Fly Ash Ratio Research Articles

Thermal and mechanical characterization of fly ash geopolymer with aluminium chloride and potassium hydroxide treated hemp shiv lightweight aggregate

This research reports an experimental study on thermal and mechanical properties of Class C fly ash (FA) based geopolymer composited with hemp shiv, to develop as a sustainable building material. Hemp shiv, being applied as the lightweight aggregate, was treated by a new complex mineralizer, AlCl3 and KOH, prior to mixing with the FA. The treated hemp shiv to fly ash by mass ratio was 0.05, 0.10, 0.15 and 0.20 while the liquid alkaline (sodium hydroxide mixed with sodium silicate) to FA ratio used was 0.6. The result showed that the treatment product (aluminium chloride, Al(OH)3), formed on the hemp shiv surfaces, served as an effective moisture absorption barrier so the geopolymerization could satisfactorily occur. The SEM result revealed that the geopolymerization was retarded when the untreated hemp shiv was employed instead. Flexural strength of the geopolymer composites increased to around 3.55 MPa in the mixes with treated hemp shiv at the ratio of 0.05–0.15 (0.05 to 0.15 mix) before being degraded to the same level (2.42 MPa) of that of the reference (0 hemp shiv) in the 0.20 mix. Fracture toughness of the geopolymer composites had been improved steadily with an increasing amount of treated hemp shiv from 0.62 to 1.17 MPa∙m1/2. Thermal conductivity of the geopolymer composites was in the range of 0.36–0.25 W/m⋅K while thermal resistance was also acceptable until 200 °C. However, compressive strength and bulk density tended to decrease with an increasing amount of the treated hemp shiv, with those of 0.05, 0.10 and 0.15 mixes having met the requirements of the ASTM C129-99a: Standard specification for nonloadbearing concrete masonry units.

Improving the Mechanical Properties of Fly Ash-Based Geopolymer Composites with PVA Fiber and Powder

In this work, polyvinyl alcohol (PVA) fiber and powder were added to geopolymer composites to toughen fly ash-based geopolymer, and their different toughening mechanisms were revealed. Firstly, different contents of active granulated blast furnace slag (GBFS) were added to the geopolymer to improve the reactivity of the GBFS/fly ash-based geopolymer, and the best ratio of GBFS and fly ash was determined through experiments testing the mechanical properties. Different contents of PVA powders and fibers were utilized to toughen the geopolymer composites. The effect of the addition forms and contents of PVA on the mechanical properties, freeze–thaw cycle resistance, and thermal decomposition properties of geopolymer composites were systematically studied. The results showed that the toughening effect of PVA fiber was better than that of PVA powder. The best compressive strength and flexural strength of geopolymer composites toughened by PVA fiber were 41.11 MPa and 8.43 MPa, respectively. In addition, the composition of geopolymer composites was explored through microstructure analysis, and the toughening mechanisms of different forms of PVA were explained. This study provided a new strategy for the toughening of geopolymer composites, which can promote the low-cost and efficient application of geopolymer composites in the field of building materials.

Investigation of Low-Calcium Circulating Fluidized Bed Fly Ash on the Mechanical Strength and Microstructure of Cement-Based Material

This present study mainly focuses on the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the mechanical property and microstructure of cement-based materials under different curing conditions. The mechanical properties test was conducted by changing variable parameters, such as LCFA content, the internal mixing ratio of LCFA and fly ash (FA), and dry and water curing conditions. Further, the hydration products and pore structure were analyzed using XRD, FT-IR, TG-DTG, NI, SEM, and BET micro-testing technology. The strength development law of LCFA on cement-based materials is discussed. The research results show that LCFA has a certain degree of self-hardening and can be used as a cementitious material in cement-based materials. Still, the loose and porous microstructure of LCFA leads to higher water requirements, which reduces the fluidity of cement-based pastes. Water curing is favorable for promoting the development of LCFA on the long-term compressive strength of cement-based materials. When the LCFA was added to the cement, the optimal substitution ratio was 20%, and the compressive strength at 91 days reached 101 MPa. In the case of compounding LCFA and FA, when the internal mixing ratio of LCFA/FA was 3 and the total content was 20%, the mechanical properties were the highest, and the compressive strength at 91 days was 92 MPa. The microscopic analysis result shows that the cumulative hydration heat of the samples decreased significantly with the increase of dosage of LCFA. The main hydration products of cement-based materials mixed with LCFA were AFt, C-S-H gel, and Ca(OH)2. AFt and C-S-H gels are critical to the strength development of OPC-LCFA samples. The active Al2O3 and active SiO2 in LCFA were involved in hydration reactions to promote the formation of C-A-H and C-S-H gel and effectively promote the development of the mechanical properties. Overdosages of LCFA would reduce the ettringite formation rate. FA is not conducive to AFt formation in the hydration process of OPC-FA samples.

