Stabilization of Expansive Soil by Lime and Fly Ash

An experimental program was undertaken to study the individual and admixed effects of lime and fly ash on the geotechnical characteristics of expansive soil.Lime and fly ash were added to the expansive soil at 4%-6% and 40%-50% by dry weight of soil,respectively.Testing specimens were determined and examined in chemical composition,grain size distribution,consistency limits,compaction,CBR,free swell and swell capacity.The effect of lime and fly ash addition on reducing the swelling potential of an expansive soil is presented.It is revealed that a change of expansive soil texture takes place when lime and fly ash are mixed with expansive soil.Plastic limit increases by mixing lime and liquid limit decreases by mixing fly ash,which decreases plasticity index.As the amount of lime and fly ash is increased,there are an apparent reduction in maximum dry density,free swell and swelling capacity under 50 kPa pressure,and a corresponding increase in the percentage of coarse particles,optimum moisture content and CBR value.Based on the results,it can be concluded that the expansive soil can be successfully stabilized by lime and fly ash.

Alkali desilicated coal fly ash as substitute of bauxite in lime-soda sintering process for aluminum production

By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process.Ca/(SiO2+TiO2)molar ratio,and NaO/Al2O3 molar ratio,sintering time,and temperature were the most significant parameters impacting on the aluminum extraction efficiency.The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2)molar ratio of 2.0,NaO/Al2O3 molar ratio of 0.98,and sintering at 1 200 ℃for 60 min.Astandard industrial dissolution method was used under conditions of caustic ratio(αk=n(NaO)/n(Al2O3)of 2.0,Al2O3 concentration of 50 g/L,sodium hydroxide concentration(Nk)of 60.78 g/L,Na2CO3 concentration of 10 g/L,temperature of 85℃, and dissolution duration of 10 min.The final aluminum extraction efficiency was 90%.

Technological and Environmental Behavior of Coal Fly Ash in Lime-Based Materials

Coal fly ash is considered an industrial by-product derived from coal combustion in thermal power plant. It is one of the most complex anthropogenic materials. Its improper disposal has become an environmental concern and resulted in a waste of recoverable resources. The aim of this paper is to study the physico-chemical characteristics of binders based on coal fly ash and lime in order to develop an eco-cement. The various characterization tests carried out are X-ray fluorescence, X-ray diffraction, compressive strengths, thermophysical properties and setting time. X-ray fluorescence and X-ray diffraction were used to determine the chemical composition and phases of fly ash, lime and binders. This allowed us to see that the chemical composition of fly ash is similar to that of cement. Compressive strengths of mortars containing 20%, 40%, 60% and 80% of fly ash have shown that fly ash has a long-term positive effect which might be related to a pozzolanic activity. The L3 binder consisting of 60% of coal fly ash and 40% lime has a higher compressive strength than the others. The binder setting start time is greater than that of cement but shorter than that of lime. The study of the thermophysical properties of the L3 binder shows that it has a higher thermal resistance than cement mortar. Moreover, it heats up less quickly because of its low effusivity compared to that of the latter. This analysis highlighted the principal characteristics that must be taken into account to use coal fly correctly in lime-based materials.

Influence Factor Analysis on Strength of Lime-Fly Ash Loess

Lime-fly ash loess is composed of fly ash, lime and loess. It is a new material in subgrade backfill. Main factors to influence the strength of lime-fly ash loess are age, amount of fly ash and lime, ratio of fly ash to lime (1:K), and moisture content. In order to observe the effect of each factor influencing the strength of lime-fly ash loess and find out the relationship between each other, this paper adopted orthogonal test design to conduct unconfined compression tests. The result shows that 90d strength can be considered to calculate the strength of lime-fly ash loess in practice. And the most important factor to influence the 90d strength of lime-fly ash loess is the amount of fly ash and lime, the second is moisture content, and then is the ratio of fly ash to lime (1:K). These achievements are significant to the design and application of lime-fly ash loess in subgrade construction of loess areas.

