Cracking of concrete must be avoided during the hardening phase in order to minimize the risk of durability problems in the future, such as corrosion of the reinforcement, water tightness and damages due to frost. Estimation of the risk of early age cracking requires knowledge of the combined effects from temperature development and mechanical behaviour during the hydration. In the present paper, the influence of fly ash on the young concrete behaviour has been investigated. The concrete is based on a Swedish cement aimed for civil engineering structures, and the fly ash is of class F. A comparison of crack risks between concrete containing fly ash in different amounts with concrete without fly ash is presented. Also a previously tested concrete containing limestone filler is considered. The fly ash was added to replace a part of the aggregate, which gives a higher heat evolution. However, a numerical stress analysis showed that the risk for early age through cracking for a typical civil engineering structure is significantly decreased in the mixes containing fly ash. The denotation typical civil engineering structure is used here for concrete structures such as tunnels, bridges, and ramps of common cross-section dimensions. In the case of fly ash added to concrete by a partial replacement of cement, the crack risk will probably be further decreased. For a self-balancing structure of young concrete there is no restraint from adjacent structures, and the temperature and moisture gradients within the young concrete cause self-stresses governed by equilibrium with zero external forces for any cut. The estimated risk for surface cracking on a self-balancing wall or slab was not improved by an addition of fly ash. It is probably an effect of the increased heat development, which most likely counteracts the positive effect of the increased early age creep for concrete containing fly ash. If the heat evolution decreases when cement is partly replaced with fly ash, the use of fly ash might reduce the risk of surface cracks.

This paper presents a numerical tendency model for evaluation of heat and strength development for concrete containing fly ash in different amounts. With the presented model, parameters for heat and strength development calculations in early age can be calculated. It facilitates the possibility to evaluate e.g. form removal times and estimations of need for protection against early freezing for concrete mixes containing fly ash in different amounts

A recently presented numerical tendency model has been applied on an assumed civil engineering structure. With the model parameters for heat and strength development calculations in early age period can be calculated. This paper shows the possibility to evaluate e.g. form removal times and estimations of need for protection against early freezing for concrete mixes containing fly ash in different amounts, with different water-to-cement ratios and at different outer conditions. The tendency model has shown to be a useful tool for production planning for concrete containing fly ash. According to the performed calculations, any replacement of cement with fly ash will significantly influence the young concrete properties. The effect on delayed strength growth increases with the increased amount of fly ash and will also increase for lower temperatures. In addition, the effect from fly ash increases at higher water-to-cement ratios

Självkompakterande betong verkar inte - trots hög andel finmaterial och snabb värmeutveckling - vara mer sprickbenägen i ung ålder än traditionell vibrerad betong. Ytan bör dock täckas eller vattnas för att undvika plastiska krympsprickor.

The load carrying capacity of damaged prestressed concrete railway sleepers has been investigated in order get information about how the cracking influences the remaining load carrying capacity compared to an un-cracked sleeper. The following tests have been performed: bending capacity of the midsection, the rail section, horizontal load capacity of the fastener, control of the concrete properties and fatigue capacity in bending of the rail section. A visual inspection and classification of the damages are also presented. The test results have been compared with calculations according to the Swedish railway code for sleepers and show that railway sleepers are quite robust. Small cracks do not seem to influence the load carrying capacity and it is first when the cracking is very severe that the load carrying capacity is reduced significantly.

The load carrying capacity of damaged prestressed concrete railway sleepers has been investigated in order to obtain information about how the cracking influences the remaining load carrying capacity compared with an uncracked sleeper. The following tests have been performed: bending capacity of the midsection, the rail section, horizontal load capacity of the fastener, control of the concrete properties and fatigue capacity in bending of the rail section. A visual inspection and classfication of the damages are also presented. The test results have been compared with calculations according to the Swedish railway code for sleepers and show that railway sleepers are quite robust. Small cracks do not seem to influence the load carrying capacity and it is first when the cracking is very severe that the load carrying capacity is reduced significantly. Udgivelsesdato: september

