Hydration of coal–biomass fly ash cement

This paper presents possibilities of use of fly ashes from co-combustion bituminous coal and biomass in cement production process. Both fly ashes coming from co-combustion bituminous coal and biomass and the ones from bituminous coal combustion were analysed. The following properties of cement were tested: heat of hydration, Ca(OH)₂ content, unreacted C₃S content and microstructure. The results showed that fly ashes from co-combustion coal and biomass retard cement hydration. Cement samples containing coal-biomass fly ashes demonstrate adverse features like lower heat of hydration, higher Ca(OH)₂ content and lower rate of C₃S hydration in comparison to the ones containing fly ashes from bituminous coal. The incorporation of coal-biomass fly ashes in cement results in an increase of porosity of cement paste, leading to a microstructure of lower density.     

碱激发剂对不同掺量粉煤灰UHPC的影响

在UHPC材料中,通过在粉煤灰0%、20%、30%、40%的掺量下掺入不同碱激发剂(氢氧化钙、氢氧化钠、硫酸钠、硫酸钙、碳酸钠、水玻璃)测试砂浆浆体流动性、经时损失和胶砂试件抗压强度、抗折强度。结果表明:在UHPC材料中,随着粉煤灰掺量的增加,流动性改善明显,对抗压抗折强度影响较大;在粉煤灰掺量较小时,碱激发剂效果不明显,随着粉煤灰掺量的增加,碱激发剂的效果逐渐凸显出来;在粉煤灰掺量为30%、40%时,硫酸钙为最为突出的碱激发剂。     

凝硬和冻融作用对干贮粉煤灰的力学性质的影响

介绍了两种低氧化钙含量的粉煤灰和一种高氧化钙含量的粉煤灰在不同制样龄期条件的强度、渗透、压缩特性试验和冻融条件下的强度试验结果 ;分析了凝硬和冻融作用对干贮粉煤灰的力学性质的影响规律。试验结果表明 ,高氧化钙含量的粉煤灰的强度指标受上述两种作用的影响显著 ;低氧化钙含量的粉煤灰的强度指标在凝硬作用下也有所提高 ,但基本不受冻融作用的影响 ;干贮粉煤灰的渗透系数受凝硬和冻融作用的影响较小     

Modeling of hydration kinetics in cement based materials considering the effects of curing temperature and applied pressure

Portland cement is the most widely used cement in the world. In the industrial by-products suitable for use as mineral admixtures in Portland concrete are ashes produced from the combustion of coal and granulated slag in metal industries. However, comparing such ashes with Portland cement, determining the hydration of this concrete is much more complex because of the reaction between calcium hydroxide and fly ash or slag. In this paper, the production of calcium hydroxide in cement hydration and its consumption in the reaction of mineral admixtures are considered in order to develop a numerical model for simulating the hydration of concrete, which contains fly ash or slag. The proposed numerical model includes the effects of water to binder ratios, slag or fly ash replacement ratios, curing temperature, and applied pressure. The heat evolution rate of fly ash- or slag-blended concrete is determined by the contribution of both cement hydration and the reaction of mineral admixtures. Furthermore, an adiabatic temperature rise in hardened blended concrete is evaluated based on the degree of hydration of the cement and mineral admixtures. The proposed model is verified through experimental data obtained from the concrete with different water-to-cement ratios and mineral admixture substitution ratios at elevated temperature and high pressure.     

电石渣-火山灰质胶凝材料固化盐渍土试验研究

以电石渣、粉煤灰和碱激发剂作为原材料制备一种盐渍土固化剂,采用正交试验方法研究各因素对固化盐渍土击实性能和抗压强度的影响,并探索电石渣-火山灰质胶凝体系固化盐渍土的固化机理和水化产物。结果表明:各因素对固化盐渍土抗压强度的影响顺序为:碱激发剂>胶凝材料掺量>m(电石渣)∶m(粉煤灰);固化盐渍土养护7 d抗压强度和水稳定性满足实际工程中对固化盐渍土强度的需求;在电石渣和碱激发剂双重激发下粉煤灰发生火山灰反应,反应产物以水化硅酸钙凝胶、钙矾石和二水石膏为主。当养护龄期为360 d时,试件内未发现明显的Ca(OH)2存留,说明固化土试件养护360 d时,火山灰反应基本完成。     

