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1.
Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry 总被引:3,自引:0,他引:3
This paper deals with two experimental methods to determine carbonation profiles in concrete. Gammadensimetry is a non-destructive test method able to measure the total penetrated CO2 and to monitor the carbonation process during laboratory accelerated tests. The second method is thermogravimetric analysis (TGA) supplemented with chemical analysis (CA): as TGA is performed on a small mortar sample not representative of the whole tested concrete, CA is needed to proportion the sample cement content, the sand content and to correct the TGA results becoming thus representative of the concrete mix. Consequently, TGA-CA gives accurate quantitative profiles in carbonated cementitious materials. Results are reported for an ordinary Portland cement paste, and three concrete mixes, containing siliceous or calcareous aggregates. The CO2 mass loss due to carbonation occurs from 530 to 950 °C, which overlaps the temperature range of the calcareous aggregate dissociation. To solve the problem, the origin of CaCO3 is carefully analyzed. Calcium carbonate ensuing from C-S-H carbonation dissociates in a lower temperature range than the more stable one ensuing from portlandite carbonation and from limestone, which enables C-S-H carbonation to be distinguished from calcareous aggregates. Therefore, TGA-CA allows the CaCO3 ensuing from C-S-H carbonation to be measured and to calculate the portlandite degraded by carbonation. Thus, the total calcium carbonates profiles can be deduced even when calcareous aggregates is present in the concrete mix. 相似文献
2.
The experimental investigation of concrete carbonation depth 总被引:2,自引:0,他引:2
Phenolphthalein indicator has traditionally been used to determine the depth of carbonation in concrete. This investigation uses the thermalgravimetric analysis (TGA) method, which tests the concentration distribution of Ca(OH)2 and CaCO3, while the X-ray diffraction analysis (XRDA) tests the intensity distribution of Ca(OH)2 and CaCO3. The Fourier transformation infrared spectroscopy (FTIR) test method detects the presence of C-O in concrete samples as a basis for determining the presence of CaCO3. Concrete specimens were prepared and subjected to accelerated carbonation under conditions of 23 °C temperature, 70% RH and 20% concentration of CO2. The test results of TGA and XRDA indicate that there exist a sharp carbonation front. Three zones of carbonation were identified according to the degree of carbonation and pH in the pore solutions. The TGA, XRDA and FTIR results showed the depth of carbonation front is twice of that determined from phenolphthalein indicator. 相似文献
3.
K. Van Balen 《Cement and Concrete Research》2005,35(4):647-657
The uptake of carbon dioxide due to the carbonation reaction of Ca(OH)2 in ambient temperature of approximately 20 °C has been studied. Different types of lime have been used and the CO2 concentration has been varied to identify the influence of different variables on the kinetics of the reaction. A closed loop system has been developed and validated that allows measurement of the carbonation progress directly from monitoring CO2 uptake. Thermal analysis (TA) was used to verify the degree of carbonation that reached up to 83%. Factor analysis on the data set has demonstrated that reaction speed is not dependent upon the CO2 concentration within the limits tested. Carbonation speed depends on the specific surface of the lime. The results of this study contribute to research carried out on lime mortar carbonation models and on the carbonation process in general. 相似文献
4.
硅酸盐水泥混凝土的碳化分析 总被引:3,自引:2,他引:3
介绍了硅酸盐水泥混凝土的碳化反应和碳化过程,分析了Ca(OH)_2与水化硅酸钙(C-S-H)的碳化作用.Ca(OH)_2发生碳化反应的同时,C-S-H也会发生碳化反应;Ca(OH)_2的碳化产物是方解石,而C-S-H碳化后会转变成无定形硅胶,可能形成稳定性差、结晶度差的球霰石、文石,其分解温度低于方解石的分解温度;C/S低、结晶度差的C-S-H凝胶易于碳化;水泥浆体孔隙溶液中的碱含量越高,碳化速度越快,深度越大. 相似文献
5.
