Fly Ash Mixtures Research Articles

Monitoring of domestic wastewater treatment via infiltration percolation using impedance spectroscopy

In this study, we treated domestic wastewater originating from the city of Oulad Frej using a novel treatment technology called percolation infiltration. The filtration medium consisted of a mixture of fly ash and sea sand sourced from the coast of Essaouiria. The filtration process yielded remarkable results, achieving an impressive reduction of 80% in COD, 70% in BOD5, 86% in suspended matter (SM), and 81–99% in heavy metals. Moreover, significant improvements were observed in terms of discoloration and pH reduction. To assess the efficacy of the domestic wastewater treatment technology, we introduced a new key indicator, complex conductivity σ * (ω), and monitored its changes before and after treatment. The impedance spectra analysis showed a strong correlation with the parameters obtained through conventional methods.

Fly ash and sorbent particles agglomeration and removal in system of electrostatic agglomerator and electrostatic precipitator

The paper presents experimental studies on the effect of sodium bicarbonate and calcium hydroxide dry, low temperature sorbent injection on the concentration and size distributions of precipitated particles (fly ash and sorbent particles mixture), fractional collection efficiency, and particles morphology. The measurements were carried out on a lab-scale system comprising unipolar electrostatic agglomerator and electrostatic precipitator. In the experiments presented in this paper, the sorbent was injected upstream of electrostatic agglomerator. Results of SEM studies revealed the process of sorbent and fly ash particles agglomeration. The measurement of resistivity of fly ash and sorbent mixtures have shown that injected sorbent has a large effect on the particles resistivity, when the temperature of dust cake is increasing. In practical situations, too high resistivity can lead to back corona discharge generation, while too low causes the particles re-entrainment; both of these phenomena can reduce the dust collection efficiency of an electrostatic system.

Study on mechanical properties of coal gangue and fly ash mixture as backfill material based on fractal characteristics.

Backfill mining can effectively alleviate the problems of surface collapse and ecological water pollution, in which the mechanical properties of backfill materials, including coal gangue and coal fly ash, have a decisive role in the effect of filling mining. In this study, we analyze the permeability characteristics of coal gangue filler through a set of homemade percolation test systems and introduce fractal characteristics to investigate the key factors affecting percolation in complex pores of broken coal gangue. The results indicate that the fractal dimensions of crushed coal gangue particles show an increasing trend with increasing axial loading and that the variation range is from 2.15647 to 2.58933. The coal fly ash concentration has a positive relationship with the acceleration factor. The permeability of crushed coal gangue follows a hierarchical distribution law and the permeability changes in the magnitude range of 10-11 ~ 10-9 m2. The fractal dimension is inversely related to the permeability of crushed coal gangue. The experimental results show that the coal gangue will be further crushed and that adding a certain concentration of coal fly ash can achieve a better water barrier, which provides theoretical support and engineering significance for the stability analysis of geological engineering and backfill mining technology.

Utilization of Granular Wastes in Transportation Infrastructure

Abstract Attributed to environmental preservation in urban infrastructure development, the recycling of waste materials produced in the coal and steel industry as well as the reusing of waste tires is a high priority in Australia. In this article, the practical applications of (i) coal wash (CW) and steel furnace slag mixtures, (ii) CW and fly ash mixtures, and (iii) rubber elements derived from recycled tires are discussed. In this regard, some examples of real-life applications are elucidated in relation to coastal reclamation as well as road and rail construction (e.g., Port Kembla, Kangaroo Valley highway, and Chullora Rail Precinct). The article outlines various aspects of site investigation, construction techniques, and the installation of instrumentation to evaluate the field performance of these waste materials in contrast to traditional (natural) quarried materials. The results from these case studies demonstrate that properly engineered granular waste mixtures can exhibit promising characteristics even to exceed the current technical standards, implying reduced intensity of maintenance. The research outcomes strongly support sustainable solutions to be embraced in the future development of transportation infrastructure, capable of withstanding increased freight loading and enhanced longevity.

