Ash Blends Research Articles

Microstructure and Mechanical Property Evaluation of Dune Sand Reactive Powder Concrete Subjected to Hot Air Curing.

The use of different sustainable materials in the manufacture of ultra-high-performance concrete (UHPC) is becoming increasingly common due to the unabating concerns over climate change and sustainability in the construction sector. Reactive powder concrete (RPC) is an UHPC in which traditional coarse aggregates are replaced by fine aggregates. The main purpose of this research is to produce RPC using dune sand and to study its microstructure and mechanical properties under different curing conditions of water curing and hot air curing. The effects of these factors are studied over a long-term period of 90 days. Quartz sand is completely replaced by a blend of crushed and dune sand, and cement is partially replaced by using binary blends of ground granulated blast furnace slag (GGBS) and fly ash (FA), which are used alongside silica fume (SF) to make a ternary supplementary binder system. Microstructural analysis is conducted using scanning electron microscopy (SEM), and engineering properties like compressive strength and flexural strength are studied to evaluate the performance of dune sand RPC. Overall, the results affirm that the production of UHPC is possible with the use of dune sand. The compressive strength of all mixes exceeded 120 MPa after 12 h only of hot air curing (HAC). The SEM results revealed the dense microstructure of RPC. However, goethite-like structures (corrosion products) were spotted at 90 days for all HAC specimens. Additionally, the use of FA accelerated the formation of such products as compared to GGBS. The effect of these products was insignificant from a mechanical point of view. However, additional research is required to determine their effect on the durability of RPC.

Investigation of the reaction mechanism of blended fly ash and rice husk ash alkali-activated binders

Investigation of the reaction mechanism of blended fly ash and rice husk ash alkali-activated binders

Effects of waste glass sand on the thermal behavior and strength of fly ash and GGBS based alkali activated mortar exposed to elevated temperature

This study investigated the thermal behavior of a series of alkali activated mortars (AAm) based on blends of fly ash (FA) and ground granulated blast furnace slag (GGBS) precursors with waste glass (WG) and natural sand (NS) as fine aggregate. Results revealed that with increasing GGBS content, the AAms deteriorate after exposure to elevated temperature owing to dehydration causing mass loss, and weakening binder- aggregate bonding, which in turn decreased residual compressive strength. The efficacy of WG on the thermal behavior and mechanical strength depends on the binder type as well as on the temperature to which the AAms were exposed. In FA rich AAms, increasing WG showed good resistance to elevated temperature (200 –800 °C). Increasing WG in GGBS rich AAms, only showed acceptable performance for AAms exposed to 600 °C and 800 °C as the melted WG formed strong bonds with the matrix. However, for samples with 100 wt% WG and 100 wt% GGBS, surface spalling occurred at 200 °C, 400 °C and 600 °C and explosive spalling at 800 °C mainly caused by the high stresses induced on the expansion of both WG and matrix during exposure to elevated temperature.

Engineering properties of waste-based alkali activated concrete brick containing low calcium fly ash and rice husk ash: A comparison with traditional Portland cement concrete brick

Alkali activated concrete bricks manufactured from waste materials are an alternative to replace PC as the principal binder in brick manufacture. The current study reports the mechanical and durability properties of blended fly ash and 20% rice husk ash (20RHA) alkali activated bricks and compares with Portland cement (PC) bricks (100PC). The 20RHA brick showed a compressive strength growth rate of 4% between 7 and 28 days as compared to 13.8% for 100PC bricks. Both achieved similar 28 days compressive strength (approximately 17 MPa). High tensile strength was observed in 20RHA this is attributed to the high bond strength at the interface of the 20RHA alkali activated binder and aggregates. In microstructural investigation, 20RHA brick displayed a stronger bond within the interfacial transition zone (ITZ) boundary compared to 100PC bricks at all ages. This makes the fracture plane more prone to pass through the aggregates than through the bond interface. Lower capillary suction near the surface for 20RHA concrete is hypothesized as the reason for the lower initial rate of absorption obtained for 20RHA when compared with 100PC. The addition of RHA makes the bricks more vulnerable to efflorescence when exposed to moisture due to the combined effect of the high porosity, a high Na2O/Al2O3 ratio and greater leaching of sodium ions.

