摘要
测试分析了不同种类硬脂酸盐改性碱激发矿渣(AAS)抗硫酸盐物理侵蚀性能及其变化规律.结果表明:在干湿循环条件下AAS受到明显物理结晶损伤;加入硬脂酸钙(CaSt)、硬脂酸钠(NaSt)后能通过降低吸水速率、改善内部孔结构、减小表观损伤,来提升AAS半浸泡-干湿循环下的抗硫酸钠物理结晶破坏能力;硬脂酸钾(KSt)的加入则加剧了AAS硫酸钠物理结晶破坏.
混凝土硫酸盐侵蚀是危害性较大的涉水环境侵蚀破坏.多种胶凝材
Li
矿渣(GGBS)来自重庆钢铁集团,比表面积为470
Binder | SiO2 | Al2O3 | Fe2O3 | MgO | CaO | Na2O | K2O | SO3 | IL | Other |
---|---|---|---|---|---|---|---|---|---|---|
P·O | 21.62 | 4.54 | 3.40 | 2.13 | 62.94 | 0.20 | 0.86 | 2.28 | 1.08 | 0.95 |
GGBS | 32.12 | 13.65 | 1.36 | 9.15 | 36.47 | 0.35 | 0.47 | 0.26 | 0.57 | 5.60 |
砂浆配合比见
ID | m(cement)/g | m(slag)/g | wSt/% | wA/% | mW/mB | mB/mS |
---|---|---|---|---|---|---|
PC | 450 | 0 | 0 | 0 | 0.45 | 1∶3 |
AAS | 0 | 450 | 0 | 5 | 0.45 | 1∶3 |
AAS‑CaSt | 0 | 450 | 0.5 | 5 | 0.45 | 1∶3 |
AAS‑NaSt | 0 | 450 | 0.5 | 5 | 0.45 | 1∶3 |
AAS‑KSt | 0 | 450 | 0.5 | 5 | 0.45 | 1∶3 |
硫酸盐侵蚀试验采用半浸泡法,参考ASTM C1585‑13 Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic‑Cement Concretes,仅试件底部接触溶液,且溶液高度不超过试件底部2 mm,分别在质量分数为5%的硫酸钠溶液和水中进行干湿循环侵蚀试验,相应试件分别记作S组和W组,在
干湿循环制度如下:(1)养护2 a的AAS试件置于浸泡液(20 ℃)中浸泡24 h;(2)取出浸泡试件,简单去除相应结晶部分,在40 ℃烘箱中干燥48 h;(3)将试件冷却至室温,放回浸泡液,完成1个循环;(4)试验进行20次循环,每次循环均更换浸泡液,以保证硫酸盐溶液浓度恒定.干湿循环次数记作N.
试件质量变化率按式(1)计算:
(1) |
式中:MC为质量变化率,mg/m
混凝土吸水速率测试参考ASTM C1585‑13中的BS 1881‑122 Testing Concrete‑Method for Determination of Water Absorption和RILEM TC 116‑PCD Permeability of Concrete as a Criterion of its Durability进行试验. 试件在40 ℃烘干箱中烘至恒重后取出,在室温(20 ℃)下冷却1~2 h,然后进行吸水试验. 试验采用半浸泡方式,在浸泡时间为0、3、5、10、15、20 min时取出试件称重,记录试件质量.
按照式(2)进行线性拟合,得到试件吸水速率.
(2) |
式中:i为单位面积吸水量,m
干湿循环0、12、20次后,在靠近试件底部损伤较为显著的位置取样,进行侵蚀产物测试.样品破碎后研磨成粉末试样,过0.075 mm(200目)筛,进行XRD和热分析. XRD使用PANalytical X’Pert 型X射线扫描仪,扫描速率为0.20(°)/s,扫描步长为0.03°.采用NETZSCH STA 449F3综合热分析仪进行TG/DTG和DSC测试,升温区间为40~1 000 ℃,升温速率为10 ℃/min,通氮气(N2)作为保护气体,流速为60 mL/min.

图1 试件在干湿循环过程中的表观变化
Fig.1 Appearance of specimens under wet‑dry cycles
由

图2 试件在干湿循环过程中的质量变化率
Fig.2 Mass variation of specimens under wet‑dry cycles
由

图3 试件在干湿循环过程中的吸水速率
Fig.3 Sorptivity of specimens under wet‑dry cycles
W组中仅试件AAS‑CaSt吸水速率在干湿循环过程中略微上升,其他试件基本保持不变. S组中试件PC的吸水速率出现先减少后增加的趋势,其余试件则几乎全呈上升趋势. 砂浆吸水速率通常与其毛细孔隙率、孔隙连通程度成正比.试件PC中化学侵蚀产物钙矾石的生成可能使得孔隙连通程度降低,进而使其吸水速率产生波动.试件AAS与加硬脂酸盐的AAS内部硫酸钠晶体富集,使得其孔隙液表面张力增加,且随着干湿循环次数的增加,其内部孔隙结构会随着硫酸钠晶体的生长而重建,造成孔隙连通性的增加,进一步增大其吸水速率.试件AAS和AAS‑KSt的吸水速率较试件AAS‑CaSt和AAS‑NaSt增幅明显,且在干湿循环至10次时,试件AAS‑KSt的吸水速率超过试件AAS,说明试件AAS‑KSt的内部孔隙连通程度更高,这一结果同本文表观损伤程度部分的结果(

