Quick lime-gypsum interactions in stabilized soil bases for concrete highways

Lime stabilization of clayey soils is very common throughout many parts of the world. Typically if heaving is observed after quick lime (CaO) stabilization, then one may think that insufficient lime and/or poor slaking and mixing techniques may be the root of the problem. Actually, there are several other reasons for the observed heaving. One explanation is that the lime may have been hard burnt, thus rendering the lime inactive until months later. Another explanation is due to the interaction of the quick lime with gypsum (CaSO₄ . 2 H₂O) in the soil to be stabilized.One may conclude that lime, Type I portland cement, or Class C fly ash stabilization of high gypsum bearing soils would at best produce poor results because of the possibility of expansion due to the formation of ettringite.     

Suppression of Sulfate Attack on a Stabilized Soil

A soil containing calcium sulfates was stabilized at 40°C, with ample moisture, by cementitious mixtures producing a range of calcium hydroxide upon hydration. Maximum expansion occurred when the stabilizing agent was lime, whereas a mixture containing portland cement, Class C fly ash, and an amorphous silica stopped the expansion. X-ray diffraction peak width and scanning electron microscopy (SEM) based image analysis showed that maximum expansion correlated with crystallization of colloidal ettringite. Ettringite was seen by SEM within an hour of mixing the soil with lime. Colloidal ettringite was not observed when portland cement, with supplementary cementing materials, was used for stabilization.     

矿渣-粉煤灰地聚物固化淤泥力学性能和路用性能研究

为实现河底淤泥的资源化处置,常采用水泥等胶凝材料固化淤泥提高承载力作为路基材料。传统固化材料能耗大、碳排放量高。为开发可持续性固化材料,本研究采用矿渣-粉煤灰二元地聚物固化淤泥,研究其力学性能及路用性能。通过研究Si/Al摩尔比、Na/Al摩尔比对地聚物凝结时间和抗压强度的影响规律,确定地聚物配合比设计。依据优化配合比固化淤泥,研究地聚物掺量、养护龄期对固化淤泥力学性能的影响,并对固化淤泥进行水稳性、加州承载比、干缩和温缩试验,以评估其路用性能;采用扫描电镜和X射线衍射等试验方法对固化淤泥进行微观分析,揭示其固化机制。试验结果表明,矿渣-粉煤灰基地聚物地质聚合产物为无定形地聚物凝胶、水化硅酸钙、水化铝酸钙等,增强了土颗粒之间的胶结并且填充了孔隙,提高了固化淤泥的力学性能和路用性能。研究结果为地聚物固化淤泥土工程应用提供了实验基础。     

Swell-shrink and strength behaviors of lime and cement stabilized expansive organic clays

Organic soils are mostly composed of decayed plant matter and weathered rock material. Often, these soils are known for their inferior engineering behavior including very high compressibility and low shear strength. In order to improve these properties, organic soils are, by and large, modified with calcium based stabilizers such as lime, cement and fly ash. However, transportation agencies in the United States have mentioned that the anticipated improvements were never achieved or the improvement obtained disappeared quickly with time. Therefore, a research study was initiated to understand the behavioral mechanisms of lime and cement stabilized organic soils. Eight natural expansive soils bearing different organic contents (varying between 2 and 6%) were selected for the present investigation. First, optimum dosages of lime and cement were determined for the selected soils. Then treated and untreated (control) specimens were prepared to study their physical and engineering behaviors of the soil specimens at varied curing periods. There is a drastic increase in unconfined compressive strength (UCS) of lime and cement treated specimens until 28 days of curing. Beyond which, a negligible improvement in UCS property was recorded for lime treated specimens and a slight decrease in UCS for cement treated soils was noticed. This reduction in strength for cement treated specimens could be attributed to the reduction in pH concentration with curing as well as the formation of inorganic calcium humic acid at this stage.     

粉煤灰贝利特水泥用作土壤固化材

以高含水粘性土为对象，研究了活性贝利特水泥的固化处理效果及固化土的强度发展特性。结果表明，这种水泥具有较普通水泥低的固化土强度发展速率，是一种良好的迟硬性土壤固化材，特别适用于高含水软弱粘性土的整体固化后再二次开挖的施工场合。     

高性能土壤固化剂的制备与性能

为适应滨州地区土壤盐渍土的土质要求,提高固化土壤的强度,以石灰、石膏为主要原料,通过正交试验的方法研究了影响滨州地区土壤的因素,确定了高性能土壤固化剂的最佳配比.对固化剂稳定土与石灰、水泥等稳定土进行对比试验,并初步分析了其固化机理.结果表明:固化剂稳定土的强度高于石灰、水泥等稳定土,且水稳与冻稳系数均大于0.90.     

