Extrusion is a process that consists in forcing a formable material to pass through a die having the cross-section of the part to be obtained. This way of processing is used with conventional and ...fibre-reinforced cement-based materials to fabricate various construction elements such as panels, pipes and roadside curbs. Recently, with the development of digital fabrication methods and especially 3D concrete printing by selective deposition, the extrusion techniques have experienced a significant increase in interest.
This letter describes the screw and ram extrusion techniques and their applications in construction industry. Furthermore, the underlying mechanisms involved during extrusion flow are delineated and the roles of rheological and hydro-mechanical behaviours (the latter one in a soil mechanics sense) in defining the extrudability – ability of being extruded – of the cementitious materials are highlighted. Finally, specific points such as flow-induced anisotropy of fibre reinforced cementitious materials or surface defects are addressed.
•The mechanism of the adsorption photocatalytic reaction of nano-TiO2 cement-based materials was summarized.•The mechanism of various factors on the photocatalytic reaction of nano-TiO2 cement-based ...materials was analyzed.•The advantages, disadvantages and applicability of various photocatalytic adsorption kinetic models are summarized.
Nano-TiO2 cement-based materials have been widely used as green building materials due to their effective photocatalytic ability to degrade air pollutants. The photocatalytic reaction adsorption kinetics can accurately describe the photocatalytic reactions of nano-TiO2 cement-based materials. In this paper, the photocatalytic reaction mechanism and adsorption kinetics of nano-TiO2 cement-based materials have been introduced. The mechanisms of the effect of environmental factors such as the nano-TiO2 photocatalytic activity, TiO2 content, reactant concentration, relative humidity, and light intensity on the photocatalytic reaction of nano-TiO2 cement-based materials have been analyzed in order to obtain an effective way to improve the photocatalytic performance. Finally, a comparative analysis of the various types of photocatalytic adsorption kinetic models has been carried out to provide a reference for establishing models with wider applicability in engineering.
•CNTs and CNFs are both the nano-structured fibrous materials with excellent properties.•The dispersion of CNTs/CNFs is the decisive factor affecting the performance of composites.•The incorporation ...of CNTs and CNFs affects the variety performance of cement-based materials.•CNTs/CNFs-modified cement-based composites have broad application prospects.
CNTs and CNFs are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites’ properties when adding CNTs/CNFs into composites. This paper briefly introduces the CNTs’/CNFs’ basic properties and dispersion methods, and elucidates the properties of cement-based composites recombining CNTs/CNFs, including the mechanical property, the deformation property, the durability property, the thermal conductivities and electrical conductivities. This paper also summarizes the problems existing in present research, and gives some proposes for future study.
•Effects of PC structures on its performance in cement-based materials.•The interactions between PC and cement-based materials are reviewed and analyzed.•The conformations of PC in solution and ...cement-based materials are discussed.
Polycarboxylate (PC) superplasticizers are being widely used in concrete mixtures due to their high water reduction rate and good slump retention at low dosage. The chemical structure of PC, including their anchoring group, main chain, side chain, molecular weight and molecular architecture, has a great impact on the performance of cement-based materials. This paper reviews the relationship between chemical structure of PCs and their performance in cement-based materials. Generally, adsorption capacity of PCs with maleic anhydride, phosphate and silanol group is higher than that of –COO− group, and is less affected when sulfate ions (SO42−) exist. Their initial dispersibility increases with the anchoring group content. PCs with long main chain, long side chains or large molecular weight exhibit higher flowability slump retention of cement pastes. The retardation effect of PC on cement hydration increases with the main chain length. Moreover, hyperbranched and star-shaped PCs show significantly better dispersion ability then conventional ones.
In many applications such as grouting, shotcrete, and 3D concrete printing, conflicting material requirements exist between the transportation and fabrication process, as fresh materials should be ...pumped easily with a low stiffening rate and a high fluidity while a rapid strength gain must occur after placement. In such applications, it is therefore imperative to achieve a stiffening control of the concrete. In this paper, we discuss how the inline mixing process of an accelerator post-pumping can be used to achieve this stiffening control. We begin with a review of the mechanisms of various commonly used accelerators. This is followed by a detailed discussion on the inline mixing process of accelerators. Finally, we also point out the problems and challenges of using accelerators in these applications.
Cement based composite materials (CBCM) with superior mechanical strength and excellent durability are always desirable in practical applications. Although considerable research has been reported in ...the past decades about the use of Nano materials (NMs) for strength and durability enhancement of cement matrix, there is little information available on the use of graphene nano-sheets and their derivatives (GND) in cement-based materials. Particularly the role of GND in hydration processes and their mechanisms of strengthening in cement matrix are unclear. In this paper, a critical review on recent research findings about GND modified cement-based materials was conducted. The review mainly discussed the influence of GND on properties of cement matrix including microstructure, hydration, mechanical properties, etc. The information revealed in this paper would not only provide a comprehensive understanding of the effect of GND on cement composites, but also provide valuable ideas and guidance for similar studies in the future.
