Basic mechanical properties and constitutive model of recycled brick-concrete aggregate
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摘要: 再生混凝土骨料中往往会混有再生砖骨料难以分离，将再生砖与再生混凝土骨料混合利用更加符合实际情况。本文以不同水胶比(0.3和0.4)、不同再生骨料取代率(体积法取代0%、50%、100%)为控制参数，研究了8组不同配合比的再生砖混骨料混凝土的抗压、劈裂抗拉、抗折和棱柱体抗压强度及单轴受压应力-应变关系。结果表明：与天然骨料混凝土相比，不同配合比再生混凝土力学性能有不同程度的下降，其中随着再生砖骨料含量的增加，其力学性能下降较显著，砖骨料替代率达到100%时抗压强度下降高达29.9%，但是仍能保证一定的力学性能储备。文中探究了水胶比与再生砖骨料掺量对混凝土力学性能的影响机制，并以试验数据为基础，建立了再生砖混骨料混凝土单轴受压本构模型和再生砖混骨料混凝土力学性能换算公式，研究结果可对此类再生混凝土结构的分析与设计提供参考。Abstract: Recycled concrete aggregate is often mixed with recycled brick aggregate, which is difficult to separate. The mixed use of recycled brick and recycled concrete aggregate is more in line with the actual situation. Different water-binder ratios (0.3 and 0.4) and different recycled aggregate replacement rates (0%, 50%, 100% replaced by volume method) were used as control parameters to study the compressive strength, splitting tensile strength, flexural strength, prism compressive strength and uniaxial compressive stress-strain relationship of eight groups of recycled brick-concrete aggregate concrete with different mix ratios. The results show that compared with natural aggregate concrete, the mechanical properties of recycled concrete with different mix ratios decrease to varying degrees. With the increase of recycled brick aggregate content, the mechanical properties decrease significantly. When the replacement rate of brick aggregate reaches 100%, the compressive strength decreases by up to 29.9%, but it can still ensure a certain mechanical property reserve. In this paper, the influence mechanism of water-binder ratio and recycled brick aggregate content on the mechanical properties of concrete is explored. Based on the experimental data, the uniaxial compression constitutive model of recycled brick concrete and the conversion formula of mechanical properties of recycled brick concrete are established. The research results can provide reference for the analysis and design of such recycled concrete structures.
