粉煤灰碱激发制备地质聚合物研究进展

由于传统硅酸盐水泥基建材生产过程排放大量CO₂,近几年以地质聚合物(地聚物)为代表的新型低碳胶凝材料成为研究热点。作为我国大宗工业固体废弃物，粉煤灰富含硅铝酸盐，通过碱激发制备地聚物可实现粉煤灰大宗消纳。综合论述了粉煤灰的碱激发反应活性评估方法，总结了粉煤灰碱激发反应机理，归纳了粉煤灰类型、激发剂、原料配比和养护制度等关键因素对地聚物形成和性能的影响规律，提出了目前研究存在的问题，并从粉煤灰活性组分评估和碱激发体系元素组成的角度，对未来研究方向进行展望。粉煤灰的反应活性评价方法主要有Rietveld全谱图拟合法、饱和石灰溶液吸收法和酸碱溶出法。粉煤灰碱激发反应过程可分为解构—重构—凝聚—聚合4个阶段，解构过程中溶出的硅铝比(Si/Al物质的量比)对凝胶结构和材料力学性能有重要影响，不同研究获得的最佳Si/Al物质的量比存在较大差异。目前关于原料配比、养护制度和凝胶结构等因素对地聚物性能影响研究获得的变化规律并不一致，为粉煤灰碱激发反应机理和地聚物合成研究带来困难，未来应针对不同类别粉煤灰理化特性，建立碱激发体系各元素配比统一的计算方法，为粉煤灰基地聚物合成时统一设...     

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。     

粉煤灰基地聚合物若干关键问题研究综述

作为一种新型可持续发展材料,粉煤灰基地聚合物具有优异的工程技术性能、突出的节能环保优势和巨大的市场潜力,成为当前研究的热点和前沿.本文针对粉煤灰基地聚合物若干关键问题综述了国内外研究现状,分析其地聚合反应机理与模型、地聚合反应过程的影响因素、水的作用、生成产物微观形貌与结构,以及其混凝土界面过渡区的状态.     

固废基道路地聚物注浆材料的组分优化及机理研究

地聚物注浆材料作为低能耗、低CO₂排放的清洁材料，在道路注浆领域应用前景广阔，在未来有望取代水泥注浆材料。为了探究材料组分及用量对地聚物注浆材料性能的影响，采用三种硅铝源灰料(粉煤灰、矿渣粉和煤矸石粉)与不同碱活化方式制备道路地聚物注浆材料，对其组成材料进行优选；然后，采用单因素试验对道路地聚物注浆材料的配合比范围进行优化；最后，利用X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、能量色散谱(EDS)和傅里叶变换红外光谱(FTIR)对道路地聚物注浆材料的物相组成、微观形貌、微区能谱和化学键组成进行分析。结果表明：以粉煤灰和矿渣粉为硅铝源灰料，KOH和水玻璃溶液为复合碱活化剂制备的道路地聚物注浆材料性能最佳；推荐道路地聚物注浆材料的配合比范围为：粉煤灰、矿渣粉质量比4∶6,水玻璃用量10%～15%(质量分数),KOH用量5%～11%(质量分数),水灰比0.50～0.65;粉煤灰和矿渣粉被碱活化后溶解并重聚生成C-(A)-S-H等无定形凝胶产物，最终形成SiO₄和AlO₄正四面体网状结构，且伴随类沸石相、碳酸盐、...     