Preparation of coal gangue-slag-fly ash geopolymer grouting materials

To prepare a low-cost geopolymer grouting material (LCGGM), the industrial solid wastes coal gangue (CG), blast furnace slag (BFS) and fly ash (FA) were used as silica-alumina materials; desulfurized gypsum and an alkaline activator were used as ligands; and small amounts of additives were supplemented. The response surface methodology (RSM) was used to design macroscopic tests of the fluidity, setting time, compressive strength and impermeability of LCGGM, and XRD, FTIR, TG-DSC and SEM-EDS were used to analyse the mechanism of action. The results showed the following: (1) Optimized formulation could be achieved at coal gangue powder: slag: fly ash ratio of 5:4:1, 1.64 M sodium silicate modulus, 6.7% sodium silicate and 5% Na2O. The LCGGM possesses clean production, high fluidity, fast setting, low bleeding rate, high compressive strength and seepage pressure, providing appealing properties as grouting materials for reinforcement. The establish regression model and response surface well reflect the impacts of various factors on the properties of the LCGGM. (2) Microscopic analysis showed that the three materials with different fineness improved the density of the stone body and participated in the hydrolytic polymerization reactions of the multiple systems at different times, which ensured the strength of the stone body in the early and late stages.

Contribution of fly ash to mortar strength development under steam and internal curing

The purpose of this study is to quantitatively evaluate the effects of steam curing and internal curing on contribution of fly ash to strength development of mortar by using cementing efficiency factor (k-value) that represents strength development performance as a binder of fly ash. In addition, the pozzolanic reaction of fly ash was evaluated from the viewpoint of calcium hydroxide consumption by using thermogravimetry and differential thermal analysis as well as the degree of fly ash reaction by using selective dissolution method. The result indicated that steam curing improved early compressive strength and internal curing improved compressive strength and k-value at all ages. Also, a linearrelationship between the degree of fly ash reaction and the k-value was shown regardless of the age and the replacement ratio of fly ash.

Mechanical properties of GGBSFA Geopolymer concrete with varying Silica Modulus at different curing conditions

Geopolymer concrete is made of waste materials such as Fly ash and ground granulated blast furnace slag (GGBS). The use of this concrete helps to reduce the stock of wastes and also reduces emission of carbon by reducing Portland cement demand. The major constituent of Geopolymer concrete is aluminium and silicon rich materials. These materials are either natural materials that are thermally activated (e.g. kaolinite) or byproducts from industries (e.g. fly ash ). These materials are activated using alkaline activating solution which polymerizes the materials and forms into networks creating hard binder. Geopolymer concrete with Fly Ash as precursor gains less strength at low rates in ambient temperature. Fly Ash Geopolymer concrete should be heat cured to improve its strength. In the present investigation effect of Silica Modulus(SiO2/Na2O) and percentage Na2o on the mechanical properties of Geopolymer concrete cured with Plastic Membrane and in ambient temperature are presented. In this alkaline activator which is combination of NaoH(NH) and Na2Sio3(NS) is used to activate the binder.8 type of mixes with fixed binder content, varying GGBS, Fly Ash ratio and Silica Modulus of Alkali solution are used to study the strength properties of Hardened concrete. It was found that the strength decreased with increase in Silica Modulus and increased with increase in percentage Na2o.M40 grade concrete is attained for a combination of Silica Modulus of 1.4 and 5.399 percent of Na2o.

