粉煤灰粒度分布对水泥性能的影响

主要研究了不同粉磨时间的粉煤灰密度、比表面积、粒度分布等颗粒特性的变化规律,以及研究了将不同粉磨时间的粉煤灰按30％比例掺人硅酸盐水泥中的水泥性能变化情况.结果表明：随着粉磨时间的增加,粉煤灰颗粒的密度、比表面积和粒度分布都呈有规律的变化;其中粉磨60 min时的粉煤灰水泥性能达到最佳.     

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).     

Influence of fly ash fineness on strength, drying shrinkage and sulfate resistance of blended cement mortar

In this paper, the influence of fineness of fly ash on water demand and some of the properties of hardened mortar are examined. In addition to the original fly ash (OFA), five different fineness values of fly ash were obtained by sieving and by using an air separator. Two sieves, Nos. 200 and 325, were used to obtain two lots of graded fine fly ash. For the classification using air separator, the OFA was separated into fine, medium and coarse portions. The fly ash dosage of 40% by weight of binder was used throughout the experiment. From the tests, it was found that the compressive strength of mortar depended on the fineness of fly ash. The strength of mortar containing fine fly ash was better than that of OFA mortar at all ages with the very fine fly ash giving the highest strength. The use of all fly ashes resulted in significant improvement in drying shrinkage with the coarse fly ash showing the least improvement owing primarily to the high water to binder ratio (W/B) of the mix. Significant improvement of resistance to sulfate expansion was obtained for all fineness values except for the coarse fly ash where greater expansion was observed. The resistance to sulfuric acid attack was also improved with the incorporation of all fly ashes. In this case the coarse fly ash gave the best performance with the lowest rate of the weight loss owing probably to the better bonding of the coarse fly ash particles to the cement matrix and less hydration products. It is suggested that the fine fly ash is more reactive and its use resulted in a denser cement matrix and better mechanical properties of mortar.     

Use of zeolite, coal bottom ash and fly ash as replacement materials in cement production

In this research, the effects of zeolite, coal bottom ash and fly ash as Portland cement replacement materials on the properties of cement are investigated through three different combinations of tests. These materials are substituted for Portland cement in different proportions, and physical properties such as setting time, volume expansion, compressive strength and water consistency of the mortar are determined. Then, these physical properties are compared with those of PC 42.5. The results showed that replacement materials have some effects on the mechanical properties of the cement. The inclusion of zeolite up to the level of 15% resulted in an increase in compressive strength at early ages, but resulted in a decrease in compressive strength when used in combination with fly ash. Also, setting time was decreased when zeolite was substituted. The results obtained were compared with Turkish Standards (TS), and it was found that they are above the minimum requirements.     

Improve the strength of concrete-filled steel tubular columns by the use of fly ash

Concrete-filled steel tubular columns (CFTs) are becoming widely used in engineering. In the present paper, the addition of fly ash and an expansive agent to the concrete of CFTs or a thin layer of fly ash to the interface between steel tube and concrete (CFTFCs) to improve the compressive strength and the bond strength of CFTs was experimentally investigated. The results show that the expansive concrete-filled steel tubular columns (CFETs) have the highest bond strength and compressive strength at the age of 7 days, and CFTFCs have higher bond strength and compressive strength than fly ash concrete-filled steel tubular columns (CFFTs), which in turn are higher than CFTs. However, both bond strength and compressive strength of CFTFCs become the highest at the age of 28 days. The morphology (size and shape) of mineralogy and microstructure of the interface at the age of 28 days were also investigated by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is shown that the strength improvement of CFTFCs mainly depends on the content of SiO₂ and CaO in the interface, and higher content of SiO₂ and/or lower content of CaO are preferred.     

粒径对粉煤灰基地聚物抗压强度的影响

为提高粉煤灰的综合利用,以工业废弃物粉煤灰为主要原料,通过碱激发制备粉煤灰基地聚物,研究了粉煤灰的粒径及粒径分布对粉煤灰基地聚物抗压强度的影响。试验结果表明:对于单峰分布不同粒径的粉煤灰来说,随着D_(50)粒径的减小,粉煤灰基地聚物的28 d抗压强度随之显著升高,早期抗压强度也随之大幅提高;对于相同D_(50)粒径下单峰和双峰分布的粉煤灰来说,单峰分布的粉煤灰基地聚物的抗压强度略低于双峰分布粉煤灰基地聚物的抗压强度;进而证明D_(50)粒径是影响粉煤灰基地聚物的因素之一,通过调节粒径分布可以改善抗压强度,为进一步控制粉煤灰基地聚物的抗压强度提供了理论基础。     

