Engineering Properties and Durability of SuperClassified Fly Ash

Engineering Properties and Durability of Super-Classified Fly Ash Concrete Research Student: Bruce K. T. Kandie Supervisor: Dr. Ewan A. Byars Research Programme 3 2 4 5 6 7 1 SPFA 8 µm Figure 2. Burning coal to produce electricity and fly ash Figure 3. Comparison between SPFA and various types of PFAs Fly ash poses a major waste disposal problem in the world (Fig 4). However, when used in blended cements it can reduce greenhouse gas emissions, the cost of concrete and improve the strength, durability and other properties of concrete. Figure 4. Fly ash disposal and utilisation in the UK The aim of this research is to develop specialist concrete mixes for high performance applications using optimised mix proportions with SPFA and compare this on a performance and economic basis with MS and BS 3892: Part 1 fly ashes. Objectives To achieve the project aim, the following objectives have been identified: i) To determine how the various replacement levels of SPFA for cement affects the fresh, hardened and the durability properties of concrete. Water demand, early and long term strength development, self-compacting concrete, creep, shrinkage, carbonation resistance, chloride resistance and sulfate resistance will be studied. ii) To measure the effect of SPFA on the microstructure of concrete. iii) On the basis of (i) and (ii), perform economic analysis to determine the most appropriate uses of SPFA in concrete. Fig 5 b shows the strength development, for a range of concrete mixes designed for 28 -day in strength, it can be seen that 5% and 10% SPFA concrete has higher strength than control up to 10 days. This is in contrast to conventional BS 3892 PFA, all of which lags behind the OPC control up to design age, as indeed do the micro-silica concrete mixes. Fig 5 c shows the strength development curve for 125 N/mm 2 strength at 28 days. This was made with a blend of SPFA and MS at replacement of 15% each. PHASE TWO Fresh Concrete Properties • Water Requirement • Setting Time • Admixture Compatibility PHASE THREE Mechanical & Physical Properties • Compressive Strength • Tensile Strength • Dry Shrinkage Extra refinement of fly ash produces Super-Classified Fly Ash-(SPFA), an ultra fine powder with average 8µm particle size. It is a very reactive pozzolan compared to BS 3892: Part 1[1] fly ashes and has high potential for use as an alternative to microsilica (MS) for high strength concrete and other applications[2]. Aim of this Research Fig 5 a shows that SPFA has a high water reducing effect compared to other cementitious material, due to it’s hydrophilic nature and spherical shape. PHASE FOUR Permeability Properties • Oxygen Diffusion • Porosity Grade 40 Mixes Water Demand Grade 120 Mix Compressive Strength N/mm 2 BS 3892: Part 1 PFAs PHASE ONE Fly Ash Characterization • Fineness • Loss on Ignition • Pozzolanicity Compressive Strength N/mm 2 Combustion of coal (Fig 1) in modern power plants (Fig 2) produces some bottom ash, but most of the burnt minerals escape with the flue gases and is called fly ash (PFA), Fig 3. This ash is subsequently removed from the gas by electrostatic precipitation. Results and Discussions % Water requirement of OPC Introduction Figure 1. Coal Sponsored by: Kenya Government Age-days Pozzolan replacement (%) (b) (a) (c) Figure 5. Shows (a) Water demand (b and c) the compressive strength curves for the SPFA and BS 3892: Part 1 fly ashes Conclusion The use of SPFA in concrete has achieved the following: • A water deduction of 18% for 30% replacement of cement (Fig 5 a). • Concrete with a strength of 125 N/mm 2 at 28 days (fig 5 c) in water curing-for normally PHASE FIVE Durability • Chloride Ingress • Sulfate Resistance • Carbonation • Freezing/Thawing PHASE SIX Economic Analysis compacted concrete, 150 N/mm 2 at 90 -days. • Self compacting concrete made with only 380 kg/m 3 cementitious cement and minimal plasticizer[3]. References 1. BRITISH STANDARDS INSTITUTION. Specification for pulverized-fuel ash for use as a cementitious component in structural concrete. BS 3892 : Part 1. BSI, London, 1993. 2. Fossey, S. D. , Byars, E. A. and Zhu, H. Y. 2003. Super-Classified PFA For Self-Compacting Concrete. ICCC-2003. Durban, South Africa, (in press). 3. Tsartsari, A. and Byars, E. A. 2000. Ultra-High Strength Concrete Using Conventional Casting. Concrete, Vol. 36 , No 1, pp 16 -17.