矿渣胶凝材料固化软土的力学性状及机制

利用矿渣胶凝材料固化软土,既可利用工业废渣,又能减少水泥的用量。以矿渣胶凝材料固化黏土、砂土二种软土。发现矿渣胶凝材料加固软土的效果远好于水泥、石灰,其9 %掺量的固化土28 d的无侧限强度达到2.0 MPa以上,普遍高于15 %掺量的水泥固化土,且其28 d固化土的软化系数普遍高于90 %以上,固化黏土后CBR值远高于同掺量的石灰固化土。X衍射结构分析表明,矿渣胶凝材料水化时产生的高强难溶的矿物晶体是其固化软土效果好的主要原因。因此,矿渣胶凝材料是一种性能优异的软土加固材料。     

Mechanical properties of lime-treated clay reinforced with different types of randomly distributed fibers

In this paper, a comparative experimental study was carried out to evaluate the effect of inclusion of different fiber types on strength of lime-stabilized clay. In this scope, a series of unconfined compressive strength tests were carried out on specimens including basalt and polypropylene fiber compacted under Standard Proctor effort (i.e., 35% by weight of soil). The effects of curing period (1, 7, 28, and 90 days), fiber type (basalt and polypropylene), fiber content (0, 0.25, 0.5, 0.75, 1%), fiber length (6, 12, and 19 mm), and lime content (0 and 9%) on strength properties were investigated. The results revealed that both basalt and polypropylene fibers increased the strength without inclusion of lime. For specimens including lime, strength of polypropylene fiber-reinforced specimens was remarkably higher than that reinforced with basalt fiber for lime-stabilized clay. However, greatest strength improvement was obtained by use of 0.75% basalt fiber of 19 mm length with 9% lime content after 90-day curing. Additionally, results of strength tests on specimens including 3 and 6% lime and 12-mm basalt fiber after 1, 7, 28, and 90-day curing were presented. It is evident that the use of 6-mm basalt fiber and 12-mm polypropylene fiber were the best options; however, efficiency of fiber inclusion is subject to change by varying lime contents. It was also observed that the secant modulus was increased by use of lime; however, strength of the correlations among secant modulus and unconfined compressive strength values was decreased by increasing amount of lime for specimens including both basalt and polypropylene fibers.     

粉煤灰和二灰对桂林红黏土力学性质的影响

为了研究粉煤灰和二灰掺量及养护时间对桂林红黏土的改良效果,进行了直剪试验、固结试验以及电镜扫描试验。试验结果表明,粉煤灰的掺入提高了红黏土的抗剪强度,但超过一定量（18%粉煤灰掺量）反而会降低红黏土黏聚力,各掺量粉煤灰红黏土随养护龄期的延长,抗剪强度呈先增后缓趋势。二灰改良红黏土,在早期强度剧增,且强度随养护时间增长而大幅增加,一定龄期内,二灰红黏土黏聚力随二灰掺量呈先增后减趋势。粉煤灰和二灰的掺入均增大了红黏土的压缩模量,且随养护时间的延长而逐渐增大。红黏土中随粉煤灰、石灰的加入,发生一系列物理化学反应,从微观结构分析得知土中孔隙减少,结构性较素红黏土好。     

Effect of Strain Rate on the Strength Characteristics of Soil–Lime Mixture

The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m²) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period.     

Behavior of expansive soils stabilized with fly ash

Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying. Disposal of fly ash, which is an industrial waste in both cost-effective and environment-friendly way receives high attention in China. In this study, the potential use and the effectiveness of expansive soils stabilization using fly ash and fly ash-lime as admixtures are evaluated. The test results show that the plasticity index, activity, free swell, swell potential, swelling pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of the curing time for the treated soil, the swell potential and swelling pressure decreased. Soils immediately treated with fly ash show no significant change in the unconfined compressive strength. However, after 7 days curing of the fly ash treated soils, the unconfined compressive strength increased significantly. The relationship between the plasticity index and swell-shrinkage properties for pre-treated and post-treated soils is discussed.     