粒径对粉煤灰基地聚物抗压强度的影响

为提高粉煤灰的综合利用,以工业废弃物粉煤灰为主要原料,通过碱激发制备粉煤灰基地聚物,研究了粉煤灰的粒径及粒径分布对粉煤灰基地聚物抗压强度的影响。试验结果表明:对于单峰分布不同粒径的粉煤灰来说,随着D_(50)粒径的减小,粉煤灰基地聚物的28 d抗压强度随之显著升高,早期抗压强度也随之大幅提高;对于相同D_(50)粒径下单峰和双峰分布的粉煤灰来说,单峰分布的粉煤灰基地聚物的抗压强度略低于双峰分布粉煤灰基地聚物的抗压强度;进而证明D_(50)粒径是影响粉煤灰基地聚物的因素之一,通过调节粒径分布可以改善抗压强度,为进一步控制粉煤灰基地聚物的抗压强度提供了理论基础。     

粉煤灰-矿渣基地聚物混凝土抗盐冻性能试验研究

对1.0、1.5、2.0三种激发剂模数和0、10%、20%、30%四种矿渣替代率下的粉煤灰-矿渣基地聚物混凝土在盐冻融循环损伤作用下的力学性能进行了试验研究。结果表明：粉煤灰-矿渣基地聚物混凝土的质量损失率呈先减小后增大的变化特征,当激发剂模数为1.0,抗盐冻整体性能最佳;矿渣对地聚物混凝土的抗盐冻性能有较大幅度提升,随着矿渣替代率增大,粉煤灰-矿渣基地聚物混凝土的质量损失率和吸水率等均呈先减小后增大的变化特征,相对弹性模量和相对抗压强度呈先增大后减小的变化特征,当矿渣替代率为20%时,抗盐冻整体性能最佳;在试验数据基础上,基于Lemaitre等效应变原理,建立冻融损伤模型,该模型可以较好描述不同矿渣替代率下粉煤灰-矿渣基地聚物混凝土随盐冻融循环次数的损伤发展趋势。     

粉煤灰地聚物的力学性能及微观结构研究

研究了在常温、常压养护条件下制备粉煤灰地聚物的工艺,物理力学性能及其水化产物微观结构。结果表明:粉煤灰地聚物在水玻璃模数为1.5,碱固比为0.3,水灰比为0.3时,28d抗压强度为35.9MPa。由FTIR、DTA/TG和超景深显微镜等表征手段推断出:在水化过程中粉煤灰内玻璃体发生了解聚—缩聚反应,即玻璃体被碱溶液溶解解聚后在其边缘发生缩聚反应,生成非结晶相N-A-S-H凝胶,且N-A-S-H凝胶随着时间延长而增加。     

粉煤灰基地聚物固化盐渍土的工程特性与微观机制

为探索粉煤灰基地聚物对盐渍土的加固效果，对固化后的土体开展了力学性能和细微观结构的试验，从本质上揭示粉煤灰基地聚物对盐渍土的固化机理。结果表明:随着粉煤灰基地聚物掺量的增加，盐渍固化土的最优干密度下降，最优含水率上升;当掺量从0增至6%时，盐渍固化土的无侧限抗压强度增加了5.5倍，而当掺量为8%时的强度没有明显提升;盐渍土的孔径分布呈双峰分布，随着地聚物掺量的增加，孔隙体积逐渐降低;盐渍固化土的阳离子交换量随粉煤灰基地聚物掺量增加而提高，且与无侧限抗压强度呈现线性相关;在盐渍土中加入粉煤灰基地聚物使土颗粒间的孔隙收缩，黏结性和密实度增强，进而达到固化的效果。本研究成果为粉煤灰基地聚物在盐渍土地区地基加固工程中的设计与施工提供了参考。     

地聚物多孔轻质高强材料的制备及孔结构特性

为了解决地聚物多孔材料质轻与高强难以取得一致性的问题,本文采用正交试验,对粉煤灰地聚物多孔材料表观密度和强度进行试验,在此基础上,利用超细矿渣粉的独特性,对双氧水发泡剂及辅助稳泡材料进行了优选,制备出抗压强度达到5.9 MPa、表观密度仅为557 kg/m3的地聚物多孔材料.结果表明:当粉煤灰/矿渣比例为1:1,双氧水掺量为2.0％,硬脂酸钙掺量为1.0％,MnO2掺量为0.3％,制备的矿渣-粉煤灰基地聚物多孔材料可以达到质轻高强的目的.采用XRD、SEM和低场核磁共振技术对多孔材料进行了微观测试,并对其抗压强度、表观密度与孔结构之间关系进行了分析.     

