It’s an oversimplification to evaluate the reactivity of fly ash in geopolymerization using bulk elemental ratios like Si/Al. In this study, quantitative XRD by means of Rietveld refinement was employed to proportionate the mineral and glass phases of five fly ashes. The chemical environment of Si and Al in the fly ashes was investigated by ²⁹Si and ²⁷Al MAS NMR spectra. By counting the contributions of Al phase from mullite, the proportion of different coordination states of Al in the glass phase was speculated. The results reveal that the coordination number of Al is directly associated with the amount of alkali cations present in the glass phase for the most fly ashes, whereby higher the alkali content, the more four fold coordinated Al species are present in the system. Five and six fold coordinated Al as well as highly polymerized silicate species are also present in the glass structure of the fly ash. All these results point to an inherent inhomogeneous glass structure in fly ash. Despite that, a reactivity index derived from the NBO/T ratio (Non-Bridging Oxygen per Tetrahedral network former, e.g. SiO₄^4-, AlO₄^5-) modelled in a simplified glass setup, correlates well with the reaction heat of the geopolymers.

使用诸如Si / Al之类的体积元素比率来评估粉煤灰在地质聚合中的反应性过于简单。在这项研究中，通过Rietveld精炼的定量XRD被用来按比例分配五个飞灰的矿物和玻璃相。用²⁹ Si和²⁷研究了飞灰中Si和Al的化学环境Al MAS NMR谱。通过计算莫来石对铝相的贡献，推测了玻璃相中铝不同配位态的比例。结果表明，对于大多数粉煤灰，Al的配位数与玻璃相中存在的碱金属阳离子量直接相关，因此，碱含量越高，系统中存在的配位Al物种越多，是四倍。在飞灰的玻璃结构中还存在五和六倍的配位铝以及高度聚合的硅酸盐。所有这些结果表明粉煤灰固有的不均匀玻璃结构。尽管如此，一个反应性指数从NBO / T比得出（Ñ导通乙起垄ö每xygen Ť以简化的玻璃设置为模型的etrahedral网络形成剂（例如SiO ₄ ^4-，AlO ₄ ^5-）与地质聚合物的反应热密切相关。