摘要
负温条件下将与环境等温的物料现场直接拌合、浇筑、免加热养护的低温施工技术称为冷施工。为了探寻负温条件下使用冷施工方案时适合硫铝酸盐水泥水化及性能发展的拌合溶液,采用水化温升表征、力学性能测试、X射线衍射结合Rietveld精修分析、扫描电子显微镜观察等方法,研究了-10℃条件下有机与无机2大类共10种溶液拌合硫铝酸盐水泥的性能演化规律及机制。结果表明:氯化钙和硝酸钙溶液可促进水化,表现为水化温升大、早期强度高,试样峰值温度分别可达23.6℃和20.4℃,12 h抗压强度分别可达21.5 MPa和16.5 MPa;两者28 d抗压强度分别为101.8 MPa和19.6 MPa。碳酸钾溶液拌合试样水化温升较大、早期强度较高,试样峰值温度可达7.7℃,12 h抗压强度可达13.9MPa,但28d抗压强度仅增长至19.3MPa。氯化镁、氯化钠和亚硝酸钠溶液水化促进作用不明显,水化温升小、早期强度低,试样峰值温度均低于5℃,12 h抗压强度均小于5 MPa,但28 d抗压强度增长明显,分别达到74.0、42.7 MPa和39.2 MPa。甲醇、乙醇、乙二醇和丙三醇溶液几乎不具备水化促进作用,水化温升不明显(试样峰值温度不超过–5℃)、12 h几乎不具备强度,且28 d后甲醇、乙醇和乙二醇溶液拌合试样的抗压强度也极低;然而,丙三醇溶液拌合试样28 d抗压强度可达到23.5 MPa。-10℃条件下宜采用氯化钙溶液拌合硫铝酸盐水泥,此条件下可获得足够高的早、后期强度。
Introduction Calcium sulphoaluminate cement has a potential application in sub-zero temperature environments due to its rapid hydration,rapid setting,fast strength development,and high early strength.In cold construction sites,such as polar regions,the materials and the concrete both are exposed to sub-zero temperatures for extended periods.It is thus necessary to investigate the formation,condensation,hardening and microstructures of calcium sulphoaluminate cement at sub-zero temperatures.Cold concreting method widely recognized involves directly blending raw materials on-site at the same temperature as the ambient environment,even at sub-zero temperatures,follows via pouring and curing fresh concrete without supplemental heating.Choosing a suitable mixing solution is crucial for the effective cold concreting technology.The mixing solution must prevent freezing of both the solution and the cement pastes at sub-zero temperatures,initiating the cement hydration reaction and enabling continuous progression.Also,the properties of the mixing solution(i.e.,p H value and ion concentration)affect the dissolution and hydration of clinker minerals,leading to consequential changes in cement characteristics.In this paper,the performance evolution laws and mechanisms of calcium sulphoaluminate cement mixed with different mixing solutions at sub-zero temperatures were investigated.Methods Deionized water was used as a solvent.Six inorganic analytical pure chemical reagents and four organic analytical pure chemical reagents were used as solutes.Each of these reagents was dissolved individually in deionized water at room temperature.The solution was stirred until in a homogeneous state and left standing for 24 h.To ensure the temperature of the materials as the environmental temperature,the calcium sulphoaluminate cement and the mixing solution both were placed in a sub-zero temperature experimental system for a storage period of at least 24 h.All processes,i.e.,sample shaping and curing,were carried out in the sub-zero temperature experimental system.At -10℃,the mixing solution and cement were poured sequentially into a mixing bowl.They were stirred at a low speed for120 s,paused for 15 s,and then stirred at a high speed for 120 s.The resultant paste was poured into the mold.After pouring,the vibrating table was used for 60 compactions.The samples were then placed on a rack for cured without being covered in the sub-zero temperature environment.Once the samples were cured to the specified age,a portion of them was taken out from the sub-zero temperature experimental system for the measurement of compressive strength.Another portion was crushed and sampled on-site.These samples were placed in anhydrous ethanol to terminate hydration at room temperature for at least 7 d.Afterwards,they were dried in vacuum at 40℃ and -0.08 MPa for no less than 24 h.A portion of the samples dried was used