Enhancing mechanical behavior of micaceous soil with jute fibers and lime additives

Micaceous soils are common in many tropical countries and regions, and in some locations with moderate climate. The soils are spongy and unstable when loaded and are not considered suitable as construction material in earth structures. To resolve the issue, this work examined performance of micaceous soil reinforced with a combination of jute fibers, hydrated lime or slag-lime. A total of 28 sample sets were prepared at various dosages. Unconfined compression tests were conducted on the samples cured for 7 d and 28 d, respectively. The test results suggested that the unconfined compressive strength(UCS) and material stiffness were increased with the inclusion of up to 1% fiber and decreased if additional fibers were used. The ductility was improved consistently with up to 1.5% fiber content. The inclusions of fibers combined with hydrated lime or slag-lime further enhanced strength and stiffness of micaceous soil, and the improvement depended on the dosages used. For the dosages examined, jute fibers outweighed lime and slag in gaining ductility, and the optimal fiber content was 1% where strength and ductility were considered.     

短切玄武岩纤维加筋膨胀土的试验研究

玄武岩纤维是一种新型的纯天然绿色纤维。本文将分散的玄武岩纤维丝掺入膨胀土中,研究玄武岩纤维加筋膨胀土的强度与变形特性。试验中,按纤维含量与干土质量比分别为0.0%,0.2%,0.4%和0.6%的比例配制试样。通过室内试验,研究表明:纤维的增加可抑制膨胀土的胀缩性;增加纤维含量,土的无侧限抗压强度和抗剪强度均有所增大,当纤维含量超过最优加筋量0.4%时,加筋膨胀土的无侧限抗压强度和抗剪强度反而会降低。因此,通过掺加玄武岩纤维增强材料,可以获得强度和韧性更高的纤维膨胀土,为膨胀土性质的改良提供一种可借鉴的方法。     

Effect of natural and synthetic fibers reinforcement on California bearing ratio and tensile strength of clay

Use of environmentally friendly approaches with the purpose of strengthening soil layers along with finding correlations between the mechanical characteristics of fiber-reinforced soils such as indirect tensile strength(ITS) and California bearing ratio(CBR) and as well as the evaluation of shear strength parameters obtained from the triaxial test would be very effective at geotechnical construction sites.This research was aimed at investigating the influence of natural fibers as sustainable ones including basalt(BS) and bagasse(BG) as well as synthetic polyester(PET) fibers on the strength behavior of clayey soil.To this end,the effects of various fiber contents(0.5%,1% and 2%) and lengths(2.5 mm,5 mm and 7.5 mm)were experimentally evaluated.By conducting ITS and CBR tests,it was found that increasing fiber content and length had a significant influence on CBR and ITS values.Moreover,2% of 7.5 mm-long fibers led to the largest values of CBR and ITS.The CBR values of soil reinforced with PET,BS,and BG fibers were determined as 19.17%,15.43% and 13.16%,respectively.The ITS values of specimens reinforced with PET,BS,and BG fibers were reported as 48.57 kPa,60.7 kPa and 47.48 kPa,respectively.The results of the triaxial compression test revealed that with the addition of BS fibers,the internal friction angle increased by about 100%,and with the addition of PET fibers,the cohesion increased by about 70%.Moreover,scanning electron microscope(SEM) analysis was employed to confirm the findings.The relationship between CBR and ITS values,obtained via statistical analysis and used for the optimum design of road pavement layers,demonstrated that these parameters had high correlation coefficients.The outcomes of multiple linear regression and sensitivity analysis also confirmed that the fiber content had a greater effect on CBR and ITS values than fiber length.     

