粉煤灰掺量对轻烧氧化镁基制备3d打印用磷酸镁水泥性能的影响

以实现轻烧氧化镁为原料制备低碳磷酸镁水泥材料的3d打印为目标,采用自主研发的混搅挤功能一化建筑3d打印设备,探究了不同粉煤灰掺量对以轻烧氧化镁为基制备磷酸镁水泥材料性能与打印性能的影响规律,并结合XRD与SEM微观试验进一步分析粉煤灰对其水化产物及晶体样貌的影响。结果表明：与重烧氧化镁相比,由轻烧氧化镁制备磷酸镁水泥的凝结时间大幅缩短;粉煤灰的加入对材料凝结时间影响较小,均在2～3 min左右,但对抗压强度与界面粘结强度有负面影响,当粉煤灰掺量为磷酸镁水泥质量的30%时,抗压强度及界面粘结强度分别下降约34.24%、48.94%;粉煤灰掺量在20%以内时,可有效改善轻烧氧化镁基磷酸镁水泥材料的干缩率,提高体积稳定性;粉煤灰中的活性物质参与水化反应,生成的水化产物与磷酸镁水泥展现出良好的化学相容性,使结构内部更为密实;当粉煤灰掺量为20%～25%时,制备的3d打印用轻烧氧化镁基磷酸镁水泥具有良好的工作性能、体积稳定性能、挤出性能以及建造性能,且满足3d打印对水泥基材料的力学要求。     

硅基材料和矿渣应用于水泥基材料的研究进展

水泥基材料是目前使用量最大的建筑材料,在实际应用过程中,水泥基材料会出现损坏,达不到预期的性能要求.水泥水化产物中存在大量结晶的Ca(OH)2,影响各种水泥水化产物之间的粘结性,造成水泥基材料性能的降低.如何增强水泥基材料的性能成了国内外研究的热点,需要找到能够有效改善水泥基材料性能的方法.查阅国内外相关文献发现,将粉煤灰、硅灰、纳米SiO2(因三种材料的主要组分为SiO2,以下统称为硅基材料)或矿渣掺入到水泥基材料中,因其具有火山灰反应,并能起到填充作用,可明显提高水泥基材料的性能.掺合料的加入可降低水泥基材料中Ca(OH)2含量,减小其晶粒尺寸,使C-S-H凝胶的数量增多,改善水泥基材料的孔隙率,提高其性能.粉煤灰和矿渣成分中有部分玻璃态物质,能减少水泥浆体用水量,增加和易性;具有较低的火山灰性,适量掺入能降低水泥浆体的水化速度;含有粉煤灰或矿渣的水泥基材料早期强度较低,后期强度较高.硅灰与纳米SiO2的火山灰活性较高,能促进水化,适量掺入能够使水泥基材料早期强度大幅提高,但后期强度发展较慢;同时也会增大水泥基材料早期收缩,增加其结构开裂的风险.不同掺合料复掺后能产生协同增强效应,可获得性能优异的复掺改性水泥基材料.本文主要介绍了硅基材料和矿渣在水泥基材料中的应用,从反应机理、水化热、强度、孔隙率等方面来阐述其在水泥基材料中的研究现状和相关成果.对目前研究中存在的相关问题进行了分析总结,以期为制备性能优异的水泥基材料提供一定的参考.     

碳纳米管增强水泥基复合材料的自收缩及抗裂性能碳纳米管增强水泥基复合材料的自收缩及抗裂性能

水泥基材料的收缩开裂已经成为其破坏的一个主要原因,受到国内外关注,碳纳米管（CNTs）作为一种纳米纤维状材料,可能可以抑制水泥基材料收缩。本文将CNTs放入水中,经过超声处理分散后,形成CNTs分散液,设置不同的CNTs掺量将其掺入到水泥基材料中,通过波纹管实验及圆环试验对该种新型复合材料的自收缩及抗裂性能进行研究。结果表明:CNTs的掺入可以很大程度上抑制水泥基材料的自收缩,最高降低率可到40%以上,且明显提高了水泥基材料的抗裂性能。水灰比的增加会提高CNTs对水泥基材料收缩的抑制效果。当CNTs的掺量为0.1wt%时,可以获得最优效果。同时,CNTs的掺入不仅对水泥基材料自收缩有抑制作用,一定程度上也会抑制水泥基材料的干燥收缩。通过将CNTs掺入到建筑结构关键部分的水泥基材料中,可以提高建筑安全系数。      

