Material development and self-healing capacity of eco-efficient ultra-high performance concrete (EEUHPC)

Doctoral Thesis for PhD degree in Civil Engineering.Ultra-high performance concrete (UHPC) is a promising type of self-compacting steel fiber-reinforced concrete, which exhibits extraordinary performances in its fresh and hardened states. It not only demonstrates ultra-high strength in compression, but also exhibits ultra-high durability characteristics. Since sustainability-related issues have become major priorities in the world ahead in recent years, therefore, a special attention to any product and service, particularly those used with an increasing pace and embrace considerable carbon footprint and substantial economic impacts, such as UHPC with high content of cement and silica fume, would be of great significance. In this scope, this research aimed to develop an eco-efficient type of UHPC as an innovative and high-tech material through partially substitution of cement and silica fume by other pozzolanic industrial-waste materials. Response surface methodology (RSM), as a statistical mixture design tool, was applied in order to create a scientific basis for developing the optimum composition with higher environmental and economic efficiency. The performance of the optimum composition, nominated as eco-efficient UHPC (EEUHPC), was evaluated through standard test methods in its fresh and hardened states. Furthermore, an effective low-energy mixing procedure, with the aim of improved flowability, was introduced. Finally, the autogenic self-healing ability of the material was studied as an important issue regarding the life cycle of the material and its capacity for structural recovery. The tests were carried out in short and long-term life of the material. Effect of different crack widths on self-healing capacity of cracked specimens was investigated as well as influence of steel fibers on energy absorption of samples in post-cracking stage.O betão de ultra elevado desempenho (BUED) é um tipo de betão autocompactável reforçado com fibras bastante promissor e que é dotado de um desempenho extraordinário tanto no estado fresco como no estado endurecido. Este tipo de betão não só apresenta ultra elevada resistência à compressão como, também, é caracterizado por ultra elevada durabilidade. Nos últimos anos as questões relacionadas com a sustentabilidade passaram a ser consideradas prioritárias em todo o mundo. Portanto, passou a ser de importância acrescida garantir especial atenção a qualquer produto ou serviço, em particular os de utilização crescente compreendendo uma considerável da pegada de carbono e impacto económico substancial, tal como o BUED, fabricado geralmente com um teor de cimento e sílica de fumo elevados. Neste âmbito, este trabalho teve como objetivo desenvolver um material inovador e de alta tecnologia, um BUED eco-eficiente, produzido com recurso à substituição parcial de cimento e sílica de fumo por subprodutos industriais com características pozolânicas. A definição das composições foi efetuada recorrendo à metodologia de superfície de resposta (MSR), uma ferramenta estatística que permitiu determinar, com base científica, as composições ótimas, com maior eficiência ambiental e económica. O desempenho da composição ótima, designada BUED eco-eficiente (BUEDEE), foi avaliado por intermédio de ensaios laboratoriais, realizados tanto no estado fresco como no estado endurecido. Além disso, foi também desenvolvido um processo de mistura eficaz e de baixa energia, concebido com o objetivo de melhorar a fluidez. Finalmente, a capacidade de autorreparação autogénea do material foi estudada como uma questão importante relacionada com o ciclo de vida do material e com a sua capacidade de recuperação estrutural. Os testes foram realizados tanto em idades iniciais como a longo prazo. O efeito da abertura de fenda na capacidade de autorreparação dos provetes fendilhados foi avaliado, assim como a influência da presença das fibras metálicas na capacidade de absorção de energia de provetes em estado pós-fendilhado

Ultra-high durable concrete: A way towards safe and durable structures

Durability of construction and building materials is a pivotal issue for any civil engineering project in the context of sustainable development. In this regard, developing any material with improved durability characteristics would be of great significance particularly for infrastructures encountered aggressive environments. Ultra-high performance concrete (UHPC) is one of this promising materials, as a high-tech self-compacting composite material, which shows advanced characteristics such as self-compactness, compressive strength higher than 150 MPa, and exceptional durability performances compared to other kinds of concrete. This material offers variety of sustainable applications. It enables designers to have slim sections with higher strength, ductility and durability for applications such as shell structures, interior and exterior architectural and structural elements in any shape and texture even in high-rise structures and aggressive environments. In this paper, the durability of a specific composition of UHPC was studied. The dense matrix of the designed UHPC exhibited ultra-high durability performance through long-term and intense carbonation and chloride-ion migration tests. As results demonstrated, even after 191 days, no carbonation depth was observed. No chloride depth was also detected after 14 days of being in the chloride solution with maximum voltage of 60 V

