Abstract
This study presents the experimental results of fresh and hardened properties of concrete incorporating high-volume fly ash (HVFA). Two kinds of low-calcium fly ash with loss on ignition (LOI) of 5% and 8% were used as replacement for cement and/or fine aggregate of 0% (control), 20%, 40%, 50%, 60% and 80% by weight of the total cementitious materials. The properties of fresh concrete tested included the slump, air content, unit weight and setting time; those of hardened concrete determined included compressive strength, modulus of elasticity, flexural strength and drying shrinkage. Test results indicate that the concretes made with high-LOI (8%) fly ash can be successfully produced for structural concrete, which contains fly ash of up to 60% of the total cementitious materials. The high-LOI fly ash-concretes with higher replacement levels presented longer setting times. However, although both the fresh and hardened properties of high LOI fly ash concretes were inferior to those of the low-LOI (5%) fly ash concretes, the high modulus of elasticity, the adequate strength development characteristics both at early and later ages (up to 365 days) and the low dry shrinkage were observed when compared to those of the control concrete with a comparable 28-day compressive strength of 30 MPa.
Highlights
Fly ash is an industrial by-product from coal-fired power plants
With the progress in water-reducing chemical admixtures [10,11], high-volume fly ash (HVFA) concrete with adequate early-age strength and reasonable workability was first introduced by Malhotra when he initiated the related studies at the Canadian Centre for Mineral and Energy Technology (CANMET) in the mid 1980s [12]
The term HVFA concrete is most commonly defined as one specific type of fly ash concrete containing more than 50% of fly ash by weight of total cementitious materials and low water-to-binder ratio (w/b) of less than 0.4 [13]
Summary
Fly ash is an industrial by-product from coal-fired power plants. The pozzolanic reaction of fly ash (FA) makes it useful in the concrete industry where the most important application for fly ash is as a partial replacement of Portland cement in concrete. The term HVFA concrete is most commonly defined as one specific type of fly ash concrete containing more than 50% of fly ash by weight of total cementitious materials and low water-to-binder ratio (w/b) of less than 0.4 [13]. In order to achieve a desired workability at such low w/b, the use of a high-range water reducer is essential for HVFA concrete in most cases. This type of concrete takes full advantage of the enhanced properties of concrete provided by fly ash and the high-early strength obtained by reducing the w/b ratio [13,14,15]. A more economically- and environmentally-friendly (i.e., reducing CO2 emissions from cement production) concrete by minimizing its cement content can be made
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