In view of the volume instability of steel slag aggregate leading to the quality problem of expansion damage in asphalt road construction,the 4.75-9.5 mm steel slag particles were treated by autoclaved carbonation tec...In view of the volume instability of steel slag aggregate leading to the quality problem of expansion damage in asphalt road construction,the 4.75-9.5 mm steel slag particles were treated by autoclaved carbonation technology,and the effects of the carbonation system(temperature and time)on the autoclaved pulverization rate,f-CaO content,and the relationship between them for the carbonated steel slag were investigated.In addition,the microstructure of the carbonated steel slag was analyzed by X-ray diffractometer(XRD),scanning electron microscope and energy dispersive spectrometer(SEM-EDS),metallographic microscope and X-ray fluorescence imaging spectrometer(XRF).The experimental results indicate that,under the initial CO_(2)pressure of 1.0 MPa,increasing the carbonation temperature leads to the increase in the crystal plane spacing of Ca(OH)_(2)that was generated by the hydration of minerals in steel slag,and promotes the transformation of carbonated CaCO_(3)from the orthorhombic system to the hexagonal system,resulting in the increase of the crystal planes spacing of them,meantime,accelerates the decomposition of RO phases and also the outward migration of Ca^(2+),Fe^(2+),and Mn^(2+)ions to cover and coat on the Si^(4+),Al^(3+)ions,and impels the formation of hydroxides such as Fe(OH)_(3)and the formation of carbonates such as Ca(Mg)CO_(3),FeCO_(3)and MnCO_(3).Carbonation at the temperature of 90℃for 3 h can reach the center of 4.75-9.5 mm steel slag particles.Meanwhile,the increase of temperature can promote the mineral reaction in steel slag,resulting in the fuzzy interface between mineral phases,increase of burrs,dispersion,crossover,reduction of grain size,and rearrangement of mineral particles.展开更多
To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requir...To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.展开更多
The iron and steel industries generate large amounts of unavoidable CO_(2)emissions as well as considerable quantities of slags.More than one-half of the emitted CO_(2)is produced in blast furnaces during ironmaking,a...The iron and steel industries generate large amounts of unavoidable CO_(2)emissions as well as considerable quantities of slags.More than one-half of the emitted CO_(2)is produced in blast furnaces during ironmaking,and thus it is meaningful to use blast furnace slags to capture CO_(2)while addressing the byproducts and flue gas of ironmaking.Mineral carbonation of slags is a promising route to achieve carbon neutrality and effective slag utilization.To exploit slag more effectively and capture CO_(2)in flue gas,an in-depth investigation into the carbonation of blast furnace slags generated with different cooling methods was conducted.The effects of the solid–liquid ratio and introduced CO_(2)concentration on carbonation were determined.The CO_(2)uptake capacity of air-cooled slag(0.04 g/g)was greater than that of water-quenched slag.The CO_(2)uptake capacities of the two slags were comparable with those of slags in previous works,indicating the potential of the two slags for CO_(2)sequestration and utilization even with low-energy input and this fact suggests that this process is feasible.展开更多
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 fo...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.展开更多
This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-dra...This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.展开更多
Minerals in Portland cement including tricalcium silicate(C_(3)S),β-dicalcium silicate(β-C_(2)S),tricalcium aluminate(C_(3)A),and tetracalcium ferroaluminate(C_(4)AF),show a significantly different activity and prod...Minerals in Portland cement including tricalcium silicate(C_(3)S),β-dicalcium silicate(β-C_(2)S),tricalcium aluminate(C_(3)A),and tetracalcium ferroaluminate(C_(4)AF),show a significantly different activity and product evolution for CO_(2)curing at various water-to-solid ratios.These pure minerals were synthesized and subject to CO_(2)curing in this study to make an in-depth understanding for the carbonation properties of cement-based materials.Results showed that the optimum water-to-solid ratios of C_(3)S,β-C_(2)S,C_(3)A and C_(4)AF were 0.25,0.15,0.30 and 0.40 for carbonation,corresponding to 2 h carbonation degree of 38.5%,38.5%,24.2%,and 21.9%,respectively.The produced calcite duringβ-C_(2)S carbonation decreased as the water-to-solid ratio increased,with an increase in content of metastable CaCO_(3)of vaterite and aragonite.The thermodynamic stability of CaCO_(3)produced during carbonation was C_(3)A>C_(4)AF>β-C_(2)S>C_(3)S.The carbonation degree of Portland cement was predicted based on the results of pure minerals and the composition of cement,and the error of predicted production of CaCO_(3)was only 1.1%,which provides a potential method to predict carbonation properties of systems with a complex mineral composition.展开更多
