scholarly journals Development of Flotation Device for Removing Unburnt Carbon in Fly Ash for Use in Hardened Cementitious Materials

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6517
Author(s):  
Hangwei Lin ◽  
Koji Takasu ◽  
Hidehiro Koyamada ◽  
Hiroki Suyama
Keyword(s):  
Elastic Modulus ◽  
Fly Ash ◽  
Drying Shrinkage ◽  
Cementitious Materials ◽  
Unburned Carbon ◽  
Ordinary Concrete ◽  
Circulating Water ◽  
Micro Bubble ◽  
Concrete Mixer ◽  
Flotation Method

The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15–30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible.

scholarly journals Characterizing the Performance of Ternary Concrete Mixtures Involving Slag and Metakaolin

2020 ◽  
Vol 5 (2) ◽  
pp. 14
Author(s):  
Matthew S. Sullivan ◽  
Mi G. Chorzepa ◽  
Stephan A. Durham
Keyword(s):  
Mechanical Properties ◽  
Thermal Expansion ◽  
Fly Ash ◽  
Coefficient Of Thermal Expansion ◽  
Drying Shrinkage ◽  
Chloride Ion ◽  
Cementitious Materials ◽  
Ternary Mixtures ◽  
Modulus Of Rupture ◽  
Ternary Blends

Ternary blends of cementitious materials are investigated. A cement replacement level of 45% is used for all ternary mixtures consisting of 15% metakaolin and 30% slag replacements. Three metakaolin and two blast furnace slag, referred to as ‘slag’ for short, products commercially available are used to compare performance in ternary blends. A mixture with a 45% fly ash replacement is included to serve as a benchmark for performance. The control mixture contains 422 kg of cement per cubic meter of concrete, and a water-to-cementitious material ratio of 0.43 is used for all mixtures with varying dosages of superplasticizer to retain workability. Mixtures are tested for mechanical properties, durability, and volumetric stability. Mechanical properties include compression, split-cylinder tension, modulus of rupture, and dynamic Young’s modulus. Durability measures are comprised of rapid chloride-ion penetrability, sulfate resistance, and alkali–silica reactivity. Finally, the measure of dimensional stability is assessed by conducting drying shrinkage and coefficient of thermal expansion tests. Results indicate that ternary mixtures including metakaolin perform similarly to the control with respect to mechanical strength. It is concluded that ternary blends perform significantly better than both control and fly ash benchmark in tests measuring durability. Furthermore, shrinkage is reduced while the coefficients of thermal expansion are slightly higher than control and the benchmark.

Research on Mechanical Properties of C100 High-Strength Concrete Used for Frozen Shaft

2012 ◽  
Vol 598 ◽  
pp. 388-392
Author(s):  
Hong Qiang Chu ◽  
Lin Hua Jiang ◽  
Ning Xu ◽  
Chuan Sheng Xiong
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Fly Ash ◽  
High Strength Concrete ◽  
High Strength ◽  
Cementitious Materials ◽  
Poisson's Ratio ◽  
Strength Concrete ◽  
Tensile Elastic Modulus ◽  
Early Strength

The mechanical properties of C100 high-strength concrete used for frozen shaft were studied in this research. The results demonstrate that: The cementitious materials 570kg/m3 concrete 28 strength is only 104.5MPa, which is lower than the C100 requirements; the early strength (3d) of the concrete doped with 30% admixture is less than 20% admixture concrete, but with the age increase, its strength gradually reaches close to concrete doped with 20% admixture, and eventually exceeds the concrete doped with 20% admixture.The tension-compression of high strength concrete doped with 15% fly ash and 15% slag is the smallest, while the tension-compression of the concrete doped 10% fly ash and 10% slag reaches the maximum.The Poisson's ratio of C100 concrete is between 0.20 and 0.24; the compressive elastic modulus is about 50GPa; and the tensile elastic modulus is about 110GPa.

scholarly journals Concrete with Reused Concrete Sand

2019 ◽  
Vol 8 (6) ◽  
pp. 4868-4873
Keyword(s):  
Elastic Modulus ◽  
Compression Strength ◽  
Drying Shrinkage ◽  
Shrinkage Strain ◽  
Ordinary Concrete ◽  
Mixed Concrete