Artificial Intelligence Prediction Model for Swelling Potential of Soil and Quicklime Activated Rice Husk Ash Blend for Sustainable Construction

Artificial intelligence (AI) algorithms of adaptive neuro-fuzzy inference system or the adaptive network-based fuzzy inference system (ANFIS) has been deployed to predict the swelling potential (SP) of treated weak soil. The soil was treated with quicklime activated rice husk ash (QARHA) and the prediction efficiency was compared with the previous outcomes of this operation from literature. The need for effective utilization of construction materials to achieve sustainable designs and monitoring of the behavior of built environment is the motivation behind the deployment of artificial intelligence in geo-environmental research and field operations. The use of ANFIS is common in different fields of science and business to predict the best fits from several data points. The results of this modeling exercise conducted with 25 datasets from mixture experimental treatment of soft soil with QARHA has shown that ANFIS is a better tool compared to the individual algorithms of ANN and FL and even the other artificial intelligence tools like scheffe, ANOVA, regression and extreme vertices methods. With performance index of 88% and correlation of about 71% in the ANFIS testing and 17% and 99% respectively in the ANFIS training, ANFIS proved to be a more powerful tool in achieving a more sustainable material utilization in earthwork constructions, design and monitoring of geotechnical systems performance.

STUDY ON THE GEOTECHNICAL PROPERTIES OF LATERITIC SOIL STABILIZED WITH BENTONITE AND GROUNDNUT SHELL ASH AS ADMIXTURE FOR CLAY LINER IN WASTE CONTAINMENT

Waste management in Nigeria is characterized by poor landfilling practices in low-lying areas with improper planning of waste dumping. Whenever the soil on site is unfit for a barrier, it is blended with conventional stabilizers, but these additives are costly, hence the need to partially replace them with cheaper materials to achieve the desired results is essential. Consistency limit and engineering properties tests were conducted on the virgin and treated soil specimens. The Bentonite was added at a constant ratio of 6% whilst the groundnut shell ash was increased in the ratio of 0%, 2%, 4%, 6%, 8% and 10%. Samples were prepared at a moulding water content of (-2% ≥ OMC ≤ 4%), adopting BSL and BSH energy levels. Preliminary laboratory test on the natural soil indicated that the soil is A-4(3) and SM according to AASHTO and USCS classification systems, respectively. From the compaction test carried out, it was observed maximum dry density (MDD) increases and optimum moisture content (OMC) decreases upon stepped addition of Groundnut shell ash (GSA). Hydraulic conductivity, volumetric shrinkage strain and UCS values recorded at 6% bentonite/ 6% groundnut shell ash content gave satisfactory results that met the acceptable values of ≤ 1× 10-9 m/s, ≤ 4%, and ≥ 200 kN/m2 for BSL and BSH energy levels, respectively. The overall acceptable range for groundnut shell ash stabilized bentonite-lateritic soil was obtained at 6% bentonite/ 6% groundnut shell ash blend for samples prepared at moulding moisture content of 19.5 – 21.0% and 16.5 – 20.0% respectively. Investigation of leaching capability of groundnut ash into the environment using batch equilibrium test showed that the desorbed values of iron and pH for the optimally modified soil falls within the acceptable values endorsed by the Nigeria industrial standard (NIS) and world health organization (WHO).

Assessment of Corrosion Performance of Steel Rebar in Snail Shell Ash Blended Cements under Marine Environments.

An attempt has been made on a constructive approach to evaluate the performance of snail shell ash (SSA) for its corrosion performance under marine environments. Corrosion performance of steel rebar in chloride-contaminated SSA with (0% to 50%) replacement levels of cement extract medium was examined through electrochemical and weight loss techniques. Initially, snail shell powder (SSP) is made by pulverizing and subsequently SSA is by thermal decomposition methods. Both SSP and SSA were characterized by X-ray diffraction, Fourier transforms infrared spectroscopy, scanning electron microscopy, and energy dispersion X-ray spectroscopy. Concrete cubes with 0% to 50% replacement levels of cement by SSA were evaluated for their mechanical properties. A critical level of 20 to 30% SSA improved both corrosion resistance and strength of concrete. Extrapolation modeling for the strength and corrosion rate with respect to later age were made. SSA is a suitable replacement material for natural limestone in cement productions.

