applied in an example which investigates the extent and severity of frost damage caused by extremely cold climate conditions in a typical concrete wall in a waterway constructed with air-entrained concrete. The results were concluded to comply with observations made in experimental work and testing of freezing air-entrained concrete under exposure conditions similar to those in hydraulic structures. Furthermore, the results indicate that the effect of short periods of time with high rates of freezing was rather small on the obtained damage. Additionally, increasing the depth of the boundary region with an initially high degree of water saturation on the upstream side had also a rather small effect on the damaged zone.

Det är via vattenvägarna som vatten transporteras från reservoaren, förbi dammen och sedan vidare nedströms i en vattenkraftsanläggning. Vattenvägarna vid en vattenkraftsanläggning kan generellt sett delas upp i yttre och inre konstruktioner. De inre vattenvägarna omfattar ett flertal konstruktioner som intag, tilloppstunnel, tilloppstub, intagssump, spiral, sugrör, svallschakt, svallgalleri och utloppstunnel. Dessa konstruktioner är vanligtvis helt eller delvis vattenfyllda vilket medför att de i många fall är svåråtkomliga för inspektion. Det är sällan ekonomiskt försvarbart att torrlägga de inre vattenvägarna enbart för inspektion till följd av det avbrott i elproduktionen som då uppstår. Dock uppkommer emellanåt möjligheten att få inspektera de inre vattenvägarna i samband med driftstopp för reparation, inspektion eller utbyte av de elgenererande delarna.

På uppdrag av Energiforsk har en genomgång av den rapportering som finns från genomförda inspektioner gjorts i ett försök att förbättra kunskapsläget gällande eventuella typskador och nedbrytningsförlopp i de inre vattenvägarna. Insamlingen av underlag har gjorts genom förfrågningar hos ägarrepresentanterna i styrgruppen för vattenkraftens betongprogram inom Energiforsk. Det erhållna underlaget omfattade både besiktningsrapporter och sammanställningar över observerade skador i de inre vattenvägarna för sammanlagt 53 olika vattenkraftverk.

Utifrån analysen av det erhållna materialet i denna studie kunde det konstateras att erosion var den vanligast förekommande skadetypen då samtliga typer av inre vattenvägar beaktas. Dock blev självklart bilden en liten annan i det fall de olika typerna av vattenvägar studeras enskilt även om erosionsskador oftast återfinns högt upp i listan över observerade skador och brister. Tidigare forskning har dock visat att det ofta är en samverkan mellan olika nedbrytningsmekanismer som resulterar i en observerad skada. Av denna anledning är det därför svårt att isolera en enskild nedbrytningsmekanism som ensam är orsaken till att just erosionsskador är den vanligast förekommande skadetypen. Det kunde också konstateras att dokumentationen av genomförda inspektioner och därmed observerade skador och brister i de inre vattenvägarna generellt sett är bristfällig hos flertalet anläggningsägare. Det bör dock poängteras att samtliga tillfrågade anläggningsägare angivit att de genomfört inspektioner men att just dokumentationen från dessa antingen saknas eller är svår att hitta.

Med ledning av resultaten från inventeringen går det att konstatera ett förbättringsbehov i förvaltningen av de inre vattenvägskonstruktionerna. Särskilt stora brister verkar råda på kännedomen om statusen hos långa tillopps- och utloppstunnlar av berg med olika grad av förstärkning. För anläggningar med gemensamma tunnlar för till- eller utlopp kan konsekvenserna av ett större tunnelras kunna vara betydande ur ekonomisk synvinkel i form av långvariga produktionsbortfall. Det rekommenderas att en strategi för hantering av detta utvecklas.

The water is transported by the waterways from the reservoir, past the dam and further downstream in a hydropower station. Generally, the waterways can be categorized to be either of channel-type or tunnel-type. The waterways of tunneltype include a number of different structures such as intakes, headrace tunnels, penstocks, intake sumps, spirals, draft tubes, surge shafts, surge galleries and tailrace tunnels. These structures are usually either fully or partially filled with water, which means that they in many cases are hard to inspect. Moreover, it is seldom financially justifiable to drain the tunnels solely to perform an inspection due to the loss of energy production that this measure entails. However, in connection to stoppage of the energy production to repair, inspect or replace some of the energy-producing parts, an opportunity to inspect the waterways of tunneltype is usually given.

In this study, a review of documentation from inspections of waterways of tunneltypes has been performed on behalf of Energiforsk to improve the state of knowledge regarding common damage types and deterioration mechanisms in this type of waterways. The collection of data has been performed by inquiring data from representatives of the utility companies in the steering committee of the research program for concrete in hydropower at Energiforsk. The obtained material includes both reports from inspections as well as compilations of observed damage in the waterways for a total of 53 different hydropower stations in Sweden.