火力发电产生的高钙粉煤灰的改性研究

本文以电厂发电采用的循环流化床燃烧煤产生的高钙粉煤灰作为研究的对象,主要是为了找到高钙灰降钙的方法,在此基础上改善高钙灰的性能,然后把这种高钙灰利用到水泥生产或混凝土中,变废为宝,变害为利,合理综合利用。     

粉煤灰-钛白石膏路基材料的研究

研究了不同的激发剂掺量对钛白石膏-粉煤灰复合材料的强度和自由线膨胀率等性能的影响,以及减水剂的作用,复合材料的耐水性和抗硫酸盐侵蚀性能等．选用三种不同类别粉煤灰与钛白石膏进行复合．试验结果表明,原状粉煤灰与高钙粉煤灰混合后再与钛白石膏复合的材料。比两种灰单独掺加时效果更好．所研制的复合材料具有较好的力学性能和优异的抗硫酸盐侵蚀性能。     

硅灰和粉煤灰在200 MPa活性粉末混凝土中的应用机理

活性粉末混凝土(RPC)由于具有超高强度、韧性及耐久性而得到快速推广应用。采用0.14的极低水胶比制备200 MPa的RPC,并测试硅灰和粉煤灰对RPC强度和微结构的影响。研究结果表明:RPC的强度随着硅灰掺量的增加呈现先增大后减小的趋势,随着粉煤灰掺量的增加而减小,适量的硅灰掺量和较小的粉煤灰掺量有助于RPC获得较高的强度。硅灰和粉煤灰均具有较高的填充效应和火山灰活性,其活性二氧化硅可与氢氧化钙水化生成水化硅酸钙,尤其是颗粒极细的硅灰,可大幅改善浆体微结构,提高RPC的强度。     

Effects of post-mercury-control fly ash on fresh and hardened concrete properties

Activated carbon injection is the most mature technology for mercury capture from coal burning power plants; however, this technology increases the carbon content and mercury concentration in the fly ash. This, in turn, may reduce the suitability of fly ash for use in concrete and call into question the safety of using fly ash derived from this process. The focus of this paper is to investigate the reuse potential of post-mercury-control fly ash in concrete by examining the influence of three fly ashes derived from the activated carbon injection on the air content, compressive strength, permeability, and resistance to freezing and thawing of concrete mixtures. Laboratory testing confirmed the influence of the carbon on the air content of the concrete. However there was no difficulty in entraining air in activated carbon injection fly ash concretes within the recommended dosage range of the air-entraining admixture. All air-entrained fly ash concretes exhibited excellent characteristics in compressive strength (?32.0 MPa, 4641 psi at 28 days), resistance to chloride-ion penetration (moderate to low at 28 days of age) and freeze–thaw (?90 average durability factor after 300 cycles). The possible leaching of toxic elements including mercury from one fly ash sample used in this study was also evaluated using the US Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure. The test results indicated that the leaching of toxic elements was much lower than the contamination level.     

Stabilization of marginal aggregates with hydraulic and puzzolanic binders based on waste materials

Natural sand deposits and waste screenings from gravel pits and quarries are abundant in parts of Sweden. Investigations have been made to stabilize such materials with binders based on waste materials. Both laboratory work and test roads have been performed. In the latter case, mainly secondary roads have been strengthened with a plant-mixed bases. Good results have been achieved with a binder made of milled granulated blast furnace slag, activated with lime or especially with both lime and waste gypsum. Sand and screenings from gravel often contain organic material, deleterous with the binders studied. In such cases, the gypsum addition also seems to counteract the negative effect of the organic material. Fly ash has recently been available in Sweden. Tests made with fly ash-lime, as often used for stabilization abroad, have shown too slow binding for a rather cold climate. Addition of waste gypsum, calcium chloride, alkali-salts or use of an alkali-rich cement kiln dust instead of commercial lime can improve the binding properties. Different fly ashes, however, react in different ways. It is often more suitable to use fly ash-cement as a binder, especially with poorly graded aggregates. The fly ash, added in an optimum amount, work as a filler and high immediate stabilities can be achieved at a correct water content. The puzzolanic properties of the fly ash, at the same time, makes it possible to reduce the cement content considerably in comparison with the case when only portland cement is used as a binder. Promising laboratory work has also been done with binders consisting of condensed silica fume or ash from fluidized bed coal combustion, both in combination with lime.     

