The anticorrosive effect of fly ash, slag and a Greek pozzolan in reinforced concrete

The influence of the addition of 15% and 30% fly ash, 15% and 30% of a Greek natural pozzolan and 50% granulated blastfurnace slag to ordinary Portland cement on the corrosion resistance of the reinforcing bars was studied in a program of long-term exposure to seawater. The use of blended cements resulted in a decrease in the corrosion rate, especially after long exposure times. The most effective protection was rendered by the 30% fly ash mix. This performance was related to the chloride content and the chloride binding capacity of the blended cements.     

Structure formation of slag ash concrete on the basis of high-calcium fly ash and silica fume

Cementless slag ash concrete may be manufactured using high-calcium fly ash and silica fume as replacements for a binder and a microfiller, and incorporating slag sand from thermal power plants (TPP) as an aggregate. This concrete consists of waste products from TPP (fly ash and slag) and ferro-alloy plants (silica fume) and contains neither natural nor artificial aggregates for lightweight and heavy concretes. Silica fume (10–20% by weight of ash) and hot water together with subsequent heat treatment of concrete products or of castin situ structures binds the excess free calcium oxide present in the ash, and thus prevents deterioration of the concrete. The processes of concrete structure formation were investigated after 24 hours, 28 days, 3 and 6 months and the physico-mechanical, deformation and special properties (frost resistance, heat conductivity, protection of reinforcement from corrosion) were studied. This concrete conforms to the Russian Federation GOST requirement for use in single, two-storey buildings. The cost of the concrete is reduced by a factor of 3 compared with that of ordinary concrete.     

新疆地区商品混凝土中粉煤灰和矿粉双掺的试验研究

本文根据混凝土设计强度的不断提高和混凝土行业可持续发展的要求,通过对粉煤灰、矿粉的单掺及粉煤灰和矿粉的双掺,对混凝土的性能进行比较研究,双掺混凝土不论是拌合物的和易性,还是混凝土的力学性能、耐久性都优于单掺混凝土。实现混凝士优化配置,并且降低成本,可以采用双掺技术,有利于环保和可持续发展。     

Efficiency of fly ash in concrete

Earlier efforts towards an understanding of the efficiency of fly ash in concrete has led to the introduction of rational methods. Based on the results available on some of the more recent pulverised fuel ashes, the authors evaluated the efficiency of fly ash in concrete over a wide range of percentage replacements (15–75%). It was clearly shown that the overall efficiency of fly ash cannot be adequately predicted using a single efficiency factor at all percentages of replacements. The overall efficiency factor (k) has been evaluated at all percentages of replacements considering the general efficiency factor (k_e) and the percentage efficiency factor (k_p). This study resulted in a quantitative assessment of the behaviour of fly ash in concrete, especially for the 28 day compressive strength at different percentages of replacement.     

Properties of fresh concrete incorporating a high volume of fly ash as partial fine sand replacement

The use of fly ash in concrete is very common nowadays, mainly as a partial replacement for cement. However, the amount actually used in many countries is only between 15 to 25 percent. Disposal of unusable fly ash raises severe ecological problems and is quite expensive, not to mention the difficulty of finding dumping sites. Increased utilization of fly ash is thus, in many countries, in the national interest. A research program was initiated on the utilization of large quantities of fly ash Class F of marginal-quality in concrete as partial fine-sand replacement. The present paper studies the effect of such replacement on the properties of fresh concrete. The mechanical properties of the hardened concrete will be presented in another paper. The workability of most fly-ash mixtures was better than that of the reference mix (without fly ash). The water requirement of the fly-ash mixtures was either the same, or higher by about 9 percent, as compared with the reference mix. The rate and volume of bleeding were rather similar for the fly ash and the reference mixes. However, a significant reduction in bleeding by the fly-ash was found in the concrete mixtures with the chemical admixtures water reducer and retarder and high-range water reducer. Setting was delayed by the fly-ash, but the additional delay, that beyond the effect of the chemical admixture proper, was much less in the mixtures with the water reducer and retarder and negligible in the mixtures with the high-range water reducer.     

Durability of concrete incorporating high-volume of low-calcium (ASTM Class F) fly ash

Research on structural concrete incorporating high volumes of low-calcium (ASTM Class F) fly ash has been in progress at CANMET since 1985. In this type of concrete, the cement content is kept at about 150 kg/m³. The water-to-cementitious materials ratio is of the order of 0·30, and fly ash varies from 54 to 58% of the total cementitious material. A large dosage of a superplasticizer is used to achieve high workability.

