摘要
采用Mini‑Mason法制备了一种高粗骨料体积分数的骨料嵌锁良好的正混凝土.结果表明:通过提高填充砂浆的流动性,能有效提升混凝土中粗骨料的体积分数至52%,并明显改善混凝土的力学性能、体积稳定性、传质性能和界面过渡区的结构,优化浆体与粗骨料的黏结状态,大幅度降低胶凝材料的用量.试验证明了Mini‑Mason工艺的可行性,并为3D打印正混凝土提供了一种新的技术优势.
水泥作为混凝土制备的主要材料,其工业生产过程中的碳排放占人类碳排放总量的7%~9
为解决上述问题,许鸽龙
水泥(C)为华新P·O 42.5普通硅酸盐水泥,其基本物理性能见
Apparent density /(kg· | Normal consistency | Setting time/min | Soundness | Flexural strength/MPa | Compressive strength/MPa | |||
---|---|---|---|---|---|---|---|---|
Initial | Final | 3 d | 28 d | 3 d | 28 d | |||
3 080 | 26.8 | 135 | 195 | Eligible | 7.1 | 9.8 | 28.3 | 52.7 |
Aggregate type | Cumulative percentage retained(by mass)/% | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
31.5 mm | 26.5 mm | 19 mm | 16 mm | 13.2 mm | 9.5 mm | 4.75 mm | 2.36 mm | 1.18 mm | 0.6 mm | 0.3 mm | 0.15 mm | 0.075 mm | |
Stone A | 0 | 19 | 88.4 | 93.9 | 97.6 | 98.3 | |||||||
Stone B | 0 | 0 | 0 | 0 | 6.7 | 70.7 | 99.4 | ||||||
Manufactured sand | 2.6 | 28.8 | 52.6 | 73.5 | 87.4 | 93.8 | 97.9 |
采用Mini‑Mason工艺,设计m(水泥)∶m(矿粉)∶m(粉煤灰)=50∶35∶15,高流态砂浆具体配合比见
Specimen | Cement‑sand ratio | Material amount/(kg· | Water‑cement ratio | |||
---|---|---|---|---|---|---|
Cement | Mineral powder | Fly ash | Sand | |||
A1 | 1.00∶1.00 | 528 | 369 | 158 | 1 055 | 0.25 |
A2 | 528 | 369 | 158 | 1 055 | 0.30 | |
A3 | 528 | 369 | 158 | 1 055 | 0.35 | |
B1 | 1.00∶1.25 | 469 | 328 | 141 | 1 172 | 0.25 |
B2 | 469 | 328 | 141 | 1 172 | 0.30 | |
B3 | 469 | 328 | 141 | 1 172 | 0.35 | |
C1 | 1.00∶1.50 | 461 | 323 | 138 | 1 333 | 0.25 |
C2 | 461 | 323 | 138 | 1 333 | 0.30 | |
C3 | 461 | 323 | 138 | 1 333 | 0.35 | |
D1 | 1.00∶1.75 | 409 | 286 | 123 | 1 432 | 0.25 |
D2 | 409 | 286 | 123 | 1 432 | 0.30 | |
D3 | 409 | 286 | 123 | 1 432 | 0.35 | |
E1 | 1.00∶2.00 | 375 | 263 | 113 | 1 500 | 0.25 |
E2 | 375 | 263 | 113 | 1 500 | 0.30 | |
E3 | 375 | 263 | 113 | 1 500 | 0.35 |
调整碎石A与碎石B的质量比mA/mB,并对其空隙率(体积分数)进行分析.具体粗骨料级配见
m(stone A)∶m(stone A) | Loose bulk density/(kg· | Stamped density/(kg· | Tap density/(kg· | Loose bulk voidage/% | Stamped voidage/% | Vibrated voidage/% |
---|---|---|---|---|---|---|
10∶0 | 1 514 | 1 641 | 1 779 | 45.4 | 40.8 | 35.8 |
9∶1 | 1 627 | 1 752 | 1 841 | 41.3 | 36.8 | 33.6 |
8∶2 | 1 696 | 1 816 | 1 882 | 38.8 | 34.5 | 32.1 |
7∶3 | 1 785 | 1 891 | 1 924 | 35.6 | 31.8 | 30.6 |
6∶4 | 1 821 | 1 932 | 1 982 | 34.3 | 30.3 | 28.5 |
5∶5 | 1 868 | 1 954 | 2 029 | 32.6 | 29.5 | 26.8 |
砂浆试件制备:砂浆试件尺寸为40 mm×40 mm×160 mm,成型1 d后脱模并进行标准养护.
混凝土试件制备:先在试模中灌注一层高流态砂浆,再将粗骨料均匀抛填在砂浆上,振捣,再灌注一层砂浆,继续抛填粗骨料并振捣,如此重复3~5次,每次振捣30~60 s,直到混凝土表面平整且基本无气泡排出.采用此混凝土制备工艺制备尺寸分别为150 mm×150 mm×150 mm、100 mm×100 mm×515 mm和100×50 mm的混凝土试件,成型24 h后脱模并进行标准养护.
参照GB/T 17671—2021《水泥胶砂强度检测方法(ISO法)》、GB/T 50081—2002《普通混凝土力学性能试验方法标准》,分别对龄期为7、28 d的砂浆和混凝土试件进行强度测试.
参照GB/T 50082—2009《普通混凝土长期性能和耐久性能试验方法标准》,采用接触法,对尺寸为100 mm×100 mm×515 mm的混凝土试件进行干燥收缩性能测试,
参照GB/T 50082—2009标准,采用电通量法,对尺寸为100×50 mm的混凝土试件进行抗氯离子渗透性能测试.
将龄期为28 d的混凝土试件破碎,选取尺寸约为10 mm×10 mm×5 mm的含粗骨料-砂浆结构的碎片,对其进行镀膜处理后,采用背散射扫描电镜(QUANTA FEG450)获取扫描电镜-背扫射电子成像(SEM‑BSE)照片.
从龄期28 d的混凝土试件中切出尺寸约为20 mm×20 mm×10 mm的含粗骨料-砂浆结构的薄片并打磨抛光,采用维氏显微硬度测试仪(HVST‑1000Z)对其进行显微硬度测定,保压时间为10 s,压痕载荷为0.098 N,在距离粗骨料表面约100 μm的距离内随机取点,距离相同的取平均值.
按照

