Fly Ash Cement Research Articles

Activity Concentration Index Values for Concrete Multistory Residences in Greece Due to Fly Ash Addition in Cement

According to 2013/59/Euratom Directive, the activity concentration index (ACI) is required to be estimated for each building material that is of concern from a radiation protection point of view. This index applies to building materials and not to constituents that cannot be used as building materials themselves. Fly ash is a byproduct of coal-fired power plants and is one of the main constituents of cement. The radioactivity in fly ash that is produced by Greek lignite power plants cannot be considered insignificant. For example, in the case of the Megalopolis power plant, the concentration for radioisotopes of the 226Ra chain is found to be about 1 kBq/kg. Since natural radionuclide concentrations, which are harmful to human health in terms of radiation exposure, exist in fly ash, ACI should be assessed for building materials containing fly ash. The present study evaluates the ACI of concrete containing fly ash cement when used in multistory residential buildings. Results showed that cement produced in Greece by the three main Greek cement production plants, containing lignite fly ash, and used as a material for concrete multistory constructions, should not be considered as “of concern from a radiation protection point of view”. Each country that wishes to evaluate the use of fly ash into constructions should repeat the method for the ACI uncertainty budget proposed in this study, to assess whether it significantly exceeds the reference value (whether it is of concern from a radiation protection point of view).

Suitability of Fly Ash-Cement Kiln Dust Columns for Stabilizing Expansive (Black Cotton) Soils

The paper focuses on the potential use of industrial wastes, which are fly ash (FA) and cement kiln dust (CKD), to stabilise expansive soils like black cotton (BC) soil for construction purposes. Although many soil stabilisation methods exist, the placement of columns consisting of industrial wastes has yet to be tested. Knowing the pozzolanic action and mechanism between the waste product and the soil, this method of placing the industrial waste as a remedy should be trialled. Therefore, this paper proposes and investigates the placement of FA-CKD columns into the soil via a series of laboratory experiments using myriad mixtures and combinations of placement of such columns. The effect of moulding water content and curing time on the BC soil’s consolidation and strength behaviour was also assessed here. Through the experiments, it is found that the optimum mixture of FA-CKD for the columns is at 90%-10%, respectively. This column mixture has been evidenced to improve the unconfined compressive strength of the soil significantly, where its performance improves with curing time. The highest strength improvement can be found at optimum moisture content, followed by wet of optimum and dry of optimum, respectively. By placing the columns in the soil with 4.5D spacing, better consolidation behaviour with a reduced swelling potential of BC soil can be found. Based on the above findings, using FA-CKD columns can improve the BC soil’s engineering behaviour, contributing to waste-to-wealth and sustainable soil stabilisation approaches.

Cracking Resistance of Steam-Cured Precast Concrete Using High Alite Cement with Modified Fly Ash

Cement with fly ash has rarely been used in Japan, mainly because its strength development is slower than ordinary Portland cement. In this research, the effect of the new type of fly ash (which was modified by the electrostatic belt separation method) with high alite (C3S) cement on cracking resistance of precast concrete prepared by steam curing was studied. The mechanical and shrinkage properties of the proposed fly ash concrete were compared with those of concrete made using OPC cement without fly ash. In order to study the cracking tendency of precast concrete with the proposed cement with fly ash, thermal stress analysis was conducted, taking into consideration the experimental data of concrete properties with the different concrete mix proportions. A standard precast concrete box culvert model was used in this 3D FEM analysis, and the distribution of temperature and relative humidity in the cross-section and induced restraint stress during and after steam curing were discussed. Steam-cured concrete with fly ash and high alite cement developed higher compressive strength on the first day of age than concrete with OPC. The proposed fly ash concrete developed high cracking resistance in the early days. On the other hand, the results showed that the drying shrinkage at later ages was the main cause of cracking.

