硫酸钠溶液pH值对硅酸盐水泥砂浆析钙及侵蚀产物的影响
|
摘要
将水泥砂浆浸泡在pH值为5,9,13的Na_2SO_4溶液中至330d,采用化学滴定法测定砂浆中Ca~(2+),OH~-的析出量,采用X射线衍射(XRD)仪和差示扫描量热法(DSC)对不同侵蚀龄期下侵蚀产物进行半定量分析,并通过扫描电子显微镜(SEM)对钙硅比和微结构进行了分析.结果表明:溶液pH值越低,Ca~(2+)析出速率越快、析出量越大,且低pH值条件下Ca~(2+)的大量析出有助于其与侵入的SO_4~(-2)结合,形成更多低溶解度的CaSO_4·2H_2O,从而加速Ca~(2+)析出和SO_4~(-2)扩散渗入;低pH值环境下大量石膏的形成伴随着Ca(OH)_2的大量消耗,且会引起C-S-H凝胶的脱钙,导致水泥砂浆的胶凝性降低,引起试件的软化和剥落.
Cement mortars were prepared and immersed in Na_2SO_4solution with different pH values, i.e. 5, 9, and 13, up to 330 days. The contents of leached Ca~(2+) and OH~- in solution were analyzed through chemical titration, and products of cement mortars during attack were analyzed by X-ray diffraction and differential scanning calorimetry. In addition, scanning electron microscope was further applied to investigate n_(Ca)/n_(Si) and microstructures. The results show that the content and rate of calcium leaching in high pH environment are larger than that in the lower pH solution. The leached Ca~(2+) will continue to react with the diffused SO_4~(-2) to form more CaSO_4·2 H_2O at the lower pH environment. The formation of gypsum in low pH value is accompanied with the consumption of calcium hydroxide, which can cause the decalcification of C-S-H gel and decrease the gelling property of cement mortar, and result in softening and spalling of the specimens.
Cement mortars were prepared and immersed in Na_2SO_4solution with different pH values, i.e. 5, 9, and 13, up to 330 days. The contents of leached Ca~(2+) and OH~- in solution were analyzed through chemical titration, and products of cement mortars during attack were analyzed by X-ray diffraction and differential scanning calorimetry. In addition, scanning electron microscope was further applied to investigate n_(Ca)/n_(Si) and microstructures. The results show that the content and rate of calcium leaching in high pH environment are larger than that in the lower pH solution. The leached Ca~(2+) will continue to react with the diffused SO_4~(-2) to form more CaSO_4·2 H_2O at the lower pH environment. The formation of gypsum in low pH value is accompanied with the consumption of calcium hydroxide, which can cause the decalcification of C-S-H gel and decrease the gelling property of cement mortar, and result in softening and spalling of the specimens.
引文
[1] 凌康,卢都友,徐江涛,等.含白云石微粉水泥砂浆的抗硫酸盐侵蚀性能[J].硅酸盐学报,2018,46(2):224-229.LING Kang,LU Douyou,XU Jiangtao,et al.Sulfate resistance of Portland cement mortars with dolomite powders[J].Journal of the Chinese Ceramic Society,2018,46(2):224-229.(in Chinese)
[2] 丁庆军,刘勇强,刘小清,等.硫酸盐侵蚀对不同养护制度UHPC水化产物微结构的影响[J].硅酸盐通报,2018,37(3):772-780.DING Qinjun,LIU Yongqiang,LIU Xiaoqing,et al.Effects of sulfate attack on microstructure of uhpc hydration products under different curing regimes[J].Bulletin of the Chinese Ceramic Society,2018,37(3):772-780.(in Chinese)
[3] NEVILLE A.The confused world of sulfate attack on concrete[J].Cement and Concrete Research,2004,34(8):1275-1296.
[4] 方祥位,申春妮,杨德斌,等.混凝土硫酸盐侵蚀速度影响因素研究[J].建筑材料学报,2007,10(1):89-96.FANG Xiangwei,SHEN chunni,YANG Debing,et al.Investigations of influence factor on the rate of concrete sulfate attack[J].Journal of Building Materials,2007,10(1):89-96.(in Chinese)
[5] 刘加平,刘玉静,石亮,等.氯盐-硫酸盐对水泥基材料的复合侵蚀破坏[J].建筑材料学报,2016,19(6):993-997.LIU Jiaping,LIU Yujing,SHI Liang,et al.Combined attack of chloride-sulfate on cement-based materials[J].Journal of Building Materials,2016,19(6):993-997.(in Chinese)
[6] WHITTAKER M,BLACK L.Current knowledge of external sulfate attack[J].Advances in Cement Research,2015,27(9):1-14.
