High-efficiency Carbonation Modification Methods of Recycled Coarse Aggregates

To solve the problem of only surface carbonation and realize high-efficiency carbonation of recycled coarse aggregate,the method of carbonated recycled coarse aggregate with nano materials pre-soaking was first put forward.The carbonation effect of modified recycled coarse aggregate with three different carbonation methods was evaluated,and water absorption,apparent density and crush index of modified recycled coarse aggregate were measured.Combined with XRD,SEM,and MIP microscopic analysis,the high-efficiency carbonation strengthening mechanism of modified recycled coarse aggregate was revealed.The experimental results show that,compared with the non-carbonated recycled coarse aggregate,the physical and microscopic properties of carbonated recycled coarse aggregate are improved.The method of carbonation with nano-SiO_(2) pre-soaking can realize the high-efficiency carbonation of recycled coarse aggregate,for modified recycled coarse aggregate with the method,water absorption is reduced by 23.03%,porosity is reduced by 44.06%,and the average pore diameter is 21.82 nm.The high-efficiency carbonation strengthening mechanism show that the pre-socked nano-SiO_(2) is bound to the hydration product Ca(OH)_(2) of the old mortar with nano-scale C-S-H,which can improve the CO_(2) absorption rate,accelerate the carbonation reaction,generate more stable CaCO_(3) and nano-scale silica gel,and bond to the dense three-dimensional network structure to realize the bidirectional enhancement of nano-materials and pressurized carbonation.It is concluded that the method of carbonation with nano-SiO_(2) pre-soaking is a novel high-efficiency carbonation modification of recycled coarse aggregate.

Repair of Second-Generation Recycled Fine Aggregate of Waste Concrete from Freeze-Thaw Environment by Carbonation Treatment

The reuse of waste recycled concrete from harsh environments has become a research hotspot in the field of construction.This study investigated the repair effect of carbonation treatment on second-generation recycled fine aggregate(SRFA)obtained from recycled fine aggregate concrete(RFAC)subjected to freeze-thaw(FT)cycles.Before and after carbonation,the properties of SRFA were evaluated.Carbonated second-generation recycled fine aggregate(CSRFA)at five substitution rates(0%,25%,50%,75%,100%)to replace SRFA was used to prepare carbonated second-generation recycled fine aggregate concrete(CSRFAC).The water absorption,porosity and mechanical properties of CSRFAC were tested,and its frost-resisting durability was evaluated.The results showed after carbonation treatment,the physical properties of SRFA was improved and met the requirements of II aggregate.The micro-hardness of the interfacial transition zone and attached mortar in CSRFA was 50.5%and 31.2%higher than that in SRFA,respectively.With the increase of CSRFA replacement rate,the water absorption and porosity of CSRFAC gradually decreased,and the mechanical properties and frost resistance of CSRFAC were gradually improved.Carbonation treatment effectively repairs the damage of SRFA caused by FT cycles and improves its application potential.

Carbonation of Dicalcium Silicate Enhanced by Ammonia Bicarbonate and Its Mechanism

The strength development law of γ-type dicalcium silicate (γ-C_(2)S) under different carbonation processes was investigated,and the carbonation mechanism of γ-C_(2)S under the action of NH_(4)HCO_(3) was clarified by using a wide range of test methods,including XRD and SEM.A method of saturated NH_(4)HCO_(3) solution as a curing agent was identified to improve the carbonation efficiency and enhance the carbonation degree of γ-C_(2)S,and then a high-strength carbonated specimen was obtained.Microhardness analysis and SEM morphology analysis were conducted on the carbonised specimens obtained under atmospheric pressure carbonisation conditions using the curing agent.It was found that γ-C_(2)S could perform carbonisation well under atmospheric pressure,which promoted the carbonisation efficiency and decreased the carbonisation cost simultaneously.Therefore,a new carbonisation process solution was proposed for the rapid carbonisation of γ-C_(2)S.

