Utilisation of Turkish fly ashes in cost effective HVFA concrete production

High-volume fly ash (HVFA) concrete is an economical and durable option for structural as well as general concreting purposes, if properly controlled ashes are employed. The aim of this study was to investigate the possibility of the use of three types of Turkish fly ashes from different sources in cost effective high-volume fly ash concrete production. For this purpose HVFA concrete mixtures were prepared by substituting 40, 50, 60 and 70% of cement by fly ash. The mechanical properties and material costs of mixtures were compared with conventional concrete at the same strength grade at 28 days. It should be noted that as an additional benefit, the long-term strength development and durability advantageous of HVFA concrete is not taken into consideration in cost analysis. Results showed that for structural applications a technically suitable and cost effective HVFA concrete can only be produced by using the fly ashes within the limits of specific chemical and physical properties. It may be possible to use other fly ashes with rehabilitation and pre-process, which may reduce the economical feasibility of fly ash usage.     

纳米秸秆灰对多孔混凝土路面力学性能的影响

本文主要研究了掺加纳米秸秆灰后对多孔混凝土路面性能的影响。根据抗压强度，弯曲强度和抗拉强度来测试多孔混凝土。结果表明，使用纳米秸秆灰材料极大提高了多孔混凝土路面的力学性能，其中纳米秸秆灰以10％质量分数替代水泥制备的多孔混凝土与其它比例制备的样品相比，表现出更加优异的强度；并且测试发现纳米秸秆灰多孔混凝土路面的抗压强度，弯曲强度和抗拉强度随着养护时间的增加而增加。     

Properties of concrete incorporating high volumes of class F fly ash and san fibers

The results of an experimental investigation to study the effects of replacement of cement (by mass) with three percentages of fly ash and the effects of addition of natural san fibers on the slump, Vebe time, compressive strength, splitting tensile strength, flexural strength and impact strength of fly ash concrete are presented. San fibers belong to the category of “natural bast fibers.” It is also known as “sunn hemp.” Its scientific (botanical) name is Crotalaria juncea. It is mostly grown in the Indian subcontinent, Brazil, eastern and southern Africa and some parts of the United States (Hawaii and Florida). A control mixture of proportions 1:1.4:2.19 with W/Cm of 0.47 and superplasticizer/cementitious ratio of 0.015 was designed. Cement was replaced with three percentages (35%, 45% and 55%) of class F fly ash. Three percentages of san fibers (0.25%, 0.50% and 0.75%) having 25-mm length were used.The test results indicated that the replacement of cement with fly ash increased the workability (slump and Vebe time), decreased compressive strength, splitting tensile strength and flexural strength and had no significant effect on the impact strength of plain (control) concrete. Addition of san fibers reduced the workability, did not significantly affect the compressive strength, increased the splitting tensile strength and flexural strength and tremendously enhanced the impact strength of fly ash concrete as the percentage of fibers increased.     

高速公路钢纤维混凝土的性能研究

结合高速公路的实际需要,研究了钢纤维掺量对混凝土性能的影响.在此基础上,研究了粉煤灰掺量对混凝土性能的影响.研究结果表明:钢纤维对于混凝土抗压强度、抗拉强度、抗折强度、磨损量存在一个最佳掺量,其最佳掺量分别是1.5％、2.0％、2.0％、2.5％.当钢纤维掺量为2.0％时,粉煤灰对于混凝土抗拉强度、抗折强度、磨损量存在一个最佳掺量,其最佳掺量分别是15％、10％、15％,但粉煤灰掺量对混凝土抗压强度影响不大.     

Properties of high-volume fly ash concrete incorporating nano-SiO2

This paper presents a laboratory study on the properties of high-volume fly ash high-strength concrete incorporating nano-SiO₂ (SHFAC). The results were compared with those of control Portland cement concrete (PCC) and of high-volume fly ash high-strength concrete (HFAC). Assessments of these concrete mixes were based on short- and long-term performance. These included compressive strength and pore size distribution. Significant strength increases of SHFAC compared to the high-volume fly ash high-strength were observed as early as after 3 days curing, and improvements in the pore size distribution of SHFAC were also observed. In this work, the hydration heat of nano-SiO₂ fly ash cement systems was also studied in comparison to the fly ash-cement systems and to the pure cement systems. In addition, the weight change of fly ash incorporating nano-SiO₂, fly ash, and nano-SiO₂ alone after immersed in saturated lime solution was also studied.     