This study examines the CO2 capture behavior of KMnO4-doped CaO-based sorbent during the multiple calcination/carbonation cycles. The cyclic carbonation behavior of CaCO3 doped with KMnO4 and the untreated CaCO3 was investigated. The addition of KMnO4 improves the cyclic carbonation rate of the sorbent above carbonation time of 257 s at each carbonation cycle. When the mass ratio of KMnO4/CaCO3 is about 0.5-0.8 wt.%, the sorbent can achieve an optimum carbonation conversion during the long-term cycles. The carbonation temperature of 660-710 °C is beneficial to cyclic carbonation of KMnO4-doped CaCO3. The addition of KMnO4 improves the long-term performance of CaCO3, resulting in directly measured conversion as high as 0.35 after 100 cycles, while the untreated CaCO3 retains conversion less than 0.16 at the same reaction conditions. The addition of KMnO4 decreases the surface area and pore volume of CaCO3 after 1 cycle, but it maintains the surface area and pores between 26 nm and 175 nm of the sorbent during the multiple cycles. Calculation reveals that the addition of KMnO4 improves the CO2 capture efficiency significantly using a CaCO3 calcination/carbonation cycle and decreases the amount of the fresh sorbent. 相似文献
6.
Ultrafine particles of CaCO3 were synthesized by dispersing the mixture of CO2 and N2 into the Ca(OH)2/H2O slurry with a micropore-plate. Because the micropore is micrometers scale, process of momentum transfer, mass transfer and reaction was significantly enhanced. The carbonation process of Ca(OH)2/H2O system was monitored with pH and conductivity. Operation conditions were investigated on the specific surface area of particles, such as initial slurry concentration and volume, gas flowrate and concentration, and temperature. The crystal structure of particles was characterized with BET, IR, TEM, SEM, etc. Results showed ultrafine particles were calcite with general shape of cube, whose size was about 40 nm and specific surface area was more than 25 m2/g. This preparation method is easy to operate. 相似文献
7.
The purpose of this article is to investigate the carbonation mechanism of CH and C-S-H within type-I cement-based materials in terms of kinetics, microstructure changes and water released from hydrates during carbonation. Carbonation tests were performed under accelerated conditions (10% CO2, 25 °C and 65 ± 5% RH). Carbonation profiles were assessed by destructive and non-destructive methods such as phenolphthalein spray test, thermogravimetric analysis, and mercury intrusion porosimetry (destructive), as well as gamma-ray attenuation (non-destructive). Carbonation penetration was carried out at different ages from 1 to 16 weeks of CO2 exposure on cement pastes of 0.45 and 0.6 w/c, as well as on mortar specimens (w/c = 0.50 and s/c = 2). Combining experimental results allowed us to improve the understanding of C-S-H and CH carbonation mechanism. The variation of molar volume of C-S-H during carbonation was identified and a quantification of the amount of water released during CH and C-S-H carbonation was performed. 相似文献
8.
Abdul-Rauf Ibrahim Jean Bosco Vuningoma Yan Huang Hongtao Wang Jun Li 《International journal of molecular sciences》2014,15(7):11350-11363
Aqueous carbonation of Ca(OH)2 is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO2 in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO2 with Ca(OH)2. The use of the IL increased the solubility of CO2 in the aqueous environment and enhanced the transport of the reactive species (Ca2+ and CO32−) and products. The presence of the IL also avoided the formation of the CaCO3 protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time. 相似文献
9.
Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags 总被引:2,自引:0,他引:2
Susan A. Bernal Ruby Mejía de Gutierrez Volker Rose 《Cement and Concrete Research》2010,40(6):898-907
Accelerated carbonation is induced in pastes and mortars produced from alkali silicate-activated granulated blast furnace slag (GBFS)-metakaolin (MK) blends, by exposure to CO2-rich gas atmospheres. Uncarbonated specimens show compressive strengths of up to 63 MPa after 28 days of curing when GBFS is used as the sole binder, and this decreases by 40-50% upon complete carbonation. The final strength of carbonated samples is largely independent of the extent of metakaolin incorporation up to 20%. Increasing the metakaolin content of the binder leads to a reduction in mechanical strength, more rapid carbonation, and an increase in capillary sorptivity. A higher susceptibility to carbonation is identified when activation is carried out with a lower solution modulus (SiO2/Na2O ratio) in metakaolin-free samples, but this trend is reversed when metakaolin is added due to the formation of secondary aluminosilicate phases. High-energy synchrotron X-ray diffractometry of uncarbonated paste samples shows that the main reaction products in alkali-activated GBFS/MK blends are C-S-H gels, and aluminosilicates with a zeolitic (gismondine) structure. The main crystalline carbonation products are calcite in all samples and trona only in samples containing no metakaolin, with carbonation taking place in the C-S-H gels of all samples, and involving the free Na+ present in the pore solution of the metakaolin-free samples. Samples containing metakaolin do not appear to have the same availability of Na+ for carbonation, indicating that this is more effectively bound in the presence of a secondary aluminosilicate gel phase. It is clear that claims of exceptional carbonation resistance in alkali-activated binders are not universally true, but by developing a fuller mechanistic understanding of this process, it will certainly be possible to improve performance in this area. 相似文献
10.
Xiaoqiang Hou Leslie J. Struble R.James Kirkpatrick 《Cement and Concrete Research》2004,34(9):1683-1696
Experimental investigations of the reactions between silica, alkali hydroxide solution, and calcium hydroxide show that alkali-silicate-hydrate gel (A-S-H) comparable to that formed by the alkali-silica reaction (ASR) in concrete does not form when portlandite or the Ca-rich, Si-poor C-S-H of ordinary portland cement (OPC) paste is available to react with the silica. Under these conditions, we observe either the formation of additional C-S-H by reaction of Ca(OH)2 with the dissolving silica or the progressive polymerization of C-S-H. The A-S-H dominated by Q3 polymerization forms only after portlandite has been consumed and the C-S-H polymerized. These conclusions are consistent with previously published results and indicate that the ASR gel of concrete forms only in chemical environments in which the pore solution is much lower in Ca and higher in Si than bulk pore solution of OPC paste. These results highlight the similarity between ASR and the pozzolanic reaction and are supported by data for mortar bar specimens. 相似文献
11.
Thermodynamic calculations disclose that significant changes of the AFm and AFt phases and amount of Ca(OH)2 occur between 0 and 40 °C; the changes are affected by added calcite. Hydrogarnet, C3AH6, is destabilised at low carbonate contents and/or low temperatures < 8 °C and is unlikely to form in calcite-saturated Portland cement compositions cured at < 40 °C. The AFm phase actually consists of several structurally-related compositions which form incomplete solid solutions. The AFt phase is close to its ideal stoichiometry at 25 °C but at low temperatures, < 20 °C, extensive solid solutions occur with CO3-ettringite. A nomenclature scheme is proposed and AFm-AFt phase relations are presented in isothermal sections at 5, 25 and 40 °C. The AFt and AFm phase relations are depicted in terms of competition between OH, CO3 and SO4 for anion sites. Diagrams are presented showing how changing temperatures affect the volume of the solid phases with implications for space filling by the paste. Specimen calculations are related to regimes likely to occur in commercial cements and suggestions are made for testing thermal impacts on cement properties by defining four regimes. It is concluded that calculation provides a rapid and effective tool for exploring the response of cement systems to changing composition and temperature and to optimise cement performance. 相似文献
12.