图4 试件在干湿循环前与干湿循环20次后的XRD图谱
Fig.4 XRD patterns of specimens before and after 20 wet‑dry cycles
S组中试件PC、AAS‑NaSt和AAS‑KSt干湿循环20次后观察到硫酸盐化学侵蚀产物类钙矾石相,在试件PC中还发现了石膏峰,表明这3组试件在遭受硫酸盐物理结晶破坏的同时,还遭受硫酸盐化学侵蚀破

图5 试件在干湿循环前与干湿循环20次后的TG/DTG 结果
Fig.5 TG/DTG results of specimens before and after 20 wet‑dry cycles respectively
由
矿渣颗粒重结晶放热峰位于750~1 000 ℃之间,可利用Origin软件扣除该区间基线,计算不同试件放热峰的面
ID | Group W | Group S | ||||
---|---|---|---|---|---|---|
N=0 times | N=12 times | N=20 times | N=0 times | N=12 times | N=20 times | |
AAS | 4.202 | 5.875 | 5.509 | 4.202 | 4.825 | 3.349 |
AAS‑CaSt | 5.279 | 4.838 | 4.839 | 5.279 | 2.255 | 3.773 |
AAS‑NaSt | 4.707 | 5.048 | 5.258 | 4.707 | 2.514 | 4.162 |
AAS‑KSt | 5.926 | 6.494 | 6.231 | 5.926 | 4.158 | 2.889 |
图

图6 试件在干湿循环下的孔径分布绝对值
Fig.6 Absolute value of pore size distribution of specimens under wet‑dry cycles

