Evaluation and optimization of Ultra-High Performance Concrete (UHPC) subjected to harsh ocean environment: Towards an application of Layered Double Hydroxides (LDHs)
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Layered double hydroxides
Silica fume
Layered double hydroxides
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To get CaTiO3catalyst with high photocatalytic properties,the effect of calcination conditions,on the photocatalytic activity of CaTiO3 was investigated.The calcination conditions included heating rate of calcination precursors,calcination temperature,calcination time and cooling rate of calcination products,The catalyst was synthesized by solid-state reaction method with Ca(NO3)2and TiO(OH)2as raw materials and NaOH as mineralizer.The physical properties of the catalyst were characterized using XRD and SEM.The experimental results showed that the activity increased until reached a maximum,and then decreased with the increasing heating rate of calcination precursors;the photocatalytic activity decreased drastically with the fast cooling rate of calcination products.Moreover,the optimal values of calcination temperature and calcination time were obtained.As a result,the CaTiO3catalysts with high photocatalytic activity can be obtained under an optimized calcination conditions after loading CoO(0.2 wt%)co-catalyst.
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Sodium sulfate
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Layered Double Hydroxides(LDHs) are lamellar mixed hydroxides.Many researchers started to pay attention to the LDHs for its high surface area and anion exchange capacities.And the application of the LDHs become popular.In the paper,we studied the composition,structure,synthesis,characterization and application of the LDHs.
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Abstract Current methods for determining sulfate resistance of fly ash concrete often require several years of testing. An accepted method that can be used to predict sulfate resistance in a few days does not exist. A hypothesis is submitted as a possible step towards development of a comprehensive theory. The sulfate reactivity of fly ash is characterized by its chemical composition. One high calcium fly ash was shown to react similarly to blast-furnace slags. Sulfate resistance of comparable fly ash concretes is shown to correlate with ash composition; therefore, based on chemical composition of fly ash, a sulfate resistance factor R is proposed. The factor is the ratio (C-5)/F, where C is calcium oxide and F is ferric oxide in percent. When R is less than 1.5, a fly ash should improve the sulfate resistance.
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Cement mortar as the basic material and the fly ash and silicon fume as the research object, experiment and research were operated through adjusting the admixture replacing dosage and changing the mixture ratio of silica fume and fly ash. By testing the fluidity and strength and data analysis and discussion, some conclusions are drawn from the analysis, such as: fly ash makes the fluidity increasing with the admixture replacing dosage below 30%, and the fluidity declines with the mixture ratio of silica fume and fly ash increasing. 7d compressive strength decreases with the admixture replacing dosage increasing, 7d compressive strength increases slowly with the mix ratio of silica fume and fly ash. With the mix ratio of silica fume and fly ash increasing, 28d compressive strength of mortar also increases, and proper mix ratio of silica fume and fly ash is 1:1.
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The effects on the low-grade concrete workability,strength and shrinkage of single fly ash,double-doped silica fume fly ash /silica fume were studied,the results show that fly ash and silica fume can improve the workability of fresh low-grade concrete and silica fume can increasing changes of concrete shrinkage in short term,resulting in early cracks,double-doped fly ash /silica fume can effectively improving the compressive strength of low-grade concrete in such a short term.
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A quantitative understanding of the efficiency of fly ash as a mineral admixture in cement-based materials is essential for its effective utilisation. The present paper is directed towards a specific understanding of the efficiency of fly ash in cementitious materials systems by considering the independency of fly ash and its dependency on the characteristics of the cementitious materials system. A new method of quantitatively evaluating the strength effect of fly ash is proposed, in which two parameters, the strength-effect index and the strengthening factor, are employed to study strength development in fly ash mortars and concretes and to further analyse the influences of water to binder ratio (w/b) and the replacement amount of fly ash on strength. Results indicate that the strength effect of fly ash in mortar systems is different from that in concrete; the strength effect of fly ash varies with both amount of fly ash and w/b. Furthermore, in a concrete system, two different optimal w/b ratios are used to maximise the strength-effect index and the strengthening factor of fly ash, respectively. An optimum amount of fly ash exists for an optimal unit strength-effect index in concrete. It is shown that the method presented in this paper is reasonable and effective in assessing the efficiency of fly ash. This information will strengthen the effective utilisation of fly ash in cementitious materials and design of fly ash concrete.
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It was studied that the effect of the addition of silica fume and flyash on concrete strength and fluidity and the rule of 28d strength of concrete with silica fume and fly ash as well as the relation of the increment of later stage strength of concrete.Using grade P.O.42.5 ordinary portland cement,medium sand,5～25mm broken stone,silica fume,flyash,proper quantity of NF-2-6 retarding high effect water-reducing agent,water cementitious materials ratio 0.28,5% of silica fume and 5%～15% of fly ash or 10%～15% of silica fume and 5%～20% of fly ash,C80 high performance concrete can be prepared;and water cementitious materials ratio 0.31,15% of silica fume,5%～10% of fly ash were adopted,C80 high performance concrete can be prepared also.The reference formula for concrete commercial mix can also be educed.
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