Evaluation of coal based bottom ash as an alternative to fine aggregate in concrete: recommendations for specifications of bottom ash and its concrete mix design
P.N. Ojha, Abhishek Singh, Amit Trivedi, Brijesh Singh, Nitin Chowdhury
Centre for Construction Development & Research, National Council for Cement and Building Materials, India
Composite fine aggregate;
Present study is an attempt to develop recommendations for specifications of bottom ash and concrete mix design guidelines by carrying out studies on bottom ash samples collected from 10 thermal power plants across India. Bottom ash samples were evaluated for physical and chemical properties. Composite fine aggregates were prepared by replacing 10-50% of conventional fine aggregate with bottom ash. 70 concrete mix trials were carried out using composite fine aggregates and mixes were evaluated for fresh, hardened and durability properties. Study indicated that maximum replacement of conventional fine aggregate with bottom ash for preparation of OPC based concrete shall not exceed 50% by weight of total fine aggregate and fineness modulus of resultant composite fine aggregate for use in concrete as fine aggregate shall be at least 1.35. The compressive strength of concrete at 28 days for all trials using composite fine aggregates were comparable with compressive strength of control concrete made with 100% conventional fine aggregates. The carbonation depth of control concrete were 6.6 mm to 9.5 mm and for concrete with composite fine aggregates, carbonation depths were 5.5 to 11.0 mm. The RCPT results of all mixes (including control mixes) shows that all mixes are lying in same class of penetrability. The electrical resistivity values of control concrete mixes were 7.1 to 6.1 k-ohm-cm and for concrete with composite fine it was 6.7 to 8.58 k-ohm-cm. Based on the results; recommendations were derived for specification of coal based bottom ash for its utilisation as an alternative to conventional fine aggregate in concrete along with guidelines for concrete mix design.
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