Comparative Characteristics of Hydrated Lime with Fine Sewage Sludge Ash (FSSA) and Coal Fly Ash (CFA)

The disposal of waste has become an environmental issue due to the limited available landfilling space. This paper aims to compare the characteristics of hydrated lime with fine sewage sludge ash (FSSA) and coal fly ash (CFA). Multiple techniques, X-ray fluorescence (XRF), X-ray diffraction (XRD), the Fourier transform infrared (FTIR), compressive strengths, thermophysical properties, and setting time were used to assess the physicochemical characteristics of the lime-based materials. X-ray fluorescence and X-ray diffraction were used to determine the chemical composition and phases of ashes, lime and binders. The results showed that the chemical composition of ashes is similar to that of cement. Besides glass, the main minerals identified in CFA and FSSA are quartz (SiO2) and anhydrite (CaSO4). Moreover, calcium aluminium oxide (Ca3Al2O6) was detected for CFA and phosphorus calcium silicate (Ca2SiO4-Ca3(PO4)2) for FSSA and minor phases were detected for both. FTIR measurements were carried out to characterize the inorganics components of different samples. Compressive strengths of mortars with different formulations have shown that both have a long-term positive effect which might be related to a pozzolanic activity. For the CFA the L3 binder consisting of 60% of coal fly ash and 40% lime has a higher compressive strength than the others while for the FSSA the L4 binder consisting of 80% fine ash and 20% lime has a higher compressive strength than the others. Both binders setting start times are greater than that of cement but shorter than that of lime. The study of the thermophysical properties of binders shows that they have a higher thermal resistance than cement mortar. Moreover, binders heat up less quickly because of their low effusivity compared to cement. Lime-based materials system could be a promising option to both relieve the waste disposal pressure and provide a potential sustainable construction material.

Liming Characteristics of a High-Calcium Dry Flue Gas Desulfurization By-Product and a Class-C Fly Ash

Due to coal’s availability and low cost, coal combustion continues to be the United States’ primary energy source. However, coal combustion produces large quantities of waste material. Some coal combustion by-products (CCBs) have chemical and physical characteristics that make them potentially useful as soil amendments. The objectives of this study were to characterize a relatively new, high-calcium dry flue gas desulfurization (DFGD) by-product and compare its agronomic liming potential to a Class-C fly ash (FA) and reagent-grade calcium carbonate (CaCO3). Calcium car-bonate equivalence (CCE), degree of fineness (DOF), and effective neutralizing value (ENV) for each CCB were determined using standard methods. The CCBs and CaCO3 were also incubated with an acidic (~4.5) clay sub-soil at application rates equiva-lent to 0, 0.5, 1, and 2 times the soil’s lime requirement and compared to an una-mended control. Soil pH was then measured periodically during a 40-day incubation. The ENV of 79.4% for the DFGD by-product and 57.3% for the FA were comparable to those of commercially available liming materials, but were significantly lower (P < 0.05) than that of reagent-grade CaCO3. After 40 days of incubation at the 0.5× ap-plication rate, both CCBs raised the pH of the clay soil to only 5.0, while the CaCO3 raised the pH to 6.5. After 40 days at the 1× rate, all three materials had raised the soil pH to between 6.5 and 7.0, although the FA increased the soil pH more slowly than did the other two materials. At the 2× rate, both CCBs increased the soil pH to between 7.5 and 8.0, while the CaCO3 increased the soil pH to only 7.0. Both CCBs appear to be useful as soil liming materials, although care should be taken to avoid over-application, as this may make the soil too alkaline for optimum plant growth.

