摘要
以预吸水低活性矿渣替代细集料作为内养护材料,研究低活性矿渣内养护砂浆自收缩与电阻率的变化规律,揭示两者的关系。结果表明:随着低活性矿渣掺量的增加,砂浆早期强度降低幅度大,随着龄期的延长,砂浆中后期强度降低幅度小于早期,建议低活性矿渣的合适掺量取为细集料质量的15%~25%;低活性矿渣内养护对砂浆电阻率发展影响明显,凝结硬化前,浆体电阻率随低活性矿渣掺量的增大而增大;凝结硬化后,浆体电阻率随低活性矿渣掺量的增大而减小;低活性矿渣内养护能有效抑制浆体各阶段的自收缩,尤其在快速收缩阶段和短暂膨胀阶段作用最为明显,同时,36 h龄期后电阻率与自收缩有很好的对应关系,可通过电阻率发展趋势预测自收缩的变化情况。
因渗透性差,外部养护水分难以进入高性能混凝土内部,由此产生的自收缩会导致其开裂敏感性提
水泥:山东鲁城P•I 42.5硅酸盐水泥,其化学成分及矿物组成指标见
烧失量 | SiO2 | Al2O3 | CaO | MgO | SO3 | Fe2O3 | 矿物熟料的组成 | |||
---|---|---|---|---|---|---|---|---|---|---|
C3S | C2S | C3A | C4AF | |||||||
0.45 | 21.32 | 4.31 | 61.26 | 2.47 | 2.55 | 3.54 | 57.22 | 19.29 | 6.34 | 10.76 |
细度(0.08 mm)/% | 密度/(g/c | 比表面积/( | 标准稠度/% | 凝结时间/min | 抗折强度/MPa | 抗压强度/MPa | |||
---|---|---|---|---|---|---|---|---|---|
初凝 | 终凝 | 3 d | 28 d | 3 d | 28 d | ||||
0.9 | 3.14 | 342 | 25.8 | 185 | 255 | 5.8 | 8.6 | 27.7 | 51.2 |
低活性矿渣:新疆宝新盛源板结高炉矿渣,破碎、筛除粒径大于4.75 mm的颗粒,细度模数为2.6,颗粒级配区间为Ⅱ区,玻璃体含量为50%,如

图1 低活性矿渣玻璃体含量
Fig. 1 Vitreous content of low active slag

(a) 低活性矿渣颗粒形貌

(b) 低活性矿渣微观形貌
图2 低活性矿渣形貌
Fig. 2 Morphology of low active slag particles
碱含量/% | 氯离子含量/% | 表观密度/(kg/ | 堆积密度/(kg/ | 紧密密度/(kg/ | 细度模数 | 压碎值/% | CaO/% | f-CaO/% | MgO/% | 吸水率/% |
---|---|---|---|---|---|---|---|---|---|---|
1.11 | 0.01 | 2 270 | 970 | 1 085 | 2.6 | 28 | 38.3 | 0.1 | 5.6 | 10 |
标准砂:ISO标准砂。
粉煤灰:新疆乌鲁木齐F类Ⅱ粉煤灰,比表面积为471
减水剂:聚羧酸高性能减水剂,减水率30%以上。
试验配合比见
序号 | 组号 | (mW/mB)E | 配合比/(kg/ | ||||||
---|---|---|---|---|---|---|---|---|---|
内养护水 | 标准砂 | 低活性矿渣 | 水 | 水泥 | 粉煤灰 | 减水剂 | |||
1 | B0 | 0.36 | 0 | 1 350 | 0 | 194.4 | 405 | 135 | 0.6 |
2 | B1 | 0.36 | 20.25 | 1 147.5 | 202.5 | 194.4 | 405 | 135 | 0.6 |
3 | B2 | 0.36 | 33.75 | 1 012.5 | 337.5 | 194.4 | 405 | 135 | 0.6 |
4 | B3 | 0.36 | 49.95 | 877.5 | 472.5 | 194.4 | 405 | 135 | 0.6 |
强度试验:参照《水泥胶砂强度检测方法(ISO法)》在标准养护箱中养护至规定龄期,然后进行测试。
电阻率试验:采用中衡港科(深圳)科技有限公司生产的无电极电阻率测定仪(CCR-3型),测试温度为(20±2) ℃,相对湿度为(50±2)%,根据
自收缩试验:采用NELD-NES730型号非接触式混凝土收缩变形测定仪检测,记录频率为1次/15 min,测试温度为(20±2) ℃,湿度为(60±5)%,测试龄期为168 h,主要通过两端的位移传感器测定无约束状态下混凝土发生的形变,测试装置如

