Geotechnical Behavior of Recycled Copper Slag-Cement-Treated Singapore Marine Clay

Copper slag is a by-product obtained from production of copper metal. As copper slag contains silica and alumina, it may exhibit pozzolanic property, and hence it may be re-use in ground improvement applications as a partial replacement of cement. Present study evaluates systematically the possible pozzolanic property of copper slag as well as studies the effect of copper slag on engineering properties of cement-treated clay. X-rays diffraction method was employed to assess the possible pozzolanic property of copper slag. Effect of copper slag on engineering properties (i.e. compressive strength and compressibility) of cement-treated clay was studied with samples prepared with constant water content and workability. The test results showed that with sufficient curing time and at constant workability, the compressive strength of cement-treated clay was found to be increased with increasing amount of copper slag at high cement content but the compressive strength remained the same with increasing amount of copper slag at low cement content. Compressibility of cement-treated clay was found to be unchanged with increasing amount of copper slag. It was concluded that copper slag can be used as partial replacement of cement in treating soft marine clay.     

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.     

Heulandite and mordenite-rich tuffs from Greece: a potential source for pozzolanic materials

The microcystalline mass of the Pliocene tuffs of Santorini and Polyegos islands, in the South Aegean Volcanic Arc, Greece, is very rich in zeolite minerals, more specifically heulandite type 3, i.e. clinoptilolite, and mordenite. In Santorini, clinoptilolite is the dominant authigenic phase and it was formed in a semi-closed system, by the activity of interstitial water within the volcaniclastic sequence. In Polyegos, mordenite dominates and it was formed by hydrothermal alteration of pyroclastics. Experiments described in this work show that the presence of the zeolite minerals has created materials with excellent pozzolanic properties. Tuffs from the two areas were calcined at 760 °C and for 12 h and then mixed with lime in a constant ratio of 1 part lime to 3 parts calcined tuff. As a result, the free lime content of the lime-calcined tuff mixtures was reduced from 25% to 2.05% (Santorini) and 1.31 % (Polyegos). Compressive strength tests were carried out on concrete cubes made with 100% Portland cement as the cementitious agent, to be used as reference cubes, and concrete cubes in which the Portland cement has been replaced in 4% and 7% proportions by the calcined tuff as pozzolans. The free lime estimation and the compressive strength tests were all carried out in accordance with the British Standards Institution (BS 4550 and BS 1881) guidelines. Early stage measurements of the compressive strength showed that pozzolan-bearing concrete cubes reached values as high as 140% of the reference cubes. The pozzolan-bearing concrete cubes maintained this superior strength throughout the entire one year period of the experiments. After 360 days, they finally maintained 107% of the compressive strength of the reference cubes.     

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。     

Effect of Natural Zeolite and Cement Additive on the Strength of Sand

It is widely known and well emphasized that the cemented sand is one of economic and environmental topics in soil stabilization. In some instances, a blend of sand, cement and other materials such as fiber, glass, nano particle and zeolite can commercially be available and effectively used in soil stabilization especially in road construction. In regard to zeolite, its influence and effectiveness on the properties of cemented sands systems has not been completely explored. Hence, in this study, based on an experimental program, it has been tried to investigate the potential of a zeolite stabilizer known as additive material to improve the properties of cemented sands. A total number of 216 unconfined compression tests were carried out on cured samples in 7, 28 and 90 days. Results show unconfined compression strength and failure properties improvements of cement sand specimens when cement replaced by zeolite at optimum proportions of 30 % after 28 days due to pozzolanic reaction. The rate of strength improvement is approximately 20–78 and 20–60 % for 28 and 90 days curing times respectively. The efficiency of using zeolite has been enhanced by increasing the cement content and porosity of the compacted mixture. The replacement of cement by natural zeolite led to an increase of the pH after 14 days. Chemical oxygen demand (COD) tests demonstrate that the materials with the zeolite mixture reveal stronger adsorptive capacity of COD in compare to cemented mixture. Scanning electron microscope images show that adding zeolite in cemented sand changes the microstructure (filling large porosity and pozzolanic reaction) that results in increasing strength.     