Influence of gluconate,lignosulfonate or glucose on the C3A hydration in the presence of gypsum with or without lime

The influence of gluconate, lignosulfonate or glucose at 0.1–0.3% dosages on the C₃A hydration in the presence of gypsum with or without lime has been examined. In the presence of lime all the admixtures at 0.3% dosage stabilize ettringite and retard its conversion to monosulfate; only 0.3% glucose retards gypsum consumption and ettringite production. In the absence of lime stabilization of ettringite by admixtures at 0.3% addition appears to be much less effective; no admixture is able to retard the ettringite production or gypsum disappearance. At 0.1% addition, the influence of admixtures seems to be negligible except when glucose is used in the presence of lime: in this case, the conversion of ettringite into monosulfate is retarded.     

单轴压缩固化泥炭土的弹塑性损伤模型试验研究

为了研究固化泥炭土的力学性能,将机制砂作为填充材料,水泥和磷石膏作为胶结材料,针对昆明泥炭土开展了一系列固化试验。根据固化土体的无侧限抗压强度试验和单轴循环加-卸载试验,讨论了泥炭土在不同水泥掺量和磷石膏掺量下的固化效果。基于损伤理论和应变等效性假设,建立了单轴压缩状态下固化泥炭土的弹塑性损伤模型。研究结果表明:固化泥炭土抗压强度随水泥掺量的增加而增大,同时随着磷石膏掺量的增加,强度增长速率表现为先增大后减小的趋势。固化泥炭土的应力-应变滞回曲线呈下部不闭合的新月形,且在塑性开始和接近破坏阶段不闭合区域面积较大,说明这两个阶段产生较大的能量损耗。最后,考虑水泥掺量和磷石膏掺量的影响,根据试验结果采用曲线拟合的方法,得到了固化泥炭土弹塑性损伤本构模型的各项参数。     

利用窑灰生产高效土壤稳定水泥的研究

研究了用纯窑灰、掺ＣａＳｏ４－ＣａＦ２复合矿经剂的窑灰煅烧熟料与适量石膏混合配制的窑灰水泥稳定土的力学性能,并探讨了煅烧温度和石膏掺量对窑灰水泥稳定土强度的影响。结果表明,窑灰水泥对土壤的稳定效果显著优于普通水泥。用于稳定土的水泥其技术指标与普通水泥有很大差异,可允许水泥中含有一定数量的ｆ－ＣａＯ,ＳＯ和碱含量。     

Mineralogical and microtextural changes associated with lime stabilization of marine clays from eastern Canada

Four clayey soils displaying the range of properties of the marine clays from eastern Canada were selected for this study. They were treated with different amounts of quick, hydrated and agricultural lime, at different water contents. The mineralogical and the microtextural aspects involved in lime stabilization of these clays as well as the mechanisms responsible for gain of strength have been investigated. In soils stabilized with quick and hydrated lime at a water content near the liquid limit, (1) the clay minerals appear to be the main targets for chemical attack, (2) reaction products of CASH and CSH types are formed, affecting the pore size distribution, and (3) the gains in strength are related to the progressive formation of these new phases.     

工业废渣复合胶凝材料泡沫轻质土制备及性能

为促进工业废渣资源化循环利用,制备工业废渣复合再生胶凝材料(RC)及相应泡沫轻质土。利用松香树脂类、蛋白类两种发泡剂和表面活性剂经高速剪切混溶制备复合类发泡剂,通过不同发泡剂种类、搅拌转速和搅拌时间下的RC泡沫土流动度、湿密度和抗压强度优选最佳工艺,不同湿密度和龄期下抗压强度对比RC泡沫土和水泥泡沫土力学性能,干缩和冻融循环试验对比RC泡沫土和水泥泡沫土耐久性,借助XRD分析RC泡沫土成分。结果表明,复合类发泡剂融合了松香树脂类发泡剂稳定性好和蛋白类发泡剂发泡倍数高的优势,RC泡沫土制备过程最佳搅拌转速为200 r/min,搅拌时间为2 min。RC和水泥两种泡沫土流动度均满足规范要求,初期抗压强度相当;随着龄期增加,RC泡沫土强度增长幅度高于水泥泡沫土,28 d和56 d龄期时RC泡沫土强度为水泥泡沫土强度的1.21倍和1.35倍。相同条件下RC泡沫土抗干缩和抗冻融性能优于水泥泡沫土。RC水化产物中增加了钙矾石,且水化硅酸钙含量高于水泥水化产物。     