Application of alkali-activated palm oil fuel ash reinforced with glass fibers in soil stabilization

The feasibility of using palm oil fuel ash (POFA) as a precursor for alkali activation reactions, in combination with glass fibers as a discrete reinforcement, has been investigated. The experimental work was focused on the shear strength (using unconfined compression tests) and the tensile strength (using indirect tensile tests and flexural tests). According to the results, it was found that the peak stress increased and the post-peak behavior was modified from a brittle to a more ductile response depending on the amount of fiber reinforcement in the alkali-activated mixtures. An analysis of the microstructures revealed that the most significant factor contributing to the enhanced behavior of the reinforced mixtures was the interaction between the geo-polymeric matrix and the fiber surface. The present work brings new insights to the soil stabilization industry by providing an effective method for enhancing the properties of soil treated by the alkali activation of POFA (a low-value agro-waste by-product) through the inclusion of glass fibers. This brings advantages over the traditional calcium-based binders (i.e., lime and cement) as their production involves the emission of carbon dioxide, one of the factors significantly contributing to global warming.     

钢筋超高性能混合纤维混凝土梁力学性能试验研究

超高性能纤维混凝土具有高强度（抗压、抗拉）、高延性和高耐久性的优势,但其抗拉强度仍远低于抗压强度。将端钩型和哑铃型钢纤维按不同比例混合,采取自密实成型和常温标准养护方法,试验研究了配置440MPa纵向钢筋的超高性能纤维混凝土梁。通过12根梁的静载试验,研究了钢纤维体积率为2.0%和2.5%时,不同纤维混合比例的钢筋超高性能纤维混凝土梁的力学性能。试验结果表明：加入钢纤维后梁的极限荷载和延性显著提高;在纤维体积率2.0%时,钢筋超高性能纤维混凝土梁比配筋相同的钢筋混凝土梁承载力提高20%~41%,延性系数提高3.9~6.7倍。钢筋端钩纤维混凝土梁的承载力和延性较钢筋混凝土梁分别提高39%和5.1倍,钢筋哑铃纤维混凝土梁的承载力和延性分别提高20%和3.9倍;钢筋混合纤维混凝土梁的承载力介于钢筋端钩和钢筋哑铃纤维混凝土梁之间。参照现行规范提出了钢筋超高性能纤维混凝土梁正截面极限弯矩的计算方法,计算结果与试验结果吻合较好。图11表6参17     

钢管混凝土边框钢纤维混凝土中高剪力墙受弯承载力计算方法

为改善中高剪力墙的抗震性能,提出钢管混凝土边框钢纤维混凝土剪力墙。通过8个剪跨比为1.5的钢管混凝土边框钢纤维混凝土中高剪力墙和1个剪跨比为1.5的钢管混凝土边框混凝土中高剪力墙的低周反复加载试验,研究钢管混凝土边框钢纤维混凝土中高剪力墙的受力机理及破坏模式,分析钢纤维体积率、钢纤维掺加高度、混凝土强度和轴压比对其抗震性能的影响。结果表明：钢管混凝土边框钢纤维混凝土中高剪力墙的破坏模式为弯曲破坏;墙体裂缝主要为典型的弯剪裂缝,钢纤维可有效限制剪力墙裂缝宽度,改善裂缝形态;随着钢纤维体积率和钢纤维掺加高度的增大,剪力墙受弯承载力、延性和耗能能力明显提高;其他参数相同的条件下,钢纤维体积率为0.5%、1.0%和1.5%剪力墙受弯承载力较未掺钢纤维剪力墙的分别提高了8.8%、14.2%和21.8%;随着混凝土强度和轴压比的提高,剪力墙受弯承载力和耗能能力明显提高,但延性降低;其他参数相同的条件下,钢纤维混凝土强度等级为C60、C80剪力墙的受弯承载力较C40剪力墙的分别提高了21.9%和39.7%;轴压比为0.2剪力墙的受弯承载力较轴压比0.1剪力墙的提高了13.5%。基于剪力墙受弯破坏特点,明确钢管和钢纤维对剪力墙受弯承载力的贡献,建立钢管混凝土边框钢纤维混凝土中高剪力墙受弯承载力计算方法,计算值与试验值偏差基本控制在10％以内,吻合较好。     