Effect of Curing Temperature and Free Lime Content in Fly Ash on Basic Properties and Autoclave Expansion of Fly Ash Mixtures

Effect of Curing Temperature and Free Lime Content in Fly Ash on Basic Properties and Autoclave Expansion of Fly Ash Mixtures

Effects of Fly Ash Composition to Mitigate Conversion of Calcium Aluminate Cement Composites

Calcium aluminate cement (CAC) is one of the alternative cements that is widely used for special applications. However, during the hydration process degradation of CAC microstructure, the so-called hydrate conversion process, hexagonal calcium aluminate hydrate (CAH10) transforms into a cubic (C3AH6) phase, resulting in increased porosity and reduced strengths. It is known that alternative means for stabilizing the CAC conversion are conducted by introducing fly ash (FA) in CAC, where its microstructure is attributed to aluminosilicates. However, no study has yet been conducted on different FA compositions influencing CAC performance. This study aims to evaluate the effects of different compositions of FA on CACs’ fresh and hardened characteristics. Results revealed that the microstructure was denser when CAC was mixed with FA. Regarding reactivity, CAC with calcium-rich FA systems is 13% faster than the silica-rich one. The higher the density and the lower the porosity of calcium-rich FA mixtures were found compared with silica-rich FA in both micro- and macro-structures. As seen in the microscopic structure, this is due to the calcium-rich phase formation.

Investigation of physicochemical processes taking place in chemically activated very high volume fly ash mixtures

In order to reduce the negative impact of cement production on the natural environment, and in particular to reduce CO2 emission, new types of binders are sought. It is beneficial to use supplementary cementitious materials, such as fly ash. A very high volume of fly ash and a reduced amount of cement in the binder can, however, result in deterioration of some properties of the final composite. Such systems require activation. The aim of this work was to investigate the effects of different activators: spent aluminosilicate catalyst (very active pozzolanic material), Na2SO4 and Ca(OH)2 on the hydration/activation processes and development of 28-day compressive strength of the blends containing a very high volume of fly ash. Activators were introduced into the system in various combinations: alone or in mixtures. The following research methods were used: calorimetry, thermal analysis, X-ray diffraction and IR spectroscopy. It was shown that each type of activation accelerates cement hydration, improves pozzolanic activity and increases compressive strength compared to the results of non-activated reference sample. However, the activation kinetics and mechanism of interaction are different for different activators. The most promising results were obtained for the combination of three activators: spent aluminosilicate catalyst, Na2SO4 and Ca(OH)2.

KAJIAN KETAHANAN BETON DENGAN TAMBAHAN CAMPURAN FLY ASH DAN LIMBAH KARBIT DALAM MEDIA ASAM DAN GARAM (DURABILITY STUDY OF SELF COMPACTING CONCRETE WITH ADDED A MIXTURE OF FLY ASH AND CALCIUM CARBIDE WASTE IN ACID AND SALT MEDIUM)

Cement is one of the building blocks of concrete. However, it releases about one ton of carbon dioxide (CO2) gas for every ton of cement produced. Therefore, it is necessary to replace cement in the manufacture of concrete. It is known that a mixture of fly ash and calcium carbide waste has a chemical composition that resembles cement containing silica, alumina, and calcium oxide compounds so that it has the potential to replace cement in making self-compacting concrete. This research was conducted by utilising fly ash waste and carbide waste as additional materials to replace the use of cement by 35% in self compacting concrete. The composition of the waste used in the concrete mix in this study consisted of 25% fly ash waste and 10% calcium carbide waste. Analysis of the elemental composition of self-compacting concrete containing fly ash and calcium carbide waste was obtained from XRF data, the compressive strength of self-compacting concrete samples was tested, their resistance in acid and salt media was studied through the results of compressive strength test analysis, then compared with self-compacting concrete containing 100% cement. The XRF results showed that the elemental composition of the mixture of fly ash, calcium carbide waste, and cement was similar to that of cement alone, but the CaO and SiO2 content of the mixture was still higher than that of cement alone. Based on the compressive strength test analysis results, it was found that the compressive strength values of the self-compacting concrete samples were lower than the compressive strength values of the control of self-compacting concrete samples (cement only). Self-compacting concrete samples soaked in acid and salt media for 28 days showed a decrease in compressive strength, both in self compacting concrete containing a mixture of fly ash, calcium carbide waste, and cement, and concrete containing only cement. The compressive strength values of the fly ash and calcium carbide waste on self-compacting concrete samples in this study were at the range of 28 MPa to 29 MPa, still within the SNI 2847-2019 quality standard, which is the normal concrete quality standard with a compressive force of 15-30 MPa, even though they have been exposed to acid or salt. This allows efforts in replacing cement in self compacting concrete by adding the composition of fly ash waste and calcium carbide waste.

