International Concrete Abstracts Portal

The effect produced by hydrothermal treatment of a mixture of two fly ashes from municipal solid wastes incineration (MSWIFA) is discussed in this work. Two kinds of fly ashes, from fluidized-bed combustion and cleaning-gas devices with different chemical composition, principally in terms of CaO and SiO2 contents, were mixed to synthesize a new low energy cement, like belite cement (Ca/Si > 2). The mixture was hydrothermally treated at 200°C and 1.24 MPa steam-pressure for periods of 1, 2, 4 and 6 hours. Changes of fly ashes compositions were characterized by X-ray diffraction (XRD), Infrared Spectroscopy (IR) and Thermal Analyses (TGA). The evolution of aqueous phase was followed by means of measurements on: pH, conductivity, chloride, sulfate and toxic metals concentration.

This research evaluated, from the ecological and economical points of view, the potential use of off-specification fly ash plus non-standard clinker ash (bottom ash or coal ash) in CLSM (Controlled Low Strength Materials). The effect of mixture proportions on the short-term as well as long-term compressive strength of CLSM is mainly investigated. A wide range of fly ash/clinker ash ratio was evaluated in order to provide a cost effective mixture design for various material costs. Two different sources of fly ash including off specification fly ash and three different sources of clinker ash were used with three levels of mixture combinations. A total of 20 mixtures was tested for the flowability, bleeding and short-term and long-term compressive strengths (strength developments up to 91 days were reported in this study). Test results showed that there is an optimum combination of fly ash clinker ash ratio on the physical properties of CLSM. Compressive strength improved with increasing the rate of replacement of clinker ash up to 5 0 percent in the case. It is found that there was no disadvantage of using off-specification fly ash and non-standard clinker ash in the physical properties of CLSM. CLSM with off-specification fly ash plus non-standard clinker ash showed excellent performance on the physical properties indicating the ecological and economical applicability to CLSM.

Several new coal-fired combustion system modifications have been designed to improve the quality of air emissions from power plants. These plant modifications have led to changes in the character of fly ash, and presented challenges for many of it’s conventional uses. For example, low NOx burner systems improve air emissions but also have the side effect of increasing the carbon in the fly ash. Wisconsin Electric Power Company (WE) has developed three new coal ash beneficiation processes for carbon and/or ammonia removal. These new processes have been demonstrated at various Wisconsin Electric coal fired-power plants located in Michigan and Wisconsin. The processes take advantage of utilizing the residual energy in high carbon fly ash and bottom ash; while also producing high quality fly ash for use as a supplementary cementing material for the concrete industry. These beneficiation processes are also designed to remove any residual ammonia contained in the fly ash from advanced NOx reduction systems such as Selective Catalytic Reduction (SCR), Selective Non-Catalytic Reduction (SNCR), and Amine Enhanced Fuel Lean Gas Rebum (AEFLGR). These new ash beneficiation processes are designed both as stand alone systems or potential additions to existing power plants. In some cases it may be advantageous to rebum high carbon coal ash from one power plant by transporting it to another where more complete combustion normally occurs.

The potential use of Malaysian fly ash cement in concrete has been studied in terms of its influence on elastic properties, volume stability and durability properties. In durability studies, the resistance to chloride ingress, sulfate attack, and suppression of alkali-aggregate reactivity were examined. The results are presented and discussed. The role of the fly ash on heat of hydration, production of roller-compacted concrete, and high-strength, high-performance concrete have been proven in practice. Understanding the influence of fly ash on both fresh and hardened properties of concrete has led to its appropriate use in many important structures in Malaysia. They include the Petronas Twin Towers, the second Malaysia Singapore Causeway, and more recently considered for the construction of a major RCC dam. Properties of fly ash concrete are discussed with examples of application.

Metakaolin is a supplementary cementitious material with pozzolanic properties. Its precursor, kaolin, does not occur in natural conditions as a pure phase but is often mixed in various proportions with many secondary minerals. Two natural clays from the same deposit, mainly composed of kaolinite and quartz have been burnt at a suitable temperature and the resulting calcined products have been blended with laboratory normal portland cement for which the nature of added calcium sulfates as well as free lime content have been varied. Subsequent properties of cement pastes and mortars such as rheology, setting time and compressive strength have been compared. Concurrently, early hydration products have been characterized by means of DSC and combined water content has been evaluated by C02-H20 analyser. The difference of behavior that has been observed as a function of the artificial pozzolan mineralogy and cement chemical parameters is discussed in the frame of the mechanism of early hydration of metakaolin blended cement.