This paper examines the impacts of substitution of reused concrete sand (RCS) with sands, on the new and hardened physiognomies of concrete. the property of RCS blended concrete was examined and likened with ordinary concrete of 40 MPa compression strength. the physiognomies of RCS concrete vary from ordinary concrete arranged with characteristic sand, as an outcome of the quality of connected mortar, old cement glue, and more fines. the outcomes demonstrate that the RCS concrete demonstrations tantamount workability in contrast with ordinary concrete. the mechanical physiognomies (compressive, flexure, split tensile and elastic modulus) of concrete developed with RCS was lower in compression to ordinary concrete however worthy up to 60percentage RCS in the blend. The drying shrinkage strain of 100percentage RCC mixed concrete at twenty-eight days was watched twice in compression to controlled concrete and it demonstrated more abrasion value in that comparison and furthermore concrete developed with 100 percent RCS indicated 41percentage and 11.3percentage lower in sorption value at ahead of schedule and later age organize individually in that examination.

scholarly journals Resistance to Chemical Attack of Hybrid Fly Ash-Based Alkali-Activated Concretes

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3389
Author(s):  
William G. Valencia-Saavedra ◽  
Ruby Mejía de Gutiérrez
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Strength Loss ◽  
Cementitious Materials ◽  
Sodium Sulphate ◽  
Unburned Carbon ◽  
Chloride Permeability ◽  
Chemical Attack ◽  
Concrete Production ◽  
Alkali Activated

The environmental impacts related to Portland cement production in terms of energy consumption, the massive use of natural resources and CO2 emissions have led to the search for alternative cementitious materials. Among these materials, alkali-activated cements based on fly ash (FA) have been considered for concrete production with greater sustainability. In the present article, the chemical durability properties (resistance to sulphates, chloride permeability, and resistance to carbonation) of a hybrid alkali-activated concrete based on fly ash–ordinary Portland cement (FA/OPC) with proportions of 80%/20% were evaluated. It is noted that the FA was a low-quality pozzolan with a high unburned carbon content (20.67%). The results indicated that FA/OPC concrete had good durability with respect to the OPC concrete, with 95% less expansion in the presence of sodium sulphate and a 2% strength loss at 1100 days, compared with the 56% strength loss of the OPC concrete. In addition, FA/OPC showed lower chloride permeability. On the contrary, the FA/OPC was more susceptible to carbonation. However, the residual compressive strength was 23 MPa at 360 days of CO2 exposure. Based on the results, FA/OPC, using this type of FA, can be used as a replacement for OPC in the presence of these aggressive agents in the service environment.

STUDY ON PROPERTIES OF FLY ASH REMOVED UNBURNED CARBON BY FLOTATION METHOD

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Yuta Niimura ◽  
Koji Takasu ◽  
Hiroki Suyama ◽  
Hidehiro Koyamada
Keyword(s):  
Fly Ash ◽  
Chemical Composition ◽  
Physical Properties ◽  
Treatment Time ◽  
Activity Index ◽  
Unburned Carbon ◽  
Pine Oil ◽  
Addition Rate ◽  
Flotation Method ◽  
Pre Treatment

When we use the fly FA-As a concrete admixture, it is known that the properties of the concrete improve. But when we made concrete with fly FA-Fresh property of concrete is adversely affected by unburnt carbon in the fly ash. If there are much quantities of unburnt carbon in the fly ash, they inhibit air entraining performance and fluidity of flesh concrete. So we developed the device removing unburnt carbon from the fly FA-By flotation method in previous studies. It was succeeded remove of unburnt carbon in the fly FA-And to clean the surface of the fly FA-By used the developed device removing unburnt carbon in the fly FA-By flotation method. In this study, it was purpose to confirm the change in the composition and physical properties between the original fly FA-And the reformed fly FA-By flotation method, and to grasp the effects that the physical properties of fly FA-Gave to the unburnt carbon removal when using flotation method. As a result, the specific surface area of reformed fly ash is larger than original fly ash. However, the change of chemical composition for reformed fly FA-By flotation method was as small as 4% at the maximum. It was considered that the addition rate of kerosene and pine oil and the pre-treatment time were changed by difference in sizes and shapes of unburnt carbon in the fly ash. Percent flow and activity index were influenced by the different of physical properties of original fly ash.