Enhancing fly ash utilization in backfill materials treated with CO_(2)carbonation under ambient conditions

The environmental concerns resulting from coal-fired power generation that produces large amounts of CO_(2)and fly ash are of great interest.To mitigate,this study aims to develop a novel carbonated CO_(2)-fly ash-based backfill(CFBF)material under ambient conditions.The performance of CFBF was investigated for different fly ash-cement ratios and compared with non-CO_(2)reacted samples.The fresh CFBF slurry conformed to the Herschel-Bulkley model with shear thinning characteristics.After carbonation,the yield stress of the fresh slurry increased significantly by lowering fly ash ratio due to gel formation.The setting times were accelerated,resulting in approximately 40.6%of increased early strength.The final strength decreased when incorporating a lower fly ash ratio(50%and 60%),which was related to the existing heterogeneous pores caused by rapid fluid loss.The strength increased with fly ash content above 70%because additional C-S(A)-H and silica gels were characterized to precipitate on the grain surface,so the binding between particles increased.The C-S(A)-H gel was developed through the pozzolanic reaction,where CaCO_(3)was the prerequisite calcium source obtained in the CO_(2)-fly ash reaction.Furthermore,the maximum CO_(2)uptake efficiency was 1.39 mg-CO_(2)/g-CFBF.The CFBF material is feasible to co-dispose CO_(2)and fly ash in the mine goaf as negative carbon backfill materials,and simultaneously mitigates the strata movement and water lost in post-subsurface mining.

A Novel Process of CO_(2) Reduction and CO_(2) Sequestration Through an Innovative Accelerated Carbonation Technique

The efiect of an innovative accelerated carbonation curing technique was evaluated on concrete containing natural zeolite powder and fine aggregate as partial replacement to alleviate the CO_(2) emission up to a certain extent from the concrete production industry and improve sequestration of CO_(2) into the concrete matrix in a stable form.An accelerated carbonation curing was accomplished by subjecting the concrete specimens to 0.5 and 0.75 M concentrations of sodium bicarbonate(NaHCO_(3)) solutions up to a curing age of 180 days after the initial 28 days of normal water curing.Tests for carbonation depth,pH value,compressive strength,calcium carbonate(CaCO_(3))content,X-ray difiraction,and thermogravimetric(TGA)analyses and Fourier transform infrared spectroscopy(FTIR)were performed to measure the extent of carbonation.The obtained results showed an increment in average compressive strength for the zeolite concrete(ZLC)mixes exposed to accelerated carbonation curing.The ZLC mixes exposed to increasing NaHCO_(3) solution concentration and exposure period exhibited greater carbonation depth and decreased pH at each depth interval indicating higher CO_(2) sequestration within the concrete matrix.The results obtained from the microstructural analysis(XRD,TGA,and FTIR)and CaCO_(3) content measurements confirm that the higher amount of CaCO_(3) formation provides a clear indication of the carbonation enhancement and CO_(2) sequestration within the concrete matrix and in turn contributing to the global warming reduction.

Quality Improvement of Recycled Concrete Aggregate by Accelerated Carbonation under Different Pressure

Due to the presence of old mortar (OM) and interfacial transition zone (ITZ),recycled concrete aggregate (RCA) is inferior to natural aggregate (NA).The purpose of this paper was to study the effect of accelerated carbonation on the macro-properties and micro-properties of RCA under different pressure(0.05,0.15,0.30 MPa).The macro-property tests included colour change,apparent density,water absorption,and crushing value of RCA.The micro-property tests included scanning electron microscopy (SEM),X-ray diffraction (XRD),thermogravimetry-differential scanning calorimetry (TG-DSC),and Vickers micro-hardness(VMH).The results showed that the change trends of apparent density,water absorption,and crushing value of RCA displayed exponential relationships as pressure increasing,with the optimum pressure of 0.30 MPa.SEM images indicated that the calcite caused by the hydration products in RCA and the Ca(OH)_(2) derived from saturated lime water improved the properties of RCA;as the apparent density increased,the water absorption and crushing value decreased.The results of XRD and TG-DSC indicated that,as the pressure increased,the masses of Ca(OH)_(2) in carbonated RCA gradually decreased,while those of CaCO_(3) gradually increased,which demonstrated that the carbonation degree gradually increased.Besides,ITZ-2 was the weakest phase in RCA,but its improvement degree of VMH by accelerated carbonation was higher than that of OM.However,RCA was not completely carbonated,but only carbonated in a certain depth after 24 h accelerated carbonation.

