Characteristics of compressed stabilized earthen block fabricated with sawdust ash based geopolymer

Abstract

Expansive soil has always been a major concern for civil engineers. The problematic swell-shrink behavior of this soil due to seasonal fluctuation of water content can be mitigated through mechanical, physical, chemical, or biological stabilization. Among chemical stabilization processes, geopolymerization has recently achieved better efficacy due to its lower carbon footprint. This study explores investigating the strength and durability characteristics of Compressed Stabilized Earthern Blocks (CSEBs) fabricated with Sawdust Ash (SDA) based geopolymer. An expansive soil of high swell index (Free Swell Index, FSI = 83.3%) was reconstituted with a mixture of NaOH (10M), Na2SiO3.9H2O (70%/30% w/w), and a variety of SDA content ranging from 0% to 20% at different compaction effort based on the workability. By varying the Alkaline Solution (A) to Binder (B) ratio (A:B) from 0.3 to 0.5, optimum A:B ratio was obtained at various amounts of SDA percentage indicating an increase in A:B ratio with increasing SDA content. Uniaxial compression tests of the samples cured at room temperature at 7 day and 28 day bulk condition showed that, the highest compressive strength (0.82 and 1.78 MPa) is obtained for the composition having 20% SDA and A:B ratio of 0.5 which also satisfies minimum strength requirements of several codes and standards. From durability perspective, around half of the samples showed efflorescence which can be mitigated thourgh moist curing. The improvement of compressive strength due to water submersion also emphasizes on the application of moist curing for enhanced strength and reduced efflorescence. The maximum flexure (0.35 MPa) and tensile strength (0.31 MPa) were obtained for the same composition (20% SDA and A:B ratio of 0.5) which is around 180% and 400% greater than unstabilized soil respectively. The microstructural analysis by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Analysis (EDXA), and Fourier Transformed Infrared Spectroscopy (FTIR) supported the formation of geopolymer as well as improved mechanical strength. Overall, the experimental results obtained in the present study corroborate the successful application of SDA based geopolymer in the fabrication of CSEBs from expansive soil.