摘要
天然水硬性石灰(NHL)是在石质文物保护领域极具潜力的灌浆材料,但较低的强度和较高的脆性限制了其应用。采用一步法原位聚合制备了2-丙烯酰胺基-2-甲基丙磺酸(AMPS)吸水树脂,得到AMPS/NHL复合材料;通过XRD、FT-IR、SEM等手段对其进行了表征,通过等温量热仪监测AMPS吸水树脂改性前后NHL的水化放热情况;利用万能试验机测试了固化浆体的力学性能(抗压、抗弯以及黏接强度)。结果表明,AMPS在NHL浆体中产生的针网状结构能够在基体中起到穿针引线的作用,加强浆体内部联系,提高黏结效果,从而显著增强浆体的力学性能。3%的AMPS改性浆体在固化28 d后,抗压强度高达5.37 MPa,较改性前提高了60.7%,黏接和抗弯强度分别提高了12.8%和32.5%。
众所周知,石窟寺遗产代表着中国丰富的历史文化,见证了华夏几千年来的人类文明发展,是极为重要的历史瑰宝。然而,这些伟大遗迹正面临着各种破坏和消亡,保护和维修成为每位守护者的责任和义务。在众多病害之中,裂隙是数量最多、最为明显的一种石质文物表面损伤,裂隙的灌浆保护和加固关乎石质文物的长久保存,具有重要意
近年来,石质文物表面的裂隙修复吸引了很多学者研究,Gao, —OH,—NH,—SO2亲水基团,拥有优异的吸水
笔者通过将AMPS单体引入天然水硬性石灰浆体
所用的天然水硬性石灰为NHL2型,购买自上海德赛堡建筑材料有限公司,主要矿物相为氢氧化钙(Ca(OH)2)、碳酸钙(CaCO3)、硅酸二钙(C2S)、石英(SiO2)。聚羧酸减水剂(PCE,型号:CQJ-JSS)由上海臣启化科有限公司提供,符合标准(JG/T223—2017
采用一步法制备原位聚合AMPS吸水树脂改性NHL,具体实验流程如下:
在烧杯中加入m(AMPS/NHL)=0,0.01,0.03的AMPS单体,用去离子水稀释并搅拌,依次加入交联剂(c(MBA)为0.03 mol/L)和引发剂(c(过硫酸铵-硫代硫酸钠)为0.017 mol/L),即可得到原位聚合物AMPS前驱液,待制备浆体使用。
按照总水灰比为W/C=0.5,PCE/NHL=0.2%的配比称取减水剂分散于去离子水中配成溶液,将称量好的NHL、减水剂溶液进行搅拌至均匀;最后加入备好的前驱液,再次搅拌后得到原位聚合AMPS改性的NHL浆体。
将新鲜浆体倒入事先备好的模具中固化成型,24 h后脱模并放在湿度90%,常温的恒温恒湿养护箱内养护至7 d和28 d龄期时,分别取出进行相应的表征和测试。
利用XRD(D8 Advance,日本)来对粉末样品进行物相成分表征及定性分析。测试靶材为铜靶,λ=1.540 6 Å,管电压40 kV,管电流40 mA,步长为0.02°,扫描范围10°~80°。将质量比为0.02︰1的粉末样品与溴化钾混合,采用压片法通过傅里叶变化红外光谱仪(FT-IR,Vertex70,扫描范围400~4 000 c
使用自然滤法测试凝胶吸水性,PAMPS的吸水倍率可以通过
, | (1) |
式中:干燥的PAMPS(记为m1)放入用水浸湿的茶袋(记为m2)中,浸泡一定时间后称量茶包总重量记为m3。
NHL浆体硬化过程主要包括水化和碳化2部分。作为浆体的主要成分硅酸二钙(C2S)和水发生水化反应,形成水化硅酸钙(C-S-H)和Ca(OH)2;二氧化碳与Ca(OH)2接触发生碳化在后期形成CaCO3。即水化、碳化产物的含量能够体现反应过程和效
由

图1 不同含量AMPS改性NHL浆体在不同固化龄期时的粉末XRD图
Fig. 1 The XRD patterns of AMPS modified NHL slurry powders at different curing ages
水硬(水化)过程:
(2) |
(3) |
气硬(碳化)化过程:
(4) |
(5) |
上一节表征确定了改性后浆体的物相成分以及APMS对浆体硬化的促进作用,但对水化主要产物C-S-H以及这些促进反应是如何通过化学键作用却不清晰,因此,利用傅里叶红外光谱仪对浆体材料的内部结构进行表征和分析,如

图2 不同含量AMPS改性NHL复合材料养护28 d时的FT-IR图谱
Fig. 2 FT-IR profile of NHL composites modified with different contents of AMPS at 28 days of curing
由键的伸缩振
键断裂聚合成
为了进一步表征改性后浆体的实际应用能力及与砂岩的相容性,模拟灌浆黏接实验对砂岩块进行黏接,并养护28 d,利用扫描电子显微镜对AMPS/NHL浆体与砂岩之间黏结界面以及改性浆体微观形貌进行表征,如

图3 不同含量AMPS改性NHL浆体黏接砂岩界面处SEM图像和浆体表面的SEM图像
Fig.3 SEM images at the interface between NHL slurry modified with different contents of AMPS and bonded to sandstone and SEM images of the slurry surface
前述表征中,XRD、FT-IR均是通过半定量分析来推测改性后水化产物的含量变化,为了能够定量确定水化过程中产物的含量以及变化,利用等温量热仪对改性前后浆体的水合放热反应(水化热)进行监测。如

图4 AMPS改性前后NHL浆体的放热水合反应速率和累积放热流量曲线
Fig. 4 Hydration heat flow and hydration total exotherm for AMPS/NHL
从
此外,聚AMPS属于吸水性树脂,具备吸收、储存和释放水的能力,从而促进NHL固化,提高复合材料的机械性能。为了探索PAMPS的吸水行为,使用了自然滤法在去离子水中进行了测试。测试结果如

图5 PAMPS的吸水倍率随时间变化曲线
Fig.5 Variation in water absorption of PAMPS
由前面化学结构和微观形貌表征得出,AMPS改性引入的羧基(—COO—)能够在浆体内部与本体游离的C

图5 AMPS改性NHL复合材料的力学性能
Fig. 5 Mechanical properties of AMPS modified NHL composites
由
采用一步法制备了一种原位聚合AMPS吸水树脂改性NHL复合灌浆材料。并通过XRD、FT-IR和SEM等温量热仪以及万能试验机等手段对其物相、结构、微观形貌、水化过程以及力学性能进行表征和测试评估,主要得出以下结论:
1)AMPS改性能够延长浆体水化的诱导期,通过原位聚合AMPS吸水树脂提供水化反应水,与浆体中的C
2)适量的AMPS可以使砂-浆间通过渗透特性产生过渡层,弱化界面,提高浆体的兼容性和黏结特性,固化28天后黏结强度可达0.69 MPa,较未改性提高了12.8%;
3)原位自生AMPS吸水树脂能够在浆体中原位聚合产生的针状产物,能够与NHL浆体形成互穿网络,从而增强结合特性和力学强度,其抗弯、抗压强度在养护28 d后可高达2.61 MPa和5.37 MPa,相比于纯相NHL显著提高,有利于实际灌浆应用。
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