Clay/Fly Ash Bricks Evaluated in Terms of Kaolin and Vermiculite Precursors of Mullite and Forsterite, and Photocatalytic Decomposition of the Methanol–Water Mixture

This study focused on mullite-based and forsterite-based ceramic bricks fired at 1000 °C from mixtures of fly ash (40 mass%) and kaolins or vermiculites (60 mass%). The structural, physical, and mechanical properties were characterized by X-ray powder diffraction, nitrogen physisorption, mercury porosimetry, thermogravimetry, and compressive strength. In the development of green-material-derived photocatalysts, we evaluated fly ash ceramic bricks based on kaolins and vermiculites, which deserve deeper research. Alkali potassium in the mixtures positively influenced the reduction of the firing temperature, shrinkage, small porosity, and high compressive strength of ceramic bricks. The crystallization of mullite in fly ash was observed on exotherm maxima from 813 to 1025 °C. Muscovite/illite admixture in kaolins precursor of mullite-based ceramics reduced the crystallization temperature of mullite by up to 70 °C. Vermiculite–hydrobiotite–phlogopite in mixed layers of a raw vermiculite precursor of forsterite-based ceramics controlled the formation of enstatite and forsterite in the temperature range from 736 ± 6 °C to 827 ± 6 °C. Mullite- and forsterite-based ceramic bricks were also investigated for photocatalytic hydrogen production. The photocatalytic generation of hydrogen in the presence of mullite-based ceramic bricks was positively correlated with the percentages of Fe2O3 in the lattice of mullites and in the presence of forsterite-based ceramics with the presence of diopside. Mullite-based ceramic produced the highest yield of hydrogen (320 µmol/gcat after 4 h of irradiation) in the presence of mullite with the highest 10.4% substitution of Fe2O3 in the lattice. The forsterite-based ceramic produced the highest hydrogen yields (354 µmol/gcat after 4 h of irradiation) over more active diopside than forsterite.

Geopolymers Based on a Mixture of Steel Slag and Fly Ash, Activated with Rice Husks and Reinforced with Guadua angustifolia Fibers

At present, the conservation of the environment represents an objective that everyone wants to achieve. The construction industry has influenced the advancement of alternative materials that comply with sustainable development. In this article, reinforced concrete was obtained by mixing 80% blast furnace slag and 20% fly ash. These concentrations were chosen because they provide the lowest porosity in the cementitious matrix. Rice husk ash was used as an activator. Guadua angustifolia fibers were used to evaluate the mechanical performance of the concrete. The composition of the raw material was determined by X-ray fluorescence, the microstructure of the fibers by AFM, and the SEM technique was used to determine the surface characteristics of guadua fibers and concrete mixes. The structural characterization using XRD, the structure of the molecules of the guadua fiber, and the composition of the mixture’s molecular mixtures were determined by FTIR spectroscopy. Its properties, such as tensile strength and flexural strength, were analyzed. The results indicated that the concrete with the addition of Guadua angustifolia fibers. The results indicated that the concrete with the addition of guadua angustifolia fibers showed the best mechanical behavior. Tensile strength was optimized, establishing values of 2.68 MPa for unreinforced concrete and up to 3.12 MPa for fiber-reinforced concrete. The flexural strength values increase at ages after 28 days due to the pozzolanic reaction generated. Values of 2.8 MPa were obtained for concrete without fiber and 3.5 MPa for concrete reinforced with guadua angustifolia fiber.

