SHIELD-DRIED SOIL PREPARED AS A HIGHLY ACTIVE ADMIXTURE

A small amount of alkali was incorporated into the mixture and subjected to modification by calcination to improve the latent hydraulicity of the shield-dried soil (SDS) mixtures for optimum utilisation. The microstructural changes that occur in SDS during hydration after calcination and mixing with PC were analysed by thermogravimetry, scanning electron microscopy and X-ray diffraction. The objective was to investigate the influence of the modified SDS on both the hydration products of the PC and the structure of the pastes. The investigation yielded the following findings: The study involved preparing a slurry composed of 30% SDS and 70% PC, and it was found that the highest latent hydraulicity occurred when the NaOH dosage was 0.05%. After 28-days, the samples reached a compressive strength of 79.36 MPa. While the compressive strength of the reference specimen composed solely of PC was 86.12 MPa. The addition of the alkali altered the surface structure of the SDS, affecting its amorphous characteristics and enhancing its latent hydraulicity. The alkali-modified SDS readily reacted with calcium hydroxide (CH), a hydration product of PC, resulting in the additional formation of monosulfate and hydrated calcium silicate, which improved the structure of the paste. However, the excessive alkali addition was found to potentially degrade the structure of the hydrated pastes.