分选与磨细粉煤灰对水泥胶砂性能的影响

研究了分选与磨细粉煤灰的颗粒分布与形貌的差异及对水泥胶砂性能的影响。研究结果表明:当勃氏比表面积相近,磨细粉煤灰的中位粒径大于分选细粉煤灰,其圆珠状颗粒较少,表面较为粗糙。在相同水胶比的条件下,掺分选粗粉煤灰的水泥胶砂流动度及强度均低;分选粗粉煤灰磨细后,不仅减少了颗粒的粘连,增加了比表面积,而且提高了粉煤灰的反应活性和水泥胶砂流动度及强度,虽其水泥胶砂流动度仍小于掺分选细粉煤灰的水泥,3d水泥胶砂强度也略低,但其28d水泥胶砂强度略高于掺分选细粉煤灰的水泥;在相同水泥胶砂流动度的条件下,掺磨细粉煤灰配制的水泥胶砂3d强度低于掺分选细粉煤灰的水泥,但随着水化龄期的增长,其差距逐步缩小,至60d时可超过后者。     

Masonry composite material made of limestone powder and fly ash

Large amounts of fly ash (FA) and limestone powder (LP) wastes are accumulating in countries all over the world. Most of these wastes are abandoned and cause certain serious environmental problems and health hazards. In this study, LP waste and class-C FA were used to produce a composite material without the addition of portland cement. LP was mixed with the FA at levels of 10, 20 and 30% by volume in the samples. LP and FA were mixed, wetted and compressed under high pressure in a steel mould. The compressive and flexural strengths were measured, and ultrasonic pulse velocity tests were performed on samples at ages of 7, 28 and 90 days. Density, water absorption and thermal conductivity values were also determined for the samples aged for 28 days. Preliminary results obtained from the tests indicate that masonry composites can be produced using LP, FA and water.     

An experimental study on strength development of concrete containing fly ash and optimum usage of fly ash in concrete

This paper presents a laboratory study on the strength development of concrete containing fly ash and optimum use of fly ash in concrete. Fly ash was added according to the partial replacement method in mixtures. A total of 28 mixtures with different mix designs were prepared. 4 of them were prepared as control mixtures with 250, 300, 350, and 400 kg/m³ cement content in order to calculate the Bolomey and Feret coefficients (K_B, K_F). Four groups of mixtures were prepared, each group containing six mix designs and using the cement content of one of the control mixture as the base for the mix design. In each group 20% of the cement content of the control mixture was removed, resulting in starting mixtures with 200, 240, 280, and 320 kg/m³ cement content. Fly ash in the amount of approximately 15%, 25%, 33%, 42%, 50%, and 58% of the rest of the cement content was added as partial cement replacement. All specimens were moist cured for 28 and 180 days before compressive strength testing. The efficiency and the maximum content of fly ash that gives the maximum compressive strength were obtained by using Bolomey and Feret strength equations. Hence, the maximum amount of usable fly ash amount with the optimum efficiency was determined.This study showed that strength increases with increasing amount of fly ash up to an optimum value, beyond which strength starts to decrease with further addition of fly ash. The optimum value of fly ash for the four test groups is about 40% of cement. Fly ash/cement ratio is an important factor determining the efficiency of fly ash.     

Influence of the fineness of sewage sludge ash on the mortar properties

Sewage sludge ash (SSA) is a recycled material and can be used in cement mortar as pozzolan. To improve the mortar properties, this research utilized mechanical grinding to adjust the fineness of SSA. Finely ground SSA with Blaine fineness of 500-1000 m²/kg was added to mortar to replace 20% of portland cement. The initial and final setting times of SSA-cement paste simultaneously prolonged when SSA fineness increased. Because of the lubricant effect and morphology improvement, the workability of SSA mortar increased when fineness increased. In addition, the pozzolanic activity of SSA and the compressive strength of mortar increased when SSA fineness did. The strength activity index (SAI) value approximately increased 5% when SSA fineness increased per 100 m²/kg. According to the results, the application of mechanical grinding to adjust SSA fineness was an effective modification to improve SSA mortar properties including workability and compressive strength.     

Colour control in fly ash as a combined function of particle size and chemical composition

This paper presents the results of an investigation on the combined effect of particle size and chemical composition on the colour of fly ash - a property that determines whether fly ash polymer composites can be engineered to have very light appearance satisfying the need for a wide range of commodity applications, particularly in the building material and computer housing industry. Four fly ash samples were collected from Tarong power plant Queensland, Australia, namely fly ash from first hopper (T59), classified fly ash from first hopper (T60), grinded and then classified fly ash from first hopper (T63) and fly ash from fourth hopper (T64). It was found that the particle size of T64 is smaller but still in the same order as T63. Colour measurement and chemical composition analysis of the different FA samples showed that there is a correlation between the particle size, chemical composition and colour of the fly ash. This information could be effectively used in fly ash recycling industry.     