粉煤灰掺量对海水海砂高性能混凝土性能的影响

通过宏观力学性能、化学收缩、pH值、氯离子浓度等测试和SEM、XRD等微观表征研究粉煤灰掺量对海水海砂高性能混凝土性能的影响。结果表明:为维系钢筋钝化膜稳定,高温蒸养时粉煤灰掺量不宜大于30%(质量分数,下同),标养时粉煤灰掺量不宜大于50%;海水海砂高性能混凝土中游离Cl^-浓度随养护时间波动,前期先升高后骤降,后期缓慢增加,标养条件下Cl^-浓度明显低于高温蒸养条件下;海水海砂高性能混凝土具有早强性,其强度随粉煤灰掺量增加大致呈下降趋势,高温蒸养可明显提高混凝土抗折、抗压强度;粉煤灰掺量越多,残留的未水化颗粒越多,高温蒸养可有效改善混凝土微观结构,提高致密性;粉煤灰掺量过多或过少均会增加硅酸盐水泥体系的化学收缩,粉煤灰掺量为30%和40%时混凝土化学收缩值较小。     

Influence of steam curing on the compressive strength of concrete containing supplementary cementing materials

Heat treatment is widely used to accelerate the strength-gaining rate of concrete. In general, the ultimate strengths of the heated-treated concrete are lower than those of the standard cured specimens. When ultrafine fly ash (UFA) is included in concrete, the pozzolanic reaction is accelerated through the heat treatment. Sometimes, various chemical activators were used to activate the reactivity of fly ash. In the current study, UFA and slag were used as a replacement for cement, steam curing and chemical activators were used to accelerate hydration of cement and fly ash, and then compared with moist curing. This paper presents the influence of steam curing on the compressive strength of concrete containing UFA with or without slag. The experimental results indicated that the concrete containing UFA has low early strength after 13-h steam curing and that the difference between the 28-day compressive strength of concrete through 13-h steam curing and that of moist-cured concrete is large, but the concrete with UFA and CaSO₄ or Ca(OH)₂ has a high early strength, thus, the reactivity of fly ash must be accelerated. Concrete containing UFA and ground slag was prepared, whose compressive strengths were improved.     

Heat evolution of high-volume fly ash concrete

In this paper, the results of a laboratory investigation conducted with heat evolution of high-volume fly ash (HVFA) concrete are presented. Heat evolution of concrete was studied by measuring the temperature increase in concrete under adiabatic curing condition. Characteristic of heat evolution of fly ash concrete was found to be strongly dependent on the replacement level of fly ash and dosage of superplasticizer used to maintain workability. It was also found that using fly ash as cement replacement resulted in a reduction on the maximum temperature rise. Increasing the replacement level of fly ash caused lower temperature rise in concrete. Superplasticizer caused a delay in peak temperature rise time; this is taken as an indicator that high-dosage superplasticizer used in concrete caused retardation in hydration of cement. Concretes having similar ingredients showed similar peak temperature rise whether they are superplasticized or not.     

粉煤灰掺量对再生混凝土力学性能和抗冻性的影响研究

研究粉煤灰掺量、再生粗骨料取代率对再生混凝土抗压强度和抗折强度的影响,并对再生混凝土在不同冻融循环次数下的抗压强度和质量损失率进行了研究.结果表明:随着粉煤灰掺量的增加,再生混凝土抗压强度呈先增大后降低的趋势,当粉煤灰掺量为15%,再生粗骨料取代率为30%时,再生混凝土的抗压强度达到最大;粉煤灰掺量对抗折强度提高幅度较小;在冻融循环低于50次时,试块抗压强度下降速度较缓,此后下降速度加快,当冻融循环达到150次时,强度损失最大;再生粗骨料取代率对试块的抗冻性影响高于粉煤灰掺量.建立了考虑再生粗骨料取代率、粉煤灰掺量因素的冻融循环作用下再生混凝土抗压强度指数衰减规律预测模型.     

粉煤灰对桥梁混凝土抗渗性能的影响规律研究

为研究粉煤灰对桥梁混凝土抗渗性能的影响,制备了不同粉煤灰掺量的混凝土样品,测试分析了桥梁混凝土抗压强度、孔隙结构、渗透高度和抗氯离子渗透性能随粉煤灰掺量和养护龄期的变化规律。研究结果表明:(1)当桥梁混凝土养护龄期为7d时,桥梁混凝土的抗压强度随着粉煤灰掺量的增多而逐渐降低;当混凝土龄期大于28d时,桥梁混凝土的抗压强度在粉煤灰掺量为30%左右时最大。(2)粉煤灰掺量为30%时,桥梁混凝土密实度达到最大,此时其内部小孔隙增大而大孔隙减小。(3)桥梁混凝土抗氯离子渗透系数随着粉煤灰掺量的增大先减小后增大,在粉煤灰掺量为30%时取得最小值。     