钢纤维增强地聚物再生混凝土单轴受压全曲线试验

为增强再生混凝土的抗压强度及延性,并进一步减少水泥制备造成的碳排放,采用粉煤灰/矿渣基地聚物100％取代再生混凝土中的普通硅酸盐水泥,并掺入钢纤维制备出钢纤维增强地聚物再生混凝土(SFGRC)。为研究其抗压性能,配制得到再生粗骨料取代率分别为0%、30%、50%、70%和100%,及钢纤维体积掺量分别为0%、0.5%、1.0%和1.5%的14组钢纤维增强地聚物再生混凝土试件,并进行单轴受压全曲线试验。结果表明：随着钢纤维的掺入,SFGRC的破坏模式由脆性向延性转变;立方体抗压强度、峰值应力对应应变、受压韧性及延性随钢纤维掺量的增加而增加;立方体抗压强度、弹性模量及受压韧性随再生粗骨料取代率的增加而降低,但峰值应力对应应变增加。引入钢纤维体积掺量和再生粗骨料取代率,对Carreira-Chu混凝土单轴受压本构模型的下降段进行修正,提出了适用于SFGRC的单轴受压本构模型,其计算结果与相应试验结果均吻合良好。     

锈蚀后钢纤维和钢纤维混凝土的力学性能

通过对剪切型、铣削型、切断型3种钢纤维和钢纤维混凝土的快速锈蚀试验,研究了锈蚀前后钢纤维的外观、弯折性能和抗拉强度的变化,以及钢纤维混凝土经过不同锈蚀时间后的抗压强度和抗拉强度的变化规律.结果表明:随锈蚀时间的增加,钢纤维的锈蚀程度逐渐增大,弯折性能和抗拉强度逐渐降低,钢纤维混凝土的抗压强度和抗拉强度随之减小.但是抗压强度和抗拉强度的变化规律有所不同,当锈蚀时间较短时,抗压强度变化不明显,在锈蚀时间超过60d以后,抗压强度显著降低.而抗拉强度随锈蚀时间的增加逐渐下降.锈蚀时间相同时,抗拉强度的降低幅度比抗压强度的降低幅度小.切断型钢纤维的抗锈蚀能力相对较好,剪切型和铣削型钢纤维的抗锈蚀能力相对较差.     

Experiments on stress-strain curve of steel fiber reinforced geopolymer recycled concrete under uniaxial compression

为增强再生混凝土的抗压强度及延性，并进一步减少水泥制备造成的碳排放，采用粉煤灰/矿渣基地聚物100％取代再生混凝土中的普通硅酸盐水泥，并掺入钢纤维制备出钢纤维增强地聚物再生混凝土(SFGRC)。为研究其抗压性能，配制得到再生粗骨料取代率分别为0%、30%、50%、70%和100%，及钢纤维体积掺量分别为0%、0.5%、1.0%和1.5%的14组钢纤维增强地聚物再生混凝土试件，并进行单轴受压全曲线试验。结果表明：随着钢纤维的掺入，SFGRC的破坏模式由脆性向延性转变；立方体抗压强度、峰值应力对应应变、受压韧性及延性随钢纤维掺量的增加而增加；立方体抗压强度、弹性模量及受压韧性随再生粗骨料取代率的增加而降低，但峰值应力对应应变增加。引入钢纤维体积掺量和再生粗骨料取代率，对Carreira-Chu混凝土单轴受压本构模型的下降段进行修正，提出了适用于SFGRC的单轴受压本构模型，其计算结果与相应试验结果均吻合良好。     

Effect of polypropylene fiber and nano-zeolite on stabilized soft soil under wet-dry cycles