Evaluation of Relations among Basic Mechanical Properties of Fly-Ash Concrete with Machine-Made Sand

2013 ◽  
Vol 438-439 ◽  
pp. 15-19
Author(s):  
Chun Jie Liu ◽  
Chun Yan Jia ◽  
Chang Yong Li
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Fly Ash ◽  
Concrete Structures ◽  
Ordinary Concrete ◽  
Strength Grade ◽  
Fly Ash Concrete ◽  
Axial Compressive Strength

Although the machine-made sand was widely used for concrete in recent years in China, it was short of studies on the relations among the basic mechanical properties of fly-ash concrete with machine-made sand (MSFAC). However, these relations such as the compressive strength, the tensile strength and the elastic modulus with the cubic compressive strength (i.e. strength grade) are the basis of design for concrete structures. This paper summarizes the test data from the published references, and discusses the relations among these properties by statistical analyses compared with those of ordinary concrete. The results show that only the tensile strength of MSFAC can be safely forecasted by the same formula of ordinary concrete specified in current Chinese design code. When the strength grade is higher than C45, the axial compressive strength of MSFAC is largely forecasted by the formula of ordinary concrete. The elastic modulus of MSFAC is larger than that of ordinary concrete, which should be prospect by the formula in this paper. This work gives out some cautions for the proper use of the MSFAC in concrete structures.

scholarly journals Shrinkage Effects of Using Fly Ash instead of Fine Aggregate in Concrete Mixtures

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Dongsheng Zhang ◽  
Pengfei Han ◽  
Qiuning Yang ◽  
Mingjie Mao
Keyword(s):  
Fly Ash ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Experimental Results ◽  
Fine Aggregate ◽  
Ordinary Concrete ◽  
Concrete Shrinkage ◽  
Substitution Level ◽  
Concrete Mixtures ◽  
Binder Ratio

China is the world’s largest emitter of fly ash, an industrial by-product of coal combustion. Motivated towards greener development, China’s engineering industries must determine how to effectively utilize this by-product, while ensuring environmental and public safety protections. This study investigated the use of fly ash instead of fine aggregate in concrete mixtures with a focus on concrete shrinkage. A series of experiments were performed in which fly ash substitution levels, water-binder ratios, and ambient humidities were each respectively and exclusively varied to determine changes in the concrete’s drying and autogenous shrinkages. Experimental results indicated that the substitution of fly ash consistently decreased the drying shrinkage relative to ordinary concrete; a substitution level of 25% optimally reduced the drying shrinkage by 20.81%. A substitution level of 15% decreased the autogenous shrinkage relative to ordinary concrete, whereas higher levels (25, 35, and 45%) increased it. Ambient humidities also affected the concrete shrinkage, but the water-to-binder ratio effects were negligible. Drying shrinkage largely occurred before 28 d, whereas autogenous shrinkage continued after 28 d. Based on these experimental results, we evaluated common theoretical shrinkage models and subsequently developed a modified shrinkage model for application to concrete containing fly ash as fine aggregate.

Engineering Properties of Concrete with a Ternary Blend of Fly Ash, Wheat Straw Ash, and Maize Cob Ash

2021 ◽  
Vol 54 ◽  
pp. 43-55
Author(s):  
Naraindas Bheel ◽  
Paul O. Awoyera ◽  
Oladimeji B. Olalusi
Keyword(s):  
Fly Ash ◽  
Wheat Straw ◽  
Drying Shrinkage ◽  
Cementitious Materials ◽  
Engineering Properties ◽  
Ternary Blend ◽  
Concrete Production ◽  
Maize Cob ◽  
Agricultural Materials ◽  
Straw Ash

