This work analyses the influence of fine concrete fractions (<5 mm) of different natures -calcareous (HcG) and siliceous (HsT)-obtained from construction and demolition waste (C&DW) on the behaviour ...of blended cement pastes with partial replacements between 5 and 10%. The two C&DW fractions were characterised by different instrumental techniques. Subsequently, their lime-fixing capacity and the physico-mechanical properties of the blended cement pastes were analysed. Lastly, the environmental benefits of reusing these fine wastes in the manufacture of future eco-efficient cement pastes were examined. The results show that HsT and HcG exhibit weak pozzolanic activity, owing to their low reactive silica and alumina content. Despite this, the new cement pastes meet the physical and mechanical requirements of the existing regulations for common cements. It should be highlighted that the blended cement pastes initially showed a coarser pore network, but then they underwent a refinement process between 2 and 28 days, along with a gain in compressive strength, possibly due to the double pozzolanic and filler effect of the wastes. The environmental viability of the blended cements was evaluated in a Life Cycle Assessment (LCA) concluding that the overall environmental impact could be reduced in the same proportion of the replacement rate. This is in line with the Circular Economy goals and the 2030 Agenda for Sustainable Development.
•Combining the fine fraction of CDW (glass and concrete) yields viable pozzolans.•Their use at 7% replacement level gives cements compliant with current standards.•Blended mortars show slightly lower ...mechanical strength and resistivity values.•Calcareous concrete wastes increase capillary absorption more than siliceous ones.
The serious technical and environmental problems associated with the management of construction and demolition wastes (CDW) have led to a worldwide growing interest in the recycling of that waste stream as secondary raw material for sustainable building applications.
This research work investigates the physical and mechanical behaviour of mortars made with ternary cements containing 7% of a binary recycled CDW mixture comprising the fine fraction (<5 mm) of recycled concrete waste (both siliceous and calcareous nature) in combination with recycled laminar glass in three different proportions (1/1, 1/2, and 2/1, respectively). To this end, the chemical composition and fineness of the anhydrous ternary cements were analysed, as well as their behaviour in paste and mortar matrices, in both fresh and hardened states, verifying the requirements established by the applicable standards.
The results attest to the viability of using these ternary cements, as their performance is comparable to that of an ordinary Portland cement (OPC), without evidencing any significant dependence on the glass content. The compressive strength values decrease by 7–8% with respect to that of the OPC mortar, revealing the prevalence of the filler effect over the pozzolanic reaction. The ternary cements analysed in this study met the chemical, physical and mechanical requirements for the elaboration of future eco-efficient cements.
From physics to chemistry of fresh blended cements Flatt, Robert J.; Roussel, Nicolas; Bessaies-Bey, Hela ...
Cement and concrete research,
October 2023, 2023-10-00, 2023-10, Letnik:
172
Journal Article
Recenzirano
Tomorrow's mineral binders are called on to integrate a growing proportion of mineral powders other than Portland clinker. This impacts most properties of industrial interest including fresh state ...properties, the focus of this paper.
We discuss the physical, physico-chemical and chemical changes that such an evolution in mix design is expected to induce.-Volume-driven effects (physics) control solid fraction, packing properties and strongly relate to particle shape, particle polydispersity and early hydrates morphology.-Surface-driven effects (physical chemistry) drive interparticle forces and admixtures adsorption, profoundly impacting the rheology by modifying the degree of dispersion.-Early hydration kinetics (chemistry) leads to hydrate nucleation and growth, which impact the above by modifying the specific surface area, admixture consumption and cohesion forces.
We discuss the above features, their independence and their interplay and extrapolate the critical research questions and needs associated to a full understanding of the fresh properties of blended cements.
This study explores certain indirect, water transport-related durability indicators for mortars made with cement in which 20% or 50% of the ordinary portland cement (OPC) is replaced by thermally ...activated coal mining waste (ACMW). The valorisation of ACMW is triply beneficial, environmentally speaking, for it reduces waste stockpiling and its processing emits less CO2 and requires less fossil fuel-based energy than OPC manufacture. Its addition was observed to generate a finer pore structure and a larger volume of pores accessible to water. In mortars with 50% ACMW, pore volume rose by approximately 30%, lowering density and consequently mechanical strength. Total water absorption declined by 13% and capillary absorption by 24% in mortars with 20% ACMW, whilst no significant variations in either parameter relative to the OPC reference were found in the materials with 50% replacement ratios. Permeability to water penetration under pressure rose substantially in both blended mortars, although as the maximum and mean depth values lay within the limits specified in Spain's structural concrete code, the materials would be classified as impermeable. The mortars with 20% replacement exhibited no greater drying shrinkage than the OPC materials, whereas the mortars bearing 50% ACMW shrank by approximately 50% more than the reference.
