Assessment of sulphates effect on pH and pozzolanic reactions of soil–lime–natural pozzolana mixtures

ABSTRACT

The geotechnical properties of subgrade soils may need to be enhanced for appropriateness in pavement construction using mineral additives such as cement, lime (L) and fly ash. An experimental investigation was undertaken to study the effects of sodium (Na₂SO₄) and calcium (CaSO₄·2H₂O) sulphates on pH and pozzolanic reactions of soil–lime–natural pozzolana (soil–L–NP) mixtures in order to choose an adequate mixture for pavement subgrade soil stabilisation. The pH was measured for different curing periods with and without sulphates. The results showed that increases and decreases in pH values depend on the type of additive and its amount, type of sulphate and its content, mineralogical composition of stabilised soil and curing period. In addition, the pH parameter can be used as an indicator to track the pozzolanic reactions process. On the other hand, clayey subgrade soils can be stabilised with Lime–Natural Pozzolana (L–NP) mixtures containing any amounts of CaSO₄·2H₂O which is highly recommended. However, Na₂SO₄ with a low content has a better effect on the behaviour of these soils but become deleterious when its content is greater than 2%. In general, the addition of sulphates accelerates both the pozzolanic reactions and NP dissolution.

KEYWORDS:

• Clayey soil
• lime
• natural pozzolana
• sulphate
• pH value

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements

The authors would like to acknowledge the director of the Habitat Laboratory and Construction Center (HLCC, Oued-Smar, Algeria) for providing excellent working conditions and financial support.