Zhenya Wang 《Fuel Processing Technology》2010,91(8):942-950
Catalytic pyrolysis of pine wood was carried out in a fixed-bed reactor heated slowly from room temperature to 700 °C under a stream of purging argon to examine the effects of the physically mixed K2CO3 or Ca(OH)2 on the pyrolysis behaviors. K2CO3 demonstrated a stronger catalysis for decomposition of hemicellulose, cellulose and lignin constituents, leading to the reduced yield of liquid product in conjunction with the increased yields of gaseous and char products because of the promoted secondary reactions of liquid product. With the addition of 17.7 wt.% of K2CO3, none of saccharides, aldehydes and alcohols was formed and the formation of acids, furans and guaiacols was substantially reduced, whereas the yields of alkanes and phenols were increased. Potassium led to an increase in the cumulative yields of H2, CO2 and CO at 700 °C. Ca(OH)2 somewhat promoted the decomposition of cellulose and lignin constituents, and the effect of Ca(OH)2 on the yields of liquid and char was opposite to that of K2CO3. With the addition of 22.2 wt.% Ca(OH)2, some groups of liquid product such as acids and aldehydes disappeared completely and the yields of saccharides, furans and guaiacols were somewhat reduced, while the yield of alcohols was remarkably increased in contrast to the result of K2CO3. The addition of Ca(OH)2 did not significantly change the total yield of gaseous product at 700 °C but enhanced the yield of H2. 相似文献
13.
New data relevant to calcium silicate hydrate (C-S-H) gels prepared at room temperature have been obtained over a time period of up to 112 weeks. X-ray diffraction (XRD) indicates equilibrium was attained after 64 weeks. Coupled with fourier transform infrared (FT-IR) spectroscopy, a phase change in C-S-H gel at Ca/Si ≈ 1.0 was identified and the occurrence of portlandite as a distinct phase for Ca/Si > 1.64. The incongruent dissolution of C-S-H gel was modeled as a non-ideal solid solution aqueous solution (SSAS) between the end-member components CaH2SiO4 (CSH) and Ca(OH)2 (CH) using equations defining the solidus and solutus curves on a Lippmann phase diagram. Despite being semi-empirical, the model provides a reasonable and consistent fit to the solubility data and can therefore be used to describe the incongruent dissolution of C-S-H gels with compositions Ca/Si ≥ 1.0. 相似文献
14.
Carbonation of fly ash in oxy-fuel CFB combustion 总被引:1,自引:0,他引:1
Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900 °C. At CO2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800 °C with CO2 concentration set at 80% and H2O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H2O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400 °C < T ? 800 °C, the higher the temperature the higher the CaO-to-carbonate conversion ratio. The presence of H2O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H2O. For T ? 400 °C, no fly ash carbonation occurred without the presence of H2O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250 °C. For T ? 300 °C, small amounts of Ca(OH)2 were found in the final product alongside CaCO3. Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined. 相似文献
15.
A breakthrough technique for the preparation of high-yield precipitated calcium carbonate 总被引:1,自引:0,他引:1
Ana M. López-Periago Carlos García-González Concepción Domingo 《The Journal of Supercritical Fluids》2010,52(3):298-5332
Precipitated calcium carbonate (PCC) is conventionally produced through the gas-solid-liquid carbonation route, which consists on bubbling gaseous CO2 through a concentrated calcium hydroxide (Ca(OH)2) slurry. However, atmospheric carbonation processes are slow and have low carbonation efficiency. A novel technology based on the combination of supercritical carbon dioxide (scCO2) and ultrasonic agitation is described here for the preparation of high-yield PCC. The combination of both techniques has demonstrated to produce outstanding improvement for the conversion of Ca(OH)2 to the stable calcite polymorph of calcium carbonate (CaCO3). These experiments were carried out at 313 K and 13 MPa using a high-pressure reactor immersed in an ultrasounds cleaner bath. The process kinetics and the characteristics of the precipitated particles using ultrasonic agitation were compared with those obtained under similar experimental conditions using mechanical stirring and non-agitated systems. The crystal characteristics of the samples obtained using the three different agitation techniques were characterized by X-ray diffraction and scanning electron microscopy. 相似文献
16.
