Sulfation of calcitic and dolomitic lime mortars in the presence of diesel particulate matter

The sulfation of four types of calcitic and dolomitic lime mortars exposed to SO₂ in the presence of particulate matter from diesel vehicle exhaust emissions has been investigated. The binders mineralogy and mortars texture are the main factors influencing the formation of deleterious sulfate salts. The type of binder also influences the pore size distribution and the total porosity of the mortars: for equal aggregate (quartz or dolomite), dolomitic lime mortars have smaller pores and higher porosity than calcitic ones. During the first 24 h exposure to SO₂, calcitic lime mortars undergo a higher weight increase than dolomitic ones due to rapid formation of gypsum on their surface. However, at the end of the sulfation test (10 days), dolomitic mortars show a higher weight increase due to massive formation of epsomite and gypsum, which is facilitated by their higher porosity and the high reactivity of Mg phases in the porous and partially carbonated binder. Control samples (not covered with diesel particulate matter) also develop calcium and magnesium sulfates upon long term exposure to SO₂. This is due to the presence of uncarbonated Ca and Mg hydroxides that promote SO₂ fixation as sulfates. However, the amount and size of sulfate crystals are significantly smaller than those observed on samples covered with diesel particulate matter. These results show that diesel particulate matter enhances the sulfation of lime mortars and demonstrate that sulfation of dolomitic lime is an important mechanism for the in situ formation of highly soluble and deleterious hydrated magnesium sulfates (epsomite and hexahydrite). The use of dolomitic limes in the conservation of monuments exposed to air pollution in urban environments may therefore pose a significant risk.     

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.     

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。     

Utilization of lime,slag and fly ash for improvement of a colluvial soil in New South Wales,Australia

In Australia, colluvial soils form large terrains which are often subjected to considerable erosion and mass movement. This study presents a laboratory evaluation of the improvement effected by hydrated lime, milled blast furnace slag and fly ash on a fine grained (erosive) colluvial soil in New South Wales, Australia. Geotechnical tests were conducted to determine the compaction and consolidation characteristics and the compressive and shear strength properties of the blended and natural soil specimens. The effect of these additives on the Atterberg limits and pH levels is also investigated. As large amounts of fly ash and steel slag are produced in New South Wales, it is economically attractive to utilize these industrial by-products for ground improvement rather than employing conventional methods such as lime treatment. This study demonstrates that for the colluvial soil tested, milled slag is the most effective in terms of improving the internal friction angle of the treated soil, while lime is the most suitable for achieving the optimum compressive strength. Non-pozzolanic fly ash is found to be inappropriate as a soil improving agent. The cost of ground treatment using the various additives is also estimated and compared.     

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     

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.     

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.     

聚丙烯纤维加固软土的试验研究

为了研究聚丙烯纤维加固软土的效果和机制,改善石灰土和水泥土的脆性破坏形式。在试验中将纤维按质量百分比为0.05 %,0.15 %和0.25 %的掺量分别掺入到素土、石灰土和水泥土中,按不同的配比配制了20组试样,进行了无侧限抗压强度试验。试验结果显示：纤维的加入能在小范围内提高素土的无侧限抗压强度,并且强度值随纤维掺量的增加而增加;而在石灰土和水泥土中只要掺入少量的纤维就能使无侧限抗压强度值得到极大的提高,增加了石灰土和水泥土的抗拉强度,改善了它们的脆性破坏形式,并使其水稳性得到改善。     

Chemical stabilization of sabkha soils at high moisture contents

Vast expanses of arid, saline soils that occur along the Arabian Gulf seaboard and elsewhere possess a very low density and strength that necessitate improvement before any actual construction takesplace. For large-scale constructions, several field improvement techniques have recently been implemented with various degrees of success. In surficial, small-scale applications, chemical stabilization provides a potential technique to improve the inferior properties of these soils, known locally as sabkha. A literature search indicates that chemical stabilization of soils usingasphalt, lime and cement is usually conducted at lower moisture contents than the optimum. Such moisture contents are also much lower than the natural moisture content of sabkha, and if applied to sabkha in the field, this wouldrequire lowering the moisture content before any stabilization commenced; whichwould be neither feasible nor economical.

In this investigation, an eastern Saudi sabkha soil was chemically stabilized at its natural moisture level, which varies from 16% to 22%. In addition to the characterization of the soil and standard compaction tests, cement and lime sabkha mixtures were prepared at five additions and cured for up to 90 days in plastic wrap. Results indicate that cement-stabilized sabkha gained high strength with time and proved to have a potential use in construction.     