Influence of Calcined Flue Gas Desulfurization Gypsum and Calcium Aluminate on the Strength and AFt Evolution of Fly Ash Blended Concrete under Steam Curing.

In order to improve the early strength of fly ash blended cement concrete under steam curing conditions, fly ash was partly substituted by calcined flue gas desulfurization (FGD) gypsum and active calcium aluminate. The effect of the composition and curing condition on the workability, mechanical property, and volume stability was systematically evaluated. The variety of hydration products and the evolution was determined by XRD to explore the formation kinetic of ettringite. Results show that the addition of calcined FGD gypsum and active calcium aluminate is able to improve the early compressive strength but using more FGD gypsum and a high sulfur aluminum ratio leads to a reduction in compressive strength from 28 to 90 days due to the increment of ettringite and crystallization of dihydrate gypsum. Both the free expansion ratio and limited expansion exhibited a continuous increasement with time, especially in the first 14 days of testing. Cracks were not observed on the surface of samples immersed in water for a year. The improvement of strength and shrinkage resistance is mainly due to the formation of ettringite generated before 14 days and the precipitation was highly limited from 14 to 28 days. Moreover, the characteristic peak of gypsum appeared after 28 days, indicating the conversion of partial of calcined FGD gypsum. The work presented here provides a new solution for improving the early strength of fly ash concrete without reducing the later strength and consuming extra energy.

Chloride Ions' Penetration of Fly Ash and Ground Granulated Blast Furnace Slags-Based Alkali-Activated Mortars.

Due to the need to reduce the CO2 emissions of mineral binders, researchers are considering the use of alkali-activated materials (AAMs) as an alternative to cementitious binders. The properties of AAMs can be more advantageous than those presented by cementitious binders, and thus they can replace Portland cement binders in some applications. Mechanical tests of AAMs are being conducted on an ongoing basis; however, durability issues related to reinforcing steel in conditions in which steel members interact with chloride ions remain unsolved. In this paper, the precursors for AAM preparations are blends of fly ash (FA) and ground granulated blast-furnace slag (GGBFS) in four slag proportions: 0%, 10%, 30% and 50% expressed as a percent of FA mass. Four alkali-activated mortars were prepared, denominated as AAM 0, AAM 10, AAM 30 and AAM 50, respectively. Their basic physical and mechanical characteristics were investigated, as were their gas transport properties. The nitrogen Cembureau method was applied to determine the permeability of the mortar. The transport properties of the chloride ions were determined using the modified NT BUILD 492 migration test. The comparison of results obtained demonstrated a positive effect of GGBFS addition in terms of an increase in bulk density, permeability, porosity and, at the same time, a reduction in chloride ion penetration. The water absorption tests also provided insight into the open pore structures of mortars. The measurements revealed a strong dependence between fluid transport through the mortars and the water absorption and initial water content of materials.

Analytical model predicting the concrete tensile stress development in the restrained shrinkage ring test

Concrete structures may experience unexpected cracking at an early age. Early age cracking can be induced by restrained deformations where tensile stress generated in concrete exceeds its tensile strength. The restrained concrete ring test is often used to evaluate the ability of concrete to resist early age cracking induced by shrinkage. This paper proposed an analytical model of the restrained ring test by capturing the effect of both restrained shrinkage and tensile creep based on the age-adjusted effective modulus theory. The analytical model allows for accurately predicting the tensile stress of the restrained concrete ring based on the experimental measurements of the time-dependent development of elastic modulus, total free shrinkage, and tensile creep of concrete. A numerical finite element simulation was also successfully carried out to validate the new analytical model. Importantly, the model was validated considering a total of 21 concretes consisting of 6 strength grades ranging from 25 MPa to 100 MPa. For each grade, one fly ash blend (30%), two GGBFS blends (40% and 60%) and a reference mix without supplementary cementitious materials were tested.

