Influence of Ca(OH)2 on Strength of Low Proportional Cemented Soil

Laboratory experimental research is performed by strengthing three different types of soil with low proportional cement to test the unconfined compressive strength of such cemented soil under different dosages of Ca(OH)2 and the different ages. The variation rules and causes of the unconfined compressive strength of these three types of age-different cemented soil with increasing the dosage of Ca(OH)2 are analyzed. The results shows that the intensity of red clay cement improves most obviously with Ca(OH)2 content increased, followed by silty clay, and sand is the weakest. The reason is that the fineness of the soil affect the strength of the cement greatly. The finer the soil, the more clay minerals in soil. The increase in Ca(OH)2 content promotes the ion exchange and the occurrence of volcanic ash, which improves the strength of cemented soil. Among the three types of soil in this experiment, the fineness of red clay particles is the best, so the intensity of red clay cement improves most obviously with Ca(OH)2 content increased.     

STUDY ON PRODUCING A RED CEMENT WITH RED CLAY AS A RAW MATERIAL

This paper studies the production of a red cement with red clay as a raw material.It is produced by a direct calcine method using red clay as a coloring agent and red slag as an additive agent,then mixing it with white cement.     

Mechanical and Chloride Diffusion Behavior of Kaolinite Clay Modified Cement-Based Material

The effects of kaolinite clay on the microstructure (pore structure, internal structure) and mechanical properties (workability, early-age and long-term flexural strength, chloride diffusion property) of the cementitious composites were tested. It is shown that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. As a result, it is suggested that the kaolinite clay would act as both filler and accelerator of cement hydration. Compared with the control specimen, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90 curing ages, respectively. The 28-day flexural strength increased slightly. It is observed that the clay modified cement mortar has lower chloride diffusion coefficient values compared to the plain mortar, and the 28-day DCl of cement mortar decreased by 53.03% with 5% clay. Compared with the controlled sample, the increase in compressive strength and the reduction in chloride diffusion coefficient of the concrete with 5% clay addition is 28.4% and 18.87% respectively. The chloride diffusion coefficient of concrete decreases with the amount of clay addition exponentially. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete.     

Influence of Pile Driving on Soil Resistance in Clay

With the increase of platform size, pipe piles with super large diameter and deep penetration are increasingly used in practice. In order to make accurate prediction of pile drivability, it is essential to evaluate the change of the soil properties under pile driving exactly, and it is the premise to predict the pile bearing capacity after pile driving. In order to learn more about the change of clay properties during pile driving, analysis on the pile driving record of 36 piles in Bohai area is conducted. According to the analysis, the soil resistance in the clay layers decreases as the depth increases, and it is very different from that in the sand layer. The FEM method is used to discuss the mechanism of this decrease. The back analysis is carried out to get more information. The results show that the clay properties are affected by the dynamic effect. The undrained shear strength of clay approximately decreases with the increase of thickness of the layer linearly. At the same time, a prediction is conducted based on results, and the result is closer to the pile driving record than that calculated by method normally used today.     

再生混凝土抗碳化性能试验研究及理论分析

通过快速碳化试验,以再生骨料掺量、水灰比、水泥用量、原始混凝土强度和矿物掺合料为影响因素,对再生混凝土的碳化性能进行研究。试验结果表明：再生混凝土的碳化深度随水灰比、再生骨料掺量的增加而减小,随原始混凝土强度的增大和水泥用量的增加而增大,适量添加矿物掺和料能降低再生混凝土的碳化深度,提升其抗碳化性能。在已有的普通混凝土碳化模型研究基础上,结合本试验和中国其他学者的试验数据,建立了再生混凝土碳化深度预测模型,模型预测结果与试验值吻合较好。     

The effect of grass roots on shear strength variations with moisture content

This study investigated the relationship between vane shear strength and moisture content for root-free and root-permeated sandy clay loam and clay soils, with a view to determining the effect of root density on the relationship. The results indicate that for both root-free and root-permeated soils, shear strength increases exponentially with decreasing moisture content. As expected, increases in root density considerably increase the magnitude of shear strength at all moisture contents investigated. In all cases, roots increased the magnitude of the shear strength of the clay soils much more than the sandy clay loam soils. Relative to the root-free soils, the roots increased shear strength in both soils by at least 500%. In the clay soils a higher relative increase of up to 850% is achieved in samples with a root density of 1.80 g cm⁻³. Also, relative to root-free soils, root permeated soils were found to exhibit a higher rate of shear strength increase with soil drying. This, it is suggested, is because of the higher shading effect of the shoots of the root-permeated samples leading to a slower rate of soil drying than in the root-free samples.     

