Stabilization of tropical kaolin soil with phosphoric acid and lime

Studies on the chemically stabilized soils have shown that the effectiveness of treatment is largely dependent on soil’s natural environment. In tropical kaolin soils, phosphoric acid may be used as an alternative to traditional alkaline stabilizers for improving soil properties. This research was carried out in an effort to identify the time-dependent soil-stabilizer reactions. Data for the study of characterization of treated samples were obtained from X-ray diffractometry, energy dispersive X-ray spectrometry, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and leaching analysis. Based on the collected data, the kaolinite mineral with pH-dependent structural properties showed slightly different behavior both in basic and in acidic mediums. Also, it was found that the chemical stabilizers preferentially attacked the alumina surface of the clay particles. Therefore, it was rational to suggest that with respect to lime and phosphoric acid treatment, aluminate hydrate compounds are more likely to be formed.     

Influence of structure on the compression and shear behaviour of a saturated lateritic clay

Lateritic clay is well recognized to contain significant amount of iron and aluminium oxides (sesquioxide). These oxides enhance the formation of soil aggregates which would greatly affect soil structure. So far, no study has been carried out purposely to investigate the influence of aggregate-dependent structure on the mechanical behaviour of the lateritic clay. In this study, structure effects on the compression and shear behaviour of a saturated lateritic clay were studied. Intact, recompacted and reconstituted specimens were studied through oedometer, isotropic compression and consolidated undrained shear tests. Microstructure of these specimens was determined using the mercury intrusion porosimetry and scanning electron microscopy (SEM) techniques and then used to explain the observed behaviour. It was found that the compressibility of recompacted/reconstituted specimens was about 90% larger than intact specimen. Different from soft clay, the influence of microstructure does not show an obvious reduction in compressibility after yielding. The peak shear strength of intact specimen was about 100% higher than those of reconstituted/recompacted specimens. The significant difference in compression and shear behaviour is mainly because the aggregates of intact specimen were about 90% larger than those of reconstituted/recompacted specimens, as revealed by the SEM results. As a result, particle contacts forming the force chain were therefore larger in the intact specimen. The intact specimen therefore became less compressible and more dilative.

     

Stabilization of lateritic soils with phosphoric acid

Summary This paper describes a laboratory study on the stabilization of lateritic soils with phosphoric acid-H₃PO₄. This method is most promising for road and airport pavement construction in tropical regions where fine textured lateritic soils (red clays and silts) occur over large areas. The iron and aluminum phosphates formed are hard and insoluble. The main source of iron is free iron oxide, and the aluminum sources are free aluminum oxide, exchangeable cations and clay minerals (hydrated aluminum silicates). Four different soil samples were studied, but the most comprehensive study was carried out with a lateritic soil evolved from weathered basaltic bedrock. The variables of the test specimens were: percentage of acid, moulding water content, compaction energy, and curing time. Strength tests performed were the axial or unconfined compression test and the indirect tensile or diametrical compression test. With 5% of phosphoric acid to dry weight of soil, values of compressive strength around 4.0 MPa were obtained after 28 days curing.     

淋溶时间对红黏土物理力学特性的影响

以湖北省鄂州市庙岭镇的红黏土为研究对象,以化学选择溶解法结合淋溶作用为处理手段,将原状土样中的游离氧化铁按梯度去除,获得连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB)溶液淋溶时间与除铁率的关系,并分析了不同淋溶时间对红黏土物理力学特性及微观孔隙结构的影响。试验结果表明,DCB溶液淋溶时间与除铁率相关性较强,除铁率与时间呈先快速增长后逐渐稳定的关系。由于游离氧化铁在土颗粒间主要起胶结作用,故淋溶时间对红黏土的物理力学特性有较大影响。随着淋溶时间的增长,黏粒与胶粒含量逐渐增大,耐热性小幅提升,无侧限抗压强度显著减小,且无侧限抗压强度变化整体趋势为前期急剧降低至后期趋于平稳。核磁共振、差热分析和电镜扫描的结果表明,随着淋溶时间的增大,庙岭红黏土内部孔隙增大,自由水减少,结合水增多,微观形态上团粒结构遭到破坏,胶结物质明显减少,结构形式从紧凑的粒团堆叠结构逐渐转化为聚集体-松散颗粒状结构。     

