Mechanical properties and strengthening mechanism of fully recycled aggregate concrete prepared by nano-SiO2 composite carbonated recycled aggregates
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摘要: 为探究碳化改性骨料对全再生骨料混凝土(FRAC)力学特性的影响规律,采用纳米SiO2复合碳化改性再生骨料并制备FRAC,测试了其抗压性能、劈裂抗拉性能及抗折性能等宏观力学特性,采用纳米压痕测试了其微观力学性能,并结合SEM微观测试,揭示了碳化全再生骨料混凝土(CFRAC)多重界面强化机制。结果表明,NS复合碳化实现了再生粗骨料高效碳化改性,CFRAC力学特性均得到显著提高,其中抗压强度、劈裂抗拉强度及抗折强度最大提高幅度分别为33.12%、48.73%及24.53%;CFRAC各相平均弹性模量及显微硬度显著提高,最大提高幅度分别为171.05%、62.96%,其中旧砂浆及骨料-旧砂浆界面过渡区(ITZ1)微观力学性能提高幅度最显著;通过“骨料墙效应”及“ITZ碳化强化效应”揭示了CFRAC强化机制。成果为再生骨料品质提升研究及FRAC推广应用提供理论支撑。Abstract: To explore the influence of carbonated aggregate on the mechanical properties of fully recycled aggregate concrete (FRAC), FRAC using NS composite carbonated recycled aggregate was prepared in this paper. Macroscopic mechanical properties of FRAC including compressive strength, splitting tensile strength and flexural strength were tested, the microscopic mechanical properties of FRAC were tested by nano-indentation. Combined with SEM microscopic test, the multiple interface strengthening mechanism of carbonated fully recycled aggregate concrete (CFRAC) was revealed. The results show that NS composite carbonation can achieve efficient carbonation modification of recycled aggregate, and the mechanical properties of CFRAC are significantly improved. The maximum increase of compressive strength, splitting tensile strength and flexural strength are 33.12%, 48.73% and 24.53%, respectively. The average elastic modulus and micro-hardness of CFRAC are significantly improved, and the maximum increase are 171.05% and 62.96%, respectively. The micro-mechanical properties of old mortar and aggregate-old mortar interface transition zone (ITZ1) are increased most significantly. The strengthening mechanism of CFRAC is revealed by ' aggregate wall effect ' and ' ITZ carbonation strengthening effect '. The results can provide theoretical support for the research on the quality improvement of recycled aggregate and application of FRAC.
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图 4 荷载-压痕深度典型曲线
Figure 4. Typical curve of load-indentation depth
Pmax represents the maximum load of the indenter, hf represents the indentation depth after unloading, hc represents the contact depth, hmax represents the maximum indentation depth, S represents the initial slope of the load-indentation depth unloading curve
表 1 碳化前后再生骨料物理特性
Table 1. Physical properties of recycled aggregate before and after carbonation
Aggregate type Water absorption/% Crush value/% Apparent density/(kg·m−3) Natural aggregate 0.6 8.1 2760 Sand 0.5 10.2 2591 Recycled fine aggregate 9.0 25.93 2453 Carbonated recycled fine aggregate 6.84(↓24%) 23.40(↓9.76%) 2512(↑2.41%) Recycled coarse aggregate 4.71 16.2 2648 Carbonated recycled coarse aggregate 3.63(↓22.93%) 15.60(↓3.70%) 2694(↑1.74%) 表 2 试验方案
Table 2. Test scheme
Series Recycled coarse aggregate
replacement percentageRecycled fine aggregate
replacement percentageCarbonation Number of test
blocks ( blocks )NA 0 0 — 3 RC 100% 0、30%、50%、70%、100% No 15 RF 0、30%、50%、70%、100% 100% No 15 CRC 100% 0、30%、50%、70%、100% Yes 15 CRF 0、30%、50%、70%、100% 100% Yes 15 Notes: NA represents concrete prepared by natural aggregates, RC represents fully recycled coarse aggregate concrete, RF represents fully recycled fine aggregate concrete, CRC represents carbonated fully recycled coarse aggregate concrete, CRF represents carbonated fully recycled fine aggregate concrete. 表 3 全再生骨料混凝土(FRAC)配合比(kg/m3)
Table 3. Mix proportion of fully recycled aggregate concrete (FRAC) (kg/m3)
Series Natural aggregate Recycled coarse aggregate Sand Recycled fine aggregate Water Cement NA 1220.36 0 703.38 0.00 167.31 371.80 RC0 0 579.96 1002.30 0.00 232.68 517.07 RC30 0 722.70 640.98 260.04 221.14 491.43 RC50 0 823.16 427.36 404.55 213.02 473.38 RC70 0 928.20 237.29 524.13 204.53 454.51 RC100 0 1095.05 0.00 652.91 191.04 424.54 RF0 1521.78 0.00 0 475.97 98.97 219.93 RF30 1065.41 445.05 0 475.97 130.81 290.68 RF50 761.94 742.93 0 482.18 149.82 332.92 RF70 403.47 918.13 0 554.58 167.30 371.77 Notes: In RC0, RC represents fully recycled coarse aggregate concrete, and 0 represents the replacement rate of recycled fine aggregate is 0%. In RF0, RF represents fully recycled fine aggregate concrete, and 0 represents the replacement rate of recycled coarse aggregate is 0%. -
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