低浓度CO_(2)矿化再生微粉理化特性影响规律

Influence law of physical and chemical properties of the recycled hardened cement powder by mineral carbonation with low concentration of CO_(2)

为减缓水泥行业排放的CO_(2)对全球气候变化的影响,采用低浓度CO_(2)对建筑垃圾回收骨料过程产生的再生微粉进行了矿化处理以部分替代高碳排放的传统水泥。研究不同矿化方式对再生微粉活性、需水量以及外加剂适应性的影响,并在此基础上明晰了低浓度CO_(2)矿化再生微粉的作用机制。结果表明,直接液相矿化后的再生微粉各项性能明显优于气固干法矿化。相比未处理的再生微粉,其需水量降低33%,活性提高14%,外加剂吸附量降低39%。再生微粉的CO_(2)矿化强化主要通过CO_(2)与再生微粉中的水化产物相氢氧化钙(Ca(OH)_(2),CH)、水化硅酸钙凝胶(Ca_(5)Si_(6)O_(16)(OH)·_(4)H_(2)O,C-S-H)、钙矾石(AFt)以及未水化的硅酸盐水泥熟料硅酸三钙(Ca_(3)SiO_(5),C_(3)S)、硅酸二钙(Ca_(2)SiO_(4),C_(2)S)等反应,生成较为致密的方解石型碳酸钙(CaCO_(3),CC)和无定形硅胶(SiO_(2)·n H_(2)O),改善孔隙结构,从而降低再生微粉的粉料需水量,提高其反应活性和外加剂适应性。CO_(2)矿化处理后的再生微粉可满足JG/T 573—2020《混凝土和胶砂用再生微粉》高比例替代水泥作为矿物掺合料使用,实现固体废弃物资源化利用的同时,CO_(2)被永久固定于再生微粉中,为水泥行业深度脱碳提供一条新途径。

In order to mitigate the negative impact of CO_(2)emitted by the cement industry on climate change,low concentration CO_(2)was used to mineralize the recycled fine powder produced in the process of recycling aggregates from construction waste,so as to partially replace the traditional cement with high carbon emission.In this work,the effects of different mineralization processes on the activity,water absorption and admixture adaptability of recycled hardened cement powder were studied,and the mineralization mechanism of recycled hardened cement powder with low concentration of CO_(2)was investigated.The results show that the performance of recycled hardened cement powder by direct aqueous mineral carbonation is much better than those of gas-solid carbonation.Compared with untreated regenerated micropowder,the water requirement of recycled hardened cement powder is reduced by 33%,and the hydration activity and additive adaptability are increased by 14%and 39%respectively.Property improvement of the recycled hardened cement powder by CO_(2)mineral carbonation is mainly due to the reaction of CO_(2)reacted with calcium hydroxide,calcium silica hydrate,ettringite and unhydrated cement clinker tricalcium silicate,dicalcium silicate to generate relatively dense calcite calcium carbonate(CaCO_(3),CC)and amorphous silica gel(SiO_(2)·n H_(2)O),refine the pores or microcracks,so as to reduce the water demand of recycled micro powder,and enhance the properties of the hydration activity and additive adaptability finally.The recycled micro powder after CO_(2)mineralization treatment can meet the requirements of JG/T 573-2020 Recycled Micro Powder for Concrete and Mortar to replace cement as a mineral admixture in a high proportion.While realizing the resource utilization of solid waste,CO_(2)is permanently fixed in the recycled micro powder,providing a new way for the deep decarbonization of the cement industry.