This paper presents data on the durability of this new type of concrete. The durability aspects considered are: freezing and thawing cycling; resistance to chloride ion permeability; and the expansion of concrete specimens when highly reactive aggregates are used in the concrete.

The investigations performed at CANMET indicate that concrete incorporating high volumes of low-calcium fly ash has excellent durability with regard to frost action, has very low permeability to chloride ions and shows no adverse expansion when highly reactive aggregates are incorporated into the concrete.     

Effect of fly ash and slag on the fracture characteristics of high performance concrete

The premature deterioration of concrete structures in aggressive environments has necessitated the development of high performance concrete (HPC). The major difference between conventional concrete and HPC is essentially the use of chemical and mineral admixtures. The improved pore structure of HPC achieved by the use of chemical and mineral admixtures causes densification of paste-aggregate transition zone, which in turn affects the fracture characteristics. Hence, studies were taken up to investigate the effect of fly ash and slag on the fracture characteristics of HPC. Beam specimens (geometrically similar and single size variable notch) with locally available fly ash (25%) and slag (50%) as cement replacement materials were prepared and tested in a servo-controlled Universal Testing Machine (UTM) under displacement control. From the value of the peak load for each beam, various fracture parameters were calculated. The results show that there is a reduction in the fracture energy due to addition of fly ash or slag, which can be attributed to the presence of unhydrated particles of size larger than that of normal flaws in concrete. Also due to densification, the post peak behaviour is steeper for the fly ash or slag based HPC mixes. The results of the investigation are presented in this paper.     

The permeability of fly ash concrete

Oxygen permeability tests were carried out on plain ordinary Portland cement (OPC) and fly ash concretes at three nominal strength grades. Prior to testing the concretes were subjected to a wide range of curing and exposure conditions. The results emphasize the importance of adequate curing to achieve concrete of low permeability, especially when the ambient relative humidity is low. In addition, the results demonstrate the considerable benefit that can be achieved by the use of fly ash in concrete. Even under conditions of poor curing, fly ash concrete is significantly less permeable than equal-grade OPC concrete, the differences being more marked for higher-grade concretes. Attempts were made to correlate strength parameters with permeability but it is concluded that neither the strength at the end of curing nor the 28-day strength provides a reliable indicator of concrete permeability. A reliable correlation was established between the water to total cementitious material ratio [w/(c+f)] and the permeability of concretes subjected to a given curing and exposure regime.     

Transport properties of self compacting concrete with limestone filler or fly ash

The durability of a cementitious material is greatly influenced by the permeability of the material for potentially aggressive substances. As the pore structure of self compacting concrete (SCC) might be different in comparison with traditional concrete (TC), some changes in durability behaviour may occur. At this moment however, it is unclear how significant these differences will be with regard to the concrete practice. In this paper, the gas and water transport in SCC with limestone filler or fly ash is investigated experimentally. Nine different concrete compositions are considered: one TC and eight SCC mixtures. Some important parameters like the water/cement (W/C) and cement/powder ratio (C/P), type of filler (limestone filler and fly ash), type of aggregate and type of cement are considered. The results of the gas and water transport are discussed and linked to experimental data concerning pore volume. Lower transport properties can be obtained by using fly ash instead of limestone as filler material, by lowering the W/C ratio, decreasing the C/P ratio at a constant W/C ratio or using blast furnace slag cement instead of portland cement. The effect of changing from gravel to crushed limestone is small. SCC is differing strongly of TC with respect to the apparent gas permeability. This difference is probably due to the differences in pore volume, as seen from MIP results.     

Valorization of co-combustion fly ash in concrete production

The purpose of this paper is to compare the effects of two different Supplementary Cementing Materials (SCMs) on mechanical and durability-related properties of structural concrete. Three mixes were produced, where coal and co-combustion fly ashes were used as partial substitute of cement (20% in volume) and compared with a control/reference concrete. Performances investigated included fresh concrete properties, compressive and tensile strength, elastic modulus, permeability, capillarity and drying/wetting resistance. Results indicate that both the SCMs can be classified as low-carbon fly ashes, and their use in concrete improves the workability of the mixes. A slight reduction of mechanical strength was observed for the concretes including both the SCMs. In addition, concrete transport properties were also slightly reduced when co-combustion fly ash was used. Wetting-drying cycles affected significantly the durability of all the mixes: compressive strength after these cycles was significantly lowered, and the cracks occurred due to the thermal stress applied, appeared to be filled by needle-shape crystals of ettringite.     

