Supplementary cementitious materials (SCM) have been used by the cement industry for decades to partly replace the portland cement fraction of concrete binders. This is particularly important today in addressing CO2 emissions from the cement manufacturing process. However, defining the reactivity of these mainly aluminosilicate‐based materials and their influence on portland cement hydration chemistry has challenged the research community and has limited SCM replacement levels in cementitious binders. In this study, aluminosilicate glasses as models for blast furnace slag and fly‐ash systems were synthesized and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 hours. Solution compositions were measured from the very first minutes of dissolution and correlated with results from complementary solid surface analysis. Initial Ca concentration maxima in the first 30 minutes of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline attributable to Ca‐reincorporation on the reacting surface. Surface‐specific analysis confirmed Ca and Al enrichment at the surface, suggesting the formation of a Ca‐modified aluminosilicate layer, supporting a dissolution‐reprecipitation mechanism for SCM reactivity. Differing chemistries are thought to be responsible for the Ca and Al reintegration on the reacting surface depending on the pH of the solution; near‐neutral conditions favor Ca‐readsorption and surface condensation reactions, whereas alkaline solutions favor Ca‐reintegration via covalently bound phases.

The reactivity of aluminosilicate glasses in cementseffects of Ca content on dissolution characteristics and surface precipitation The partial replacement of Portland cement (PC) by glassy aluminosilicates in cementitious binders has been common practice for decades, offering concretes with increased durability and long term strength compared with PC concretes. However, these concretes typically display a much lower rate of strength development and this limits practical levels of cement replacement. The factors contributing to strength development in concrete are complex but amongst them is the reactivity of the SCM, which has been associated with glass content, and composition with respect to the ratio of network modifiers to network formers, etc. This paper revisits the assessment of reactivity using a fundamental dissolution approach and highlights a rapid migration of soluble constituents, specifically Ca, to the surface on contact with an activating solution. The conditions which affect the composition of Ca-bearing precipitates and their role in ongoing hydration is discussed.

Formaldehyde is commonly used as an alkylating agent in the pharmaceutical industry. Consequently, its residual level in drug substances and/or their intermediates needs to be accurately quantified. Formaldehyde is a small, volatile molecule with a weak chromophore (the carbonyl group), and its direct analysis by GC-FID and HPLC-UV is difficult. For these reasons, the majority of papers found in the literature are based upon a derivatisation process (most commonly using the desensitised explosive 2,4-dinitrophenylhydrazine) prior to the analysis of formaldehyde. A novel high-performance liquid chromatography (HPLC) method with UV detection for its quantification in a pharmaceutical is described in this paper. The method proposed herein is based upon a derivatisation reaction between formaldehyde and 4-methylbenzenesulfonohydrazide (MBSH) before analysis by HPLC-UV. Selectivity, linearity, limit of quantification, accuracy, repeatability, intermediate precision, and solution stability were successfully assessed as per ICH guideline Q2(R1), and the method has also been validated in a good manufacturing practice (GMP) laboratory in the UK.