摘要
研究了偏高岭土、玻璃粉和石灰石粉对水泥石强度和热膨胀系数的影响.并采用热重分析仪、压汞仪和扫描电镜分析了不同水泥石的水化产物、孔结构和微观形貌.结果表明:偏高岭土、玻璃粉和石灰石粉的掺入可以降低水泥石的热膨胀系数,并且降低程度随着其掺量的增大而增大;掺加偏高岭土的水泥石中水化产物增多,孔隙率降低,微观结构致密,抗压强度增大,热膨胀系数减小;掺加玻璃粉的水泥石中水化产物减少,孔隙率增大,强度和热膨胀系数的降低幅度较大;掺加石灰石粉的水泥石强度和热膨胀系数的降低幅度最大.
混凝土作为一种多相复合材料,一般由水泥石、骨料和界面过渡区组成.其中水泥石的热膨胀系数介于10×1
水泥石的热膨胀系数在初凝时刻出现最大值,而后随着龄期的增加迅速减小,在终凝时刻达到最小值,之后又随着龄期的增加而缓慢增
鉴于此,本文研究了偏高岭土、玻璃粉和石灰石粉对水泥石强度和热膨胀系数的影响规律,并利用热重分析仪、压汞仪和扫描电镜对其影响机理进行分析,以期为偏高岭土、玻璃粉和石灰石粉在混凝土中的应用以及抑制混凝土温度开裂提供指导依据.
水泥(C)为曲阜中联水泥有限公司生产的基准水泥,偏高岭土(MK)由内蒙古超牌建材科技有限公司提供,玻璃粉(GP)由聊城莘县伟明建筑材料加工厂提供,石灰石粉(LF)由哈尔滨阿城万顺石材钙粉加工厂提供.4种原材料的化学组

图1 原材料的粒径分布
Fig.1 Particle size distribution of raw materials
水泥石的配合比见
将尺寸为5×25 mm的水泥石试样真空干燥至恒重,采用德国耐驰公司生产的402EP型热膨胀仪测定其热膨胀系数,仪器测试准确度为0.03×1
参照GB/T 17671—1999《水泥胶砂强度检验方法(ISO法)》测定水泥石试件28 d的抗压强度和抗折强度.取强度测试后的水泥石试样碎块,用无水乙醇浸泡48 h终止水化,在真空干燥箱内干燥5 d.部分块体研磨并过筛(45 μm),制备粉末样品,进行热重分析(TG);部分块体用于压汞(MIP)和扫描电镜(SEM)测试.TG测试采用德国Linseis公司生产的L70/2171型热重分析仪,测试过程中使用氮气作为保护气体,温度为25~1 000 ℃,升温速率为10 ℃/min.MIP测试采用美国Micromeritics公司生产的 9500型压汞仪,最大压力为414 MPa.SEM测试采用德国蔡司公司生产的EVO MA10型扫描电镜,加速电压为2 kV.
掺加偏高岭土、玻璃粉和石灰石粉后,水泥石热膨胀系数如

图2 水泥石的热膨胀系数
Fig.2 Thermal expansion coefficient of cement pastes
掺加偏高岭土、玻璃粉和石灰石粉后,水泥石的抗压强度和抗折强度见

图3 水泥石的抗压强度和抗折强度
Fig.3 Compressive strength and flexural strength of cement pastes

图4 水泥石的TG‑DSC曲线
Fig.4 TG‑DSC curves of cement pastes
由
由
Hallet
30-550 ℃ | (1) |
400-500 ℃ | (2) |
式中:w30-550 ℃为水泥石在30~550 ℃之间的质量损失率;w400-500 ℃为水泥石在400~500 ℃之间的质量损失率.
根据式(

图5 水泥石中化学结合水和Ca(OH)2的含量
Fig.5 Contents of bound water and Ca(OH)2 in cement pastes