Recently, intelligent responsive materials have received increasing attention due to the controllability of their wettability. However, research has primarily focused on the surface properties of ...materials such as sponges and copper meshes, with a notable lack of investigation into cement-based materials in this regard. Currently, multi-functionality has become an inevitable trend in the development of cement-based materials. The controllable and adjustable wettability of cement-based materials can further expand their application scope. In this article, saturated fatty acids and dicarboxylic acids were selected to modify cement-based materials, fully utilizing their rich hydroxyl characteristics. Firstly, the feasibility of developing pH-stimuli-responsive surfaces on cement-based substrates with chosen raw materials was rapidly verified using the immersion method. When the mass fraction of dicarboxylic acid in the modifier is between 60 % and 80 %, the modified substrate surface exhibits hydrophobicity towards neutral liquids and hydrophilicity towards alkaline liquids. Based on this, the corresponding sodium salts of organic acid were synthesized and used as additives, which were then mixed with cement to prepare modified cement-based materials with switchable wettability. Through acid solution treatment, the modified hardened cement paste can transform from initially hydrophilic to hydrophobic, and the conversion angle can reach 90°. This study broadens the application field of intelligent response surfaces and enriches the functionality of cement-based materials.
•Surface modification of cement-based materials using a mixture of saturated fatty acids and dicarboxylic acids.•Rapid preparation of pH-responsive surfaces by immersion method to achieve hydrophilicity for alkaline liquids and hydrophobicity for neutral liquids.•Verification of the modification effect and investigation of the mechanism for achieving switchable wettability of cement-based materials.
Different models have been proposed to investigate and predict the carbonation process of cement-based materials. This paper firstly introduces the carbonation process occurred in cement-based ...materials and those influential factors. Then the proposed empirical, thermodynamic, kinetic and numerical models to characterize the carbonation process of cement-based materials are reviewed. The theoretical basis, input parameters and major applications of different models are summarized and discussed. The advantages and disadvantages of those models are comparatively reviewed. Finally, modelling of early CO2 curing of fresh cement-based materials is also reviewed and compared with the carbonation of hardened cement-based materials.
•Parameters and different forms of empirical carbonation models are summarized.•Thermodynamic carbonation modelling process and solving methods are discussed.•Kinetic carbonation models of diffusion, dissolution and reactions are compared.•Finite element and machine learning methods applied to carbonation are reviewed.
•Carbonation kinetics of alternative binder materials requires further investigation.•Carbonation resistance of OPC is higher than that of alternative binder materials•Cement-based materials can be ...used as CO2 storage systems.•Recently developed carbonate binders are reviewed.
This article summarizes the existing knowledge regarding the carbonation of cement-based materials and identified the areas which require further investigations. Available studies regarding the carbonation test scenarios, influences of supplementary cementitious materials (SCMs) on carbonation resistance, and effects of carbonation on the properties of cement-based materials are reviewed here. In addition to ordinary portland cement (OPC) based materials, this article has reviewed the performances of sulfoaluminate belite and alkali activated materials (AAM) while subjected to carbonations. Some very recent topics such as the potential of CO2 storage in concrete and the newly developed carbonate binders are also discussed.
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•Photocatalytic cement-based materials are reviewed for purifying water sustainably.•Function mechanism and material classification are introduced.•Main fabrication methods and key ...performances are demonstrated.•Environment impacts are discussed from the views of material and water.•Several challenges and perspectives are also pointed out for future research.
An inadequate supply of clean water remains one of the greatest problems to the sustainability of modern society. Owing to the inherent immobilization properties of cement-based materials and energy-saving features of photocatalysts, photocatalytic cement-based materials combining both have emerged as a potential platform for sustainable water purification without compromising mechanical performance under light irradiation. The current review exclusively summarizes the existing information on photocatalytic cement-based materials for sustainable water purification. First, the mechanisms (binding and purification) and the material classifications (cement-based materials and photocatalysts) were introduced. Second, the two main fabrication strategies (internal mixing and external coating) and three key performances (mechanical, photocatalytic, and durability properties) were demonstrated. Third, the material-related and environment-related impact were discussed. It is concluded that the research domain involving photocatalytic cement-based materials for sustainable water purification is in its initial phases, emphasizing the need for increased research attention to both laboratory exploration and pilot- or large-scale applications.
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