Hydration Characteristics of Low-Heat Cement Substituted by Fly Ash and Limestone Powder

Structural Formation of Soil Concretes Based on Loam and Fly Ash, Modified with a Stabilizing Polymer Additive

Finding new ways of recycling production waste to improve the characteristics of various building materials is an urgent scientific task. This article substantiates the possibility of the disposal of fly ash in the composition of soil concrete, which is used in the construction of the structural layers of road pavements, foundations of buildings and structures, as well as sites for various purposes. The scientific novelty lies in the fact that the structure formation of soil concretes based on loam and fly ash and modified with a stabilizing additive is being studied for the first time. It was found that the investigated fly ash, according to its hydraulic properties, is classified as latent active and can be introduced into the compositions of road soil concrete modified with additives of various resources. The effectiveness of the complex method of stabilization, due to changes in soil properties as a result of the use of the binding and stabilizing additives of polymer nature “Kriogelit”, is shown. It was found that the optimal content of binder and fly ash in the samples was 8 and 10 wt.%, respectively. It was established that the use of the stabilizing additive “Kriogelit” makes it possible to obtain soil concrete with the highest strength (compressive strength 2.5 MPa, flexural strength 0.5 MPa) and frost resistance of at least F15. The microstructure, the degree of dehydration and carbonization, and the phase composition of the initial raw mixtures and soil concretes stabilized with the addition of “Kriogelit” were studied by methods of scanning electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, thermogravimetry, and infrared spectroscopy. It was shown that organo-mineral complexes, with the participation of polymer and montmorillonite, are formed in stabilized soil concrete. It was revealed that structure formation is accompanied by the physical adsorption of the polymer on active centers of silicate minerals, carbonization, and hydration–dehydration processes. It was found that the reason for the increase in the strength of stabilized soil concretes is the hydrophobization of the porous structure of minerals, as well as the formation of calcium oxide silicate and dicalcium hydrated silicate. By the method of performing biotests with the test objects Daphnia magna Straus and Chlorella vulgaris Beijer, it was proven that the developed road concretes modified with the stabilizing additive “Kriogelit” do not have an acute toxic effect on the test objects and are safe for the environment and human health.

Performance of Polymer Cementitious Coatings for High-Voltage Electrical Infrastructure

This paper investigates the electrical, thermal and mechanical properties as well as the environmental performance of polymer cementitious composites (PCCs) as sustainable coating materials for underground power cables and as high-voltage insulators. Particular focus is placed on the optimised mix design and the effect of the manufacturing method on the performance of PCCs, incorporating liquid styrene and acrylic (SA) monomers, wollastonite and muscovite. Microstructural investigations, together with results from strength tests, indicate that the manufacturing method is a key performance parameter. Experimental results show that PCC mixes containing 25% SA emulsion, 12.5% wollastonite and no muscovite provide the most favourable dielectric properties from the mixes investigated. The PCC material has a dielectric strength up to 16.5 kV/mm and a dielectric loss factor lower than 0.12. Additional experiments also show that PCC has good thermal stability and thermal conductivity. The mechanical strength tests indicate that PCC specimens possess reliable strengths which are applicable in structural design. Environmental assessments also show that PCCs possess significantly lower embodied energy and embodied carbon than conventional plastic insulating materials.

Effect of Morphologically Controlled Hematite Nanoparticles on the Properties of Fly Ash Blended Cement

Several types of hematite nanoparticles (α-Fe₂O₃) have been investigated for their effects on the structure and properties of fly ash (FA) blended cement. All synthesized nanoparticles were found to be of spherical shape, but of different particle sizes ranging from 10 to 195 nm depending on the surfactant used in their preparation. The cement hydration with time showed 1.0% α-Fe₂O₃ nanoparticles are effective accelerators for FA blended cement. Moreover, adding α-Fe₂O₃ nanoparticles in FA blended cement enhanced the compressive strength and workability of cement. Nanoparticle size and size distribution were important for optimal filling of various size of pores within the cement structure.

Estimating the Impact of Nanophases on the Production of Green Cement with High Performance Properties

Ordinary Portland cement (OPC) production is energy-intensive and significantly contributes to greenhouse gas emissions. One method to reduce the environmental impact of concrete production is the use of an alternative binder, calcium sulfoaluminate cement, which offers lower CO₂ emissions and reduces energy consumption for cement production. This article describes the effect of adding nanophases, namely belite, calcium sulfoaluminate, calcium aluminum monosulfate (β-C₂S, C₄A₃S, and C₄AS, respectively) on OPC’s properties. These phases are made from nanosubstances such as nano-SiO₂, calcium nitrate (Ca(NO₃)₂), and nano-aluminum hydroxide Al(OH)₃ with gypsum (CaSO₄·2H₂O). The impact of β-C₂S, C₄A₃S, and C₄AS nanophases on the capabilities of cements was assessed by batch experimentations and IR, XRD, and DSC techniques. The results showed that the substituting of OPC by nano phases (either 10% C₄A₃S or 10% C₄A₃S and 10% β-C₂S) reduced setting times, reduced the water/cement ratio and the free-lime contents, and increased the combined water contents as well as compressive strength of the cement pastes. The blends had high early and late compressive strength. The IR, XRD, and DSC analyses of the blends of 10% C₄A₃S or 10% C₄A₃S and 10% β-C₂S cement displayed an increase in the hydrate products and the presence of monosulfate hydrate. The addition of 10% C₄AS or 10% C₄AS and 10% β-C₂S to OPC reduced the setting times, decreased the W/C ratio, free lime, the bulk density, and increased the chemically-combined water and compressive strength. Overall, the results confirmed that the inclusion of the nanophases greatly enhanced the mechanical and durability properties of the OPCs.

Strength Development and Thermogravimetric Investigation of High-Volume Fly Ash Binders

To address sustainability issues by facilitating the use of high-volume fly ash (HVFA) concrete in industry, this paper investigates the early age hydration properties of HVFA binders in concrete and the correlation between hydration properties and compressive strengths of the cement pastes. A new method of calculating the chemically bound water of HVFA binders was used and validated. Fly ash (FA) types used in this study were sourced from Indonesia and Australia for comparison. The water to binder (w/b) ratio was 0.4 and FA replacement levels were 40%, 50% and 60% by weight. Isothermal calorimetry tests were conducted to study the heat of hydration which was further converted to the adiabatic temperature rise. Thermo-gravimetric analysis (TGA) was employed to explore the chemically bound water (W_B) of the binders. The results showed that Australian FA pastes had higher heat of hydration, adiabatic temperature rise, W_B and compressive strength compared to Indonesian FA pastes. The new method of calculating chemically bound water can be successfully applied to HVFA binders. Linear correlation could be found between the W_B and compressive strength.