Triaxial test analysis and discrete element simulation of CFBC

In order to explore the mechanical behavior and crack propagation of cement fly ash stabilized brick-concrete gravel (CFBC) base mixture under three-dimensional compression, firstly, the triaxial loading tests of three different proportions of mixtures were carried out through laboratory tests. The axial load is controlled by a load control loading system, the sampling frequency is 5 Hz, and the triaxial specimen is loaded at a rate of 0.1 MPa /s.The stress–strain curves of the mixture under four different confining pressures were obtained, and the failure characteristics and strength characteristics were analyzed. Secondly, the SEM analysis of the specimens under different confining pressures was carried out, and the microstructure parameters of the mixture under four different confining pressures of 0 MPa, 0.5 MPa, 1.0 MPa and 1.5 MPa were studied based on the PCAS analysis software. On this basis, a three-dimensional discrete element model was established to numerically reproduce the triaxial test of the specimen. The results show that the failure mode of the specimen is mainly related to the confining pressure, and the crack shape has the characteristics of top-down in the direction of principal stress.Through the stress–strain curve, it can be seen that with the increase of confining pressure, the peak stress of the specimen is also increasing. In the BCA1 ratio, the peak stress of the 1.5 MPa confining pressure is increased by 23 % compared with the non-confining pressure. In addition, the cement fly ash stabilized brick-concrete gravel mixture specimen has a larger bearing capacity than other concrete brittle materials.PCAS pore analysis showed that the main controlling factors affecting the porosity of the mixture were brick content and confining pressure, which in turn affected the shear strength and peak stress of the mixture, and the porosity of BCA1 < BCA3 < BCA5; the numerical simulation results show that the failure mode and stress–strain curve of the specimens with the shear strength error of less than 3 % and the friction angle error of less than 6 % are in good agreement. The maximum displacement particle clusters appear on the upper and lower edges of the specimen, and the sliding zone angle of the specimen is about 45° under all stress paths except the horizontal sliding zone under the uniaxial stress state, which reflects that the numerical model is consistent with the mechanical response at the macro scale. The use of three-dimensional discrete element models in the field of construction engineering can simulate and optimize the use of the above materials in construction sites to minimize waste and maximize efficiency.

Effect of Nano-SiO2/Steel fiber on the mechanical properties and sulfate resistance of High-Volume fly ash cement materials

The flexural strength, compressive strength, water absorption, and sulfate resistance of high-volume fly ash cement mortar hybrid containing 0–2.5 wt% nano-silica dioxide (Nano-SiO2, NS) and 0–2.0 vol% steel fibers (SF) were studied in this paper. Fly ash (FA) was used to replace 50 wt% of Portland cement. The resistance to sulfate attack was tested by exposing the specimens to 5.0 wt% sodium sulfate solution, and the flexural strength, compressive strength, and mass loss after 3, 6, and 9 months of erosion were determined. Specimens cured at normal condition were tested at the same ages for comparison. Moreover, the microstructure and pore structure were also investigated. The test results show that the combined addition of NS and SF significantly enhanced the flexural and compressive strength of high-volume fly ash mortar and significantly reduced its water absorption. Compared with control mortar, the addition of 1.0 vol% SF and 2.0 wt% NS increased the flexural and compressive strength by 70.6 % and 53.7 % respectively at the age of 28 days, and the water absorption of mortar was decreased by 45.0 % at the age of 90 days. The hybrid addition of NS and SF improved the sulfate resistance of mortar, reduced the mass loss rate of sulfate attack, and enhanced the residual strength of mortar after sulfate attack. In addition, the mercury injection test showed that adding NS and SF can obviously refine the pores of high-volume fly ash mortar, and reduce the internal average pore diameter.

Selection of eco-friendly alternative brick for sustainable development; A study on Technical, Economic, Environmental and Social feasibility

The pursuit of sustainable development has become increasingly important in addressing the challenges of environmental degradation and resource depletion. The construction industry accounts for significant global resource consumption and pollution. The study aims to investigate the selection of alternative bricks for sustainable development. Social, Economic, Environmental and Technical feasibility was studied to identify the best alternative brick. Five different bricks, i.e., Fired clay brick (FCB), Fly ash cement brick (FACB), Fly ash geopolymer brick (FAGB), Recycled concrete waste geopolymer brick (RCWB) and recycled brick waste geopolymer brick (RBWB), were developed and their technical and environmental impacts were studied. A life cycle analysis (LCA) of one brick was carried out, and seven impacts were studied and reported in this paper. Multi-criteria decision-making methodology (MCDM) was used to select the best brick. In addition, the microstructural properties of recycled geopolymer brick were investigated to study the morphology and mineralogy of the brick’s mixes. Sustainability Index (SI) indicates that fired bricks contribute a higher environmental impact per compressive strength in comparison with alternative bricks. According to the Analytical Hierarchy process (AHP), RBWB is the preferred choice with an overall weight of 0.22, followed by fly ash cement brick (0.217). The mineral resource scarcity (MRS) of 82–87 % can be reduced if alternative recycling waste materials were used in production of brick.