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糖尿病是一种严重威胁人类健康的慢性病。全球糖尿病患者人数从1980年的1.08亿增加到2023年的5.37亿。葡萄糖传感器在糖尿病的诊断和治疗中起着重要作用[1-3]。糖尿病患者要定期检测生理血糖水平，并将血糖水平维持在正常浓度范围内。而且，准确评价食品中的葡萄糖含量对维持糖尿病患者血液中葡萄糖的生理水平至关重要[4-5]。食品和饮料中葡萄糖含量的信息对生产者和消费者都有参考价值。葡萄糖检测在葡萄酒酿造工艺和乳制品工业的发酵过程中是至关重要的[4-5]。迄今为止，检测葡萄糖的方法很多。在各种分析方法中，电化学葡萄糖传感器具有灵敏度高、选择性好、操作简单、成本低等优点，并能实现自我监控和床边血糖检测[5-8]。基于酶的电化学葡萄糖传感器已经商业化并取得了巨大的成功。由于自然酶容易受到环境(温度、湿度、酸碱度等)影响，非酶葡萄糖传感器受到广泛关注[1-3, 8]。
金属-有机框架(Metal-origanic frameworks，MOFs)材料是一类新兴的多孔材料，存在电化学传感器应用潜力[9-12]。它们具有金属活性位点丰富、表面积大、结构多样、孔径可调和功能可调等优点。Li等[13]开发了Co-MOF纳米片阵列构建葡萄糖检测平台，其灵敏度为
10886 μA·L/(mmol·cm2)，检测极限为1.3 nmol/L。Khan等[14]以MOF-199为前驱体合成 CuO/C复合材料，催化葡萄糖的氧化反应。Cu-MOFs修饰电极在0.06至5 mmol/L的线性范围内，对葡萄糖氧化显示出相对较好的电催化活性，其灵敏度为89 mA·L/(mmol·cm2)，检测限为10.5 nmol/L。在另一份报告中，球形Ni-MOFs 颗粒在单独使用时表现出较差的电化学葡萄糖传感性能[15]。然而，当它们与碳纳米管的杂交后，对葡萄糖检测的灵敏度为13.85 mA·L/(mmol·cm2)，检测极限为0.82 mmol/L，线性范围为1至1.6 mmol/L。此外，Zha等[16]开发了基于NiCo-MOF/C复合材料的无创血糖检测平台，其高灵敏度和检测极限分别为2701.29 μA·L/(mmol·cm2)和0.09 μmol/L。MOFs衍生复合材料在电化学葡糖糖传感器领域得到一定程度的应用。另一方面，随着实时传感设备和护理点设备的发展需要，经济的、可靠的、规模化的电极制备方法受到广泛关注[17]。作为一种商业化电极制备方法，丝网印刷技术具有设备简单、图案设计灵活、操作简单、经济等特点[17]。该技术在生物传感器领域，尤其指尖血糖检测中取得商业成功。Li等[18]实验组通过丝网印刷技术开发了一种具有优化三电极配置的多功能电化学平台，检测葡萄糖浓度。Ji等[19]实验组基于智能手机的循环伏安系统，采用石墨烯修饰的丝网印刷电极检测葡萄糖浓度。因此，本文在室温条件合成Co基MOFs(Co-ZIF-67)，采用丝网印刷技术，制备了Co-ZIF-67修饰的商业银-碳电极，研究其对葡萄糖的传感性能。
1. 实验方法
1.1 原材料与试剂
六水硝酸钴(Co(NO3)2·6H2O，99.5%) 、聚乙烯醇(PVA，92%~94%)、聚乙烯吡咯烷酮(PVP，K23-27)、甲醇(CH2OH，99.5%)、3-(N-吗啉)丙磺酸钠(MOPs-Na，C7H14NO4SNa，99.5%)、羟乙基纤维素(HEC)、丙烯酰胺(C3H5NO，99.0%)、抗坏血酸(C6H6O8，99.0%)、半乳糖(C6H12O6，99.0%)、羧甲基纤维素((C6+2yH7+x+2yO2+x+3yNay)n)、柠檬酸(C6H8O7，99.5%)、葡萄糖(C6H12O6，96%)和葡聚糖(DEAE-Dextran，70 kDa)购自上海阿拉丁生化科技股份有限公司。过硫酸铵(H8N2O8S2，98.5%)购自上海麦克林生化科技有限公司。
1.2 材料表征
采用X-射线衍射仪(Smartlab9kw，Rigaku)对样品的物相和晶体结构进行表征。通过X射线光电子能谱(ESCALAB 250Xi，赛默飞)对样品的元素和表面信息进行分析。采用扫描电子显微镜扫描电镜(SEM，SU8100，日立)和透射电子显微镜(TEM，JEM2100，JEOL)对样品进行形貌表征。通过电化学工作站(CH650E，上海辰华仪器有限公司)评估修饰电极对葡萄糖的电化学传感性能。本研究配制了不同浓度葡萄糖(0.1~0.5 mmol/L)的0.1 mol/L氢氧化钠溶液。
1.3 Co-ZIF-67及Co-ZIF-67修饰电极的制备
Co-ZIF-67纳米材料在室温条件下制备而成。合成过程中，12 mmol/L的Co(NO3)2·6H2O完全溶解于100 mL甲醇中，记为溶液 A；48 mmol/L的2-甲基咪唑溶解于
1000 mL甲醇中，记为溶液 B。溶液B迅速地加入到溶液A中，形成混合液C。该混合液C磁力搅拌10 min后，在室温环境下静置24 h，形成沉淀物。采用甲醇清洗沉淀物，并在60℃干燥过夜，得到紫色Co-ZIF-67粉末。把20 mg Co-ZIF-67在1 mL的超纯水中超声30 min，得到溶液D。0.55 g MOPs 钠盐，0.075 g的羟乙基纤维素，1.75 g丙烯酰胺和0.05 g过硫酸铵分别溶解于25 mL的超纯水中，磁力搅拌2 h后形成混合浆料。将1 mL溶液D与9 mL浆料磁性搅拌1 h后，形成 Co-ZIF-67丝网印刷油墨。
