Mineralogy and microstructure effects on the stiffness of activated slag treated alluvium

P Sargent,M Rouainia,N H Jaber

doi:10.1680/jgele.19.00055

Abstract

Alkali-activated alumino-silicate-based industrial waste products have recently proven to be beneficial as low-carbon alternatives to ordinary Portland cement binders for strengthening soft soils. This paper examines the small-strain stiffness behaviour of a UK silty alluvial soil in its natural state and artificially cemented using sodium hydroxide-activated ground-granulated blast-furnace slag (GGBS). Undrained triaxial testing with bender element measurements revealed that the initial small strain shear stiffness (Gmax), shear strength and hydraulic conductivity of the alluvium were all significantly enhanced after 28 d curing. Microstructural and mineralogical analyses were carried out on stabilised soil to understand the mechanisms better through which the enhanced engineering performances were achieved. Through hydration and pozzolanic reactions, a significant proportion of the clay minerals within the original soil had been converted into new cementitious hydrates. These were observed to infill pore spaces, coating soil and GGBS particle surfaces and increased interparticle bonding throughout the matrix of the material. The outcomes from this study have the potential to contribute towards improving current practices for modelling cemented soils and ultimately making geotechnical designs involving deep soil mixing less conservative.

Highlights

Soft alluvial soils possess low bearing capacities and high compressibilities, presenting difficulties in the design and construction of foundations
There have been many unconfined compressive strength (UCS)-based laboratory studies undertaken on soils stabilised with IWMs including ground-granulated blast-furnace slag (GGBS), pulverised fly ash (PFA) and biomass ash as partial replacements to CEM-I (Al-Tabbaa & Evans, 1998; Ahnberg, 2007; Horpibulsuk et al, 2010; Ghadir & Ranjbar, 2018)
This paper presents results from an investigation into the degradation of Gmax for a soft alluvium stabilised with a new sodium hydroxide-activated GGBS binder after 28 d curing and the resulting mineralogical and microstructural modifications

Summary

INTRODUCTION

Soft alluvial soils possess low bearing capacities and high compressibilities, presenting difficulties in the design and construction of foundations. Rios et al (2017) performed another triaxial-based study on a silty sand stabilised with alkali-activated fly ash, to assess their small-to-large strain behaviour after 28 and 90 d curing. They observed that the strength development behaviour of alkali-activated PFA-stabilised soil contrasted with cement-stabilised counterparts, whereby peak strengths for the latter were recorded after 28 d whereas strength development continued for the former – doubling in initial elastic stiffness (E0) from approximately 2·9 GPa after 28 d to 6·3 GPa after 90 d. Mineral phase identification was enabled through the use of the PANalytical High Score Plus software and the ICDD Powder Diffraction File 2 Database, sets 1–49 (ICDD, 1999)

RESULTS AND DISCUSSION

I Na K K

CONCLUSIONS AND RECOMMENDATIONS