In recent years, recycled materials mostly available in abundant quantities in local agricultural fields are considered as potential constituent material for concrete production. Also, cement production emits many toxic gases in the atmosphere, which causes environmental pollution and greenhouse gases. Thus, recyc;ed materials, such as fly ash (FA), wheat straw ash (WSA), and maize corn ash (MCA) are condered as cementitious binders in concrete for sustainable development. This study aims to determine the engineering properties of concrete with a ternary blend of fly ash, wheat straw ash, and maize cob ash. A total of 73 concrete cubes, 42 reinforced concrete prisms and 42 concrete cylinders were cast to examine mechanical properties of concrete at 7, 28, and 56 curing days. At 28 days (maturity period), the experimental results showed an increase in compressive, tensile, and flexural strength by 12.28%, 9.33%, and 9.93%, respectively, at 9% substitution of ternary cementitious materials (TCM). However, the density of concrete was reduced by 9.92%, with an increase in the TCM content after 28 days. Moreover, the modulus of elasticity was improved by 14.23% with an increase in the content of TCM up to 18% after 28 days, and drying shrinkage of concrete was reduced with the introduction of TCM content after 50 days. However, the workability of fresh concrete decreased as the percentage of TCM increased. Results of this study proved that agricultural materials investgated could be good fit as binder in cementitious composites.

scholarly journals Optimizing the usage of fly ash in concrete mixes

2017 ◽  
Author(s):  
◽  
Sabelo N. F. Zulu
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
South African ◽  
Drying Shrinkage ◽  
Cost Comparison ◽  
Ordinary Concrete ◽  
Air Content ◽  
Cement And Concrete ◽  
One Year ◽  
The Cost

Improving on our construction practices to promote sustainable development in engineering and to promote eco-friendly living is vital in the fight against global warming and associated problems. This study looked at one of the ways in which engineering can contribute to this fight through promoting the recycling of waste by-products such as fly ash (FA), on a larger scale in the cement and concrete industry, by utilizing the FA to the optimum. In this study concrete mixes of 25 MPa, 35 MPa and 50 MPa with FA partially substituting the cement at 30%, 40%, 50% and 60% were produced and numerous tests were performed to determine the optimum amount of FA that can be used and still obtain better or comparable concrete to ordinary concrete. Testing for concrete properties was conducted under laboratory conditions over a period of one year. In addition, a cost comparison between ordinary concrete and FA concrete was undertaken. The results obtained show that the increase in FA content influenced the rheological properties of fresh concrete favorable. The recorded slump increased with the increase of FA content. Increasing the FA content prolonged the setting of concrete, with the ordinary concrete taking 1 hour 45 min to set, compared to more than 2 hours for FA mixes. The FA increase had negligible effects on the air content of the concrete mixes. The drying shrinkage of concrete increased with the increase of FA content, with the strain ranging from 0,045% to 0,56%. The compressive strength results show that the control mixes with 30% FA content attained the highest compressive strength over a year. In some cases, the 40% FA strength was compatible to the 30% FA strength. The durability index results showed the control mix of 30% FA attaining better results for Oxygen Permeability Index and Sorptivity Index, with the 40% FA mix following closely. The higher FA content mixes (50% and 60%) attained better Chloride Conductivity results than the lower FA content mixes. Increasing the FA content does affect the performance of the concrete at early stages, however concrete with acceptable strength and good durability qualities can be produced even with 50% FA volume. Increasing the FA content can also significantly reduce the cost of producing and working with concrete. The practice of utilizing higher FA content in concrete can be beneficial for the South African cement and concrete industry without compromising the quality of the cement products concrete structures.

Study on Influence of Composite Ultra-Fine Fly Ash on Crack Resistance of Pavement Concrete

2012 ◽  
Vol 204-208 ◽  
pp. 3686-3690
Author(s):  
Qi Tao Qin ◽  
Yi Jin Li
Keyword(s):  
Elastic Modulus ◽  
Fly Ash ◽  
Crack Resistance ◽  
Tensile Deformation ◽  
Drying Shrinkage ◽  
Deformation Capacity ◽  
Test Results ◽  
Resistance Evaluation ◽  
Evaluation Indexes ◽  
Pavement Concrete

The crack resistance evaluation indexes of concrete were chosen, which were used to study the influence of ultra-fine fly ash on the crack resistance of pavement concrete. The concrete flat test was made to testify the concluded law. The test results show that composite ultra-fine fly ash improves the crack resistance of pavement concrete. The main reason is that it reduces the elastic modulus and drying shrinkage of concrete and improves the ultimate tensile deformation capacity.

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