Tests on Alkali-Activated Slag Foamed Concrete with Various Water-Binder Ratios and Substitution Levels of Fly Ash

To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.

Effect of MSWI Fly Ash and Incineration Residues on Cement Performances

The activities of municipal solid waste incineration （MSWI） fly ash and incineration residues were studied contrastively, through the component analysis and the activity ratio tests. The mechanical properties, hydration mechanism and leaching toxicity of the hardened cement paste mixing with MSWI fly ash and incineration residues were investigated. The experimental results indicated that the active constituents （CaO＋Al2O3＋Fe2O3） in MSWI fly ash were higher than those in incineration residues. Therefore the activity ratio of MSWI fly ash was 43.58%, twice as much as that of incineration residues. Meanwhile, the hydration of cement was delayed by mixing with MSWI fly ash and incineration residues, which also reduced the cement strength markedly. By adding with exceeding 20% MSWI fly ash, the specimens expanded and microcracks appeared. The leaching toxicities of cement pasted mixed with MSWI fly ash and incineration residues were lower than the Chinese national standard. Accordingly the cement mixed by MSWI fly ash and incineration residues can be considered as the environment-friendly materials.

High Performance of Fly Ash Derived Li ₄SiO₄-Based Sorbents for High Temperature CO₂Capture

It is urgent to develop excellent solid CO2 sorbents with higher sorption capacity, simpler synthetic process, better thermal stability and lower costs of synthesis in CO2 capture and storage technologies. In this work, a number of Li4SiO4-based sorbents synthesized by lithium carbonate with three different kinds of fly ashes in various molar ratios were developed. The results indicate that the Li2CO3:SiO2 mole ratio used in the sorbents synthesis significantly affects the CO2 absorption properties. The sorption capacity increased with the excess of Li2CO3 first and then decreased when the excessive quantity was beyond a certain amount. The experiments found that FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4, HCl/CFA-Li4SiO4_0.3 presented the best sorption ability among these fly ash derived Li4SiO4 samples, and the corresponding weight gain was 28.2 wt%, 25.1 wt% and 32.5 wt%, respectively. The three sorbents with the optimal molar ratio were characterized using various morphological characterization techniques and evaluated by thermogravimetric analysis for their capacity to chemisorb CO2 at 450°C - 650°C, diluted CO2 (10%, 20%) and in presence of water vapor (12%). The adsorption curve of FA- Li4SiO4_0.6 at different temperatures was simulated with the Jander-Zhang model to explore the influence of carbon dioxide diffusion on adsorption reaction. Further experiments showed that the adsorbent had a good sorption capacity in a lower partial pressure of CO2 and the presence of steam enhanced the mobility of Li+. What’s more, FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4 and HCl/CFA-Li4SiO4_0.3 particles showed satisfactory sorption capacity in fixed-bed reactor and excellent cyclic sorption stability during 10 sorption/ desorption cycles.

Research on physical and chemical properties and soundness of dry desulphurized fly ash used as a construction material

The physical and chemical properties and soundness of Baosteel Power Plant＇ s dry desulphurized fly ash were systematically investigated and compared with those of the similar byproducts produced by some other domestic power plants. The feasibility of these byproducts used as a construction material was also analyzed. The results show that Baosteel＇s dry desulphurized fly ash is a kind of ash with high calcium and high sulfur contents, which has the characteristics of volcanic ash activity. It contains sulfate and sulfite, and is easy to cause sulfate activation. It has higher activity compared with common fly ash. But higher calcium sulfite and free-CaO contents in ash will bring about soundness concerns to users. Therefore, quality tests and volume control will be necessary when fly ash is used as a construction material.

Bearing Capacity of Embedded Strip Footing on Geogrid-Reinforced Fly Ash

Fly ash is a pozzolanic waste from the burning of coal ash in thermal power plant which will be unchangeable in India and increasing environmental pollution. There is an urgent need of increasing bulk utilization of fly ash in geotechnical application. In this regard, a study was undertaken to investigate the bearing capacity of fly ash slopes (β) with the strip footing of width (B) 0.1 m located at different edge distances (De = 1B, 2B, 3B) from slope crest. These tests were conducted in the laboratory and the pressure-settlement behaviour of strip footing on unreinforced and reinforced fly ash slope having an angle of 45? was studied. The embedment ratio (Z/B = 0.30), and the depth of first layer of polyester geogrid reinforcement were investigated with different footing edge distances (De = 1B, 2B, 3B). From the experiment, pressure and settlements were measured and subsequently, the pressure settlement curves were drawn. It is observed from test results that the load carrying capacity is found to increase with an edge distance in both cases: unreinforced and reinforced slope. Also, a substantial increase is observed in the bearing capacity with the addition of geogrid reinforcement. It is observed that, the bearing capacity ratio (BCR) decreases with edge distance increase. These investigations demonstrate that both, the ultimate bearing capacity and settlement characteristics of the foundation, can be improved due to the inclusion of reinforcements within the fill.

