Optimisation of Environment-friendly SCFRC mixes use in precast Concrete Industry

The concept of green concrete has been progressively introduced in concrete technology. At the same time, new generations of superplasticisers have become widely available and self-compacting concrete is being increasingly implemented. The aim of this research is to study the impact that different sustainable materials have on both fresh and hardened properties of Self-Compacting Fibre Reinforced Concrete (SCFRC) in order to implement their use in a precast concrete company. Different combinations of cement, mineral additions (active and inert), polypropylene fibres, superplasticisers, and aggregates have been considered. Fresh state performance has been assessed by means of: slump flow test, V-funnel, and J-ring. Concrete compressive strength values at different ages have been retained as representative of the material's performance in its hardened state. All these properties have been correlated with SCFRC proportioning parameters. The importance of interactions between mineral additions and between these and superplasticiser is emphasised, as well as the different consequences of using powders as cement replacement or as mineral additions.

Optimisation of Environment-friendly SCFRC mixes use in precast Concrete Industry (PDF Download Available). Available from: http://www.researchgate.net/publication/263304799_Optimisation_of_Environment-friendly_SCFRC_mixes_use_in_precast_Concrete_Industry [accessed Jun 5, 2015].

Performance of sustainable SCC mixes with mineral additions for use in precast concrete industry

The aim of this research was to study the impact that different mineral powders have on the properties of self-compacting concrete (SCC) in order to obtain relations that make it possible to optimize their dosages for being used in precast concrete applications. Different combinations and contents of cement, mineral additions (active and inert), superplasticizers, and aggregates are considered. A new approach for determining the saturation point of superplasticizers is introduced. The fresh state performance was assessed by means of the following tests: slump flow, V-funnel, and J-ring. Concrete compressive strength values at different ages up to 56 days have been retained as representative of the materials’ performance in its hardened state. All these properties have been correlated with SCC proportioning. As a result, a number of recommendations for the precast concrete industry arise to design more stable SCC mixes with a reduced carbon footprint.

Cement As a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of ⁹⁰Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its β-decay on the cement paste structure. We show that ⁹⁰Sr is stable when it substitutes the Ca²⁺ ions in C-S-H, and so is its daughter nucleus ⁹⁰Y after β-decay. Interestingly, ⁹⁰Zr, daughter of ⁹⁰Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for ⁹⁰Sr storage.