Model investigation of the low-carbon MgO-treated soil foundation based on CO_(2) overall carbonation

The overall carbonation of MgO-admixed soil provides not only an efficient and environmentally friendly technique for improving soft ground but also a permanently safe solution for CO_(2) sequestration.To evaluate the carbon sequestration potential and promote the carbonation application in soil improvement,a laboratory-scale model investigation is designed under pressurized carbonation considering the influences of MgO dosage and CO_(2) ventilation mode(way).The temperature,dynamic resilience modulus,and dynamic cone penetration(DCP)were tested to assess the carbonation treatment effect.The physical,strength,and microscopic tests were also undertaken to reveal the evolution mechanisms of CO_(2) migration in the MgO-carbonated foundation.The results indicate that the temperature peaks of MgO-treated foundation emerge at w20 h during hydration,but occur at a distance of 0e25 cm from the gas source within 6 h during carbonation.The dynamic resilience moduli of the model foundation increase by more than two times after carbonation and the DCP indices reduce dramatically.As the distance from the gas inlet increases,the bearing capacity,strength,and carbon sequestration decrease,whereas the moisture content increases.Compared to the end ventilation,the middle ventilation produces a higher carbonation degree and a wider carbonation area.The cementation and filling of nesquehonite and dypingite/hydromagnesite are verified to be critical factors for carbonation evolution and enhancing mechanical performances.Finally,the overall carbonation model is described schematically in three stages of CO_(2) migration.The outcomes would help to facilitate the practical application of CO_(2) sequestration in soil treatment.

Synergistic Use of CO_(2) Pretreatment and Accelerated Carbonation Curing for Maximum Recycling of Steel Slag

Two carbonation approaches are considered for studying the effects on the hardening mechanisms of slurries made of 100 wt%electric arc furnace steel slag (EAF) slag or 80 wt%EAF slag incorporating 20 wt% of Portland cement,which are applied during the hot-stage pretreatment with simulated gas for raw steel slag or the accelerated carbonation curing of slurry.The mechanical strengths,carbonate products,microstructures and CO_(2) uptakes were quantitatively investigated.Results manifest that accelerated carbonation curing increases the compressive strengths of steel slag slurry,from 17.1 MPa (binder of 80 wt% EAF and 20 wt%cement under standard moisture curing) to 36.0 MPa (binder of 80 wt%EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 52%.In contrast,hot-stage carbonation applied during the pretreatment of steel slag increases the compressive strengths to 43.7 MPa (binder of 80 wt%carbonated EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 67%.Hotstage carbonation of steel slag is found for particle agglomeration,minerals remodeling and calcite formed,thus causing an activated steel slag with a dense structure and more active components.Accelerated carbonation curing of steel slag slurry paste results in the newly formed amorphous CaCO_(3),calcite crystalline and silica gels that covered the pores of the matrix,facilitating microstructure densification and strength improvement.Adopting the combinative methods of the hot-stage CO_(2) pretreatment and accelerated carbonation curing creates a promising high-volume steel slag-based binder with high strengths and CO_(2) storage.

Unveiling the Carbonation Behavior and Microstructural Changes of Magnesium Slag at 0℃

Magnesium slag(MS)is an industrial byproduct with high CO_(2)sequestration potential.This study investigates the carbonation behavior and microstructural changes of MS during wet carbonation at 0℃.XRD,TG,FTIR,SEM,and BET techniques were used to characterize the phase composition,microstructure,and porosity of MS samples carbonated for different durations.The results showed that the main carbonation products were calcite,vaterite,and highly polymerized silica gel,with particle sizes around 1μm.The low-temperature environment retarded the carbonation reaction rate and affected the morphology and crystallization of calcium carbonate.After 480 min of carbonation,the specific surface area and porosity of MS increased substantially by 740%and 144.6%,respectively,indicating improved reactivity.The microstructure of carbonated MS became denser with calcite particles surrounded by silica gel.This study demonstrates that wet carbonation of MS at 0℃significantly enhances its properties,creating an ultrafine supplementary cementitious material with considerable CO_(2)sequestration capacity.

Effect of Ultra-low Temperature on Carbonation Performance of SFRRC and Prediction Model

Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provides a theoretical basis for the application of SFRRC in ultra-low temperature engineering.The experimental results show that ultra-low temperatures can significantly weaken the carbonization resistance of SFRRC.When the temperature reaches 160℃,the carbonization depth increases by 67.66%compared with the normal state.The proper amount of steel fiber has an evident influence on the carbonation resistance of the material.However,when the addition amount exceeds the optimum content,the carbonation resistance of the material decreases.The grey prediction model established by constructing the original sequence can reasonably predict the carbonation resistance of SFRRC after ultra-low temperatures.

