Performance based concrete mix-design aggregate and micro mortar optimization applied on self-compacting concrete containing fly ash

Sammanfattning: 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.