This thesis is dealing with the field of self-compacting concrete (SCC). SCC is supposed to fill the form properly and enclose the reinforcement without any external vibration. The fresh properties of such a concrete are thus essential. SCC was first introduced in Japan in the middle of 1980th. Due to the high demands on its fresh properties, the mix-design process is more complex for SCC than for normal vibrated concrete and generally, it has higher content of powder materials, such as cement and mineral additives. In this thesis, a performance based mix-design method is proposed. Performance based means that concrete shall be composed regarding the properties of available materials and due to the properties of the element to be cast. The main objective with performance based concrete mix-design is to utilize the properties of the available materials to increase the cost- effectiveness in concrete production. The main part of the thesis has been to propose how available materials can be combined, due to their specific properties, for further use in concrete. The material selection shall, in addition to the material related properties, be based on the performance of the structural element to be cast. In the thesis, a method to choose an appropriate micro mortar is presented as well as how an appropriate aggregate grading curve can be combined based on material related properties. To fully utilize the potential of the suggested method, a connection parameter between micro mortar and aggregates is introduced. A structured method for how decisions can be made, based on results from micro mortar tests and aggregate optimization tests, to compose a SCC mix that is appropriate for its specific field of application is suggested. SCC has a relatively high content of powder materials. In addition to cement, lime-stone filler or fly ash is often used. Fly ash is an industrial by-product from coal-fired power stations and it has been proven to be a sufficient concrete making material when replacing cement in varying amounts. Swedish concrete producers do not have a tradition in using fly ash in any wider extension because of the lack of nationally produced fly ashes. However, there is an increasing interest to use more fly ash as filler material in concrete in Sweden. Fly ash is a pozzolnaic material, which means that it will influence the young and hardened properties. This thesis contains an investigation of the effect of fly ash on the hardening properties. A numerical prediction model for heat development and strength growth is presented. The prediction model will for instance facilitate the possibility to calculate appropriate form removal times for concrete with different water to powder ratios containing varying amounts of fly ash. In addition, the risk for early thermal cracking of concrete containing fly ash in varying amounts has been investigated. It was concluded that mixes containing fly ash and limestone filler have an increased early-age creep. It was also concluded from a numerical stress analysis that the risk for early age through cracks is significantly decreased for mixes containing fly ash. The estimated risk for surface cracks was not improved by an incorporation of fly ash. The estimated risk for surface cracks for concrete containing limestone filler was significantly lower in comparison to the other tested mixes, i.e. Portland cement concrete and concrete containing fly ash, which might be a combined effect from moderate heat development and increased early-age creep.

Självkompakterande betong (SKB) skall fylla formen och omsluta armeringen utan yttre vibrering. SKB introducerades i mitten av 1980-talet och Japan var pionjärer inom området. För att SKB skall kunna flyta ut ordentligt utan att ballasten separerar så ställs det höga krav på den färska betongen. Den största skillnaden mellan SKB och normal-vibrerad betong nämns ofta som lägre vatten pulver tal, större andel cementpasta, lägre andel grovballast samt inblandning av effektiva superplastiserare. Mycket forskning har bedrivits inom området sedan SKB introducerades för första gången, och flertalet proportionerings metoder har utvecklats genom åren. I den här avhandlingen ges ett förslag på hur man kan välja tillgängligt material på bästa möjliga sätt så att det passar det tänkta tillämpningsområdet, s.k. utförandebaserad optimering. Syftet med utförandebaserad optimering är att tillvarata egenskaperna från det tillgängliga materialet på bästa möjliga sätt.Metodiken bygger på enkla verktyg för att karakterisera egenskaper som är av vikt för den färska betongblandingen. En metodik för finbruksoptimering tillsammans med en metod för hur man kan välja en lämplig graderingskurva föreslås. Resultaten från dessa två kopplas sedan samman med en föreslagen kopplingsparameter, vilken möjliggör en direkt översättning mellan finbruksfasen och den valda graderingen. En strukturerad metod föreslås för hur delmaterialen kan sättas samman utifrån tillämpningsområdet samt hur justeringar kan göras för att förändra de färska egenskaperna. Självkompakterande betong innehåller en relativt hög andel finpulvrigt material, tex. kalkstensfiller, silika eller flygaska. Flygaska är en mineralprodukt som uppstår vid koleldning vid el- och värmeproduktion. Flygaskans sfäriska och släta partiklar i kombination med dess låga densitet har visat sig ha fördelaktiga egenskaper i den färska betongen. Flygaska har inte varit särskilt vanligt vid svensk betongtillverkning, främst på grund liten inhemsk produktion av högkvalitativ flygaska. Intresset för flygaska har dock ökat under de senaste åren. Då flygaska har pozzolana egenskaper så kommer dess inblandning i betong att påverka de unga och mogna egenskaperna.Den här avhandlingen inkluderar en undersökning av flygaskans inverkan på egenskaperna i den unga betongen. En numerisk tendensmodell är etablerad, vilken gör det möjligt att prediktera värme- och hållfasthetsutveckling i en betong innehållande flygaska i varierande mängd samt för varierande vattencementtal. Det möjliggör beräkningar av t.ex. formrivningstid eller åtgärder för att förhindra tidig frysning då flygaska används. Risken för tidiga temperatursprickor hos betong innehållande flygaska har även testats. Resultaten visar att risken för genomgående sprickor minskar signifikant för betong innehållande flygaska i jämförelse med betong tillverkad av endast Portland cement. Risken för tidiga ytsprickor blir dock inte förbättrad med inblandning av flygaska.