Preparation of municipal solid waste incineration fly ash-based ceramsite and its mechanisms of heavy metal immobilization

With an increase in municipal solid waste incineration (MSWI) fly ash and its dangerous characteristics, the manner of its disposal has caused widespread concerns. In this study, ceramsite was prepared by using MSWI fly ash, civil sludge, and contaminated soil as the main raw materials; then, a certain proportion of clay was added as an additive. The optimum MSWI fly ash content and sintering conditions were investigated, and the immobilization mechanisms of heavy metals were explored. Based on the obtained results, the optimum preparation conditions were a preheating temperature of 400 °C, a preheating time of 10 min, a sintering temperature of 1150 °C, and a sintering time of 20 min. Moreover, the optimal raw material ratio of MSWI fly ash, civil sludge, contaminated soil, and flint clay was 30%:40%:15%:15%. Under these optimum preparation conditions, the obtained ceramsite showed the following excellent performance parameters: a 1-h water absorption of 0.97%, bulk density of 998.7 kg/m3, and cylindrical compressive strength of 37.84 MPa. Furthermore, the leaching of heavy metals was far less than the standard GB5085.3-2007. The immobilization of heavy metals in the ceramsite was mainly caused by the glass phase encapsulation and the formation of new crystal phase with the heavy metals. In addition, the generation of aluminosilicates played a positive role in the immobilization of heavy metals. Thus, the reuse of MSWI fly ash by preparing fly ash-based ceramsite is one of the effective methods for reducing solid wastes.

Prediction of permeability for fully weathered granite amended with fly ash by fractal dimensions

Fully weathered granite (FWG) is a commonly used material for filling the subgrade of the highway. Existing conventional laboratory experiments indicated that it can be classified as sandy soil as per its particle diameter. Blending fly ash within FWG, referring to fly ash-amended fully weathered granite (FAFWG), seems to heighten its strength and bearing capacity. To estimate the optimal proportion of fly ash, the unconfined compressive strength (UCS) tests had been conducted on six categories of FWG specimens with different contents of fly ash and lime (as an activator) for optimization. The California bearing ratio (CBR) tests on the FWG specimens and those with the optimal proportion of fly ash (12%) and lime (4%) had been further conducted to evaluate the improvement effect of fly ash and lime on engineering properties. The permeability of FAFWG also is compliant with different blending ratios of fly ash and governs the durability of subgrades. For convenience, it was theoretically presented in terms of a fractal dimension of specimens by the image recognition technique. The rationality of the proposed method has been verified by the falling head permeability tests.

The Effect of Different Curing Temperatures on the Properties of Geopolymer Reinforced with Micro Steel Fibers

In this study, geopolymer mortar was designed in various experimental combinations employing 1% micro steel fibers and was subjected to different temperatures, according to the prior works of other researchers. The geopolymer mortar was developed using a variety of sustainable material proportions (fly ash and slag) to examine the influence of fibers on its strength. The fly ash weight percentage was 50%, 60%, and 70% by slag weight to study its effect on the geopolymer mortar's properties. The optimal ratio produced the most significant results when mixed at a 50:50 ratio of fly ash and slag with 1% micro steel fibers at curing temperature 240oC for 4 hours through two days. The compressive strength of the geopolymer mortar increased by 11%, 11.5%, and 14% after 3, 7, and 28 days when utilizing fibers. The result shows that fly ash with a ratio of 50% by weight of slag improved the compressive strength of the mixture. It was discovered that a combination with 50% of the weight of fly ash with micro steel fibers, when treated at 240oC for curing age of 3, 7, and 28 days, had a flexural resistance rate of 28%, 30%, 33% higher than a mixture without fibers.

