CO_2碳化矿渣-CaO-MgO加固土效能与机理探索

CO_2碳化联合工业固废协同加固土技术是旨在替代传统水泥固化方法的新型技术尝试。以工业废料——矿渣为主要材料,辅以活性MgO和CaO形成矿渣-CaO-MgO固化体系,将固化土料均匀搅拌制样后进行CO_2碳化试验。通过无侧限抗压强度、扫描电镜和X射线衍射等试验,探究固化剂掺量、配比、碳化时间和初始含水率等因素对碳化加固土效果的影响。结果表明:CO_2碳化对土体加固具有明显改良效果,碳化24 h试样抗压强度最高可提升25.77倍;碳化试样抗压强度与固化剂掺量(6S4L0M除外)、活性MgO占比呈正相关;碳化试样强度随碳化时间先增加后趋于平缓(或略微下降)、最佳碳化时间为6 h左右,随初始含水率增加而先增加后下降、最佳含水率为16%左右;活性MgO碳化效能明显优于活性CaO,矿渣中低活性CaO并不能显著改良自身碳化性能。CO_2碳化作用促使碳酸盐晶体(CaCO_3、MgCO_3)生成,晶体发育程度与碳化时间、固化剂掺量及活性等因素有关;碳酸盐晶体有效填充试样内部孔隙并黏结土颗粒,形成整体骨架结构使试样强度得以大幅提升。     

活性MgO碳化固化土的渗透特性研究

碳化固化法是一种低碳搅拌处理软土的创新技术,碳化反应生成的产物能有效降低固化土的孔隙率。在已有研究的基础上,着重研究碳化土的渗透特性,以利于其工程应用。采用室内渗透试验,系统研究了活性MgO掺量、碳化时间、初始含水率和CO_2通气压力对MgO碳化粉土和碳化粉质黏土渗透系数的影响规律,并与相同固化剂掺量、相同初始含水率下水泥固化土的渗透系数进行了对比。结果表明:活性MgO碳化土的渗透系数随MgO掺量的增加而降低,与相同掺量下水泥固化土的渗透系数处于同一数量级;MgO碳化粉土的渗透系数明显大于碳化粉质黏土的渗透系数;当MgO碳化粉土和粉质黏土碳化6.0 h时,相应的渗透系数达到最小(10-6);通气压力对MgO碳化土的渗透系数影响不大,在通气压力为200 k Pa时渗透系数较小。因此,活性MgO碳化土具有与水泥固化土相近的抗渗性能,有良好的推广应用前景。     

CO2碳化矿渣-CaO-MgO加固土效能与机理探索

CO₂碳化联合工业固废协同加固土技术是旨在替代传统水泥固化方法的新型技术尝试。以工业废料——矿渣为主要材料,辅以活性MgO和CaO形成矿渣-CaO-MgO固化体系,将固化土料均匀搅拌制样后进行CO₂碳化试验。通过无侧限抗压强度、扫描电镜和X射线衍射等试验,探究固化剂掺量、配比、碳化时间和初始含水率等因素对碳化加固土效果的影响。结果表明：CO₂碳化对土体加固具有明显改良效果,碳化24 h试样抗压强度最高可提升25.77倍;碳化试样抗压强度与固化剂掺量（6S4L0M除外）、活性MgO占比呈正相关;碳化试样强度随碳化时间先增加后趋于平缓（或略微下降）、最佳碳化时间为6 h左右,随初始含水率增加而先增加后下降、最佳含水率为16%左右;活性MgO碳化效能明显优于活性CaO,矿渣中低活性CaO并不能显著改良自身碳化性能。CO₂碳化作用促使碳酸盐晶体（CaCO₃、MgCO₃）生成,晶体发育程度与碳化时间、固化剂掺量及活性等因素有关;碳酸盐晶体有效填充试样内部孔隙并黏结土颗粒,形成整体骨架结构使试样强度得以大幅提升。     

