Publication: Influence of rha and ggbs as ternary blended binders on properties of high strength green concrete
Date
2020-10-01
Authors
Ishak, Nuril Izzeaty
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Abstract
The use of high volume of GGBS in producing high strength concrete indicated
some limitation due to slowing of the hydration reaction at the early age which leads
to retardation in setting and lower the initial strength. This limitation causes a major
problem for the precast industry especially when time, cost and quality became a main
concern. To keep the production cycle more efficient, the combined solution of using
highly reactive material of RHA in GGBS-cement mixture together with acceleration
of SCM-OPC hydration through thermal treatment provides sufficient maturity to be
reached at early ages for the precast products. Thus, the main objectives of this
research are to evaluate the influence of RHA and GGBS as partial replacement of
cement on the hydration process, mechanical strength and fluid transport properties of
high strength green concrete (HSGC) under various steam curing regimes. The
chemical compositions and physical properties of RHA and GGBS have been studied
via XRF analysis, XRD techniques, thermal analysis and particle size analysis. RHA
obtained from boiler fired rice husk ash was treated via heat treatment at 650°C for 6
hours to remove the unburned carbon and subsequently milled for 60 minutes to
increase its reactivity. The RHA was used in the production of HSGC mixture with
inclusion at 5, 10, 15 and 20% by mass of cement with GGBS was kept constant at
50%. The results show that the inclusion of 10% RHA in GGBS-cement concrete
mixture provides a synergistic effect that leads to the improvement on workability and
setting time compared to the other mixtures. Besides, the higher the amount of RHA
and GGBS, the higher the content of SiO2 to react with C-H via pozzolanic reaction
resulted to high formation of C-S-H gel that was observable as the curing age
increased. The inclusion of 60% RHA and GGBS as partial replacement of cement
exhibited low Ca/Si ratio that increased the formation of C-S-H gels through hydration
reaction and improved the strength performances up to 80 MPa at the age of 28 days.
Whereas the transport properties results indicated that the inclusion of RHA cured
under 2 hours delay period prior to steam curing at temperature of 60°C had greater
contribution towards permeability reduction and low tendency against water
absorption and porosity at later ages. The overall results show a good correlation
between strength performances and fluid transport properties, as 60% SCM was
included as ternary blended binder in HSGC.