纳米SiO_2对硫铝酸盐水泥水化硬化的影响

研究了不同掺量纳米SiO_2对硫铝酸盐水泥抗压/抗折强度的影响,即掺入纳米SiO_2使水泥砂浆早期抗压/抗折强度显著提高,后期抗折强度未出现倒缩现象且具有较大的上升空间,掺3%纳米SiO_2水泥砂浆2,8h,1,3,28和56d抗折强度相比空白样分别提高了44.84%,41.80%,37.85%,37.78%,42.32%和65.03%。并通过XRD、SEM-EDS及水化热揭示了强度发展的影响机理。即水化早期的微集料填充作用、结晶成核作用使硬化浆体微观结构均匀密实,并促进了硫铝酸盐水泥8h前的水化;水化后期纳米SiO_2的火山灰效应进一步提高了水泥的水化程度。     

纳米CaCO_3中间体对水泥基材料性能的影响

以纳米CaCO3中间体为研究对象。采用凝结时间、力学性能、XRD和SEM测试方法,研究了不同掺量纳米CaCO3中间体对水泥基材料性能的影响,掺量分别为0%、0.5%、1%和2%。结果表明：纳米CaCO3中间体可明显提高水泥抗压强度,掺量1%时,12h、72h和28d龄期的浆体抗压强度分别比基准提高了54%、24%和39%;掺纳米CaCO3中间体后,水泥的需水量变化不大,但凝结时间随掺量的增加而缩短;纳米CaCO3中间体通过晶核作用,细化水化产物晶型,降低孔隙率,改善微观结构,从而提高水泥基材料的抗压强度。     

淀粉基水化温升抑制剂对水泥-粉煤灰复合胶凝材料水化的影响

本实验主要研究了淀粉基水化温升抑制剂( TRI)对水泥-25%粉煤灰、水泥-50%粉煤灰复合胶凝材料凝结时间、抗压强度、水化放热历程的影响,并与纯水泥进行比较.通过对比TRI在水泥和粉煤灰上的吸附性能和水化产物的变化,对其影响机理进行了分析.结果表明:随TRI掺量增加,凝结时间都延长,早期强度都降低,复合体系后期(60 d)强度存在损失,但不影响纯水泥后期强度,水化放热速率峰值都大幅度降低,缓解了集中放热.水泥对TRI的吸附能力更强,导致复合体系中单位水泥吸附的TRI更多,使得降峰效果更好,同时也导致凝结时间延长更多,增大早期强度损失. TRI不影响纯水泥最终水化程度,但会延缓粉煤灰的火山灰反应,因此降低了复合体系60 d强度.     

基于纳米二氧化硅和碳纳米管耦合的水泥基材料性能研究

通过在水泥基材料中加入纳米二氧化硅和碳纳米管,设计了一种基于纳米改性的水泥基表面强化材料,研究了该水泥基表面强化材料的力学性能和抗裂性能。结果表明:随着纳米二氧化硅颗粒掺量的增加,表面强化材料的抗压强度先增大后减小,碳纳米管的加入能够显著提高表面强化材料的抗裂性能。2%纳米二氧化硅、0.1%碳纳米管掺量的表面强化材料性能最优。     

TiO2纳米颗粒对水泥-粉煤灰体系水化硬化及氯离子侵蚀的影响

利用微量热分析、X射线衍射(XRD)、差热分析(DSC)、扫描电子显微镜(SEM)、压汞测孔仪(MIP)等手段研究了TiO_2纳米颗粒对水泥粉煤灰体系水化硬化以及抗氯离子侵蚀的影响。研究发现:TiO_2纳米颗粒的异相晶核效应和微集料填充效应协同作用,促进了水泥熟料的水化,加快了粉煤灰的二次水化进程并降低了硬化水泥石的孔体积,使水泥粉煤灰材料的微观结构更加均匀密实,提高了水泥粉煤灰材料的力学性能和抗氯离子侵蚀性能。     