分级粉煤灰对地质聚合物发泡材料性能的影响

为了研究分级粉煤灰对发泡材料性能的影响,在相同的制备工艺和配方下,采用原灰与其分选出不同粒径的分级灰及其复配材料进行对比,通过调控发泡剂用量和分级灰的配比,制备了不同等级密度的轻质粉煤灰基地聚物发泡材料。结果表明:原灰的粒径分布范围广,采用100%原灰制备不同等级地聚物发泡材料,28 d抗压强度值均低于标准值要求;以北京低碳清洁能源研究所专利技术将原灰分选出的2种分级灰(FA-2和FA-1),可提高地聚物发泡材料的抗压强度。FA-2与FA-1复配比率不小于1∶1时,可制备不同等级的发泡材料。     

Suitability of Sarawak and Gladstone fly ash to produce geopolymers: A physical,chemical, mechanical,mineralogical and microstructural analysis

Two types of fly ash sourced from Sarawak, Malaysia and Gladstone, Australia reflect differences in chemical compositions, mineral phase and particle size distributions. In this paper, the Sarawak fly ash was used to produce geopolymer in comparison to the well-developed Gladstone fly ash-based geopolymer. Characteristics of fly ash and mixtures proportions affecting compressive strength of the geopolymers were investigated. It is found that the variations of both fly ash types on particle size distributions, chemical compositions, morphology properties and amorphous phase correspond to the compressive strength. The results obtained show that after 7 days, geopolymer using Sarawak fly ash has lower compressive strength of about 55 MPa than geopolymer using Gladstone fly ash with strength of about 62 MPa. In comparison with Gladstone fly ash-based geopolymer, it showed that Sarawak fly ash-based geopolymer can be a potential construction material. Moreover, the production of Sarawak fly ash-based geopolymer aids to widen the application of Sarawak fly ash from being treated as industrial waste consequently discharging into the ash pond.     

粉煤灰基地聚合物无机涂料的制备与性能

以低钙型粉煤灰为主要原料,硅酸钠和氢氧化钠为复合碱激发剂,硅烷偶联剂(KH550)为增强材料,硅丙乳液为辅助成膜物质制备地聚合物无机涂料。研究了硅烷偶联剂掺量、反应温度以及水固比对地聚合物无机涂料的成膜性、耐水性和耐洗刷性等性能的影响,并通过XRD、FTIR、SEM、TG-DSC分析了无机涂料的微观结构及其耐高温性能。结果表明,当制备温度为60 ℃、水固比为0.31(质量比)、硅烷偶联剂掺量为3.6%(质量分数)时,地聚合物无机涂料在室温下的成膜性良好,无开裂现象,涂料24 h内质量吸水率为1.84%,耐洗刷性可达12 000次,7 d时硬度为154 s。地聚合物无机涂层内部主要是无定形的硅铝酸盐凝胶,硅烷偶联剂经水解、键合生成簇状产物填充在涂层的孔隙之间,增加了涂层的密实性,抑制了裂纹的产生。涂层在25~800 ℃的失重率为12.0%~13.0%,未发现明显的地聚合物热分解现象,说明涂层耐高温性能良好。     

Improving compressive strength of fly ash-based geopolymer composites by basalt fibers addition