淋溶时间对红黏土物理力学特性的影响

以湖北省鄂州市庙岭镇的红黏土为研究对象,以化学选择溶解法结合淋溶作用为处理手段,将原状土样中的游离氧化铁按梯度去除,获得连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB)溶液淋溶时间与除铁率的关系,并分析了不同淋溶时间对红黏土物理力学特性及微观孔隙结构的影响。试验结果表明,DCB溶液淋溶时间与除铁率相关性较强,除铁率与时间呈先快速增长后逐渐稳定的关系。由于游离氧化铁在土颗粒间主要起胶结作用,故淋溶时间对红黏土的物理力学特性有较大影响。随着淋溶时间的增长,黏粒与胶粒含量逐渐增大,耐热性小幅提升,无侧限抗压强度显著减小,且无侧限抗压强度变化整体趋势为前期急剧降低至后期趋于平稳。核磁共振、差热分析和电镜扫描的结果表明,随着淋溶时间的增大,庙岭红黏土内部孔隙增大,自由水减少,结合水增多,微观形态上团粒结构遭到破坏,胶结物质明显减少,结构形式从紧凑的粒团堆叠结构逐渐转化为聚集体-松散颗粒状结构。     

高温下红黏土热导率的变化规律试验研究

目前国际上对高温下土壤热导率的试验和模型预测研究比较缺乏,通过KD2 Pro测试两种红黏土在较广温度范围（5~90℃）和含水率范围内的热导率,并选择IPCHT模型预测高温下体积含水率-热导率的变化规律。测试结果表明,两种红黏土的热导率对体积含水率的敏感程度与温度有关,且热导率均随温度的升高而增大,在90℃时热导率最高可达5℃的3~4倍。60~90℃范围内热导率随体积含水率的变化存在明显的临界含水率（对应土壤的塑性指数）,但相同温度、体积含水率下,柳州红黏土中水汽潜热传输效应较桂林红黏土要明显。模型预测研究表明,除粉砂质黏壤土外,高温下IPCHT模型预测效果均不理想,经传质增强因子ξ修正后,柳州红黏土以及细砂的热导率预测值和实测值均相符得较好（RMSE < 30%）,但桂林红黏土的整体预测效果仍较差。     

论铝土矿床成因及矿床类型

铝土矿全部是风化作用形成的，无一例外。地球上含铝（含少量铝质也可以）岩石在适宜的气候和地形条件下，风化成红土矿物，包括铝土矿物及少量粘土矿物、含铁矿物及少量含钛矿物等风化壳铝土物质（红土铝土物质）。第四纪以前的古风化作用形成的是古风化壳铝土物质（古红土铝土物质），迁移就位以后便形成风化壳铝土矿床（红土铝土矿床）。深埋地下经过成岩变化，再随地壳抬升进入地壳浅部，或地表的叫古风化壳铝土矿床。我国９８％是古风化壳铝土矿床，即国外所称的喀斯特铝土矿床。由于其迁移就位方式不同，便形成了不同的风化壳和古风化壳（亚型）矿床     