碱激发地质聚合物固化软土的研究进展

软土地基处理是工程界公认的有较高风险的工程领域,传统软土固化中大量使用硅酸盐水泥,不仅消耗自然资源,还会对环境产生不良影响,使用环境友好型碱激发地质聚合物替代传统硅酸盐水泥越来越受到国内外学者的重视。论文基于国内外已有研究成果,从碱激发地质聚合物固化土发展历史、碱激发地质聚合物种类、碱激发地质聚合物反应机理、碱激发地质聚合物固化土力学特性和各类性能等方面进行研究进展的综述分析,重点谈论地质聚合物处理软土的力学特性,并对不同碱激发地质聚合物在软土地基加固中抗渗性能、抗冻融性能、抗腐蚀性能等进行分析,对碱激发地质聚合物在软土地基加固中的应用进行系统梳理和展望,以期引导和提升碱激发地质聚合物在软土地基加固中的应用,实现我国地基加固可持续发展。     

石灰-水泥-粉煤灰改性磷石膏对水泥物理性能的影响研究

采用石灰、水泥、粉煤灰对磷石膏进行改性处理,测定了改性磷石膏中硫酸根的溶解性能,对比了原状磷石膏与改性磷石膏对水泥物理性能的影响,并结合X射线衍射（XRD）和扫描电镜（SEM）分析了改性前后磷石膏对水泥不同龄期水化产物的影响。结果表明：随着石灰掺量的增加改性磷石膏的pH逐渐增大,当石灰掺量为4%（质量分数）时磷石膏的pH达到12.22,此时磷石膏中的可溶性磷、氟转化成难溶性的磷酸盐、氟化钙;随着水泥和粉煤灰掺量的增加,改性磷石膏的溶解性能呈现降低趋势。当石灰掺量为4%、水泥掺量为10%（质量分数）、粉煤灰掺量为10%（质量分数）时,改性磷石膏经过7 d养护在水中浸泡8 h所得滤液中硫酸根的质量浓度为0.30 g/L,比未改性磷石膏在水中浸泡8 h所得滤液中硫酸根的质量浓度降低了81.8%。与掺加未改性磷石膏的水泥浆体相比,掺加改性磷石膏的水泥浆体的水灰质量比由0.41降低到0.38、初凝时间和终凝时间分别缩短34.6%和27.2%、28 d抗压强度提高21.1%。石灰、水泥、粉煤灰改性处理磷石膏后,生成的水化硅酸钙和钙矾石等水硬性产物包裹在石膏颗粒表面,使硫酸根在水中的溶出速率降低,减少了对水泥中铝酸三钙的影响,使得硬化体内部结构变得致密、力学性能显著提高。     

水化产物钙矾石在软土地基加固中的增强作用

通常加固软土地基是使用第一的水泥用为固化剂。研究与实践表明,由于软土中孔隙量很高,采用工业废石膏与水泥配合加固软土,其中产生的水化产物钙矾石可以高效率的填充孔隙,对固化工的强度增长有显著的增强作用,从而得固人疆土工与单纯用水泥加固相比有大幅度的提高,钙矾石形成过程中,液相ＣａＯ,ＯＨ浓度决定钙矾石的形貌和膨胀性能,不同土样对ＣａＯ,ＯＨ消耗量不同,导致固化上液相中ＣａＨ,ＯＨ,浓度不同,因而,对不     

Influence of character of clinker on the early hydration process and rheological property of cement paste

Influence of characteristics of alite and interstitial phase in five Japanese clinkers on early hydration of cement and rheological properties of fresh cement paste was investigated. The yield value of fresh cement paste increased rapidly at first due to the formation of ettringite, later due to the formation of C-S-H until it reached setting. The setting time was strongly influenced by alite intense hydration, which started when Ca(OH)₂ saturation ratio in the liquid phase approached a maximum value. That position mainly was dependent upon the free CaO content in clinker and was partially dependent upon water soluble alkali content in clinker and hydraulic reactivity of alite itself. Changing the burning degree of clinker and the hydraulic modulus of raw mix, and intergrinding of clinker with quick lime are practical ways to reduce slump loss and to set an optimum setting time for concrete. All of these methods are related to free lime content for which optimum amounts are varied with burning degree of clinker and quick lime.     