Mercury in coal ash and its fate in the Indian subcontinent: A synoptic review

In the Indian subcontinent power generation is mainly dependent upon the thermal power units and coal is burnt as a fuel for the production of heat and electricity. In India, bituminous and sub-bituminous coals are used which contain over 40% of ash. At present, 80-90 million tons of fly ashes are generated from 85 existing coal based thermal power plants. Coal contains trace metals of which mercury is most toxic for humans and aquatic fauna. The problem of mercury in the society is not new, but in recent years the Indian subcontinent has gained the reputation of being "a dumping ground for mercury". This study focuses on mercury in fly ash and its releases to the atmosphere and soils cross the country. The utilisation of coal ash in India is also addressed although it is still in its nascent stage. About 10% of produced fly ashes are used in India whereas in Western countries its use is typically over 70%. Regulations from India's Ministry of Environment and Forestry should increase coal fly ash utilisation, although this would require that cost-effective new technology is put to use. As to the release of Hg from ashes disposed of in the environment, the scarce literature suggests that this is negligible or zero, and less problematic than wet or dry deposition of Hg from flue gases.     

加压粉煤灰硅钙板

普通粉煤灰硅钙板以消石灰为钙质材料，产品的抗折强度低，易折断，一般单张不能作隔断墙板，只适用于建筑吊顶。研究的加压粉煤灰硅钙板，以水泥代替消石灰，选择适宜的钙硅比，增加一道加压工序，经普通蒸养和压蒸养护，抗折强度提高２倍以上，扩大了该产品的应用领域，而生产成本增加不多，具有明显的技术、经济效益。介绍主要原材料的质量要求、配方设计、生产工艺、产品性能，分析生产中常见疵病产生原因和解决办法。     

Comparison of multiple regression analysis using dummy variables and a NARX network model: an example of a heavy metal adsorption process

In the present study, the adsorption characteristics of coal fly ash obtained from the Kangal Power Plant, Turkey and activated fly ash in the planetary ball mill were investigated to remove the heavy metal ions from aqueous solutions. The adsorption capacity was compared for the first time using a multiple regression analysis with dummy variables and a non‐linear auto regressive exogenous (NARX) network model. An equation was obtained for all types of adsorbents or heavy metals using the regression of q_e on the dummy variables. The predictive ability of NARX was found to be better than that of multiple regression using dummy variables. These models can also be successfully implemented on the experimental data to evaluate the adsorption process. In addition, fly ash is a low cost alternative since it is a more economical and environmentally friendly adsorbent and it is abundant in both nature and from waste material from industry.     

燃煤锅炉碱性废物及其脱硫能力的研究

通过对燃煤锅炉排放碱性废物及其可利用形式的分析，指出其含量受煤种、水质、燃烧方式、灰渣处理方式等多因素影响。实测了一台4t／h链条炉的排污水、离子树脂反洗水，设计了飞灰碱性溶出率的条件试验，并从理论上计算了碱性废物烟气脱硫的可能性。为便于比较，采用了将脱硫能力折合为单位蒸吨脱除率的表示方法。研究结果表明，在试验条件下单位蒸吨锅炉碱性废物可脱除0．415kg的SO2，占总排放量1．275kg的32．56％。其中排污水、反洗水和飞灰分别占8．63％、23．06％和0．87％。反洗水虽有脱硫能力，但成分复杂，可对水循环系统产生腐蚀，实际中尚未利用。飞灰脱硫能力低，因试验煤种钙镁氧化物含量仅为6．5％，在PH值为2．61时达到13．23％平衡溶出率：试验结果表明：飞灰碱性物质溶出率与PH值，搅拌时间有关。PH值低，溶出率大，搅拌时间长，溶出率高。飞灰的脱硫能力主要取决于煤灰的碱性氧化物含量。对碱性含量不高的飞灰，碱性溶出率少，利用其进行烟气脱硫的能力非常有限。这一点不同于钙镁含量高的褐煤和某些低硫煤。     

Optimization of fineness to maximize the strength activity of high-calcium ground fly ash – Portland cement composites

Depending on their physical and chemical properties and the amount of replacements with cement, fly ashes may provide an economical production possibility in concrete industry and improve the mechanical and durability performance of concrete. In recent years, ultrafine fly ash has become one of the necessary ingredients of high-performance concrete. However, many of the fly ashes are coarse in nature, hence grinding is necessary to obtain sufficient performance in concrete production. In this study, the effect of grinding on strength activity of ground high-calcium fly ashes was investigated. Physical characteristics such as sieve fineness, grain particle size characteristics and Blaine specific surface area were also determined and compared with raw fly ash. Some case studies and possible interactions between fineness of fly ash, strength and water demand of mortars were discussed. The optimization of fineness coupled with the adjustment of water content were found as the key parameters of effective utilization of high-calcium fly ashes from the view point of strength maximization of cement mortars.     

