Factors Affecting Engineering Properties of Microfine Cement Grouted Sands

An experimental investigation was conducted in order to evaluate the influence of distance from the injection point and of parameters pertinent to the cement, the suspension and the sand on the effectiveness of microfine cement grouts. Three different cement types, each at three different gradations having nominal maximum grain sizes of 100, 20 and 10 μm, were used. Grouting effectiveness was evaluated by injecting suspensions with water to cement (W/C) ratios of 1, 2 and 3, by weight, into five uniform sand fractions with different grain sizes and eight composite sands with different gradations, using a specially constructed apparatus. Unconfined compression and permeability tests were conducted on the resulting grouted sand specimens, after curing for 28 and 90 days. Microfine cement grouted sands obtained unconfined compression strength values of up to 14.9 MPa and permeability coefficients as low as 1.3 × 10^?6 cm/s or by up to 5 orders of magnitude lower than those of clean sands. The W/C ratio and the bleed capacity of suspensions as well as the effective grain size and the permeability coefficient of sands are very important parameters, since they affect substantially the grouted sand properties and are correlated satisfactorily with them. The strength and permeability of grouted sands can increase, decrease or remain constant with distance from the injection point depending on the easiness of suspension penetration into the sands. The improvement of grouted sand properties with increasing distance from the injection point is consistent with the observed increase of the cement content of grouted sands.     

Utilization of Silica Fume to Maximize the Filler and Pozzolanic Effects of Stabilized Soil with Cement

Silica fume is identified as a pozzolan and supplementary cementitious material that can utilize to improve the mechanical properties of stabilized soil with cement. Silica fume wherein mixes with cemented soil in a proper dosage, it is susceptible to induce pozzolanic effect in cemented soil due to its fineness and high content of SiO₂ and Al₂O₃. The pozzolanic effect is vital to ensure ongoing strength of stabilized soil with cement. Up to now, stabilization of clay with cement and silica fume is not completely explored. This paper investigates: (i) the capability of utilizing the silica fume as a supplementary material for cement to maximize the filler and pozzolanic effects of compacted and stabilized soil (ii) the mechanical properties of compacted and stabilized clay with various proportions of cement and silica fume. For this purpose, a total of 120 untreated and stabilized soil admixtures were prepared by replacing ordinary Portland cement with silica fume. The influence of partial replacement of cement with silica fume on the bearing capacity, shear and compressive strength of compacted and stabilized soil was investigated. To achieve such aims, the stabilized soil specimens were examined in laboratory under direct shear, unconfined compression and California bearing ratio tests. Based on the findings of this paper the 28-day UCS of the stabilized soil with 2% partial substitution of cement with silica fume is almost 3.5-fold greater than that of the untreated. It was found that the optimum mix design for the stabilized soil is 6% cement and 2% silica fume. In conclusion, a notable discovery is that the partial substitution of cement with 2% silica fume in the optimum mix design significantly refined the pore spaces as a result of pozzolanic activity and filler effect of silica fume.     

石灰-水泥复合土增强机制研究

利用比强度方法分析水泥土及石灰水泥土无侧限抗压强度,对石灰水泥土的增强机制进行了研究。采用内蒙古河套粉质黏土拌制水泥土及石灰水泥土试件,水泥土和石灰水泥土掺入不同量的氢氧化钙、碳酸钙和水泥,并按标准养护28 d,进行单轴抗压试验,测得水泥土及石灰水泥土的无侧限抗压强度值。研究结果表明：石灰水泥土和水泥土中存在化学胶凝和物理填充两大类作用。其中石灰水泥土中存在水化作用、硬凝作用、离子交换及团粒化作用和复合作用等4类化学增强作用;水化作用是水泥土和石灰水泥土强度增长的最主要来源;熟石灰能够抑制水化作用。     

含砂量对水泥土强度影响的试验研究

天然软土尤其三角洲地区的淤泥或淤泥质黏土常含砂,以含细砂或粉细砂为主,系统研究水泥土强度与含砂量的关系,为水泥土性能改良、强度设计及水泥土搅拌法施工提供直接依据。选取珠江三角洲两处典型的淤泥、淤泥质黏土,按天然含水率配制试验用土,掺加不同含量的细砂制成含砂水泥土试件,养护到不同龄期,对其进行无侧限抗压强度试验,得到了水泥土强度与含砂量及其他关联影响因素关系的变化规律。主要结论是：细砂颗粒在水泥土中起到了细骨料的作用,有利于提高水泥土强度;考虑水泥土的含砂量、水土质量比、水泥掺入比和实际水灰比等因素,得到了含砂淤泥水泥土强度估算公式;在不含砂淤泥水泥土中掺入2 %干细砂时其强度约提高25 %,掺入15 %~25 %干细砂则可提高40 %~60 %。     

Behavior of cemented sands—I. Testing

This paper is accompanied by a study on constitutive modelling issues of cemented sands. The concentration here is on experimental issues related to the triaxial testing of cemented sands. A preliminary investigation is performed aiming to identify potential effects of specimen size and slenderness on the stress–strain–strength characteristics of cemented sands. A comprehensive experimental study follows where clean sand specimens, as well as specimens with 2, 4 and 6 per cent cement content, are tested. The aim of the study is to examine the effects of cement content and confinement on the shear strength, stiffness, softening and dilation characteristics of cemented sand. © 1997 John Wiley & Sons, Ltd.     

