Strength Of Fly Ash Research Articles

Microstructure Study on Optimization of High Strength Fly Ash Based Geopolymer

The compressive strength and microstructural characteristics of fly ash based geopolymer with alkaline activator solution were investigated. The sodium hydroxide and sodium silicate were mixed together to form an alkaline activator. Three parameters including NaOH molarity, mix design (fly ash/alkaline activator ratio and Na2SiO3/NaOH ratio), and curing temperature were examined. The maximum strength of 71 MPa was obtained when the NaOH solution of 12M, fly ash/alkaline activator of 2.0, Na2SiO3/NaOH of 2.5 and curing temperature of 60°C were used at 7th days of testing. The results of SEM indicated that for geopolymer with highest strength, the structure was dense matrix and contains less unreacted fly ash with alkaline activator

Effect of Metakaolin Mixed with Fly Ash on the Strengths of Concrete

This paper studies the effect of metakaolin mixed with fly ash on the compressive strength of concretes. The results show that in order to improve the property and reduce the price of metakaolin, metakaolin can be used with fly ash together, and the optimal content of metakaolin in concrete is not bigger than 10%. The content of metakaolin affects the early compressive strength of fly ash concrete significantly. When the water-bind ratio is 0.31 and the amount of metakaolin and fly ash is 35%, which the metakaolin content is 8%, the compressive strength can increase up to 54MPa; when the mixed additive and metakaolin are 25% and 8%, the compressive strength reaches 68MPa.

Effects of Modified Gypsum on Autoclaved Products Strength

The modified tests are put on by selecting gypsum from different habitats, using doping technology and calcination technology. The tests results can be summarized as follows. Different kinds of gypsums have different effects on the strength of fly ash autoclaved products, and so do the gypsums collected from different habitats. Low-purity gypsums helps to improve the strength of autoclaved products. Low-purity scatter of gypsum can be achieved by means of natural doping and artificial doping, and natural doping is better. Calcined gypsum could increase the strength of fly ash products within a certain range, and the best calcining temperature is about 650°C.

Permeability of Anti-Chloride Ion of Fly Ash Recycled Concrete

Adding fly ash to recycled concrete with super-substitute technique, comparing the 28d strength of fly ash recycled concrete(FARC) with the 28d strength of ordinary recycled concrete(ORC), the compressive strength of fly ash recycled concrete slightly decreased with the increase of the fly ash and the admixture of renewable aggregate. Along with the increase of mixing amount of the air entraining and water-reducing agent, the compressive strength of fly ash recycled concrete tends to reduce. The order of the factors that affect the chloride ion diffusion coefficient of recycled concrete is fly ash admixture→mixing amount of the air entraining and water-reducing agent→admixture of recycled coarse aggregate→polypropylene fibre admixture, which provides a basis for the application of recycled concrete engineering in the environment which is affected by chlorine salt in the north frigid area .

Experimental Study on Sustainable Concrete with the Mixture of Low Calcium Fly Ash and Lime as a Partial Replacement of Cement

Even though the use of fly ash in concrete is nowadays a common practice, its relatively slow pozzolanic reactivity hinders its greater utilization; hence efficient methods of activation are on demand. This study was carried out to evaluate the influence of lime as a chemical activator on the mechanical and durability properties of high strength fly ash concrete. Mixtures were made with 0, 30, 40, and 50% of cement replaced by low calcium fly ash. Corresponding mixtures were also made with the same amount of fly ash and addition of 10% of lime to each mixture. For each concrete mixture, slump, compressive strength, water absorption, sorptivity, apparent volume of permeable voids, and resistance to chloride-ion penetration were measured. The results obtained showed that addition of lime improved the compressive strength significantly at all ages. The strength of all the fly ash mixtures containing lime surpassed that of the corresponding Portland cement mix at 60 days. Addition of lime also improved the sorptivity and resistance to chloride-ion penetration of the fly ash concrete. It however increases the water absorption and the volume of permeable voids of the fly ash concrete.

Crack Resistance Evaluating of HSC Based on Thermal Stress Testing

In order to evaluate the crack resistance of high strength fly ash concrete, concretes with different contents of silica fume and fly ash were compared with same strength grade by adjusting water to binder ratio. Compared with the concrete with 5% silica fume plus 35% fly ash，concrete with 40% fly ash has same mechanical properties and tensile strain as well as lower drying shrinkage. Complex crack resistance of high strength fly ash concretes were evaluated by Temperature Stress Testing Machine (TSTM). The results show that fly ash concretes have outstanding crack resistance because of higher allowable temperature differential and lower cracking temperature.

Prediction of the Strength Development of Fly Ash Concrete

The effect of fly ash in improving the mechanical properties of concrete is investigated and the existing concrete strength development models are studied. Based on the chemic reactivity properties between fly ash and cement, an appropriate concrete strength model are chosen, and a new model for the fly ash strength factor combing Maturity method is built up and the factors are regressed by existing experimental datum. A total of 24 concretes, including two concretes were produced with two partial fly ash replacement ratios (23.7%, 32.7%). The cubic samples produced from ash fly concrete were demoulded after a day, and cured at standard temperature ( in GB/T 50081-2002) with 100% relative humidity until 28 days, then cured in water. The compressive strength tests were carried out on the cubic specimens at different ages. The compressive strength with time was evaluated by using the new predicted model. It was found that the calculated results by new method are fit the experimental data well.