Nano-zeolite was used in the present study as a substitute for a part of lime and then inclusion polypropylene fiber in stabilized soil matrix to develop the soil stabilization method with lime and to improve the efficiency of this technique. In so doing, specimens of soft soil with 5, 10 and 15% of modifier L (lime), LZ (lime-nano-zeolite) and LZF (lime-nano-zeolite-fiber) were prepared, and were subjected to 1–7 wet-dry cycles. Then, microstructure and macrostructure tests were performed on the specimens. The results of the analyses, indicated that the optimal replacement of lime with nano-zeolite would be 40%, and the optimal amount of polypropylene fibers inclusion would be 1% in the stabilized soil matrix. Major reduction in lime consumption would yield a 40% increase in compressive strength and a 21% improvement in durability. The results also showed that the specimen containing 15%LZF would have excellent durability against environmental conditions and very good performance in terms of unconfined compressive strength (UCS), tensile strength and weight loss. Before and after applying 7 wet-dry cycles, the UCS increased by 39% and 16%, respectively. The results of this study indicate that LZF modifier is a suitable option for lime-based stabilization in areas under wet-dry cycles.     

棕榈纤维加筋土强度特性试验研究

通过无侧限抗压与直接剪切试验,研究了不同干密度与加筋率对棕榈纤维加筋土强度特性的影响。试验过程中,设置干密度为1.55 g/cm~3、1.6 g/cm~3、1.65 g/cm~3,加筋率为0、0.2%、0.4%、0.6%,在最优含水率下进行正交试验,并对其加固机理进行分析。结果表明:棕榈纤维可有效提高试样的无侧限抗压强度和抗剪强度。在含水率和干密度一定时,加筋黏土的抗压强度与抗剪强度随加筋率增大而增大;当加筋率超过最优加筋率0.4%时,试样的无侧限抗压强度反而随纤维含量的增加而降低。棕榈纤维与土颗粒通过摩擦力与黏聚力结合,在适宜加筋率下,纤维相互交织形成空间网状结构,增加了试样强度。随着加筋率持续增大,纤维在试样内部交织成团,纤维与土颗粒有效接触点降低,破坏了试样完整性,削弱了加筋效果。研究结果为棕榈纤维加固土体的理论研究与工程实践提供参考依据,以期减少土岩边坡滑坡、泥石流等地质灾害的发生。     

聚丙烯纤维混凝土力学性能试验研究

试验研究了聚丙烯纤维混凝土的抗压强度、抗剪强度、抗冲磨强度及弯曲性能，并与钢纤维混凝土进行了对比。结果表明：在混凝土基体不变情况下，低掺量聚丙烯纤维(掺量为0．91kg／m^3)略微降低混凝土的抗压强度和抗剪强度，少许提高混凝土的抗弯强度，显著提高混凝土的弯曲韧性和断裂能，从而起到阻裂和增韧作用，而对混凝土的抗冲磨性能几乎没有改善。另外．网状聚丙烯纤维对混凝土抗弯强度和韧性的改善优于聚丙烯单丝纤维，但它们较钢纤维的增强增韧效果还有一定差距。     

纤维加筋非饱和黏性土的剪切强度特性

纤维加筋是近些年发展起来的一种土质改良技术,系统掌握纤维加筋土的力学性质对评价纤维加筋土工程的稳定性和进一步推广该技术在工程中的应用具有重要意义。为了了解纤维加筋的剪切强度特性,以非饱和黏性土为研究对象,以聚丙烯纤维为加筋材料,在控制含水率和干密度条件下开展了一系列直剪试验。借助扫描电镜,从微观的角度探讨了纤维的增强机理,并对相关宏观力学性质进行了分析。结果表明：纤维加筋能有效提高土体的抗剪强度,且抗剪强度随纤维掺量的增加而增加;相对于内摩擦角,纤维对黏聚力的增强效果要明显得多;纤维加筋土的抗剪强度随含水率的增加而减小,随干密度的增加而增加;总体上,低含水率和高密实度条件有利于发挥纤维的拉筋效果,提高纤维对强度的贡献。此外,纤维加筋在提高土体峰值剪切强度的同时,还能增加土体破坏时对应的应变及破坏后的残余强度,改善土体的破坏韧性。由扫描电镜分析可知,单根纤维一维拉筋作用和纤维网三维拉筋作用是纤维加筋土的主要增强机理,增强效果则取决于纤维-土界面力大小;剪切面上的纤维在剪切过程中呈现拔出和拉断两种失效模式。     