利用化工废石膏制备新型道路建筑材料的研究

研究了激发剂对化工废石膏-粉煤灰新型道路建筑材料的强度和自由线膨胀率等性能的影响，以及减水剂的作用和新型道路建筑材料的抗硫酸盐侵蚀性能等。本研究选用3种不同类别粉煤灰与化工废石膏进行复合试验的结果表明，当原状粉煤灰与高钙粉煤灰混合后再与化工废石膏复合研制的材料，比两种灰单独掺加的效果更好，本研究研制的新型道路建筑材料具有较高的力学性能和优异的抗硫酸盐侵蚀性能。     

高掺量粉煤灰水泥浆体长期水化碱环境的变化

通过测试2组水胶比和5种粉煤灰掺量水泥浆体不同龄期的粉煤灰水化反应程度、Ca(OH)2含量、孔隙液的pH值和碱金属离子的变化,探讨了高掺量粉煤灰水泥浆体长期水化碱环境的稳定性.结果显示:粉煤灰长龄期的水化反应程度较低,其掺量(质量分数)小于60%时,不能完全消耗水泥水化所产生的Ca(OH)2,而Ca(OH)2对水泥浆体孔隙液碱度起维持作用,在整个碱环境稳定时,水泥浆体中未溶解的Ca(OH)2对碱环境无直接影响.     

水泥细度与成分对混凝土温升的影响

大体积混凝土的绝热温升影响因素众多,其中水泥细度与组成成分的影响研究较少。分别测试了不同水泥细度及碱含量、粉煤灰掺量与石膏含量等对混凝土温升的影响规律。研究结果表明,随着水泥比表面积的增加,混凝土绝热温升值与温升速率随着水泥细度增加而增大;水泥碱含量在0.4%~1.2%范围内,水泥碱含量增加,其最大温升值减小,水泥碱含量过高或过低都会延长混凝土温升时间;粉煤灰的掺入有利于降低混凝土最大温升值;石膏含量增加也对控制混凝土温升有利。     

高掺量粉煤灰对GFRC改性的可行性研究

采用 5 0℃恒温水浴加速老化的试验方法 (加速老化龄期分别为 3d、7d、14d、2 8d、6 0d和 90d) ,从宏观力学性能的角度研究了采用粉煤灰、纯硅酸盐水泥与耐碱玻纤复合取代低碱水泥与耐碱玻纤复合制备GFRC制品的可行性问题。研究结果表明 ,采用粉煤灰、纯硅酸盐水泥与耐碱玻纤复合的技术是可行的。根据粉煤灰试件的后期强度与试件老化后玻纤表面的形貌分析结果 ,粉煤灰的最佳掺量为 6 0 % ,粉煤灰掺量过高时 ,后期强度开始降低 ;粉煤灰掺量过低时 ,耐碱玻纤就存在化学腐蚀的可能。     

粉煤灰深度处理二级出水中磷的实验研究

为了探索除磷的优良吸附材料和新方法,本实验对粉煤灰与PFS联用、碱改性粉煤灰处理二级出水中的磷进行了实验研究,结果表明：粉煤灰与PFS联用处理3 mg/L的含磷模拟废水去除率可达72%,两者联用可使吸附与混凝发挥协同作用,强化处理效果;而用2 mol/L的氢氧化钠碱改性粉煤灰后,当投加改性粉煤灰8 g,以30 r/min的转速搅拌5 min时,对含磷模拟废水的去除率可达90%,碱改性后,粉煤灰在发挥其吸附作用的同时,与磷酸根离子产生羟磷灰石化学沉淀,强化了除磷效果,且可实现泥水分离。比较分析上述2种方法,碱改性粉煤灰既能有效除磷又能实现泥水分离,且药剂成本较低,工艺简单,值得推广应用。