西安建筑科技大学学报(自然科学版)

磷酸镁水泥(Magnesium Phosphate Cement,简称MPC)是一种早期强度高、凝结硬化快、干缩变形小、粘结能力强的胶凝材料,可用于高架桥、机场跑道和市政主干道的快速修补等方面.然而,MPC存在韧性差、抗裂性能差的缺点,严重限制了MPC在实际修复工程中的应用.经前期研究发现,在MPC中掺入椰子纤维(Coconut Fiber,简称CF)能有效提高其抗裂性能,然而,CF对MPC力学性能的影响规律和作用机理尚未清晰,因此,需要对椰子纤维加固磷酸镁水泥(Coir Fiber Reinforced Magnesium Phosphate Cement,简称CF-MPC)这一新型生态复合材料进行系列研究.本文主要研究不同体积掺量(1%、2%、3%、4%)CF在不同养护龄期(7 d、28 d)下对MPC静态受压性能的影响.首先,通过静态压缩试验分析了椰子纤维掺量和养护龄期对CF-MPC试件的破坏形态、抗压强度、应力-应变曲线和能量吸收性能的影响规律; 其次,通过扫描电子显微镜(Scanning Electron Microscope,简称SEM)和X射线衍射(X-ray diffraction,简称XRD)分析,测试了不同CF掺量在不同养护龄期下,CF-MPC微观结构和水化组分的变化规律,从本质上探明了CF对上述宏观力学性能的影响机理.结果表明:在7 d、28 d两个养护龄期下,CF掺量对MPC静态抗压性能的影响相似.当CF掺量高于1%时,MPC脆性明显降低,且CF掺量为2%时,试件破坏形态由脆性变为一定的延性; CF-MPC试件抗压强度、弹性模量和割线模量随椰子纤维掺量的增加而略有降低,但随龄期的增长而增大; 能量吸收随着CF掺量的增加及龄期的增长均呈增大趋势,且当CF掺量为4%、龄期为28 d时能量吸收达到最大; 微观分析中,随着CF掺量的增长,主要水化产物六水磷酸钾镁(MgKPO4·6H2O,简称MKP)逐渐减少,而随着龄期的增长MKP逐渐增加.

Magnesium phosphate cement(MPC)is a kind of cementing material with high early strength, quick setting and hardening, small drying and shrinkage deformation, and strong bonding ability, which can be used for rapid repair of viaducts, airport runways, and municipal main roads. However, some of its defects, e.g., the low toughness and poor crack resistance, become obstacle to further applications. Previous study has shown that the anti-cracking performance of MPC can be significantly improved by adding appropriate amount of coconut fiber(CF). However, the effect law and action mechanism of CF on the mechanical behavior of the MPC are not yet clear. Thus, it is necessary to carry out a systematic study on coconut fibre reinforced magnesium phosphate cement(CF-MPC), which is a new ecological composite material. In this paper, the effects of different CF volume dosages(1%, 2%, 3%, 4%)at different curing ages(7 d, 28 d)on the static compression performance of MPC has been studied. Firstly, a uniaxial static compression test was conducted to analyze the influence of CF dosage and curing age on the failure mode, compressive strength, stress-strain curve, and energy absorption performance of CF-MPC. Secondly, the microstructure and hydration components of CF-MPC with different CF dosage at different curing ages were tested and analyzed by means of scanning electron microscope(SEM)and X-ray diffraction(XRD), and the influence mechanism of CF on the macroscopic mechanical properties of MPC was revealed. The results showed that the effects of CF dosage on MPC static compression performance at the curing ages of 7 d and 28 d were similar. When CF dosage was higher than 1%, the brittleness of MPC was significantly reduced, and when CF dosage was 2%, the failure mode of the specimen changed from brittleness to a certain ductility. The compressive strength, elastic modulus and secant modulus of CF-MPC specimens decreased slightly with the increase of coconut fiber content, but increased with the increase of age. Energy absorption increased with the increase of CF dosage and curing age, and reached the maximum when CF dosage was 4% and curing age was 28 d. In microscopic analysis, the main hydration product, potassium magnesium phosphate hexahydrate(MKP), gradually decreased with the increase of CF dosage, while MKP gradually increased with the growth of curing age.

