三元复合胶凝体系中硅灰和粉煤灰反应程度的确定

采用选择性溶解法和非蒸发水量法定量研究了不同龄期、不同掺量水泥-硅灰-粉煤灰三元复合胶凝体系中矿物掺合料的反应进程。用同细度同掺量的惰性石英粉替代粉煤灰以消除粉煤灰的稀释效应和异核成核效应,得到三元复合胶凝体系中硅灰的反应程度;根据三元复合胶凝体系中矿物掺合料的整体反应程度,计算了粉煤灰的反应程度。结果表明,硅灰的火山灰反应在复合胶凝体系水化1 d时就已经开始,并呈现早期快而后期慢的特点;而粉煤灰的火山灰效应,在7 d以后才开始并加快。在三元复合胶凝体系中,硅灰和粉煤灰的反应程度均随着粉煤灰掺量的提高而降低。     

电学方法研究掺有窑灰水泥的水化特性

利用非接触式电阻率新方法,研究普通硅酸盐水泥及粉煤灰和粉磨时间分别为1h、3h和4h的窑灰混掺后胶凝材料的水化特性.试验结果表明,窑灰分别粉磨1h、3h和4h后,在同样掺量情况下,对水泥浆体早期电阻率随时间的变化有明显的影响.高碱度和高Cl-、高SO3含量将直接影响到窑灰作为混合材或直接回窑后水泥的早期水化特性.不同掺量的粉煤灰在一定程度上可以平衡窑灰水泥浆体系中的碱,同时窑灰中的碱也可激发粉煤灰的早期活性,在熟料掺量小于50%时仍可获得较高的早期强度.     

早龄期复合胶凝材料的裂纹扩展阻力分析

研究了不同组成的复合胶凝材料硬化浆体(硅酸盐水泥,硅酸盐水泥 粉煤灰,硅酸盐水泥 矿渣,硅酸盐水泥 硅灰,硅酸盐水泥 硅灰 粉煤灰)早龄期时裂纹扩展阻力的发展,探讨了粉煤灰掺量对裂纹扩展阻力的影响.结果表明:早龄期时,在相同水胶比条件下,掺加硅灰使胶凝材料体系裂纹扩展阻力明显降低,在低水胶比条件下,掺加一定量的粉煤灰能够明显增加体系的裂纹扩展阻力,掺加20%的粉煤灰能使胶凝材料具有较高的裂纹扩展阻力.     

石灰石粉和含铝相辅助性胶凝材料的协同作用对混凝土抗碳化性能的影响

为了研究石灰石粉和含铝相辅助性胶凝材料的协同作用对混凝土抗碳化性能的影响,选取了两种含铝相辅助性胶凝材料和石灰石粉以不同比例取代水泥,并采用差热分析、XRD和压汞法测试了其水化产物和微观结构。研究结果表明,单掺石灰石粉降低了混凝土的抗碳化性能,当石灰石粉掺量约为10%时,混凝土的碳化深度最低。当复掺石灰石粉和含铝相辅助性胶凝材料时,两者反应生成了碳铝酸钙,增大了固相体积,优化了孔结构,它们的协同作用提高了混凝土的抗碳化性能。当石灰石粉掺量为5%~15%,粉煤灰掺量小于10%,或者矿粉掺量为10%~30%时,混凝土的碳化深度最低。     

纳米二氧化硅对苯丙共聚物/水泥复合胶凝材料凝结硬化的影响

采用纳米二氧化硅作为调凝物质以期解决苯丙共聚物/水泥复合胶凝材料凝结硬化慢的问题。通过测定纳米二氧化硅改性苯丙共聚物/水泥复合胶凝材料的凝结时间及早期强度,分析纳米二氧化硅对复合胶凝材料凝结硬化过程的影响;采用等温量热法测定纳米二氧化硅改性苯丙共聚物/水泥的水化热,并采用X射线衍射仪对其水化产物进行表征;综合以上分析结果探讨纳米二氧化硅的作用机制。结果表明:掺入二氧化硅能有效促进复合胶凝材料的凝结硬化,二氧化硅掺量为1. 25%时促进作用最为显著;掺入纳米二氧化硅可促进铝酸三钙和硅酸三钙的水化,加快钙钒石和氢氧化钙的生成,缩短复合胶凝材料的水化诱导期和加速期,加快水泥水化进程,从而缩短凝结时间,提高早期强度。     

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.     

