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  • 1.
    Humad, Abeer
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Civil Engineering Department, Babylon University, Hillah, Iraq.
    Kothari, Ankit
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Provis, John L.
    Department of Materials Science and Engineering, University of Sheffield, Sheffield, United Kingdom.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    The Effect of Blast Furnace Slag/Fly Ash Ratio on Setting, Strength, and Shrinkage of Alkali-Activated Pastes and Concretes2019In: Frontiers in Materials, ISSN 2296-8016, Vol. 6, no 9Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to determine the effects of partial fly ash substitution in to a series of alkali-activated concrete based on a high-MgO blast furnace slag BFS. Mixes were activated with various amounts of sodium silicate at alkali modulus (mass ratio SiO2/Na2O) values of 1.0, 0.5, and 0.25. The results showed that, an increase in the fly ash content extended the initial setting time but had very little effect on the final setting time, although the early age compressive strength was decreased. The fly ash addition had no effect on the drying shrinkage but lowered the autogenous shrinkage. The mixes activated with sodium silicate at a lower alkali modulus showed a significantly higher autogenous shrinkage but lower drying shrinkage values. Severe micro cracking of the binder matrix was observed only for mixes without fly ash, activated with sodium silicate solution at higher alkali modulus. Decreasing the alkali modulus resulted in a higher autogenous shrinkage, less micro cracking and a more homogenous structure due to more extensive formation of sodium-aluminate-silicate-hydrate gel (N-A-S-H), promoted by the addition, and more extensive reaction of the fly ash.

  • 2.
    Kothari, Ankit
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Restoration of Deteriorated Concrete Columns byWrapping with an Ecological UHPC2019In: Restoration of Deteriorated Concrete Columns byWrapping with an Ecological UHPC, MDPI, 2019Conference paper (Other academic)
    Abstract [en]

    Ultra high performance concrete (UHPC) is self-compacting, reaching compressive strengthover 200 MPa and flexural strength exceeding 30 MPa material. The used very low W/C ratio andhigh amount of Portland cement often exceeding 900 kg/m3, addition of up to 30% of silica fumeproduces a very dense and nearly impermeable binder matrix. In this research, cement wassubstituted with limestone filler to lower the effective CO2 footprint. Prepared concrete mixes hadhigh slump flow of 850 mm and reached the compressive strength of 150 MPa after 28 days. Fullscalecolumns having dimension of 30 × 30 × 250 cm were produced using self-compacting concrete(Figure 1a,b), having the 28 days compressive strength of 40 MPa. External surfaces of the 3 monthsold columns were water jetted to simulated real case scenario (Figure 1c). For the test, the columnswere surrounded by a plywood formwork leaving less than 3 cm of spacing between the concretesurface and the formwork (Figure 1d). The concrete was poured from top of the column and with nosegregation reached the bottom and perfectly filled the mold. Test included determination of basicmechanical properties, bond strength between UHPC and “old” concrete, crack formation and frostdurability. All results exceeded expectations.

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