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 ...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.展开更多
Carbonation is a natural aging process that occurs in all types of concrete. One of its primary implications is the acceleration of steel corrosion caused by the phenomena of depassivation. The goal of this research i...Carbonation is a natural aging process that occurs in all types of concrete. One of its primary implications is the acceleration of steel corrosion caused by the phenomena of depassivation. The goal of this research is to investigate the carbonation of quarry sand-based concrete. The concrete is made of 100% crushed sand 0/6.3, gravel 8/15, and 15/25 from the Arab Contractor quarry in Nomayos, Cameroon, with CEM II B-P 42.5 R from CIMENCAM (Cimenteries du Cameroun). The study employed two admixtures: one with a dual superplasticizing and reducing action (Sikamen) and another with a water-repellent effect (Sika liquid). Carbonation was performed on concrete samples at the following dates: 0, 7, 14, 28, 56, 90, 180 days, one year, and six months. Carbonated concrete (CC) and non-carbonated concrete (NCC) samples are compared in terms of their physical attributes and mineralogical characteristics. The results of this investigation reveal that after more than a year and six months of carbonation, porosity decreases and permeability increases. Despite the high fineness modulus of quarry sand, the compressive strength of quarry sand-based concrete is satisfactory. Carbonation depth is relatively high on some dates, exceeding the minimal cover value for concrete reinforcement. Sikament additive increases concrete compactness and durability while decreasing permeability. Sika water repellant mixes with the lime in cement to generate complimentary crystallizations that block the mortar’s capillaries, making it watertight.展开更多
To compare the results obtained under both natural and accelerated environments,the pH values of carbonated concrete were measured,the variation of pH values was determined,and the variations of Ca（OH）2 and CaCO3 co...To compare the results obtained under both natural and accelerated environments,the pH values of carbonated concrete were measured,the variation of pH values was determined,and the variations of Ca（OH）2 and CaCO3 contents in the carbonated concrete under natural condition and high CO2 concentration accelerated climate environments were determined by microcosmic test methods such as DTA and X-ray diffraction.The experimental results showed that the overall variation trend of pH values and phase component of carbonation layer of concrete under accelerated climate environments with high CO2 concentrations were the same as those under natural conditions.Therefore,the carbonation processes of concrete were considered consistent under both conditions.However there was a difference in the length of semi-carbonation zones.The one measured under high CO2 concentration accelerated climate environments was shorter than that under natural condition.Experimental investigation showed that it was caused by the differences in climate condition（temperature and relative humidity） as well as the properties of the concrete.The concentration of CO2 and the duration of the carbonation process have no effect on the length of semi-carbonation zone.Thus,it is acceptable to simulate the natural condition by applying the high CO2 concentration artificial accelerated carbonation technique for the purpose of the study of carbonation process of concrete.展开更多
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 ...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.展开更多
In order to evaluate the carbonation life of newly-built concrete structures,two kinds of nondestructive methods are adopted to test the thickness of the concrete cover and the ultrasonic velocity of two newly-built t...In order to evaluate the carbonation life of newly-built concrete structures,two kinds of nondestructive methods are adopted to test the thickness of the concrete cover and the ultrasonic velocity of two newly-built tunnel structures.Simultaneously a probabilistic method is proposed based on the relationship between the accelerated carbonation rate and the ultrasonic velocity.This proposed method is applied to evaluate the carbonation related lives of two newly-built tunnels and the results indicate that even under nearly the same environment and CO2 combining conditions,there exits a big difference in the probabilistic carbonation lives between the two tunnels;i.e.,the probabilistic lives of Tunnel A and Tunnel B are 94.0% and 82.3% and the corresponding maximum discrepancies are 11.6% and 27.0%,respectively.Thus,it can be concluded that the scattered quality of the concrete cover is attributed to the differences in construction technique,which eventually leads to the diversity in the evaluated probabilistic carbonation lives of the two tunnels.展开更多
