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An Evaluation of Fly Ash Concrete Compressive Strength Under Typical Scottish Curing Conditions This MSc Project evaluated the use of coal power stations by-product, fly ash in concrete and its response to freeze-thaw conditions and compressive strength. Freeze-thaw durability is typically required for use of concrete in Scotland. Utilising this waste product a partial cement replacement has been indicated to lower costs, reduce the embodied carbon of concrete of the concrete and this project aims to act as a driver for promoting its use. University of Glasgow, charity number SC004401 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 10 15 20 25 30 35 40 45 50 55 60 Probability of occurrence Cube Compressive Strength (Mpa)) Sample Group Bell Curves Group A Group B Group C FS Group C PW Group D FS Group D PW Group Target Mean 28day Strength (f cm ) Mean 28day Strength (f cmE ) Designed characterisCc strength class (f ck ) Sample CharacterisCc strength class (f ckE ): f ckE =f cmE – (σ*1.64) A 43.1MPa 46.4MPa 30 MPa 46.4 – (0.958*1.64) = 44.8 MPa B 43.1MPa (37.1MPa) 35.0MPa 30 MPa 35.0 – (1.703*1.64) = 32.2MPa C FS 43.1MPa (37.1MPa) 29.0MPa 30 MPa 29.0 – (1.030*1.64) = 27.3MPa C PW 43.1MPa (37.1MPa) 27.5MPa 30 MPa 27.5 – (0.488*1.64) = 26.7MPa D FS 43.1MPa (37.1MPa) 20.6MPa 30 MPa 20.6 – (1.877*1.64) = 17.5MPa D PW 43.1MPa (37.1MPa) 21.5 MPa 30 MPa 21.5 – (0.271*1.64) = 21.0MPa Figure 3; Pozzolanic reaction within matrix (Sear, 2011) Figure 3; Pozzolanic reaction within matrix (Sear, 2011) Rachel Davidson 2055940D, Supervisor: Dr Łukasz Kaczmarczyk Project Objectives: •Develop cost effective laboratory curing regime to emulate on site curing conditions •Ensure samples develop as homogenous material so compressive strength can be properly assessed •Show FA is a viable material for inclusion in structural concrete Laboratory Investigation: •150mmx150mmx150mm sample cubes • Concrete designed to BS EN XF1 C30 class •30% Fly ash cement mass replacement •28 day compressive strength testing •AEA and superplasticers excluded from design mix Group Curing Regime A (0% FA) 28 day wet cured in water tank B 28 day wet cured in water tank C Fully Saturated 10 days wet cured in water tank followed by 18 days of freezing and thawing in water tank in 24 hour cycles C PlasCc Wrapped 10 days wet cured in water tank followed by wrapping samples in plasRc band into 18 days of freezing and thawing in air in 24 hour cycles D Fully Saturated 3 days wet cured in water tank followed by 25 days of freezing and thawing in water tank in 24 hour cycles D PlasCc Wrapped 3 days wet cured in water tank followed by wrapping samples in plasRc band into 25 days of freezing and thawing in air in 24 hour cycles Results: Group B; Before & After Testing Group D FS; Before & After Testing ASTM semi-submerged curing procedure Project curing procedure Conclusions: •Under ambient conditions 30% FA (B) produces sufficient strength for C30 class concrete •Under freeze-thaw curing conditions C required further development of the design mix to meet C30 strengths; recommendation for extending 10 day curing period or BS EN required concrete class into be increased by one class if involving FA (excluding AEA & superplasticers) •Group D confirmed inadequate curing period lead to inadequate low 28day compressive strength •FS vs. PW suggested FS thawed faster experiencing cracking due to heightened thermal gradient and wrapping may have impeded hydration. Further experimental data is required. Recommendations for future research: • Develop and improve laboratory curing conditions of freeze-thaw samples • Develop FA concrete design mix, perhaps replace fine aggregates with FA