石灰粉煤灰固化石油污染土的渗透特性及其工程再利用探讨

固化改性污染土的渗透性是推进污染土工程再利用需关注的指标之一。借助GDS环境土柔性壁渗透测试仪,优选兼具吸附与固化作用的石灰粉煤灰作为固化材料,以围压、渗透压、污染强度为变量参数,以固化前后石油污染土的渗透系数及土中残余含油量为指标,结合X射线衍射和扫描电镜,厘清渗透性演变及污染物迁移扩散规律,并以此探讨固化石油污染土的工程再利用性。研究结果表明:固化产物对石油分子的吸附作用弱化了石油斥水性,增加了渗透的有效通道,固化石油污染土的渗透系数较未固化石油污染的提高了两个数量级;土体干密度增大会增强对石油的吸附截流作用,围压、渗透压及污染水平的增大会增强土颗粒间相互作用,均引起石油污染土及固化石油污染土渗透性降低。固化作用可有效控制渗透作用下石油污染物的迁移扩散,各部位的残余含油量均非常接近于初始含油量,避免了渗透污染风险。结合石灰粉煤灰固化石油污染土力学特性(抗压强度为1280.10 kPa,抗剪强度为388.88 kPa)、渗透性(渗透系数为4.28×10^(−6)~7.39×10^(−6) cm/s)及迁移控制性(波动率为0.30%~4.90%),石灰粉煤灰固化石油污染土可考虑用于有防渗要求的路基类填筑材料进行工程再利用。

基于离散元的废旧二灰碎石与土混合料承载比细观力学特性研究

建筑垃圾应用于路基过程中,其材料承载力对道路服役性能具有重要影响。为评价建筑垃圾用于路基填料时的细观力学特性,该文利用离散元软件对不同含石率的废旧二灰碎石与土混合料进行承载比试验,并利用离散元法揭示强度形成机理。结果表明:混合料的承载比随含石率增大不断增加,含石率为80%时达到最大值。在离散元模拟承载比试验中,空隙率随着二灰碎石土的含石量的增大先降低后增大,当含石率为80%时混合料的空隙率最小,此时能达到最佳的承载效果。随着含石率的逐渐增大,废旧二灰碎石之间的颗粒相互嵌挤,形成骨架结构,因此能够有效承担来自贯入杆的荷载。

煤气化灰渣在水泥与熟石灰中的应用

对煤气化灰渣(CGFA)在普通硅酸盐水泥(OPC)和熟石灰中的潜在用途及再利用价值进行探讨,包括与聚羧酸高效减水剂的相容性、熟石灰-CGFA体系和OPC-CGFA体系的力学性能。基于X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)研究了2种体系的反应机理和反应产物。结果表明,CGFA的反应性可以通过研磨显著提高,而具有低火山灰反应性的未研磨CGFA可以部分替代混凝土中的天然河砂。熟石灰和OPC可以提供碱性环境以促进地质聚合反应的发生。2种体系试样的28 d最大抗压强度分别达到14.43 MPa(CGFA质量分数60.0%)和35.79 MPa(CGFA质量分数35.7%)。混合物特征峰的强度随着质量分数的增加而降低,表明Ca(OH)_(2)与CGFA提供的SiO_(2)发生反应,形成C―S―H。

固化电解金属锰渣在软土路基填筑中的应用研究

电解金属锰渣可以作为软土路基填筑的材料,但电解金属锰渣的含水率过高,且具有一定的毒性。研究通过对电解金属锰渣进行固化,探究了其固化的机理,然后设计了固化电解金属锰渣路用性能验证实验,分析其在软土路基填筑中的应用效果。实验结果表明,加入固化剂固化后最大干密度增加,最优含水率降低。CBR值特性实验中,在掺量为6%时,添加水泥的CBR值增长了54.22%,添加石灰的CBR值增长了62%;在石灰掺量为3%时,CBR值达到为14%。电解锰渣回弹模量实验中,加入固化剂后,回弹模量增长。实验结果说明了固化后的电解金属锰渣具有较好的路用性能,研究将对提高软土路基填筑质量、降低工程风险具有重要的实践意义。