磷酸镁水泥固化铜污染土的冻融稳定性研究

为研究重金属污染土的固化强度和长期稳定性,以磷酸镁水泥固化铜污染土为研究对象,进行基于冻融循环次数、磷酸镁水泥掺量、铜离子浓度等因素的强度和扫描电镜试验,给出冻融循环作用下固化铜污染土的无侧限抗压强度特征以及微观机制。研究表明:随着冻融循环次数增多、铜离子浓度的提高及磷酸镁水泥掺量的减少,固化土的无侧限抗压强度逐渐降低。3和12次冻融循环下固化污染土的无侧限抗压强度降低率最小,无侧限抗压强度降低率在冻融循环次数为6～9次时达到峰值。磷酸镁水泥固化低浓度重金属铜污染土的抗冻稳定效果显著,随金属离子浓度的增加固化土的冻融稳定性能降低。基于扫描电镜试验得到固化污染土的微观孔隙结构,当铜离子浓度0.5%且冻融6次时,磷酸镁水泥掺量从5%到20%,微观统计孔隙所占百分比减小17.43%,验证了强度变化机制。研究成果为我国冻土地区的重金属污染场地固化处理的长期稳定性评价提供参考,具有理论指导意义和工程应用价值。     

基于活性氧化镁掺量的碳化砌块性能及机理研究

通过室内试验,研究了活性氧化镁掺量对碳化砌块抗压强度、微观特性和耐久性的影响.结果表明:3种活性氧化镁掺量(质量分数)下的砌块在碳化0~14d时,其抗压强度逐渐增加,在碳化14~28d时,其抗压强度略有降低,当活性氧化镁掺量为35%时,碳化砌块的抗压强度明显高于活性氧化镁掺量为15%和25%时;活性氧化镁的碳化产物主要是水碳镁石、水菱镁石和球碳镁石,活性氧化镁掺量越高,其碳化产物越多、砌块内部孔隙越小;活性氧化镁掺量为35%的试样耐久性最好.     

高含水率吹填淤泥固化土强度特性及预测模型

高淤泥初始含水率以及低固化剂掺量是吹填造陆工程和疏浚淤泥资源化利用工程的常见特点,形成的固化土含水率和强度与其关系密切.本文通过室内试验,探讨了吹填淤泥固化土含水率和强度与养护龄期、固化剂掺量、淤泥初始含水率之间的关系,并尝试选择合适的参数,建立固化土无侧限抗压强度预测模型.研究表明,各龄期的固化土含水率随固化剂掺量增...     

二氧化碳泡沫法碳化加固软弱土的初探研究

已有研究表明,活性Mg O固化土经CO2碳化数小时可达到或超过相同掺量水泥固化土28d的强度,碳化形成的镁式碳酸化合物能有效降低天然土的含水率、孔隙率,并显著提高土体强度,但在软土中尤其是黏土中通气具有一定难度。本研究选用十二烷苯磺酸钠作为起泡剂,用CO2泡沫处理Mg O混合土,养护后进行含水率、力学特性和酸碱特性测试。结果表明,含水率随养护时间的增加而降低;无侧限抗压强度随着初始含水率增加而呈现先增大后减小;Mg O掺量越高,强度越大。CO2泡沫固化土的p H值处于10.0~10.87范围内,远低于相应水泥固化土(11.5以上),随养护时间的增加,p H值逐渐下降。但强度增长与预期强度相差甚远,需要对起泡剂和操作工艺上需进行进一步优选。     

活性MgO–粉煤灰固化淤泥微观机制研究

以武汉东湖淤泥为研究对象,研究低碳环保活性MgO–粉煤灰复合型材料固化淤泥的宏观效能及内在机制。通过无侧限抗压强度、X射线衍射、扫描电镜、热重和压汞等系列试验,深入探索固化淤泥的抗压强度、化学成分、结构形貌及微观孔隙等特征随活性MgO–粉煤灰掺量、MgO/粉煤灰配比和养护龄期多种因素的演变规律。结果表明:活性MgO–粉煤灰可有效提高固化淤泥无侧限抗压强度,且随养护龄期、活性MgO–粉煤灰掺量及MgO/粉煤灰配比增加而提高。水化产物Mg(OH)_2和M-S-H等胶结产物生成是活性MgO–粉煤灰固化淤泥宏观力学强度提高的本质原因。活性MgO–粉煤灰掺量与MgO/粉煤灰配比增加,引起水化产物Mg(OH)_2和水化硅酸镁M-S-H衍射峰峰值逐渐增强、热重质量损失逐渐增多、团粒内孔隙更多地转化为颗粒间孔隙,导致固化淤泥微观结构更加致密、整体性更强,宏观上表现为力学特性大幅改善。上述结果深入完善了活性MgO–粉煤灰固化淤泥宏微观特征演变过程,建立了活性MgO–粉煤灰内在化学反应诱发固化淤泥性能改良的全过程模型。研究成果可为绿色低碳活性MgO–粉煤灰复合型材料在淤泥固化等实际工程中应用提供理论依据。     

