Generalized Structural Description of Calcium–Sodium Aluminosilicate Hydrate Gels: The Cross-Linked Substituted Tobermorite Model

Structural models for the primary
strength and durability-giving
reaction product in modern cements, a calcium (alumino)­silicate hydrate
gel, have previously been based solely on non-cross-linked tobermorite
structures. However, recent experimental studies of laboratory-synthesized
and alkali-activated slag (AAS) binders have indicated that the calcium–sodium
aluminosilicate hydrate [C-(N)-A-S-H] gel formed in these systems
can be significantly cross-linked. Here, we propose a model that describes
the C-(N)-A-S-H gel as a mixture of cross-linked and non-cross-linked
tobermorite-based structures (the cross-linked substituted tobermorite
model, CSTM), which can more appropriately describe the spectroscopic
and density information available for this material. Analysis of the
phase assemblage and Al coordination environments of AAS binders shows
that it is not possible to fully account for the chemistry of AAS
by use of the assumption that all of the tetrahedral Al is present
in a tobermorite-type C-(N)-A-S-H gel, due to the structural constraints
of the gel. Application of the CSTM can for the first time reconcile
this information, indicating the presence of an additional activation
product that contains highly connected four-coordinated silicate and
aluminate species. The CSTM therefore provides a more advanced description
of the chemistry and structure of calcium–sodium aluminosilicate
gel structures than that previously established in the literature.

现代水泥中赋予主要强度与耐久性的反应产物——钙（铝）硅酸盐水化凝胶的结构模型，此前仅基于非交联的托贝莫来石结构。然而，近期对实验室合成及碱激发矿渣（AAS）胶结材料的实验研究表明，在这些体系中形成的钙-钠铝硅酸盐水化凝胶[C-(N)-A-S-H]可以显著地进行交联。本研究提出了一种模型，将C-(N)-A-S-H凝胶描述为交联与非交联托贝莫来石结构的混合体（交联替代托贝莫来石模型，CSTM），该模型能够更恰当地描述该材料的光谱与密度信息。对AAS胶结材料的相组成及铝配位环境进行分析表明，由于凝胶的结构限制，无法通过假设所有四面体铝均存在于托贝莫来石型的C-(N)-A-S-H凝胶中来完全解释AAS的化学性质。CSTM的应用首次使得这一信息得以调和，指出存在一种额外的活化产物，其中含有高度连接的四配位硅酸盐和铝酸盐物种。因此，CSTM为钙-钠铝硅酸盐凝胶结构的化学与结构描述提供了比文献中先前建立的描述更为先进的理解。