不同含盐量的石灰粉煤灰固化石油污染土抗剪性能试验研究

为研究石油污染土的剪切特性,以不同含盐量的固化石油污染滨海盐渍土为研究对象,对石灰、粉煤灰稳定碎石固化石油污染土进行力学强度性能试验与微观分析。研究结果表明:随含盐量的增大,石灰粉煤灰固化石油污染土(简称污染土)的黏聚力和内摩擦角均先增大后减小;含盐量相同,污染土的黏聚力和内摩擦角均随石灰、粉煤灰质量分数的增大而先增大后减小,随石油质量分数的增大而减小;含盐量为1%,石油、粉煤灰、石灰质量分数分别为4%、20%、10%时,污染土的黏聚力和内摩擦角最大;污染土的应力-应变曲线在不同石灰、粉煤灰、石油质量分数下均先增大后减小并趋于稳定;不同含盐量下,污染土的微观结构特征和宏观土样抗剪强度参数的变化规律一致。

氢氟酸废液协同含铅飞灰无害化处理研究

为了使碱性含铅飞灰达到危险废物填埋限值,使用氢氟酸废液作为含铅飞灰的稳定化药剂,在探究出氢氟酸废液的最佳用量后,以石灰作为pH调节剂,水泥做固化剂,可使总铅、无机氟化物的浸出毒性低于《危险废物填埋污染控制标准》(GB19598-2019)要求。结果表明,氢氟酸废液的加入量为10%(质量分数),石灰的加入量为4%(质量分数)调节pH在7.10~7.15之间时稳定化效果显著,最优结果为pH=7.15,总铅质量浓度0.145 mg/L,无机氟化物质量浓度3.7 mg/L。

石灰粉煤灰稳定再生料基层级配设计与力学性能研究

为了获取再生砖混料用于道路基层混合料的适宜掺量,研究了石灰粉煤灰稳定再生料基层的配合比与力学性能间的作用关系,即:首先进行混合料级配设计,通过分级填充振捣试验确定粗集料比例;然后以室内击实试验确定细集料占比,同时以压碎值和无侧限抗压强度确定再生料的掺配方式;最后进行不同再生料掺量和石灰粉煤灰稳定类无机结合料剂量下的无侧限抗压强度和抗压回弹模量试验,确定其力学性能的变化规律。研究结果表明:3档粗集料比例为19∶22∶17,细集料占比为42.5%时密实程度最好;以再生料方式替换的砖混比为4∶6,粒径替换顺序为先10~20 mm、再5~10 mm;7 d和28 d抗压强度最大值分别达到1.347、2.756 MPa,且二者随再生料掺量的增加其衰减趋势相似;在高再生料掺量下采用20%~25%石灰粉煤灰剂量的180 d抗压回弹模量效果较好;7 d无侧限抗压强度与180 d抗压回弹模量的拟合度较高。该石灰粉煤灰稳定再生料类基层的配合比设计方案验证了建筑垃圾粗集料用于道路基层的可行性,并且建立了抗压回弹模量与抗压强度值的关系模型,可为建筑垃圾在道路基层施工的应用提供参考。

固化滨海盐渍土力学及溶陷特性研究

滨海盐渍土作为一种特殊土,具有溶陷、盐胀、腐蚀等不良的工程特性,为研究石灰+粉煤灰+水泥固化盐渍土改良材料土作为路基土的适用性,开展了液塑限、击实、无侧限抗压强度、三轴压缩、溶陷性试验,分析不同条件对改良盐渍土物理性指标、力学性能、溶陷特性的影响。结果表明:液塑限随固化剂掺入量的增加基本呈线性增加趋势,塑性指数减小;固化剂的加入使盐渍土最大干密度减小,最优含水率变化不明显;固化剂掺量和养护期龄对滨海盐渍土的力学性能影响显著;固化剂掺量小于14%时溶陷沉降量随固化剂掺量的增加呈减小趋势,提高含水率、压实度可以有效地降低固化盐渍土的溶陷沉降量。

石灰粉煤灰基层铣刨旧料在有轨电车路基结构中的应用研究

有轨电车轨道大多沿现状道路敷设,工程施工中就需要破除道路。道路破除产生的废料形成了环境负担,也增加了工程成本。本文基于亦庄新城现代有轨电车T1线工程实际,在部分基底换填段采用现有道路铣刨产生的石灰粉煤灰(二灰)旧料替代AB组料进行填筑,经专业试验室对换填料及现场填筑段进行物理力学试验,验证了石灰粉煤灰铣刨旧料在有轨电车路基结构中替代传统AB组料的可行性。

