摘要
通过四点弯曲强度、黏结强度、冻融循环及热重、压汞和扫描电镜等试验研究了乙烯-乙酸乙烯酯共聚乳液(EVA)和硅烷乳液对高韧性防水砂浆力学性能和抗冻性的影响规律及作用机理. 结果表明:EVA基本不影响砂浆后期弯曲性能,但显著提高其与基层的黏结强度;随EVA掺量增加,砂浆孔隙率先增大后减小,抗冻性先降低后提高;硅烷乳液的掺入显著降低了水化产物在聚乙烯醇(PVA)纤维表面的附着,导致砂浆弯曲性能下降;当硅烷乳液掺量较高时,PVA纤维与基体界面粗糙度明显增加,砂浆弯曲性能提高;内掺硅烷乳液增加了毛细孔含量,有助于缓解孔隙水结冰产生的膨胀应力,从而显著提高砂浆抗冻性.
中国高铁的路基防水封闭层主要采用纤维混凝土材料,但因其脆性大、变形适应性差、接缝多等缺点,导致其在应用时出现了不同程度的开裂、粉化等问题,显著降低了封闭层的防水效
Azadmanesh
采用北京金隅集团股份有限公司提供的P‧O 42.5水泥(物理性能指标见
Density/ (g∙c | Specific surface area/( | Normal consistency/% | Soundness/mm | Setting time/min | Measured flexural strength/MPa | Measured compressive strength/MPa | |||
---|---|---|---|---|---|---|---|---|---|
Initial | Final | 3 d | 28 d | 3 d | 28 d | ||||
3.08 | 376 | 28.5 | 1.0 | 185 | 250 | 5.7 | 8.2 | 30.5 | 48.2 |
Diameter/mm | Length/mm | Density/(g∙c | Elastic modulus/GPa | Tensile strength/MPa | Elongation/% |
---|---|---|---|---|---|
0.039 | 12 | 1.2 | 40 | 1 600 | 7 |
参照前期研发的低收缩砂浆基础配合比m(水泥)∶m(粉煤灰)∶m(矿渣)∶m(纤维)∶m(砂)∶m(水)=1.000∶0.080∶0.020∶0.018∶0.500∶0.400,添加减水剂确保浆体扩展度基本保持稳定.以水泥质量为基准,设置EVA的掺量(wEVA)为0%、1.0%、1.5%和2.0%;设置硅烷乳液的掺量(wH)为0%、0.5%、1.0%和1.5%.
试件的制备过程为:(1)将水泥、粉煤灰、砂、矿渣混合后在低速(62 r/min)搅拌1 min,然后逐次加入水、乳液和减水剂;(2)接着低速搅拌1 min,再高速(125 r/min)搅拌1 min;(3)加入PVA纤维后,重复步骤(2);(4)将拌和均匀的砂浆倒入模具中振动成型,24 h后拆模并养护至规定龄期.
制备2批40 mm × 40 mm × 160 mm的试件,一批放入标准养护室((20 ± 2) ℃,相对湿度RH≥ 98%)中分别养护至3、28 d,然后采用WAW600型万能试验机,按照T/CECS 997—2022《高韧性混凝土加固砌体结构技术规程》测试试件的弯曲性能. 另一批标养至25 d,按照DL/T 5126—2021《聚合物改性水泥砂浆试验规程》,称量试件初始质量和冻融循环后的质量并拍照,采用质量损失率和外观破坏形貌来评判其抗冻性能.
将拌和均匀的砂浆倒入装有应变计的100 mm × 100 mm × 300 mm的模具中.为了模拟砂浆的实际应用环境,采用自然养护方式进行养护. 砂浆的收缩情况自成型时刻开始监测直至养护28 d后结束. 使用JMDK⁃Ⅱ型钢弦式应变采集仪采集砂浆内部的应变与温度数据. 参考文献[
(1) |
式中:为给定龄期高韧性防水砂浆的热膨胀系数,μm/(m·℃);为初始采集温度,℃; T为终止采集温度,℃.
将预先养护28 d的砂浆试件(40 mm×40 mm×80 mm,28 d抗压强度为40 MPa)放入40 mm ×40 mm×160 mm模具的一端,在另一端浇筑高韧性防水砂浆制备复合试件,标养28 d后按照JC/T 2381—2016《修补砂浆》进行测试,采用抗弯强度评定高韧性防水砂浆与基块之间的黏结强度.
EVA乳液对高韧性防水砂浆弯曲荷载-位移(F‑)曲线的影响见