图7 试件在干湿循环下的孔径分布相对值
Fig.7 Relative value of pore size distribution of specimens under wet‑dry cycles
由
由
在S组中,试件孔径比例变化同W组相似,即试件AAS、AAS‑KSt同试件AAS‑CaSt、AAS‑NaSt呈现相反趋势.结合硫酸钠组质量变化率结果(
(1)硬脂酸钙CaSt和硬脂酸钠NaSt可在5%硫酸盐半浸泡-干湿循环试验中显著提升碱矿渣AAS的抗硫酸钠物理结晶破坏能力,硬脂酸钾KSt则加剧了AAS的硫酸钠物理结晶破坏过程.
(2)在5%硫酸盐半浸泡-干湿循环试验中,AAS各试件均出现明显的表面硫酸盐结晶,其主要损伤形式为表层粉化脱落,属于典型硫酸钠物理结晶破坏现象;普通硅酸盐水泥砂浆试件PC、掺NaSt、KSt试件AAS‑NaSt和AAS‑KSt内部均发现钙矾石生成,表明这3种试件还存在硫酸盐化学侵蚀风险.
(3)试件AAS、AAS‑KSt吸水速率较高,硫酸盐晶体能够在孔隙结构中得到较快生长,随着干湿循环次数的增加,硫酸盐晶体加速形成,使内部孔隙被粗化;而对于吸水速率较低的试件AAS‑CaSt与AAS‑NaSt,硫酸钠结晶使其内部孔隙细化.
(4)在5%硫酸盐半浸泡-干湿循环初期,硫酸钠可与AAS中未反应矿渣继续反应,对试件损伤有一定修复作用.
参考文献
郑毅,王爱国,刘开伟,等.不同地聚物砂浆抗硫酸盐侵蚀性能及其机理分析[J].建筑材料学报,2021,24(6):1224‑1233. [百度学术]
ZHENG Yi, WANG Aiguo, LIU Kaiwei, et al. Sulfate resistance and mechanism analysis of different geopolymer mortars[J]. Journal of Building Materials,2021,24(6):1224‑1233. (in Chinese) [百度学术]
李闯, 范颖芳, 王耀宇, 等. 钢筋-煤系偏高岭土水泥砂浆抗氯盐‑硫酸盐侵蚀性能[J]. 建筑材料学报, 2022, 25(5):447‑453. [百度学术]
LI Chuang, FAN Yingfang, WANG Yaoyu, et al. Corrosion resistance to chloride and sulfate salt attack of steel bar‑cement motar containing coal metakaolin[J]. Journal of Building Materials, 2022, 25(5):447‑453. (in Chinese) [百度学术]
赵前, 林宗寿. 石灰石矿渣水泥抗硫酸盐性能的研究[J]. 建筑材料学报, 2012, 15(6):825‑828. [百度学术]
ZHAO Qian, LIN Zongshou. Research on sulphate resistance of the limestone slag‑cement mortars[J]. Journal of Building Materials, 2012, 15(6):825‑828. (in Chinese) [百度学术]
孙道胜, 叶哲, 刘开伟, 等. 碱矿渣胶凝材料的固砂特性及抗硫酸盐侵蚀性能[J]. 材料导报, 2020, 34(10):10061‑10067. [百度学术]
SUN Daosheng, YE Zhe, LIU Kaiwei, et al. Consolidation characteristics and sulphate resistance of alkali‑activated slag cementitious materials[J]. Materials Reports, 2020, 34(10):10061‑10067. (in Chinese) [百度学术]
GARTNER E. Industrially interesting approaches to low‑CO2
cements[J]. Cement and Concrete research, 2004, 34(9):1489‑1498. [百度学术]
郑娟荣, 杨长利, 陈有志. 碱激发胶凝材料抗硫酸盐侵蚀机理的探讨[J]. 郑州大学学报:工学版, 2012, 33(3):1‑4. [百度学术]
ZHENG Juanrong, YANG Changli, CHEN Youzhi. Discussion on the mechanism of the resistance of alkali‑activated cementing material to external sulphate attack[J]. Journal of Zhengzhou University (Engineering Science), 2012, 33(3):1‑4. (in Chinese) [百度学术]
ALLAHVERDI A, HASHEMI H, MAHINROOSTA M. Resistance of alkali‑activated slag cement against sodium sulphate[J]. Iranian Journal of Materials Science and Engineering, 2020, 17(1):23‑24. [百度学术]
LAW D W, ADAM A A, MOLYNEAUX T K, et al. Durability assessment of alkali activated slag(AAS) concrete[J]. Materials and Structures, 2012, 45(9):1425‑1437. [百度学术]
LI Q, YANG K, YANG C H. An alternative admixture to reduce sorptivity of alkali‑activated slag cement by optimising pore structure and introducing hydrophobic film[J]. Cement and Concrete Composites, 2019, 95:183‑192. [百度学术]
LI Q, YANG K, WANG L, et al. A novel admixture to improve durability of alkali‑activated slag by reducing water sorptivity and optimising the process of activation[J]. Cement and Concrete Composites, 2023, 142:105193. [百度学术]
熊德意. 硬脂酸盐对碱矿渣水泥石改性效果与影响机理研究[D]. 重庆:重庆大学, 2022. [百度学术]
XIONG Deyi. Study on efficiency and mechanisms of stearate salts on improving the struture of alkali‑activated slag cement[D]. Chongqing:Chongqing University, 2022. (in Chinese) [百度学术]
SCHERER G W. Stress from crystallization of salt[J]. Cement and Concrete Research, 2004, 34(9):1613‑1624. [百度学术]
THAULOW N, SAHU S. Mechanism of concrete deterioration due to salt crystallization[J]. Materials Characterization, 2004, 53(2‑4):123‑127. [百度学术]
刘开伟, 程星星, 孙道胜, 等. 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[J]. 建筑材料学报, 2019, 22(2):179‑185. [百度学术]
LIU Kaiwei, CHENG Xingxing, SUN Daosheng, et al. Effect of pH value of sulphate solution on calcium leaching and products of cement mortars[J]. Journal of Building Materials, 2019, 22(2):179‑185. (in Chinese) [百度学术]
肖建敏, 李辉, 雷睿欣. 碱矿渣水泥早期反应产物结构演化过程[J]. 建筑材料学报,2024,27(5):381‑390. [百度学术]
XIAO Jianmin, LI Hui, LEI Ruixin. Microstructural evolution of early reaction products in alkali‑activated slag cement at early age[J]. Journal of Building Materials,2024,27(5):381‑390. (in Chinese) [百度学术]
COLLEPARDI M. A state‑of‑the‑art review on delayed ettringite attack on concrete[J]. Cement and Concrete Composites, 2003, 25(4/5):401‑407. [百度学术]
YE H L, CHEN Z J, HUANG L. Mechanism of sulfate attack on alkali‑activated slag:The role of activator composition[J]. Cement and Concrete Research, 2019, 125:112‑118. [百度学术]
ZHANG J, SHI C J, ZHANG Z H, et al. Reaction mechanism of sulfate attack on alkali‑activated slag/fly ash cements[J]. Construction and Building Materials, 2022, 318:126052. [百度学术]
KOCABA V, GALLUCCI E, SCRIVENER K L. Methods for determination of degree of reaction of slag in blended cement pastes[J]. Cement and Concrete Research, 2012, 42(3):511‑525. [百度学术]
朱效宏, 李青, 康晓娟, 等. 干湿循环硫酸盐环境下碱矿渣水泥C(N)‑A‑S‑H凝胶结构演化规律[J]. 硅酸盐学报, 2021, 49(11):2529‑2537. [百度学术]
ZHU Xiaohong, LI Qing, KANG Xiaojuan, et al. Nano structural change of C(N)‑A‑S‑H gel in alkali‑activated slag pastes subjected to wetting‑drying cyclic sulphate attack[J]. Journal of the Chinese Ceramic Society, 2021, 49(11):2529‑2537.(in Chinese) [百度学术]
JIN S S, ZHANG J X, HAN S. Fractal analysis of relation between strength and pore structure of hardened mortar[J]. Construction and Building Materials, 2017, 135:1‑7. [百度学术]