图6 水泥石的孔径分布曲线
Fig.6 Pore size distribution curves of cement pastes

图7 水泥石的孔隙率
Fig.7 Porosity of cement pastes

图8 水泥石的SEM照片
Fig.8 SEM images of cement pastes
由
偏高岭土主要是由无定形硅酸铝(Al2O3·2SiO2)组成,在碱性环境下,偏高岭土会溶出活性的Al2O3和SiO2.这些活性物质可以与水泥石中的Ca(OH)2发生水化反应生成大量的水化产物(C‑S‑H、C2ASH8和C4AH13等
石灰石粉和玻璃粉的火山灰活性较低.掺加石灰石粉和玻璃粉后,水泥浆体中有效胶凝材料的含量降低,使得水化产物减少(水泥石中C‑S‑H和Ca(OH)2的含量同时降低,见
(1)偏高岭土、玻璃粉和石灰石粉的掺入可以降低水泥石的热膨胀系数,降低程度随着矿物掺和料掺量的增大而增大.在掺量相同的条件下,掺加偏高岭土水泥石的热膨胀系数最大,掺加玻璃粉水泥石的次之,掺加石灰石粉水泥石的最小.
(2)掺加偏高岭土后水泥石的化学结合水含量增加,而氢氧化钙含量减少,热膨胀系数因而降低.掺加玻璃粉和石灰石粉后,水泥石的化学结合水和氢氧化钙含量均减少,热膨胀系数因而显著降低.在掺量相同的条件下,掺加石灰石粉水泥石的氢氧化钙含量最大,掺加玻璃粉水泥石的次之,掺加偏高岭土水泥石的最小.
(3)随着偏高岭土的掺量由0%增至24%,水泥石的孔隙率由20.24%降低为10.31%,孔径分布的峰值由38.5 nm降低为3.0 nm,致使水泥石的密实度和强度提高.掺加玻璃粉后水泥石的孔径分布峰值不变,但孔隙率增大,因此强度降低.掺加石灰石粉后水泥石的孔隙率和孔径分布峰值均增大,抗压强度和抗折强度均降低.
参考文献
QIANG Z, LI K, FEN‑CHONG T, et al. Effect of porosity on thermal expansion coefficient of cement pastes and mortars[J]. Construction and Building Materials, 2012, 28(1):468‑475. [百度学术]
MEYERS L S. Thermal coefficient of expansion of Portland cement:Long time tests[J]. Industrial and Engineering Chemistry Research, 1940, 32(8):1107‑1112. [百度学术]
章瑞, 水中和, 王桂明. 硬化水泥石热膨胀性能的调节及其机理研究[J]. 南水北调与水利科技, 2009, 7(6):228‑230,233. [百度学术]
ZHANG Rui, SHUI Zhonghe, WANG Guiming. Adjustment of thermal expansion behaviour of hardened cement paste and its mechanisms[J]. South‑to‑North Water Transfers and Water Science & Technology, 2009, 7(6):228‑230,233. (in Chinese) [百度学术]
玄东兴, 水中和, 曹蓓蓓. 水泥基材料组分热变形差异性研究[J]. 武汉理工大学学报, 2007, 29(1):30‑32. [百度学术]
XUAN Dongxing, SHUI Zhonghe, CAO Beibei. Investigation on thermal deformation divergence between components of cement‑basted materials[J]. Journal of Wuhan University of Technology, 2007, 29(1):30‑32. (in Chinese) [百度学术]
黄杰. 现代混凝土早龄期热膨胀系数预测模型及其应用[D]. 南京:河海大学, 2010. [百度学术]
HUANG Jie. Prediction model of thermal expansion coefficient of modern concrete and its application in early age[D]. Nanjing:Hohai University, 2010. (in Chinese) [百度学术]
丁士卫. 水泥石热变形性能试验研究[D]. 南京:东南大学, 2006. [百度学术]
DING Shiwei. Experimental research on thermal deformation of hardened cement paste[D]. Nanjing:Southeast University, 2006. (in Chinese) [百度学术]
SHUI Z H, RUI Z, CHEN W, et al. Effects of mineral admixtures on the thermal expansion properties of hardened cement paste[J]. Construction and Building Materials, 2010, 24(9):1761‑1767. [百度学术]
史才军, 王德辉, 贾煌飞, 等. 石灰石粉在水泥基材料中的作用及对其耐久性的影响[J]. 硅酸盐学报, 2017, 45(11):1582‑1593. [百度学术]
SHI Caijun, WANG Dehui, JIA Huangfei, et al. Role of limestone powder and its effect on durability of cement‑based materials[J]. Journal of the Chinese Ceramic Society, 2017, 45(11):1582‑1593. (in Chinese) [百度学术]
李碧雄, 汪知文, 饶丹, 等. 废玻璃在水泥混凝土中的应用研究评述[J]. 硅酸盐通报, 2020, 39(8):2449‑2457. [百度学术]
LI Bixiong, WANG Zhiwen, RAO Dan, et al. Review on application of waste glass in cement concrete[J]. Bulletin of the Chinese Ceramic Society, 2020, 39(8):2449‑2457. (in Chinese) [百度学术]
SHI Z G, SHUI Z H, LI Q, et al. Combined effect of metakaolin and sea water on performance and microstructures of concrete[J]. Construction and Building Materials, 2015, 74:57‑64. [百度学术]
BAKOLAS A, AGGELAKOPOULOU E, MOROPOULOU A, et al. Evaluation of pozzolanic activity and physicomechanical characteristics in metakaolin‑lime pastes[J]. Journal of Thermal Analysis and Calorimetry, 2006, 84(1):157‑163. [百度学术]
THIERY M, VILLAIN G, DANGLA P, et al. Investigation of the carbonation front shape on cementitious materials:Effects of the chemical kinetics[J]. Cement and Concrete Research, 2007, 37(7):1047‑1058. [百度学术]
HALLET V, DE BELIE N, PONTIKES Y. The impact of slag fineness on the reactivity of blended cements with high‑volume non‑ferrous metallurgy slag[J]. Construction and Building Materials, 2020, 257:119400. [百度学术]
LIU S H, WANG L, LI Q L, et al. Hydration properties of Portland cement‑copper tailing powder composite binder[J]. Construction and Building Materials, 2020, 251:118882. [百度学术]
SHUI Z H, ZHANG R, CHEN W, et al. Effects of mineral admixtures on the thermal expansion properties of hardened cement paste[J]. Construction and Building Materials, 2010, 24(9):1761‑1767. [百度学术]
ZHAO D D, KHOSHNAZAR R. Microstructure of cement paste incorporating high volume of low‑grade metakaolin[J]. Cement and Concrete Composites, 2020, 106:42‑50. [百度学术]
ABDOLHOSSEINI QOMI M, ULM F J, PELLENQ R J M. Physical origins of thermal properties of cement paste[J]. Physical Review Applied, 2015, 3(6):064010. [百度学术]
XU H, ZHAO Y, VOGEL S C, et al. Anisotropic thermal expansion and hydrogen bonding behavior of portlandite:A high‑temperature neutron diffraction study[J]. Journal of Solid State Chemistry, 2007, 180(4):1519‑1525. [百度学术]