Growing Nanocrystalline Graphene on Aggregates for Conductive and Strong Smart Cement Composites

Lightweight Calcium-Silicate-Hydrate Nacre with High Strength and High Toughness

Low flexural strength and toughness have posed enduring challenges to cementitious materials. As the main hydration product of cement, calcium silicate hydrate (C-S-H) plays important roles in the mechanical performance of cementitious materials while exhibiting random microstructures with pores and defects, which hinder mechanical enhancement. Inspired by the "brick-and-mortar" microstructure of natural nacre, this paper presents a method combining freeze casting, freeze-drying, in situ polymerization, and hot pressing to fabricate C-S-H nacre with high flexural strength, high toughness, and lightweight. Poly(acrylamide-co-acrylic acid) was used to disperse C-S-H and toughen C-S-H building blocks, which function as "bricks", while poly(methyl methacrylate) was impregnated as "mortar". The flexural strength, toughness, and density of C-S-H nacre reached 124 MPa, 5173 kJ/m3, and 0.98 g/cm3, respectively. The flexural strength and toughness of the C-S-H nacre are 18 and 1230 times higher than those of cement paste, respectively, with a 60% reduction in density, outperforming existing cementitious materials and natural nacre. This research establishes the relationship between material composition, fabrication process, microstructure, and mechanical performance, facilitating the design of high-performance C-S-H-based and cement-based composites for scalable engineering applications.

Tailoring electrochemically exfoliated graphene electroactive pathways in cementitious composites for structural health monitoring of constructions

Manipulating and exerting a nanoscale control over the structure of multicomponent materials represents a powerful strategy for tailoring multifunctional composites for structural health monitoring applications. The use of self-sensing, electroactive cementitious composites in large-scale applications is severely hindered by the absence of clear directives and a thorough understanding of the electrical conduction mechanisms taking place within the cement matrix. Here we report on a nanoscale approach towards this goal which is accomplished via the development of a novel, multifunctional cementitious composite incorporating electrochemically exfoliated graphene (EEG). The use of commercially available poly(carboxylate ether)-based superplasticizer allowed us to embed in the cement mortar up to 0.8 wt% of EEG which is fully dispersed in the matrix. The multiscale investigation made it possible to assess the effect of such high dosages of EEG on the mechanical performance and hydration degree of cementitious composites. We used electrochemical impedance spectroscopy to monitor the formation of electroactive EEG-based percolation paths for charge transfer within cement mortar, the latter displaying resistivities of 2.67 kΩ cm as well as EEG-cement-EEG capacitive paths with capacitance of 2.20 × 10-10 F cm-1 for composites incorporating 0.6 wt% of EEG. Noteworthy, we have proposed here for the first time an electrical equivalent circuit for the impedance spectroscopy analysis of cementitious composites with high loadings of graphene, exceeding the percolation threshold. These findings underscore the potential of nanoscale structures for civil engineering applications and more specifically may open new avenues for the technological application of graphene-based cementitious composites in self-sensing structures.

Near Room Temperature Production of Segregated Network Composites of Carbon Nanotubes and Regolith as Multifunctional, Extra-Terrestrial Building Materials

Constructing a semi-permanent base on the moon or Mars will require maximal use of materials found in situ and minimization of materials and equipment transported from Earth. This will mean a heavy reliance on regolith (Lunar or Marian soil) and water, supplemented by small quantities of additives fabricated on Earth. Here it is shown that SiO2-based powders, as well as Lunar and Martian regolith simulants, can be fabricated into building materials at near-ambient temperatures using only a few weight-percent of carbon nanotubes as a binder. These composites have compressive strength and toughness up to 100 MPa and 3 MPa respectively, higher than the best terrestrial concretes. They are electrically conductive (>20 S m-1) and display an extremely large piezoresistive response (gauge factor >600), allowing these composites to be used as internal sensors to monitor the structural health of extra-terrestrial buildings.

Functionalized graphene-based materials for cementitious applications

Graphene-based materials (GBM) are promising cementitious composite additives that can significantly improve the mechanical characteristics and durability of concrete due to their unique properties, such as high surface area and aspect ratio and excellent tensile strength, to name a few. To display their full potential, GBM have to be homogeneously dispersed into the aqueous environment of cement-based matrices. The present study addresses the issue of limited dispersibility in the aqueous media of GBM through the chemical functionalization of mono- and few-layer graphene structures with hydrophilic aryl sulfonate groups and shows that a series of mortar samples containing modified GBM exhibit increased flexural and compressive strength by up to 17% and 30%, respectively, compared to mortar references without additives.

