Methods for Evaluating Fly Ash for Use in Highway Concrete

Properties of concrete mixtures containing slag cement and fly ash for use in transportation structures

Due to the large quantity of fly ash produced during the combustion of coal, it has become necessary to give greater applicability to this residue of low commercial value. The residue contains inorganic oxides which can act on the crystalline structure of zeolites, namely silicon and aluminum oxide. The coal ash was submitted to physical and chemical treatments with the aim of potentiating the silicon and aluminum extraction from the residue. The pure ash and the treated ashes were characterized by: X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FTIR). By means of the carried out characterizations it was observed that the treatments were effective for the extraction of aluminosilicates from the matrix. The treatments did not affect the morphology, the crystalline phases and neither the chemical composition of the ashes. Seeing this, the coal ash and its treatments showed to be a precursor for the synthesis of zeolites.

With a geological reserve of over 170 billion tons, coal is the most abundant energy source in Mongolia with six operating thermal power stations. Moreover, in Ulaanbaatar city over 210000 families live in the Ger district and use over 800000 tons of coal as a fuel. The three thermal power plants in Ulaanbaatar burn about 5 million tons of coal, resulting in more than 500000 tons of coal combustion by-products per year. Globally, the ashes produced by thermal power plants, boilers, and single ovens pose serious environmental problems. The utilization of various types of waste is one of the factors determining the sustainability of cities. Therefore, the processing of wastes for re-use or disposal is a critical topic in waste management and materials research. According to research, the Mongolian capital city's air and soil quality has reached a disastrous level. The main reasons for air pollution in Ulaanbaatar are reported as being coal-fired stoves of the Ger residential district, thermal power stations, small and medium-sized low-pressure furnaces, and motor vehicles. Previously, coal ashes have been used to prepare advanced materials such as glass-ceramics with the hardness of 6.35 GPa, geopolymer concrete with compressive strength of over 30 MPa and zeolite A with a Cr (III) removal capacity of 35.8 mg/g. Here we discuss our latest results on the utilization of fly ash for preparation of a cement stabilized base layer for paved roads, mechanically activated fly ash for use in concrete production, and coal ash from the Ger district for preparation of an adsorbent. An addition of 20% fly ash to 5-8% cement made from a mixture of road base gave a compressive strength of ~ 4MPa, which exceeds the standard. Using coal ashes from Ger district prepared a new type of adsorbent material capable of removing various organic pollutants from tannery water was developed. This ash also showed weak leaching characteristics in water and acidic environment, which opens up an excellent opportunity to utilize.

Evaluation of blends tincal waste, volcanic tuff, bentonite and fly ash for use as a cement admixture

The basic aim of this research is to evaluate the feasibility of using geogrid incorporated C&D wastes and fly ash as road base or subbase material by conducting laboratory tests and finite element analysis. Various laboratory tests were conducted on C&D waste to check its suitability in base/sub-base course, and finite element analysis was done by using PLAXIS 2D to check the effectiveness of geosynthetic reinforcement. Fly ash was used for the stabilization of subgrade soil (BC soil) and also used in the form of a compacted layer over a stabilized subgrade to improve the bearing ratio. Geogrid reinforcement was used to reduce the critical strains in the pavement. It is concluded that Geosynthetic at middle of base course shows the least settlement of pavement and reducing critical strain.

Although the potential for substantial energy conservation by the use of fly ash in blended cements is well recognized, present test methods and standard specifications do not appear to be adequate to insure predictable performance. A review of the literature led to an analysis of the scientific bases for existing tests for water requirement for pozzolanic activity. Questions are raised concerning the use of fixed proportions in both tests. It is suggested that proportions be adjusted in the mortar flow test to take into account the 45-μm (No. 325) sieve residue of the fly ash. It is also suggested that variable proportions of fly ash and cement be used in the pozzolanic activity tests to facilitate optimization of concrete properties.

Wet storage effects on fly ash mean that processing may be necessary to achieve the physical properties required for use in concrete. This paper considers drying, de-agglomeration and milling of various wet stored fly ashes at laboratory and pilot/benchtop scales, towards meeting these. In the laboratory, different batch quantities and milling times with as-received/pre-screened materials were examined using a ball mill. Greater particle size reductions were obtained with increased milling time but at gradually reducing rates. Pre-screening and batch quantity had relatively minor effects on particle size reductions, with small differences also found between wet and dry stored fly ash. Extended milling time resulted in a darkening of colour; slight increases in loss-on-ignition, the main oxides content and crystalline components; reductions in water requirement (to a point); and greater reactivity. Similar effects were generally noted in concrete for the superplasticising admixture dose to achieve a target slump and compressive (cube) strength. At pilot/benchtop scale, a dryer-pulveriser and spiral jet mill were used, which gave general agreement with the behaviour noted in the laboratory, but with the effects tending to be less. Fineness levels in Standards were achievable, with subsequent performance in concrete, appearing to depend on the milling process used.