土工合成材料与土界面作用特性的研究

土工合成材料加筋土工程中 ,土工合成材料与填料的界面作用特性是最关键的技术指标 ,因此利用直剪试验和拉拔试验研究土工合成材料与填料的界面作用特性是非常必要的。本文以 5种不同种类的国产土工合成材料为加筋材料 ,以砂和石灰粉煤灰为填料 ,通过直剪试验和拉拔试验比较各种国产土工合成材料与填料的界面作用特性 ,得到一些有益的结论 ,可指导土工合成材料的优选和研究加筋机理。

石灰-粉煤灰-水泥稳定煤矸石混合料的研究

为分析石灰-粉煤灰(二灰)稳定煤矸石混合料用于季节性冰冻地区路面基层的技术可行性,在对煤矸石进行活性、物理、力学和耐久性试验研究基础上,设计了15组二灰稳定煤矸石混合料配合比,并测试了它们在饱水状态下的无侧限抗压强度.结果表明:这些混合料的无侧限抗压强度均能满足高速公路和一级公路对基层和底基层的强度设计要求.以第2组混合料配合比(生石灰、粉煤灰、煤矸石的质量分数分别为5%,15%,80%)为基础,通过不同水泥掺量试件的外观变化、质量损失、强度损失及极限冻融循环次数的抗冻融试验发现,掺入水泥能显著改善二灰稳定煤矸石混合料的强度和抗冻性,当水泥掺量占试件总质量的3%时,混合料的强度及抗冻性都达到了15次冻融循环的工程设计要求.

粉煤灰和石灰对突发性污染土壤中重金属化学形态的影响

利用石灰和粉煤灰对突发性污染土壤中重金属进行修复,采用TCLP法和Tessier浸提法对修复后土壤进行评价。结果表明,当石灰用量为土重的0.1%时,培养1个月,突发性污染土壤中Cu、Cd浸提量(TCLP法)比对照分别下降68.13%和76.67%;当粉煤灰用量为土重的8%时,土壤Cu、Cd浸提量比对照分别下降61.58%和71.67%。两种土壤经修复后,Cu、Cd浸提量均降至国际标准值以下,原因是施用粉煤灰和石灰后,土壤中Cu、Cd的形态由交换态向碳酸态和铁锰态发生转化。

土工合成材料加筋的试验研究

以 6种不同种类的国产土工合成材料为加筋材料 ,即针刺无纺土工织物、涤纶纤维经编土工格栅、玻璃纤维土工格栅、单向塑料拉伸土工格栅、双向塑料拉伸土工格栅和土工网 ,进行三轴试验比较各种土工合成材料对砂的加筋效果 ;进行直剪试验和拉拔试验比较各种土工合成材料与填料 (砂和石灰粉煤灰 )的界面作用特性 ,得到一些有益的结论 ,可指导土工合成材料的优选和研究土工合成材料的加筋机理。

电阻率法评价膨胀土改良的物化过程

掺石灰、粉煤灰是工程中通常采用的改良膨胀土的方法。土电阻率是土的基本物理指标之一,其变化可反映土的其他物理性质指标的变化。通过掺灰改良膨胀土不同养护龄期下的电阻率测试以及膨胀量、膨胀力及无侧限抗压强度等试验研究,探讨了掺灰改良膨胀土养护过程中的物理化学反应过程。根据养护过程中的电阻率随龄期的变化规律,可将改良膨胀土的物理化学反应过程划分为瞬时反应阶段、主体反应阶段、残余反应阶段和稳定阶段4个不同阶段。针对改良膨胀土质量控制和评价体系中存在的不足,提出了基于电阻率指标的改性膨胀土的质量评价方法,通过试验证实了该方法的有效性和实用性。