纳米二氧化硅对丁苯共聚物/硫铝酸盐水泥复合砂浆物理力学性能的影响

为厘清纳米二氧化硅(NS)和丁苯共聚物乳液(SB)在硫铝酸盐(CSA)水泥中的协同作用，同时解决SB/CSA水泥复合砂浆凝结时间长、抗压强度低的问题，采用NS和SB对CSA水泥砂浆进行复合改性，研究改性复合砂浆物理力学性能随NS掺量的变化，并通过测定水化放热及水化产物分析NS在SB/CSA水泥复合砂浆中的作用机制。结果表明：NS可有效缩短SB/CSA水泥复合砂浆的凝结时间，提高其抗压强度，并与SB对CSA水泥砂浆抗折强度提升具有协同作用；NS最佳掺量为1.5%,此时与不加NS的纯SB改性砂浆相比，28 d抗压和抗折强度分别提高了28%、30%。同时，掺入NS会降低复合砂浆的流动度，提高表观体积密度，降低含气量和干燥收缩率，并略微降低毛细孔吸水率。NS可通过促进无水硫铝酸钙和硫酸钙反应，进一步加快SB/CSA水泥复合浆体的水化进程，提高钙矾石的含量，从而缩短凝结时间并提高力学强度。     

Na2SO4·10H2O对磷酸钾镁水泥水化硬化的影响

磷酸钾镁水泥凝结硬化过快及水化放热集中的问题严重制约着其大规模工程应用,相变材料的吸热储能功能为解决这一问题提供新途径。研究了无机水合盐Na_2SO_4·10H_2O(NS)对磷酸钾镁水泥(MKPC)水化温升、工作性能和抗压强度的影响,并结合XRD、FT-IR、SEM等分析手段及其水化放热速率曲线探究了NS对MKPC性能的影响机制。结果表明:NS的溶解和相变过程吸收大量热,同时释放出结晶水,降低了MKPC体系中Mg~(2+)、PO_4~(3-)和H~+的溶出速率及浓度,MKPC系统内部水化反应速率降低,凝结时间延长,流动度增大,水化放热和水化温升变得更加平缓,在水化早期,MKPC的硬化体强度随NS掺量增加略有降低。在一定的NS掺量(≤4%)内,MKPC水化产物的结晶度提高,后期强度稳定增长,掺有2%NS的MKPC的28d强度将高于基准组。     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

脱硫石膏对大掺量粉煤灰-矿渣粉干混砂浆性能的影响

针对大掺量粉煤灰、矿渣粉导致干混砂浆早期强度和后期强度较低的问题,研究脱硫石膏对该干混砂浆性能的影响;采用X射线衍射、扫描电镜及孔结构分析等手段进行微观机理讨论。结果表明,在大掺量粉煤灰矿粉干混砂浆中掺加占胶凝材料总质量6%～8%的脱硫石膏,对和易性无不良影响,并可显著提高浆体的抗压强度及拉伸粘结强度,收缩率降低10%以上,并改善抗碳化能力,使砂浆体积更稳定;脱硫石膏对粉煤灰及矿渣粉起到激发硫酸盐和碱性的双重作用,并在一定程度上促进水泥水化;胶凝材料的水化产物改善砂浆浆体内部结构,使砂浆浆体中的孔隙大大减少。     

Advance treatment by nanographite for Portland pulverised fly ash cement (the class F) systems

