Yang Yuanquan, Fang Bodong, Zhang Guanhua, Guo Jinbo, Liu Runqing
School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China.
Liaoning Transportation Planning and Design Institute Co., Ltd., Shenyang 110159, China.
Materials (Basel). 2022 Jan 26;15(3):943. doi: 10.3390/ma15030943.
Retarders are important factors controlling the hydration and properties of magnesium potassium phosphate cements (MKPCs). Boric acid and borax are the most commonly used retarders for MKPC which could control the setting time in a wide range upon changing their content. However, with the increase in borax content, the early strength of MKPC can be reduced, and boron compounds are now included in the EU candidate list of substances of very high concern for authorization, due to their reproductive toxicity. Exploring alternative set retarders to boron compounds is, thus, of significance. This work investigated the effects of a candidate retarder, namely, sodium alginate, on the setting time, mechanical properties, hydration products, and microstructures of MKPC. Sodium alginate presented dramatically retarding effects on MKPCs in the range of 0% to 2% (by mass of water). One percent of sodium alginate by mass of water could extend the setting time of MKPCs from 15 min to 35 min, which presented a better retarding effect than borax (a typical retarder for MKPCs) and produced higher early strength of MKPCs. Adding no more than 1% of sodium alginate did not have a notably adverse effect on the formation of hydration product over the long term, but an unfavorable effect could be found regardless of the sodium alginate content, which could reduce the compressive strength of MKPCs.
缓凝剂是控制磷酸镁钾水泥（MKPC）水化和性能的重要因素。硼酸和硼砂是MKPC最常用的缓凝剂，改变其含量可在较宽范围内控制凝结时间。然而，随着硼砂含量的增加，MKPC的早期强度会降低，并且由于硼化合物具有生殖毒性，现在已被列入欧盟高度关注物质候选授权清单。因此，探索硼化合物的替代缓凝剂具有重要意义。本研究考察了一种候选缓凝剂海藻酸钠对MKPC的凝结时间、力学性能、水化产物和微观结构的影响。海藻酸钠在0%至2%（相对于水的质量）范围内对MKPC表现出显著的缓凝作用。相对于水的质量1%的海藻酸钠可将MKPC的凝结时间从15分钟延长至35分钟，其缓凝效果优于硼砂（MKPC的典型缓凝剂），并使MKPC具有更高的早期强度。添加不超过1%的海藻酸钠对长期水化产物的形成没有明显不利影响，但无论海藻酸钠含量如何，均会发现有不利影响，这会降低MKPC的抗压强度。