Effects of alkaline-activated fly ash and Portland cement on soft soil stabilisation

This paper studies the effects of sodium-based alkaline activators and class F fly ash on soil stabilisation. Using the unconfined compressive strength test (UCS), the effectiveness of this binder is compared with that of a common cement-based binder. Influence of the activator/ash ratio, sodium oxide/ash ratio and sodium hydroxide concentration was also analysed. Sodium hydroxide concentrations of 10, 12.5 and 15 molal were used for the alkaline-activated specimens (AA), with activator/ash ratios between 1 and 2.5 and ash percentages of 20, 30 and 40 %, relatively to the total solids (soil + ash). UCS was determined at curing periods of 7, 28, 90 and 365 days, and the most effective mixtures were analysed for mineralogy with XRD. The results showed a clear increase in strength with decreasing activator/ash ratio (up to a maximum of 43.4 MPa), which is a positive result since the activator is the most expensive component in the mixture. Finally, UCS results of the cement and AA samples, at 28 days curing, were very similar. However, AA results proved to be just between 20 and 40 % of the maximum UCS obtained at 1 year curing, while cement results at 28 days are expected to be between 80 and 90 % of its maximum.     

Investigation of Cement–Bentonite Slurry Samples Containing PFA in the UCS and Triaxial Apparatus

Three mixtures of cement–bentonite slurry containing 28, 36 and 44 % PFA (as a proportion of cementitious materials) were tested using the unconfined compressive strength and triaxial apparatus to determine the stress–strain and shear strength relationships for samples cured for various periods. The samples were batched using 4 % bentonite and 20 % cementitious materials (by mass of water) and allowed to cure underwater once extruded from sealed moulds. Curing periods of 14, 28 and 90 days were selected to investigate the changes in behaviour at durations commonly specified (28 and 90 days) as well as providing insight into changing behaviour with curing (additional curing periods of 7 and 60 days were investigated on a smaller number of samples to increase understanding). Two rates of displacement were used (1.0 and 1.3 mm/min) and four confining pressures (0, 50, 100 and 200 kPa). Shear strength and strain at peak deviator stress of the samples do not appear to vary considerably with confining pressure. For samples containing 28 % PFA, the majority of physical properties exhibited by the cement–bentonite samples change with curing period up to 60 days, where after the properties become similar to those cured for 90 days.     

Improvement of Clayey Soil with Lime and Industrial Sludge

Industrial waste generation has reached up to millions of tons yearly. One way to solve the problems of the large accumulating amount of waste could be to incorporate it into the soil; thus, finding a way for the use of industrial waste could be a quest for soil improvement studies. Industrial sludge in certain pozzolanic form reacts with soil and possesses cementitious properties. This paper illustrates the utilization of lime, steel and copper sludge in improvement of high plasticity clayey soil. The influence of stabilizer type, different curing times and various ratios of lime to sludge are evaluated by Atterberg limits, standard proctor compaction, unconfined compressive strength and unconsolidated undrained strength in triaxial test. The  test results show that adding lime and sludge results in an increase in maximum strength. Moreover, the strength of soil increases with the increase of curing time. Utilizing stabilizers also influences plasticity index and compaction parameters. Finally, the results demonstrate that steel sludge has better performance than that of copper sludge in term of strength development.     

Hydro-mechanical evaluation of stabilized mine tailings

. In this study, mine tailings waste was stabilized using a combination of lime, fly ash type "C", and aluminum. Treated samples were subjected to mineral identification for evaluating the formation of ettringite and gypsum. Also, unconfined compression, hydraulic conductivity, and cyclic freeze and thaw tests were performed to evaluate the hydro-mechanical properties of the stabilized samples. Experimental results have shown that the application of lime and fly ash type "C" to high sulfate content tailings has improved its plasticity, workability, and volume stability. Moreover, upon addition of aluminum to lime and fly ash in a sulfate-rich environment, ettringite and calcium sulfo-aluminate hydrate are formed in these samples. Application of 5% lime, 10% fly ash type "C", in combination with 110 ppm aluminum, resulted in the formation of a solid monolith capable of producing more than 1,000 kPa of unconfined compressive strength, and reduced tailings permeability to 1.96᎒^–6 cm s^–1, which is less than the recommended permeability of 10^–5 cm s^–1 by most environmental protection agencies for reusability of solidified/stabilized samples. The permeability of the treated tailings samples remained below the recommended permeability, even after exposing the treated samples to 12 freeze and thaw cycles. Therefore, based on the experimental results, it is concluded that treatment of high sulfate-content tailings with lime and fly ash, combined with the availability of aluminum for reactions, is a successful method of solidifying highly reactive mine tailings.     