芳纶纤维、粉煤灰对混凝土性能的影响

研究了掺加芳纶纤维、粉煤灰对混凝土的力学、抗渗性能的影响。结果表明,芳纶纤维、粉煤灰对混凝土的抗压强度影响不明显,抗折强度、抗渗性能得到明显提高。掺加0．6％的芳纶纤维和10％的粉煤灰时,试样的力学性能和抗渗性能最优,抗折强度提高了30．77％,抗压强度提高了5．69％,抗渗性能提高了24．6％。     

低温养护下矿物掺合料湿喷混凝土力学性能及配比优化研究

为系统研究粉煤灰掺量、硅灰掺量及养护温度对湿喷混凝土力学性能的影响规律,通过设计正交试验对湿喷混凝土抗压强度进行极差和方差分析。结果表明:湿喷混凝土抗压强度随养护龄期增加而增大,但抗压强度增幅随养护龄期延长而减弱;增加硅灰和粉煤掺量均能有效提高湿喷混凝土抗压强度,但粉煤灰掺量超过10%(质量分数,下同)后,粉煤灰掺量的增加对混凝土后期抗压强度没有显著的影响;三因素对湿喷混凝土抗压强度影响程度顺序为硅灰掺量>养护温度>粉煤灰掺量;湿喷混凝土抗压强度对矿物掺合料的敏感性与养护温度呈正相关,增大养护温度能够提高矿物掺合料对湿喷混凝土抗压强度的改善效果;随着养护温度的提高,团絮状胶凝物质大量生成,水化产物黏结得更为密实,混凝土的抗压强度和承载性能得到进一步增强;构建多元非线性回归模型能够对混凝土抗压强度进行预测,并且湿喷混凝土在硅灰掺量、粉煤灰掺量及养护温度分别为15%、15%和10 ℃时具有最佳的抗压强度。     

用于北方满族民居墙体的再生混凝土性能研究

通过试验研究了再生混凝土作为北方满族民居建造材料的可行性。研究重点:再生骨料的物理性质测定、再生混凝土基本力学性能试验,以及粉煤灰、聚丙烯纤维以及附加水对其力学性能的影响。通过试验得到,再生混凝土立方体抗压强度最高应力达37.1 MPa、轴心抗压强度平均应力28.4 MPa、静力受压弹性模量平均应力22 300 MPa、抗折强度平均应力3.8 MPa、劈裂抗拉强度平均应力1.68 MPa。结果表明:在再生混凝土中加入粉煤灰和聚丙烯纤维都对立方体抗压强度有所提高,但附加水的加入对立方体抗压强度产生了降低作用。整体来说,再生混凝土各方面的力学指标都能满足一定的强度要求。因此可以作为北方满族民居的建设材料。     

粉煤灰、矿粉对水工混凝土体积稳定性的影响

采用对比的方法,实验研究了粉煤灰、矿粉对水工混凝土的工作性、抗压强度、弹性模量、干缩和受压徐变的影响。结果表明,在粉煤灰、矿粉等量取代部分水泥后,混凝土的工作性改善,抗压强度和抗压弹模与基准样相近,而28d以后的干缩明显减小;掺有粉煤灰、矿粉的混凝土随养护龄期的延长、强度的增加,其受压徐变逐渐减小;当粉煤灰掺量(质量分数)从15%增加到25%时,混凝土的徐变增大;对于相同掺量(15%)的粉煤灰、矿粉混凝土,经60d养护后加荷其徐变基本相同。     

粉煤灰加气混凝土砌体力学性能与节能效应分析

利用室内试验方法制备了粉煤灰加气混凝土砌块和砌体,分别测试了混凝土砌块的抗拉抗压强度和砌体的抗拉和抗剪强度,分析了砌体抗压和抗剪强度随砂浆厚度的变化规律。在此基础上,建立了粉煤灰加气混凝土砌体节能效应的FLAC 3D数值计算模型。研究表明:(1)粉煤灰加气混凝土砌块的抗拉压强度平均值分别为4.53 MPa和0.75MPa;(2)粉煤灰加气混凝土砌体的整体抗压和抗剪强度随砂浆厚度的增大而分别减小和增大;(3)粉煤灰加气混凝土砌体的平均传热系数小于普通灰砂砖砌体,且随砂浆厚度的增大而减小。     

