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.     

钛渣晶核剂对赤泥粉煤灰微晶玻璃性能的影响?

采用烧结法以钛渣代替二氧化钛为晶核剂制备了高掺量的赤泥粉煤灰微晶玻璃,主要考查钛渣掺量对微晶玻璃产品的理化性能、物相组成及微观结构的影响.结果表明,主晶相均为钙铝黄长石,次晶相为钙铁透辉石和钙长石;结晶程度随钛渣含量而增加,微晶玻璃颜色逐渐变深,但钛渣含量过高,晶体会发生凝结现象;当钛渣掺量为6．6％时,固废总掺量达到了95．3％,抗压强度、抗折强度、显微硬度、耐酸性、耐碱性分别为89．43和53．13 MPa、6．62 GPa、0．041％、0．15％,产品性能达到建筑用微晶玻璃JC/T872-2000的质量标准.     

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。     

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. And the curing agent could prevent the concrete carbonation. And the mechanism was explained.     

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.     

基于饱和面干骨料的粉煤灰混凝土配合比设计及碳化性能研究

本文以设计试验研究基于饱和面干骨料的粉煤灰混凝土为主,并通过试验数据分析得出结论：相同水胶比的情况下,随着粉煤灰掺量的增加,混凝土7d、28d强度逐渐下降,拌和物坍落度也平稳下降;自然养护条件和标准养护条件对碳化深度有一定的影响;饱和面干骨料粉煤灰混凝土的强度测定期应当延迟。     

Coal fly ash and synthetic coal fly ash aggregates as reactive media to remove zinc from aqueous solutions

Coal fly ash (CF) and synthetic coal fly ash aggregates (SCFAs) were evaluated as low-cost reactive media for the remediation of groundwater contaminated with Zn. The SCFAs were prepared by mixing CF, sodium silicate, and deionized (DI) water. Serial batch kinetic and static tests were conducted on both CF and SCFAs, under various conditions (i.e., pH, initial Zn concentration, reaction time, and solid dosage), using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on both CF and SCFAs. The final rather than the initial pH of the solution had a greater effect on the removal of Zn. At pH>7.0, the removal of Zn was due to precipitation, whereas at <7.0, the removal of Zn was due to adsorption onto the reactive media. The removal of Zn increased with increasing dosage of the reactive medium and decreasing initial Zn concentration. The results of the column and batch tests were comparable. Preferential flow paths were observed with CF, but not SCFA. The hydraulic conductivity of CF was more significantly decreased than that of SCFA with increasing dry density of the specimen.     

Effect of curing method on characteristics of cold bonded fly ash aggregates

This paper discusses the influence of normal water curing, autoclaving and steam curing on the properties of a typical class-C fly ash aggregate. The 10% fines value, water absorption, and porosity of aggregates are correlated with SEM and XRD results to understand the influence of various factors and material characteristics. An increase in duration of normal water curing significantly improved the aggregate properties. Autoclaving and steam curing resulted in relatively lower enhancement in the properties as compared to normal water cured aggregate. Between the accelerated curing methods, autoclaved aggregate possessed properties closer to the normal water cured aggregate due to the dense microstructure formation. Continuation of normal water curing, after initially subjecting the aggregates to accelerated curing, exhibited only a marginal improvement in the properties.     

Air void system in concrete containing circulating fluidized bed combustion fly ash

The increased use of advanced coal-burning technologies for power generation, such as circulating fluidized bed combustion (CFBC), results in new waste products. The potential for using CFBC fly ash in air-entrained concrete was investigated in order to assess the influence of CFBC fly ash on the microstructure of air voids in hardened concrete. A special specimen surface preparation technique for contrasting the image and enabling measurements of air voids size and distribution using an automated image analysis procedure was used. The microstructure of air voids was evaluated on the basis of the total air content, the spacing factor, and the specific surface of air voids. It was found that a satisfactory air void system in concrete could be produced when using CFBC fly ash for partial replacement of cement. The air-void system was characterized by a decreased specific surface of voids and an increased spacing factor.     

Shrinkage characteristics of alkali-activated fly ash/slag paste and mortar at early ages

The purpose of this study is to investigate the shrinkage characteristics of alkali-activated fly ash/slag (henceforth simply AFS) and the factors affecting it. A series of tests were conducted to determine the chemical shrinkage, autogenous shrinkage and drying shrinkage. The microstructures and reaction products were also characterized through XRD and SEM/EDS analyses. An increase in the slag content from 10% to 30% resulted in a denser matrix and showed a higher Ca/Si ratio of C–N–A–S–H in the microstructure. Higher sodium silicate and slag contents in a mixture caused more chemical, autogenous, and drying shrinkage, but led to a higher compressive strength. From the test results, it can be concluded that the autogenous shrinkage of AFS mortar occurs mainly due to self-desiccation in hardened state rather than volume contraction by chemical shrinkage in fresh state. The AFS paste showed higher drying shrinkage than ordinary Portland cement (OPC), which may be caused by the higher mesopore volume of the AFS paste compared to that of OPC paste.     