用似水灰比对水泥土无侧限抗压强度的预测

对以连云港地区的海相软土为原料的水泥土进行了一系列物理、强度试验,分析了含水量、水泥用量和龄期对水泥土强度的影响,提出了似水灰比的概念用于水泥土强度的预测。采用提出的水泥土强度预测公式,根据某一似水灰比、龄期28 d某种的水泥土室内试验强度,可以预测不同含水量、不同水泥用量和不同龄期的水泥土室内试验强度。通过比较分析发现,得出水泥土强度预测公式可以很好地应用于其他研究者已经发表的水泥土试验数据,进一步验证了所提出的强度预测公式的有效性。     

掺绿砂改良膨胀土室内试验研究

绿砂高额的处理费用与其具有的再利用潜力相比,使绿砂再利用的研究得到重视,尤其对公路路基改良具有很大的利用潜力。针对膨胀土路基的胀缩问题,围绕绿砂及膨胀土-绿砂混合物进行一系列室内土工试验,探讨绿砂作为公路膨胀土路基改良剂的可行性。在不同含水率及不同配比条件下,对绿砂以及绿砂改良后膨胀土的基本物理性质、击实特性、力学特性等进行室内对比试验分析。分析结果表明,绿砂改良膨胀土试样的强度主要取决于试样的含水率、掺砂率;随着掺砂率的增加,塑性指数逐渐降低,最佳含水率也随之减小,最大干密度增大的幅度变化很小,无侧限抗压强度先降低而后提高,其后又降低。     

水泥偏高岭土复合稳定粉砂土渗透特性试验研究

水泥稳定粉砂土抗渗性能受粉砂土自身渗透性能、水泥用量、水灰比等因素影响显著,如何在提升其抗渗性能的同时降低水泥用量是提升工程经济效益的关键。通过开展不同水泥偏高岭土掺比、初始用水量、水泥偏高岭土总掺量以及养护龄期条件下的室内渗透试验,研究了上述因素对水泥偏高岭土复合稳定粉砂土抗渗性能的影响规律,探讨了上述因素及无侧限抗压强度与渗透系数之间的经验关系。结果表明：水泥与偏高岭土掺比为5:1时,水泥偏高岭土复合稳定粉砂土抗渗性能最佳,且该掺比不随水泥偏高岭土总掺量的改变而变化;水泥偏高岭土复合稳定粉砂土渗透系数随初始用水量增加呈非线性递增,随水泥偏高岭土总掺量增加和养护龄期发展呈先快后慢降低;基于试验结果归纳提出了4个关于初始用水量、水泥偏高岭土总掺量、养护龄期和无侧限抗压强度的水泥偏高岭土复合稳定粉砂土渗透系数经验模型。研究成果可为水泥稳定粉砂土抗渗性能提升提供理论参考与借鉴。     

Stabilization of Expansive Soil with Cement Kiln Dust and RBI Grade 81 at Subgrade Level

The present research work deals with an expansive high plastic clayey soil with cement kiln dust (CKD) and stabilizer (RBI Grade 81). The physical and engineering properties of soil are plasticity, compaction, unconfined compressive strength (UCS), consolidation and California bearing ratio (CBR) of the clayey soil and clay treated with CKD and stabilizer were determined. Soil chemistry was examined before and after treatment using scanning electron microscope (SEM) and elemental dispersive spectrometer. The clay mixed with CKD, CKD and RBI Grade 81 was found that optimum contents are 10 % (CKD), 15 % CKD with 4 % RBI Grade 81, respectively. The result indicates that CKD alone will decrease maximum dry density and increase optimum moisture content. CKD with RBI Grade 81 slightly increases maximum dry density and decreases optimum moisture content. UCS increased with CKD alone and CKD with RBI Grade 81 from 88.3 to 976 kN/m², respectively. CBR values were increased by the addition of CKD, CKD with RBI Grade 81 from 1.65 to 21.7 %. With the curing time of 3, 14 and 28 days, UCS and CBR values were increased due to pozzolanic reaction from cementations material. The treated soil has considerable reduction in compression index. SEM images clearly indicate the formation of CSH and CAH gel.     

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.     

Stabilization of desert sands using municipal solid waste incinerator ash

This paper presents experimental results on the use of incinerator ash in stabilizing desert sands for possible use in geotechnical engineering applications. The incinerator ash was added in percentages of 2, 4, 8, 10 and 12%, by dry weight of sand. Laboratory tests such as compaction, unconfined compression, shear box and hydraulic conductivity were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in unconfined compressive strength and shear strength parameters (c and φ). Thus, incinerator ash can be used to improve the shear strength characteristics of desert sands. The permeability of the sand–incinerator ash mixture was relatively low.     

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.     