Experimental Investigation and Numerical Model for Chloride Diffusivity of Long-Age Fly Ash Cement Slurry

Fly ash is a by-product of coal-fired thermal power plants and offers great potential for the use of resources. To effectively improve the durability of reinforced concrete structures in marine environment and achieve waste to treasure, fly ash is widely used as a pozzolanic material due to its long-hydration characteristics and effects of micro-aggregate, micro-filling and secondary hydration. In this study, both the experimental investigation and numerical simulation are carried out to study the chloride transport characteristics of fly ash cement paste. The variation in chloride diffusivity with fly ash content, water-to-binder ratio and curing age up to 360 days is studied via accelerated conductivity measurement, and it is found that the above three experimental variables have a significant impact on the chloride diffusivity. For the influence of the dosage of fly ash, the optimum dosage is 30%. By introducing specific rules for the particle distribution, the fresh fly ash cement paste is first made. Based on the volume change characteristics of fly ash and cement particles after hydration, the vector hydration model of fly ash cement paste is established by considering the water shortage effect caused by hydration layer interference. After the accuracy of this hydration model is verified by the results from third-party experiments, the random walk algorithm is proposed to calculate the diffusion coefficient of the reconstructed mineral admixture cement paste. By comprehensive comparison with the experimental results from the third-party and self-conducted experiments, the numerical model for predicting the chloride diffusivity of fly ash cement paste is verified.

Durability of cementitious mortar: Incorporation of highly dispersed superplasticizer modified graphene oxide in fly ash blended mortar

The present study focuses on the utilization of superplasticizer stabilized graphene oxide (GO) as a reinforcing agent in the fly ash blended cement mortar (30–70 ratio of FA/OPC). GO is moderately stable in water solvent medium while, it agglomerates in the alkaline cement pore solution owing to the interference caused by Mg2+, Na+, Ca2+, and OH− etc. So, here an effort has been made to stabilize the GO via superplasticizer's (PCE-SP) steric effect and has further been used as a reinforcing phase in the cement-fly ash-based mortars. The UV–visible (Agilent Pro) spectrometry was used to measure the degree of stabilization via absorbance values. The increased dispersion of GO due to PCE-SP steric stabilization as compared to without PCE-SP has been monitored by UV–Visible spectroscopy. The results have shown that incorporation of 0.08 % PCE-GO (by weight percentage of blend) amended compressive and split-tensile strength of the mortars by 39.85 % and 48.90 % as compared to control-FA specimen at the curing age of 90 days, respectively. Furthermore, the results achieved were equal or even superior than 100 % cement-based mortar (control-OPC). Micro-structural results showed the acceleration of pozzolanic reactions on the nucleation sites supplied by the PCE-GO's functionalities. Mercury Intrusion Porosimeter studies shows that porosity of fly ash-cement mortar was reduced in comparison to control-FA mortar by 51.5 % after 0.08 % PCE-GO incorporation. The cumulative pore volume also contracted from 0.057 to 0.025 cc/g, depicting densification of C–S–H gel network owing to the synergism acting between FA and PCE-GO in cement-FA matrix. Porosity results are also complying with the enhanced electrical resistivity and reduced water absorption values of mortars. In terms of weight loss and compressive strength gain over various exposure periods, mortars incorporating PCE-GO performed better than control samples in all durability-related aspects. PCE-GO incorporation also resulted in improved acid and sulfate attack resistance, owing to the reduced leaching of calcium ions from hydrated cement-FA matrix. This led to lesser deterioration of PCE-GO incorporated mortars owing to reduced ettringite and gypsum formation, as confirmed by XRD and SEM mapping studies. Overall, the incorporation of PCE-GO in mortars has demonstrated significant enhancements in properties. This development holds great promise for the advancement of the construction and infrastructure sectors. The utilization of high-performance mortars has the potential to enhance the strength, durability, and sustainability of structures, thereby making a valuable contribution to the development of safer and more resilient built environments. Furthermore, the utilization of PCE-GO in an innovative manner has the potential to revolutionize construction methodologies and materials in forthcoming times.

