Study on the engineering properties of GGBS-MICP synergistic solidification of silty-sandy soil

To facilitate the reutilization of solid waste and the solidification of soil，this study integrates ground granulated blast-furnace slag(GGBS) with microbial induced carbonate precipitation(MICP) technology，referred to as GGBS-MICP. It aims to investigate the engineering properties of silty-sandy specimens solidified with various particle sizes and dosages of GGBS combined with MICP technology through a series of tests，including unconfined compressive strength(<italic>UCS</italic>)，triaxial compression，erosion resistance，Ca²⁺ utilization quantity，pH values，and scanning electron microscopy(SEM). Compared to silty-sandy specimens treated solely with GGBS and MICP，those solidified by GGBS-MICP exhibit a significantly increased <italic>UCS</italic>. Finer GGBS particles yield a more pronounced enhancement，especially with&lt;10<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>μm</mml:mtext></mml:mrow></mml:math></inline-formula>GGBS-MICP. For&lt;10<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>μm</mml:mtext></mml:mrow></mml:math></inline-formula>GGBS-MICP solidified silty-sandy samples with/without <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>，the peak values of effective bonding strength <italic>c</italic>' and internal friction angle<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>φ</mml:mi><mml:mo>′</mml:mo></mml:mrow></mml:math></inline-formula>occur at 1% and 3% GGBS dosages，respectively. Adequate <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>effectively enhances the erosion resistance of GGBS-MICP solidified samples against the saline solutions，and the erosion resistance follows the sequence：water&gt;1%Na₂SO₄&gt;1%NaCl. SEM analysis reveals a denser C-S-H gel structure in GGBS-MICP samples，with GGBS being capable of regulating the crystal morphology of bio-CaCO₃，where the crystal growth of vaterite predominates over that of calcite and aragonite. The difference in pH values(ΔpH) between&lt;10<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>μm</mml:mtext></mml:mrow></mml:math></inline-formula> GGBS-MICP and original GGBS-MICP solidified silty-sandy samples indicates that ΔpH1 without Ca²⁺ is greater than ΔpH2 with<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>. The increase in<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>utilization quantity with increasing GGBS dosages in GGBS-MICP(with<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>) samples highlights the importance of sufficient calcium sources for the effective solidification using GGBS-MICP technology. Therefore，the adoption of&lt;10<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>μm</mml:mtext></mml:mrow></mml:math></inline-formula>3%GGBS-MICP(with<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>) solidification approach greatly enhances the engineering properties of silty-sandy soil，achieving the efficient utilization of solid waste，and aligning with the strategies of green and sustainable development.