Pozzolanic fly ash as a hydraulic barrier in land fills

The liner plays an important role in controlling migration of contaminants present in the leachate in waste containment systems such as land fills and impoundments. Although questions have been raised about the performance of clay liners, they are increasingly used singly or as double liners in disposal sites. Though the clay liners possess many advantages such as low permeability and large attenuative capacity, they also possess high shrinkage potential and hence can crack under unsaturated conditions causing instability and increase in leakage rates. Further, the permeability of the clay linear can increase due to clay–pollutant interaction. This study examines the potential of pozzolanic fly ash as a hydraulic barrier in land fill. The behaviour of three different types of fly ashes, showing a range of physical properties and chemical composition from three different sources are reported in the study. Geotechnical properties, needed to evaluate the use of fly ashes as barriers, such as shrinkage, compaction, permeability, consolidation and strength characteristics are reported. The results show that fly ashes possess low shrinkage and hence do not crack. Compacted fly ashes undergo very little volume changes. They also show that pozzolanic fly ashes develop good strength properties with time. Pozzolanic fly ashes containing sufficient lime develop strength even without addition of lime. Non-pozzolanic fly ashes do not develop strength even on addition of lime. Fly ashes generally consist of silt size particles and consequently possess high permeability. However, pozzolanic fly ashes with lime exhibit low permeability on curing because of the formation of gelatinous compounds which block the pores. Thus, pozzolanic fly ashes appear to be promising for construction of liners to contain alkaline leachate.     

氯盐对水泥固化土应力应变特性影响分析

以人工制备的方法配制了不同氯盐含量的土样,并掺入不同含量的普通硅酸盐水泥对其进行固化处理。采用无侧限抗压强度试验对氯盐含量对水泥固化土的应力应变特征影响规律进行分析。试验结果表明:随着氯盐含量的增加,水泥固化土的无侧限抗压强度和变形模量降低,破坏应变随之增大,应力-应变关系曲线由脆性破坏向塑性破坏转化; 增加水泥用量可以减缓氯盐对水泥固化土的不良影响; 但水泥固化土变形模量与无侧限抗压强度的比值与氯盐含盐量大小无明显关系。     

Influence of grain size gradation of sand impurities on strength behaviour of cement-treated clay

In nature, soils are often composed of varying amounts of clay, silt and sand. Variation of the percentage of these compositions can affect the final strength of the soils when stabilised with cement. In this study, focus was placed on clayey soils with different gradation of sand impurities up to 40% in mass. An extensive study of such clayey soils treated with cement was investigated. For the results, it is noted that water:cement ratio was a major influence of strength development of cement-treated clayey soils. In contrast, the soil:cement ratio was found to have minor effects on the strength development. The presence of sand impurities has a significant reduction on the strength development of the cement-treated clayey soil mixture due to more free water available for hydration. The use of free-water:cement ratio is adopted which was shown to be capable of adjusting for such change in amount of free water and water holding capacity of the clay which is determined with Atterberg’s liquid limit tests. The effects of gradation (fine, coarse and well-graded) of the sand impurities were found to affect strength development minimally, owing to similarities in their liquid limits when mixed with clay. Ordinary Portland cement (OPC)-treated clayey soils produced a more rapid gain in strength but lower final strength at 28 days of curing as compared with Portland blast furnace cement (PBFC). This is found to be persistent for different gradation of sand impurities. A linear correlation can be established based on the log of the unconfined compressive strengths developed at different curing age, with slopes of these linear trends found to be similar for PBFC and OPC-treated clayey soil specimens. Finally, a strength prediction model comprising of these findings is developed. The parameters adopted in this model coincide with values proposed by past studies, thereby validating the robustness of the model. The practical benefits from this study offer a quality control scheme to forecast long-term performance of cement-treated clayey soils as well as optimise cement dosage in cement stabilisation to produce a more cost-effective and less environmental-invasive usage of the technology in geotechnical applications.

     

上海黏性土与水泥混合后强度增长特性试验研究

对于使用水泥与上海黏性土进行混合加固的土体,其强度增长特性与水泥含量、加固土的初期pH值、养护时间有关。以上海4类黏土为研究对象,对加固土的强度增长特性进行了试验研究;探讨了加固土的养护时间、水泥含量、初期pH等与加固土强度的关系。试验结果表明,当上海黏土中水泥含量或者加固土的初期pH值大于某一临界值时,水泥加固土的强度将迅速增加,对于上海黏土,该临界pH值为11.7,对应的水泥含量为17%～20%。但当水泥含量达到一定值后,它对土体的pH值的影响开始变小,而且水泥土的强度趋于稳定的时间变长。     

Influence of mix uniformity on the induced solidification of dredged marine clay

Ground improvement with soil solidification has been widely applied and has proven to be an effective pre-treatment of soft soil deposits. The solidification procedure usually involves addition and thorough mixing of hydraulic binders with in situ soils, consequently transforming the soft materials into a stronger and stiffer stratum for load bearing. Much has been done on the binder’s effectiveness and resulting enhanced properties of the soils, but not as much has been reported of the factors governing in situ mixing efficiency in producing uniform mixtures. While advancement in machinery and computerization of operations have significantly improved soil mixing, individual factors contributing to the process can be further examined to refine the effectiveness. This paper describes a series of laboratory tests, mainly unconfined compressive strength tests complemented with X-ray computer tomography, conducted on cement-stabilized dredged Kawasaki clay of different uniformities. A number of factors affecting uniformity were examined, namely the water/cement (WC) ratios, number of cement layers in the initial state as well as the number of mixing cycles adopted. Test specimens were prepared based on a systematic combination of these factors to enable a comprehensive cross-analysis of the results. It was found that the clay’s initial consistency was markedly altered by cement addition, which resulted in either enhanced or reduced workability of the mixture. While increased mixing vigor could apparently overcome poor distribution of binder in the mixture, the resulting strength remained very much affected by the WC ratio, suggesting dependency of the mixture’s overall uniformity on a combination of the factors.     