引言
1 试验内容及方案设置
2 试件结果与分析
3 结论

表1 试件配合比
Tab.1 Specimen mix ratio

图1 试件及压缩试验仪器<br/>Fig.1 Specimens and compression test instruments

图1 试件及压缩试验仪器
Fig.1 Specimens and compression test instruments

表2 MPC基本配合比
Tab.2 Basic mix ratio

表3 氧化镁粉末的化学成分<br/>Tab.3 Chemical composition of magnesium oxide powder

表3 氧化镁粉末的化学成分
Tab.3 Chemical composition of magnesium oxide powder

表4 粉煤灰的化学成分<br/>Tab.4 Chemical composition of fly ash

表4 粉煤灰的化学成分
Tab.4 Chemical composition of fly ash

表5 椰子纤维的物理参数和力学性能<br/>Tab.5 Physical parameters and mechanical properties of coconut fiber

表5 椰子纤维的物理参数和力学性能
Tab.5 Physical parameters and mechanical properties of coconut fiber

图2 原材料前期处理<br/>Fig.2 Preliminary treatment of raw materials

图2 原材料前期处理
Fig.2 Preliminary treatment of raw materials

图3 试件制备流程<br/>Fig.3 Specimens preparation process

图3 试件制备流程
Fig.3 Specimens preparation process

图4 试件破坏模式<br/>Fig.4 Failure mode of specimen

图4 试件破坏模式
Fig.4 Failure mode of specimen

图5 各组试件破坏形态<br/>Fig.5 Failure pattern of each sample

图5 各组试件破坏形态
Fig.5 Failure pattern of each sample

图6 不同龄期、CF掺量下MPC的抗压强度和相对递减率<br/>Fig.6 Compressive strength and relative delative rate of MPC at different curing ages and CF dosages

图6 不同龄期、CF掺量下MPC的抗压强度和相对递减率
Fig.6 Compressive strength and relative delative rate of MPC at different curing ages and CF dosages

图7 MPC微观形貌及组成<br/>Fig.7 Microstructure and composition of MPC

图7 MPC微观形貌及组成
Fig.7 Microstructure and composition of MPC

图8 不同龄期、CF掺量下MKP和氧化镁XRD最大峰值<br/>Fig.8 XRD maximum intensity of MKP and magnesium oxide at different ages and CF dosages

图8 不同龄期、CF掺量下MKP和氧化镁XRD最大峰值
Fig.8 XRD maximum intensity of MKP and magnesium oxide at different ages and CF dosages

图9 MPC与CF-MPC的SEM图<br/>Fig.9 SEM diagram of MPC and CF-MPC

图9 MPC与CF-MPC的SEM图
Fig.9 SEM diagram of MPC and CF-MPC

图10 应力-应变曲线构型<br/>Fig.10 Stress-strain curve configuration

图10 应力-应变曲线构型
Fig.10 Stress-strain curve configuration

图11 不同龄期、CF掺量下应力-应变曲线<br/>Fig.11 Stress-strain curves at different cuings ages and CF dosages

图11 不同龄期、CF掺量下应力-应变曲线
Fig.11 Stress-strain curves at different cuings ages and CF dosages

图12 不同龄期、CF掺量下MPC的切线模量和割线模量<br/>Fig.12 Tangent modulus and secant modulus of MPC at dfferent curing ages and CF dosages

图12 不同龄期、CF掺量下MPC的切线模量和割线模量
Fig.12 Tangent modulus and secant modulus of MPC at dfferent curing ages and CF dosages

图13 “桥联效应”及其失效形式<br/>Fig.13 “Bridge effect” and its failure forms

图13 “桥联效应”及其失效形式
Fig.13 “Bridge effect” and its failure forms

图14 不同龄期、CF掺量下MPC的能量吸收和相对增长率<br/>Fig.14 Energy absorption and relative growth rate of MPC at different curing ages and CF dosages

图14 不同龄期、CF掺量下MPC的能量吸收和相对增长率
Fig.14 Energy absorption and relative growth rate of MPC at different curing ages and CF dosages

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备注

引言

1 试验内容及方案设置

2 试件结果与分析

3 结论

期刊信息