将Co-ZIF-67油墨均匀的丝网印刷在商业银-碳电极的工作区域，经烘干(45℃，15 min)、贴亲水膜、裁剪，制备了便携式一次性条形葡萄糖检测电极。该电极包括一个工作电极，一个对电极。工作电极的表面积为3.78 mm×0.252 mm=
0.9526 mm2。每个电极所分析的溶液量为10 μL。亲水膜的作用是形成流道，吸附检测样品。Co-MOF修饰电极的制备过程见图1。![]()
图 1 Co-ZIF-67修饰电极的制备过程Figure 1. Preparation of Co-ZIF-67 modified electrodesMOFs—Metal-origanic frameworks2. 结果与讨论
2.1 Co-ZIF-67物相分析
采用XRD技术研究了Co-ZIF-67的晶体结构。从图2(a)可以看出，在2θ=10.4°、12.7°、14.7°、16.4°、18.0°、22.1°、24.4°、26.5°、29.8°、30.5°和32.5°时，分别对应于ZIF-67的(002)、(112)、(022)、(013)、(222)、(114)、(233)、(134)、(044)、(244)、(235)晶面，这与已报道的ZIF-67样品的XRD结果一致[20-22]。采用X射线光电子能谱(XPS)对Co-ZIF-67的表面信息进行了分析。从图2(b)可以看出，样品包含Co2p、O1s、N1s、C1s、Co3s和Co3p核能级区域。Co2p和 C1s的XPS精细谱分别如图2(c)和图2(d)所示。Co2p精细谱含有两个主峰，其中780.1 eV峰来自Co2p3/2；795.3 eV峰来自Co2p1/2。激振峰分别位于785.5和801.7 eV。除了主峰，C1s精细谱还有两个拟合峰。结合能位于286.2和288.1 eV，分别归属于C—N和C—O。上述结果表明，Co-ZIF-67已经被成功制备。采用SEM和TEM研究了样品的形貌。如图3(a)~3(f)所示，Co-ZIF-67呈现多面形，且尺寸分布相对较窄。
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图 2 Co-ZIF-67的XRD图谱(a)、XPS全谱(b)、Co2p (c)和C1s (d)精细谱Figure 2. XRD pattern (a), XPS spectra (b), Co2p (c) and C1s regions (d) of Co-ZIF-67![]()
图 3 Co-ZIF-67在不同放大倍数的SEM和TEM图像Figure 3. SEM and TEM images of Co-ZIF-67 at different magnifications2.2 Co-ZIF-67的电催化性能
采用循环伏安(CV)技术评估了Co-ZIF-67修饰电极的电化学性能。图4(a)是Co-ZIF-67修饰电极在50 mV/s扫速时对0.3 mmol/L葡萄糖在不同pH值溶液中的响应信号。很明显，当pH=13时，Co-ZIF-67表现出对葡萄糖较大的催化活性。当葡萄糖浓度增加时，Co-ZIF-67修饰电极电流信号也随之增强(图4(b))。然而，信号的区分度不大。图4(c)是Co-ZIF-67修饰电极在不同扫速(10、30、50、70、90、110和130 mV/s)下对葡萄糖信号的变化。随着扫速增大，电流信号明显得到加强。将0.5 V电流强度与扫描速度的算术平方根进行拟合，其线性关系为：I (μA/cm2)=0.14v1/2–0.12 (R2=0.988，R2为决定系数)。这说明Co-ZIF-67修饰电极对应的电化学反应是受扩散控制的[23]。
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图 4 Co-ZIF-67修饰电极在不同pH值(a)、葡萄糖浓度(b)、扫速(c)对葡萄糖的CV测试曲线；(d)扫描速率(v)的算数平方根与电流(I) (0.5 V)之间的线性关系Figure 4. CV curves of Co-ZIF-67 modified electrodes with different pH (a), glucose concentrations (b), and scan rates (c); (d) Corresponding linear relationship between the arithmetic square root of the scanning rate (v) and current (I, 0.5 V)R2—The coefficient of determination, which determinates the linear relationship of the fit curve采用差分脉冲伏安法(Differential pulse voltammetry，DPV)进一步评估了Co-ZIF-67修饰电极的电化学性能。如图5(a)所示，在0~0.5 mmol/L 葡萄糖溶液中观测了Co-ZIF-67修饰电极表面的氧化和还原反应，其对葡萄糖可能的催化机制为：Co-ZIF-67修饰电极对葡萄糖表现出较CV更强的DPV响应信号，这也表明，Co-ZIF-67对葡萄糖确实存在电催化效果[24-27]。