Mix design for fly ash based oil palm shell geopolymer lightweight concrete

• The mix design of OPS geopolymer concrete differs widely from the procedure used for conventional concrete.
• The increase in water, OPS and fine aggregate contents reduces strength.
• The use of activator solution with 14 molarity and OPS in SSD condition is recommended.
• The mix FA content of 480 kg/m3 and W/FA ratio of 0.34 is considered for structural grade concrete.

This paper presents the experimental results of an on-going research project to produce geopolymer lightweight concrete using two locally available waste materials – low calcium fly ash (FA) and oil palm shell (OPS) – as the binder and lightweight coarse aggregate, respectively. A total of 32 mixes using different mixture proportions were prepared to get an appropriate mix design for fly ash based oil palm shell geopolymer lightweight concrete (OPSGPC). A mixture of sodium hydroxide and sodium silicate in different molarities was used as an alkali activator. The variables used in this investigation include the fly ash content, molarity and condition of OPS. The proposed mix design differs widely from the procedure used for mix proportioning of concrete produced with conventional lightweight and normal weight aggregates. The increase in FA content reduces the strength significantly due to additional water used for workability. The increase in molarity from 14 M to 16 M did not have desired effect on the compressive strength. However, the use of OPS with SSD condition produced higher strength than that of AD condition. The OPSGPC with 14 M, FA content of 480 kg/m3 and water to FA ratio of 0.34 produced 28-day compressive strength of about 32 MPa and is recommended for producing structural grade 30 OPSGPC. The demoulded densities of OPSGPC were within the limit of 2000 kg/m3 for lightweight concrete.