Orthogonal experimental design for compressive strength of recycled coarse aggregate concrete with silica fume-slag-fly ash hybrid micro-powders

Recycled Coarse Aggregate Concrete (RAC) is a type of concrete that uses recycled coarse aggregate (RCA) instead of natural coarse aggregate (NCA), which helps to reduce the negative environmental impact of construction waste. In order to improve the low compressive strength of RAC and solve the problem of shortage of natural aggregates, this paper develops a high-performance concrete called recycled coarse aggregate concrete with silica fume-slag-fly ash hybrid micro-powders (HMRAC) by replacing part of the cement with a mixture of micronized silica fume (SF), slag (SG) and fly ash (FA) and using RCA of 50% mass instead of NCA. The optimum combination parameters and prediction model for the compressive strength of HMRAC were also proposed by orthogonal experimental design. A constant water-cement ratio of 0.45 and a 50% mass replacement of natural coarse aggregate (NCA) by recycled coarse aggregate (RCA) were adopted in the experiment, and the mass replacement ratios of silica fume (SF), slag (SG), and fly ash (FA) for ordinary Portland cement (OPC) were used as the test variables. In total, 16 combinations were tested, including a control group where 50% of the NCA mass was replaced by RCA. First, we investigated the degree and significance of the effect of the mass substitution ratio of SF, SG, and FA on the compressive strength of HMRAC using analysis of variance (ANOVA) and extreme difference analysis. Then, we determined the optimal combination ratio of SF, SG, and FA. Secondly, multiple regression analysis was used to propose a multiple regression model for predicting the compressive strength of HMRAC. Finally, we computed and analyzed the carbon emissions of HMRAC. The results indicated that the mass substitution rates of FA and SG had a greater effect on the compressive strength, and the mass substitution rate of SF had a lesser effect on the compressive strength. The interaction of SF, SG, and FA can significantly enhance the compressive strength of RAC. The optimal compressive strength performance of HMRAC was observed when the proportions were as follows: SF constituted 10%, SG made up 15%, and FA accounted for 5%. The regression model has reasonable accuracy and a small standard deviation of residuals. It can effectively predict the compressive strength value of HMRAC, aligning well with the experimental results. It exhibits a superior carbon reduction rate of 21.90%, compared to conventional concrete.

A STUDY ON CONCRETE CONTAINING THE SANDSTONE SLURRY AND FLY ASH PARTIALLY REPLACED WITH SAND AND CEMENT

Now a day’s the waste is produced in immense amounts during construction and coal burning, this study mainly focused on the utilization of sandstone slurry produced during sandstone cutting and Class-F fly ash produced by coal-burning. In this study a deep analysis is taken after 28 days’ testing, six concrete mixes were prepared one is conventional as M20, and trial mix batches are a total of five, three specimens were taken from each concrete mix separately to determine the engineering properties of the prepared specimen. Fly ash partly replaced with the cement in % of 5%,10%,15%,20%,25% and Sandstone slurry partially replaced with sand in % of 10%,20%,30%,40%,50%. Water cement ration took .4-.7%, after 28 days specimens were tested of water curing at ±2, 270C. Sulfate bath is prepared for durability test with 5% Na2SO4 and prepared specimen left for 28 days curing in prepared sulfate bath after completion of 28 days’ normal water curing, the specimen was tested after 56-day curing, acidic nature was maintained for prepared bath, on daily basis pH value has been noted if found more than 6.9 pH than sulphuric acid is added to keep the acidic nature of prepared bath. Only 5% FA and 10% SSS specimen show strength increment up to 14.477% and after sulfate bath, no change was found in specimen’s volume. In compressive strength maximum strength increased up to 19.39%, from 5% FA and 10% SSS replacement. In splitting tensile strength maximum strength increased 11.37% with 10% FA and 20% SSS.