不同地区粉煤灰合成防渗材料的渗透性能分析

粉煤灰由于具有良好的火山灰效应和微集料效应可以应用在混凝土中,以提高混凝土的渗透性能。通过采集白城和吉林热电厂的粉煤灰进行合成防渗材料实验,研究不同地区粉煤灰与氯化钠掺和料配比,以确定防渗性能最优的掺和比,并分析不同地区粉煤灰聚合物渗透性能影响因素。研究表明,相同条件下,水力除灰方式不同,粉煤灰含水量不同,粉煤灰含水率越高,相对密度越小,防渗性能越好。

不同粗骨料取代率下粉煤灰再生混凝土的力学性能研究

为探讨不同再生粗骨料取代率下粉煤灰对再生混凝土力学性能的影响,以及再生混凝土抗折强度与再生粗骨料取代率、水胶比之间的关系,以RC30设计强度等级为基础设计了16组配合比,制作了96块再生混凝土试块,主要进行了再生混凝土的抗压强度试验和抗折强度试验。得出如下结论:随粉煤灰掺量的增加,不同再生粗骨料取代率,抗压强度变化规律有所不同;再生粗骨料取代率为0、30%和40%时,抗压强度随粉煤灰掺量的增加整体呈下降趋势;而当再生粗骨料取代率为50%时,随粉煤灰掺量的增加,抗压强度先减小后增大。粉煤灰掺量大于20%时,天然骨料混凝土的抗压强度急剧下降,而再生骨料混凝土的抗压强度降低幅度均较小,大掺量粉煤灰在再生混凝土中或将有更大的应用空间。通过观察抗折强度试件破坏断面,分析再生混凝土变形破坏特征。粉煤灰的掺入提高了天然骨料混凝土的抗折强度,且掺量为20%强度最高。再生粗骨料取代率为30%时,随粉煤灰掺量变化抗折强度整体呈下降趋势,但下降幅度很小;再生粗骨料取代率为40%和50%时,呈先减后增再减的趋势。天然骨料混凝土的折压比随粉煤灰掺量的增加而提高;再生混凝土折压比随粉煤灰掺量的变化趋势与抗折强度一致,但变化幅度略小。粉煤灰对再生混凝土抗折强度的影响大于抗压强度;再生粗骨料取代率为30%,粉煤灰掺量为10%为较优掺量。提出再生混凝土抗折强度预测式。

自密实全再生混凝土单轴受压性能及强度指标换算关系研究

为深入了解自密实全再生混凝土单轴受压力学性能,以水胶比(0.36、0.40、0.45)与粉煤灰掺量(20%、30%、40%、50%、70%)为变化参数,设计并制作11组(共99个)自密实全再生混凝土试件对其立方体抗压强度、轴心抗压强度和弹性模量进行试验研究,观察试件受压破坏过程及破坏形态,获取各力学性能指标的变化趋势,基于试验结果及现有文献成果,建立强度指标换算关系,并提出自密实全再生混凝土的本构方程。研究表明:自密实全再生混凝土受压破坏过程及破坏形态与普通混凝土相似,总体上自密实全再生混凝土立方体抗压强度、轴心抗压强度及弹性模量随水胶比、粉煤灰掺量的增加而降低,所提计算式可较好预测自密实全再生混凝土的单轴受压性能指标及本构关系。

水下不分散混凝土的配制及性能影响

采用单一变量法和正交试验法,探究了水胶比、絮凝剂掺量和粉煤灰掺量对水下不分散混凝土流动性、抗压强度及抗渗性能的影响。结果表明:絮凝剂掺量对混凝土流动性影响最大,为保证施工时混凝土有较好的流动性,絮凝剂掺量不宜过多,采用粉煤灰适量取代水泥,能节约经济成本,提高混凝土的流动性。水胶比对混凝土抗压强度和抗渗性能的影响最大,当水胶比为0.39、絮凝剂掺量为3.0%、粉煤灰掺量为15%时,水下不分散混凝土的抗压强度与抗渗性能最高。

基于离散元的废旧二灰碎石与土混合料承载比细观力学特性研究

建筑垃圾应用于路基过程中,其材料承载力对道路服役性能具有重要影响。为评价建筑垃圾用于路基填料时的细观力学特性,该文利用离散元软件对不同含石率的废旧二灰碎石与土混合料进行承载比试验,并利用离散元法揭示强度形成机理。结果表明:混合料的承载比随含石率增大不断增加,含石率为80%时达到最大值。在离散元模拟承载比试验中,空隙率随着二灰碎石土的含石量的增大先降低后增大,当含石率为80%时混合料的空隙率最小,此时能达到最佳的承载效果。随着含石率的逐渐增大,废旧二灰碎石之间的颗粒相互嵌挤,形成骨架结构,因此能够有效承担来自贯入杆的荷载。