粉煤灰地聚合物力学性能影响因素研究综述

粉煤灰地聚合物是以粉煤灰为硅铝质原料制备的,具有强度高、耐高温、耐腐蚀、有效固封金属离子等优点。但它固有的脆性以及需高温养护才能快速获得高强度的特点限制了其运用范围,而以纤维作为增强材料不仅可以提高粉煤灰地聚合物的强度,还可以改善其延性和韧性。本文主要从粉煤灰原料特性、碱激发剂、养护制度和增强材料四方面入手,重点阐述了粉煤灰粒径和化学组成,碱激发剂的种类、用量和模数,升温养护时间和初期养护温度对抗压强度的影响,以及纤维对粉煤灰地聚合物抗压强度和弯曲性能的影响。最后,根据现有的研究成果,对四种影响因素分别是如何影响粉煤灰地聚合物力学性能进行总结。     

基于碱式硫酸镁水泥的新型泡沫混凝土的制备及性能研究

以轻烧氧化镁粉、七水硫酸镁为水泥主要原材料,利用化学发泡法制备了容重为100~500 kg/m3的碱式硫酸镁水泥泡沫混凝土(BMSCFC),研究了容重、外掺粉煤灰等对BMSCFC物理性能的影响,并且比较了相同容重下的改性氯氧镁泡沫混凝土.结果表明:随着BMSCFC 容重的增大,其体积吸水率减小、导热系数和抗压强度增大;外掺粉煤灰增强了BMSCFC抗压强度的同时降低了其保温性能,外掺粉煤灰量为轻烧氧化镁粉质量的150%时,容重为402 kg/m3,抗压强度为2.22 MPa,导热系数为0.138896 W/(m· K);与改性氯氧镁发泡混凝土相比,碱式硫酸镁发泡混凝土具有更好的抗压强度和保温性能.     

等强度条件下粉煤灰对补偿收缩混凝土变形性能的影响

通过测定水中限制膨胀率和水养7d转干空后的限制膨胀率,计算干燥收缩落差,讨论粉煤灰在等强度条件下对补偿收缩混凝土变形性能的影响.结果表明:等强度条件下掺加适量粉煤灰可以明显地促进限制膨胀率的增长;掺量过大容易导致早期约束不足,降低对限制膨胀的促进作用.粉煤灰可以明显降低混凝土转干空后早期的干燥收缩落差.随着粉煤灰掺量增加,干燥收缩落差进一步降低,空气中放置28 d后均表现为膨胀.对于硫铝酸钙-氧化钙类膨胀剂和粉煤灰复掺的补偿收缩混凝土,膨胀剂最小用量的要求可以适当降低.     

Properties of fly ash-modified cement mortar-aggregate interfaces

This paper investigates the effect of fly ash on strength and fracture properties of the interfaces between the cement mortar and aggregates. The mortars were prepared at a water-to-binder ratio of 0.3, with fly ash replacements from 15 to 55%. Notched mortar beams were tested to determine the flexural strength, fracture toughness, and fracture energy of the plain cement and fly-ash modified cement mortars. Another set of notched beams with mortar-aggregate interface above the notch was tested to determine the flexural strength, fracture toughness, and fracture energy of the interface. Mortar-aggregate interface cubes were tested to determine the splitting strength of the interface. It was found that a 15% fly ash replacement increased the interfacial bond strength and fracture toughness. Fly ash replacements at the levels of 45 and 55% reduced the interfacial bond strength and fracture toughness at 28 days, but recovered almost all the reduction at 90 days. Fly ash replacement at all levels studied increased the interfacial fracture energy. Fly ash contributed to the interfacial properties mainly through the pozzolanic effect. For higher percentages of replacement, the development of interfacial bond strength initially fell behind the development of compressive strength. But at later ages, the former surpassed the latter. Strengthening of the interfaces leads to higher long-term strength increases and excellent durability for high-volume fly ash concrete.     

养护温度和粉煤灰对补偿收缩混凝土膨胀效能的影响

研究了养护温度和粉煤灰掺量对补偿收缩混凝土的膨胀效能和强度的影响。结果表明：20、40℃养护时混凝土的各龄期强度均匀增长;60℃养护能极大地促进早期强度增长,后期强度增长缓慢。粉煤灰在不同养护温度下对混凝土的早期强度发展都有抑制作用;长期高温养护后,粉煤灰活性逐渐显现,显著促进混凝土的强度增长,且粉煤灰掺量越大,混凝土强度增幅越大。硫铝酸钙–氧化钙类膨胀剂的膨胀效能发挥对温度非常敏感,养护温度越高,膨胀剂的水化速度越快,膨胀作用发挥越早;适量掺加粉煤灰有利于膨胀效能的发挥,掺量越大,膨胀随温度增长的增幅越大。大掺量粉煤灰补偿收缩混凝土的强度发展和限制膨胀率的温度敏感性均很高。