活性MgO碳化固化土的干湿循环特性试验研究

碳化固化技术是一种利用二氧化碳对搅拌有活性氧化镁的土体进行碳化,以达到快速提高强度的低碳搅拌处理软土的创新技术。通过室内试验研究干湿循环对碳化固化土物理力学特性的影响,并与相同掺量下水泥固化土进行对比。结果表明:活性Mg O固化粉土碳化3 h试样的无侧限抗压强度可达5 MPa,粉质黏土碳化24 h试样可达2.6 MPa;干湿循环后碳化固化土的干密度降低,而水泥土干密度基本不变;6次干湿循环后粉土碳化试样的无侧限抗压强度仍然能达到4 MPa以上,为水泥固化粉土强度的2倍,具有较好的抗干湿循环性能;经过6次干湿循环后,粉质黏土碳化试样的残余强度仅为35%,而水泥固化粉质黏土降到65%,表明固化粉质黏土的抗干湿循环性能均较差,且粉质黏土碳化试样的抗干湿循环能力不及水泥固化粉质黏土试样。通过X射线衍射(XRD)、电镜扫描(SEM)及压汞试验(MIP)测试表明干湿循环对粉土碳化试样的累计孔隙影响不大,因此粉土试样仍然具有比较大的密实度来保证试样强度;粉质黏土碳化试样因孔隙增加明显而变得疏松,因此强度显著降低。     

木质素改良粉土热学与力学特性相关性试验研究

为揭示木质素改良粉土热学与力学特性随养护龄期的演化规律,通过击实试验、热阻系数测试、无侧限抗压强度试验、回弹模量试验、压汞试验和扫描电镜分析试验,探讨改良土热阻系数、强度和刚度与木质素掺量、含水率和养护龄期的变化规律,同时定性/定量评价改良土微观结构变化,分析改良土热学特性与力学特性间的相互关系。结果表明:改良土最大干密度较素土增加,最优含水率减小,干密度对含水率变化的敏感性增加;热阻系数随掺量和养护龄期增加而增加,60 d养护龄期后热阻系数趋于相同,热阻系数与土体密实度和组成成分的热传导特性密切相关;改良土强度随掺量和龄期增长而增加,28 d龄期12%掺量改良土强度约为素土强度6倍;回弹模量的变化特征与无侧限抗压强度类似,对于改良粉土,木质素最优掺量约为12%;改良土孔隙总体积和平均孔径显著减小,木质素包裹、连结土颗粒并填充孔隙,形成更致密土体结构。     

Mechanical performances and microstructural characteristics of reactive MgO-carbonated silt subjected to freezing-thawing cycles

The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances.Under the binder content of 15% and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T) cycles.After different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression tests.Besides,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM) and mercury intrusion porosimetry(MIP) tests.The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt.The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T cycles.There is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly.After 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,respectively.The total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore.The findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.     

Hydraulic conductivity characteristics of carbonated reactive magnesia-treated silt

Carbonation of reactive magnesia (MgO) has recently received increasing attention in the area of soil stabilization and ground improvement. However, as a critical parameter in terms of long-term seepage behavior in the geotechnical analysis, the hydraulic conductivity of carbonated reactive MgO-stabilized silt has not been fully studied. In this context, the effect of water-MgO ratio (ratio of initial water content to MgO content, w₀/c) and carbonation time on hydraulic conductivity (or permeability) characteristics was systematically investigated. Serial microstructural tests including mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses were applied to elucidate the intrinsic mechanisms. The obtained results indicate that as the initial water-MgO ratio decreases, the void ratio gradually decreases and the reduction of hydraulic conductivity becomes less prominent because of the little presence of flow paths. The hydraulic conductivity of carbonated MgO-admixed silt similar to that of PC-treated silt is mainly governed by the porosity, and its correlation with void ratio is proposed in the article. The variations of permeability with void ratio are consistent with those of the cumulative pore volume from MIP results in general, and the medium pores (3–30 μm) are substantiated to be the primary contributor in controlling the permeability. SEM and DSC analyses reveal that the cementation of soil particles and filling of hydrated magnesium carbonates marginally reduce the voids and permeability. The reasons for changes of permeability behaviors have been confirmed by the pore-size distribution and microstructure characteristics.