此外，溶液中没有葡萄糖时，Co-ZIF-67修饰电极在0.4~0.6 V有一个不明显的氧化还原峰。随着葡萄糖浓度的增加，该修饰电极的响应信号也随之增强，氧化还原峰变得更加明显，这主要是由于高电位下碱性溶液中Co-ZIF-67中Co2+被氧化为Co3+。此时，Co3+因从葡萄糖得电子(变为Co2+)并不断将葡萄糖氧化为葡萄糖酸从而产生电流信号[28-29]。因此，Co-ZIF-67修饰电极具有较好的电催化性能。如图5(b)所示，Co-ZIF-67修饰电极的电流平均值(0.55 V)与葡萄糖浓度呈线性关系，其线性方程为：I (μA/cm2)=−3.730×C(mmol/L) − 5.720 (R2=
0.9639 )。![]()
图 5 (a) Co-ZIF-67修饰电极在不同葡萄糖浓度中的差分脉冲伏安法(DPV)测试曲线；(b)每5支Co-ZIF-67修饰电极在0.55 V电位对不同浓度葡萄糖的平均电流响应信号；(c) Co-ZIF-67修饰电极对不同葡萄糖浓度的安培响应；(d)每5支电极对不同葡萄糖浓度的平均响应电流(取第15 s数值)Figure 5. (a) Differential pulse voltammetry (DPV) curves of Co-ZIF-67 modified electrodes in the presence of glucose; (b) Linear relationship between average DPV current density response and different glucose concentrations of every five electrodes at 0.55 V; (c) Amperometric response of Co-ZIF-67 modified SPEs to different glucose concentration; (d) Corresponding linear curve of average current density of five electrodes in the 15th s to glucose concentrations采用安培响应技术在Co-ZIF-67修饰电极上对葡萄糖的传感性能做了进一步的评估。图5(c)显示随着电解质溶液中葡萄糖浓度的增加，响应电流随之增强。安培响应电流与葡萄糖浓度之间呈线性关系(图5(d))，其方程为：I (μA/cm2)=−1.390×C(mmol/L)−2.630 (R2=
0.9504 )。经过处理，Co-ZIF-67修饰电极对葡萄糖的检测灵敏度为1390 nA·L/(mmol·cm2)，检测限为0.58 μmol/L (S/N=3)，线性范围为0.1~0.5 mmol/L。值得一提的是，与已报道的电极相比，Co-ZIF-67修饰电极的灵敏度具有较大的优势，如表1所示[27, 29-34]。表 1 Co-ZIF-67修饰电极及其他电极的葡萄糖传感性能Table 1. Glucose sensing performance of Co-ZIF-67-modified electrodes and other previously reported electrodesType of electrode Sensitivity/(μA·L·mmol−1·cm−2) Detection limit/(μmol·L−1) Linear range/(mmol·L−1) Ref. Ag NPs/MOF-74(Ni) 1290 4.7 0.01-4 [27] NF/NiCo2O4 NWs@Co3O4 NPs 8163.2 – 0.001-1.7 [29] CuCo-MOF 6861 0.12 – [30] Ni2Co1-BDC/GCE 3925.3 0.29 0.0005 -2.8995 [31] Ni/Co(HHTP)MOF/CC 3250 0.1 0.0003 -2.312[32] MIL-88A@NiFe-PB 1963.2 0.12 0.005-1 [33] Ni3(HHTP)2/CNT 4774 4.1 0.004-3.9 [34] Co-MOFs/SPEs 1.393 0.58 0.1-0.5 This work Notes: CC—Carbon cloth; BDC—1, 4-benzenedicarboxylic acid; GCE—Glassy carbon electrode; HHTP—2, 3, 6, 7, 10, 11-hexahydroxytriphenylene; MIL—Materials from Institute Lavoisier; PB—Prussian blue; CNT—Carbon nanotubes; NF—Nickel foam; NWs—Nanowires; NPs—Nanoparticles; SPEs—Screen-printing electrodes. 2.3 抗干扰性、稳定性和重现性