Yueying Wu Hongmei Bai Jizhi Zhou Cuixia Chen Xia Xu Yunfeng Xu Guangren Qian 《Applied Clay Science》2009,42(3-4):591-596
Layered double hydroxides CuxZn6 − xCr2(OH)16(CO3)·4H2O with different molar ratios of Cu/Zn/Cr were synthesized by accelerated carbonation. The products were characterized by XRD, SEM, FT-IR and TG-DTG-DSC-MS. The chemical stability was tested by the modified Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the products were the mixture of CuxZn6 − xCr2(OH)16(CO3)·4H2O and (CuZn)2(CO3)(OH)2, with similar thermal behavior. All products were chemically stable with reduced leaching at pH > 6 (Cu2+, Zn2+) or > 5 (Cr3+). 相似文献
17.
Nicholas H. Florin 《Chemical engineering science》2009,64(2):187-2142
The carbonation characteristics of pure CaO derived from nano-sized CaCO3 were investigated as part of a multi-cycle performance study which showed potential for exploiting the properties of nano-sized CaO sorbents in a continuous CO2 capture-and-release process. To help understand the approach to the decay asymptote, which is established through multiple capture-and-release cycles, a qualitative model was proposed. The rate of approach and residual conversion defined by the decay asymptote represents the establishment of an equilibrium between the pore volume and surface area loss during thermal sintering; and the pore volume and surface area regeneration as a consequence of a solid-state diffusion mechanism, and the subsequent release of CO2 in the next calcination cycle. This qualitative explanation is valid for all CaO derived CO2 sorbents. 相似文献
18.
Soo Chool Lee Chun Yong Ryu Dhanusuraman Ragupathy Joong Beom Lee Jae Chang Kim 《Fuel》2011,90(4):1465-3842
A new regenerable alumina-modified sorbent was developed for CO2 capture at temperatures below 200 °C. The CO2 capture capacity of a potassium-based sorbent containing Al2O3 (KAlI) decreased during multiple CO2 sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO3)(OH)2 phase, which could be converted into the original K2CO3 phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO2 capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO2 capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al2O3 with 60 wt.% K2CO3 was about 128 mg CO2/g sorbent. This excellent CO2 capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO3 phase during CO2 sorption, unlike the KAlI30 sorbent which formed the KHCO3 and KAl(CO3)(OH)2 phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO3)(OH)2 phase which was prepared by impregnation of Al2O3 with K2CO3 in the presence of CO2. 相似文献
19.
Carbonation curing provides a promising method for both CO2 sequestration and strength improvement of cement-based materials. To date, there is little knowledge about the influence of carbonation curing on Ca leaching resistance of cement-based materials due to the occurrence of both physical and chemical transformation. It was the first time that Ca solid-liquid equilibrium curves were experimentally established for cement pastes with different carbonation degrees in this paper. Experimental results demonstrated that on the one hand, carbonation curing improves the leaching resistance of cement paste by sequestrating Ca in insoluble CaCO3; on the other hand, potential negative effects may occur due to the accelerated decalcification and increased solubility of C–S–H after carbonation curing. Results of NMR showed that both carbonation curing and Ca leaching can increase the Si chain length and polymerization degree of C–S–H. Additionally, a modified mathematical model was established to simulate the leaching process of carbonation-cured cement paste and it was also verified by energy-dispersive spectroscopy (EDS) results. Therefore, the long-term leaching resistance of cement-based materials is possibly degraded by the carbonation curing treatment. 相似文献
20.
Xin Li 《Powder Technology》2011,206(3):358-361
The regular and well-dispersed NaAl(OH)2CO3 whiskers were successfully synthesized via facile hydrothermal route using aluminium isopropoxide and NaHCO3. The effects of reactants and reaction temperature on the structure and morphology of NaAl(OH)2CO3 whiskers have been investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo-gravimetric analysis (TGA) were employed to characterize the synthesized samples. Most NaAl(OH)2CO3 whiskers possess an average diameter of about 500 nm and lengths ranging from 10 to 30 μm. NaAl(OH)2CO3 whiskers exhibit excellent flame retardant performance and mechanical strength in poly(ethylene-co-vinyl acetate) matrix (EVA). 相似文献