     

氧化镁活性对碳化固化效果影响研究

碳化固化技术是近年来提出的一种低碳搅拌处理软弱土创新技术。该技术先采用Mg O水泥与土进行搅拌,再利用CO2对之进行碳化,以达到快速提高强度的目的。针对Mg O活性对碳化固化的影响规律进行了室内试验研究,并分析了其微观机理。结果表明:试样能在3~6 h内完成大部分碳化,碳化24 h后达到稳定,氧化镁活性对碳化固化效果有显著影响,具体表现为氧化镁活性越高,试样碳化后碳化度越高、碳化产物越多、孔隙体积越小、微观结构越密实;试样碳化后体积明显增长,但氧化镁活性对体积变化影响不大,3种氧化镁试样体积膨胀均为16%左右;氧化镁活性越高试样强度越大,高活性氧化镁试样碳化6 h的强度可达标准养护28 d水泥土强度,稳定强度达到2.5 MPa,而低活性氧化镁试样强度仅为0.5 MPa;试样碳化稳定后高活性试样p H值为9.6,低活性试样p H值为9.0,均低于水泥土p H值。     

Laboratory-scale model of carbon dioxide deposition for soil stabilisation

Olivine sand is a natural mineral,which,when added to soil,can improve the soil's mechanical properties while also sequester carbon dioxide(CO_2)from the surrounding environment.The originality of this paper stems from the novel two-stage approach.In the first stage,natural carbonation of olivine and carbonation of olivine treated soil under different CO_2 pressures and times were investigated.In this stage,the unconfined compression test was used as a tool to evaluate the strength performance.In the second stage,details of the installation and performance of carbonated olivine columns using a laboratory-scale model were investigated.In this respect,olivine was mixed with the natural soil using the auger and the columns were then carbonated with gaseous CO_2.The unconfined compressive strengths of soil in the first stage increased by up to 120% compared to those of the natural untreated soil.The strength development was found to be proportional to the CO_2 pressure and carbonation period.Microstructural analyses indicated the presence of magnesite on the surface of carbonated olivinetreated soil,demonstrating that modified physical properties provided a stronger and stiffer matrix.The performance of the carbonated olivine-soil columns,in terms of ultimate bearing capacity,showed that the carbonation procedure occurred rapidly and yielded a bearing capacity value of 120 k Pa.Results of this study are of significance to the construction industry as the feasibility of carbonated olivine for strengthening and stabilizing soil is validated.Its applicability lies in a range of different geotechnical applications whilst also mitigates the global warming through the sequestration of CO_2.     

黏粒含量对固化淤泥力学性质的影响

采用人工配制不同黏粒含量的淤泥研究黏粒含量对固化淤泥力学性质的影响。研究发现,淤泥中黏粒含量对固化淤泥的力学性质存在显著影响,当水泥量为5.0%时,固化淤泥强度随黏粒含量的增加呈增加趋势;当水泥量高于7.5%时,对于不同水泥量都存在一个对应的适宜黏粒含量CCop,在该黏粒含量时固化淤泥的无侧限抗压强度最大,破坏应变最小。适宜黏粒含量CCop随着水泥量增加而有所增加,但龄期对其没有影响。三轴试验结果发现,当黏粒含量为CCop时固化淤泥黏聚力c达到最大,内摩擦角?则随黏粒含量的增加呈现减小趋势。对于不同黏粒含量下固化淤泥的应力–应变关系的研究发现,当水泥量不超过5.0%时,固化淤泥都表现出理想弹塑性的特性;当水泥量大于5.0%时固化淤泥都存在破坏峰值,表现出脆性破坏模式,而且随着黏粒含量的增加破坏应变先减小后增加;当黏粒含量为CCop时,固化淤泥对应的破坏应变接近最小。因此,当黏粒含量为CCop时,固化淤泥将出现最大强度和最小变形。该研究结果对淤泥固化实际应用中的材料配制具有重要意义。     

高液限粉土的承载比特性及其利用建议

通过对高液限粉土进行不同浸水条件下的承载比试验,研究高液限粉土浸水、不浸水的强度变化规律,并对浸水条件下水泥改良粉土的强度特征进行探讨。试验结果表明:浸水条件下粉土的CBR值小于3%;不浸水的粉土CBR值与4%水泥改良粉土的浸水CBR值受初始制样含水量控制,但整体比浸水CBR值高。从CBR值随含水量的变化规律可以看出,粉土对水十分敏感。对此,提出粉土用于路基填筑的利用原则和具体的处置措施。