Strength-Gain Characteristics and Swelling Response of Steel Slag and Steel Slag–Fly Ash Mixtures

The shear strength and stiffness characteristics of steel slag indicate that it can potentially be utilized as a competent base/subbase material of bound and unbound pavement layers. However, concerns with respect to the utilization of steel slag remain due to its long-term swelling, corrosivity, and leaching characteristics. In this study, long-term swelling and corrosivity tests were performed on basic-oxygen-furnace steel slag (BOFSS) and electric-arc-furnace ladle steel slag [EAF(L)SS] generated in Indiana, USA. In order to reduce the 1D swelling strains of these slags, 5%, 10%, and 20% Class C fly ash (CCFA) and 10% ground rubber replacement ratios were used to prepare steel slag mixtures for testing. The improvement due to CCFA replacement was evaluated by performing unconfined compression and long-term swelling tests on selected steel slag–CCFA mixtures. The seven-day unconfined compression strengths of 90% EAF(L)SS + 10% CCFA and 90% BOFSS + 10% CCFA mixtures were 2,387 and 3,768 kPa, respectively. After nine months of monitoring, the maximum 1D swelling strains of soaked samples of BOFSS and EAF(L)SS mixtures prepared with 10% CCFA replacement were 0.1% or less. The unconfined compression and swelling test results for the steel slag–CCFA mixtures indicated superior strength gain characteristics and negligible swelling strains with time than for steel slags.

Pemanfaatan Limbah Fly Ash dan Spent Bleaching Earth sebagai Substitusi Semen pada Beton Mutu Normal Skala Produksi

In the era of industry and technology in Indonesia, environmental problems due to waste are problems that require wise handling. Fly Ash (FA) waste from PLTU activities and Spent Bleaching Earth (SBE) waste resulting from the palm oil production process are very abundant, thus polluting the environment. Indonesia is currently prioritizing physical infrastructure development, which aims to improve connectivity and encourage economic growth in every sector. The development process that occurs increases the use of concrete. Concrete has a tremendous impact on the environment because most of its composition is cement. The use of cement in the manufacture of concrete results in the emission of large amounts of CO2 gas into the atmosphere, which causes an increase in global warming. The use of concrete can have a lower environmental impact if the use of cement is reduced as much as possible by adding a mixture of FA and SBE wastes. This research will utilize FA and SBE waste in the manufacture of normal concrete production weights and aim to determine the optimal composition of FA and SBE waste that is economically and environmentally feasible. The results of the research by applying FA and SBE substitutions show that FA is better than bleaching earth in the resulting compressive strength. The optimal composition of FA as a substitute for cement to achieve the quality of the planned concrete is 15%, while the composition of SBE as a substitute for cement is 10%. Keywords: concrete, Fly Ash (FA), Spent bleaching earth (SBE), concrete compressive strength ABSTRAK In the era of industry and technology in Indonesia, environmental problems due to waste are problems that require wise handling. Fly Ash (FA) waste from PLTU activities and Spent Bleaching Earth (SBE) waste resulting from the palm oil production process are very abundant, thus polluting the environment. Indonesia is currently prioritizing physical infrastructure development, which aims to improve connectivity and encourage economic growth in every sector. The development process that occurs increases the use of concrete. Concrete has a tremendous impact on the environment because most of its composition is cement. The use of cement in the manufacture of concrete results in the emission of large amounts of CO2 gas into the atmosphere, which causes an increase in global warming. The use of concrete can have a lower environmental impact if the use of cement is reduced as much as possible by adding a mixture of FA and SBE wastes. This research will utilize FA and SBE waste in the manufacture of normal concrete production weights and aim to determine the optimal composition of FA and SBE waste that is economically and environmentally feasible. The results of the research by applying FA and SBE substitutions show that FA is better than bleaching earth in the resulting compressive strength. The optimal composition of FA as a substitute for cement to achieve the quality of the planned concrete is 15%, while the composition of SBE as a substitute for cement is 10%. Kata kunci: beton, Fly Ash (FA), Spent bleaching earth (SBE), kuat tekan beton