纳米二氧化硅对纤维固化土力学性质的影响

为了提高聚乙烯醇纤维-石灰改良土的抗冻性与水稳定性,在改良土中加入纳米SiO2,通过试验研究纳米SiO2对聚乙烯醇纤维-石灰改良土强度以及抗冻性与水稳定性的影响。试验结果表明,纳米SiO2可以有效的提高纤维固化土的抗压强度,当石灰掺量为8%,纳米SiO2掺量为1.3%时,土体的抗压强度达到峰值;与单独掺加石灰和单独掺加纳米SiO2的土体相比,同时掺加石灰和纳米SiO2可以使土体的抗冻性与水稳定性得到显著增强。     

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement (CSA), ordinary Portland cement (OPC), and calcium sulfate (CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength (UCS), splitting tensile strength (STS), and volume change of fiber-added expansive mixtures were determined at different time periods (i.e. the strengths on the 28th day, and the volume changes on the 1st, 7th, 14th, 21st, and 28th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to 50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and 16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.     

钢管混凝土边框钢纤维混凝土剪力墙受剪承载力计算

通过5个钢管混凝土边框钢纤维混凝土剪力墙和1个钢管混凝土边框混凝土剪力墙的低周反复加载试验,研究钢管混凝土边框钢纤维混凝土剪力墙的受力机理及破坏模式,分析钢纤维体积率和混凝土强度对其抗震性能的影响。结果表明：钢管混凝土边框钢纤维混凝土剪力墙的破坏模式为剪切破坏;墙体裂缝主要为典型的斜裂缝,钢纤维可有效限制剪力墙裂缝宽度,改善裂缝形态;随着钢纤维体积率的增大,剪力墙受剪承载力、延性和耗能能力明显提高;其他影响因素相同的条件下,钢纤维体积率为0.5%、1.0%和1.5%的剪力墙受剪承载力较未掺钢纤维剪力墙的分别提高了4.4%、12.7%和18.6%;随着混凝土强度的提高,剪力墙受剪承载力和耗能能力明显提高,但延性降低;其他影响因素相同的条件下,钢纤维混凝土强度等级为CF60、CF80剪力墙的受剪承载力较CF40剪力墙的分别提高了24%和37%。结合对文中及国内外相关文献试验数据的综合分析,提出了考虑钢纤维体积率和混凝土强度等影响的钢管混凝土边框钢纤维混凝土剪力墙受剪承载力计算方法,与试验结果吻合较好。     

Shear strength behavior of clayey soil reinforced with polypropylene fibers under drained and undrained conditions

The fundamental mechanisms controlling shear strength and deformability behavior of clay-fiber mixtures have still not been well established, nor the constraints that may affect their performance of shearing under different drainage conditions. This study aims to understand the behavior of a clay soil mixed with polypropylene fibers using results from drained and undrained triaxial compression tests, and to provide necessary calibration data for a shear strength prediction model. In drained tests, shear strength increased with fiber inclusion for a given mean effective stress, represented by an increase in apparent cohesion. In the undrained tests, the shear strength was not affected by pore water pressure generation. Results from the drained and undrained tests indicate that the fiber content had a greater influence on the apparent cohesion than on the friction angle. Drainage affected the improvement in the peak shear strength of fiber-reinforced soils, with superior improvement in the drained tests. As the percent improvement in shear strength decreased with increasing effective confining stresses for both tests, the difference in behavior in the drained and undrained tests was attributed to the strain at failure, with failure occurring at large strains in the drained tests but at smaller strains in the undrained tests.     

