Up to 100% Replacement of Natural Materials from Residues: Recycling Blast Furnace Slag and Fly Ash as Self-Leveling Cementitious Building Materials.

The objective of this research is to study the use in the construction industry of recycled slag (SL) and fly ash (FA) using from 0.1 to 5% calcium sulfate (wCS¯). These wastes have been used to make ternary mixture systems and evaluated in terms of technological properties as cementitious materials for building applications. Studying their micro-structure as hydration products, setting times and mechanical properties shows a way to develop new mixtures from high proportion of waste, which are alternatives to the traditional nature ternary systems: Portland cement (PC), calcium aluminate cement (CAC) and calcium sulphate (CS¯). Based on previous work with natural products, the selected SL/FA ratios were 9 and 2.3 and the sulphate contents were 0, 1 and 5%. The water/binder ratio used for these cementitious mixes was 0.4. The specimens prepared for strength determination were prisms of 10 × 10 × 60 mm. The pastes were prepared and cured at 20 °C and 98% relative humidity for 1 day and then either stored at 20 °C at 98% humidity (dry) or immersed in distilled water (wet) for 14 and 28 days. The results showed that both FA and SL mixed with CS¯ produce ettringite after 28 days of setting, and this phase was the main crystalline hydrated product in all mixes. Calcium sulphate stimulates the hydration reactions of the mixes and the strength increases when the CS¯ content is higher due to ettringite formation, while the setting time decreases, as happened in the systems prepared with natural materials.

Reactivity of Binary Construction and Demolition Waste Mix as Supplementary Cementitious Materials.

Calcareous and siliceous CDW wastes from concrete and glass wastes when mixed in binary mixtures has been analyzed in this study. Fine CDW fractions (<5 mm) of different sorts are selected: siliceous waste (HsT), calcareous waste (HcG) and laminated glass waste. The binary mixtures HsT/glass and HcG/glass at mix-proportions of 1:1, 2:1 and 1:2, respectively, are analyzed with a range of characterization techniques (XRD, TG/DTA, SEM-EDX, NMR, FT-IR) in the pure pozzolan/lime system over a reaction time of 90 days. The results showed that the incorporation of highly reactive recycled glass modified the pozzolanic reaction of the binary mixtures with respect to each particular concrete waste (of low activity). The principal mineralogical phases of the reaction were calcite and C-S-H gel, the latter modifying the C/S and A/S ratios as a function of either the silica or the lime-based concrete waste and the glass content of the mixtures. A higher degree of polymerization, morphology, and sodium content of C-H-S gel formed when glass was added.

Tensile and Flexural Properties of Cement Composites Reinforced with Flax Nonwoven Fabrics.

The aim of this study is to develop a process to produce high-performance cement-based composites reinforced with flax nonwoven fabrics, analyzing the influence of the fabric structure-thickness and entanglement-on mechanical behavior under flexural and tensile loadings. For this purpose, composite with flax nonwoven fabrics with different thicknesses were first prepared and their cement infiltration was evaluated with backscattered electron (BSE) images. The nonwoven fabrics with the optimized thickness were then subjected to a water treatment to improve their stability to humid environments and the fiber-matrix adhesion. For a fixed thickness, the effect of the nonwoven entanglement on the mechanical behavior was evaluated under flexural and direct tension tests. The obtained results indicate that the flax nonwoven fabric reinforcement leads to cement composites with substantial enhancement of ductility.

A force field for tricalcium aluminate to characterize surface properties, initial hydration, and organically modified interfaces in atomic resolution.

Tricalcium aluminate (C3A) is a major phase of Portland cement clinker and some dental root filling cements. An accurate all-atom force field is introduced to examine structural, surface, and hydration properties as well as organic interfaces to overcome challenges using current laboratory instrumentation. Molecular dynamics simulation demonstrates excellent agreement of computed structural, thermal, mechanical, and surface properties with available experimental data. The parameters are integrated into multiple potential energy expressions, including the PCFF, CVFF, CHARMM, AMBER, OPLS, and INTERFACE force fields. This choice enables the simulation of a wide range of inorganic-organic interfaces at the 1 to 100 nm scale at a million times lower computational cost than DFT methods. Molecular models of dry and partially hydrated surfaces are introduced to examine cleavage, agglomeration, and the role of adsorbed organic molecules. Cleavage of crystalline tricalcium aluminate requires approximately 1300 mJ m(-2) and superficial hydration introduces an amorphous calcium hydroxide surface layer that reduces the agglomeration energy from approximately 850 mJ m(-2) to 500 mJ m(-2), as well as to lower values upon surface displacement. The adsorption of several alcohols and amines was examined to understand their role as grinding aids and as hydration modifiers in cement. The molecules mitigate local electric fields through complexation of calcium ions, hydrogen bonds, and introduction of hydrophobicity upon binding. Molecularly thin layers of about 0.5 nm thickness reduce agglomeration energies to between 100 and 30 mJ m(-2). Molecule-specific trends were found to be similar for tricalcium aluminate and tricalcium silicate. The models allow quantitative predictions and are a starting point to provide fundamental understanding of the role of C3A and organic additives in cement. Extensions to impure phases and advanced hydration stages are feasible.