偏高岭土协同石灰钝化红黏土水敏性的机制

红黏土水敏性强,添加石灰等碱性材料处治后,能获得即刻的改良效果,但由于红黏土呈弱酸性,石灰改良后其长期性能会衰减。为提高石灰稳定红黏土（简称La+L）的长期性能,添加偏高岭土（4%）协同石灰（5%）稳定红黏土（简称La+L+MK）,改善其水敏性和酸?碱互损作用。制备8种初始含水率的压实试样（初始孔隙比相同）,养护到预定时间后开展无侧限抗压强度试验,同时,测定试样的钙离子浓度、电导率和pH值。结果表明：初始含水率为26%左右时,改良土的无侧限抗压强度最高,初始含水率偏高或偏低都不利于改良土的强度增长。究其原因,试样偏干时,缺少水分,石灰水化不充分,不能形成游离态钙离子,无法进行火山灰反应,颗粒之间无法形成胶结;试样偏湿时,火山灰反应形成的胶结强度不及过量水分引起的基质吸力丧失量。试样的钙离子浓度和电导率变化规律,证实了以上原因解释的猜想。当然,添加偏高岭土后,能够显著改善偏湿状态下的石灰土强度。即使浸水饱和后,相对石灰改良土,也能够保持较高的强度,充分证明偏高岭土能够有效降低石灰土水敏性,提高其耐久性。偏高岭土直接提供了大量硅、铝氧化物,且将土体pH值降到有利于硅、铝氧化物溶解的碱性范围,加速火山灰反应,缓减或抑制石灰?红黏土的互损作用。     

Lime stabilization of clay minerals and soils

Clay soil can be stabilized by the addition of small percentages, by weight, of lime, thereby enhancing many of the engineering properties of the soil and producing an improved construction material. In order to illustrate such improvements, three of the most frequently occurring minerals in clay deposits, namely, kaolinite, montmorillonite and quartz were subjected to a series of tests. As lime stabilization is most often used in relation to road construction, the tests were chosen with this in mind. Till and laminated clay were treated in similar fashion. With the addition of lime, the plasticity of montmorillonite was reduced whilst that of kaolinite and quartz was increased somewhat. However, the addition of lime to the till had little influence on its plasticity but a significant reduction occurred in that of the laminated clay. All materials experienced an increase in their optimum moisture content and a decrease in their maximum dry density, as well as enhanced California bearing ratio, on addition of lime. Some notable increases in strength and Young's Modulus occurred in these materials when they were treated with lime. Length of time curing and temperature at which curing took place had an important influence on the amount of strength developed.     

黏土矿物与碱激发地聚物的相互作用机理

土体固化的核心问题之一就是使用适宜的固化剂固化黏土矿物。通过扫描电镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射(XRD)以及X射线光电子能谱(XPS)等试验方法,研究不同碱含量下碱激发地聚物固化的蒙脱石、伊利石和高岭土的微观结构、物质组成及物理化学反应过程,探究碱激发地聚物与黏土矿物之间的相互作用机理。研究结果表明:黏土矿物经碱激发地聚物固化后,由松散颗粒转变为块状致密结构;随着地聚物中碱含量的增加,Si、Al及Ca元素电子结合能下降;蒙脱石在衍射角为5°左右(001)峰形右移,层间距减小;蒙脱石吸附水含量减小,亲水能力下降,矿物活性被限制。     

The potentials of lime stabilization of lateritic soils

The paper reviews lime stabilization of lateritic soils and shows that all Nigerian lateritic soils from A-1-a soil to A-7-6 soil used in the investigation, improved their engineering characteristics substantially by the addition of lime. The plasticity indices of the soils were reduced whereas the plastic limits increased; the liquid limits increased slightly, the maximum dry density decreased and the optimum moisture content increased. From the results of Durability and CBR tests, only the A-1 soil and A-2 soil have any potential as competent base materials and consequently only these require any further field tests. 6% lime is recommended for these field tests. The other soils that do not qualify for bases may be utilized as sub-base materials.     

