This paper studies the microstructure variation induced by super-absorbent polymer (SAP) to understand the mechanism of macroscopic strength improvement of stabilized soil. The fabric changes of cement–lime stabilized soil were analyzed with respect to the variation of SAP content, water content, lime content and curing time, using mercury intrusion porosimetry (MIP) tests. It can be observed that the delimitation pore diameter between inter- and intra-aggregate pores was 0.2 μm for the studied soil, determined through the intrusion/extrusion cycles. Experimental results showed that fabric in both inter- and intra-aggregate pores varied significantly with SAP content, lime content, water content and curing time. Two main changes in fabric due to SAP are identified as: (1) an increase in intra-aggregate pores (<0.2 μm) due to the closer soil–cement–lime cluster space at higher SAP content; and (2) a decrease in inter-aggregate pores represented by a reduction in small-pores (0.2–2 μm) due to the lower pore volume of soil mixture after water absorption by SAP, and a slight increase in large-pores (>2 μm) due to the shrinkage of SAP particle during the freeze–dry process of MIP test. Accordingly, the strength gain due to SAP for cement–lime stabilized soil was mainly due to a denser fabric with less inter-aggregate pores. The cementitious products gradually developed over time, leading to an increase in intra-aggregate pores with an increasing proportion of micro-pores (0.006–0.2 μm). Meanwhile, the inter-aggregate pores were filled by cementitious products, resulting in a decrease in total void ratio. Hence, the strength development over time is attributable to the enhancement of cementation bonding and the refinement of fabric due to the increasing cementitious compounds.

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Keywords: Fabric, Soil stabilization, Microstructure, Super-absorbent polymer (SAP)