Mass GGBFS Concrete Mixed with Recycled Aggregates as Alkali-Active Substances: Workability, Temperature History and Strength

This study provides the results of an experiment on the possibility of using high-volume ground granulated blast furnace slag (HVGGBFS)-based concrete as mass concrete. In addition to the control concrete, the total weight of the binder was 75% ground granulated blast furnace slag (GGBFS) and 25% ordinary Portland cement (OPC). For the aggregates, both natural and recycled aggregates were used. Three specimens with dimensions of 800 mm × 800 mm × 800 mm were prepared to simulate mass concrete. The workability, temperature aging and strength of the mass concrete were tested. The test results showed that utilizing HVGGBFS concrete as mass concrete can significantly reduce the heat of hydration due to the low heat of hydration of GGBFS, while the heat of hydration of GGBFS and recycled aggregate combination is 11.2% higher than normal concrete, with a slump that is 31.3% lower than that of plain concrete. The results also showed that the use of recycled aggregates in HVGGBFS concrete can significantly reduce workability. However, the compressive strength is higher than when natural aggregates are used due to the alkali activation effect caused by the recycled aggregates. The compressive strength at 7 and 28 days increased by 33.7% and 16.3%, respectively.

Research and Development of Self-Waterproofing Concrete for Tunnel Lining Structure and Its Impermeability and Crack Resistance Characteristics

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability.

Dynamics of reduced graphene oxide: synthesis and structural models

Technological advancements are leading to an upsurge in demand for functional materials that satisfy several of humankind's needs. In addition to this, the current global drive is to develop materials with high efficacy in intended applications whilst practising green chemistry principles to ensure sustainability. Carbon-based materials, such as reduced graphene oxide (RGO), in particular, can possibly meet this criterion because they can be derived from waste biomass (a renewable material), possibly synthesised at low temperatures without the use of hazardous chemicals, and are biodegradable (owing to their organic nature), among other characteristics. Additionally, RGO as a carbon-based material is gaining momentum in several applications due to its lightweight, nontoxicity, excellent flexibility, tuneable band gap (from reduction), higher electrical conductivity (relative to graphene oxide, GO), low cost (owing to the natural abundance of carbon), and potentially facile and scalable synthesis protocols. Despite these attributes, the possible structures of RGO are still numerous with notable critical variations and the synthesis procedures have been dynamic. Herein, we summarize the highlights from the historical breakthroughs in understanding the structure of RGO (from the perspective of GO) and the recent state-of-the-art synthesis protocols, covering the period from 2020 to 2023. These are key aspects in the realisation of the full potential of RGO materials through the tailoring of physicochemical properties and reproducibility. The reviewed work highlights the merits and prospects of the physicochemical properties of RGO toward achieving sustainable, environmentally friendly, low-cost, and high-performing materials at a large scale for use in functional devices/processes to pave the way for commercialisation. This can drive the sustainability and commercial viability aspects of RGO as a material.

Recycling of Tire-Derived Fiber: The Contribution of Steel Cord on the Properties of Lightweight Concrete Based on Perlite Aggregate

The increasing amount of waste from the vulcanization industry has become a serious environmental challenge. Even the partial reuse of the steel contained in tires as dispersed reinforcement in the production of new building materials may contribute to reducing the environmental impact of this industry while supporting the principle of sustainable development. In this study, the concrete samples were made of Portland cement, tap water, lightweight perlite aggregates, and steel cord fibers. Two different addition of steel cord fibers (1.3% and 2.6% wt. of concrete, respectively) were used. The samples of lightweight concrete based on perlite aggregate with steel cord fiber addition showed a significant increase in compressive (18-48%), tensile (25-52%), and flexural strength (26-41%). Moreover, higher thermal conductivity and thermal diffusivity were reported after incorporating steel cord fibers into the concrete matrix; however, the specific heat values decreased after these modifications. The highest values of thermal conductivity and thermal diffusivity were obtained for samples modified with a 2.6% addition of steel cord fibers and were equal to 0.912 ± 0.002 W/mK and 0.562 ± 0.002 µm²/s, respectively. Maximum specific heat, on the other hand, was reported for plain concrete (R)-1.678 ± 0.001 MJ/m³ K.