In this study, ASTM Class C fly ash used as an alumino-silicate source was activated by metal alkali and cured at low temperature. Basalt fibers which have excellent physical and mechanical properties were added to fly ash-based geopolymers for 10–30% solid content to act as a reinforced material, and its influence on the compressive strength of geopolymer composites has been investigated. XRD study of synthesized geopolymers showed an amorphous phase of geopolymeric gel in the 2θ region of 23°–38° including calcium-silicate-hydrate (C-S-H) phase, some crystalline phases of magnesioferrite, and un-reacted quartz. The microstructure investigation illustrated fly ash particles and basalt fibers were embedded in a dense alumino-silicate matrix, though there was some un-reacted phase occurred. The compressive strength of fly ash-based geopolymer matrix without basalt fibers added samples aged 28 days was 35 MPa which significantly increased 37% when the 10 wt%. basalt fibers were added. However, the addition of basalt fibers from 15 to 30 wt% has not shown a major improvement in compressive strength. In addition, it was found that the compressive strength was strong relevant to the Ca/Si ratio and the C-S-H phase in the geopolymer matrix as high compressive strength was found in the samples with high Ca/Si ratio. It is suggested that basalt fibers are one of the potential candidates as reinforcements for geopolymer composites development.     

Fibre-reinforced boroaluminosilicate geopolymers: A comparative study

This paper investigates the effect of fibres on the physical and mechanical behaviour of boroaluminosilicate geopolymers (BASG) compared to conventional aluminosilicate binders. The use of various types of fibres by the means of reinforcing geopolymers against flexural loads is very common. In this work, fly ash and ground granulated blast furnace slag (GGBS) are utilised as raw materials to generate geopolymer specimens. Different alkaline solutions comprising sodium hydroxide, sodium silicate, and borax are prepared to activate precursors. The sodium silicate solution is substituted with borax by 30?wt% and 70?wt% in order to produce fly ash and slag-based BASG respectively. Steel and polymer fibres are employed in the mixtures for reinforcement. Three-point bending and mini slump tests are conducted for assessing the flexural strength, elastic modulus, toughness, and flow of geopolymer specimens. A pair plotting interpretation is also used in order to illustrate the patterns. The obtained results indicate that the fly ash-based BASG mortar shows superior flexural strength to the GGBS-based BASG mortar. The flexural strength of fly ash-made aluminosilicate geopolymer declines from 7.3?MPa to 6.4?MPa with an increase in the content of steel fibres from 1% to 2%. Inversely, raising the percentage of steel fibres in the fly ash-based BASG mortar caused a slight growth in the flexural strength of specimens. The polypropylene fibres, when added sufficiently, play a significant role in improving the toughness of fly ash-based BASG and slag-based aluminosilicate mixtures, more than 0.8 and 0.7?J surge in the toughness respectively. In addition, the polypropylene and steel fibres perform well in improving the elastic modulus of slag-based BASG and fly ash-based aluminosilicate binders. While keeping the water to binder ratio constant, introducing the steel fibre increased the flow of fly ash-based geopolymers. Nonetheless, the polymer fibres declined the flow of mortars.     

富镁镍渣-粉煤灰基地质聚合物的制备与性能表征

以工业固体废弃物富镁镍渣和粉煤灰为原料,以水玻璃和NaOH为碱激发剂,制备了一系列富镁镍渣-粉煤灰基地质聚合物。研究了不同粉煤灰掺量对地质聚合物力学性能的影响,并测定地质聚合物的线性收缩和碱溶出,通过XRD、IR、DTA等手段对产物进行表征。结果表明:富镁镍渣-粉煤灰基地质聚合物的强度随粉煤灰的掺入先升高后降低,当掺量为30%(质量分数)时,地质聚合物的抗压强度可达最高值22.15 MPa,较镍渣基地质聚合物强度提高42.2%;XRD分析表明富镁镍渣中MgO以镁橄榄石相存在,而非游离态,故地质聚合物具有良好的体积安定性。     

Comparative performance of geopolymers made with metakaolin and fly ash after exposure to elevated temperatures

This paper presents the results of a study on the effect of elevated temperatures on geopolymers manufactured using metakaolin and fly ash of various mixture proportions. Both types of geopolymers (metakaolin and fly ash) were synthesized with sodium silicate and potassium hydroxide solutions.