Experimental study on compressive strength and frost resistance of steam cured concrete with mineral admixtures

The study of frost resistance and mechanical properties of steam cured concrete is helpful to understand the state of precast concrete elements in a complex environment. In this paper, the compressive strength of concrete under 10 working conditions, such as standard cured system, steam cured system, no mineral admixtures, single ground granulated blast furnace slag (GGBS) and fly ash (FA) mixed with GGBS, was tested at the age of 180d. It is found that the compressive strength of concrete under standard cured system is 4.71% to 18.46% higher than that under steam cured system, although steam cured improves the strength at the initial stage. The addition of FA and GGBS can make up 14% to 16% strength defects caused by steam cured system. The compressive strength of steam cured concrete (ZF40℃) is the highest when the steam cured temperature is 40℃ and the mixture ratio of FA and GGBS is 2:3. On this basis, the frost resistance of ZF40℃ specimens was studied. The results showed that the surface degradation degree of steam cured concrete gradually deepened with the increase of freeze–thaw (F-T) cycles, and the extracted surface roughness ranged from 0.066 ∼ 0.505 mm. The relative dynamic elastic modulus and mass loss rate decreased with the increase of F-T cycles, and the maximum loss rate were 69.4% and 1.41%, respectively. In addition, the compressive strength test, acoustic emission (AE) signal monitoring and acquisition of pore structure characteristics were carried out to understand the mechanical properties of steam cured concrete under F-T cycles conditions. The results show that the compressive strength decreases with the increase of F-T cycles, and the strength loss rate is within 10% per 50 cycles. The overall activity of AE signal decreases with the increase of F-T cycles, andthe damage form gradually changes from the initial tensile damage to the later shear damage. Porosity and pore size range basically increase with the increase of F-T cycles. Pore deterioration is the main reason for the decrease of compressive strength of steam cured concrete under F-T environment.

Pullout resistance of geogrid and steel reinforcement embedded in lightweight cellular concrete backfill

Lightweight Cellular Concrete (LCC) has been increasingly used as backfill material for retaining walls, ground improvement, and pavements due to its low self-weight, quick installation, and high compressive strength as compared with soils. This paper presents a series of pullout tests performed in the laboratory to investigate the pullout resistance of geogrid (extensible reinforcement) and steel strip (inextensible reinforcement) embedded in LCC. Pullout displacements and pullout forces were monitored using displacement transducers (DT) and a load cell during the pullout process. This study investigated the effects of age, normal stress, fly ash, the presence of a cold joint, and re-pullout on the pullout resistance and calculated the pullout resistance factors F* for geogrid and steel strip embedded in LCC. Test results show that for the geogrid embedded in LCC, the maximum pullout force increased as the normal stress increased. For the steel strip embedded in LCC, the maximum pullout force was independent of the normal stress and increased as the age and the cement to fly ash ratio increased. Test results also show that the presence of a cold joint did not reduce the pullout resistance, while the re-pullout test had lower pullout resistance compared to the original pullout test for the same specimen. The pullout resistance factors F* for steel strips were greater than those for geogrids and these factors decreased as the normal stress increased.

Resistance of Geopolymer, Epoxy and Cement Mortar to Hydrocarbon-Based Synthetic Engine Lubricant, Hydraulic Fluid, Jet Fuel and Elevated Temperatures

Due to routine maintenance of aircraft on the concrete pavement at army airbases, a large part of the pavement surface is often found saturated with different hydrocarbon-based oil, fuel, and fluid. In addition, the pavement concrete is subjected to the aircraft’s exhaust temperature during operation. This study examined the resistance ability of 3 different cementitious materials: (i) epoxy, (ii) fly ash (FA) based geopolymer with various alkali to fly ash (AL/FA) ratios and (iii) Portland cement (PC) mortar under a simulated airfield circumstance. The mortar specimens were repetitively exposed to a mixture of synthetic engine oil, hydraulic fluids, jet fuel and elevated temperatures (175 °C) for 5 months simultaneously. During the exposures, geopolymer and PC mortar both suffered saponification. The degree of saponification of geopolymer samples is found to be highly reliant on the AL/FA ratios. On the contrary, the epoxy mortar was found to be resistant to saponification. It was also found that the PC mortar developed numerous thermal cracks but epoxy and geopolymer did not experience any visual thermal cracks under the same conditions.

Experimental Investigation of Unconfined Compression Strength and Microstructure Characteristics of Slag and Fly Ash-Based Geopolymer Stabilized Riverside Soft Soil.