Frost salt scaling resistance of concrete containing CFBC fly ash

The possibility for using coal combustion by-products in concrete exposed to frost-salt aggression was investigated. The research was aimed to assess an influence addition of circulating fluidized bed combustion (CFBC) fly ash on frost-salt scaling of air-entrained concrete. For evaluation of the resistance of concrete to frost salt scaling the test called “depth sensing indentation” (DSI) was applied. The DSI test method was implemented on a universal testing frame using a standard Vickers indenter. Experimental tests were performed on cement paste specimens and concrete specimens designed with partial replacement of cement with coal combustion by-products. The mass of scaled material in standard frost salt scaling resistance tests on concrete was inversely proportional to the Vickers hardness of the paste containing CFBC fly ash; the best-fit arithmetic relationship is provided.     

包覆金红石型TiO_2功能性粉煤灰微珠制备和表征分析

以硫酸钛为钛源,粉煤灰厚壁空心微珠为基体,采用化学沉积和900~1 000℃煅烧2h的联合工艺制备了表面镀覆金红石型TiO2的功能性粉煤灰微珠。借助激光粒度分析仪、X射线衍射仪、场发射扫描电子显微镜、X射线能谱仪等表征技术对包覆前后微珠粒径分布、化学成分、表面形貌和结构进行了对比分析。275 W红外灯对上表面分别涂抹掺原微珠涂料和掺功能性微珠(占涂料质量的20%)涂料的水泥砂浆基板照射2 h,后者基板下表面温度比前者约低1.4℃,这是粉煤灰微珠表面金红石型TiO2热反射效应作用的结果。     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Effect of fire exposure on cracking,spalling and residual strength of fly ash geopolymer concrete

Fly ash based geopolymer is an emerging alternative binder to cement for making concrete. The cracking, spalling and residual strength behaviours of geopolymer concrete were studied in order to understand its fire endurance, which is essential for its use as a building material. Fly ash based geopolymer and ordinary portland cement (OPC) concrete cylinder specimens were exposed to fires at different temperatures up to 1000 °C, with a heating rate of that given in the International Standards Organization (ISO) 834 standard. Compressive strength of the concretes varied in the range of 39–58 MPa. After the fire exposures, the geopolymer concrete specimens were found to suffer less damage in terms of cracking than the OPC concrete specimens. The OPC concrete cylinders suffered severe spalling for 800 and 1000 °C exposures, while there was no spalling in the geopolymer concrete specimens. The geopolymer concrete specimens generally retained higher strength than the OPC concrete specimens. The Scanning Electron Microscope (SEM) images of geopolymer concrete showed continued densification of the microstructure with the increase of fire temperature. The strength loss in the geopolymer concrete specimens was mainly because of the difference between the thermal expansions of geopolymer matrix and the aggregates.     

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 concrete incorporating fly ash and ground granulated blast-furnace slag

This paper presents a laboratory study on the influence of combination of fly ash (FA) and ground granulated blast-furnace slag (GGBS) on the properties of high-strength concrete. A contrast study was carried out for the concrete (GGFAC) incorporating FA and GGBS, control Portland cement concrete and high-volume FA high-strength concrete (HFAC). Assessments of the concrete mixes were based on short- and long-term performance of concrete. These included compressive strength and resistance to H₂SO₄ attack. The microstructure of the concretes at the age of 7 days and 360 days was also studied by using scanning electron microscope. The results show that the combination of FA and GGBS can improve both short- and long-term properties of concrete, while HFAC requires a relatively longer time to get its beneficial effect.     

粉煤灰陶粒在污水处理中的应用进展

粉煤灰陶粒是由粉煤灰为主要原料，掺加少量粘结剂和固体燃料，经混合、成球、高温焙烧而成。由于其比表面积大、表面能高，且内部存在着铝、硅氧化物等活性点，具有良好的吸附性能，并且易于再生，便于重复利用，因此粉煤灰陶粒是一种廉价的吸附剂。综述了粉煤灰陶粒用作水处理滤料以及其在含金属离子的废水、腐殖废水、含磷废水、含氟废水、含油废水处理中的应用，并对今后的研究方向进行了展望。     

Strategies of using fly ash and their effect on properties of cement mortar

Abstract

Three different ways of using fly ash, namely, partial replacement of cement, or sand, or both cement and sand in the cement mortar, were studied in this investigation. The replacement varied from 10 percent to 60 percent by weight. The effects of design parameters such as water‐cement ratio and curing temperature on the replacements were studied. In this paper, strategies of using fly ash in concrete construction were also proposed in order to conserve resources.     

Transport properties of high volume fly ash roller compacted concrete

This paper describes research on the transport properties of high-volume fly ash roller compacted concrete (RCC). The mixes were developed through incorporating 50–260 kg/m³ cement and high volumes of fly ash ranging from 40% to 85% by mass of the total cementitious material. The concretes were investigated for permeability, absorption, sorption and chloride diffusion. The study showed that RCCs of moderate cement and moderate fly ash contents had lower values of permeability, absorption, sorption and chloride diffusivity.