Analysis of Strength Parameters of Paving Blocks with inclusion Sea Sand

Start with the Scarcity of materials in concrete so sand has steadily gained prominence as the most frequent building material used in the construction industry. As the population increases, so does the need for residential and commercial space. The most essential resource for mankind, river sand, is being mined out of riverbeds more frequently. One ton of regular Portland (OPC) cement is produced in India for every tonne of CO2 that is released into the environment. By substituting cementitious materials like fly ash and ground-granulated blast furnace slag for ordinary cement, we can lower the number of greenhouse gases that are emitted into the atmosphere. To create sustainable concrete pavement blocks, this experimental work has been carried out with the use of cementitious elements including fly ash and ground granulated furnace slag (GGBS) as a replacement for cement, and to enhance public transportation, this research is focused on creating paver blocks that contain sea sand as fine aggregate. This experimental investigation was conducted to investigate different sustainable concrete strength properties with 0% sea sand, 50% Sea Sand and 50% M sand, and 100% sea sane used to partially replace the mix proportion. Results of mechanical parameters such as Compressive strength, water absorption, abrasion resistance, and carbonation of these sustainable concrete pavement blocks are presented also a cost analysis of paving blocks was evaluated.

Investigation of different ways of activation of fly ash–cement mixtures: part 2—mechanical activation

AbstractIntroducing supplementary cementitious materials (SCM), e.g. fly ash, into cement composite results in ecological benefits. However, in the case of high amount of SCM used as a replacement of a part of cement, there are problems related to the development of the desired properties of the final composite. Such mixtures often require activation. In the first part of this series of publications, the results of chemical activation (using Na2SO4 and Ca(OH)2) of a mixture with a very high content of fly ash were discussed. The aim of this work was to investigate the influence of mechanical activation on hydration and microstructure of the binder composed of 80% of fly ash and 20% of cement. Mechanical activation was performed using a planetary ball mill. The following instrumental methods were used to investigate the activated fly ash-cement pastes: calorimetry, TG/DTG, FTIR spectroscopy, X-ray diffraction and scanning electron microscopy (SEM) coupled with EDS. It was shown that concomitant grinding of cement and fly ash is more effective compared to separate grinding. Mechanism of hydration/activation of such mixtures was discussed in detail.

Effect of low-calcium and high-magnesium ferronickel slag on the microstructure and micromechanical properties of alkali-activated blended ground granulated blast furnace slag

In recent years, low-calcium and high-magnesium ferronickel slag (FNS) has been gradually used in the preparation of alkali-activated cements (AACs). An in-depth exploration of the microstructural characteristics is crucial for a thorough understanding and enhancement of the macroscopic behaviors of AACs. In this study, the microstructural composition and micromechanical properties of the alkali-activated ground granulated blast furnace slag (GGBS)-FNS cements (AASF) prepared with sodium silicate and sodium hydroxide as alkali activators were quantitatively studied. Backscattered electron image analysis (BSE-IA) and nanoindentation were selected to reveal the micromechanical properties of different phases in FNS particles and AASF pastes. The results show that the elastic modulus of sodium aluminosilicate hydrate (N-A-S-H) in alkali-activated FNS cement is about 17 GPa, which is similar to that of the gel phase in alkali-activated fly ash cement (AAFA) and alkali-activated metakaolin cement (AAMK), confirming that the micromechanical property of N-A-S-H gel is independent of the kind of precursor materials. The Ca/Si and Al/Si of the hydration products in AASF gradually decline as FNS is incorporated, whereas the Mg/Al steadily rises, increasing the elastic modulus of the inner hydration product (IP) phase in AASF. The reaction degree of GGBS is higher in the sodium silicate-activated AASF system, while more N-A-S-H gels are formed in the sodium hydroxide-activated AASF system. The incorporation of FNS is conducive to improving the reaction degree of GGBS, resulting in the increase of calcium silicoaluminate hydrate (C-A-S-H) content and a significant decrease in IP content in AASF.