The strength of the fly ash-based geopolymer increased after exposure to elevated temperatures (800 °C). However, the strength of the corresponding metakaolin-based geopolymer decreased after similar exposure. Both types of geopolymers were subjected to thermogravimetric, scanning electron microscopy and mercury intrusion porosimetry tests. The paper concludes that the fly ash-based geopolymers have large numbers of small pores which facilitate the escape of moisture when heated, thus causing minimal damage to the geopolymer matrix. On the other hand, metakaolin geopolymers do not possess such pore distribution structures. The strength increase in fly ash geopolymers is also partly attributed to the sintering reactions of un-reacted fly ash particles.     

The microstructural and mechanical properties of geopolymer composites containing glass microfibres

This paper presents the effects of microfibre contents on mechanical properties of fly ash-based geopolymer matrices containing glass microfibres at 0, 1, 2 and 3 mass%. The influence of glass microfibres on the fracture toughness, compressive strength, Young's modulus and hardness of geopolymer composites are reported, as are the microstructural properties investigated using scanning electron microscopy. Results show that the addition of 2 mass% glass microfibres was optimal, exhibiting the highest levels of fracture toughness, compressive strength, Young's modulus and hardness. The results of the microstructural analysis indicate that the glass microfibres act as a filler for voids within the matrix, making a dense geopolymer and improving the microstructure of the binder. This leads to favourable adhesion of the composites, and produces a geopolymer composite with good mechanical properties, comparable to pure geopolymer. The failure mechanisms in glass microfibre-reinforced geopolymer composites are discussed in terms of microstructure.     

Micromechanics constitutive modelling and optimization of strain hardening geopolymer composite

This paper investigates the micromechanics constitutive modelling and optimization of a fiber-reinforced strain-hardening geopolymer composite (SHGC) recently developed by the authors. Micromechanical parameters of the developed fly ash-based SHGC were independently measured or deduced to compute the analytical crack bridging (σ-δ) relation of the composite. The predicted σ-δ relation was compared with the experimental test results. It was confirmed that the previously developed micromechanics-based model can reasonably predict the σ-δ relation of fly ash-based SHGCs. Using the verified model, a parametric study was then performed to evaluate the effects of fiber length, fiber surface oil-coating, and matrix fracture toughness on critical (minimum) fiber content required to exhibit saturated pseudo strain-hardening (PSH) behavior. The results indicated that the critical fiber content in fly ash-based SHGCs is mainly governed by the energy-based criterion. It was demonstrated that the fiber surface oil coating, the increase of fiber length and the reduction of matrix fracture toughness are effective approaches to reduce the critical fiber content. Using the model, it was demonstrated that fly ash-based SHGCs can be systematically optimized by proper tailoring of the material constituents to achieve saturated PSH behavior with the lowest amount of fiber, and thereby the lowest cost.     

Microstructural and compositional change of NaOH-activated high calcium fly ash by incorporating Na-aluminate and co-existence of geopolymeric gel and C–S–H(I)

This study explores the reaction products of alkali-activated Class C fly ash-based aluminosilicate samples by means of high-resolution synchrotron X-ray diffraction (HSXRD), scanning electron microscope (SEM), and compressive strength tests to investigate how the readily available aluminum affects the reaction. Class C fly ash-based aluminosilicate raw materials were prepared by incorporating Na-aluminate into the original fly ashes, then alkali-activated by 10 M NaOH solution. Incorporating Na-aluminate reduced the compressive strength of samples, with the reduction magnitude relatively constant regardless of length of curing period. The HSXRD provides evidence of the co-existence of C–S–H with geopolymeric gels and strongly suggests that the C–S–H formed in the current system is C–S–H(I). The back-scattered electron images suggest that the C–S–H(I) phase exists as small grains in a finely intermixed form with geopolymeric gels. Despite providing extra source of aluminum, adding Na-aluminate to the mixes did not decrease the Si/Al ratio of the geopolymeric gel.