掺粉煤活性粉末混凝土基本力学性能研究

为探究在掺粉煤灰情况下,养护制度、水胶比、钢纤维掺量对活性粉末混凝土(Reactive Powder Concrete, RPC)基本力学性能的影响规律,文中完成了78个100 mm立方体和26个100 mm×100 mm×300 mm棱柱体掺粉煤灰RPC试件的单轴受压试验,基于试验结果考察了RPC立方体抗压强度与棱柱体抗压强度之间的关系,建立掺粉煤灰RPC弹性模量、横向变形系数、峰值应变、峰值应力等基本力学参数的预测模型。试验结果表明,粉煤灰的加入明显提升了RPC的基本力学性能。

基于响应面分析胶凝砂砾石材料渗透性能研究

为研究不同配合比对胶凝砂砾石渗透性能的影响,选取3个因素(粉煤灰掺量、水胶比、砂率),利用响应面法对试验结果进行影响因素的显著性分析,得出胶凝砂砾石渗透系数对单因素和两两因素交互作用的敏感程度。结果表明:粉煤灰、砂率对渗透系数呈现出极强敏感强度,水胶比对渗透系数敏感强度最低;另外因素之间的两两交互作用对渗透性能的影响从高到低依次为水胶比和砂率、粉煤灰和砂率、粉煤灰和水胶比;通过响应面数学模型得出最优配合比为粉煤灰掺量为22 kg/m^(3)、砂率为20%、水胶比为1.0。

锚具槽回填微膨胀自密实混凝土试验研究

为解决长距离引水隧道无黏结预应力结构锚具槽混凝土振捣不密实或发生较大塑形变形导致开裂脱空等问题,研究粉煤灰掺量、膨胀剂掺量和水胶比对强度、限制膨胀率等性能的影响,设计了微膨胀自密实混凝土,测定其自身体积变形和自收缩变化。结果表明:水胶比0.40,粉煤灰掺量25%,膨胀剂用量30kg/m^(3)时,28d抗弯拉强度和抗压强度分别为4.77,53.6MPa,抗渗等级大于W11,混凝土60d自身体积变形率为20×10^(-6),趋于基本稳定,90d干燥收缩率约为-460×10^(-6),应加强微膨胀自密实混凝土的保湿养护,延长保湿养护的时间,以利于膨胀剂性能的发挥。

辅助胶凝材料对高浆骨比砂浆流变特性的影响

通过研究粉煤灰漂珠、硅灰、纳米二氧化硅及传统粉煤灰对高浆骨比砂浆的流变性能及力学性能影响。研究表明:(1)砂浆28d抗压抗折强度,随硅灰单掺掺量提高(至7.5%)而提高,继续增加至10%,强度不增反降;浆体流动性、屈服应力及低转速黏度则随掺量提高逐渐降低;高转速黏度随掺量先少量降低,掺量达到10%,黏度急速上升。(2)单掺漂珠(5%~25%),砂浆28d强度显著提高,但随掺量提高强度逐渐降低;屈服应力与高转速黏度随掺量提高而提高;流动度与低转速黏度也显著提高,但随掺量增加而降低。单掺粉煤灰对浆体强度提高程度有限,流动度则随掺量提高而提高。(3)复掺硅灰(5%)与漂珠(5%~25%),强度提高不明显,且随漂珠掺量提高而降低,屈服应力随掺量提高而提高,黏度先提高后降低。(4)外掺纳米二氧化硅(0.5%~2.5%)显著提高浆体黏度与屈服应力,并降低流动度,当掺量超过1.5%强度有所降低。因此,对高浆骨比砂浆,硅灰及漂珠掺量均宜控制在小掺量(5%),以获得较好的综合力学与流变性能。纳米二氧化硅可根据需求用以调控浆体流变性能,但需注意其对强度的影响。

基于灰关联理论的混凝土抗压强度影响因素分析

基于灰色关联分析具备的发现系统中各因素对系统结果影响差别的特性,运用灰色关联分析方法,分析了粉煤灰掺量、砂率和水灰比等因素对混凝土抗压强度影响的显著程度。结果表明,粉煤灰掺量对混凝土抗压强度的影响最为显著,与实际实验结果基本一致。分析得出,灰关联分析方法具备一定的结果分析优势,对于现场混凝土试配具有较好的参考意义。