温郁金的石灰土栽培及其营养元素动态变化初步研究

为探索原产浙江温州地区的药用植物温郁金是否能在石灰土上生长,通过盆栽试验对比研究了温郁金在石灰土和红壤上生长及其生长过程中N、P、K、Ca、Mg、Fe 6种元素含量的动态变化。结果表明: 温郁金不但可以在石灰土上生长,而且其药用部位(莪术之一)的产量、莪术油的含量及莪术油中主要药用组分β -榄香稀等的含量都较大;石灰土上生长的温郁金在生长前期较快地表现出老叶明显发黄的缺肥症状,而红壤植株在追加N、P、K 3种大量元素后功能叶子呈现黄白色,且夹带有褐色斑点的缺肥症状;石灰土中Fe元素有效态含量比红壤低一个数量级,但在石灰土上种植的温郁金植株其Fe元素含量并不比红壤上的低。由此认为: ( 1)温郁金基本可以在石灰土上引种栽培;石灰土种植温郁金对施加化肥诱发的土壤元素缺乏具有较强的抵抗性; ( 2)温郁金元素的吸收受地质背景制约。      

石灰改良高液限土强度特性的函数模型研究

针对广西荔玉高速路基沿线产生的大量高液限土弃方问题,采用生石灰对高液限土进行改良处理。选取弃土场的高液限土,分别配制不同初始含水率、不同石灰掺量的试样进行侧限压缩试验和快剪试验,采用基本初等数学函数模型拟合不同饱和状态、不同初始含水率下石灰掺量对试件压缩特性和抗剪强度影响。结果表明:(1)高液限土的压缩系数随石灰掺量增加呈指数形式减小;(2)不同饱和状态试件的黏聚力和内摩擦角随石灰掺量增加呈二次函数形式变化;(3)高液限土具有水敏性,饱和素土试件最大抗剪强度对应的含水率较击实试验最大干密度对应的含水率高3%～6%;(4)当初始含水率不高于26.73%时,建议石灰掺量不低于6%,否则改良高液限土的石灰掺量不低于8%,可在满足经济性的前提下达到较好的改良效果。     

重塑石灰土的力学特征与性能劣化机制分析

石灰土在公路等工程中应用很广泛,随着公路改扩建等工程的迅速增多,面临如何处理与利用废弃石灰土的难题。通过对比分析素土、石灰土、重塑石灰土的压缩、强度等力学指标,探讨重塑石灰土的力学特征。结果表明,重塑石灰土压缩系数与石灰土相比提高了2～3倍,无侧限抗压强度损失了30%～40%,内摩擦角增大了1.2倍,黏聚力降低了40%。提出用劣化系数评价重塑石灰土的力学特性劣化程度,并从石灰处治红黏土的团粒化、碳化、灰结机制等角度分析了重塑石灰土性能劣化的本质原因。与素土相比,石灰土的黏粒（d <0.002 mm）含量减少而粗粒（d >0.074 mm）含量增加,从而提高了石灰土的内摩擦角。但重塑过程则破化了石灰土中的胶结结构致使重塑石灰土的黏聚力降低,从而影响重塑石灰土的其他力学性能指标。     

石灰改性红砂岩残积土工程性质试验研究

为研究石灰改性红砂岩残积土的工程性质并确定最佳掺量,以恩施地区红砂岩残积土为研究对象,制备不同石灰掺量的改良土试样,并进行击实、压缩、无侧限抗压试验。结果表明,随着石灰掺量的增大:改良土最优含水量逐渐增大,最大干密度逐渐减小;改良土压缩系数先减小后增大,压缩模量先增大后减小,对应的最优石灰掺量为7%;改良土无侧限抗压强度先提高后降低,对应的最优石灰掺量为9%。出现上述规律的主要原因是:石灰发生的水化、离子交换、碳酸化、结晶等作用,增强了砂土颗粒之间的黏结,提高了土的整体性,使石灰土压缩、强度特性得到改良。然而,过多的石灰会以自由灰的形式存在于土颗粒空隙之间,导致土体的压缩变形量增大,无侧限抗压强度降低。     

