Mechanical properties of high strength concrete with high volume replacement

Richards, Thomas (2016) Mechanical properties of high strength concrete with high volume replacement. BEng dissertation, University of Portsmouth.

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    This project investigated the maximisation of fly ash replacement within a concrete mix, thus analyse the effects of large amounts of fly ash as a replacement for cement. This research was performed to understand to what level cement can be replaced within concrete and still produce a workable, industry applicable strength concrete.
    Mixes containing 10% silica fume with 30, 50, 70 and 80% fly ash were tested for compression and sorptivity. Concrete was compression tested at 1, 3, 7, 28, 56 and 90 days. Results conclude that control (10% silica fume, 90% cement) recorded the highest readings at 90-days with reductions in strength when increasing fly ash content. However, lowering the water-binder ratio increased strength profoundly without noticeably reducing workability. It has been determined that the ‘dilution effect’ and the chemical shape and characteristics of fly ash are responsible for the slow rate of strength development and the fluidity of mixes.
    Sorptivity was tested at 28, 56 and 90 days, with the control sample absorbing the least amount of water. Increasing fly ash content increased absorption of water. Correlations were drawn between strength and sorptivity, showing stronger mixes absorbing less, due a denser binder matrix and lower connectivity between pores.
    The significance of this report highlights a concrete achieving 30MPa at 28 days containing only 20% cement. Industry standard ST3 requires 30N/mm2 of which this meets the criteria, at a potentially lower cost and emission of CO2 when compared to CEMI.

    Item Type: Dissertation
    Departments/Research Groups: Faculty of Technology > School of Civil Engineering and Surveying
    Depositing User: Beth Atkins
    Date Deposited: 06 Sep 2016 10:20
    Last Modified: 06 Sep 2016 10:20

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