Gypsum Induced Strength Behaviour of Fly Ash-Lime Stabilized Expansive Soil

Physical and engineering properties of soil are improved with various binders and binder combinations. Fly ash and lime are commonly used to improve the properties of expansive soils. An attempt has been made, in this paper, to examine the role of gypsum on the physical and strength behaviour of fly ash-lime stabilized soil. The change in strength behaviour is studied at different curing periods up to 90 days, and the mechanism is elucidated through pH, mineralogical, microstructural and chemical composition study. The strength of soil-fly ash mixture has improved marginally with the addition of lime up to 4 % lime and with curing period for 28 day. Significant increase in strength has been observed with 6 % lime and enhanced significantly after curing for 90 days. The variations in the strength of soil with curing period is due to cation exchange and flocculation initially, and binding of particles with cementitious compounds formed after curing. With addition of 1 % gypsum to soil-fly ash-lime, the strength gain is accelerated as seen at 14 day curing. The accelerated strength early is due to formation of compacted structure with growth of ettringite needles within voids. However, strength at curing for 28 day has been declined due to annoyance of clay matrix with the increase in size of ettringite needle; and again increased after curing for 90 days. The rearrangement of clay matrix and suppression of sulphate effects with formation of cementitious compounds are observed and found to be the main responsible factors for strength recovered.     

Stabilization of a Clayey Soil with Fly Ash and Lime: A Micro Level Investigation

Pavement structures on poor soil sub grades show early distresses causing the premature failure of the pavement. Clayey soils usually have the potential to demonstrate undesirable engineering behavior, such as low bearing capacity, high shrinkage and swell characteristics and high moisture susceptibility. Stabilization of these soils is a usual practice for improving the strength. This study reports the improvement in the strength of a locally available cohesive soil by addition of both fly ash and lime. Analysis using X-ray diffraction, scanning electron microscopy, coupled with energy dispersive spectroscopy, thermal gravimetric analysis, zeta potential and pH value test was carried out in order to elucidate the stabilization mechanism. The micro level analysis confirmed the breaking of montmorrillonite structure present in the untreated clay after stabilization. In the analysis, it was also confirmed that in the stabilization process, pozzolanic reaction dominated over the cation exchange capacity.     

Suppression of swelling associated with ettringite formation in lime stabilized sulphate bearing clay soils by partial substitution of lime with ground granulated blastfurnace slag (GGBS)

Ettringite related swelling in lime-stabilized sulphate bearing clay soil systems has only been reported within the last decade although similar expansive behaviour has been reported in concrete over many years. The use of ground granulated blastfurnace slag (GGBS), an industrial by-product, is well established as a binder in many cement applications where it provides enhanced durability and high resistance to sulphate attack. This paper reports on efforts to extend the use of GGBS to highway and other foundation layers by determining the beneficial effect of the suppression of swelling of lime-stabilized clay soils, particularly in the presence of gypsum. The paper describes the results of laboratory tests on lime-stabilized kaolinite containing different levels of added gypsum and on lime-stabilized gypsum (selenite) bearing Kimmeridge Clay to which, in both cases, the lime has progressively been substituted with GGBS. The tests determine the linear expansion behaviour of compacted cylinders, during moist curing in a humid environment at 30°C and during subsequent soaking in de-ionized water. The results illustrate that substitution of lime with GGBS produces significant reduction in linear expansion of lime-stabilized clay soils particularly those containing gypsum.     

广西红粘土击实样强度特性与胀缩性能

通过对广西贵港红粘土重型击实样的室内试验研究,探讨了其力学特性、胀缩性能、孔径分布特征与含水量之间的关系。结果表明：干密度指标总体上能反映红粘土击实样的强度规律,但非饱和击实样强度峰值对应的含水量因基质吸力作用而偏小,饱和后土体由于吸水膨胀与基质吸力的消失,使得强度峰值对应含水量较饱和前明显增大,红粘土在最优含水量下压实,虽可获得很高的压实度,但饱和后的强度并非最大;红粘土击实样的胀缩性能主要由含水量决定,同时,受到干密度的影响;孔隙主要以孔径在0.01～0.05μm范围内的小孔隙为主,为进一步掌握红粘土的工程力学特性提供了帮助。     

Mineralogical changes and geotechnical properties of an expansive soil interacted with caustic solution