To solve the issues of insufficient early strength of cement stabilized soil and high resource cost, high reduction cost, and high environmental cost induced by the application of cement, the slag and fly ash-based geopolymer was adopted as the stabilizer to treat riverside soft soil. This study mainly investigated the effects of stabilizer content, slag-to-fly ash ratio, and alkaline activator content on the strength of geopolymer stabilized soils with different curing ages. Unconfined compressive strength (UCS), scanning electron microscope (SEM), and X-ray energy spectrum analysis (EDS) tests were carried out. The results show that the stabilizer content, slag–fly ash ratio, and alkaline activator content have a decisive influence on the UCS of geopolymer-stabilized soil. The mix-proportions scheme of geopolymer stabilized riverside soft soil, with a geopolymer content of 15%, a slag–fly ash ratio of 80:20, and an alkaline activator content of 30%, is considered optimum. It is proven by SEM that the uniformly distributed gelatinous products formed in the geopolymer-stabilized soil bind the soil particles tightly. Moreover, the EDS analysis confirms that the gelatinous products are mainly composed of C-S-H gel and sodium-based aluminosilicate (N-A-S-H).

Fracture behaviors of HVFA-SCC mixed with seawater and sea-sand under three-point bending

This paper aims to study the fracture behaviors of high-volume fly ash-self-compacting concrete (HVFA-SCC) mixed with seawater and sea-sand (SWSS) or freshwater and river sand (FWRS). Three-point bending test were performed on 24 notched beams fabricated with varying in replacement ratio of fly ash (0%, 30%, 50%, and 70%) and the type of water and sand (SWSS and FWRS). The initial and unstable fracture toughness of these test specimens are determined by the double- K fracture model. The effect of fly ash replacement ratio and type of water and sand on the fracture parameters is analyzed and discussed. In addition, the cohesive fracture toughness of all the test specimens is calculated by using Gauss–Chebyshev integral method and the weight function method based on the bilinear tensile softening curve given in CEP-FIP Model Code. A comparison of fracture toughness parameters of determined from the experimental approach and analytical approaches is presented in these SCC specimens. Results show that SCC mixed with SWSS replacing FWRS can improve the unstable fracture toughness and fracture energy, and decrease its brittleness behavior. The cohesive fracture toughness of SWSS-SCC specimens is underestimated by these analytical methods based on the tensile softening curve given in CEP-FIP Model Code.

Experimental Investigation on Fresh and Hardened Properties of High Calcium Flyash Based Geopolymer Concrete

The most important cause of the climate changes in the past few decades are due to the emission of CO2.It may be due to human or natural processes such as disposal of waste material from the thermal power plant, consuming natural resources or production of cement etc. Due to increase in infrastructure created the demand of more construction industries. Increasing importance of environmental protection and energy storage has led to the investigation of alternative binders to replace the cement. Geopolymers are an alternative binder for cement concrete production because of their superior mechanical properties. In the present investigation, for developing the Geopolymer concrete (GPC), high calcium fly ash is used as an alternative binder with Na2SiO3 and NaOH as alkaline liquids. Fresh and hardened properties of GPC are examined by appropriate experiments. Alkaline liquid to High calcium Fly ash ratio (AL: HCF) of 0.45, 0.55,0.6 and 0.65 are used with 8M of NaOH and the developed GPC is kept in ambient curing for 7 days, 28 days, and 56 days. It was observed that with an increase of AL to HCF ratio in the fresh GPC increased the workability of GPC. Increase of AL to HCF ratio in GPC mix increased the compressive strength, tensile strength and flexural strength up to a certain limit.

Study on Mechanical and Microscopic Properties of Fly Ash Cement‐Based Materials in High Geothermal Environment