Investigating the effects of stabilization carried out using fly ash and polypropylene fiber on the properties of highway clay soils

Improving highway subgrades is the most crucial step that increases the performance and longtime durability of pavements. Using fly ash to improve the properties of subgrades and synthetic fibers as additives to increase their strength in recent years is an effective method. It is essential to determine how fly ashes affect the strength properties of subgrade soils in the long term with a time-dependent curing effect and how synthetic fibers affect the strength properties of subgrade soils, especially in the short term before curing. Furthermore, another vital issue is determining the extent to which freeze–thaw cycles that occur during winter months due to regional climatic conditions reduce the strength of the subgrade soils. For this purpose, a regional high-plasticity soil representing the problematic subgrade was reinforced with fly ash at different percentages (10%, 20%, 30% and 40%), and a series of experiments were carried out to determine the plasticity, compressibility and strength properties of these soil mixtures. Besides the clayey soil and fly ash, the microstructures of these mixtures were also examined by XRF, XRD spectrometry, FT-IR spectroscopy and SEM analyses and the relationships between mechanical behavior and microstructure were tried to be explained. Furthermore, the impact of polypropylene fibers added to the soil at 0.5% of the dry mass and freeze–thaw cycles on the strength of the subgrade soils was determined. The results showed that the effective fly ash mixture ratio for stabilization with fly ash was 10%, and when the 28-day unconfined compressive strengths of the fly ash mixture and the natural soil were compared, the fly ash mixture increased the strength by 85.8%. Furthermore, the fiber additives were determined to increase the shear strength at ratios ranging from 3.0% to 21.0% and that approximately 80% strength loss occurred in the natural soil due to freeze–thaw cycles, but fly ash and synthetic fiber additives can increase the strength by compensating for the strength loss caused by freeze–thaw cycles.

Penyisihan Krom Dalam Limbah Cair Laboratorium Dengan Metode Adsorpsi dan Fitoremediasi

The laboratory is one of the units that produce liquid waste which in addition to having infectious properties is also toxic, which if not managed properly will have the potential to damage the ernvironment and living things. Laboratory wastewater treatment is important because the treament and procurement of WWTPs that meet the requirements are very high cost, therefore it is neceessary to do research to find a simple but effective liquid waste treatment technology to reduce the level of liquid waste parameters, easy to make, using local materials, and the price is affordable. This study aims to determine the performance of sandston/gravel media, fly ash, vetiver (Vetiveria Zizanoides L), and the third mixture in reducing chromium content in laboratory wastewater by applying adsorption and phytoremediatioon methods. The liquid waste used is artificial waste made of Potassium Dichromate with a concentration of 15 mg/L. This research was conducted on a laboratory scale, using beaker. Adsorption experiments were carried out on fly ash and gravel media with weight variations of 20 g (2% w/v), 30 g (3% w/v) and 50 g (5% w/v). Phytoremediation experiments were carried out on vetiver (Vetiveria Zizanoides L) with variations in plant weight, namely 70 g (2% w/v), 170 g (3% w/v) and 200 g (5% w/v), while fro adsorption experiments the mixture of gravel and fly ash was carried our with variatons in weight of 40 g (2% w/v), 60 g (3% w/v) and 100 g (5% w/v) with ration of 1:1, respectively. The mixture of gravel, fly ash and plants was carried out in a ratio of 1:1:1 with a weight of 100 g each. Observations were made on chromium levels on day 1 and 15. The results showed that the removal of chromium levels in each adsorption experiment using gravel was an average of 0,32 mg/L, whilae adsorption using fly ash average 1.58 mg/L; 10.135 for fly ash; 2.00% for gravel, and 24.16% for vetiver. The decrease ini chromium levels with vetiver plants was 3,78 mg/L on average. The highest removal efficiency (RE) value of 76.64% occured in the adsorption and phytoremediation experiments using vetiver plants and a mixture of fly ash and gravel media a ratio (1:1:1) with each weight of 100 g (5% w/v).