Global warming and climate changes are the major environmental challenges globally. With CO2 emission being one of the main greenhouse gases emitted to the environment, and cement and concrete production amounting to about 10% of the global CO2 emission, there is a need for the construction industry to utilize an environmentally sustainable material as an alternative to cement. This study analyzed the cost, CO2 emission and strength properties of green self-compacting concrete (SCC) ternary blend containing fly ash, calcium carbide residue (CCR), and crumb rubber (CR) as a replacement material by volume of cement, cementitious material, and fine aggregate, respectively. Cement was replaced with fly ash at 0% and 40% by volume. CCR was used as a replacement at 5% and 10% by volume of cementitious materials, CR replaced fine aggregate in proportions of 10% and 20% by volume. The result indicated that the mix with 0% fly ash and 20% CR replacement of fine aggregate was the most expensive and had the highest CO2 emission. However, the mix with 10% CR, 40% fly ash, and 10% CCR had the lowest CO2 emission and was therefore the greenest SCC mix. The 28-day maximum compressive strength of 45 MPa was achieved in a mix with 0% CR, 0% fly ash, and 10% CCR, while the utmost 28-day splitting tensile strength of 4.1 MPa was achieved with a mix with 10% CR, 0% fly ash, and 5% CCR, and the highest flexural strength at 28 days was 6.7 MPa and was also obtained in a mix with 0% CR, 0% fly ash, and 5% CCR. In conclusion, a green SCC can be produced by substituting 40% cement with fly ash, 10% fine aggregate with CR, and 10% CCR as a replacement by volume of cementitious material, which is highly affordable and has an acceptable strength as recommended for conventional SCC.

The placement of conventional concrete mixtures in underwater construction results in a high percentage of material loss owing to washout of cement paste. The current paper presents the influence of antiwashout admixture (AWA) on various properties of concrete. Eleven self-flowing concrete (SFC) mixtures using type II cement were proportioned. A combination of low water–cement (w/c), high cement contents, AWAs, fly ash and silica fume were used to enhance the resistance of fresh concrete to washout. The concrete mixtures were proportioned to be highly flowable, self-levelling and cohesive. The w/c materials ratios ranged between 0·35 and 0·39, which corresponds to a typical underwater concrete mixture. The concrete mixtures were tested for slump, slump flow, washout resistance and compressive strength. The compressive strength of each concrete mixture cast under water was determined at 3, 7 and 28 days and compared with the compressive strength of the same concrete mixture cast under normal conditions (in air). Test results indicated that the use of an AWA facilitates the production of flowable concrete mixtures with the added benefit of lower washout loss. Concrete mixture proportioned using type II cement and fly ash at a 15% level of replacement was found to develop SFC that had better fresh and hardened properties and was more resistant to washout. The self-flowing underwater concretes developed 28-day compressive strengths ranging from 20 to 28 MPa.

Concrete as the basic material of the structure in the construction of buildings is composed of hardening a certain mixture of water, cement, and aggregate. Concrete material is familiar in the field of Civil Engineering, because almost every building uses concrete as the main structure and complement, be it bridges, water buildings, or buildings. Because concrete is a composite material, the quality of concrete depends on each of the forming materials (Tjokrodimuljo. K,1996). This study used fly ash and steel slag added materials. In this study using an experimental method that aims to determine the effect of adding fly ash and steel slag levels with a percentage of fly ash 10% and steel slag 20%, fly ash 20% and steel slag 10% from the use of cement and fine aggregates and using conventional concrete as a comparison , and the cement water factor is determined to be the same in all variations, which is 0.45. Until thel used is cylindrical (d = 15cm; h = 30cm), the quality of concrete is planned to be 20 MPa. The number of samples is 18 pieces, each variation consists of 6 pieces tol, 3 samples for concrete compressive strength aged 7 days and 3 samples for concrete compressive strength aged 28 days. In the slump test, there was a reduction in the slump value, which was 12 cm for conventional concrete, 11 cm for variation I concrete mixture and 8 cm for variation 2 concrete mixture. The results of the compressive strength test showed an increase in maximum compressive strength at the age of 7 & 28 days with a percentage of fly ash 20% and steel slag 10% which was 19.91 MPa & 29.82 MPa and the lowest compressive strength occurred in conventional concrete, which was 16.32 MPa at the age of 7 days and 25.19 Mpa at the age of 28 days. With a percentage increase of 15.5% from conventional concrete

This paper presents the results of a study to evaluate the potential of modified fly ash for use as a construction material. Study results indicate that modified flay ash with and without cement developed adequate compressive strength to be used as fill material in embankments and dykes. Compacted modified ash also exhibited very low permeability characteristics. Replacement of 35% cement by modified fly ash produced 20% more strength than portland cement mix at 28 days.