Abstract： Two Canadian limestones with different properties were tested to determine the effect of SO2 during the carbonation of sorbent on the CO2 capture performance in Ca- looping. When the reaction gas is mixed w...Abstract： Two Canadian limestones with different properties were tested to determine the effect of SO2 during the carbonation of sorbent on the CO2 capture performance in Ca- looping. When the reaction gas is mixed with SO2, the carbonation ratio of the sorbent is always lower than that without SO2 for each cycle under the same conditions, and the sulfation ratio increases almost linearly with the increase in the cycle times. At 650 ℃, there is little difference in the carbonation ratio of the sorbent during the first four cycles for the two carbonation time, 5 and 10 rain at 0. 18% SO2. The indirect sulfation reaction that occurs simultaneously with the carbonation of CaO is responsible for the degradation of the sorbent for CO2 capture, and the carbonation duration is not the main factor that affects the ability of the sorbent. 680℃ is the best carbonation temperature among the three tested temperatures and the highest carbonation ratio can be obtained. Also, the sulfation ratio is the highest. The probable cause is the different effects of temperature on the carbonation rate and sulfation rate. A higher SO2 concentration will decrease the carbonation ratio clearly, but the decrease in the carbonation capability of the sorbent is not proportional to the increase of the SO2 concentration in flue gases.展开更多
Based on the test results, the differences of the carbonized depth of concrete measured by phenolphthalein indicator and rainbow indicator were discussed, the effects of the water to cement ratio of concrete, the carb...Based on the test results, the differences of the carbonized depth of concrete measured by phenolphthalein indicator and rainbow indicator were discussed, the effects of the water to cement ratio of concrete, the carbonized age and the relative humidity of environment on the carbonized depth of concrete and the depth of half-carbonized zone corresponding to green zone measured by rainbow indicator were also analyzed. It is proved that the depth measured by phenolphthalein indicator is always smaller than that measured by rainbow indicator, and the half-carbonized zone can only be measured by rainbow indicator. The carbonized and half-carbonized depths of concrete are influenced by the carbonation age, the water to cement ratio of concrete and the relative humidity of environment. It is suggested that the phenolphthalein indicator can be used to measure the carbonized depth of concrete when the strength grade of concrete is below C45, otherwise, the rainbow indicator should be utilized.展开更多
The shajiang river bridge on the appearance test, concrete rebound detection, concrete cover depth detection, concrete carbonation depth detection, concrete chlorine ion content detection, and the detection results in...The shajiang river bridge on the appearance test, concrete rebound detection, concrete cover depth detection, concrete carbonation depth detection, concrete chlorine ion content detection, and the detection results in statistics and analysis. Based on the bridge of the service the atmospheric environment parameters and testing data, the paper calculates and analyzes the main stress components the carbonation bridge reliability index and remaining life of carbide, assessing the bridge for the service life and reinforcement maintenance and offer the scientific basis.展开更多
Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-ca...Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of im- portant parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.展开更多
Large quantities of COand blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial COemission reduction and comprehensive utilisation of the sol...Large quantities of COand blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial COemission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant,（NH）SO, was used to extract calcium and magnesium from blast furnace slag（main phases of gehlenite and akermanite） by using low-temperature roasting to fix COthrough 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）SO-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 NHreleased 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 CaSOand SiO） were carbonated using（NH）COand NHHCOsolutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCOand（NH）Mg（CO）·4 HO,respectively. The latter can be selectively decomposed to magnesium carbonate at 100-200 °C to recover the NHfor reuse. In the present route, the total COsequestration 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 CaCOand SiO, 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.展开更多
Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement ...Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure in the investigation. The influence of the water-cement ratio, age, and addition of chloride to the fresh mix on chloride content in the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. The dissolved chloride content decreases with increase in the water-cement ratio. The amount of bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the dissolved chloride content of the pore solution has been observed. With complete carbonation, the dissolved chloride content in cement mortar and hardened cement paste increases by a factor between 2 and 12. The bound chloride decreases by 27%--54%. As expected, the pH value decreases from around 13.2 to as low as 8.0 due to car- bonation. It can be concluded that carbonation not only lowers the pH value but liberates bound chloride. This is one obvious reason why the combined action of chloride penetration and carbonation accelerates steel corrosion and shortens the service life of reinforced concrete structures.展开更多
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-bas...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.展开更多
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 prep...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.展开更多
Combined with DTG analysis, X-Ray diffraction analysis （XRD） and field emission scanning electron microscopy analysis （FSEM） affiliated with energy dispersive spectrometer analysis （EDS）, the early hydration and...Combined with DTG analysis, X-Ray diffraction analysis （XRD） and field emission scanning electron microscopy analysis （FSEM） affiliated with energy dispersive spectrometer analysis （EDS）, the early hydration and carbonation behavior of cement paste compacts incorporated with 30% of dolomite powder at low water to cement ratio （0.15） was investigated. The results showed that early carbonation curing was capable of developing rapid early strength. It is noted that the carbonation duration should be strictly controlled otherwise subsequent hydration might be hindered. Dolomite powder acted as nuclei of crystallization, resulting in acceleration of products formation and refinement of products crystal size. Therefore, as for cement-based material, it was found that early carbonation could reduce cement dosages to a large extent and promote rapid strength gain resulting from rapid formation of products, supplemental enhancement due to water release in the reaction of carbonation, and formation ofnanometer CaCO3 skeleton network at early age.展开更多
基金Funded by the Natural Science Foundation of Hebei Province(No.E2020209010)the Science and Technology Plan Project of Tangshan(No.19150225E)the Key R&D Projects of North China University of Science and Technology(No.ZD-ST-202301)。
文摘In view of the volume instability of steel slag aggregate leading to the quality problem of expansion damage in asphalt road construction,the 4.75-9.5 mm steel slag particles were treated by autoclaved carbonation technology,and the effects of the carbonation system(temperature and time)on the autoclaved pulverization rate,f-CaO content,and the relationship between them for the carbonated steel slag were investigated.In addition,the microstructure of the carbonated steel slag was analyzed by X-ray diffractometer(XRD),scanning electron microscope and energy dispersive spectrometer(SEM-EDS),metallographic microscope and X-ray fluorescence imaging spectrometer(XRF).The experimental results indicate that,under the initial CO_(2)pressure of 1.0 MPa,increasing the carbonation temperature leads to the increase in the crystal plane spacing of Ca(OH)_(2)that was generated by the hydration of minerals in steel slag,and promotes the transformation of carbonated CaCO_(3)from the orthorhombic system to the hexagonal system,resulting in the increase of the crystal planes spacing of them,meantime,accelerates the decomposition of RO phases and also the outward migration of Ca^(2+),Fe^(2+),and Mn^(2+)ions to cover and coat on the Si^(4+),Al^(3+)ions,and impels the formation of hydroxides such as Fe(OH)_(3)and the formation of carbonates such as Ca(Mg)CO_(3),FeCO_(3)and MnCO_(3).Carbonation at the temperature of 90℃for 3 h can reach the center of 4.75-9.5 mm steel slag particles.Meanwhile,the increase of temperature can promote the mineral reaction in steel slag,resulting in the fuzzy interface between mineral phases,increase of burrs,dispersion,crossover,reduction of grain size,and rearrangement of mineral particles.
基金funded by the Technology Funding Scheme of China Construction Second Engineering Bureau LTD(2020ZX150002)the National Natural Science Foundation Project of China(12262018).
文摘To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.