Influence of Silica Modulus and Curing Temperature on the Strength of Alkali-Activated Volcanic Ash and Limestone Powder Mortar

This present study evaluates the effect of silica modulus (Ms) and curing temperature on strengths and the microstructures of binary blended alkali-activated volcanic ash and limestone powder mortar. Mortar samples were prepared using mass ratio of combined Na2SiO3(aq)/10 M NaOH(aq) of 0.5 to 1.5 at an interval of 0.25, corresponding to Ms of 0.52, 0.72, 0.89, 1.05 and 1.18, respectively, and sole 10 M NaOH(aq). Samples were then subjected to ambient room temperature, and the oven-cured temperature was maintained from 45 to 90 °C at an interval of 15 °C for 24 h. The maximum achievable 28-day strength was 27 MPa at Ms value of 0.89 cured at 75 °C. Samples synthesised with the sole 10 M NaOH(aq) activator resulted in a binder with a low 28-day compressive strength (15 MPa) compared to combined usage of Na2SiO3(aq)/10 M NaOH(aq) activators. Results further revealed that curing at low temperatures (25 °C to 45 °C) does not favour strength development, whereas higher curing temperature positively enhanced strength development. More than 70% of the 28-day compressive strength could be achieved within 12 h of curing with the usage of combined Na2SiO3(aq)/10 M NaOH(aq). XRD, FTIR and SEM + EDX characterisations revealed that activation with combined Na2SiO3(aq)/10 M NaOH(aq) leads to the formation of anorthite (CaAl2Si2O8), gehlenite (CaO.Al2O3.SiO2) and albite (NaAlSi3O8) that improve the amorphosity, homogeneity and microstructural density of the binder compared to that of samples synthesised with sole 10 M NaOH(aq).

Investigation of waste clay brick as partial replacement of geopolymer binders for rigid pavement application

Waste clay brick (WCB) is identified as a feasible alternative cementitious material for producing geopolymer binders to replace ordinary Portland cement (OPC). This study investigated mechanical properties and environmental impacts of one-part geopolymer binders at ambient curing conditions, employing binary blends of WCB with fly ash or slag, while using anhydrous solid sodium metasilicate as the sole activator. WCB was replaced separately with fly ash and slag at 20%, 40%, 60% and 80% by mass to obtain the aluminosilicate precursors. Combination of the aluminosilicate precursors and the solid activator was considered as the total binder. The effect of the alkali activator content, particle size and water-to-binder ratio on compressive strength development were investigated. The strengths of the geopolymers were compared with minimum concrete strength requirements indicated in Australian pavement design guidelines and American Association of State Highway and Transportation Officials (AASHTO) guidelines. The experimental results indicated an optimum activator content of 10% by mass of the total binder for all binary geopolymer systems. Compared to WCB alone and WCB-fly ash blends, binary geopolymer systems of WCB-slag blends showed higher compressive strengths. WCB-slag blends showed high early strength gain and achieved more than 22% and 48% of its corresponding 28-day strength within 24 h and 72 h, respectively. Highest 28-day compressive strength of 81.8 MPa was achieved for the binder with 40% WCB and 60% slag in the precursor. The strength further improved to 96.8 MPa by reducing WCB particle size from 150 µm-passing to 75 µm-passing. Additionally, the environmental impacts associated with the different blends were evaluated considering carbon dioxide emission and energy consumption during their production. These values were subsequently compared with those of OPC manufacturing. The comparison showed that WCB based geopolymer binders can reduce carbon emissions up to 78% and energy consumption up to 85%.

Research on the Ash Melting Characteristics of Blended Coal Based on DFT Calculations

Low-ash-melting-point bituminous coal and high-ash-melting-point anthracite coal are mixed and burned in different proportions. The ash melting characteristics of blended coal were determined experimentally. At the same time, the ash samples of bituminous coal, anthracite, and blended coal were analyzed by X-ray diffraction (XRD), and the ash melting characteristic improvement mechanism of blended coal was analyzed by quantum chemical calculations. The results show that when high-ash-melting-point anthracite is added, the ash melting characteristics of blended coal are improved, and the deformation temperature, softening temperature, hemispheric temperature, and flow temperature of the blended coal are significantly increased. The melting point of blended coal ash with a bituminous coal ratio of less than 50% can meet the requirements of blast furnace injection. The reason for the improved melting characteristics of the blended coal ash is that mullite in anthracite ash reacts with gehlenite in bituminous coal ash during the combustion process to produce anorthite.