This is a full article that overcomes such some negative side effects as rapid coagulation and reduced early strength in class F fly ash-substituted cement (FFA-SC) by serving nano graphite particle (nG). This study uses class F fly ash (FFA), nG, and ASTM type I cement as constituent materials to prepare proper pulverized fly ash–Portland cement combinations (35% FFA + 65% ASTM I + 1.1% nG i.e.). Pastes include lime and/or lime + nG, and tap water to examine ups and downs in Ca(OH)₂ content. Mortars also contain these prepared cements, tap water and/or tap water + super plasticizer (SP), and mortar sand in order to measure fluidity, flexural strength, and compressive strength according to present standard methods. Results indicate for FFA-SC system that the nano graphite particle increases the reduced early strength gain at early age, and the SP reduces the rapid coagulation. The use of nG also shows to be favorable in terms of the Ca(OH)₂ content, the fluidity and the flexural strength gain, and compressive strength gain in FFA-SC system when compared to the pure Portland cement with and without nano graphite particle.     

Compressive strength and microstructural analysis of fly ash/palm oil fuel ash based geopolymer mortar

This paper presents the effects and adaptability of palm oil fuel ash (POFA) as a replacement material in fly ash (FA) based geopolymer mortar from the aspect of microstructural and compressive strength. The geopolymers developed were synthesized with a combination of sodium hydroxide and sodium silicate as activator and POFA and FA as high silica–alumina resources. The development of compressive strength of POFA/FA based geopolymers was investigated using X-ray florescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field emission scanning electron microscopy (FESEM). It was observed that the particle shapes and surface area of POFA and FA as well as chemical composition affects the density and compressive strength of the mortars. The increment in the percentages of POFA increased the silica/alumina (SiO₂/Al₂O₃) ratio and that resulted in reduction of the early compressive strength of the geopolymer and delayed the geopolymerization process.     

水泥-粉煤灰-硅灰基超高性能混凝土水化过程微观结构的演变规律

超高性能混凝土(UHPC)具有卓越的力学性能和耐久性能,应用前景广阔。采用扫描电镜背散射电子图像、热重法和氮气吸附法系统研究了水泥-粉煤灰-硅灰基UHPC浆体水化过程中微观结构的演变过程。结果表明:UHPC浆体在早期水泥水化较快,但7d后水化变得较为缓慢,粉煤灰在UHPC浆体中反应较为缓慢,28d时反应程度仅为7%;UHPC浆体中Ca(OH)2含量早期上升快速,由于硅灰和粉煤灰的火山灰反应逐渐消耗,3d后含量开始下降,但28d时浆体中仍存在部分Ca(OH)2;此外,在水化过程中,UHPC浆体的比表面积不断降低,孔隙率逐渐下降,水化产物变得更为致密。     

Effect of supplementary cementitious materials on shrinkage and crack development in concrete

The autogenous and drying shrinkage of Portland cement concrete, and binary and ternary binder concretes, were measured and compared. The binary and ternary binder concretes were formed by replacing part of the cement with fly ash, very fine fly ash and/or silica fume. Restrained shrinkage test was also performed to evaluate the effect of binder type on early age cracking. After the cracking of the restrained ring samples, crack widths were measured and compared with the results of an R-curve based model, which takes post-peak elastic and creep strains into account.The incorporation of fly ash and very fine fly ash decreased the autogenous shrinkage strain but increased the drying shrinkage strain. Since the total shrinkage strains of both the ternary and the binary concrete mixtures were similar, the strength development became an important factor in the cracking. The lower strength of the concrete with ternary binders led to earlier cracking compared to the binary binder concrete. Portland cement concrete cracked the earliest and had the greatest crack width. Measured crack widths were in accordance with the crack widths calculated with the R-curve model.     

Influence of fly ash as a cement addition on the hardened properties of recycled aggregate concrete

The effects of the use of Class F fly ash as a cement addition on the hardened properties of recycled aggregate concrete were determined. In this study, four series of concrete mixtures were prepared with water-to-cement (w/c) ratios of 0.55, 0.50, 0.45 and 0.40. The recycled aggregate was used as 0%, 20%, 50% and 100% replacements of coarse natural aggregate. Furthermore, fly ash was employed as 0% and 25% addition of cement. Although the use of recycled aggregate had a negative effect on the mechanical properties of concrete, it was found that the addition of fly ash was able to mitigate this detrimental effect. Also, the addition of fly ash reduced the drying shrinkage and enhanced the resistance to chloride ion penetration of concrete prepared with recycled aggregate. Moreover, it was found that the drying shrinkage and chloride ion penetration decreased as the compressive strength increased. Compared with the results of our previous study, the present study has quantified the advantages of using fly ash as an additional cementitious material in recycled aggregate concrete over the use of fly use as a replacement of cement.     