Indirect mineral carbonation of blast furnace slag with(NH4)2SO4 as a recyclable extractant

Large quantities of CO_2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO_2 emission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant,(NH_4)_2SO_4, was used to extract calcium and magnesium from blast furnace slag(main phases of gehlenite and akermanite) by using low-temperature roasting to fix CO_2 through aqueous carbonation. The process parameters and efficiency of the roasting extraction, mineralisation, and Al recovery were investigated in detail. The results showed that the extractions of Ca, Mg, and Al can reach almost 100% at an(NH4)_2SO_4-to-slag mass ratio of 3:1 and at 370°C in 1 h. Adjusting the p H value of the leaching solution of the roasted slag to 5.5 with the NH_3 released during the roasting resulted in 99% Al precipitation, while co-precipitation of Mg was lower than 2%. The Mg-rich leachate after the depletion of Al and the leaching residue(main phases of CaSO_4 and SiO_2) were carbonated using(NH_4)_2CO_3 and NH_4HCO_3 solutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCO_3 and(NH_4)_2 Mg(CO_3)_2·4 H_2O,respectively. The latter can be selectively decomposed to magnesium carbonate at 100-200 °C to recover the NH_3 for reuse. In the present route, the total CO_2 sequestration capacity per tonne of blast furnace slag reached up to 316 kg, and 313 kg of Al-rich precipitate, 1000 kg of carbonated product containing CaCO_3 and SiO_2, and 304 kg of carbonated product containing calcium carbonate and magnesium carbonate were recovered simultaneously. These products can be used, respectively, as raw materials for the production of electrolytic aluminium, cement, and light magnesium carbonate to replace natural resources.

Strength Development and Products Evolution of β-C2S and γ-C2S Induced by Accelerated Carbonation Curing

Low calcium β-C2S and γ-C2S minerals with low hydration activity was activated by accelerated carbonation curing to be used as new binding materials.Synthetic β-C2S and γ-C2S were synthetized and compacted to prepare cube samples and then subjected to CO2 chamber for accelerated carbonation curing.The CO2 uptake,mechanical strength,and microstructure changes of β-C2S and γ-C2S were analyzed by TG,XRD,MAS-NMR,and MIP.The experimental results indicate the CO2 uptake of γ-C2S is much higher than that of β-C2S,but the compressive strength of γ-C2S samples is lower than that of β-C2S.Calcium carbonate and other carbonation products stack in the pore structure and the porosity is reduced from about 42% to 30.1% and 22.0% for β-C2S and γ-C2S samples after 2 h carbonation curing,respectively.The difference in compressive strength development is caused by the different properties of carbonation products.Except for calcium carbonate,there also exists obvious difference in properties of amorphous phases:γ-C2S formed silica gel in the whole carbonation progress;however,β-C2S can react to produce silica gel and C-S-H gel with high Van der Waals forces,and C-S-H gel will continue to react with CO2 to form calcium carbonate and silica gel in later carbonation reaction;In addition the microhardness of carbonated β-C2S was more higher than that of γ-C2S.

Process simulation and energy integration in the mineral carbonation of blast furnace slag

Large quantities of blast furnace(BF) slag and CO_2 are discharged annually from iron and steel industries, along with a large amount of waste heat.The mineral carbonation of BF slag can not only reduce emissions of solid waste but also realize the in-situ fixation of CO_2 with low energy consumption if integrated with the waste heat utilization.In this study, based on our previous works, Aspen Plus was employed to simulate and optimize the carbonation process and integrate the process energy.The effects of gehlenite extraction, MgSO_4 carbonation,and aluminum ammonium sulfate crystallization were studied systematically.The simulation results demonstrate that 2.57 kg of BF slag can sequester 1 kg of CO_2, requiring 5.34 MJ of energy(3.3 MJ heat and 2.04 MJ electricity), and this energy includes the capture of CO_2 from industrial flue gases.Approximately 60 kg net CO_2 emission reduction could be achieved for the disposal of one ton of BF slag.In addition, the by-product,aluminum ammonium sulfate, is a high value-added product.Preliminary economic analysis indicates that the profit for the whole process is 1127 CNY per ton of BF slag processed.

Effect of Carbonation and Drying-Wetting Cycles on Chloride Diffusion Behavior of Coral Aggregate Seawater Concrete

Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.

