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To solve the disposal of large quantities of construction waste clay, this study proposes a new method for preparing controlled low strength materials (CLSM). Flow tests, unconfined compressive strength (UCS) tests, hydraulic conductivity tests and scanning electron microscope (SEM) analyses were performed on cement-treated construction waste clay with different additive content (e.g. sodium hexametaphosphate (SHMP), water glass, and phosphogypsum (PG)). The influence of additive content on the mechanical and microstructural properties of cement-treated clay-based CLSM was analyzed. The results indicated that the SHMP greatly enhanced the flowability of samples, adding 1%SHMP increased the fluidity of the sample by more than 80%, whereas 5% water glass had negligible effect. Additionally, the 10% PG improved the flowability retention, making it have higher flowability after 30 mins (more than 200 mm). SHMP interacted with Ca2+, significantly influencing the cement hydration; notably, 1% content resulted a notable reduction of samples from 167.5 kPa to 21.5 kPa at 1 day. Although increasing SHMP content improved the early strength, it led to a decrease in later strength, with the maximum late strength observed at 2% SHMP. Both PG and water glass also contributed to late strength enhancement, though higher SHMP levels diminished their effects. While SHMP markedly improved permeability resistance (less than 8 × 10−8 cm/s after 28d), hydraulic conductivity showed minimal variation with increased dosage. The combination of SHMP, PG and water glass effectively enhances the flowability and strength of clay-based CLSM at low water content, solving the contradiction between fluidity and strength. This promotes the sustainable development of green building materials.

为处置大量建筑废弃黏土，本研究提出一种制备可控低强度材料（controlled low strength materials, CLSM）的新方法。对掺加不同外加剂（如六偏磷酸钠（sodium hexametaphosphate, SHMP）、水玻璃、磷石膏（phosphogypsum, PG））的水泥固化建筑废弃黏土，开展了流动度试验、无侧限抗压强度（unconfined compressive strength, UCS）试验、渗透系数试验及扫描电子显微镜（scanning electron microscope, SEM）微观分析。本研究分析了外加剂掺量对水泥固化黏土基CLSM力学性能与微观结构特性的影响。研究结果表明，六偏磷酸钠可显著提升试样流动度，掺加1%的六偏磷酸钠可使试样流动度提升80%以上，而5%掺量的水玻璃对流动度的影响可忽略不计。此外，10%掺量的磷石膏可改善流动度保持性，使试样在静置30分钟后仍保有较高流动度（大于200mm）。六偏磷酸钠可与钙离子发生相互作用，显著影响水泥水化进程；值得注意的是，掺加1%的六偏磷酸钠可使试样1d龄期抗压强度从167.5kPa大幅降至21.5kPa。尽管提高六偏磷酸钠掺量可改善早期强度，但会降低后期强度，当掺量为2%时试样后期强度达到最大值。磷石膏与水玻璃均可促进后期强度提升，但六偏磷酸钠掺量过高会削弱二者的作用效果。虽然六偏磷酸钠可显著提升抗渗性能（28d龄期渗透系数小于8×10^-8 cm/s），但渗透系数随六偏磷酸钠掺量增加的变化幅度极小。六偏磷酸钠、磷石膏与水玻璃的复配体系可在低含水率条件下有效提升黏土基CLSM的流动度与强度，解决了流动度与强度之间的矛盾，助力绿色建材的可持续发展。