Effect of fine aggregate replacement with Class F fly ash on the mechanical properties of concrete

This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (sand) was partially replaced with Class F fly ash. Fine aggregate (sand) was replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of Class F fly ash by weight. Tests were performed for properties of fresh concrete. Compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were determined at 7, 14, 28, 56, 91, and 365 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of fine aggregate (sand), and can be effectively used in structural concrete.     

Effect of fine aggregate replacement with Class F fly ash on the abrasion resistance of concrete

This paper presents the abrasion resistance of concrete proportioned to have four levels of fine aggregate replacement (10%, 20%, 30%, and 40%) with Class F fly ash. A control mixture with ordinary Portland cement was designed to have 28 days compressive strength of 26 MPa. Specimens were subjected to abrasion testing in accordance with Indian Standard Specifications (IS: 1237). Tests were also performed for fresh concrete properties and compressive strength. Tests on compressive strength and abrasion were performed up to 365 days.Test results indicated that abrasion resistance and compressive strength of concrete mixtures increased with the increase in percentage of fine aggregate replacement with fly ash. Abrasion resistance of concrete was improved approximately by 40% over control mixture with 40% replacement of fine aggregate with fly ash, and concrete with fine aggregate replacement could be suitably used.     

Strength properties of high-volume fly ash roller compacted and workable concrete, and influence of curing condition

A laboratory investigation was carried out to evaluate the strength properties of high-volume fly ash (HVFA) roller compacted and superplasticised workable concrete cured at moist and dry curing conditions. Concrete mixtures made with 0%, 50% and 70% replacement of normal Portland cement (NPC) with two different low-lime Class F fly ashes, good and low quality, were prepared. Water-cementitious material ratios ranged from 0.28 to 0.43. The compressive, flexural tensile and cylinder splitting tensile strengths were measured and presented. The relationship between the flexural tensile and compressive strengths was discussed. The influence of loss on ignition (LOI) content of fly ash on water demand and the strength of concrete was also discussed. The influence of moist and dry curing conditions on the high-volume fly ash (HVFA) concrete system was assessed through a proposed simple efficiency factor. The study showed that producing high-strength concrete was possible with high-volume fly ash content. LOI content increased the water demand of fresh concrete. HVFA concrete was found to be more vulnerable to dry curing conditions than was NPC concrete. It was concluded that HVFA concrete was an adequate material for both structural and pavement applications.     

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.     

玄武岩纤维增强粉煤灰水泥浆体的耐久性及缺陷分析

采用环境扫描电镜和能谱仪表征了玄武岩纤维的耐酸碱腐蚀性能。通过玄武岩纤维的抗弯增强效果和相对动弹性模量的变化情况评定了玄武岩纤维在水泥基体中的耐久性。用XCT（X-ray computed tomography）研究了玄武岩纤维对掺或不掺粉煤灰的水泥浆体内部缺陷的尺寸与分布的影响。结果表明：玄武岩纤维的耐酸腐蚀性能优于耐碱腐蚀性能;粉煤灰的掺入能显著提高玄武岩纤维增强水泥的后期抗折强度提高率和相对动弹性模量增长速率;粉煤灰和玄武岩纤维的掺入均使基体内部总的缺陷体积分数增大,但粉煤灰掺入玄武岩纤维水泥浆体明显降低了尺寸在0.007～0.01mm3内的缺陷数量。     

High-percentage replacement of cement with fly ash for reinforced concrete pipe

Fly ash is commonly used as a substitute for cement within concrete in various applications. Manufacturers of reinforced concrete products commonly limit the quantity of fly ash used to 25% or less by weight. Test cylinders with varying percentages of Class C (25-65%) and Class F (25-75%) fly ash and a water-reducing admixture (WRA) were created under field manufacturing conditions and tested for 7-day compressive strength. Seven-day compressive strength for the concrete/fly ash/WRA was found to be highest when the concrete mix included approximately 35% Class C or 25% Class F fly ash. However, substitution ratios of up to 65% Class C or 40% Class F fly ash for cement met or exceeded American Society for Testing and Materials (ASTM) strength requirements for manufacture of Class I, II and III reinforced concrete pipe (RCP).     