Performance assessment of seawater fly ash cement paste with integrated physicochemical- geochemical simulation platform and experimental validation

The shortage of river sand and fresh water for concrete production has become a severe issue, accompanied by a significant increase in infrastructural constructions, especially for coastal areas. Therefore, the possibility of utilizing seawater and sea sand as alternative raw materials for concrete components has attracted broad research interest in recent decades. This paper presents experimental, and simulation investigation to comprehensively study the material performance of seawater fly ash cement paste (SFCP). An integrated simulation platform is adopted to achieve the performance assessment, in which the physicochemical and geochemical processes can be addressed, such as the hydration of cement particles, formation of micro-pore structure, multi-species migration and equilibria, activity effect, the thermodynamic balance between the matrix skeleton and pore solution. A comparison of experiment and simulation showed that the properties of SFCP from micro to macroscale are consistently associated and fairly explained through the integrated simulation platform for further practical realization.

Preparation of phosphogypsum-based cemented paste backfill and its environmental impact based on multi-source industrial solid waste

Cemented Paste Backfill (CPB) technology is considered as an effective method to solve the serious problems caused by the solid wastes’ accumulation, and to mitigate the risk of mined-out areas. However, the serious influence on the environment and higher pro-treating costs of solid wastes limits their application in CPB. Meanwhile, due to the high carbon emissions and high costs of Portland cement, its use as a binder in CPB is also limited. This paper used raw phosphogypsum (PG) as filler. Yellow phosphorus slag (YPS), fly ash (FA), steel slag (SS), and Portland cement were mixed to make a composite binder. Solid wastes addition was ranged from 80% to 98%. The feasibility of CPB co-preparation with a high percentage of multi-source industrial solid waste was verified by analyzing the performance and environmental impact of CPB produced with different percentages of solid wastes. The results showed that a higher PG addition was harmful to the property of CPB, leading to a lower fluidity, longer setting time, and weaken strength. However, the development and use of composite binder offset those negative aspects effectively. Composite binder is a CaO-rich binder that provides an alkaline environment for hydration reactions which enhanced CPB strength. Because its unconfined compressive strength reached to 3.1 MPa ∼ 19.5 MPa after 60 d’s curing. This will provide a highly strengthen support to the mine to be filled with CPB, thus hindering its re-collapse. The gradually increased hydration products observed from the microstructural characterization further corroborated the strength development path of the CPB. Moreover, the adsorption and precipitation process in the alkaline system contributed to the stabilization of the contaminants from those solid wastes. Therefore, the CPB technology based on the multi-source industrial solid waste is considered as a green, promising, and cost-saving choice on supporting safe mining and mitigating environmental pollution.

Microstructure and Water Retention Kinetics in Autogenous Cured Self-Compacting Concrete Blends Using Super Absorbent Polymer.

This research aimed to determine how a super absorbent polymer affects the microstructural characteristics and water retention kinetics of a new composite made by substituting granite pulver (GP) and fly ash (FA) for cement. Understanding the mechanics of water movement is crucial for comprehending the effectiveness of autogenous curing. Several experiments were conducted to analyze the water mitigation kinetics of super absorbent polymer (SAP) in the hydrating cement paste of autogenous cured self-compacting concrete (GP-ACSSC) mixtures. In the first hours following casting, water sorptivity, water retention, and hydration tests were carried out. The effects of various concentrations of SAP and GP, which was utilized as an alternative cement for the production of sustainable concrete that leads to reduction in carbon footprint, on the autogenous cured self-compacting concrete with reference to the abovementioned properties were explored. The investigation showed that releasing the curing water at a young age, even around the beginning of hydration, allowed homogenous and almost immediate distribution of water across the full cured paste volume, which improved the water retention kinetics. Compared to the control mixtures, the addition of SAP up to 0.6% and the substitution of cement with GP up to 15% had favorable impacts on all water kinetics parameters.

