大掺量粉煤灰早期活性激发及其作用机理
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摘要
针对水泥基材料中大掺量粉煤灰早期激发效率低的问题,本文选取不同品种化学试剂以单掺、双掺的形式获得6种不同类型的激发剂,通过宏微观系列试验相结合的方法,确定激发剂的种类、掺量、复掺的最佳比例和粉煤灰激发要求的最低pH;并通过X-射线衍射法(XRD)、电子扫描显微镜(SEM)、微区能谱分析(EDS)、热重分析(TG)和氮气吸附测试(BET)探明激发剂的激发时效和激发机理。结果表明:Ca(OH)_2是粉煤灰水化的前提条件,双掺激发优于单掺,其最佳组合为Ca(OH)_2+Na_2SiO_3,比例为3∶1,最佳掺量为3%;粉煤灰掺量为50%时,单掺Ca(OH)_2和复掺激发剂的作用时效分别为7 d和3 d,维持粉煤灰-水泥体系能够反应的最低pH值是13.11; Ca(OH)_2+Na_2SiO_3激发剂既促进了水泥的水化又激发了粉煤灰早期活化,使粉煤灰结构在钠-钙-硫共同作用下快速裂解、水化,提高了粉煤灰-水泥的早期强度。
To address the low early excitation efficiency of high-volume fly ash in cement-based materials,we selected six different types of activators from different chemical reagents in either single-addition or double-addition form. Then,by combining a series of macro and micro experiments,we determined the type,dosage,and optimal ratio of the double addition of the activator,and the minimum pH required for fly ash excitation. Next,we determined the activation and activation mechanisms of the activators by X-ray diffraction( XRD),scanning electron microscopy( SEM),energy dispersive spectroscopy( EDS),thermogravimetric analysis( TG),and nitrogen adsorption tests( BET). The results show that calcium hydroxide is a prerequisite for the hydration of fly ash,and that the optimum combination is Ca( OH)_2+ Na_2 SiO_3 at a ratio of 3 ∶1. The optimum dosage is 3%. When the content of fly ash is 50%,the time effect of an activator for single and double addition is seven days and three days,respectively.The minimum pH value for the reaction of a fly-ash cement system is 13. 11. The results of the microscopic series show that the activator Ca( OH)_2+Na_2 SiO_3 not only promotes the hydration of cement,but also stimulates the early activation of fly ash,which means the fly ash can be quickly cracked and hydrated under the action of the sodiumcalcium-sulfur ions to improve the early strength of fly-ash cement.
To address the low early excitation efficiency of high-volume fly ash in cement-based materials,we selected six different types of activators from different chemical reagents in either single-addition or double-addition form. Then,by combining a series of macro and micro experiments,we determined the type,dosage,and optimal ratio of the double addition of the activator,and the minimum pH required for fly ash excitation. Next,we determined the activation and activation mechanisms of the activators by X-ray diffraction( XRD),scanning electron microscopy( SEM),energy dispersive spectroscopy( EDS),thermogravimetric analysis( TG),and nitrogen adsorption tests( BET). The results show that calcium hydroxide is a prerequisite for the hydration of fly ash,and that the optimum combination is Ca( OH)_2+ Na_2 SiO_3 at a ratio of 3 ∶1. The optimum dosage is 3%. When the content of fly ash is 50%,the time effect of an activator for single and double addition is seven days and three days,respectively.The minimum pH value for the reaction of a fly-ash cement system is 13. 11. The results of the microscopic series show that the activator Ca( OH)_2+Na_2 SiO_3 not only promotes the hydration of cement,but also stimulates the early activation of fly ash,which means the fly ash can be quickly cracked and hydrated under the action of the sodiumcalcium-sulfur ions to improve the early strength of fly-ash cement.
引文
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[8]黄士元,许丽萍.粉煤灰水泥浆体的组成、结构与力学性能[J].上海建材学院学报,1989,2(3):201-210.HUANG Shiyuan,XU Liping. Constituent,structure and mechanical properties of fly ash cement paste[J]. Shanghai institute of building materials,1989,2(3):201-210.
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[11]HOANG K,JUSTNES H,GEIKER M. Early age strength increase of fly ash blended cement by a ternary hardening accelerating admixture[J]. Cement and concrete research,2016,81:59-69.
[12]KATZ A. Microscopic study of alkali-activated fly ash[J].Cement and concrete research,1998,28(2):197-208.
[13]黄士元,蒋家奋,杨南如,等.近代混凝土技术[M].西安:陕西科学技术出版社,1998.
[2]LUO Zhongtao,MA Baoguo,YANG Jiujun,et al. Effects of fineness on activity character of fly ash[J]. Advanced materials research,2011,266:114-117.
[3]ZHANG Longsheng,LI Guhua,HUANG Wu,et al. The effect of slate powder on fly ash in suppressing alkali activity of slate aggregate[J]. Applied mechanics and materials,2013,357-360:1450-1454.
[4]WANG Hailiang,ZHANG Xiedong. Study on the effect of fly ash mix amount in large volume pile cap concrete on heat of hydration[J]. Applied mechanics and materials,2015,744-746:832-836.
[5]ALAKA H A,OYEDELE L O. High volume fly ash concrete:the practical impact of using superabundant dose of high range water reducer[J]. Journal of building engineering,2016,8:81-90.
[6]SINGH N,SINGH S P. Carbonation resistance and microstructural analysis of low and high volume fly ash self compacting concrete containing recycled concrete aggregates[J]. Construction and building materials,2016,127:828-842.
[7]KARAHAN O. Transport properties of high volume fly ash or slag concrete exposed to high temperature[J]. Construction and building materials,2017,152:898-906.
[8]黄士元,许丽萍.粉煤灰水泥浆体的组成、结构与力学性能[J].上海建材学院学报,1989,2(3):201-210.HUANG Shiyuan,XU Liping. Constituent,structure and mechanical properties of fly ash cement paste[J]. Shanghai institute of building materials,1989,2(3):201-210.
[9]钱文勋.粉煤灰早期活性激发及其机理研究[D].南京:南京水利科学研究院,2002.
[10]张茂亮,杨久俊.激发剂在大掺量粉煤灰水泥中的应用研究[J].材料导报,2007,21(6):146-148.ZHANG Maoliang,YANG Jiujun. Study on the application of excitant in cement gelatin with high volume fly-ash[J].Materials review,2007,21(6):146-148.
[11]HOANG K,JUSTNES H,GEIKER M. Early age strength increase of fly ash blended cement by a ternary hardening accelerating admixture[J]. Cement and concrete research,2016,81:59-69.
[12]KATZ A. Microscopic study of alkali-activated fly ash[J].Cement and concrete research,1998,28(2):197-208.
[13]黄士元,蒋家奋,杨南如,等.近代混凝土技术[M].西安:陕西科学技术出版社,1998.