图1 EVA乳液对高韧性防水砂浆弯曲荷载-位移(F‑)曲线的影响
Fig.1 Effect of EVA emulsion on F‑ curves of high toughness waterproof mortar
Time/d | wECA/% | Bending strength/MPa | Maximum displacement/mm | Bending toughness/(kJ∙ |
---|---|---|---|---|
3 | 0 | 13.652 | 1.834 | 144.889 |
1 | 13.570 | 1.697 | 119.331 | |
2 | 12.434 | 1.673 | 96.747 | |
28 | 0 | 10.066 | 1.309 | 54.306 |
1 | 9.891 | 1.244 | 50.949 | |
2 | 9.844 | 1.212 | 56.157 |
纤维增韧水泥砂浆的弯曲性能与纤维、基体和二者界面的协同效应密切相关.当纤维与基体黏结较弱时,纤维多呈拔出模式,此时适当提高界面黏结强度以及纤维拔出过程中的摩擦应力均有利于增强纤维的桥接作用,进而提高砂浆的弯曲性能;而当纤维与基体的黏结过强时,纤维呈断裂模式,无法发挥裂纹桥接作用,从而导致砂浆的弯曲性能显著降低. 通常认为,适当调节纤维与基体的界面黏结使纤维被稳定拔出是实现高韧性的前

图2 EVA乳液对高韧性防水砂浆的界面黏结强度和收缩的影响
Fig.2 Effect of EVA emulsion on interface bonding strength and shrinkage of high toughness waterproof mortar

图3 EVA乳液对高韧性防水砂浆抗冻性的影响
Fig.3 Effect of EVA emulsion on the frost resistance of high toughness waterproof mortar
研究表明,水泥基材料的冻融破坏主要由砂浆孔隙特征及自身强度决定,即孔隙率越高或强度越低,冻融循环导致的质量损失率越

图4 EVA乳液对硬化水泥浆的化学结合水和Ca(OH)2含量的影响
Fig.4 Effect of EVA emulsion on chemical bound water and Ca(OH)2 in hardened cement pastes (28 d)
Mehta

图5 EVA乳液对高韧性防水砂浆孔结构的影响
Fig.5 Effect of EVA emulsion on the pore structure of high toughness waterproof mortar (28 d)

图6 EVA乳液对高韧性防水砂浆微观形貌的影响及作用机理示意图
Fig.6 Effect of EVA emulsion on microstructure of high toughness waterproof mortar and its working mechanism(28 d)
硅烷乳液对高韧性防水砂浆弯曲性能的影响如

图7 硅烷乳液对高韧性防水砂浆弯曲性能的影响
Fig.7 Effect of silane emulsion on bending properties of high toughness waterproof mortar
前人研究指出,当界面化学脱黏能过低时,滑移阶段的界面摩擦应力是决定纤维增强水泥砂浆弯曲性能的关

图8 硅烷乳液对高韧性防水砂浆黏结强度和收缩的影响
Fig.8 Effect of silane emulsion on bonding strength and shrinkage of high toughness waterproof mortar

图9 硅烷乳液对高韧性防水砂浆抗冻性的影响与作用机理示意图
Fig.9 Effect of silane emulsion on frost resistance of high toughness waterproof mortar and working mechanism

图10 硅烷乳液对硬化水泥浆的化学结合水和Ca(OH)2含量的影响
Fig.10 Effect of silane emulsion on chemical bound water and Ca(OH)2 in hardened cement pastes (28 d)

图11 硅烷乳液对高韧性防水砂浆孔结构的影响
Fig.11 Effect of silane emulsion on pore structure of high toughness waterproof mortar (28 d)
尽管硅烷乳液改变了砂浆中毛细孔孔壁的亲疏水性,降低了其毛细吸水作用,但仍有少量水分可以进入到砂浆孔隙中. 当孔隙水占比较低时,毛细孔的增加反而为水结冰膨胀提供了足够的空间,缓解了孔隙膨胀应力(见

图12 硅烷乳液对高韧性防水砂浆微观形貌的影响及机理图
Fig.12 Effect of silane emulsion on microstructure of high toughness waterproof mortar (28 d)
(1)在一定掺量范围内,EVA乳液对高韧性防水砂浆28 d弯曲性能影响不大,但对水泥石与纤维的黏结性具有正反两方面作用,即:一方面EVA乳液的加入抑制了水泥水化,减少了纤维与水泥水化产物的黏结性;另一方面其自身的胶黏性增强了纤维与基体的黏结.高EVA掺量时纤维呈现明显的拉丝断裂破坏,难以有效发挥裂纹桥接作用.
(2)掺入EVA乳液轻微减少了砂浆收缩,显著增加了砂浆与基层的黏结强度. 随着EVA乳液掺量的增加,砂浆的抗冻性先下降而后明显提高,与总孔体积及大孔体积先增加后减少的规律相对应.
(3)硅烷乳液在抑制水泥水化的同时在水化产物表面形成了一层憎水膜,极大削弱PVA纤维与水泥基体的黏结,使弯曲性能显著下降;但在高硅烷掺量时会使纤维-基体的界面粗糙度明显提升,有利于增大纤维拔出过程的摩擦应力,进而轻微提升高韧性防水砂浆的弯曲性能.
(4)掺入硅烷乳液显著降低了砂浆的收缩及砂浆与基层的界面黏结强度. 此外,硅烷乳液的加入明显增加了毛细孔体积,有助于缓解冻融循环过程中孔隙水结冰产生的膨胀应力. 砂浆抗冻性随硅烷乳液的掺入显著提高.
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