(a) 测定仪主机

(b) 试样测试装置
图3 非接触式混凝土收缩变形测定仪
Fig. 3 Non-contact measuring instrument for concrete shrinkage deformation

(a) 抗压强度

(b) 抗折强度
图4 不同低活性矿渣掺量对砂浆力学性能的影响
Fig. 4 Effect of different low active slag content on mechanical properties of mortar

图5 不同低活性矿渣掺量对砂浆自收缩的影响
Fig. 5 Effect of different low active slag content on autogenous shrinkage of mortar
根据上述分析,低活性矿渣内养护能有效抑制浆体各阶段的自收缩,尤其在快速收缩阶段和短暂膨胀阶段作用最为明显。主要有两方面原因:1)水泥水化和环境干燥都将引发水泥石毛细孔自由水含量减少、内部相对湿度下降,进而在毛细孔内形成弯月面,引发毛细负压力,导致混凝土收

图6 不同低活性矿渣掺量砂浆电阻率发展曲线
Fig. 6 Resistivity development curve of mortar with different low activity slag content
目前自收缩测试方法复杂多样,但电阻率的测试方法精确且统一,并且由于浆体的自收缩和电阻率发展都是由水泥水化引起,自收缩受到水泥水化的直接影响,而电阻率则是水泥水化过程的直观表
(1) |

图7 36 h后样品自收缩与电阻率的关系
Fig. 7 Relationship between autogenous shrinkage and resistivity of samples after 36 h
组号 | |||
---|---|---|---|
B0 | 9.965 5 | -49.496 7 | 0.986 4 |
B1 | 17.394 1 | -230.990 8 | 0.963 5 |
B2 | 12.047 5 | -183.327 5 | 0.974 5 |
B3 | 6.600 3 | -153.120 2 | 0.931 7 |
综上所述,电阻率与自收缩呈良好的线性关系。主要原因在于,样品内部的孔隙被离子浓度随时间变化的水溶液所充满,这些孔相数目的改变通过电阻率的变化反映出来,则电阻率表征浆体内部孔结构及孔隙率的变化,同时孔相数目和毛细孔变化又是造成自收缩的决定性原因,故自收缩随电阻率的变化而变化,其为水泥水化的宏观表现,电阻率为水化的直观表达。
1)低活性矿渣掺量增加时,砂浆早期强度下降,但随着龄期的延长,砂浆中后期强度降低幅度小于早期,建议低活性矿渣的合适掺量取细集料质量的15%~25%。
2)低活性矿渣内养护对砂浆电阻率的发展影响明显,凝结硬化前,浆体电阻率随低活性矿渣掺量的增大而增大;凝结硬化后,浆体电阻率随低活性矿渣掺量的增大而减小,其中,砂浆水化进程的溶解结晶期延后,诱导凝结期、硬化加速期和硬化减速期均有所提前。
3)低活性矿渣内养护能有效抑制浆体各阶段的自收缩,尤其在快速收缩阶段和短暂膨胀阶段作用最为明显。
4)在龄期36 h后,低活性矿渣内养护砂浆的电阻率与自收缩有很好的线性相关性,可通过电阻率发展趋势预测自收缩的变化情况。
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