Singh, G V P B and K V L, Subramaniam
(2016)
Concrete using Siliceous Fly ash at very High Levels of Cement Replacement: Influence of Lime Content and Temperature.
In: 2nd RN Raikar Memorial International Conference & Banthia-Basheer International Symposium on Advances in Science & Technology of Concrete, 18-19 December, 2015, The Lalit, Mumbai.
Abstract
Potential for producing viable binders at very high levels
of cement replacement (60% and above) with fly ash is
explored. The role of lime content and temperature on
the efficiency of fly ash in contributing to strength gain
is investigated using quantitative X-ray diffraction (XRD)
analysis. Results of fly ash characterization are presented
using quantitative X-ray diffraction (XRD) to identify
its reactive potential associated with the amorphous
silica content. A new method for quantitative phase
analysis of the amorphous phase contributions in the
XRD spectrum is presented. A strength-based efficiency
factor which provides a measure of the contriubtion of
fly ash is introduced. Temperature is shown to increase
the efficiency of fly ash by accelerating the dissolution of
the reactive amorphous content. Efficiency of fly ash in
the binary high volume fly ash-cement blend is limited
by the availability of lime. Increasing the lime content in
the system provides significant enhancement in strength,
but it does not influence the dissolution of fly ash With
the availability of lime, the efficiency is limited by the rate
of contribution of reactive Silica from fly ash, which is
influenced strongly by temperature. Concrete strengths of
30 MPa and higher were achieved with 65% replacement of
cement with fly ash and total cement content of 100 kg/m3.
The strength gain in concrete is shown to be related to the
depletion of lime in the system, formation of amorphous
hydration products and the depletion of Si/Al content from
fly ash. An investigation of the underlying mechanisms
reveals the potential for further strength enhancement by
effectively engaging all the reactive components of fly ash.
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