United Arab Emirates limestones: impact of petrography on thermal behavior

The thermal behavior of selected limestones from representative localities of the United Arab Emirates is investigated for their suitability for soft-burnt lime production. The limestone samples were collected from the Ghalilah, Musandam, Shauiba, Muthaymimah, Dammam and Asmari formations. The samples were characterized for petrography, mineral and chemical composition, together with physico-mechanical characteristics. Investigative methods included transmitted light microscopy (TLM), cathodoluminescence (CLM) and scanning electron microscopy (SEM), as well as X-ray micro-tomography (μ-CT), XRD, XRF and Archimedes method. The limestone samples were fired in an electrical muffle furnace for 0.25, 0.5, 1 and 2 hours at 800, 900, 1,000 and 1,100 °C. After firing the lime grains were tested to determine their hydration rate and microfabric. The Ghalilah and Musandam limes show the lowest and highest maximum hydration rates, respectively, due mainly to the impure nature of the former, and the smaller lime crystallites and dominance of post-calcination micro-cracks of the latter. The Dammam and Asmari limes preserve a “ghost” microfabric of the original limestone. Higher allochem contents impose lower activation energy requirements for calcination, which implies earlier calcination of the allochems. The Musandam, Shauiba and Muthaymimah limestones may be useful for the production of reactive soft-burnt lime under the applied firing conditions, however, the Dammam and Asmari limestones need more advanced calcination conditions than the applied ones. The Ghalilah limestone was found to be unsuitable for the production of lime.     

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。     

Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive

Summary The stabilization of Malaysian soil by mixing with rice husk ash, a locally available waste material, to improve its engineering properties is described. Stabilizing agents, i.e. cement and lime, were added to produce the reaction products which are responsible for the enhancement of the engineering properties. Based on the strength development, it seems that lime is the more effective stabilizing agent. However, the cheap waste material can be used as partial replacement for the more expensive cement in the cement-treatment of the soil. A durability study was carried out to evaluate the effectiveness of this stabilization method.     

Effect of polypropylene fibre and lime admixture on engineering properties of clayey soil

In order to reduce the brittleness of soil stabilized by lime only, a recent study of a newly proposed mixture of polypropylene fibre and lime for ground improvement is described and reported in the paper. To investigate and understand the influence of the mixture of polypropylene fibre and lime on the engineering properties of a clayey soil, nine groups of treated soil specimens were prepared and tested at three different percentages of fibre content (i.e. 0.05%, 0.15%, 0.25% by weight of the parent soil) and three different percentages of lime (i.e. 2%, 5%, 8% by weight of the parent soil). These treated specimens were subjected to unconfined compression, direct shear, swelling and shrinkage tests. Through scanning electron microscopy (SEM) analysis of the specimens after shearing, the improving mechanisms of polypropylene fibre and lime in the soil were discussed and the observed test results were explained. It was found that fibre content, lime content and curing duration had significant influence on the engineering properties of the fibre–lime treated soil. An increase in lime content resulted in an initial increase followed by a slight decrease in unconfined compressive strength, cohesion and angle of internal friction of the clayey soil. On the other hand, an increase in lime content led to a reduction of swelling and shrinkage potential. However, an increase in fibre content caused an increase in strength and shrinkage potential but brought on the reduction of swelling potential. An increase in curing duration improved the unconfined compressive strength and shear strength parameters of the stabilized soil significantly. Based on the SEM analysis, it was found that the presence of fibre contributed to physical interaction between fibre and soil whereas the use of lime produced chemical reaction between lime and soil and changed soil fabric significantly.     

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.     

重塑石灰土的强度恢复方法与机制初探

石灰稳定土工程翻修改造后会产生大量的石灰土弃渣,为避免污染环境和节约工程投资,需重新利用破碎的石灰土进行填筑。但石灰土破碎后强度急剧降低,需要添加胶凝材料提升其力学性能。以重塑石灰土为研究对象,通过添加5%石灰或水泥进行再改良,对比分析两种再改良土的强度和压缩性等力学指标,结果表明,石灰再改良土的力学特性优于水泥再改良土。借助粒度分析、电镜扫描、X衍射和热重分析试验手段揭示了石灰再改良土性能优越的内在机制,发现石灰再改良土中的石灰和石灰土团粒能形成很好的胶结;但水泥未能和石灰土团粒形成有效胶结,自身形成了边-面和边-边接触的片状多孔架构。重塑石灰土残存的氢氧化钙是引起水泥再改良土性能劣于石灰再改良土的主要诱因。     

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.