图1 减水剂掺量对砂浆扩展度和泌水率的影响
Fig.1 Effect of water reducer content on dispersion degree and bleeding rate of mortars
在减水剂掺量为1.0%,水灰比mW/mC=0.30的条件下,调整灰砂比mC/mS,得到砂浆的扩展度以及泌水率如

图2 灰砂比对砂浆扩展度和泌水率的影响
Fig.2 Effect of cement‑sand ratio on dispersion degree and bleeding rate of mortars
取减水剂掺量为0.9%,按照

图3 粗骨料级配对混凝土粗骨料体积分数的影响
Fig.3 Effect of coarse aggregate grade on volume fraction of concrete coarse aggregate

图4 砂浆扩展度对混凝土粗骨料体积分数的影响
Fig.4 Effect of mortar dispersion degree on volume fraction of concrete coarse aggregate
按照

图5 灰砂比对混凝土粗骨料体积分数的影响
Fig.5 Effect of cement‑sand ratio on volume fraction of concrete coarse aggregate
填充砂浆抗压强度与其制备的混凝土抗压强度的关系如

图6 填充砂浆抗压强度与其制备的混凝土抗压强度关系
Fig.6 Relationship between compressive strength of filling mortar and compressive strength of prepared concrete
粗骨料体积分数对混凝土抗压强度的影响如

图7 粗骨料体积分数对混凝土强度的影响
Fig.7 Effect of volume fraction of coarse aggregate on compressive strength of concrete
不同粗骨料体积分数下混凝土的干缩性能见

图8 不同粗骨料体积分数下混凝土的干缩性能
Fig.8 Dry shrinkage of concretes with different volume fractions of coarse aggregates
混凝土的抗氯离子渗透性能是评价混凝土耐久性能的重要指标,可通过电通量法直观反映.粗骨料体积分数对混凝土电通量的影响如

图9 粗骨料体积分数对混凝土电通量的影响
Fig.9 Effect of volume fraction of coarse aggregates on concrete electric flux
粗骨料对混凝土抗氯离子渗透性能的影响形式包括稀释作用、绕行作用以及界面过渡区逾渗效
界面过渡区(ITZ)较砂浆主体以及粗骨料而言,其结构相对疏松,且强度较
采用SEM‑BSE对龄期28 d的C60普通混凝土和Mini‑Mason法制备的正混凝土(填充砂浆配比为

图10 两种工艺下混凝土界面过渡区的SEM‑BSE微观形貌图
Fig.10 SEM‑BSE micromorphology in ITZ of concretes from two processes

图11 两种混凝土中界面过渡区的显微硬度
Fig.11 Microhardness of ITZ in two kinds of concretes

图12 不同混凝土中原材料的体积分数
Fig.12 Volume fraction of raw materials in different concretes
(1)适当降低灰砂比可改善砂浆的离析泌水,当砂浆泌水率不大于0.7%时,砂浆仍保有较好的工作性,Mini‑Mason法制备的正混凝土中粗骨料的体积分数随着砂浆扩展度的增大而提高.
(2)随着粗骨料体积分数的提高,Mini‑Mason法制备的正混凝土抗压强度、干缩性能以及抗氯离子渗透性能都得到了提升,胶凝材料的用量显著降低.
(3)采用Mini‑Mason法制备正混凝土,优化了填充砂浆的分布状态,改善了混凝土界面过渡区的微观结构,提高了界面过渡区的显微硬度,削弱了界面过渡区对混凝土力学性能和耐久性能带来的负面影响.
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