Utilization of fly ash with silica fume and properties of Portland cement-fly ash-silica fume concrete

This paper reports the normal consistency, setting time, workability and compressive strength results of Portland cement-fly ash-silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in initial setting time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement-fly ash-silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.     

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 steam curing on class C high-volume fly ash concrete mixtures

The effect of steam curing on concrete incorporating ASTM Class C fly ash (FA), which is widely available in Turkey, was investigated. Cement was replaced with up to 70% fly ash, and concrete mixtures with 360 kg/m³ cementitious content and a constant water/binder ratio of 0.4 were made. Compressive strength of concrete, volume stability of mortar bar specimens, and setting times of pastes were investigated. Test results indicate that, under standard curing conditions, only 1-day strength of fly ash concrete was low. At later ages, the strength values of even 50% and 60% fly ash concretes were satisfactory. Steam curing accelerated the 1-day strength but the long-term strength was greatly reduced. Setting time of fly ash-cement pastes and volume stability of mortars with 50% or less fly ash content were found to be satisfactory for standard specimens. In addition, for steam curing, this properties were acceptable for all replacement ratios.     

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.     

水泥颗粒粒度分布分形维与其胶砂抗压强度的关系研究

为研究水泥颗粒粒度分布分形维与其胶砂抗压强度的关系,利用粒度分布分形维的计算模型分析了有关文献报道的10种水泥颗粒粒度分布分形维值,结果表明:定量表征其分形特征的分形维值在2.325～2.435之间,各水泥颗粒粒度分布具有分形特征;分析了水泥颗粒粒度分布分形维值与水泥3d抗压强度、28d抗压强度的关系,分析表明:化学组成和矿物组成基本相同的条件下,水泥颗粒粒度分布分形维与水泥胶砂的3d、28d抗压强度具有较好的正线性相关关系。     

Effect of pumice and fly ash incorporation on high temperature resistance of cement based mortars

The effects of high temperature on the mechanical properties of cement based mortars containing pumice and fly ash were investigated in this research. Four different mortar mixtures with varying amounts of fly ash were exposed to high temperatures of 300, 600, and 900 °C for 3 h. The residual strength of these specimens was determined after cooling by water soaking or by air cooling. Also, microstructure formations were investigated by X-ray and SEM analyses.Test results showed that the pumice mortar incorporating 60% fly ash revealed the best performance particularly at 900 °C. This mixture did not show any loss in compressive strength at all test temperatures when cooled in air. The superior performance of 60% FA mortar may be attributed to the strong aggregate-cement paste interfacial transition zone (ITZ) and ceramic bond formation at 900 °C. However, all mortar specimens showed severe losses in terms of flexural strength. Furthermore, specimens cooled in water showed greater strength loss than the air cooled specimens. Nevertheless, the developed pumice, fly ash and cement based mortars seemed to be a promising material in preventing high temperature hazards.     

活化增钙粉煤灰对水泥性能的影响

测试了将增钙粉煤灰物理活化或化学活化后作混合材,水泥在凝结时间、安定性、强度方面的变化。结果表明:利用化学活化和物理活化对增钙粉煤灰进行改性可提高其极限掺量,同时改善其安定性,水泥强度得到有效提高。     

Analysis of mechanism on water-reducing effect of fine ground slag, high-calcium fly ash, and low-calcium fly ash

The addition of ultrafine powder (UFP) to concrete can improve the fluidity of concrete, showing a water-reducing effect. The aim of this article was to analyze the water-reducing mechanism of UFP both experimentally and theoretically. Three UFPs—fine ground slag, high-calcium fly ash, and low-calcium fly ash—were chosen for the study. The contrastive experiments were done to investigate the fluidity of mortars with 30%, 45%, 60%, and 75% equivalent cement replaced by fine ground slag, high-calcium fly ash, and low-calcium fly ash, respectively. The results showed the physical and chemical characteristic of the powders, such as their grain morphology, glass phase activities, densities, specific areas, and their grain cumulating conditions, can strongly affect their water-reducing effect.     

Mechanical behaviour of various mortars made by combined fly ash and limestone in Moroccan Portland cement

Physico-chemical properties and mechanical behaviour of ternary cements made by Portland cement, fly ash and limestone are studied. The mixtures at various compositions of clinker, gypsum fly ash and limestone are intimately ground and compared to other compositions without fly ash. Blended fly ash cements are also studied. The results show that fly ash acts as grinding agent by reducing the required time to obtain the same percentage of particles retained on a 80-μm sieve as the standard cement. Fly ash cements lead to an important extension of setting time than limestone cements. The replacement of clinker by limestone gives better mechanical strengths than the mixtures containing fly ash at early days; after 28 days, the cements prepared by incorporation of fly ash gain an important strength. From mechanical point of view, an optima dosage was obtained at 77% clinker, 2% gypsum, 7.5% fly ash and 13% limestone composition.