派酶-土壤-黑麦草根系复合体抗剪强度试验研究

摘要: 提出一种派酶-土壤-黑麦草根系复合体,即在含派酶土壤中加入黑麦草根系。探讨了不同含酶量及含根量下复合体的抗剪强度,并在具有不同含酶量的土壤中种植黑麦草种子。由试验结果可知：黑麦草种子可以在含派酶土壤中存活并生长;在考察范围内,复合体的抗剪强度随含酶量的增加而增大,φ值随含酶量的Jiao Xin增加先增大后减小。     

柠檬酸对铬污染不同质地土壤萃取与淋洗的研究

为了探索柠檬酸对不同质地铬（Cr）污染土壤的萃取条件及淋洗效率,进行了不同浓度、固液比、时间的萃取和土柱淋洗试验。结果表明：柠檬酸对铬污染不同质地土壤修复效果为：砂土＞壤土＞粘土;砂土、壤土所需萃取条件较小,粘土较大。不同萃取条件对铬污染土壤萃取效果影响较大：柠檬酸浓度为0.05 mol/L时,3种土壤萃取效果较好。3种质地土壤最佳固液比和时间分别为：粘土1/14,32 h;砂土1/6,16 h;壤土1/10,28 h。通过柠檬酸淋洗,粘土在10~20 cm土层发生再吸附,砂土与壤土在30~40 cm土层发生再吸附。本研究为铬污染土壤修复了提供技术支持。     

复合土钉支护转角有利影响范围

基坑复合土钉墙转角处有明显的空间效应,受力变形较小,对支护结构有利,但不清楚转角定量的有利影响范围,目前设计中仍按照与基坑中部一样保守设计,为在此范围内降低土钉用量,避免保守设计,对水泥土搅拌桩复合土钉支护结构建立了全尺寸整体三维有限元模型,这种模型包含基坑的转角,能考虑基坑的空间效应,通过建立接触面单元,能考虑土体和搅拌桩、土体和土钉的相互作用,量化分析了基坑转角对支护结构受力和变形的有利影响范围,计算结果表明,基坑转角对开挖面水平位移、地表沉降、坑底隆起、土钉轴力的有利影响范围分别约为1.3、1、1、1.2倍的开挖深度。经与实际工程现场实测值对比,验证了该模型分析结果的可靠性,同时分析结果优于平面二维和局部三维有限元模型,结论为复合土钉支护结构的优化设计和安全施工提供了理论依据和研究方法。     

污水环境对水泥土力学性能的影响试验研究

由于多数地下水泥土工程直接与地下腐蚀性介质环境接触,必将导致水泥土材料的逐步劣化甚至失效破坏。以某市区工地附近明渠排放的污水作为侵蚀性介质,制作了不同水泥掺量的水泥土试件,通过对比试验,研究了污水环境和清水环境下不同水泥掺量、不同龄期的水泥土抗压强度和抗剪强度。结果表明,在污水或清水环境下,相同水泥掺量水泥土30 d龄期的抗压强度几乎相等,随着龄期的增加其抗压强度均逐步增大,但污水环境下其抗压强度增长的幅度明显小于清水环境,90 d后清水环境的水泥土抗压强度不再增长,而污水环境的抗压强度开始降低;污水环境和清水环境下的水泥土内摩擦角和黏聚力随龄期、水泥掺量的增加均逐步增大,污水环境下龄期90 d后的内摩擦角和黏聚力均开始降低。     