Reduction of carbon content in waste-tire combustion ashes by bio-thermal treatment

Application of bio-catalyst (NOE-7F) in thermal treatment can adequately dispose dark-black fly ashes from co-combustion of both waste tires and coal. After thermal treatment of fly ashes by adding 10% NOE-7F, the carbon contents reduced by 37.6% and the weight losses increased by 405%, compared with the fly ashes without mixing with NOE-7F. The combustion behaviors of wasted tires combustion fly ashes with NOE-7F were also investigated by both thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results verify that NOE-7F has positive effects on the combustion of residual carbon and toxic polycyclic aromatic hydrocarbons (PAHs) enhance the energy release and reduce the toxicity during the process of thermal treatment. Furthermore, using NOE-7F to dispose high-carbon content fly ashes did improve the compressive strength of fly ashes and concrete mixtures. Therefore, NOE-7F is a promising additive which could decrease treatment cost of high-carbon content fly ashes and reduce the amount of survival toxic PAHs.

Development of High Strength Fly Ash Glass-ceramics by Concrete Sludge Addition

Development of High Strength Fly Ash Glass-ceramics by Concrete Sludge Addition

Development of High Strength Fly Ash Glass Ceramics: Influence of Additive on Material Properties

Development of High Strength Fly Ash Glass Ceramics: Influence of Additive on Material Properties

An economic feasibility model for ash use in flowable fill with integration of logistics and contaminant leaching factors

Encasement of utility cables and pipes in flowable fill monoliths formed in trenches requires the use of materials that satisfy both strength and contaminant leachability limits. Coal combustion ash is often readily available for use in flowable fill construction. The use of ash in desirably large quantities, calls for the determination and selection of the maximum ash mix fraction that meets strength requirements for excavatability and contaminant leachability. Initial economic feasibility assessments can then be performed in terms of the costs and revenues of installing flowable fill using the ash mix fraction selected. In this paper, the methodology is demonstrated by testing monoliths of flowable fill containing 0–20% (by weight) of coal combustion fly ash for Unconfined Compressive Strength (UCS) and leachability indices, Li values of selenium and arsenic. It was found that the monolith containing 20% by weight of ash satisfied the excavatable fill maximum strength requirements of 2070 N/m², and selenium and arsenic minimum Li values of 17.0 and 14.0, respectively. An economic feasibility estimation methodology is presented to relate ash sale revenues and flowable fill placement costs for various mix fractions of ash.

早強セメントとフライアッシュから調製したフライアッシュセメントの物性とエコロジカル評価

早強セメントとフライアッシュから調製したフライアッシュセメントの物性とエコロジカル評価

Compaction behaviour of fly ashes

Fly ashes are used widely in many geotechnical applications. In most of the applications, compaction of the fly ashes is essential to improve their engineering behaviour. This paper presents the compaction behaviour of fly ashes along with the mechanisms controlling their behaviour. To this end, their compaction curves have to be presented on recently proposed volume-based parameters, namely solid volume occupation and water volume content, instead of weight-based parameters such as dry density and water content. For a given fly ash the variation in solid volume occupation with water volume content for any given compactive effort has been explained as being due to variation in the pore water pressure. Fly ashes resist the external compactive effort by shear resistance and positive pore water pressure development. The strength of fly ashes at any point on the dry side of optimum is the same, and on the wet side of optimum decreases with water volume content. The variation between the compaction curves of different fly ashes is essentially due to their differences in fineness and frictional characteristics.

Flexural behavior of high strength fly ash concrete beams

Abstract The minimum void concept was used to proportion high strength fly ash concrete. Numerous trial batches were made to determine the optimum mix proportion. Nine beams were cast from optimum mix to investigate the flexural behavior of this type of concrete. The requirements specified in current ACI 318 for modulus of elasticity of concrete, modulus of rupture of concrete, flexural strength of beam sections, effective moment of inertia of flexural members, maximum tension reinforcement ratio and minimum tension reinforcement for seismic design were examined for their application to high strength fly ash concrete.

High Early Strength Fly Ash Concrete for Precast/Prestressed Products

72 Presents field applied research to report the advantages of using a high quality ASTM C-618 Class C fly ash on water demand, workability and compressive strength of concrete. The research was performed at two precast/prestressed concrete plants to identify optimum mixture proportions for production of high early strength concrete with high fly ash contents. Tests were carried out on nominal 5000 psi (34 MPa) concrete utilizing fly ash produced at Wisconsin Electric Power Company's Pleasant Prairie Power Plant. Fly ash replacement improved workability, decreased water demand, and increased strength while maintaining the high early strength requirements of precast/prestressed concrete operations.

Effectiveness of fly ash for strength and durability of concrete

The effectiveness, K, of a fly ash can be defined as the ratio of the amount of cement replaced to the amount of fly ash added, provided the specified requirements of the concrete are maintained. It is generally assumed that the effectiveness of a fly ash can be treated as a constant. This paper presents results on concrete made with various mix proportions using three different cements and fly ash from three different sources. It was found that the K factor of each fly ash in achieving common 28-day compressive strength varies over a wide range depending on the amount of fly ash used, the type of cement, the incorporation of chemical admixtures and the particular strength level chosen. Besides strength, K can also be calculated for other properties. For the materials used in this investigation, the K factors with respect to carbonation were found to be unequal to K factors for strength.

Early Strength Fly Ash Concrete for Structural Applications

Extensive data are presented on the properties, in the fresh and hardened state, of fly ash concrete containing normal weight and light weight aggregates suitable for structural applications. Tests on reinforced concrete beams and slabs are reported to show that fly ash concrete can exhibit structural performance similar to that of conventional concrete with adequate safety factors and predicted by existing codes.