Upcycling Fly Ash, Red Clay Brick Waste, and Paper Sludge as Feedstock for Manufacturing a Lightweight Extruded Composite: Design and Characterization

In the context of the circular economy and the adoption of one of its business models, namely ”resource recovery”, this study presents an opportunity to valorize industrial and urban wastes using alkaline activation technology to produce hybrid binders. Several alkali-activated binders were produced using response surface methodology based on a mixture of 45/45/10 clay brick waste, fly ash, and Portland cement. The compressive strength and setting time of each were evaluated. The hybrid cementitious pastes achieved up to 45 MPa after 28 days of setting. Based on the experimental data, two binders were selected as the cementitious matrix for composites, with paper sludge as the lightweight aggregate. Incorporating up to 45% volume of paper sludge allowed extrusion of the materials. The addition of paper sludge reduced the compressive and flexural strength. These results were explained by the decrease in density and the increase in porosity. However, there was an improvement in the thermal properties of the composites; in particular, the thermal conductivity range between 0.35 and 0.49 W/mK. Finally, it was found that the composites with 25% volume of paper sludge had the best combination of properties, positioning them as potential construction materials.

Use of ultraviolet pretreatment to enhance carbonation properties of fly-ash cement under accelerated carbonation at different CO2 concentrations

Use of ultraviolet pretreatment to enhance carbonation properties of fly-ash cement under accelerated carbonation at different CO2 concentrations

Early-age shrinkage behavior of cement-fly ash paste under wind speeds: A study using BSE-IA and MIP techniques

While laboratory studies have shown that fly ash (FA) can reduce shrinkage in cement-based materials in the absence of wind, its impact on cement-based materials under wind speed conditions has not been extensively studied. This research investigates the influence of FA on the early-age shrinkage of cement paste under various wind speeds. The corresponding changes in pore structure were tested using mercury intrusion porosimetry (MIP) and backscattered electron image analysis (BSE-IA). The results show that under wind speed conditions, FA is not effective in reducing early-age shrinkage of cement paste. In fact, high levels of FA content can increase shrinkage values under wind speed conditions. Both wind speed and FA increase water evaporation, but they have different impact times. Although both wind speed and FA decrease mesopore content below 50 nm and increase water evaporation, they have opposite effects on early-age shrinkage. This suggests that mesopore content and water evaporation alone cannot fully characterize the change trend of early drying shrinkage. The two-factor parameter rs, which combines water evaporation and MIP-based pore size distribution, can effectively characterize drying shrinkage trends under the combined effects of wind speed and FA. BSE-IA can intuitively characterize pore size distribution above 200 nm, while the results of MIP underestimate the distribution of large capillary pores. Therefore, the current rs obtained based on MIP may be smaller than the actual value. With the advancement of testing technology in the future, rs can be further optimized.

Prospects of sustainable geotechnical applications of manufactured sand slurry as controlled low strength material

Rapid changes in the construction industry for infrastructure development require extensive use of building materials from a variety of sources. As natural resources deplete at a faster rate in recent years, new materials are being explored, and recycled materials are being discovered for various applications. The slurry obtained during the washing of mined quarry sand (also called as M Sand Slurry or MSS) is found to be disposed as mining waste causing environmental pollution. In the present study, we propose an innovative methodology to recycle the MSS as a suitable replacement of fine aggregate by imparting sufficient strength and workability to produce a composite, commonly called as controlled low strength material (CLSM). We have optimized the mix proportioning of MSS by adding fly ash (up to 15%) and Portland cement (up to 10%). Various tests on the plastic properties (flowability, bleeding, hardening time) and hardened properties (ultimate compressive strength or UCS) were performed on the selected mixtures. The optimum mixture of CLSM with MSS provided excellent flowability (at 200 mm), bleeding rate (3–5%) and UCS up to 1.12 MPa. The improved binding effect on the poor-graded MSS has been attributed to the pozzolanic reaction in presence of fly ash and cement, as evident from the microstructural analysis. Based on the excavation criteria (ACI 229R), the selected mixtures have high removability modulus (1.2–2.5) except for two proportions (with only MSS, and with very low fly ash) while all combinations have sufficient strength (UCS < 2.1 MPa), making them suitable for various geotechnical applications. Further, to address the sustainability aspects of MSS-based CLSM utilization, a strategic framework is proposed based on the Life Cycle Assessment (LCA) approach for the mining industries. It is observed that MSS-based CLSM can reduce the cost of earthworks approximately by 62% (compared to the river sand) and 32% (compared to the available alternate sand). Hence, based on the environmental, economic and mechanistic aspects, we demonstrate that MSS-based CLSM can be effectively adopted for sustainable geotechnical applications.