Performance of Steel Fiber-Reinforced Alkali-Activated Slag-Fly Ash Blended Concrete Incorporating Recycled Concrete Aggregates and Dune Sand

This study evaluates the performance of alkali-activated slag-fly ash blended concrete made with recycled concrete aggregates (RCA) and reinforced with steel fibers. Two blends of concrete with ground granulated blast furnace slag-to-fly ash ratios of 3:1 and 1:1 were used. Natural aggregates were substituted with RCA, while macro steel fibers with 35 mm of length and aspect ratio of 65 were incorporated in RCA-based mixtures at various volume fractions. Fine aggregates were in the form of desert dune sand. Mechanical and durability characteristics were investigated. Experimental results revealed that RCA replacement decreased the compressive strength of plain concrete mixtures with more pronounced reductions being perceived at higher replacement percentages. Mixtures made with 30%, 70%, and 100% RCA could be produced with limited loss in the design compressive strength upon incorporating 1%, 2%, and 2% steel fibers, by volume, respectively. In turn, splitting tensile strength was comparable to the NA-based control while adding at least 1% steel fiber, by volume. Moreover, higher water absorption and capillary sorptivity and lower ultrasonic pulse velocity, bulk resistivity, and abrasion resistance were reported during RCA replacement. Meanwhile, incorporation of steel fibers densified the concrete and enhanced its resistance to abrasive forces, water permeation, and water transport. Analytical regression models were developed to correlate hardened concrete properties to the 28-day cylinder compressive strength.

Support Vector Machine (SVM)-Based Optimal Design Procedure of Fly Ash Blended Concrete

A support vector machine (SVM) is widely used for predicting the properties of fly ash blended concrete. However, the studies about the optimal design of fly ash blended concrete based on SVM are very limit. This study shows an SVM-based optimal design procedure of fly ash blended concrete. First, we built an SVM model and evaluated the compressive strength of fly ash blended concrete considering the effects of water to binder ratio, fly ash replacement ratio, and test ages. Second, we made parameter studies based on the SVM model. The parameter studies show that fly ash can improve the late age strength of concrete. This improvement is obvious for concrete with lower water to binder ratio. The optimal fly ash replacement ratio increases as the water to binder ratio decreases.

A study on the impact of material synergy in geopolymer adobe: Emphasis on utilizing overburden laterite of aluminium industry

This paper describes the process and scientific approach adopted to utilize overburden laterite of aluminum industry as primary raw material for the development of energy efficient geopolymeric bricks. The geopolymer bricks were developed at ambient temperature with a ternary blend of laterite along with different reject materials of other industrial origin viz. fly ash, rice husk ash, blast furnace slag, different soil from barren lands etc., having sodium hydroxide and sodium silicate as alkali activator. Compressive strength, water absorption, efflorescence and bulk density for the developed blocks were assessed for different considered mix design. The bricks developed using laterite, fly ash and rice husk ash blend showed compressive strength as high as 23 MPa while fulfilling the other criteria of Indian standard 1077:1998. These bricks also shown to have less density, water absorption and more compressive strength compared to commercially available burnt clay and fly ash bricks. Based on the results obtained, synergistic use of over burden laterite along with other industrial rejects is recommended for developing energy efficient building blocks for its bulk utilization. The developed process confirmed zero regeneration of rejects and associated environmental impacts.

Geopolymers Based on Mechanically Activated Fly Ash Blended with Dolomite

This study reports the effect of natural dolomite addition to fly ash and the mechanical activation of this blend on the geopolymerization process. Dolomite was replaced with fly ash at 1, 3, 5, and 10 wt.%. Geopolymers were synthesized at ambient temperature using NaOH solution as an alkaline agent. The geopolymerization process, reactivity of the raw material, compressive strength, and microstructure were studied using X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy. It was shown that blending fly ash with dolomite and mechanical activation improved the geopolymer strength, especially during the early age of curing. For geopolymers prepared using a 90% fly ash + 10% dolomite blend cured for 7 d, the strengths were 8.2-, 2.3-, and 1.4-fold higher than those for geopolymers prepared using 100% FA for 30 s, 180 s, and 400 s milling times, respectively. A simple method for evaluating the increments of mechanical activation, carbonate additives, and the synergistic effect in the increase in the compressive strength of the composite geopolymer is proposed.