纳米颗粒粉煤灰绿色混凝土的耐久性试验研究

为配制高性能绿色混凝土,用不同质量分数的粉煤灰（0%~30%）来替代水泥,并在混凝土中掺入不同质量分数纳米颗粒氧化锌（0%~3%）来提高混凝土的抗压强度、抗拉强度和抗氯离子性能。通过制备30组混凝土试块进行试验,得出：1）在粉煤灰替代率相同的情况下,随着纳米颗粒氧化锌含量的增加,纳米颗粒氧化锌粉煤灰混凝土的抗压强度、抗拉强度和抗氯离子性能均逐渐增加。2）在纳米颗粒氧化锌含量相同的情况下,随着粉煤灰替代率的增加,纳米颗粒氧化锌粉煤灰混凝土的抗压强度和抗拉强度均逐渐下降。但纳米颗粒氧化锌粉煤灰混凝土的抗氯离子性能却逐渐提高。因此,当纳米颗粒氧化锌质量分数为1%时,建议粉煤灰的替代率在10%以下;当纳米颗粒氧化锌质量分数为2%时,建议粉煤灰的替代率在20%以下;而纳米颗粒氧化锌质量分数为3%时,建议粉煤灰的替代率仍在20%以下,因此不建议纳米颗粒氧化锌的掺量超过2%。     

掺粉煤灰的桥面铺装层混凝土的性能

用掺20％的C级粉煤灰水泥制备了一种新的粉煤灰混凝1（fly ash concrete,FAc）面层材料,总的胶凝材料（cementitious materials,CM）密度为394kg／m^3,并根据设计需要添加了一定量的纤维以增强材料的抗裂性能。本实验测试了面层材料的抗压和抗折强度、黏接强度、收缩率、渗透系数、残...     

粉煤灰混凝土抗盐冻性能的研究

研究粉煤灰混凝土在水中和硫酸镁溶液中的抗冻性,探讨粉煤灰掺量、含气量及砂率对混凝土抗冻性的影响。试验结果表明：粉煤灰掺量25％对混凝土的抗冻盐性能有利,在相同粉煤灰掺量时,适量引气可大大延缓混凝土相对动弹性模量的下降,在保持水胶比一定时,适当的砂率也会在一定程度上改善混凝土的抗盐冻性能。     

双掺粉煤灰及偏高岭土对混凝土性能的影响研究

通过测试混凝土抗压强度、劈拉强度、抗渗、抗碳化、抗冻性能,研究了粉煤灰和偏高岭土单掺、复掺时对混凝土性能的影响。同时分析了粉煤灰和偏高岭土对混凝土性能的作用机理。研究结果表明:当粉煤灰掺量为胶凝材料的15%、偏高岭土掺量为胶凝材料的12%,相比普通混凝土,复掺粉煤灰及偏高岭土混凝土28d抗压强度提高了15.8%、劈拉强度提高了20.4%、渗透系数降低了69.1%、碳化深度降低了29.3%,200次冻融循环后,相对动弹性模量提高了33.1%、混凝土质量损失降低了43.8%。复掺粉煤灰及偏高岭土适用于制备高性能混凝土。     

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.     

Use of ground coarse fly ash as a replacement of condensed silica fume in producing high-strength concrete

This paper presents a method of improving coarse fly ash in order to replace condensed silica fume in making high-strength concrete. The coarse fly ash, having the average median diameter about 90-100 μm, yields a very low pozzolanic reaction and should not be used in concrete. In order to improve its quality, the coarse fly ash was ground until the average particle size was reduced to 3.8 μm. Then, it was used to replace Portland cement type I by weights of 0%, 15%, 25%, 35%, and 50% to produce high-strength concrete. It was found that concrete containing the ground coarse fly ash (FAG) replacement between 15% and 50% can produce high-strength concrete and 25% cement replacement gave the highest compressive strength. In addition, the concrete containing FAG of 15-35% as cement replacement exhibited equal or higher compressive strengths after 60 days than those of condensed silica fume concretes. The results, therefore, suggest that the FAG with high fineness is suitable to use to replace condensed silica fume in producing high-strength concrete.     

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。     

Benefits of fly ash utilization in concrete road cover

The world faces a number of environmental issues. Many of these problems are man-made, the results of industrialization and building. There are many ways to help our world to become more environmentally friendly and healthier. Cutting back of carbon dioxide emissions by using less energy consumptive materials in the building industry is one of them. Waste products used as a replacement of old raw materials lead to the less energy consumption and cost saving. The tests results of energy waste (fly ash) exploitability as a partial cement replacement into the concrete cover of pavement is described in this paper. Compressive and flexural strengths at hardened ages of 7, 28, 90 days, chemical resistance, freezing and thawing of fly ash concrete composites were measured and compared with the reference specimen (C 30/37), which met the requirements of STN 73 6123 Building of road element.     

