To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chroma...To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.展开更多
Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The ...Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.展开更多
The early-age thermal cracking easily generates and severely impairs the durability of concrete.The temperature rising inhibitor(TRI)was utilized to regulate the temperature evolution by controlling the cement hydrati...The early-age thermal cracking easily generates and severely impairs the durability of concrete.The temperature rising inhibitor(TRI)was utilized to regulate the temperature evolution by controlling the cement hydration process.This paper aimed to investigate the pore structure formation and hydration characteristics of cement paste containing TRI by low-field nuclear magnetic resonance.The experiment showed that the T_(2) peak of cement paste shifted from 7.32 ms to 0.23 ms regardless of TRI addition.But the pattern of pore structure formation was changed with TRI addition,that is,the pore structure formation was delayed,and the pore successively shifted to left in two parts.In addition,TRI addition significantly prolonged the duration of gel pore formation and greatly decreased the increase rate of gel water,which implied that TRI introduction hindered the growth of C-S-H,and subsequently decreased the hydration rates and delayed the main hydration peak.Meanwhile,TRI dissolved and diffused rapidly at 40℃,delaying the hydration of cement paste seriously.Moreover,TRI brought about the C-S-H nucleation homogeneous and the ion concentration uniform,which might reduce the localized curvature occurring on the sheet of C-S-H,and then decreased the T_(2) intensity of capillary water and gel water.展开更多
【意义】大环烷烃是一类具有单环结构而环碳数较大(n>10)的饱和脂肪烃类化合物,在油页岩、原油、土壤及高等植物中均有检出,其具有确切的生物母源信息,可以清晰地指示样品的原始沉积环境。大环烷烃碳数范围不固定,与长链烷基烯烃、...【意义】大环烷烃是一类具有单环结构而环碳数较大(n>10)的饱和脂肪烃类化合物,在油页岩、原油、土壤及高等植物中均有检出,其具有确切的生物母源信息,可以清晰地指示样品的原始沉积环境。大环烷烃碳数范围不固定,与长链烷基烯烃、烷基环己烷等化合物相比,不仅在色谱上具有相同的等间距流出特征,而且它们的质谱分子离子(C_(n)H_(2n))和特征碎片离子(m/z 97、111、125)也一模一样,极易造成误判,亟须对其结构特征进行精准厘定。【进展】系统梳理了相关的文献,并以澳大利亚悉尼盆地藻烛煤(torbanite)为对象,分离纯化单体化合物后完成核磁(Nuclear Magnetic Resonance,NMR)结构解析;类比环己烷断裂模式,提出三条质谱裂解途径,完整阐释了其特征碎片的生成机制;进一步归纳了大环烷烃可能的生物合成路线。【结论与展望】NMR结构鉴定表示大环烷烃具有特殊的单体饱和环烷烃结构。Torbanite中丛粒藻来源的大环烷烃类化合物最初的生物前体可能是长链的油酸,经长链不饱和聚醛中间体最终环化而成。未来可以逐步完善高等植物来源的大环烷烃的生物合成途径,并对其相关比值参数进行归纳总结以应用于实际地质样品中。展开更多
基金Projects(U1534207,11790283,51878583)supported by the National Natural Science Foundation of China。
文摘To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.
基金Projects(51878245,U1965105)supported by the National Natural Science Foundation of ChinaProject(2019GSF110006)supported by the Key Research and Development Program of Shandong Province,China+2 种基金Project(2020Z035)supported by the Ningbo 2025 Science and Technology Major Project,ChinaProject(KJ2017B01)supported by the Scientific Research Project of Department of Education of Anhui Province,ChinaProject(2019CEM001)supported by the State Key Laboratory of High Performance Civil Engineering Materials,China。
文摘Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.
基金Projects(51878245,U1965105) supported by the National Natural Science Foundation of ChinaProject(2017YFB0310100) supported by the National Key R&D Program of ChinaProject(2019CEM001) supported by the State Key Laboratory of High Performance Civil Engineering Materials,China。
文摘The early-age thermal cracking easily generates and severely impairs the durability of concrete.The temperature rising inhibitor(TRI)was utilized to regulate the temperature evolution by controlling the cement hydration process.This paper aimed to investigate the pore structure formation and hydration characteristics of cement paste containing TRI by low-field nuclear magnetic resonance.The experiment showed that the T_(2) peak of cement paste shifted from 7.32 ms to 0.23 ms regardless of TRI addition.But the pattern of pore structure formation was changed with TRI addition,that is,the pore structure formation was delayed,and the pore successively shifted to left in two parts.In addition,TRI addition significantly prolonged the duration of gel pore formation and greatly decreased the increase rate of gel water,which implied that TRI introduction hindered the growth of C-S-H,and subsequently decreased the hydration rates and delayed the main hydration peak.Meanwhile,TRI dissolved and diffused rapidly at 40℃,delaying the hydration of cement paste seriously.Moreover,TRI brought about the C-S-H nucleation homogeneous and the ion concentration uniform,which might reduce the localized curvature occurring on the sheet of C-S-H,and then decreased the T_(2) intensity of capillary water and gel water.
文摘【意义】大环烷烃是一类具有单环结构而环碳数较大(n>10)的饱和脂肪烃类化合物,在油页岩、原油、土壤及高等植物中均有检出,其具有确切的生物母源信息,可以清晰地指示样品的原始沉积环境。大环烷烃碳数范围不固定,与长链烷基烯烃、烷基环己烷等化合物相比,不仅在色谱上具有相同的等间距流出特征,而且它们的质谱分子离子(C_(n)H_(2n))和特征碎片离子(m/z 97、111、125)也一模一样,极易造成误判,亟须对其结构特征进行精准厘定。【进展】系统梳理了相关的文献,并以澳大利亚悉尼盆地藻烛煤(torbanite)为对象,分离纯化单体化合物后完成核磁(Nuclear Magnetic Resonance,NMR)结构解析;类比环己烷断裂模式,提出三条质谱裂解途径,完整阐释了其特征碎片的生成机制;进一步归纳了大环烷烃可能的生物合成路线。【结论与展望】NMR结构鉴定表示大环烷烃具有特殊的单体饱和环烷烃结构。Torbanite中丛粒藻来源的大环烷烃类化合物最初的生物前体可能是长链的油酸,经长链不饱和聚醛中间体最终环化而成。未来可以逐步完善高等植物来源的大环烷烃的生物合成途径,并对其相关比值参数进行归纳总结以应用于实际地质样品中。