[7] 席耀忠.近年来水泥化学的新进展—记第九届国际水泥化学会议[J].硅酸盐学报,1993,21(6):577-588.XI Yaozong.Recent process in cement chemistry- notes on the 9th international congress on the chemistry of cement[J].Journal of the Chinese Ceramic Society,1993,21(6):577-588.(in Chinese)
[8] CHABRELIE A.Mechanisms of degradation of concrete by external sulfate ions under laboratory and field conditions[D].Lausanne:Swiss Federal Institute of Technology in Lausanne,2010.
[9] BELLMANN F,ERFURT W,LUDWIG H M.Field performance of concrete exposed to sulphate and low pH conditions from natural and industrial sources[J].Cement and Concrete Composites,2012,34(1):86-93.
[10] LIU K W,DENG M,MO L W.Influence of pH on the formation of gypsum in cement materials during sulfate attack[J].Advances in Cement Research,2015,27(8):487-493.
[11] ROZIèRE E,LOUKILI A,HACHEM R E,et al.Durability of concrete exposed to leaching and external sulphate attacks[J].Cement and Concrete Research,2009,39(12):1188-1198.
[12] XIONG C,JIANG L,XU Y,et al.Deterioration of pastes exposed to leaching,external sulfate attack and the dual actions[J].Construction and Building Materials,2016,116:52-62.
[13] TIAN B.Microanalytical and microstructural studies on the mechanism of sulfate attack[D].West Lafayette:Purdure University,1998.
[14] PLANEL D,SERCOMBE J,BESCOP P L,et al.Long-term performance of cement paste during combined calcium leaching-sulfate attack:kinetics and size effect[J].Cement and Concrete Research,2006,36(1):137-143.
[15] RICHARDSONI G.The nature of C-S-H in hardened cements[J].Cement and Concrete Research,1999,29(8):1131-1147.
[2] 丁庆军,刘勇强,刘小清,等.硫酸盐侵蚀对不同养护制度UHPC水化产物微结构的影响[J].硅酸盐通报,2018,37(3):772-780.DING Qinjun,LIU Yongqiang,LIU Xiaoqing,et al.Effects of sulfate attack on microstructure of uhpc hydration products under different curing regimes[J].Bulletin of the Chinese Ceramic Society,2018,37(3):772-780.(in Chinese)
[3] NEVILLE A.The confused world of sulfate attack on concrete[J].Cement and Concrete Research,2004,34(8):1275-1296.
[4] 方祥位,申春妮,杨德斌,等.混凝土硫酸盐侵蚀速度影响因素研究[J].建筑材料学报,2007,10(1):89-96.FANG Xiangwei,SHEN chunni,YANG Debing,et al.Investigations of influence factor on the rate of concrete sulfate attack[J].Journal of Building Materials,2007,10(1):89-96.(in Chinese)
[5] 刘加平,刘玉静,石亮,等.氯盐-硫酸盐对水泥基材料的复合侵蚀破坏[J].建筑材料学报,2016,19(6):993-997.LIU Jiaping,LIU Yujing,SHI Liang,et al.Combined attack of chloride-sulfate on cement-based materials[J].Journal of Building Materials,2016,19(6):993-997.(in Chinese)
[6] WHITTAKER M,BLACK L.Current knowledge of external sulfate attack[J].Advances in Cement Research,2015,27(9):1-14.
[7] 席耀忠.近年来水泥化学的新进展—记第九届国际水泥化学会议[J].硅酸盐学报,1993,21(6):577-588.XI Yaozong.Recent process in cement chemistry- notes on the 9th international congress on the chemistry of cement[J].Journal of the Chinese Ceramic Society,1993,21(6):577-588.(in Chinese)
[8] CHABRELIE A.Mechanisms of degradation of concrete by external sulfate ions under laboratory and field conditions[D].Lausanne:Swiss Federal Institute of Technology in Lausanne,2010.
[9] BELLMANN F,ERFURT W,LUDWIG H M.Field performance of concrete exposed to sulphate and low pH conditions from natural and industrial sources[J].Cement and Concrete Composites,2012,34(1):86-93.
[10] LIU K W,DENG M,MO L W.Influence of pH on the formation of gypsum in cement materials during sulfate attack[J].Advances in Cement Research,2015,27(8):487-493.
[11] ROZIèRE E,LOUKILI A,HACHEM R E,et al.Durability of concrete exposed to leaching and external sulphate attacks[J].Cement and Concrete Research,2009,39(12):1188-1198.
[12] XIONG C,JIANG L,XU Y,et al.Deterioration of pastes exposed to leaching,external sulfate attack and the dual actions[J].Construction and Building Materials,2016,116:52-62.
[13] TIAN B.Microanalytical and microstructural studies on the mechanism of sulfate attack[D].West Lafayette:Purdure University,1998.
[14] PLANEL D,SERCOMBE J,BESCOP P L,et al.Long-term performance of cement paste during combined calcium leaching-sulfate attack:kinetics and size effect[J].Cement and Concrete Research,2006,36(1):137-143.
[15] RICHARDSONI G.The nature of C-S-H in hardened cements[J].Cement and Concrete Research,1999,29(8):1131-1147.