基金supported by the Science and Technology Research Partnership for Sustainable Development(SATREPS)。
文摘The iron and steel industries generate large amounts of unavoidable CO_(2)emissions as well as considerable quantities of slags.More than one-half of the emitted CO_(2)is produced in blast furnaces during ironmaking,and thus it is meaningful to use blast furnace slags to capture CO_(2)while addressing the byproducts and flue gas of ironmaking.Mineral carbonation of slags is a promising route to achieve carbon neutrality and effective slag utilization.To exploit slag more effectively and capture CO_(2)in flue gas,an in-depth investigation into the carbonation of blast furnace slags generated with different cooling methods was conducted.The effects of the solid–liquid ratio and introduced CO_(2)concentration on carbonation were determined.The CO_(2)uptake capacity of air-cooled slag(0.04 g/g)was greater than that of water-quenched slag.The CO_(2)uptake capacities of the two slags were comparable with those of slags in previous works,indicating the potential of the two slags for CO_(2)sequestration and utilization even with low-energy input and this fact suggests that this process is feasible.
基金Funded by Joint Funds of the National Natural Science Foundation of China(No.U1904188)the Jiangxi Provincial Department of Education Science and Technology Project(Nos.GJJ171079,GJJ181023,and GJJ181022)。
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.41925012 and 42230710)the Key Laboratory Cooperation Special Project of Western Cross Team of Western Light,CAS(Grant No.xbzg-zdsys-202107).
文摘This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.
基金Funded by Hainan Provincial Natural Science Foundation of China(No.522QN279)State Key Laboratory of High Performance Civil Engineering Materials(No.2023CEM004)Natural Science Foundation of Jiangsu Province(No.BK20231088)。
文摘Minerals in Portland cement including tricalcium silicate(C_(3)S),β-dicalcium silicate(β-C_(2)S),tricalcium aluminate(C_(3)A),and tetracalcium ferroaluminate(C_(4)AF),show a significantly different activity and product evolution for CO_(2)curing at various water-to-solid ratios.These pure minerals were synthesized and subject to CO_(2)curing in this study to make an in-depth understanding for the carbonation properties of cement-based materials.Results showed that the optimum water-to-solid ratios of C_(3)S,β-C_(2)S,C_(3)A and C_(4)AF were 0.25,0.15,0.30 and 0.40 for carbonation,corresponding to 2 h carbonation degree of 38.5%,38.5%,24.2%,and 21.9%,respectively.The produced calcite duringβ-C_(2)S carbonation decreased as the water-to-solid ratio increased,with an increase in content of metastable CaCO_(3)of vaterite and aragonite.The thermodynamic stability of CaCO_(3)produced during carbonation was C_(3)A>C_(4)AF>β-C_(2)S>C_(3)S.The carbonation degree of Portland cement was predicted based on the results of pure minerals and the composition of cement,and the error of predicted production of CaCO_(3)was only 1.1%,which provides a potential method to predict carbonation properties of systems with a complex mineral composition.
基金financially sponsored by Qing Lan Project in Jiangsu Province of China(2023)Scientific Research Project of Taizhou Polytechnic College(TZYKY-22-4).
文摘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.
文摘Carbonation is a natural aging process that occurs in all types of concrete. One of its primary implications is the acceleration of steel corrosion caused by the phenomena of depassivation. The goal of this research is to investigate the carbonation of quarry sand-based concrete. The concrete is made of 100% crushed sand 0/6.3, gravel 8/15, and 15/25 from the Arab Contractor quarry in Nomayos, Cameroon, with CEM II B-P 42.5 R from CIMENCAM (Cimenteries du Cameroun). The study employed two admixtures: one with a dual superplasticizing and reducing action (Sikamen) and another with a water-repellent effect (Sika liquid). Carbonation was performed on concrete samples at the following dates: 0, 7, 14, 28, 56, 90, 180 days, one year, and six months. Carbonated concrete (CC) and non-carbonated concrete (NCC) samples are compared in terms of their physical attributes and mineralogical characteristics. The results of this investigation reveal that after more than a year and six months of carbonation, porosity decreases and permeability increases. Despite the high fineness modulus of quarry sand, the compressive strength of quarry sand-based concrete is satisfactory. Carbonation depth is relatively high on some dates, exceeding the minimal cover value for concrete reinforcement. Sikament additive increases concrete compactness and durability while decreasing permeability. Sika water repellant mixes with the lime in cement to generate complimentary crystallizations that block the mortar’s capillaries, making it watertight.