Mechanical properties of structural concrete incorporating a high volume of Class F fly ash as partial fine sand replacement

A research program was carried out on the utilization of large quantities of Class F fly ash of marginal quality in structural concrete as partial fine sand replacement. The present paper studies the effect of such replacement on the properties of hardened concrete. The effect on the properties of the fresh concrete was presented in another paper [1]. The properties studied were: compressive strength, modulus of elasticity, drying shrinkage and water penetration under pressure. The cement content of the concrete mixtures was maintained constant. Also, the consistency and slump were kept constant by adjusting the amount of the mixing water. The test results show clearly that fly ash of marginal quality, as partial fine sand replacement, has a beneficial effect on the compressive strength of structural concrete, particularly at later ages, and also on the modulus of elasticity. The drying shrinkage of the fly ash mixtures was similar or somewhat lower than that of the reference mix. The maximum penetration depth of water under pressure of the fly ash concrete mixtures was somewhat smaller than that of the reference mix.

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Résumé Un programme de recherches a été entrepris sur l'utilisation de grandes quantités de cendres volantes de qualité marginale (Classe F) en remplacement partiel de sable fin. Cet article étudie les effets de tels remplacements sur les propriétés du béton durci. Les effets sur les propriétés du béton frais ont été présentés dans un autre article [1]. Les propriétés étudiées étaient la résistance à la compression, le module d'élasticité, le retrait de séchage et la pénétration de l'eau sous pression. La teneur en ciment des formules de béton a été maintenue constante. La consistance et l'affaissement ont également été maintenus constants par ajustement de la quantité d'eau. Les résultats montrent clairement que les cendres volantes de qualité marginale, en tant que remplacement partiel de sable fin, ont un effet bénéfique sur la résistance à la compression du béton, en particulier à des ages avancés, ainsi que sur le module d'élasticité. Le retrait de séchage des formules contenant des cendres volantes était égal ou légèrement inférieur à celui du mélange de référence. Dans des formules contenant des cendres volantes, la profondeur maximale de pénétration de l'eau sous pression était légèrement inférieure à celui de la formule de référence.

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Editorial note Dr. D. Ravina works at the Faculty of Civil Engineering and the National Building Research Institute of the Technion Israel Institute of Technology, a RILEM Titular Member. He is a corresponding member of TC 094-CHC on Concrete for Hot Countries.     

粉煤灰陶粒混凝土的抗盐冻性能

为了评价桥面铺装中应用的轻骨料混凝土长期耐久性,利用R ILEM推荐混凝土抗盐冻性能试验标准(CDF)研究了粉煤灰陶粒混凝土与普通混凝土的抗盐冻性能.结果表明:相同强度等级的掺加矿物掺合料的粉煤灰陶粒混凝土的抗盐冻性能明显优于普通混凝土的抗盐冻性能.复掺矿物掺合料混凝土的抗盐冻性能优于单掺矿物掺合料混凝土的抗盐冻性能.与普通混凝土相比,通过SEM-EDXA的分析,掺与未掺矿物掺合料陶粒与水泥石之间的界面过渡区的范围明显变小,这是粉煤灰陶粒混凝土抗除冰盐性能优良的重要原因.     

Sintering of MSW fly ash for reuse as a concrete aggregate

The sintering process of municipal solid waste (MSW) fly ash was investigated in order to manufacture sintered products for reuse as concrete aggregates.Four types of fly ash resulting from different Italian MSW incineration plants were tested in this study. A modification of the chemical composition of MSW fly ash--through a preliminary four-stage washing treatment of this material with water--was attempted to improve the chemical and mechanical characteristics of sintered products.The sintering treatment of untreated or washed fly ash was performed on cylindrical compact specimens (15 mm in diameter and 20mm in height) at different compact pressures, sintering temperatures and times.The sintering process of untreated MSW fly ashes proved to be ineffective for manufacturing sintered products for reuse as a construction material, because of the adverse chemical characteristics of these fly ashes in terms of sulfate, chloride, and vitrifying oxide contents.A preliminary washing treatment of MSW fly ash with water greatly improved the chemical and mechanical characteristics of sintered products and, for all the types of fly ash tested, the sintered products satisfied the Italian requirements for normal weight aggregates for use in concretes having a specified strength not greater than 12 and 15N/mm(2), when measured on cylindrical and cubic specimens, respectively.A compact pressure of 28 N/mm(2), a sintering temperature of 1140 degrees C, and a sintering time of 60 min were the best operating conditions for manufacturing sintered products of washed MSW fly ash.     