掺烧比对污泥与垃圾协同焚烧的影响

污泥作为城市污水处理的副产物,是一种产量高、危害大的固体废物。目前针对市政污泥的处置主要有堆肥、填埋和焚烧3种方式。随着污泥焚烧技术的深入发展,该处理方式以废物减量化程度高、能量可回收,同时能有效降低病原微生物和有机污染物质的危害等优势,已成为污泥处置的主要方法。本文结合污泥协同垃圾焚烧实际运行数据,采用理论计算、理化检测等方法,研究了掺烧比对烟气和飞灰排放指标的影响。结果表明,当掺烧比在10%左右时,烟气排放指标完全能满足GB18485-2014排放标准的要求,但SO 2指标多次超欧盟标准。每吨绝干污泥焚烧后约产生0.4 t的灰渣,其中灰量占60%,渣量占40%。当掺烧比提高时,飞灰比例增加,但飞灰比例基本在6%左右波动。

干湿-盐浸作用下水工混凝土耐久性研究

文中主要研究水工混凝土在干湿-盐浸作用下耐久性的变化及其劣化机理,对不同水灰比和不同粉煤灰掺量的水工混凝土进行质量损失、抗压强度、动态弹性模量以及XRD测试。结果表明,不同水灰比对水工混凝土耐久性影响较大,水灰比越小,耐久性越好;粉煤灰可以显著改善混凝土的耐久性,最佳掺量为20%,其质量损失率、抗压强度损失率和相对动弹性模量在8次循环后分别为4.02%、19.07%和67.32%;通过XRD测试,发现水工混凝土在硫酸盐侵蚀后生成的石膏和钙矾石,是造成水工混凝土发生侵蚀破坏的主要因素。

砂胶比对地聚合物砂浆强度与干缩性能的影响

为了研究砂胶比对地聚合物砂浆强度与干缩性能的影响,对不同砂胶比条件下砂浆的抗折强度、抗压强度、折压比、干缩率以及孔隙率进行了测试。实验结果表明,地聚合物砂浆的抗折强度和抗压强度随着砂胶比的增大而先增加后降低,且分别在砂胶比为0.4和0.2时达到最大;在探究范围内,折压比随着砂胶比的增大而增大;干缩率随砂胶比的增加呈现出先降低后升高的变化趋势,且砂胶比在0.3时最小;随着砂胶比的增大,地聚合物砂浆的孔隙率和孔径增大,砂浆的致密性明显降低。试验可为地聚合物砂浆的配比优化和后续研究提供有益参考。

粉煤灰对水泥土三轴剪切峰值强度的影响性分析

针对考虑粉煤灰影响的珠三角水泥土三轴峰值剪切强度尚未得到深入研究这一问题,采用室内试验方法,对胶凝材料总掺入比、龄期、围压和粉煤灰掺入比等因素及其对三轴剪切强度之间的影响性进行分析,并揭示各因素与强度之间的影响规律。研究结果表明:试样的峰值强度均随围压逐渐增加,且呈现出相关性很好的线性相关关系。总体上试样的峰值强度随胶凝材料总掺入比逐渐增加。试样的峰值强度均随龄期逐渐增加,但并未表现出很好的线性关系。试样的峰值强度均先随粉煤灰掺入比逐渐增加,当粉煤灰掺入比超过一定程度后,峰值强度随粉煤灰掺入比有所下降。试验围压对峰值强度的影响没有明显的规律,峰值增量大部分处于0~1.5 MPa范围内。龄期也表现出类似的影响规律。试样的峰值强度增量均先随粉煤灰掺入比逐渐增加,当粉煤灰掺入比超过一定程度后,峰值强度增量随粉煤灰掺入比有所下降。研究结果可为珠三角软土区水泥土处理的设计与施工提供试验依据。

两类三元胶凝体系的构建及配比优化

为了保证混凝土材料性能,同时实现低碳、绿色化发展,本文以矿渣粉(GS)、粉煤灰(FA)和石灰石粉(LS)等辅助胶凝材料(SCMs)替代55%(质量分数)水泥(C)制备了两种三元胶凝体系,即粉煤灰-矿渣粉-水泥体系(FGC)和石灰石粉-矿渣粉-水泥体系(LGC),研究了体系中FA-GS、LS-GS比例变化对三元胶凝材料粉料堆积密实度、工作性和强度的影响,并结合微观结构分析确定了三元胶凝体系的最佳配比。结果表明,随着两种三元胶凝体系中GS占比的增大,试样密实度和流动性略微减小,试样抗压、抗折强度以及环境效益逐渐增大。在FA-GS和LS-GS质量比均为3∶8时,两种胶凝体系制备的胶砂试样中后期强度均能接近甚至超过纯水泥试样。