From the analysis of the obtained material in this study, it could be concluded that erosion was the most common type of damage observed in waterways of tunneltype if all types of such structures are considered. However, the results become a bit different if the different types of structures are studied individually, even though erosion often is observed to be one of the most commonly observed damage types. Previous research has, however, shown that an observed damage often is a consequence of a series of deterioration mechanisms that together cause a degradation of the material. Therefore, it is hard to isolate one single deterioration mechanism that is the only reason why erosion is the most commonly observed damage type in waterways of tunnel-type. Furthermore, it could be concluded that the documentation of performed inspections generally is inadequate at the utility companies and consequently also the documentation of observed damage and defects in the waterways. It should, however, be noticed that all companies stated that they have performed inspections but that the documentation from these is either missing or hard to find.

With results from the study in mind a need for improvement in the management of the inner waterways is obvious. Especially regarding the knowledge on the status of long headrace and tailrace tunnels in rock with different degree of support. For facilities with common head-/tailrace tunnels for several units, the consequences of a larger failure could be substantial in terms of financial losses from no production. It is recommended to develop a strategy for management of inner waterways.

In cold regions where the water surface of a river or lake freezes during the winter, concrete dams may be subjected to a pressure load from the ice sheet. This pressure load may constitute a large portion of the total horizontal load acting on a small dam. From a dam safety perspective, it is important to determine the design value of the ice load. In February 2016, a prototype of an ice load panel was installed on a Swedish concrete dam. The 1x3m2 panel measures the ice pressure with three load cells. In this paper, the ice load measured on the Swedish dam is predicted using a Canadian empirical model, previously developed from a 9-year field program to estimate the ice loads caused by thermal effects and variation in water level. The predictions from the model could not accurately predict the measured ice loads. Since the current understanding of ice load is limited, it is not possible to determine whether the measurement, the model or both are inaccurate.

Understanding the early-age behaviour of concrete is of importance for designing durable concrete structures. To contribute to the improvement of this, a hygro-thermo-chemo-mechanical model is presented that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is based on a multiphase porous media framework, using the Thermodynamically Constrained Averaging Theory (TCAT) as starting point to derive the governing equations of the system. This allows for a systematic treatment of the multiscale properties of concrete and how these develop during hydration, e.g. chemical and physical fixation of water. The proposed mathematical model is implemented within the context of the Finite Element Method (FEM), where all physical fields are solved in a fully-coupled manner. Chosen properties of the model are demonstrated and validated using three experimental results from the literature. Generally, the simulated results are in good agreement with the measurements.

Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.

The purpose of this study is to show the influence and significance of including water filling of air pores when studying moisture conditions in concrete structures cast with air-entrained concrete and in contact with free water. Especially if the aim is to assess the risk for frost damages in different regions of the structure, based on a critical degree of saturation, in order to ultimately perform a service life prediction. A hygro-thermo-mechanical multiphase model that includes the effect of water filling in air pores, recently presented by the authors, is briefly described and applied in two numerical examples. The results show moisture distributions that would not be possible to capture without the air pore filling included in the model. More importantly, the general shape of these distributions complies well with measured distributions in real concrete structures as well as with distributions obtained in laboratory measurements.

Betongkonstruktioner belägna i kalla och fuktiga miljöer riskerar att skadas av frostsprängning under de kyliga vintermånaderna på grundav vattnets nioprocentiga volymsexpansion då det fryser inuti betongen. För att begränsa denna problematik är det vanligt att till exempel dammar, broar och betongvägar byggs med lufttillsatt betong i både Sverige och andra delar av världen. Trots detta observerasfrostskador frekvent i sådana konstruktioner. Det är därför viktigtatt kunna uppskatta när i tiden frostskador förväntas uppkomma i en konstruktion samt kunna bedöma omfattningen av en redan uppkommen skada. För att göra detta, utvecklades numeriska modeller i ett pågående doktorandprojekt vid KTH, finansierat av Svenskt Vattenkraftscentrum (SVC). Doktorandprojektet har som mål att bidra till en förbättring av dessa typer av bedömningar genom att beskriva de komplexa processer som är förknippade med frysning i lufttillsatt betong.

Drying shrinkage of concrete is often estimated using a phenomenological approach where it is assumed that shrinkage is proportional to the change in internal humidity. In this study, a mechanistic approach was used which instead aims to mathematically describe the physical processes of drying shrinkage. Simulations of two laboratory tests were made and compared to results from two models based on the phenomenological approach. The results show that the developed model can describe drying shrinkage of concrete equally well as the phenomenological models but without the need to specify the final drying shrinkage strain.