图6(a)描述了Co-ZIF-67修饰电极抗干扰性能。从图上可以看出，干扰物质抗坏血酸(AA，3 mmol/L)、艾考糊精(INN，0.164 mol/L)、半乳糖(GAL，8 mmol/L)、谷胱甘肽(GSH，30 mmol/L)、麦芽糖(MAL，0.584 mol/L)引起的响应电流变化分别为−3.9%、−14.3%、−19.3%、−14.6%和−8.4%。与干扰物质相比，滴加0.1 mmol/L葡萄糖溶液时电流响应的显著变化表明。因此，Co-ZIF-67修饰电极具有较强的抗干扰能力。随后，通过长时间空气存放观察Co-ZIF-67修饰电极对0.1 mmol/L 葡萄糖的电流响应来评估的其稳定性。如图6(b)所示，Co-ZIF-67修饰电极表现出良好的稳定性。16天后，该电极仍然具有96%的初始响应。重现性是对电极的一个重要衡量标准。如图6(c)所示，Co-ZIF-67修饰电极的相对标准方差(Relative standard deviation，RSD)仅为10%，这说明该电极具有较好的重现性。
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图 6 (a)干扰检查：5支Co-ZIF-67修饰电极 对0.1 mmol/L 葡萄糖(GLU)、0.164 mol/L 艾考糊精(INN)、9 mmol/L 半乳糖(GAL)、30 mmol/L谷胱甘肽(GSH)和0.584 mol/L 麦芽糖(MAL) 的平均安培响应；(b)稳定性：每5支Co-ZIF-67修饰电极在第1 d、4 d、7 d、10 d、13 d和16 d内对0.1 mmol/L 葡萄糖的安培响应信号；(c)重现性：10支Co-ZIP-67修饰电极对0.1 mmol/L 葡萄糖的响应Figure 6. (a) Interference examination: Average amperometric responses of five CuO nanomaterials modified SPEs to 0.1 mmol/L glucose (GLU), 0.164 mol/L alcodextrin (INN), 9 mmol/L galactose (GAL), 30 mmol/L glutathione (GSH) and 0.584 mol/L maltose (MAL); (b) Stability of every 5 Co-ZIF-67 modified electrodes to 0.1 mmol/L glucose on the 1st, 4th, 7th, 10th, 13th and 16th days; (c) Reproducibility of Co-ZIF-67 modified electrodes to 0.1 mmol/L glucose2.4 血清测试
为了研究Co-ZIF-67修饰电极在实际样品中检测葡萄糖的性能，我们进行了加标回收实验(拜安进血糖仪(拜安进血糖试纸(葡萄糖脱氢酶)，拜耳公司))。将血清稀释在NaOH溶液中，血清浓度为0.12 mmol/L。如表2所示，葡萄糖的回收率在93.97%~101.5%，RSD小于6.2%。这也表明Co-ZIF-67修饰电极具有潜在应用。
表 2 Co-ZIF-67修饰的Ag-C电极检测血清样品的葡萄糖含量(n=3)Table 2. Glucose detection in human serum samples using Co-ZIF-67 modified Ag-C electrodes (n=3)Sample Serum glucose/(mmol·L−1) Added glucose/(mmol·L−1) Detected glucose/(mmol·L−1) RSD/% Recovery rate/% Human
serum0.12 0.18 0.29 6.20 93.97 0.28 0.39 4.37 101.5 0.36 0.47 3.90 98.97 Note: RSD—Relative standard deviation. 3. 结 论
(1)基于室温合成的Co-ZIF-67，采用丝网印刷技术批量构建了Co-ZIF-67修饰的商业银-碳电极。
(2) Co-ZIF-67修饰电极表现出优异的葡萄糖电催化性能：0.58 μmol/L的检测极限，1.393 μA·L/(mmol·cm2)的灵敏度，高的抗干扰性，96%的空气稳定性。
(3)研究表明，Co-ZIF-67的低能耗合成及其Co-ZIF-67修饰电极的批量化制备为葡萄糖传感器的发展提供一个可参考的方向。
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图 4 再生砖混骨料混凝土抗压试验破坏形态
RBA—Recycled brick aggregate; RCA—Recycled concrete aggregate
Figure 4. Failure modes of mixed recycled aggregate concrete comperessive test