We report a macrocyclic ligand (H3 L 6 ) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth ...nitrogen atom of the macrocycle. The X-ray structures of the YL 6 and TbL 6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (1H, 13C, and 89Y) and DFT calculations indicated that the structure of the YL 6 complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the EuL 6 and TbL 6 complexes revealed Ln3+-centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The YL 6 complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10–5 M). Studies using the 90Y-nuclide confirmed fast radiolabeling since 90YYL 6 is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the 90YYL 6 complex. All of these experiments combined suggest the potential application of H3 L 6 derivatives as Y-based radiopharmaceuticals.
In recent years, the development of ternary cements has become a priority research line for obtaining cements with a lower carbon footprint, with the goal to contribute to achieve climate neutrality ...by 2050. This study compared ordinary Portland cement (OPC) durability to the performance of ternary cements bearing OPC plus 7% of a 2:1 binary blend of either calcareous (Hc) or siliceous (Hs) concrete waste fines and shatterproof glass. Durability was measured further to the existing legislation for testing concrete water absorption, effective porosity, pressurized water absorption and resistance to chlorides and CO
. The experimental findings showed that the 7% blended mortars performed better than the reference cement in terms of total and effective porosity, but they absorbed more pressurized water. They also exhibited lower CO
resistance, particularly in the calcareous blend, likely due to its higher porosity. Including the binary blend of CDW enhanced chloride resistance with diffusion coefficients of 2.9 × 10
m
s
(calcareous fines-glass, 7%Hc-G) and 1.5 × 10
m
s
(siliceous fines-glass, 7%Hs-G) compared to the reference cement's 4.3 × 10
m
s
. The siliceous fines-glass blend out-performed the calcareous blend in all the durability tests. As the mortars with and without CDW (construction and demolition waste) performed to similar standards overall, the former were deemed viable for the manufacture of future eco-efficient cements.
This study evaluates the sulphate resistance of blended cement derived from the addition of thermally activated coal waste as pozzolan, at replacement levels of 0%, 20% (CMW20) and 50% (CMW50) with a ...multi-method approach. The pastes were prepared at a w/b ratio of 0.5, using a water-reducing admixture in the blended pastes to compensate for their high water demand. Sulphate resistance is reduced in CMW20 pastes, while long-term benefits are observed for CMW50 pastes, although moderate signs of deterioration are observed at the beginning of the exposure. The initial damage in CMW50 pastes is attributable to the precipitation of products (mainly ettringite and monosulphoaluminate) in the small capillary pores (<0.01 μm). This is prevented in OPC and CMW20 pastes since their microstructure allow the precipitation in the macropores (>0.05 μm). The greater long-term resistance of CMW50 pastes was explained by thermodynamic calculations, which suggests that the lower calcium leachability of these cements prevented gypsum formation. This, together with the higher content of carboaluminate phases, leads to lower supersaturation levels in the pore solution with respect to ettringite, reducing stresses derived from sulphate exposure.
This research work focuses on the performance of mortars containing ichu ash as a potential environmentally-sound alternative to traditional pozzolans (at 6% and 10% replacement levels) under CO2 and ...chloride ion rich environments, in order to evaluate the capacity of this material to produce more sustainable and durable blended cements. The results indicate that ichu ash increases the susceptibility to carbonation, although mortars with 6% ichu ash content behave similarly to OPC ones. However, both density and mechanical strength improve after 250 days of carbonation for both ichu-blended mortars. In terms of resistance to chloride penetration, the addition of ichu ash contributes to retaining the ions in the superficial layers of the mortars, inhibiting their advance. It was found that formulations with both 6% and 10% ichu ash content produced a reduction in the chloride diffusion coefficient of approximately 60%. This phenomenon was mainly attributed to the refinement and increased complexity of the microstructure of the mortars due to the pozzolanic effect. Therefore, it was found that in certain types of environments, ichu ash can be an interesting tool to improve the durability of cements while reducing their environmental footprint and exploiting local resources.
A chloride-induced accelerated corrosion test was conducted on steel bars embedded in mortar specimens prepared with thermally activated coal mining waste (ACMW). ACMW was observed to prompt two ...opposite effects: a delay in chloride ion penetration and a reduction in the critical chloride content needed to initiate corrosion. Service life predictions based on the findings revealed that adding 20% or 50% ACMW to cement improved reinforcement corrosion resistance. Optimal results were observed for 20% replacement, in which the mean reinforcement section loss was 21% lower than in OPC.
The present research study analyses, for the first time, the viability of using thermally activated ichu grass as a supplementary cementitious material for the design of future eco-cements. To this ...end, the ichu ash resulting from the activation was characterised and its pozzolanic activity, the evolution of its mineralogical phases during the pozzolanic reaction and the physical-mechanical behaviour of the blended cementitious matrices were analysed. The results show that ichu ash exhibited high pozzolanic activity in a pure pozzolan/lime system as a consequence of its high reactive silica content. Conversely, its use in a pozzolan/cement system gave rise to negative effects due to the presence of important alkali contents in the ash (9.6% Na2O eq). The blended cements presented greater water demand, reduced capillary absorption, increased resistivity and lower mechanical properties (10–14%) as well as reduced average pore size than the reference mortar. These blended cement matrices comply with the physical-mechanical requirements established in the standards for the production of eco-cements.
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