基金Funded by the National Natural Science Foundation of China (No.50538070,50878207)
文摘To compare the results obtained under both natural and accelerated environments,the pH values of carbonated concrete were measured,the variation of pH values was determined,and the variations of Ca（OH）2 and CaCO3 contents in the carbonated concrete under natural condition and high CO2 concentration accelerated climate environments were determined by microcosmic test methods such as DTA and X-ray diffraction.The experimental results showed that the overall variation trend of pH values and phase component of carbonation layer of concrete under accelerated climate environments with high CO2 concentrations were the same as those under natural conditions.Therefore,the carbonation processes of concrete were considered consistent under both conditions.However there was a difference in the length of semi-carbonation zones.The one measured under high CO2 concentration accelerated climate environments was shorter than that under natural condition.Experimental investigation showed that it was caused by the differences in climate condition（temperature and relative humidity） as well as the properties of the concrete.The concentration of CO2 and the duration of the carbonation process have no effect on the length of semi-carbonation zone.Thus,it is acceptable to simulate the natural condition by applying the high CO2 concentration artificial accelerated carbonation technique for the purpose of the study of carbonation process of concrete.
基金Funded by Hubei Technology Innovation Key Program (No.2018AAA004)。
文摘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.
基金Key Construction Project of Nanjing Yangtze River Tunnel(No.7612005822)the National Basic Research Program of China(973Program)(No.2009CB623203).
文摘In order to evaluate the carbonation life of newly-built concrete structures,two kinds of nondestructive methods are adopted to test the thickness of the concrete cover and the ultrasonic velocity of two newly-built tunnel structures.Simultaneously a probabilistic method is proposed based on the relationship between the accelerated carbonation rate and the ultrasonic velocity.This proposed method is applied to evaluate the carbonation related lives of two newly-built tunnels and the results indicate that even under nearly the same environment and CO2 combining conditions,there exits a big difference in the probabilistic carbonation lives between the two tunnels;i.e.,the probabilistic lives of Tunnel A and Tunnel B are 94.0% and 82.3% and the corresponding maximum discrepancies are 11.6% and 27.0%,respectively.Thus,it can be concluded that the scattered quality of the concrete cover is attributed to the differences in construction technique,which eventually leads to the diversity in the evaluated probabilistic carbonation lives of the two tunnels.
基金The National Natural Science Foundation of China(No.51276064)the Natural Science Foundation of Beijing City(No.3132028)
文摘Abstract： Two Canadian limestones with different properties were tested to determine the effect of SO2 during the carbonation of sorbent on the CO2 capture performance in Ca- looping. When the reaction gas is mixed with SO2, the carbonation ratio of the sorbent is always lower than that without SO2 for each cycle under the same conditions, and the sulfation ratio increases almost linearly with the increase in the cycle times. At 650 ℃, there is little difference in the carbonation ratio of the sorbent during the first four cycles for the two carbonation time, 5 and 10 rain at 0. 18% SO2. The indirect sulfation reaction that occurs simultaneously with the carbonation of CaO is responsible for the degradation of the sorbent for CO2 capture, and the carbonation duration is not the main factor that affects the ability of the sorbent. 680℃ is the best carbonation temperature among the three tested temperatures and the highest carbonation ratio can be obtained. Also, the sulfation ratio is the highest. The probable cause is the different effects of temperature on the carbonation rate and sulfation rate. A higher SO2 concentration will decrease the carbonation ratio clearly, but the decrease in the carbonation capability of the sorbent is not proportional to the increase of the SO2 concentration in flue gases.