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图 5 再生砖混骨料混凝土劈裂抗拉强度
Figure 5. Splitting tensile strength of mixed recycled aggregate concrete
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图 6 再生砖混骨料混凝土劈裂抗拉试验破坏形态
Figure 6. Failure modes of mixed recycled aggregate concrete splitting tensile test
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图 8 再生砖混骨料混凝土抗折试验破坏形态
Figure 8. Failure modes of mixed recycled aggregate concrete flexural test
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图 10 再生砖骨料-砂浆界面过渡区(ITZ)的SEM图像
CH—Calcium hydroxide; Aft—Ettringite; C-S-H—Hydrated calcium silicate
Figure 10. SEM images of ITZ between recycled brick aggregate and mortar
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图 11 再生砖混骨料混凝土典型应力-应变曲线
fc—Peak stress; εc—Peak strain
Figure 11. Typical stress-strain curve of mixed recycled concrete
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图 12 再生砖混骨料混凝土轴心受压破坏形态
Figure 12. Failure mode of axial compression of mixed recycled concrete
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图 13 再生砖混骨料混凝土单轴受压应力-应变曲线
σ—Stress; ε—Strain
Figure 13. Stress-strain curves of mixed recycled aggregate concrete under uniaxial compression
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图 14 再生砖混骨料混凝土峰值应力与峰值应变
Figure 14. Peak stress and peak strain of mixed recycled concrete
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图 15 再生砖混骨料混凝土弹性模量及其试验值和计算值之比
Figure 15. Modulus of elasticity and ratio of test value to calculated value of mixed recycled concrete
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图 16 无量纲化和拟合再生砖混骨料混凝土单轴受压本构曲线
Figure 16. Dimensionless and fitting constitutive curves of mixed recycled aggregate concrete under uniaxial compression
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图 17 再生砖混骨料混凝土试验曲线与拟合曲线对比
Figure 17. Comparing test curve and the fitting curve of mixed recycled aggregate concrete
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图 18 再生砖混骨料混凝土各力学性能换算公式
Figure 18. Conversion formula of mechanical properties of mixed recycled aggregate concrete
表 1 砖骨料(RBA)、再生混凝土骨料(RCA)及天然骨料(NA)的物理性能
Table 1 Properties of recycled brick aggregate (RBA), recycled concrete aggregate (RCA) and natural aggregate (NA)