膨胀土与红黏土石灰改性对比试验研究

为探讨石灰改性膨胀土与红黏土的强度发展规律,以生石灰与消石灰改性的南阳膨胀土与郴州红黏土为研究对象,进行了无侧限抗压、固结快速直剪和固结压缩试验的对比研究。研究发现：在1 a养生龄期内,石灰改性的南阳膨胀土与郴州红黏土无侧限抗压强度与养生龄期的对数基本呈线性关系;按大于最佳含水率3%制样的强度在养生28 d以后高于按最佳含水率制样;生石灰改性效果比消石灰改性效果好,由于矿物成分不同,石灰改性南阳膨胀土的效果比石灰改性郴州红黏土好     

Compression Behavior of Mine Tailings Amended with Cementitious Binders

The objective of this study was to evaluate the effect of fly ash amendment on the compression behavior of mine tailings. Natural and synthetic (i.e., laboratory prepared) mine tailings were used to assess the effects of tailings composition and tailings solids content on compressibility. Three types of off-specification fly ashes and Type I–II Portland cement were used as cementitious binders. Tailings-fly ash mixtures were prepared at solids content of 60–75% (water content = 33–67%), water-to-binder ratios of 2.5 and 5, and were cured for 0.1 days (2 h), 7, and 28 days. Bi-linear compression curves on semi-log plots were observed in most of the binder-amended tailings specimens. The break in slope on the compression curve was identified as the breaking stress, whereupon cementitious bonds were broken. The breaking stress increased with an increase in fly ash content, which was attributed to a lower water-to-binder ratio and void volume-to-binder volume ratio that produced more effective particle bonding. Breaking stress also increased with an increase in CaO content and CaO-to-SiO₂ ratio of fly ash, which resulted in more effective bonding between particles. The effect of curing time on the breaking stress of fly ash amended specimens was characterized by (1) an increase in breaking stress via increase in curing time and cementitious bond formation or (2) a constant breaking stress with curing time due to competing mechanisms during loading. Specimens cured under a vertical stress showed an increase in breakings stress with applied load water removal prior to cementitious bond formation that reduced the water-to-binder ratio and led to more effective cementation.     

不同龄期下粉煤灰水泥土的UU抗剪强度试验研究

针对不同养护龄期对于粉煤灰水泥土抗剪强度影响的问题,采用不固结不排水三轴剪切试验从宏观力学的角度分析养护龄期对粉煤灰水泥土的影响,结合SEM试验和XRD试验从微观角度分析试样内部结构与物质成分。试验结果表明:从宏观角度分析,粉煤灰水泥土的应力-应变曲线呈现应变软化型,试样的抗剪强度随养护龄期的增加逐渐增大且28 d的抗剪强度最大,同时,由于试样内部各物质之间的反应随养护龄期的增加而持续进行,龄期越长试样内部各物质之间的胶结作用越强,致使试样的内摩擦角和黏聚力随养护龄期逐渐增大;从微观角度分析,试样内部生成的结晶物质(钙矾石)与胶凝物质(C-S-H凝胶)等填充试样内部的大孔隙且相互黏结,导致试样愈加密实,抗剪强度增大。本文旨在为粉煤灰等材料固化黄土的抗剪强度提供试验依据,为粉煤灰等工业副产品在工程中的应用提供参考,对粉煤灰的利用和环境保护具有参考意义。     

Use of Sewage Sludge Ash and Hydrated Lime to Improve the Engineering Properties of Clayey Soils

Using various additives has been considered as one of the most common stabilization methods for improvement of engineering properties of fine-grained soils. In this research the effect of sewage sludge ash (SSA) and hydrated lime (HL) on compressive strength of clayey soil was investigated. For this purpose, 16 kinds of mixtures or treatments were made by adding different amounts of SSA; 0, 5, 10 and 15% by weight and HL; 0, 1, 3 and 5% by weight of a clayey soil. First, compaction characteristics of the treatments were determined using Harvard compaction test apparatus. So that, 12 unconfined compressive strength test specimens were made using Harvard compaction mold from each treatments taking into account four different curing ages, including 7, 14, 28 and 90 days in three replications. Therefore, a total of 192 specimens were prepared and subjected to unconfined compressive strength tests. The results of this study showed that the maximum dry density of the treated soil samples decreases and their optimum water content increases by increasing the amount of SSA and hydrated lime in the mixtures. It is also found that the adding of HL and SSA individually would increase the compressive strength up to 3.8 and 1.5 times respectively. The application of HL and SSA with together could increases the compressive strength of a clayey soil more efficiently even up to 5 times.     