Quaternary blended cement mortars containing wood ash, glass and slag powders

AbstractA quaternary supplementary cementitious materials as partial replacement of ordinary Portland cement decreases CO2 emission. This paper has investigated the properties of mortars made from different quaternary blends of wood ash, steel slag powder and glass powder with ordinary Portland cement at different replacement levels of 0, 24, 25, and 30% by weight of the binder. The blended mortar mixtures tested for flow, compressive strength and density. The results showed that the flow of mortars is decreased with the combined use of steel slag powder, glass powder, and wood ash compared with control mix. Compressive strength reduced with the combination of steel slag powder, glass powder and wood ash but this reduction effects is acceptable especially at 24% replacement contain super-plasticizer compared with the ecological benefit.

Signatures of rare earth element distributions in fly ash derived from the combustion of Central Appalachian, Illinois, and Powder River basin coals

The distribution of Rare Earth elements (REE) in coal-derived fly ashes can have distinctive patterns when fly ashes are produced from different coals within or between basins, such as the Pennsylvanian Class F fly ashes from the Illinois and Central Appalachian basins. Both the Fire Clay coal and a blend of a number of eastern Kentucky coals show strong Gd peaks and an H-type distribution in the Upper Continental Crust-corrected plots. The Fire Clay coal-derived ash has a higher heavy REE concentration than the blended coal-derived ash. The Illinois Basin-derived fly as has an overall lower REE concentration than the latter ashes. Class C fly ash derived from Powder River Basin coals has, with the exception of an Eu peak, a flatter distribution of REE and an overall L-type or indistinct H- versus L-type distribution. The signatures of the REE in fly ashes may be useful in predicting their behavior in the extraction of the REE; simple extrapolations from the basic concentrations and the predicted extraction percentages for ashes from different basins are not necessarily indicative of the actual distribution of the extracted REE.

Investigating embodied carbon, mechanical properties, and durability of high-performance concrete using ternary and quaternary blends of metakaolin, nano-silica, and fly ash.

Research for alternative binders has become a necessity due to cement's embodied carbon, climate change, and depletion of natural resources. These binders could potentially reduce our reliance on cement as the sole binder for concrete while simultaneously enhancing the functional characteristics of concrete. Theoretically, the use of finer particles in the cement matrix densifies the pore structure of concrete and results in improved properties. To validate this hypothesis, current research was designed to investigate how the value-added benefits of nano-silica (NS) and metakaolin (MK) in fly ash (FA)-blended cement affect the mechanical and durability characteristics of concrete when used asternary and quaternary blends. Additionally, the cost-benefit analysis and environmental impact assessment were conducted. It was observed that the synergy of MK and NS used in FA-blended cement had a greater impact on enhancing the functional characteristics of concrete, while 10% MK as ordinary Portland cement (OPC) replacement and 1% NS as an additive in FA-blended OPC concrete was the optimum combination which achieved 94-MPa compressive strength at the age of 91 days and showed more than 25% increment in the flexural and splitting tensile strengths compared to the control mix (MS00). The ultrasonic pulse velocity and dynamic modulus of elasticity were significantly improved, while a significant reduction in chloride migration of 50% was observed. In terms of environmental impact, MS100 (30% FA and 10% MK) exhibited the least embodied CO2 emissions of 319.89 kgCO2/m3, while the highest eco-strength efficiency of 0.268 MPa/kgCO2·m-3 with respect to 28-day compressive strength was exhibited by MS101. In terms of cost-benefit, MS00 was determined the cheapest, while the addition of MK and NS increased the cost. The lowest cost of producing 1 MPa was exhibited by MS01 with a merely 0.04-$/MPa/m3 reduction compared to MS00.