Is it possible to achieve High-Quality Concrete with Partial Substitution of Fly Ash?

This study aims to determine the characteristics of high-quality concrete using fly ash as a partial replacement for PCC cement. Tests include slump testing, density factor and concrete compressive strength testing. Two variations of the concrete mix are made, namely the variation without fly ash and the 15% fly ash mixture. The results of this study indicate that the characteristics of concrete with fly ash substitution require the same amount of water as the concrete without fly ash to achieve the desired slump value. The density factor values obtained are also the same. In the concrete compressive strength test, the variation of the 15% fly ash mixture was higher than that of the 0% fly ash mixture.

An experimental investigation on concrete blocks using Ferrock as a green binding material

Environmental pollution is one of the greatest concerns humankinds has faced in the recent decade due to unprecedented usage of resources and subsequent waste generation in tandem with industrialization, which has had a huge impact. Among the activities humans do, construction is one of the most vulnerable, which creates large quantities of pollution due to the production of various construction wastes during the production of ingredient materials and their usage. Concrete is usually used in the construction of buildings and infrastructure. Concrete, one of the most widely used construction materials, necessitates the use of cement, which is one of the major polluters. The cement industry is one of the main sources of carbon dioxide, a potent greenhouse gas. The cement industry produces nearly 8% of all man-made greenhouse gas emissions worldwide. Industrial industries are becoming increasingly interested in reducing concrete-related carbon emissions. Many studies have been performed on the development of green concrete by substituting other renewable and sustainable materials for cement. Ferrock is used as a substitute for cement in this study to create Ferrock Concrete. Ferrock is a mixture of iron dust, fly ash, lime powder, metakaolin, and oxalic acid that is used as a binder. It reacts with CO2 and water, producing iron carbonates thanks to the action of an oxalic acid catalyst. During the hardening process, ferrock concrete absorbs carbon dioxide. The specific objective of this study is to design a Ferrock concrete and compare it with M25 grade of conventional concrete. Parameters including workability, compressive strength, split tensile strength and flexural strength are compared with conventional concrete to obtain its real performance.

The Effect of Fly Ash Mixture on Concrete Compressive Strength

Fly ash is a waste from the steam power plant industry that can be used as added material in making concrete. This is because the chemical compounds in fly ash are almost the same as cement. The purpose of this study was to determine the compressive strength of concrete with partial replacement of cement with fly ash. The composition of partial replacement of cement with fly ash is 0%, 20%, 25%, 30%, and 35%. The planned concrete quality is 30 MPa and tested at the age of 7 days and 28 days. The test results show the average compressive strength of the concrete for all variations of both 7-day and 28-day replacement is less than 30 MPa. The greater composition of fly ash used, the smaller the compressive strength value of the concrete. This is caused by the slow hydration process because fly ash is pozzolans which delay the hydration process. In addition, the reduction of cement content will also result in a decrease in compressive strength, this is because the bonding capacity of the aggregate decreases. However, when viewed based on the density of the concrete, the fine fly ash grains can make the concrete denser.

Data‐driven approach for investigating and predicting of compressive strength of fly ash–slag geopolymer concrete