The behaviour of an artificially cemented sandy gravel

The major section of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. This deposit consists of gravely sand to sandy gravel with some cobbles and is dominantly cemented by carbonaceous materials. In order to understand the mechanical behaviour of this soil, a series of undrained triaxial compression tests and unconfined compression tests were performed on uncemented and artificially cemented samples. Portland cement type I was used as the cementation agent for preparing artificially cemented samples. Uncemented samples and lightly cemented samples (1.5% cement) tested at high confining pressure showed contractive behaviour accompanied with positive excess pore water pressure and a barrelling failure mode. However, cemented samples and uncemented samples tested at low confining pressure (25 and 50 kN/m²) showed dilative behaviour accompanied with negative excess pore water pressure. Shear zones were formed in these samples and a clear peak in excess pore water pressure and stress ratio against strain could be observed. Test results showed that the limiting stress ratio surface for cemented samples is curved and expands as the cementation and density increase. Unconfined compression strength of cemented samples increases with increases in cementation and density as well.     

硫酸侵蚀下水泥土的电阻率特性研究

通过室内试验模拟了水泥土试块受不同浓度硫酸（H2SO4）溶液侵蚀的过程,采用电阻率法研究了电阻率与各参数、无侧限抗压强度之间的关系。结果表明,受H2SO4侵蚀后,水泥土电阻率、孔隙水电阻率、水泥土抗压强度均随着溶液浓度的增加而减小,而水泥土的结构因子和重度均随着溶液浓度的增加而增加,水泥土抗压强度与水泥土电阻率成正比。在试验的基础上,考虑侵蚀因素对水泥土电阻率的影响,通过对Archie法则进行修正,得到了H2SO4侵蚀下水泥土电阻率模型。通过对无侧限抗压强度试验结果的分析,并结合试块表观变化,提出了利用电阻率来评价侵蚀程度的方法。     

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.     

Effects of soil pulverization quality on lime stabilization of an expansive clay

Lime stabilization is an effective way of stabilizing expansive clays, which cause significant environmental problems both as earth and foundation materials. There are considerable environmental benefits in using the in situ lime-stabilized expansive soils in the construction of road pavements, fill or foundations instead of importing valuable granular materials. However, due to high plastic nature of these clays, achieving appropriate pulverization in field applications is a difficult task. This paper presents the results of a laboratory investigation to determine the effects of soil pulverization quality on lime stabilization of a local expansive clay. Effect of mellowing the soil–lime mixtures for 24 h was also studied to find out whether this would compensate for poor pulverization. The clay studied had swelling pressures varying between 300 and 500 kN/m² and free swell potential as high as 19%. In this study, 3, 6 and 9% lime by dry weight were used for lime-stabilized samples. Unconfined compression strength, failure strain and Secant Elasticity Modulus values were measured through unconfined compression strength testing. The results of the study showed that lime stabilization improved plasticity, workability, compressive strength, elastic moduli and swelling and compressibility behavior of the expansive clay. While mellowing did not have a definite effect on the measured strength and moduli values, soil pulverization quality considerably affected the unconfined compression strength and Secant Elasticity Modulus values. The higher the percentage passing No. 4 sieve, the higher the effectiveness of lime treatment. Based on the data obtained in this study, two original equations were derived to assign Secant Elasticity Modulus based on unconfined compression strength, for different soil pulverization qualities. Microfabric investigations conducted by Environmental Scanning Electron Microscope and Mercury Intrusion Porosimetry exposed the effect of lime stabilization on fabric, porosity and pore size distributions. The results of the study clearly demonstrated that if enough time and effort were not given to soil pulverization process in lime stabilization works in field applications, lower performance and therefore increased environmental problems should be expected.     

Laboratory Characterization of Cemented Tailings Paste Containing Crushed Waste Rocks for Improved Compressive Strength Development

This paper aims at investigating some physical and mechanical characteristics of cemented tailings paste incorporating different amounts of crushed waste rocks (hereinafter called paste aggregate fill, PAF) for underground stope filling. Different mixture formulations were prepared with three classes of crushed waste rocks (or aggregate) grain size, namely 0/10, 0/15 and 0/20 mm. The amount of crushed waste rocks in the PAF mixtures ranges from 10 to 50% by volume (% v/v) (or 8–45% by mass, %m) of dry mill tailings and crushed waste rocks. The results show that the addition of crushed waste rocks in cemented tailings paste mixtures allows a significant unconfined compressive strength (UCS) development after 28 and 90 days of curing. The highest UCS was obtained from the mixtures containing 50% v/v of crushed waste rocks of class of size 0/15 mm. The PAF mixtures with the coarser crushed waste rocks (class of size of 0/20 mm) exhibit some particles segregation.     

普硅水泥和矿渣水泥加固滨海软土效果对比分析

采用室内无侧限抗压强度试验,证明了矿渣硅酸盐水泥和普通硅酸盐水泥在加固滨海软土的效果方面存在较大的差异。通过X射线衍射分析,对两种水泥加固软土效果差异的内在机制和原因进行了探讨。结果显示,水泥土的强度与水泥水化产物的生成量之间存在一致性,矿渣水泥加固土可生成更多的水化产物,并能够限制软土中可溶盐对水泥土的影响。