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。     

复合膨胀掺合料对水化热和混凝土温升的影响

本文系统研究了复合胶凝材料的水化温升、水化温峰出现时间和水化热。分析讨论了复合胶凝材料中粉煤灰、矿粉掺量的变化对水化温升和温峰出现时间以及 7天内各龄期水化热的影响 ,结果表明 :复合胶凝材料的水化放热速度和早期水化热显著降低 ,且随掺合料增加降低幅度增大 ,但 7天水化热并不一定降低。在水化热研究的基础上 ,设计制作了 5 0 0× 5 0 0× 5 0 0mm半绝热状态的大体积混凝土模拟试样 ,测度分析了复合胶凝材料对大体积混凝土温度峰值与温峰出现时间的影响 ,同时分析讨论了混凝土温升与胶凝材料水化热之间的相互关系     

纳米SiO2与粉煤灰协同改性水泥基材料性能研究

通过调整纳米SiO_2与粉煤灰的比例,研究了两者协同作用对水泥基材料性能的影响。结果表明,纳米SiO_2(NS)和粉煤灰协同作用效果优于NS单一掺加,3%(质量分数,下同)纳米SiO_2和不大于30%的粉煤灰同时掺加可以补偿粉煤灰引起的早期强度降低,且砂浆28d抗压强度不降低。随着NS掺量增加水泥基材料的干燥收缩增大,粉煤灰可以改善纳米SiO_2对干燥收缩的不利影响。随着NS掺量的增加,试件的抗冻性和抗氯离子渗透性能均得到提升,掺加3%NS与30%粉煤灰使水泥基材料达到最佳耐久性能。NS可以缩短水泥水化诱导期,加速水泥水化进程,且使胶凝体系总放热量增加。在水泥粉煤灰体系中掺入NS后,非蒸发水含量在早期明显增多,但在后期增长缓慢。     

大掺量钢渣微粉-水泥碱激发特性

为解决钢渣微粉在水泥基复合材料中掺配比例较低的问题，采用力学性能测试、 XRD、 SEM、 FTIR等方法研究激发剂种类、掺量等对钢渣微粉-水泥胶凝材料力学强度和微观结构的影响。结果表明：碱性激发剂可提高钢渣微粉水化速度、增大复合胶凝材料抗压强度，但激发剂种类对胶凝材料激发效果具有差异性；碳酸钠与三乙醇胺复合激发后效果显著，3、 7、 28 d龄期的最佳强度与未掺加激发剂实验组的相比分别提高47%、 72%、 69%;激发剂对复合胶凝材料浆体水化产物种类没有影响；三乙醇胺具有悬浮稳定效应以及降低溶液表面张力的能力，与碳酸钠的强腐蚀效应作用在钢渣微粉水泥体系中协同强化水化反应，使复合胶凝体系中生成更多的水化产物并且相互交织成复杂密实的空间结构。     

Properties of MSW fly ash-calcium sulfoaluminate cement matrix and stabilization/solidification on heavy metals

In this paper, investigations were undertaken to formulate the properties of fly ash-calcium sulfoaluminate (CSA) cement matrix by blending MSW fly ash with CSA cement. The compressive strength, pore structure, hydration phases, and leaching behavior of Zn and Pb doped MSW fly ash-CSA cement matrices were determined by XRD, MIP, DSC, FTIR, EDX, TCLP leaching test and other experiments. The results showed that the addition of MSW fly ash to form fly ash-CSA cement matrix reduced the compressive strengths of matrices and made the pore distribution of matrices coarser, compared to that of pure CSA cement matrix. However, fly ash-CSA cement matrix could effectively immobilize high concentration of heavy metal such as lead and zinc with much lesser leaching of TCLP. Besides ettringite AFt, Friedel phase was a new hydration phase formed in the matrix. The formation of these hydration phases was responsible for huge reservoir of heavy metal stabilization by chemical fixing. Therefore, it could be postulated that MSW fly ash-CSA cement matrix was a potential new constituent of S/S matrix for high concentration of heavy metals such as Zn and Pb ions.     