High-volume fly ash ultra-high performance concret

Ultra-high performance concrete (UHPC) is a kind of high-tech composite material which shows superb characteristics compared to other kind of concrete such as self-compactness, compressive strength higher than 150 MPa and exceptional durability performances. In this research, compared to known commercially available UHPCs, a more eco-efficient paste for UHPC was developed. In this regard, cement and silica fume, as two main constituents of the prevalent UHPC compositions and particularly with high cost and environmental impacts, were replaced by fly ash (FA) as a waste material up to 25% of cement weight while with 13% and 16% of it the highest fluidity and strength could be achieved. In the next step finer fly ash was studied also. Ultra fine fly ash (UFFA) with mean particle size of 4.48  showed its applicability to be used in UHPC with 20% of cement weight substitution resulting in a paste with 153 MPa strength and 37.5 cm flow diameter. Furthermore, addition of at least 5% silica fume seems to be a prerequisite regarding strength gain of UHPC paste. Metakaoline as another pozzolanic material improved the strength of the paste while reduced the fluidity demonstrating its inability to be applied in UHPC with required high workability criteria.info:eu-repo/semantics/publishedVersio

Random walk forecast of urban water in Iran under uncertainty

There are two significant reasons for the uncertainties of water demand. On one hand, an evolving technological world is plagued with accelerated change in lifestyles and consumption patterns; and on the other hand, intensifying climate change. Therefore, with an uncertain future, what enables policymakers to define the state of water resources, which are affected by withdrawals and demands? Through a case study based on thirteen years of observation data in the Zayandeh Rud River basin in Isfahan province located in Iran, this paper forecasts a wide range of urban water demand possibilities in order to create a portfolio of plans which could be utilized by different water managers. A comparison and contrast of two existing methods are discussed, demonstrating the Random Walk Methodology, which will be referred to as the â On uncertainty pathâ , because it takes the uncertainties into account and can be recommended to managers. This On Uncertainty Path is composed of both dynamic forecasting method and system simulation. The outcomes show the advantage of such methods particularly for places that climate change will aggravate their water scarcity, such as Iran

Eco-efficient ultra-high performance concrete development by means of response surface methodology

The research described in this paper represents a statistically based model with the help of response surface methodology (RSM) aiming to study the applicability of this method to ultra-high performance concrete (UHPC) mixture design and its optimization. Besides, the effects of silica fume, ultra-fine fly ash (UFFA) and sand as three main variable constituents of UHPC on workability and compressive strength as the main performance criteria and responses of this high-tech material were investigated. The models proposed here demonstrate a perfect correlation among variables and responses. Furthermore, through performing a multi-objective optimization, cement and silica fume, as two main constituents of UHPC affecting its eco-efficiency and cost, were substituted by UFFA and sand as much as possible. Finally, an eco-efficient UHPC with cement and silica fume content of 640 kg/m3 and 56.3 kg/m3 respectively and compressive strength and flow diameter of 160.3 MPa and 19 cm was developed.info:eu-repo/semantics/publishedVersio

Effective low-energy mixing procedure to develop high-fluidity cementitious pastes

Preparing a high fluidity paste is a major step in ultra-high performance concrete (UHPC) development with respect to its self-compacting ability as well as its ultra-high strength. In this regard, some experiments have been carried out in order to study various superplasticizer (SP) addition methods and times. Among these procedures, stepwise and delayed methods seem to be more efficient compared to direct addition of SP with or immediately after water addition. However, few studies regarding water addition time and method have been conducted since now. In this research work, the effects of water and SP addition methods on the fluidity of paste were investigated. The results demonstrated that stepwise and delayed water beside delayed SP addition remarkably reduce the flow time. This maximum fluidity was achieved after totally 15 minutes of mixing including 3 minutes after 70% of water addition to powder, as first-part water, 6 minutes after SP addition and finally an extra 6 minutes after second-part water which is 30% of the total water. Based on this procedure, the opportunity for developing self-compacting and durable UHPC could be accessible. Furthermore, using higher content of aggregates and supplementary cementitious materials would be possible due to higher fluidity of the paste which finally results in an eco-efficient UHPC