Development of sintered aggregate derived from POFA and silt for lightweight concrete

Abstract

The decline in available natural resources and generation of waste materials has brought about a high environmental impact. A potential solution is artificial aggregate fabrication from waste materials. Comprehensive findings have been reported on the performance of industrial waste modified as geo-polymer or cementitious substitution for concrete application. Furthermore, some commercial artificial aggregates made from waste such as LECA, Lytag and others form the basis for further exploitation. A valuable area of investigation is using known cementitious POFA activated by binary activator combined with silt to produce an artificial aggregate. Thus, the present study investigates the physical, mechanical, thermal properties and microstructure of optimised sintered POFA-silt (S-POFA) aggregate on lightweight concrete (LWC). Firstly, characterisation analysis of raw materials, POFA and silt is conducted. Then, the effect of different mix proportion ratios of POFA and silt on the S-POFA aggregate properties is studied with sintering temperature (1150 °C) defined from a preliminary study. Then, the selected optimised sintered S-POFA aggregate is applied as coarse aggregate for concrete production to determine its performance. Based on the result, the increase of POFA proportion increases the density and mechanical properties but shows a declining trend in water absorption. This observation is due to the formation of a dense matrix for the internal microstructure of S-POFA aggregate. Sintered S-POFA aggregate with 40% POFA shows better strength performance with optimum results and is therefore used for concrete mix. Besides, the density of the S-POFA aggregate shows that all the samples are categorised as lightweight aggregate. S-POFA LWC with 28 d strength of more than 30 MPa with density less than 2000 kg/m3 is obtained. Moreover, this concrete provides a low coefficient for capillary absorption and shrinkage. Internal curing allows further hydration to enhance strength development in concrete. In conclusion, this result indicates that S-POFA LWC with both acceptable workability and strength can be achieved through incorporation with sintered S-POFA aggregate.