Type Stacking density/(kg·m−3) Apparent density/(kg·m−3) Crush index/% Water absorption/% 24 h 3 d RBA 890 1697 22.4 20.3 21.7 RCA 1450 2693 9.8 3.5 3.6 NA 1550 2780 7.2 1.2 — 
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表 2 再生砖混骨料混凝土配合比
Table 2 Mix proportion of mixed recycled aggregate concrete
Sample w/b Water/
(kg·m−3)Cement/
(kg·m−3)Sand/
(kg·m−3)NA/
(kg·m−3)RCA/
(kg·m−3)RBA/
(kg·m−3)Water reducer/% NC(0.3) 0.3 138 460 570 1150 0 0 1.2 0%RBC(0.3) 138 460 570 0 1120 0 50%RBC(0.3) 138 460 570 0 560 350 100%RBC(0.3) 138 460 570 0 0 700 NC(0.4) 0.4 185 460 570 1150 0 0 0.5 0%RBC(0.4) 185 460 570 570 1120 0 50%RBC(0.4) 185 460 570 0 560 350 100%RBC(0.4) 185 460 570 0 0 700 Notes: NC—Natural aggregate concrete; RBC—Mixed recycled aggregate concrete; w/b—Water cement ratio; The numbers 0%, 50% and 100% represent the volume replacement rate of brick aggregate in recycled aggregate, respectively.
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表 3 再生砖混骨料混凝土轴心受压试验主要试验结果
Table 3 Main test results of mixed recycled concrete axial compression test
Sample Peak stress
fc/MPaPeak strain
εc/10−3Ascending portion 0.4fc Strain of 0.4fc Elastic
modulus/GPaDescending
portion 0.85fcPeak strain
of 0.85fcNC(0.3) 38.60 1.253 15.31 0.491 31.18 32.81 1.321 0%RBC(0.3) 35.48 1.277 14.19 0.507 27.99 30.16 1.385 50%RBC(0.3) 30.89 2.242 12.36 0.894 13.83 26.26 2.352 100%RBC(0.3) 27.72 2.413 11.09 1.041 10.65 23.56 2.518 NC(0.4) 35.63 1.507 14.25 0.483 29.50 30.29 1.647 0%RBC(0.4) 33.80 1.571 13.52 0.631 21.43 28.73 1.662 50%RBC(0.4) 29.61 2.174 11.84 0.884 13.39 25.17 2.264 100%RBC(0.4) 26.35 2.561 10.54 1.137 9.27 22.39 2.679
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表 4 再生砖混骨料混凝土弹性模量计算值与试验值
Table 4 Calculated and experimental values of elastic modulus of mixed recycled concrete
Sample Test value/
GPafcu
/MPaCalculated value/GPa Ratio NC(0.3) 31.18 47.9 34.19 0.912 0%RBC(0.3) 27.99 41.5 32.94 0.850 50%RBC(0.3) 13.83 36.7 31.46 0.439 100%RBC(0.3) 10.65 33.6 30.93 0.344 NC(0.4) 29.50 42.6 33.17 0.889 0%RBC(0.4) 21.43 36.2 31.66 0.677 50%RBC(0.4) 13.39 32.5 30.60 0.437 100%RBC(0.4) 9.27 30.4 29.93 0.311 Note: fcu—Compressive strength.