水泥/玄武岩纤维复合固化剂分别对泥炭质土静力特性的影响

为了研究单掺水泥及复合固化剂(由水泥、生玄武岩纤维、石灰和生石膏组成)对滇池地区高原湖相泥炭质土静力特性的影响,对不同掺量水平下的水泥改良土和复合固化剂改良土进行静三轴不固结不排水剪切试验,研究了两种改良土的三轴应力应变关系与抗剪强度变化规律。研究表明:随掺量的增加,两种改良土的主应力差峰值强度增大;当掺入复合固化剂的质量分数为15%时,相比5%、10%两个掺量水平,复合固化剂改良土的三轴应力应变关系由“应变硬化型”转变为“应变软化型”,且抗剪强度显著提升;当改良土的内部结构发生破坏时,水泥改良土的抗剪强度有较大损失,而复合固化剂改良土仍保持较高的抗剪强度。     

Mechanism of expansion associated with ettringite formation

Ettringite formation in portland cement concretes can be responsible for both deleterious and beneficial phenomena. Several hypotheses on the mechanism of expansion associated with ettringite formation are reviewed, and a new hypothesis is proposed. Experimental evidence is presented in support of the new hypothesis. It is shown that in the presence of lime the nature of ettringite formed is colloidal, and not long lath-like crystals. It is proposed that colloidal ettringite is able to attract a large number of water molecules which cause interparticle repulsion, thus causing an overall expansion of the system.     

A dimensional description of the unconfined compressive strength of artificially cemented fine-grained soils

Abstract

This study aims at establishing a universal predictive model for the unconfined compressive strength (UCS) of artificially cemented fine-grained soils. Model development, its validation and calibration were carried out using a comprehensive database gathered from the research literature. The dimensional analysis concept was successfully extended to the soil–cement UCS problem, thereby leading to a practical dimensional model capable of simulating the UCS as a function of the blend’s index properties — that is, cement content, specific surface area, curing time, and the compaction state parameters (including water content and dry density). The predictive capability of the proposed model was examined and further validated using routine statistical tests, as well as conventional fit-measure indices which resulted in R²?>?0.95 and NRMSE < 5%. A sensitivity analysis was also carried out to quantify the relative impacts of cement content, curing time and soil plasticity on the UCS. The higher the soil plasticity, the higher the positive sensitivity to cement content, implying that soils of higher plasticity would require higher cement contents for stabilization. On the contrary, the higher the soil plasticity, the lower the positive sensitivity to curing time, indicating a more effective cement hydration in soils of lower plasticity. Finally, an explicit calibration procedure, involving a total of three UCS measurements for three recommended soil–cement mix designs, was proposed and validated, thus allowing for the proposed model to be implemented with confidence for predictive purposes, preliminary design assessments and/or soil–cement optimization studies.     

固硫灰渣水化浆体中钙矾石稳定性

流化床燃煤固硫灰渣(简称固硫灰渣)含有大量烧粘土质矿物,还含有较多f-CaO和无水石膏,因此固硫灰渣水化浆体中含有一定量的钙矾石.用X射线衍射和化学分析方法研究钙矾石含量随水化龄期的变化规律,并以此反映其稳定性.结果显示:在标准养护条件下,钙矾石含量从1 d至28 d水化龄期呈逐渐增长趋势,但在28 d龄期后则显著减少.研究表明固硫灰渣水化浆体中的钙矾石是不稳定的,在一定龄期后会出现明显分解现象.     

Fluoride removal capacity of cement paste

The objectives of this study are to assess the feasibility of using the cement paste as an alternative agent for fluoride removal and to investigate fluoride removal capacity of the cement paste. Initially, screening experiments were conducted to evaluate Ca-bearing materials (cement, cement paste, lime). The cement paste was competitive to lime, common fluoride removal agent. Various Ca-bearing hydrates such as portlandite, calcium silicate hydrate (CSH), and ettringite in the cement paste were identified to remove fluoride by precipitating CaF₂ and/or adsorbing F^– ions. In the batch slurry experiments using cement paste and lime simultaneously, 50–67% of lime can be substituted by cement paste to satisfy fluoride effluent limitation of 15 mg/L. Fluoride removal reactions in cement paste slurries were strongly affected by pH, and an optimal pH for the cement paste slurries exists between 7.0 and 11.5. From the result of the column experiment to observe the successive fluoride removal capacity of cement paste, the real hydrofluoric acid wastewater concentration of 1150 mg/L immediately reduced to the level of less than 15 mg/L. These results indicate that the cement paste generally has advantageous characteristics as an economical and viable substitute for lime to remove fluoride.