Concrete sleepers cracked due to delayed ettringite formation have been exposed to fatigue loading. The applied load has been varied between 20 and 62,5 kN where 62,5 kN corresponds to an axle load of 25 tons. 6 of 13 tested sleepers failed after 223 to 136 670 load cycles. 7 of 13 sleepers managed to carry more than 2 million load cycles, which is equivalent to train traffic for about 7 years. The most common type of fracture is bond failure between the wires and the concrete. It is not possible to determine the quality of the bond strength through visual inspections since no relation between the outer and the inner crack pattern has been found. All tested sleepers were classified as red sleepers (severe cracking).

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.

Avdelningen för konstruktionsteknik vid Luleå tekniska universitet (LTU) har på uppdrag av Banverket utfört undersökning av spruckna betongsliprars bärförmåga. I rapporten redovisas resultat, provning och utvärdering av bärförmågan för uppspruckna respektive ej uppspruckna järnvägssliprar av betong. Uppsprickningen tros bero på s.k. försenad ettringitbildning. De sliprar som provats är: 13 spruckna betongsliprar tillhörande klass 1(röda sliprar) 11 delvis uppspruckna betongsliprar tillhörande klass 2 (gula) 4 ej spruckna betongsliprar tillhörande klass 3 (gröna) De prov som utförts är: Böjprov i mittsnitt Böjprov i rälläge Dragprov av befästning (horisontalkraftskapacitet) Kontroll av sliprarnas betonghållfasthet I rapporten redovisas även hur den visuella inspektionen och klassificeringen av sliprarna utförts. Dessutom presenteras möjliga brottmekanismer för befästningarna när de belastas horisontellt. Målet med provningarna har varit att få en uppfattning om hur uppsprickningen påverkar bärförmågan. Resultaten från försöken har jämförts med beräkningar enligt gällande norm. Försöksresultaten visar att ett fåtal sprickor inte påverkar bärförmågan nämnvärt utan det är först när ett väl utvecklat spricksystem utvecklats som bärförmågan avtar avsevärt. Alla gröna och gula sliprar uppfyller i stort sett uppställda krav och även huvuddelen av sliprarna i klass 1, dvs. röda sliprar, har tillräcklig bärförmåga, med en brottsäkerhetsfaktor som varierar mellan 1,65 och 2,13 (böjprov i rälläge). Det är främst när långa längsgående horisontella sprickor uppträder som en väsentlig reduktion i bärförmåga uppträder. Dessa sprickor finns på ca hälften av de röda sliprar som provats (8 av 13).

This report is a review of literature in the area of optical fibre sensors. The report is mainly directed against optical fibre sensors for civil engineering structures but is also include a short and basic theory for fibre optics and a brief review of different kinds of sensors

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.

This licentiate thesis consists of three papers, A-C. In Paper A the consequence of using self-compacting concrete for civil engineering applications regarding the fresh and young stage and possible consequences on production techniques are studied. This study includes an investigation and evaluation of production techniques for a full-scale project, and an examination of fresh and hardening concrete properties for SCC where influences from different ingoing materials are investigated. The outcome from the project was satisfactory. In paper B various concrete mixes have been examined in order to find possible relations between workability tests and rheological parameters in order to make it possible to classify a fresh self-compacting concrete mix according to rheological properties. In paper C load carrying capacities of cracked as well as un-cracked concrete railway sleepers have been investigated. The cracking is believed to be caused by delayed ettringite formation.The tests show that 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 significant.

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.