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表 5 再生砖混骨料混凝土本构参数a和b
Table 5 Constitutive parameters a and b of mixed recycled aggregate concrete
Sample Parameter of a Parameter of b Fitting parameter Variation/% Fitting parameter Variation/% NC 0.361 0.00 31.301 0.00 0％RBC 0.463 28.25 54.505 74.13 50％RBC 0.222 −38.50 60.624 93.68 100％RBC 0.018 −95.01 71.659 128.94
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目的
废弃粘土砖块约占我国建筑垃圾总量的30%~50%，其往往与废弃混凝土混杂在一起难以分离。现有研究表明将废弃混凝土块和废弃黏土砖块一同破碎后作为再生砖和再生混凝土混合再生粗骨料使用是可行的，但是再生砖混骨料混凝土的材料性能及其设计方法目前尚未统一，这严重阻碍了此类再生混凝土的工程应用。本文研究了再生砖混骨料混凝土的基本力学性能与单轴应力-应变关系，并通过对过镇海本构模型进行修正，提出了一个可用于对此类再生混凝土进行结构分析与设计的本构模型。
方法以不同水胶比(0.3和0.4)、不同再生骨料取代率(体积法取代0%、50%、100%)为控制参数配置混凝土。在配置时先将细骨料和水泥在搅拌机中混合搅拌2min。然后加入粗骨料，搅拌2min后再加入水和少许减水剂，搅拌1min。测试搅拌均匀的混凝土拌合物的坍落度，若不满足则加入少许减水剂继续搅拌，重复至坍落度达到试验要求。将调制好的混凝土制作为18个立方体(100mm×100mm×100mm)和18个棱柱(100mm×100mm×400mm)用以测试混凝土试块的抗压强度，劈裂抗拉强度，抗折强度以及进行单轴压缩应力-应变全曲线试验。试块在室内养护1d后拆模，移入养护箱中继续养护，养护条件设定为标准养护条件(T=(20±2)℃，RH≥95%)。以试验数据为基础提出再生砖混骨料混凝土力学性能换算公式，并通过修正过镇海本构模型，建立再生砖混骨料混凝土单轴受压本构模型。
结果与天然骨料混凝土相比，不同配合比再生混凝土力学性能有不同程度的下降，其中随着再生砖骨料含量的增加，其力学性能下降较为显著，与对照组相比，全再生砖骨料混凝土的抗压、劈裂抗拉和抗折强度分别下降了29.9%、28.5%和15.56%。掺砖骨料混凝土的峰值应变明显增加，且弹性模量显著降低。观察各试块的破坏形态发现，几乎所有砖骨料呈断裂形态，黏结砖骨料的水泥胶界面并未裂开。对于砖混再生骨料混凝土，黏结再生混凝土骨料的水泥胶界面和砖骨料同时开裂，但再生混凝土骨料大部分并未开裂。再生砖混骨料混凝土的劈裂抗拉强度、抗折强度、峰值应力、峰值应变与其抗压强度均表现出较强的相关性.
结论再生砖骨料的高吸水性与高孔隙率造成的薄弱区域对混凝土力学性能有重要影响，再生砖混骨料混凝土脆性指数明显高于普通混凝土。砖骨料与再生混凝土骨料的老砂浆-新砂浆界面过渡区强度低是导致试块抗压强度降低的主要原因。砖骨料替代率达到100%时抗压强度下降高达29.9%，但是仍能保证一定的力学性能储备。对试验结果进行了拟合，得到了再生砖混骨料混凝土力学性能换算关系。建立了再生砖混骨料混凝土单轴受压本构模型，为此类再生混凝土的理论模型研究提供参考。
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废弃粘土砖块约占我国建筑垃圾总量的30%~50%，其往往与废弃混凝土混杂在一起难以分离。现有研究表明将废弃混凝土块和废弃黏土砖块一同破碎后作为再生砖和再生混凝土混合再生粗骨料使用是可行的，但是再生砖混骨料混凝土的材料性能及其设计方法目前尚未统一，这严重阻碍了此类再生混凝土的工程应用。
本文配制了0.3和0.4两种水胶比情况下的对照混凝土(只含天然粗骨料)和不同取代率情况下的再生砖混骨料混凝土(100%再生混凝土骨料，100%再生砖骨料和50%再生混凝土骨料+50%再生砖骨料)。研究了不同配合比试块的立方体抗压、劈裂抗拉和抗折强度，以及应力-应变关系等内容。根据试验数据建立了再生砖混骨料混凝土单轴受压本构模型与再生砖混骨料混凝土力学性能换算公式，为此类再生混凝土材料的设计与应用提供参考。
砖混再生混凝基本土力学性能
再生砖混骨料混凝土各力学性能换算公式
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