Study on Carbonation Damage Constitutive Curve and Microscopic Damage Mechanism of Tailing Recycled Concrete

To improve the resource utilization of recycled aggregate concrete(RAC)and make use of the unique pozzolanic activation characteristics of iron ore tailing(IOT),the constitutive curves of tailing recycled concrete(TRC)before and after carbonization were analyzed theoretically,experimentally and microscopically.Firstly,according to the experimental data,the damage constitutive and related damage parameters of TRC were theoretically established by Weibull probability distribution function.Secondly,the comprehensive damage parameter b under different working conditions was studied.Finally,the damage mechanism was formed by EDS and SEM.The results showed that the damage constitutive model based on Weibull probability distribution function was in good agreement with the experimental results.Under each carbonization period,the b first decreased and then rose with the increase of tailings content.When its content was 30%,the b values of TRC were minimized,which were 22.14%,20.99%,25.39%lower than those of NAC,and 41.09%,34.89%,35.44%lower than those of RAC,indicating that IOT had a relatively good optimization effect on the constitutive curve of RAC.The microscopic analysis results also proved that the IOT addition with a proper amount would improve the matrix structure of RAC and increased its compactness,but when the content was higher,it would also cause harmful cracks in its matrix structure and reduced its density.Therefore,the optimal tailing content was about 30%.This paper provided a new method for damage constitutive calculation and analysis of TRC before and after carbonization.

Ultra-fine grinding and mechanical activation of mine waste rock using a high-speed stirred mill for mineral carbonation

CO_2 sequestration by mineral carbonation can permanently store CO_2 and mitigate climate change. However, the cost and reaction rate of mineral carbonation must be balanced to be viable for industrial applications. In this study, it was attempted to reduce the carbonation costs by using mine waste rock as a feed stock and to enhance the reaction rate using wet mechanical activation as a pre-treatment method. Slurry rheological properties, particle size distribution, specific surface area, crystallinity, and CO2 sequestration reaction efficiency of the initial and mechanically activated mine waste rock and olivine were characterized. The results show that serpentine acts as a catalyst, increasing the slurry yield stress, assisting new surface formation, and hindering the size reduction and structure amorphization. Mechanically activated mine waste rock exhibits a higher carbonation conversion than olivine with equal specific milling energy input. The use of a high-speed stirred mill may render the mineral carbonation suitable for mining industrial practice.

NO removal performance of CO in carbonation stage of calcium looping for CO_(2) capture

Calcium looping realizes CO_(2)capture via the cyclic calcination/carbonation of CaO.The combustion of fuel supplies energy for the calciner.It is unavoidable that some unburned char in the calciner flows into the carbonator,generating CO due to the hypoxic atmosphere in the carbonator.CO can reduce NO in the flue gases from coal-fired power plants.In this work,NO removal performance of CO in the carbonation stage of calcium looping for CO_(2)capture was investigated in a bubbling fluidized bed reactor.The effects of carbonation temperature,CO concentration,CO_(2)capture,type of CaO,number of CO_(2)capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed.CaO possesses an efficient catalytic effect on NO removal by CO.High temperature and high CO concentration lead to high NO removal efficiency of CO in the presence of CaO.Taking account of better NO removal and CO_(2)capture,the optimal carbonation temperature is 650℃.The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO_(3).Besides,the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO_(2)capture cycles.This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO,hindering the diffusion of NO and CO.The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO.The presence of char promotes NO removal by CO in the carbonator.CO_(2)/NO removal efficiencies can reach above 90%.The efficient simultaneous NO and CO_(2)removal by CO and CaO in the carbonation step of the calcium looping seems promising.

Microstructure of β-Dicalcium Silicate after Accelerated Carbonation

The present work presents the microstructure of β-Ca_2SiO_4(β-C_2S) after accelerated carbonation. The synthesis procedure of β-C_2S was examined first, and the crystalline and amorphous structure, the distribution and the pore structure of β-C_2S carbonation products were also determined by X-ray diffraction(XRD) quantitative analysis, simultaneous thermal analyzer(TG/DTA), Fourier transform-infrared spectroscopy(FT-IR), high resolution ^(29)Si magic angle spinning nuclear magnetic resonance(^(29)Si NMR), N_2-sorption techniques, and scanning electron microscopy(SEM), respectively. Test results indicate that carbonation products are dramatically formed in the initial 2 h. The main carbonation products are crystalline calcite and amorphous three-dimensional network silica gels, which contain nanometer-sized pores. The calcite, silica gels and un-carbonated β-C_2S are distributed hierarchically.

Carbonation Resistance and Anticorrosive Properties of Organic Coatings for Concrete Structures

The present study examines the behavior of three major categories of organic coatings which are applied on the surface of concrete structures and specifically conventional, high performance and nanotechnology paint systems. The comparison is achieved in the means of anticorrosion properties under the presence of chloride ions and carbonation resistance. The evaluation methods included electrochemical measurements in order to assess corrosion properties and the determination of steel’s mass loss after the end of the experimental procedure. Carbonation depth was measured using phenolphthalein as indicator after accelerated and physical exposure. From the results so far it can be shown nanocoatings gave promising results regarding induced chloride ion corrosion.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.