Effect of temperature and aging on the mechanical properties of concrete: Part I. Experimental results

This paper reports the results of curing temperature and aging on the strength and elastic modulus and the Part II paper suggests a prediction model based on these experimental results. Tests of 480 cylinders made of Types I, V, and V cement+fly ash concretes, cured in isothermal conditions of 10, 23, 35, and 50 °C and tested at the ages of 1, 3, 7, and 28 days are reported. According to the experimental results, concretes subjected to high temperatures at early ages attain higher early-age compressive and splitting tensile strengths but lower later-age compressive and splitting tensile strengths than concretes subjected to normal temperature. Even though the elastic modulus has the same tendency, the variation of elastic modulus with curing temperature is not so obvious as compressive strength. Based on the experimental result, the relationships among compressive strength, elastic modulus, and splitting tensile strength are analyzed, considering the effects of curing temperature, aging, and cement type.     

粉煤灰混凝土抗酸雨侵蚀的研究

不同粉煤灰掺量(0,20%,40%,60%)高性能混凝土经不同pH值(1、2、4)硫酸溶液浸泡后,研究其相对动弹性模量和质量损失规律.试验表明,随着溶液酸性的增加,混凝土破坏严重;粉煤灰掺量为20%～60%时,混凝土抗酸性能有所增加;高掺量粉煤灰混凝土在酸性环境中浸泡,当粉煤灰掺量为60%时,混凝土以相对动弹性模量损失...     

粉煤灰微珠掺量对透水混凝土的影响

本文研究了不同粉煤灰微珠掺量对透水混凝土工作性、透水系数、连续空隙率、抗压强度及劈裂抗拉强度的影响。通过单要素控制变量法研究发现：粉煤灰微珠掺量范围在20%～30%时,微珠对透水混凝土工作性及抗压性能的提升作用最为有效。粉煤灰微珠掺量为10%时,透水混土的连通空隙率有明显提高。透水系数与粉煤灰微珠掺量整体呈负相关联系。透水混凝土劈裂抗拉强度受“粉煤灰微珠”掺量的影响较小。     

碱式硫酸镁水泥混凝土在硫酸盐溶液中的损伤过程研究

采用干湿循环的试验方法研究碱式硫酸镁水泥(BMSC)混凝土抗硫酸盐腐蚀性能.以质量变化和相对动弹模量作为评价指标,研究了不掺加矿物掺合料(BMSC)、掺加30％粉煤灰(BMSC-F)碱式硫酸镁水泥和普通硅酸盐水泥(POC)混凝土抗硫酸盐腐蚀性能.结果表明:干湿循环前期,混凝土的质量缓慢增加;后期,混凝土的质量损失比较明显.在干湿循环的环境下,BMSC混凝土的Erd变化包括以下4阶段:上升段,缓慢下降段,线性上升段,加速下降段;POC混凝土的Erd随着干湿循环次数的增加,呈现先升高后下降的趋势.同等条件下,BMSC混凝土的抗硫酸盐腐蚀性能优于POC混凝土;掺加粉煤灰有利于提高BMSC混凝土的抗硫酸盐腐蚀能力.     

碱-磷渣-粉煤灰胶凝材料的性能与硬化浆体结构

为充分利用磷渣和粉煤灰两种工业废渣生产高性能胶凝材料,研究了不同磷渣/粉煤灰配合比的碱-磷渣-粉煤灰胶凝材料性能,并用扫描电子显微镜和压汞仪分析了硬化浆体的细观结构和孔结构.结果表明:碱-磷渣-粉煤灰胶凝材料的凝结时间正常,在粉煤灰掺量为0～30 %(质量分数)范围内,随粉煤灰的掺量的增加,碱-磷渣-粉煤灰胶凝材料的凝结时间略有延长.与普通硅酸盐水泥相比,碱-磷渣胶凝材料的抗压强度较高,其3d和28d抗压强度分别可达到30.9MPa和98.8MPa,但其抗折强度相对较低.掺加粉煤灰后碱胶凝材料的抗压强度降低,而抗折强度提高.碱-磷渣-粉煤灰胶凝材料的耐蚀性和抗冻性能均显著优于硅酸盐水泥,其干缩比硅酸盐水泥的大.用部分粉煤灰取代磷渣粉可一定程度减小干缩.碱-磷渣-粉煤灰胶凝材料硬化浆体的结构非常致密,其孔隙率和平均孔径均小于普通硅酸盐水泥硬化浆体.     

Autoclaved SIFCON with high volume Class C fly ash binder phase

The effect of incorporating high volume of Class C fly ash (FA) on mechanical properties of autoclaved SIFCON (slurry infiltrated fiber concrete) has been investigated in this study. Cement was replaced with up to 60% FA in SIFCON compositions and three different steel fiber volumes (2%, 6% and 10%) were used. Test results were presented in comparison with the control mix (0% FA and 0% fiber). Mechanical properties were positively affected almost at every FA replacement. Moreover, by increasing the fiber volume, flexural strength and toughness were remarkably increased. This behavior was more pronounced at 10% fiber volume. At this fiber volume ratio, flexural strength of 55 MPa could be achieved with 60% FA replacement.