Experimental investigation of eco-friendly high strength fiber-reinforced concrete developed with combined incorporation of tyre-steel fiber and fly ash

Aimsnnnnnn n This thesis investigated the use of fly ash in concrete by establishing reliable andnaccurate test data on the properties of concrete incorporating different fly ashncontent. In addition, the study focussed on typical uses by local governmentnauthorities in pathways, such as footpaths and bicycle ways, and also looked atnenvironmental impacts, incorporating durability and construction constraints in thenlife cycle costing issues. The aims of the project were:nnn nnn b To obtain experimental data on mechanical properties and durabilityncharacteristics of fly ash concrete containing 23-50% fly ash with a 28-dayncompressive strength of 25MPa;n b To assess the effect of curing on the properties of concrete incorporatingndifferent percentages of fly ash; andn b To draw conclusions as to the cost effectiveness of concrete incorporatingnlarge amounts of fly ash by comparing life cycle assessments that includendurability, construction and environmental factors.nnnnn n Scopenn n This investigation of the high volume fly ash concrete was for the purpose ofnextending its application in footpaths and bicycle ways. Several concrete mixesnusing fly ash at levels ranging between 23-50% as a partial replacement ofnPortland cement were investigated. All concrete mixes had a 28-day compressivenstrength of 25MPa, and were applicable to the footpaths and bicycle waysnconstruction. The effect of fly ash on the mechanical properties of the concretenmixes was determined under standard moist curing and ambient conditions. Thentested properties included setting time, compressive strength, splitting tensilenstrength, flexural tensile strength, drying shrinkage and abrasion resistance.nnnnnn n The test apparatus, procedures and testing data are described in detail. Testnresults are reported and compared. In addition to the experimental work, a simplenlife cycle assessment (LCA) and life cycle cost analysis (LCCA) were undertaken to evaluatenthe environmental impact and cost effectiveness of using high volume flynash in concrete pavement construction. The energy consumption and CO2nemissions were compared between high volume fly ash concrete and the typicalncommercial concrete in the environmental life cycle assessment. The life cycle costnanalysis included the costs of initial material cost, construction, rehabilitation, andnresidual values in the whole life cycle period of pavement structures.nnnnnn n Conclusionsnn n According to the analysis of the experimental results, it is feasible to producenconcrete with fly ash replacement of up to 50%, without significantly altering thenconcrete properties in the hardened state. However, high volume fly ash concretenwith 50% fly ash replacement retarded the setting time by up to 6.5 hours, whichnshould be considered in LCCA. High-volume fly ash concrete gained highernultimate strength under standard moist curing conditions. In typical pavementnconstruction, it is often difficult for the design engineer to ensure that adequatencuring, as per the construction specification, occurs. Indeed, evidence suggestsnthat in many applications curing of concrete pavements does not occur at all.nHowever, without adequate curing, no strength development was observed after 28ndays for high volume fly ash concrete. The 28-day abrasion resistance is verynsimilar for all mixes with various fly ash percentages, but use of a curing compoundnincreased the wear and tear properties of fly ash concrete to some extent.nnnnnn n Based on the information provided by the local industry and the results of thenenvironmental life cycle assessment and life cycle cost analyses, the followingnconclusions are summarized:nnn nnn b From the environmental life cycle assessment, 50% fly ash concrete is the bestnalternate for pavement design with 20% energy and CO2 savings compared tontypical concrete;n b However, in terms of life cycle cost analysis, when variability is considered innthe inputs (cost, setting time, service life, etc.), the typical 23% fly ash concretenwould be the most cost effective material in footpath and bicycle waysnapplications; andn b The results of LCCA are highly dependent on the setting time of concrete.nWhen using setting accelerator admixture in high volume fly ash concrete, the costneffectiveness is dependent on the efficiency of the admixture to reducensetting time. Without an increase in construction cost, the high volume fly ashnconcrete would have a similar life cycle cost to typical concrete.n

Innovations in material technology are expected to reduce the use of commercial cement and replace it with other environmentally friendly materials with the same performance as normal concrete. Aim: This study aim to analyze the mechanical property of High-Volume Fly Ash Concrete (HVFAC) using F class fly ash with different mix percentages. Methodology and Results: The experiment was conducted in laboratory scale. Four variations of test specimens consisted of: 1 variation (F0), which is conventional concrete with 100% Portland cement as control specimen, and three variations of HVFC (F70, F80, and F90), which were made with fly ash content (%) 70, 80, and 90 of total cementitious. Fresh concrete testing to determine workability, while hard concrete testing is done by density and compressive strength tests at the age of 3, 7, and 28 days on specimens that have been treated with the water submerged curing method. Conclusion, significance, and impact of study: All HVFAC specimens fulfill the Self Compacting Concrete (SCC) category. The compressive strength test results at 28 days showed that the addition of fly ash percentage caused a decrease in compressive strength values in all HVFAC variants, but still exceeded the minimum requirements of high and medium quality concrete. All HVFAC variations meet the requirements of ASTM C618-23 based on the evaluation of Strength Activity Index (SAI) values at 7 and 28 days of age. The utilization of 90% fly ash as a cement substitute resulted in an environmentally friendly concrete product based on the concept of cleaner production.

Compressive strength and microstructure properties of modified concrete incorporated effective microorganism and fly ash