The type and amount of clay mineral plays an important role in the behaviour of fine-grained soils. Clay minerals are the primary source and moisture is often the external agent of swelling in soils. Also soils may exhibit increased/reduced swelling due to interaction with chemicals. Alkalis used in industrial operations are one such example. Concentrations of alkali and mineral type are the key factors in such interactions. The present paper reports the changes in the properties of an expansive Black Cotton soil containing a mixed layer mineral, rectorite upon interaction with high concentration caustic solutions. X-ray diffraction studies have shown that the rectorite present in the soil undergoes changes with increase in the concentration of alkali. Saponite gets transformed to nantronite. Small amount of kaolinitic mineral present in the soil also reacts with alkali producing some changes in its mineralogy. Many hydroxides are produced. Differential thermal analysis studies have been supportive of these changes. Consequent of these changes, the soil-specific surface increases, changes its Atterberg limits and free swell volume increases. The results have been supported by the characteristics and behaviour of samples contaminated in the field with alkali from an alumina extraction plant.     

Geotechnical characterisation of lateritic soils from south-western Nigeria as materials for cost-effective and energy-efficient building bricks

Lateritic soils which have been described as highly weathered tropical or subtropical residual soils were studied with an attempt to establish its suitability or otherwise as sustainable material in building bricks and housing development that will meet the present challenge of sustaining the environment without costing too much and maintaining a high standard of strength, durability and aesthetics. Index properties of the tested lateritic soils revealed them as mostly well graded, comprising both cohesive (silt and clay) and cohesionless (sand and gravel) soil fraction. The geotechnical analyses on the studied lateritic soil revealed a strong compressive strength with a relatively sound dry density which could guarantee a good durability in resulting bricks made from these soil materials. Further test on the strength and durability of the compressed earth bricks (CEBs) made from these lateritic soils revealed a brick with compressive strength ranging between 6.33 and 15.57 MPa which is considered to be of good strength coupled with its sound durability strength established over a period of more than one year under a complete cycle of weather and seasonal conditions. In conclusion, lateritic soils from the study area were found to be suitable as materials for bricks (CEB) with good compressive and durability strength which qualifies them as sustainable and cost-effective materials for low-cost housing development.     

马家树水库大坝防渗土料分散性判别和改性试验

基于分散性土修建挡水建筑物易受破坏而造成工程安全事故等因素考虑,开展双比重计试验、碎块试验、针孔试验、孔隙水阳离子试验和交换性钠百分比试验,对马家树大坝防渗土料的分散性及其改性措施进行研究。试验结果表明,马家树大坝防渗土料属于低液限黏土,易溶盐和饱和孔隙水溶液中含有大量的钠离子,酸碱度呈强碱性或极强碱性;土样中的黏土矿物主要以伊利石为主,含有少量的高岭石、绿泥石和蒙脱石;分散性试验综合判别土料属于分散性土和过渡性土;石灰剂量为0.25 %时就对分散性土产生显著改性作用。研究表明,黏性土产生分散性的主因是土体中含有较多的钠离子和酸碱度呈强碱性;石灰是一种有效的分散性土改性剂。     

Effect of Cement and Quarry Dust on Shear Strength and Hydraulic Characteristics of Lithomargic Clay

The lithomargic clay constitutes an important group of residual soils existing under lateritic soils. This soil is found on the western and eastern coasts of India over large areas. This soil is a problematic one and is very sensitive to water and loses a greater part of its strength when becomes saturated. These high silt deposits have invited many problems such as slope failures, foundation failures, embankment failures, uneven settlements etc. In this investigation an attempt is made to study the effect of cement and quarry dust on shear strength and hydraulic characteristics of the lithomargic clay after the stabilization. Microfabric and mineralogical studies were carried out to find out the reason for the strength development of the stabilized soil using SEM and XRD analysis. The results indicated that there is an improvement in the properties of the lithomargic clay with the addition of cement and quarry dust. The XRD results indicated the formation of CSH and CAH, which are responsible for strength development in the stabilized soil.