Improved geopolymerization of bottom ash by incorporating fly ash and using waste gypsum as additive

This research studied the improvement of the geopolymerization of bottom ash (BA) by incorporating fly ash (FA) and using flue gas desulfurization gypsum (FGDG) as additive. The BA:FA ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 were used as the blended source materials. The source materials were then replaced with 0%, 5%, 10%, and 15% of FGDG. NaOH, sodium silicate and temperature curing were used to activate the geopolymer. Test results indicated that the increase in FA content in the BA–FA blends improved the strengths of geopolymer mortars owing to the high glassy phase content and high reactivity of FA compared to those of BA. The use of up to 10% of FGDG as additive also significantly increased the strengths of geopolymer. In this case, the compressive strength enhancement was due to the increase in the Al³⁺ leached from BA in the presence of ${\text{SO}}_4^{2-}$ and the formation of additional calcium silicate hydrate.     

Strength development of concretes with ordinary Portland cement,slag or fly ash cured at different temperatures

This paper presents the results of an investigation on the effect of Portland cement replaced by fly ash or granulated blast-furnace slag on the concrete strength at different curing temperatures. Compressive strength results are analysed according to the hyperbolic strength-age function by introducing a power indexn. The regression analysis is done considering different n values andt _o (final setting times) values.     

Properties of self-compacting concrete containing class F fly ash

An experimental program was carried out to study the properties of self-compacting concrete (SCC) made with Class F fly ash. The mixes were prepared with five percentages of class F fly ash ranging from 15% to 35%. Properties investigated were self-compactability parameters (slump flow, J-ring, V-funnel, L-box and U-box), strength properties (compressive and splitting tensile strength), and durability properties (deicing salt surface scaling, carbonation and rapid chloride penetration resistance).     

Effects of different curing regimes on the compressive strength properties of self compacting concrete incorporating fly ash and silica fume

This paper presents the effect of air curing, water curing and steam curing on the compressive strength of Self Compacting Concrete (SCC). For experimental study, SCC is produced with using silica fume (SF) instead of cement by weight, by the ratios of 5%, 10% and 15%, and fly ash (FA) with the ratios of 25%, 40% and 55%. It is observed that mineral admixtures have positive effects on the self settlement properties. The highest compressive strength was observed in the concrete specimens with using 15% SF and for 28 days water curing. Air curing caused compressive strength losses in all groups. Relative strengths of concretes with mineral admixtures were determined higher than concretes without admixtures at steam curing conditions.     

Thermal activation on calcium silicate slag from high-alumina fly ash: a technical report

The fly ash with alumina composition from 45 to 55 % has been found in China in last 10 years, which attracts great attention from Chinese government and related alumina industry. Chinese government and its state-owned enterprises have successfully extracted the Al as alloy product from the high-alumina fly ash. However, to recycle the calcium silicate slag as residue from the Al industry is still undetermined. In this report, an innovative process is introduced to achieve the regional sustainability for the high-alumina fly ash industry, and it is found that the cementitious material composed of calcium silicate slag met with the mechanical requirements of 32.5 cement for road pavement. The chemical and mineral analysis show that the calcium silicate slag has high CaO content, which reaches up to 48.64 %. C₂S and C₃A are the dominant mineral phases by XRD analysis indicating its potential pozzolanic activity during the hydration process. Thermal activation from 200 to 900 °C was applied to enhance its pozzolanic activity for the calcium silicate slag and it proved that 600 °C is the optimal calcination temperature due to the decomposition of calcite and clay minerals. Also the mineral phase amorphization was also observed during the XRD analysis, which might also contribute to the enhanced pozzolanic properties at 600 °C. Although the designed cementitious material contains a large quantity of solid waste, none of the hazardous heavy metals exceed the EPA limits. This short article originally reported a promising direction for managing solid waste for Al industry and enhancing utilization efficiency for the enterprise internal solid wastes.