基金Funded by Outstanding Youth Science Foundation of Henan Province of China (No. 04120002300)
文摘Based on the test results, the differences of the carbonized depth of concrete measured by phenolphthalein indicator and rainbow indicator were discussed, the effects of the water to cement ratio of concrete, the carbonized age and the relative humidity of environment on the carbonized depth of concrete and the depth of half-carbonized zone corresponding to green zone measured by rainbow indicator were also analyzed. It is proved that the depth measured by phenolphthalein indicator is always smaller than that measured by rainbow indicator, and the half-carbonized zone can only be measured by rainbow indicator. The carbonized and half-carbonized depths of concrete are influenced by the carbonation age, the water to cement ratio of concrete and the relative humidity of environment. It is suggested that the phenolphthalein indicator can be used to measure the carbonized depth of concrete when the strength grade of concrete is below C45, otherwise, the rainbow indicator should be utilized.
文摘The shajiang river bridge on the appearance test, concrete rebound detection, concrete cover depth detection, concrete carbonation depth detection, concrete chlorine ion content detection, and the detection results in statistics and analysis. Based on the bridge of the service the atmospheric environment parameters and testing data, the paper calculates and analyzes the main stress components the carbonation bridge reliability index and remaining life of carbide, assessing the bridge for the service life and reinforcement maintenance and offer the scientific basis.
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(No.U1202274)the National Natural Science Foundation of China(No.51204040)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China(No.20120042110011)the Fundamental Research Funds for the Central Universities(No.N140204015)
文摘Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of im- portant parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.
基金financial support of the National Key R&D Program of China(2016YFB0600904)
文摘Large quantities of COand blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial COemission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant,（NH）SO, was used to extract calcium and magnesium from blast furnace slag（main phases of gehlenite and akermanite） by using low-temperature roasting to fix COthrough 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）SO-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 NHreleased 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 CaSOand SiO） were carbonated using（NH）COand NHHCOsolutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCOand（NH）Mg（CO）·4 HO,respectively. The latter can be selectively decomposed to magnesium carbonate at 100-200 °C to recover the NHfor reuse. In the present route, the total COsequestration 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 CaCOand SiO, 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.
基金Project supported by the Basic Research Program(973)of China(No.2009CB623230)the Natural Science Foundation of Shan-dong Province,China(No.ZR2011EEQ031)
文摘Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure in the investigation. The influence of the water-cement ratio, age, and addition of chloride to the fresh mix on chloride content in the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. The dissolved chloride content decreases with increase in the water-cement ratio. The amount of bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the dissolved chloride content of the pore solution has been observed. With complete carbonation, the dissolved chloride content in cement mortar and hardened cement paste increases by a factor between 2 and 12. The bound chloride decreases by 27%--54%. As expected, the pH value decreases from around 13.2 to as low as 8.0 due to car- bonation. It can be concluded that carbonation not only lowers the pH value but liberates bound chloride. This is one obvious reason why the combined action of chloride penetration and carbonation accelerates steel corrosion and shortens the service life of reinforced concrete structures.
基金The authors would like to make an appreciation to the National Natural Science Foundation of China(No.51874280)the Fundamental Research Funds of the Central Universities(No.2021ZDPY0211)for financial support.
文摘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.
基金Funded by the National Natural Science Foundation of China(Nos.51808354,51808351 and 51808532)the National Natural Science Foundation of Liaoning,China(No.20180550127)+1 种基金the China Postdoctoral Science Foundation(No.2018M641712)the State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)。
文摘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.
基金Funded by the National Key Research Program(973 Program)(No.2013CB035901)the National Natural Science Foundation of China(No.51379163)
文摘Combined with DTG analysis, X-Ray diffraction analysis （XRD） and field emission scanning electron microscopy analysis （FSEM） affiliated with energy dispersive spectrometer analysis （EDS）, the early hydration and carbonation behavior of cement paste compacts incorporated with 30% of dolomite powder at low water to cement ratio （0.15） was investigated. The results showed that early carbonation curing was capable of developing rapid early strength. It is noted that the carbonation duration should be strictly controlled otherwise subsequent hydration might be hindered. Dolomite powder acted as nuclei of crystallization, resulting in acceleration of products formation and refinement of products crystal size. Therefore, as for cement-based material, it was found that early carbonation could reduce cement dosages to a large extent and promote rapid strength gain resulting from rapid formation of products, supplemental enhancement due to water release in the reaction of carbonation, and formation ofnanometer CaCO3 skeleton network at early age.