Through simulating a hot and humid environment of high‐ground‐temperature tunnel and taking advantage of mechanics performance testing, differential thermal analysis (DTA) technology, and scanning electron microscope (SEM) observation technology, the macroscopic and microscopic properties of cement‐based materials and their performance improvement measures can be investigated. Also, the mechanism of improvement can be revealed from the perspective of the hydration degree and microstructure. The experimental results indicate that under the hot and humid environment of high ground temperature, adding fly ash could efficiently weaken the early high‐temperature curing effect of cement‐based materials, improving their physical properties. But the mechanical strengths of cement‐based materials go through a transformation from increase to decline with the rise of fly ash, appearing a maximum value in the process. Meanwhile, the differential thermal analysis and the microstructure analysis show that a hot and humid environment enhances the pozzolanic activity of fly ash and an appropriate ratio of fly ash could improve the microstructure of cement slurry, but when fly ash covers more than 30% of the mix of cement‐based materials, the quantity of the alkaline exciting agent, calcium hydroxide, is not enough to meet the needs of the active effect of fly ash and the hydration degree of fly ash becomes extremely low. Last, under a hot and humid environment of high ground temperature, fly ash saturation in cementing material should range from 20% to 30% in mass of total binder, which makes for long‐term performance of cement‐based materials.

Optimisation of mix proportions for the cemented sand and gravel in cold region

Cemented sand and gravel (CSG) is recognised as having poor quality due to its high porosity. An experimental study was carried out on the mix proportion design of CSG, taking into account the strength and frost resistance requirements of CSG dams in frozen areas. The main factors affecting the compressive strength and frost resistance of CSG were determined by orthogonal experiments. The influencing factors are water/binder ratio, fly ash, cement consumption, admixture and sand ratio, every factor sets up two cases, and the orthogonal table L8 (24) is adopted. There is a positive correlation between compressive strength and frost resistance, as the test results show. An optimal function about compressive strength and frost resistance to improve the quality of CSG in cold region was proposed, in which, weight was determined by OWA operator and entropy weight method to eliminate the influence of extreme values in the subjective evaluation. With the application of the function, significant factors influencing the desired performance of CSG are sand ratio, cement consumption, water/binder ratio and content of fly ash, while the optimum mix proportion is water/ binder ratio of 1.0, ratio of sand of 0.2, while 60 kg/m3 and 40 kg/m3 for the contents of fly ash and cement. The results can provide a theoretical basis for application and design of CSG dam in cold region.

Flame Resistance Characteristics of Woven Jute Fiber Reinforced Fly Ash Filled Polymer Composite

Due to their unique characteristics, natural fiber reinforced polymer composites have recently been increasingly utilised to replace traditional materials. Fire retardant resins can increase flammability, and they have a deleterious influence on the mechanical properties of the material (Fan et al., 2020). As a result, this experiment examined the flammability of woven jute fiber reinforced with fly ash. The specimens were created by hand layup using a L9 orthogonal array and varying ratios of jute fiber, fly ash, and time for chemical fiber treatment. Vertical and horizontal flammability tests are conducted in accordance with ASTM D635 and ASTM D3801, respectively. According to the test results, the inclusion of fly ash significantly reduces flammability. In this work, 5 wt% inclusion of the jute fiber, 15 wt% addition of the fly ash, and with 10 hours, NaOH treatment produces a composite with minimum burning rates of 10.2 mm/min in horizontal UL‐94 tests. To determine the link between input and output characteristics, various regression models from machine learning are used. Multilayer perception produced a stronger association in both horizontal and vertical testing, according to the models.

The Key Application Technology of Desulfurized Gypsum in Dry-Mixed Mortar

In this paper, in view of the problem of low early and late strength of dry-mixed mortar prepared by cement-fly ash-slag powder composite cementing system, the ratio of mixing fly ash and slag powder to replace cement is 70%. To study the effect of desulfurization gypsum (FGD) on improving the activity of the system. The results show that adding desulfurized gypsum, which accounts for 6% to 8% of the total mass of the cementitious material, has no adverse effect on the workability and can significantly improve the compressive resistance of the slurry. Strength and tensile bonding strength, shrinkage rate is reduced by more than 10%, and the ability to resist carbonization is improved to make the mortar volume more stable.

Mix-ratio optimization for air-tight tunnel concrete

In this paper, we studied the effect of fly ash and mix ratio on the compressive strength of air-tight concrete, the introduced fly ash would decrease the early compressive strength of concrete. With curing age increasing, the gape in the compressive strength between concrete without fly ash and concrete containing fly ash is decreasing. Moreover, concrete containing fly ash showed smaller air permeability, the introduced fly ash improved the airtightness of concrete.