The hydration properties of pastes containing municipal solid waste incinerator fly ash slag

This study investigated the hydration properties of Type I, Type III and Type V cements, mixed with municipal solid waste incinerator fly ash, to produce slag-blended cement pastes. The setting time of slag-blended cement pastes that contained 40% slag showed significantly retardation the setting time compared to those with a 10% or even a 20% slag replacement. The compressive strength of slag-blended cement paste samples containing 10 and 20% of slag, varied from 95 to 110% that developed by the plain cement pastes at later stages. An increased blend ratio, due to the filling of pores by C-S-H formed during pozzolanic reaction tended to become more pronounced with time. This resulting densification and enhanced later strength was caused by the shifting of the gel pores. It was found that the degree of hydration was slow in early stages, but it increased with increasing curing time. The results indicated that it is feasible to use MSWI fly ash slag to replace up to 20% of the material with three types of ordinary Portland cement.     

The capacity of ternary blends containing slag and high-calcium fly ash to mitigate alkali silica reaction

The efficiency of ternary blends containing high-calcium fly ash and slag in mitigating alkali-silica reaction (ASR) was evaluated. The concrete prism expansions showed that the ternary blends did not offer significant advantage over binary blends of portland cement and either of the individual material at the same total SCM content. The ability of a particular blend to mitigate ASR was related to its capacity to retain alkalis in its hydration products, as evaluated by an alkali leaching test. For the slag and fly ash used in this study, the capacity to retain alkalis increased with the ability of the blend to consume Ca(OH)₂ during its pozzolanic reaction. For the blends investigated here, the alkali leaching test was more realistic than the accelerated mortar bar test in predicting the 2-year expansion of concrete prisms. The adopted alkali leaching test is proposed to be used as a tool to compare the efficacy of different cementing blends to mitigate ASR.     

The effects of supplementary cementing materials in modifying the heat of hydration of concrete

This paper is intended to provide guidance on the form and extent to which supplementary cementing materials, in combination with Portland cement, modifies the rate of heat evolution during the early stages of hydration in concrete. In this investigation, concretes were prepared with fly ash, condensed silica fume and ground granulated blastfurnace slag, blended with Portland cement in proportions ranging from 5% to 80%. These concretes were subjected to heat of hydration tests under adiabatic conditions and the results were used to assess and quantify the effects of the supplementary cementing materials in altering the heat rate profiles of concrete. The paper also proposes a simplified mathematical form of the heat rate curve for blended cement binders in concrete to allow a design stage assessment of the likely early-age time–temperature profiles in large concrete structures. Such an assessment would be essential in the case of concrete structures where the potential for thermally induced cracking is of concern.     

Ultrasonic characterization of the curing process of PCC fly ash–cement composites

The effects of the type of fly ash, mix proportion, and curing process on the pozzolanic reaction of fly ash–cement paste were investigated by ultrasonic techniques. Specifically, the speed of sound (SOS) and broadband ultrasonic attenuation (BUA) were used to investigate hydration activities of the fly ash–cement composite. SOS provided direct evidence of the delay in the hydration activity caused by mixing fly ash to the cement. The rapid heat of evolution during hydration activity, as indicated by a rapid increase in SOS, resulted in early stiffening of the Class C fly ash–cement composite. However, Class C fly ash–cement composite achieved a lower elastic modulus compared with Class F fly ash–cement composite. The hydration activity is observed to be highly dependent on the type of fly ash substituted for cement in the composite. The BUA provided the indirect evidence of ionic activities occurring during the hydration period and viscoelastic properties of the material.     

Thermal behaviour of ESP ash from municipal solid waste incinerators

Stricter environmental regulations demand safer treatment and disposal of incinerator fly ashes. So far no sound technology or a process is available for a sustainable and ecological treatment of the waste incineration ashes, and only partial treatment is practised for temporary and short-term solutions. New processes and technology need to be developed for comprehensive utilization and detoxification of the municipal solid waste (MSW) incinerator residues. To explore the efficiency of thermal stabilisation and controlled vitrification, the thermal behaviour of electrostatic precipitator (ESP) ash was investigated under controlled conditions. The reaction stages are identified with the initial moisture removal, volatilisation, melting and slag formation. At the temperature higher than 1100 °C, the ESP ashes have a quicker weight loss, and the total weight loss reaches up to 52%, higher than the boiler ash. At 1400 °C a salt layer and a homogeneous glassy slag were formed. The effect of thermal treatment on the leaching characteristics of various elements in the ESP ash was evaluated with the availability-leaching test. The leaching values of the vitrified slag are significantly lowered than that of the original ash.     