石灰及其外加剂固化天津滨海软土的试验研究

天津滨海软土力学性质较差,不能直接满足工程需要,在软土中加入固化剂能有效提高软土的工程力学性能,但若在固化剂中再添加适量外加剂,又能再次提高固化土的强度。本文以石灰作为主剂,水泥、石膏作为辅剂改良天津滨海软土,以无侧限抗压强度作为固化效果判断标准,同时进行相应的微观结构测试,并对破坏后的试样进行抗压试验。试验结果表明:水泥的最佳掺量仅随石灰掺量不同而变化,如12%的石灰固化土中,水泥掺量不超过3%可以最好地提高石灰固化土强度; 石膏则不能改善土体强度,并且会使土体水稳定性差,遇水开裂。纯石灰固化土及掺外加剂的石灰固化土都是低压缩性土,各种力学性质都得到明显提高,其破坏形式为脆性破坏,破坏后强度很低且不能恢复,在实践中值得重视。微观结构分析表明:固化土中有CSH网状胶凝(水化硅酸钙)、针状钙矾石、无定形文石(CaCO3)、Ca(OH)2晶体等能够填充孔隙、胶结颗粒的物质生成,有效、适量的生成物有利于固化土强度的提高。土体中总孔隙个数及总颗粒个数都随荷载的增加而增多,孔隙面积、孔隙等效直径及颗粒等效直径都随荷载的增加而减少。     

CaO对钙矾石固化/稳定化重金属铅污染土的影响

为研究CaO的赋存形态及含量对钙矾石固化/稳定化重金属铅污染土效果的影响,采用高铝水泥提供AlO2-,纯石膏或磷石膏提供SO42-,高铝水泥、石膏、普通硅酸盐水泥或生石灰提供CaO,制备不同组分固化剂配比的固化土,测试试样强度和孔隙溶液pH值等宏观物理力学指标,通过醋酸缓冲溶液法测试试样的铅溶出量,对比分析不同固化剂固化土的矿物成分与微观结构特征。结果表明,钙矾石固化/稳定化重金属铅污染土效果显著;钙矾石对孔隙的填充作用带来的增强效果不能代替水化硅酸钙胶结土颗粒的胶结作用,普通硅酸盐水泥对试样的强度更有利,但其后期强度增幅不大,而生石灰有利于固化土强度的持续增长;生石灰较普通硅酸盐水泥对钙矾石的形成、稳定和重金属Pb2+的固化/稳定化更有利;磷石膏和纯石膏对试样的pH值、无侧限抗压强度及钙矾石固化/稳定化重金属Pb2+的效果影响较小;固化土体微观结构特征表明,CaO含量对钙矾石生成形态及作用效果影响显著。当CaO含量较低时,早期生成的钙矾石将向单硫型硫铝酸钙转化。研究成果可丰富重金属污染场地原位处理技术,具有重要的理论意义和工程应用价值。     

Deformation Modulus of Fly Ash Modified with Lime and Gypsum

Deformation modulus of fly ash is one of the most important mechanical properties generally used in different design problems and also as an input parameter to sophisticated numerical techniques employed to assess the response of different structures resting on fly ash fill or embankment made of fly ash. Deformation modulus is usually expressed in terms of compressive strength. This paper presents the deformation modulus of fly ash modified with lime alone or in combination with gypsum at different strain levels. The values of deformation modulus obtained from both unconfined compression test and unconsolidated undrained triaxial test results are presented herein. The specimens for unconfined compression test and for undrained triaxial tests were cured up to 90 and 28 days, respectively. The effects of addition of lime (4–10%) and gypsum (0.5 and 1.0%) on the deformation modulus of class F fly ash are highlighted. With addition of lime and gypsum, the class F fly ash achieved the deformation modulus in the range of 190 MPa in UCS test and up to 300 MPa in triaxial test specimens tested under all round pressure of 0.4 MPa. Based on the present test results empirical relationships are developed to estimate deformation modulus of modified fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus at different strain levels are also developed.     