for the microscopic observation,while another portion was ground and further analyzed for the phase composition.Results and discussion Ca Cl_(2)/Ca(NO_(3))_(2) solution is capable of accelerating hydration,resulting in an increased hydration temperature and a greater early strength.The peak temperature reaches up to 23.6℃ and 20.4℃,and the compressive strength at 12 h reaches 21.5 MPa and 16.5 MPa,respectively.Furthermore,the compressive strengths at 28 d are 101.8 MPa and 19.6 MPa,respectively.K_(2)CO_(3) solution generates an increased hydration temperature and results in a high early strength,with a peak temperature of 7.7℃ and a compressive strength of 13.9 MPa at 12 h.However,the compressive strength only increases to 19.3 MPa after a 28-d period.Mg Cl_(2),Na Cl and Na NO_(2) solutions exhibit a limited effect on enhancing hydration,presenting a low heat evolution and an early strength at their peak temperature of<5℃ and the compressive strength of<5 MPa after 12 h.Nonetheless,after a 28-d period,their compressive strength increases to 74.0,42.7 MPa and 39.2 MPa,respectively.After 12-h hydration,the main products formed from Ca Cl_(2),Ca(NO_(3))_(2),Mg Cl_(2),Na Cl and Na NO_(2) in calcium sulphoaluminate cement are AFt and AFm phases,having a needle-bar and flake morphology.Also,the main products formed from K_(2)CO_(3) solution-mixed samples are Ca CO_(3) and K_(2)SO_(4) phases,having a cube and ellipsoid morphology.CH_(3)OH,CH_(3)CH_(2)OH,(CH_(2)OH)_(2) and C_(3)H_8O_(3) solutions have a slight promotion effect on the hydration,resulting in a negligible heat evolution(peak temperature of<-5℃),minimal strength development at 12 h,and extremely low compressive strength for the samples after 28 d.However,the compressive strength of C_(3)H_8O_(3) solution-mixed samples reaches 23.5 MPa after 28 d.For the samples mixed with four organic solutions,no hydration products such as AFt appear after 12-h hydration.Conclusions Ca Cl_(2) and Ca(NO_(3))_(2) solutions with the same ions(Ca^(2+))as the cement minerals promoted cement hydration,resulting in an increased temperature and a greater early strength.Mg Cl_(2),Na Cl and Na NO_(2) solutions had negligible effects on the hydration,leading to a decreased temperature and a weaker early strength.CO_(3)^(2-)in K_(2)CO_(3) solution reacted with Ca^(2+)produced due to the dissolution of anhydrite to create Ca CO_(3) precipitates.This reaction increased the freezing point of the solution and reduced its frost resistance,causing the sample to freeze and preventing the effective cement hydration reactions.The hydroxyl group of alcohol molecule in CH_(3)OH,CH_(3)CH_(2)OH,(CH_(2)OH)_(2) and C_(3)H_(8)O_(3) solutions was adsorbed by Ca~(2+)on the surface of cement particles to form an adsorption film.This film delayed hydration.In addition,the interaction between water and cement particles also impeded when the alcohol molecule contained a methyl group,exacerbating a retarding effect.
作者
张鸿飞
任俊儒
叶家元
任雪红
张洪滔
翟牧楠
栾政彬
ZHANG Hongfei;REN Junru;YE Jiayuan;REN Xuehong;ZHANG Hongtao;ZHAI Munan;LUAN Zhengbin(State Key Laboratory of Green Building Materials,China Building Materials Academy,Beijing 100024,China;Department of Military Installations,Army Logistics Academy of PLA,Chongqing 401331,China)
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2024年第2期624-640,共17页
Journal of The Chinese Ceramic Society
基金
军队后勤科研项目(BLJ18C014)
国家自然科学基金重点项目(51832006)
中国建材集团攻关专项资助项目(2021HX0304)。
关键词
冷施工
拌合溶液
硫铝酸盐水泥
水化
cold concreting
mixing solution
calcium sulphoaluminate cement
hydration