聚丙烯纤维和水泥对粘性土强度的影响及机理研究

选取聚丙烯纤维和水泥作为加固材料,在室内试验的基础上,研究了单独的纤维和水泥对粘性土强度的影响及其的综合作用,分析了它们的作用机理。试验中,3种不同百分比(0.05%,0.15%和0.25%素土重)的纤维和两种不同百分比的(5%和8%素土重)水泥分别掺入到粘土试样中,配制了12组试样,进行了无侧限抗压试验。试验结果表明,纤维和水泥均能够提高土体的强度,纤维的加入改善了水泥土样的脆性破坏模式;纤维水泥土样的强度远远高于相同掺量下的纯纤维土和纯水泥的强度,甚至高于它们的强度之和。运用扫描电镜(SEM)从微观层次上分析了纤维和水泥加固粘性土的力学机理,发现纤维表面与土介质之间的粘结力和摩擦力对加固效果有直接影响。     

云母影响水泥软黏土强度的试验研究

软黏土具有压缩性强、承载能力低的特点,实际工程中多用水泥作为固化剂对软黏土进行加固。云母是软黏土中较为常见的一种片状矿物,其含量和颗粒大小会影响水泥加固后的软黏土即水泥软黏土的强度。通过无侧限抗压强度试验和直接剪切试验研究云母含量及目数对水泥软黏土抗压强度及抗剪强度的影响,提出了云母含量、目数与水泥软黏土抗压强度、抗剪强度指标值之间的关系。试验中云母目数设定为10,20,40,80目共4个梯度,云母含量设定为0%、8%、16%、24%、32%共5个梯度。试验结果表明,云母含量的增加以及云母目数的减小会导致水泥软黏土无侧限抗压强度和抗剪强度的降低,且其对无侧限抗压强度的不利影响更为显著。含10目32%云母的水泥软黏土的强度减少量最大,此时无侧限抗压强度为0.33 MPa,是不含云母水泥软黏土的25.5%;黏聚力为76.5 kPa,比不含云母时减少了12.24 kPa;内摩擦角由不含云母时的23.71°降低至21.77°。云母自身的片状形态及其对水泥水解水化作用、离子交换作用的阻碍是造成水泥软黏土强度降低的主要原因。     

城市河道淤泥特性及改良试验初探

以南京内秦淮河疏浚淤泥为例,通过土工试验、XRD和X射线荧光光谱试验等方法,研究了城市河道淤泥的物理性质、矿物成分、化学成分等特性。试验结果显示:秦淮河淤泥粘粒含量低、有机质含量极高,矿物成分主要有石英和少量粘土矿物等。为了实现淤泥的资源化处理,运用水泥、石灰无机固化材料对淤泥进行固化改良试验及改性土无侧限抗压强度试验,结果表明随着水泥掺量增加,水泥固化土由塑性破坏向脆性破坏过渡,破坏应变在1.8%~2.2%,而石灰固化土均表现为脆性破坏,且破坏应变小于水泥土,为1%左右。水泥固化土28d强度为670kPa,固化效果优于石灰,但略低于处理一般软土的固化土强度。研究结果对处置城市河道淤泥有一定参考价值。     

An approach to characterisation of multi-scale pore geometry and correlation with moisture storage and transport coefficients in cement-stabilised soils

An experimental approach to the characterisation of the complex, multi-scale pore geometry in cement-stabilised soils is presented, in which the pore size distribution inclusively spans at least six orders of magnitude from ~3 nm up to >3 mm. These most likely result from the combined effects of granular inter-particle packing, clay/cement clothing and bridging effects, cement hydration and clay/cement pozzolanic reactions, and alteration of larger pore geometries as a result of solid mass mobilisation and transport following capillary wetting/drying regimes. Experimental data are presented and were obtained through a combination of X-ray computed tomography, mercury intrusion porosimetry and N₂ physisorption supported by ‘wet mode’ environmental scanning electron microscopy. Data strongly suggest that macropore/capillary pore size distribution, mean pore size, sorptivity and transport coefficients are a function of particle size distribution (when compaction energy is constant). Mesopore size distribution, which dominates hygric sorption/desorption behaviour, occurs within the clay/cement matrix and also appears to be strongly influenced by the particle size distribution of the granular phase. All other factors being equal, manipulation of granular particle size distribution can be used to engineer the hygric (vapour) and capillary (liquid) potentials and also the fluid transport coefficients of these materials.     