河道淤泥气泡混合轻质土剪切流变特性及模型

利用剪切流变试验对以水泥为固化剂的河道淤泥气泡混合轻质土的流变特性进行了试验研究。试验结果表明,经固化处理的河道淤泥气泡混合轻质土在荷载作用下具有类似于硬粘性土的流变特征。剪切流变可以分为3个阶段：在剪应力水平较低时,剪切流变曲线呈衰减稳定型;随着剪应力水平的提高,剪切流变曲线呈非稳定的等速型;当剪应力水平增大到一定程度时,剪切流变曲线呈加速型。河道淤泥气泡混合轻质土的流变性随着混合轻质土强度的提高而降低。根据试验所呈现的剪切流变规律,可以发现河道淤泥气泡混合轻质土的剪切流变符合七元件黏弹塑性剪切流变模型,模型能够比较好地描述河道淤泥混合轻质土在各种剪应力水平下的衰减、等速以及加速流变过程。     

Experiments on influence of slurry kinds on mechanicalbehavior of interface between gravel and concrete

The mechanical behavior and mechanism of the interface between structure and coarse grained soil are investigated through simple shear tests on the conditions of bentonite slurry, clay slurry and without slurry, respectively. The results indicate that different kinds of slurry have important influence on shear strength. Compared with the interface without slurry, the shear strength with bentonite slurry reduces by 45% approximately, significantly more than clay slurry which reduces by 10%. The value of the friction angle with bentonite slurry is about 60% of that with clay slurry. Shear displacement increases as upright stress increases when reaches its failure states at the same height, and shear displacement with bentonite slurry is smaller than that with clay slurry when with the same upright stress and height. The upright displacement with bentonite slurry is greater than that with clay slurry under the same upright stress. In addition, shear dilatation is apparent under the low normal stress when without slurry. Otherwise, it appears as shear contraction.     

Effects of colloidal lignite on the stability of soil aggregates

As an alternative to the simple physical mixing of crushed lignite as an organic additive in soil restoration this study examined the potential benefits to structural stabilisation that might result from prior dispersion of the humic acid content in an alkaline aqueous slurry. When added to an unstable sandy loam topsoil, a clay loam subsoil and pure bentonite clay at a mixing ratio of 1:25, large increases in water stable aggregation were observed. However, additions at the same mixing ratio had no effect on the stability of two sandy mine waste materials or pulverised fuel ash. Because of the high application rates needed to alter aggregate stability, colloidal lignite was not considered to be useful as a substitute for more effective water soluble polymers. However, dispersion in aqueous ammonia prior to application could be used as a means of adsorbing humic materials on to clay mineral surfaces during the construction of synthetic topsoils.     

On Elasto-Plastic Consolidation Settlement of Saturated Soft Clay

The specific properties of soft clay are characterized by higher void ratio, lower permeability and higher compressibility, the consolidation settlement of soft clay is affected by the imposed stress history, the stress paths, the consolidation pressure and the soil properties. In this paper, the porous media theory based on the mixture theory was applied in the study on the consolidation settlement of soft clay, which was more rigorous than the conventional consolidation settlement theory and the coupling between soil and water can be taken into account in the analysis.     

Application of the pumping coal gangue cemented filling materials in roadside

To take full advantage of gangue for roadside supporting in coal mines physical properties of coal gangue are tested. The collapsed slump uniaxial compression strength and initial setting time of gangue binder backfill material with different water-cement ratios and admixture contents are researched. Experimental studies show that the best ratio of water cement coarse aggregate fine aggregate and admixtures is 1:2:5.6:1.6:0.02 for site pumping of roadside packing support. The collapsed slump 28 d uniaxial compression strength and initial setting time of gangue binder backfill material are 210 mm 20.8 MPa 224 min respectively under such ratio. It could satisfy the requirement of site supporting and the initial setting time of binder backfill material under such ratio is about 50 min shorter in site than indoor.     

水泥稳定三峡库区风化砂回弹模量试验及模型评估

以水泥稳定三峡库区风化砂的回弹模量值为研究对象,在风化砂中分别掺入3%、5%、7%、9%的水泥制作试样,然后各自养护7、14、21、28、35、56、70 d,开展室内回弹模量试验。试验结果表明:掺水泥能显著提高风化砂的回弹模量值。在相同的养护龄期下,随着水泥掺量的增加,回弹模量值逐渐增大,增长的幅度先大后小,二者呈现良好的对数函数关系;在相同的水泥掺量下,随着养护龄期的增长,回弹模量值也逐渐呈线性增大,且在最初养护的28 d内,回弹模量值的增长占整个测试期内的95%左右。通过回归分析,分别建立了水泥掺量与回弹模量值之间、养护龄期与回弹模量值之间的数学模型,再通过补充试验,进一步验证了所建数学模型的正确性及精确度。     