Simulation of a temperature rise in concrete incorporating fly ash or slag

Granulated slag from metal industries and fly ash from the combustion of coal are among the industrial by-products and have been widely used as mineral admixtures in normal and high strength concrete. Due to the reaction between calcium hydroxide and fly ash or slag, compared with Portland cement, the hydration of concrete containing fly ash or slag is much more complex. In this paper, by considering the producing of calcium hydroxide in cement hydration and the consumption of it in the reaction of mineral admixtures, a numerical model is proposed to simulate the hydration of concrete containing fly ash or slag. The heat evolution rate of fly ash or slag blended concrete is determined from the contribution of both cement hydration and the reaction of mineral admixtures. Furthermore, a temperature rise in blended concrete is evaluated based on the degree of hydration of cement and mineral admixtures. The proposed model is verified with experimental data on the concrete with different water-to-cement ratios and mineral admixtures substitution ratios.     

矿物掺合料早期水化活性的测试和分析

本文采用环境扫描电子显微镜(ESEM)和热重-差热(TG-DTA)分析仪对磨细矿渣微粉、高钙粉煤灰、低钙粉煤灰的早期水化活性进行了系统测试和分析.理论和试验结果分析表明,掺合料取代水泥时,浆体早期抗压强度的提高取决于掺合料自身参与水化反应的速度和水化产物的数量.水化产物在掺合料颗粒表面沉积的速度和浆体中硅酸盐、铝酸盐水化产物的非蒸发水量随掺合料活性的提高而提高.掺合料活性按磨细矿渣微粉、高钙粉煤灰、低钙粉煤灰的顺序降低,将磨细矿渣微粉或高钙粉煤灰与低钙粉煤灰复合,可以克服低钙粉煤灰大掺量取代水泥时混凝土早期强度降低的缺陷,这是提高低钙粉煤灰在高强高性能混凝土中掺量的一个有效措施.     

Assessment of Pb-slag, MSWI bottom ash and boiler and fly ash for using as a fine aggregate in cement mortar

Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fraction of MSWI bottom ash from a grate furnace (SF), and boiler and fly ash from a fluidised bed incinerator (BFA), were characterized and used to replace the fine aggregate during preparation of cement mortar. The chemical and mineralogical behaviour of these wastes along with the reactivities of the wastes with lime and the hydration behaviour of ordinary Portland cement paste with and without these wastes added were evaluated by various chemical and instrumental techniques. The compressive strengths of the cement mortars containing waste as a partial substitution of fine aggregates were also assessed. Finally, leaching studies of the wastes and waste containing cement mortars were conducted. SLG addition does not show any adverse affect during the hydration of cement, or on the compressive strengths behaviours of mortars. Formation of expansive products like ettringite, aluminium hydroxide and H2 gas due to the reaction of some constituents of BFA and SF with alkali creates some cracks in the paste as well as in the cement mortars, which lower the compressive strength of the cement mortars. However, utilization of all materials in cement-based application significantly improves the leaching behaviour of the majority of the toxic elements compared to the waste as such.     

Emission of Pb and PAHs from thermally co-treated MSWI fly ash and bottom ash process

Municipal solid waste incinerator (MSWI) fly ash was regarded as a hazardous material because concentrations of TCLP leaching solution exceeded regulations. Previous studies have investigated the characteristics of thermally treated slag. However, the emissions of pollutant during the thermal treatment of MSWI fly ash have seldom been addressed. The main objective of this study was to evaluate the emission of Pb and PAHs from thermally co-treated MSWI fly and bottom ash process. The experimental parameters included the form of pretreatment, the proportion of bottom ash (bottom ash/fly ash, B/F=0, 0.1 and 1) and the retention time. The toxicity of thermally treated slag was also analyzed. The results indicated that (1) Pb emission occurred only in the solid phase and that PAHs were emitted from both solid and gas phases during thermal treatment process. (2) Washing pretreatment reduced not only the TCLP leaching concentration of Pb (from 15.75 to 1.67 mg/L), but also the emission of PAHs from the solid phase during thermal treatment process. (3) Adding bottom ash reduced the TCLP leaching concentration of thermally treated slag. (4) The concentration of Pb emission increased with retention time. (5) The thermal treatment reduced the toxicity of raw fly ash effectively, the inhibition ratio of raw fly ash and thermal treated slag were 98.71 and 18.35%, respectively.