环境湿度对玻璃纤维增强水泥力学性能的影响

通过开展在不同龄期、不同环境湿度下玻璃纤维增强水泥(GRC)试件的抗折强度、抗压强度试验和基体pH值测定,研究了环境湿度对掺加粉煤灰和硅灰等活性矿物掺合料的GRC试件力学性能的影响。结果表明:环境湿度对GRC试件的抗折强度有重要影响,相对湿度越大,随着龄期增加, GRC试件抗折强度降低越严重;在温度60℃、相对湿度95%条件下,经过56 d龄期后,掺有40%粉煤灰和10%硅灰的GRC试件抗折强度比未掺加粉煤灰和硅灰的GRC试件的抗折强度提高48.5%、抗压强度提高23.6%, GRC基体pH值降低6%。在相同的湿度条件下,掺有粉煤灰和硅灰试件的pH值在各个龄期都低于普通硅酸盐水泥试件,说明粉煤灰和硅灰的掺入能降低水泥水化液相的碱度,进而延缓了纤维受侵蚀的速度,显著改善了GRC试件的力学及耐久性能。通过对试验结果进行分析,利用MATLAB软件建立了GRC试件抗折强度和抗压强度与水泥砂浆基体pH值及时间的关系式。      

Influence of clays on the shrinkage and cracking tendency of SCC

The influence of different types of clay on the shrinkage and cracking tendency of fly ash modified self-consolidating concrete (SCCF) for the application of slipform paving were investigated in this study. The mortar phase of each mix was tested for autogenous shrinkage, total free shrinkage under drying and restrained shrinkage cracking. The mechanical properties (flexural strength, compressive strength, and modulus) were studied to supplement the results of the shrinkage and cracking tests. The plain SCCF mix was compared against the clay-modified SCCF mixes, as well as conventional SCC and slipform concrete (SFC) mixes. The results showed that the very early-age autogenous shrinkage of SCCF mortar was increased by the addition of clays due to adsorption effects. The effects of the clays on total shrinkage under long-term drying were found to depend mainly on the pozzolanic reactivity, but these effects were very slight at low dosages of about 1% by mass of binder. The early-age cracking tendency was aggravated by the clays composed of purified magnesium alumino silicate and metakaolin, but little influenced by the clay composed of kaolinite, illite and silica. Overall, the SCC mixture modified with both fly ash and a small amount of clay showed comparable shrinkage and early-age cracking performances as conventional SFC.     

Strength and resistance to sulfate and sulfuric acid of ground fluidized bed combustion fly ash–silica fume alkali-activated composite

Fluidized bed combustion (FBC) is an environmentally friendly process for burning of coal and is used in many small factories located in urban area. The FBC fly ash is an environmental problem and needs good disposal or utilization. This research studied the strength and resistance to sulfate and acid of alkali-activated FBC fly ash–silica fume composite. The FBC fly ash was interground with silica fume (at the dosage levels of 1.5%, 3.75% and 5.0%) to make the source material homogenous with increased reactivity. Addition of silica fume enabled the adjustment of SiO₂/Al₂O₃ ratios (6.55-7.54) of composite and improved the strength and resistance to sulfate and acid of composite. The composite with 3.75% silica fume showed the optimum strength with 28-day compressive strength of 17.0 MPa. The compressive strengths of composite with 3.75% silica fume immersed in 5% magnesium sulfate solution and 3% sulfuric acid solutions were substantially higher than the control. The strength loss was from the high calcium content of FBC fly ash and incorporation of silica fume thus increased the durability of the composite.