Preliminary Discussion on Mixing Design of Porous Concrete

Porous concrete is an eco-concrete with high porosity and high strength,whose application was restricted to some extent,because there is lack of appropriate and unitive mixing design method.According to the features of porous concrete,proportion design idea of porous concrete whose major design parameter was porosity and strength was satisfied by changing variety of cementing material and aggregate size.The design method of porous concrete was that the raw materials were selected according to design requirement at first,secondly,aggregate dosage per unit volume of porous concrete was calculated,thirdly,dosage of cementing material was calculated by apparent density of aggregate and porosity of design requirement,finally,cement dosage of the unit physical volume and water dosage were calculated by water cement ratio deter mined by requirement of forming process.The test result indicated that this mixing design method of porous concrete was reliable and feasible.     

不同质地土壤下缓释尿素与常规尿素配施对水稻产量及其生长发育的影响

以早熟晚粳南粳44为材料,分别在2种质地的土壤上,研究270 kg hm^-2施氮条件下, 2种缓释尿素(硫包衣尿素SCU)单施及与常规尿素(PU)按2种不同比例混配一次性基施对水稻产量及其生长发育的影响。结果表明,与PU分施相比,SCU2单施与SCU1+PU(1∶1)、SCU1+PU(2∶1)及SCU2+PU(2∶1)配施处理水稻产量、生长中后期氮素吸收量、氮素吸收利用率与偏生产力、干物质积累以及茎鞘可用性糖颖花比均显著提高,抽穗后期根系α-萘胺氧化量维持较高水平,下降幅度小;产量、氮素吸收量、氮肥吸收利用率、偏生产力及干物质积累量在黏土上略高于在沙土上;抽穗期与抽穗后10 d根系α-萘胺氧化量在黏土上低于在沙土上,抽穗后20 d、30 d在两种土上差异不大。SCU单施及与PU配施基本上能满足水稻生长需求,SCU1与PU配施效果明显优于单施;SCU2单施效果最佳,SCU2+PU(2∶1)次之,SCU2+PU(1∶1)效果不显著。     

Effects of Stone Powder on Wet Packing Density of Cement and Performances of Concrete

The amount of limestone powder, which is a by product of manufactured fine aggregate, is larger and larger with the increase of manufactured fine aggregate. Environment will be severely polluted if the powder is improperly used. The effects of limestone powder on workability, compressive strength, and impermeability of concrete were studied when cement is substituted for the mass proportion of 0, 10, 15, 20 percent with it. The results show that the performances of concrete are better improved when the percentage of limestone powder is about 10 percent. The wet packing density of mixture of limestone powder and cement was measured, and it shows that the degree of density was biggest when limestone powder is 10 percent. This shows that the best mixing proportion of limestone powder and cement may be determined through measuring the change of compactness of mixture of limestone powder and cement.     

Study on mechanical behaviors of interface with cemented soil slurry between gravel and concrete by simple shear tests

The mechanical behaviors of the interface between coarse-grained soil and concrete are investigated by simple shear tests under conditions of cemented soil slurry (clay mixed with cement grout). The results show that the relation curve between shear stress and shear strain appears stress-strain softening and shear dilatation is significant. The point of peak strength and the position when the shear dilatation occurs are related to normal stress. In addition, shear dilatation occurs before the shear stress reaches peak value. In shear failure state, with the same height, the shear displacement increases as the normal stress increases. While with the same normal stress and at the same height, the shear displacement increases as the concrete content increases. A particle flow model of simple shear test between interface between coarse-grained soil and concrete is constructed by PFC (particle flow code). The disturbed height of the sample and the main influence factors are determined by analyzing the laws of particle motion at different heights inside the sample. The PFC results show disturbed height of the sample is related to maximum particle diameter of the soil, normal stress and roughness of the interface (with or without slurry) etc. In terms of the coarse-grained soil, the shear displacement is significant in the area which is close to the interface and about 3-4 times of the maximum particle diameter, and informed the obvious shear band. Further, the thickness of the interface can be regarded as the value.