Shear strength and failure mechanism of needle-punched geosynthetic clay liner

The internal shear strength of a geosynthetic clay liner (GCL) within composite liner systems is crucial for the stability of landfills and should be carefully considered in the design. To explore the shear strength and failure mechanism of the extensively used needle-punched GCL, a series of displacement-controlled direct shear tests with five normal stress levels (250–1000 kPa) and eight displacement rates (1–200 mm/min) were conducted. The shear stress to horizontal displacement relationships exhibit well-defined peak shear strengths and significant post-peak strength reductions. The monitoring results of the thickness change indicate that the degree of volumetric contraction is related to the reorientation of fibers and dissipation of pore water pressure. Furthermore, the peak and residual shear strengths both depend on the displacement rate because of the rate-dependent tensile stiffness of needle-punched fibers and shear strength of the soil/geosynthetic interface. Through additional tests and lateral comparison, it was discovered that the shear behavior of sodium bentonite, degree of hydration, and pore water pressures all affect the shear mechanisms of the NP GCL. In particular, the failure mode transfers from fiber pullout to fiber rupture with the increase in water content as the hydrated bentonite particles facilitate the stretching of needle-punched fibers.     

基于单根纤维拉拔试验的波形纤维加筋土界面强度研究

纤维/土界面间的力学作用特性是决定纤维加筋土工程性质的关键因素。为了改善纤维/土界面作用力,开发了一种新型的波形纤维作为加筋材料,并自主设计了一套拉拔试验装置,对单根纤维加筋土开展了多组拉拔试验,定量获得了波形纤维加筋土的拉拔特性及界面剪切强度,通过与传统直线形纤维对比,分析了波形纤维/土界面的力学作用机理,并从理论上探讨了波形纤维的最大临界加筋长度。结果表明：提出的单根纤维拉拔试验方法及设计的试验装置为研究纤维/土界面力学作用提供了有效的途径,试验结果具有较好的可重复性;直线形纤维的拉拔曲线呈典型的单峰特征,拉力达到峰值后迅速减小到残余值并逐渐趋于稳定,而波形纤维的拉拔曲线呈显著的多峰特征,曲线波长与纤维的波长基本一致;通过对比,波形纤维/土界面剪切强度明显高于直线形纤维,强度值提高了178%,极大改善了纤维的加筋效果,此外,波形纤维拉拔曲线各峰值对应的界面剪切强度及残余剪切强度随拉拔位移呈指数递减趋势;利用测得的纤维/土界面剪切强度,结合纤维自身的抗拉强度和一些假设条件,能确定纤维的最大临界加筋长度,对实际工程设计有一定参考意义。     

A comparison of the performances of polypropylene and rubber fibers in completely decomposed granite

This fundamental study investigates how two very different types of fibers, very elongated polypropylene fibers with high tensile resistance, and larger rubber fibers with a smaller aspect ratio and low shear and Young's moduli affect the compression and shearing of a soil. The same host soil was used for both types of fibers, a well-graded decomposed granite. As well as providing a realistic base for the study with its well graded nature, the decomposed granite's tendency to contract upon shearing is used to highlight the underlying mechanisms causing any difference in behavior. The soil mixtures were prepared at an optimal fiber content for each kind. The general patterns of behavior of the reinforced soils, such as the stress-dilatancy behavior, and the normal compression and critical state lines, are compared. It is found that the specimens with rubber fibers are initially much less stiff than those with polypropylene fibers, so that they require larger deformations to reach failure. At failure, they can provide as much extra strength as polypropylene fibers if the rubber fiber-soil mixture has been consolidated to a low confining stress, although very much larger quantities are needed, even to the point of being unrealistic for engineering applications. At high confining pressures, the rubber fibers, which have become slack during compression, tend to lose in efficiency. The soil reinforced with polypropylene fibers develops consistently higher strength, but the compressive nature of the base soil has the effect of hindering their full mobilization as would be seen in a dilative soil.