水泥稳定再生沥青路面/红土混合物用于软土改良的效果评估

评估了水泥稳定再生沥青路面（RAP）/边缘红土混合物作为碎石桩骨料替代传统采石场骨料的潜力,研究了混合材料在不同RAP置换率和有效约束压力下的不排水剪切强度变化。RAP置换率分别为10%、30%和50%（按干重计）,普通硅酸盐水泥含量分别为1%和3%。很明显,RAP的置换增加了大颗粒,同时减少了细小颗粒,因此增加了压实度。在低于先期固结压力的有效应力下,RAP−土颗粒混合物表现出与孔隙压力降低相关的应变硬化性能。当RAP置换率增加时,水泥稳定的RAP−土颗粒混合物应力−应变曲线的应变软化性能减弱。胶结作用提高了黏聚力,而内摩擦角未产生明显的变化。水泥稳定的RAP−土颗粒混合物的强度和刚度主要取决于胶结强度和RAP置换率。抗剪强度随着非稳定和水泥稳定的RAP−土颗粒混合物的RAP置换率增加而提高,而水泥稳定的RAP−土颗粒混合物的刚度由于沥青黏结剂的高能量吸收而下降。     

改良土静强度试验及结果分析

本文研究了粉粘土及粘土在加入不同配比的石灰、水泥、粉煤灰时的静三轴强度的变化规律 ,通过分析比较 ,得出了不同掺合料的掺合比与强度的关系 ,为设计、施工及养护提供可靠的依据 ,以满足高速铁路基床底层及基床以下路堤填料的技术要求.     

江苏丹徒前黄水泥配料粘土矿床矿石工业利用试验研究

系统了介绍了生产水泥的石灰石，下蜀粘土，硫酸渣三组分配料的工艺性能试验成果，提供了一套有关采用现代水泥工艺生产出符合ＡＳＴＭ的Ｉ型水泥的试验数据，同时，其试验成果可代同类矿床勘探借鉴。     

红粘土地区水泥土强度的试验研究

红粘土是亚热带气候条件下形成的一种特殊土质。含有红粘土的地基多具有上硬下软的特点,下部红粘土为天然地基软弱下卧层。采用深层搅拌法处理,可充分发挥上部硬塑红粘土的作用,形成复合地基。通过试验得到了水泥红粘土的基本力学参数。在对试验结果进行回归分析后,给出了水泥土强度的影响因素及其与强度的关系,以及不同水泥掺量、龄期水泥土之间的强度推算公式。     

On the behavior of the cured electroosmotic chemical treated clay

Followed the proposed ECT procedure that was the injection of 0.75 M CaCl₂ solution for 72 h, then 1.5 M KOH solution for 48 h, then sodium silicate solution for 72 h and then deionized water for 168 h, the clay strength can be improved from anode to cathode entirely. To further improve the clay strength, curing the sample for different periods and applying electric field over the sample were studied. The cone resistance, water content, pH value, Ca²⁺ concentration and the XRD pattern were tested or analyzed in each test. Results show that injection of deionized water was a key phase to produce a full improvement of the treated clay, which cannot be replaced by the application of an electric field only and without injecting water. Curing the treated clay after injecting deionized water can yield a higher clay strength in the cathode area significantly due to pozzolanic reaction but produce a lower clay strength in the anode area because the formed NaOH decomposed the gel structure of the sodium silicate solution. To obtain a better strength after injection of deionized water for 168 h, the treated clay had to be cured for about 28 days, along with a dry anode compartment.

     

外加剂对桂林含有机质水泥红黏土力学性质影响的试验研究

红黏土是碳酸盐岩在湿热环境下经过风化作用形成的一种特殊性土,孔隙大、含水量高,而其结构性强且存在上硬下软的成层分布特征,上部为坚硬、硬塑状态,下部为软塑、流塑状态。水泥搅拌法因其有加固效果好、造价低、工期短、污染小等特点被广泛应用在处理软弱红黏土。近年来环境和工程地质条件不断恶化,造成大面积红黏土被有机质污染,严重影响地基的强度,但是研究表明合理使用外加剂可以改善被有机质污染红黏土的物理力学性质。本文从外加剂掺量和类型对抗剪强度、压缩系数、无侧限抗压强度等方面进行室内试验研究,得出外掺剂种类和掺量与它们之间的关系。结果表明:其间的相关性较好。