Effect of nano-SiO2/CaCO3 compound incorporation on the properties of fully recycled coarse aggregate concrete
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摘要: 与天然粗骨料相比，再生粗骨料因其破碎过程中产生不可避免的损伤以及附着的旧砂浆使其基本物理性能较差，制备所形成再生混凝土(RAC)因其多重界面而使其力学及耐久性能较差。为了进一步提升RAC性能，基于此，开展了不同纳米SiO2(NS)与纳米CaCO3(NC)单/复掺改性全再生粗骨料混凝土(FRAC)力学及吸水性能的试验研究，其中NS掺量为S=1%、2%、3%，NC掺量为C=1%、3%、5%，并通过SEM方法在微观尺度上表征了纳米材料单/复掺对其微观形貌的改性效果。结果表明：无论纳米材料单掺还是复掺形式，在适量的掺入范围内，RAC抗压强度和劈裂抗拉强度均随着纳米材料掺量的增加而增大；但当NC掺量达到5%时，会生成过量的低碳型水化碳铝酸钙，其发生团聚后RAC强度会出现一定程度的降低，但总体仍高于未改性前的强度，当复掺比例为1%NS和3%NC时，可达到3%NS单掺的效果。RAC毛细吸水质量和吸水率随着纳米材料掺量的增加呈现下降的趋势，总体上复掺改善效果好于单掺情况，且纳米材料最佳掺量为3%。SEM结果也进一步证实，当两种纳米材料复掺量为3%时(S3C3)，RAC内部孔隙和微裂缝最少，且界面过渡区(ITZ)更致密，表明纳米材料复掺改性效果较好。Abstract: Compared with natural coarse aggregate, the basic physical properties of recycled coarse aggregate are relatively poor due to the inevitable damage in the crushing process and the attached old mortar, and the mechanical properties and durability of the prepared recycled aggregate concrete (RAC) are worse due to its formed multiple interface structures. To further improve the performance of RAC, based on this, the mechanical properties and water absorption behavior of fully recycled coarse aggregate concrete (FRAC) modified by different nano-SiO2 (NS) and nano-CaCO3 (NC) single-mixed or compound-mixed were respectively investigated. The NS content (S) was 1%, 2% and 3%, and the NC content (C) was 1%, 3% and 5%. The modification effect of single/compound-mixed nanomaterials on the micromorphology was characterized by SEM observation. The results show that the compressive strength and splitting tensile strength of RAC increase with the addition of nanomaterials within the appropriate incorporation range no matter the single-mixed and multiple-mixed forms. However, when the NC content reaches up to 5%, excessive low-carbon hydrated calcium carboaluminate will be generated, and the RAC strength will decrease to a certain extent after agglomeration, but the overall strength is still higher than that before modification, the effect of 3%NS single admixture can be achieved when the complex admixture ratio is 1%NS and 3%NC. The cumulative mass of capillary water absorption and water absorption rate of RAC decrease with the increase of nanomaterial content. In general, the improvement effect of compound mixing is better than that of single mixing, and the optimal content of nanomaterial is 3% in this study. The results of SEM observation also further confirm that when the mixture amount of the two nanomaterials is 3% (S3C3), the least internal pores and microcracks and the denser interfacial transition zone (ITZ) in RAC indicate the better modification effect of the nanomaterials.
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Key words:
- recycled aggregate concrete /
- nano-SiO2 /
- nano-CaCO3 /
- mechanical properties /
- durability
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图 2 纳米材料分散液及投射电镜图像
Figure 2. Nanomaterials dispersion solution and transmission electron microscopy images
图 4 NS/NC复掺对全再生混凝土抗压强度的影响
Figure 4. Effect of NS/NC mixture on the compressive strength of FRAC
图 5 NS/NC单/复掺对全再生混凝土劈裂抗拉强度的影响
Figure 5. Effect of NS/NC mixture on splitting tensile strength of FRAC
图 6 单/复掺NS和NC改性FRAC的毛细吸水曲线
Figure 6. Capillary water absorption curves of FRAC modified by NS and NC single/compound incorporation
图 7 不同NS和NC单/复掺量对FRAC吸水率的影响
Figure 7. Effects of different NS and NC single/compound dosages on water absorption of FRAC
图 8 NS和NC单/复掺改性FRAC的SEM图像
Figure 8. SEM images of FRAC modified by single/compound mixture of NS and NC
图 9 NS和NC单/复掺改性FRAC的XRD分析
Figure 9. XRD analysis of FRAC modified by single/compound mixture of NS and NC
图 10 NS和NC掺量对FRAC孔隙率、平均孔径和孔径分布的影响
Figure 10. Effect of NS and NC content on porosity, mean pore size and pore size distribution of FRAC
图 11 NS和NC改性FRAC骨料-旧砂浆界面处显微硬度变化
Figure 11. Microhardness values at the interface between NS and NC modified FRAC aggregate and old mortar
表 1 再生粗骨料的物理性能指标
Table 1. Physical properties index of recycled coarse aggregate
Type Water
absorption/
%Moisture
content/
%Crush
index/
%Apparent
density/
(kg·m−3)RCA 5.2 4.0 19.12 2706.2 
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表 2 NS和NC分散剂溶液的物理性质
Table 2. Physical properties of NS and NC dispersant solution
Type Appearance Granular size Mass concentration pH NS Clear liquid 155 nm 30% 9.0-11.0 NC Clear liquid 402 nm 20% 9.5-10.5
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表 3 全再生混凝土(FRAC)配合比(kg/m3)
Table 3. Mix proportion of fully recycle aggregate concrete (FRAC) (kg/m3)
Groups C W AW S RCA SP NS NC S0C0 380 152 26 627 1269 2.28 0 0 S1C0 380 152 26 627 1269 2.28 12.7 0 S2C0 380 152 26 627 1269 2.28 25.3 0 S3C0 380 152 26 627 1269 2.28 38 0 S0C1 380 152 26 627 1269 2.28 0 19 S0C3 380 152 26 627 1269 2.28 0 57 S0C5 380 152 26 627 1269 2.28 0 95 S1C1 380 152 26 627 1269 2.28 12.7 19 S1C3 380 152 26 627 1269 2.28 12.7 57 S1C5 380 152 26 627 1269 2.28 12.7 95 S2C1 380 152 26 627 1269 2.28 25.3 19 S2C3 380 152 26 627 1269 2.28 25.3 57 S2C5 380 152 26 627 1269 2.28 25.3 95 S3C1 380 152 26 627 1269 2.28 38 19 S3C3 380 152 26 627 1269 2.28 38 57 S3C5 380 152 26 627 1269 2.28 38 95 Notes: C represents cement; W and AW means water content and additional water content in the RAC mix; S means the used sand; RCA means recycled coarse aggregate; SP means polycarboxylate superplasticizer; NS and NC mean the nano-silica and nano calcium carbonate, respectively.
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