偏高岭土增强石灰-水泥固化淤泥的耐久性研究

淤泥富含有机质，分解后产生腐殖酸，进而影响淤泥固化效果。仅掺入12%水泥固化淤泥，当标准养护期超过60 d，其强度不增反减。联合掺入3%石灰和12%水泥，固化淤泥的pH值持续180 d处于10.5以上；无侧限抗压强度由750 kPa（养护期28 d）提升到1 500 kPa（120 d），说明借助石灰营造强碱性环境，可以提高水泥固化淤泥的强度；但养护到180 d后，其强度又降到1 250 kPa；钙离子浓度变化规律表明，这是由于腐殖酸溶蚀水泥和石灰的水化胶结物所致。借助偏高岭土卓越的火山灰反应能力，掺入3.0%偏高岭土，提升石灰（3%）?水泥（12%）固化淤泥的耐久性，发现180 d养护期内，其强度始终处于增长趋势，究其原因是偏高岭土富含无定形硅、铝氧化物，具有快速捕获氢氧化钙溶液中钙离子的能力，形成稳定的胶结物，而且不易受腐殖酸的侵蚀作用，证明偏高岭土能够有效提升石灰?水泥固化淤泥长期强度。     

Classification,shear strength,and durability of expansive clayey soil stabilized with lime and perlite

An experimental study was performed to investigate the effect of perlite and perlite–lime admixtures on classification, shear strength, and durability properties of an expansive soil containing smectite clay minerals. Two types of mixtures, namely soil–perlite and soil–perlite–lime, were prepared with different percentages of perlite and compacted with standard Proctor energy at their optimum water contents. Samples of 38 mm diameter and 76 mm height for durability tests and square samples of 60 mm edge for shear box test were taken and preserved until test time in a desiccator. Disturbed samples were also taken to determine liquid and plastic limits. The expansive soil shows behavior of fine sand and silt due to pozzolanic reactions in microstructure caused by addition of lime and perlite. Although apparent cohesion of treated soil decreased with increasing amount of perlite for both types of samples, perlite–lime-treated samples had higher apparent cohesion than only perlite-treated samples. Large increments in angle of shearing resistance were obtained with increasing usage of perlite. Samples stabilized with only perlite could not show enough durability at the durability tests based on volumetric stability and unconfined compression strength. However, samples stabilized with lime and more than 30 % perlite proved to have enough durability and shear strength.     

Characterization of phosphoric acid- and lime-stabilized tropical lateritic clay

The effect of calcium-based stabilizers such as lime on the geotechnical properties of tropical soils has been reported by many researchers. However, the amount of literature available on the micro-structural, molecular, and leaching characteristics of lime and in particular phosphoric acid-stabilized lateritic clays has been limited. This research was carried out in an attempt to identify the time-dependent soil-chemical reactions. In addition, the possible mechanisms that contributed to the stabilization process were discussed in the light of various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry (EDAX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) etc. Based on the results it was found that in lime-treated samples, the coating action of free iron oxides on clay particles imposed inhibitive effects on the dissolution of clay alumina. On the other hand, in phosphoric acid-stabilized soil, due to the increase in solubility of metal oxides and also the subsequent release of clay alumina the formation of cementitious compounds were more feasible. From engineering point of view, the phosphoric acid-stabilized lateritic soil showed the highest degree of improvement with an approximately threefold strength increase in comparison with the natural soil over an 8-month curing period.     

流态地聚物固化土强度特性及其强度预测

地聚物胶凝材料能够替代水泥基胶凝材料作为固化剂应用于狭窄肥槽回填等工程问题中,有效降低水泥生产过程中的污染及能耗,但目前对于流态地聚物固化土胶凝材料的研究较少。采用3种新型绿色胶凝材料联合碱激发剂固化工程渣土形成流态地聚物固化土,通过对比其无侧限抗压强度,探究每种胶凝材料对于固化土强度特性的影响,同时建立强度预测模型,分析不同因素对于强度的影响程度。研究结果表明：固化土的强度随着碱激发剂模数的增加先提高后降低;固化土强度随着高炉矿渣（GGBS）、粉煤灰、稻壳灰掺量的增加均呈上升趋势,随着稻壳灰粒径的增长呈下降趋势;碱激发剂模数增至1.2、GGBS掺量增至10%、粉煤灰掺量增至8%和稻壳灰掺量增至11%时,固化土强度提升最为显著;强度预测模型预测结果的平均相对误差仅为5.57%,预测结果较为精准;预测模型中各层权值的计算结果表明养护龄期对于固化土强度影响最大,稻壳灰粒径影响程度最小。研究结果可以为固化土在实际工程的应用提供理论支持。