AbstractFly ash–slag geopolymer concrete is an intangible material that does not use conventional Portland cement, thereby reducing CO2 emissions into the environment, and helping to increase sustainable development. However, compared with conventional concrete, the compressive strength of fly ash–slag geopolymer concrete is complexly dependent on many factors. Using the data‐driven approach for investigating and predicting fly ash–slag geopolymer concrete compressive strength is a suitable choice. This study introduces 11 easily accessible machine learning models in open‐source libraries of the Python programming language such as support vector machine, random forest (RF), gradient boosting (GB), AdaBoost, decision trees, light GB machine, extreme GB (XGB), K‐nearest neighbors, multivariable regression, Gaussian process regression, and CatBoost (CatB). Based on a dataset of 158 samples, 14 inputs, and 1 output variable compressive strength, the performance of 11 machine learning models was evaluated through 4 criteria including coefficient of determination, root mean square error, mean absolute error, and mean absolute percentage error combined with 10 repeats of 10‐fold cross‐validation. Four models have the best performance based on the above four criteria value in determining compressive strength for testing dataset sorted descending is CatB > XGB > RF > GB. Global Shapley (SHAP) value‐based CatB and XGB indicates three groups of factors with decreasing influence on compressive strength of geopolymer concrete: group I (slag, molarity, coarse aggregate, curing temperature, and alkaline activator/binder) > group II (Na2SiO3 content, NaOH content, fine aggregate, fly ash content), curing period > group III (extra water added, NaOH/Na2SiO3, superplasticizer content, rest period). Extra water added, NaOH/Na2SiO3, superplasticizer content, rest period have insignificant influence on the compressive strength value of geopolymer concrete. The greater the slag content in the slag–fly ash mixture, the greater the compressive strength of geopolymer concrete. The optimum molarity of NaOH concentration is about 14–16 M for designing the compressive strength of geopolymer concrete. SHAP values partial dependence plots (PDP) and PDP indicate that alkaline activator/binder optimal values exist to achieve high compressive strength. The compressive strength increases with curing temperature between 20 and 100°C. PDP values show that the tendency to increase compressive strength with increasing coarse aggregate content from about 750 to 1250 kg/m3.

Research on effects of the cement and magnesium oxide contents on some characteristics of stabilized dredging soil in Ca Mau province

Using a mixture of cement combined with additives including (fly ash, blast furnace slag and magnesium oxide) to harden dredged silt as a substitute for sand is necessary in construction areas where sand resources are scarce nature. In the study, the mixtures (cement + fly ash + ground blast furnance slag + magnesium oxide) were used to harden mud in brackish and salt water areas in Ca Mau province of the Mekong Delta. The experimental results show that when hardening dredged sludge with content of 6% Cement combined with a mixture of ground blast furnace slag, fly ash and MgO, the viscosity, internal friction angle, adhesive force and compressive strength of the mixture sludge solidification will improve. The higher the ratio of MgO content, the lower the viscosity; the greater the internal friction angle, adhesive force and compressive strength of the hardened sludge. However, in order to balance the design requirements of the sludge after hardening, it was found that: With the rate of 4% fly ash, 2% ground blast furnace slag and 0.5% MgO, the design requirements were met, the quality of the dredging soil after hardening meets the requirements according to TCVN 8217:2009, equivalent to the hard plastic state (0.25 < IL < 0.5, Ctc = 32÷57 kPa and  = 11 ÷ 18°). With such hardening mud quality, it will meet the requirement of replacing sand for embankment, embankment and other works in Ca Mau in particular, and the whole Mekong Delta in general.

Modification of Used Rubber Tire Mortar with Fly Ash Addition

Used tire rubber mortar has been studied for its physical, mechanical, and dynamic properties. Adding used tire rubbers to the mortar is considered effective in improving the brittle properties of the mortar, as well as increasing the mortar's elasticity and damping ability. However, the higher the tire rubber content, the lower the strength of the mortar. Therefore, the use of tire rubber mortar has some limitations. This study investigates the possibility of fly ash as an admixture in tire rubber mortar to enhance its compressive strength. The compressive strength test follows the provisions of ASTM C-109, with a cube-shaped test object measuring 5x5x5 cm3. The specimen type consists of normal mortar, 30%, and 40% tire rubber mortar. Variations in fly ash content are 0%, 5%, 10%, 15%, 20%, 25%, and 30%, respectively. Compressive strength tests were conducted when the mortar was 14, 28, and 56 days. With five specimens for each variation, 245 specimens were tested. The test results show that adding fly ash can be recommended to increase the compressive strength of tire rubber mortar, with a maximum content of 20% by weight of cement. The tire rubber mortar with fly ash mixture experienced a significant strength in 28 – 56 days due to the escalation of fly ash adhesion between the rubber paste and cement.