Latest ArticlesAbrasion-resistant concrete is crucial for the durability and safety of hydraulic engineering structures, bridge piers, coastal embankments, and other specialized infrastructure. These structures are exposed to harsh conditions such as high-velocity water flow, sand erosion, and debris impacts. This review examines recent advancements in abrasion-resistant concrete materials, focusing on material composition, characterization methods, and abrasion damage mechanisms. It aims to provide theoretical insights and practical guidance for developing durable concrete in demanding environments.
Abrasion resistance is enhanced by optimizing material composition, including supplementary cementitious materials (SCMs), fiber reinforcement, wear-resistant aggregates, rubber particles, and ultra-high-performance concrete (UHPC). SCMs such as silica fume, fly ash, and slag powder improve hydration products and densify the microstructure, significantly enhancing abrasion resistance. However, excessive silica fume can cause shrinkage cracking. Fiber reinforcement, particularly steel fibers (0.75%-1.00% by volume), improves tensile strength and abrasion resistance, with reported increases of over 20%. Wear-resistant aggregates, including iron ore and recycled glass, play a critical role, with their mechanical properties and particle size significantly influencing performance. Rubberized concrete (5%-25% rubber content) absorbs impact energy, reducing abrasion damage, though excessive rubber content may compromise strength. UHPC, with its exceptional strength and density, offers superior abrasion resistance, and further optimization of its fiber, aggregate, and cementitious components is key to its performance in complex environments.
Concrete abrasion resistance is evaluated using various characterization methods that simulate different mechanisms of wear. The underwater method (ASTM C1138, DL/T 5150—2017) measures bed load impacts in high-velocity water flow. The sandblasting test, or water-borne sand jet method, simulates suspended load erosion under varying impact angles and velocities. The ring method and high-speed ring method (SL/T 352—2020) assess abrasion in low-velocity sand-laden water flow, while the rotating jet method simulates high-speed suspended load abrasion. The water-borne sand jet method combines suspended load and cavitation effects to provide a comprehensive evaluation of abrasion resistance. Recently, 3D scanning technology has been increasingly adopted to characterize surface morphology, offering precise measurements of wear depth and volume loss for detailed analysis of abrasion damage.
Abrasion damage mechanisms in concrete involve bed load impact, suspended load abrasion, and cavitation erosion. Bed load impact, caused by large particles such as rocks, results in brittle failure, surface spalling, and internal microcracking, as simulated by the underwater steel ball method. Suspended load abrasion, driven by the continuous scouring of sand particles, gradually erodes the cement paste and exposes aggregates, as modeled by the sandblasting and rotating jet methods. Cavitation erosion, caused by the collapse of bubbles in high-velocity water, forms erosion pits that expand over time, as simulated by the water-borne sand jet method. In real-world environments, concrete is often subjected to combined abrasion mechanisms alongside environmental stressors such as freeze-thaw cycles, debris flow, and seawater exposure. For example, freeze-thaw cycles weaken the concrete matrix, exacerbating erosion by suspended sediments. These combined effects significantly accelerate abrasion damage, highlighting the need for a deeper understanding of the synergistic interactions between abrasion mechanisms and environmental factors.
This review highlights recent progress in abrasion-resistant concrete materials, emphasizing material composition, characterization methods, and damage mechanisms. It offers valuable insights for enhancing durability in harsh environments. Future research should focus on optimizing UHPC composition for specific applications, exploring the combined effects of environmental stressors on abrasion resistance, and leveraging advanced techniques such as 3D scanning for precise damage assessment. By clarifying abrasion mechanisms and improving material performance, this research will drive innovation in hydraulic engineering and coastal protection, ensuring infrastructure resilience in demanding service conditions.
Carbon dioxide emissions from cement kiln flue gas constitute a significant contributor to global climate change and environmental pollution. As global emission reduction targets progress, research and application of carbon capture, utilization, and storage (CCUS) technologies have increasingly become critical strategies for mitigating CO2 emissions. Among these technologies, the calcium cycle method demonstrates substantial potential due to its low cost, high efficiency in CO2 trapping, and broad applicability, particularly in the context of cement kiln flue gas. However, traditional calcium-based materials, such as limestone, face challenges including high precalcination temperatures and resource wastage, highlighting the need for more efficient and sustainable alternatives.
Calcium carbide slag, an industrial by-product, has shown significant promise as a material for the calcium cycle method. It contains a high proportion of reactive CaO, along with inert components such as alumina and magnesium oxide. These inert components enhance resistance to sintering after preburning. However, repeated use of calcium carbide slag leads to pore structure collapse, particle agglomeration, and sintering, severely diminishing its adsorption performance and posing a significant barrier to practical application.
To address these challenges, various modification techniques have been explored to improve the absorption efficiency and sintering properties of calcium carbide slag, as well as to mitigate the impact of SO2 and NOx in flue gas on CO2 absorption.
Organic acid modification has been identified as an effective strategy to enhance the adsorption performance of calcium carbide slag. Through reactions with calcium hydroxide to form organic calcium salts, pyrolysis at high temperatures releases small molecules that disrupt the original structure of the slag. This process increases porosity, specific surface area, and CO2 adsorption capacity. Different organic acids, due to their distinct molecular structures, yield variations in the molecular weight of organic calcium salts and the types and quantities of small molecules released during pyrolysis. Consequently, modifying calcium carbide slag with specific organic acids allows tailoring of its pore structure to enhance CO2 adsorption performance.
Doping modification technology is another effective approach. By incorporating various substances into the slag, the properties of calcium carbide slag can be optimized through different chemical reaction mechanisms. Inert materials serve as structural frameworks, inhibiting CaO grain migration and growth to improve anti-sintering performance. Doping with oxygen-deficient materials facilitates CO2 diffusion and O2- migration, while potassium and sodium salts increase defect concentrations in the CaCO3 product layer, enabling more efficient Ca2+ migration and enhanced CO2 absorption.
Hydration processes also play a critical role in influencing sintering. While CaCO3 typically decomposes at high temperatures, introducing water vapor during calcination reduces the partial pressure of CO2, promoting its conversion to CaO. Water vapor also shortens decomposition residence time and slows sintering, delaying sintering deactivation and improving stability. By optimizing calcination temperatures and water vapor concentrations, the CO2 adsorption performance and stability of calcium carbide slag can be enhanced over multiple cycles.
In the context of cement kiln flue gas treatment, SO2 and NOx pose additional challenges to the CO2 trapping performance of calcium carbide slag. SO2, being strongly acidic, preferentially reacts with CaO to form dense CaSO4 layers, which accumulate over cycles, diminishing adsorbent activity. Research suggests that specific modification methods or adjustments in the absorption sequence (e.g., absorbing CO2 before SO2) can mitigate these effects. Regarding NOx, calcium carbide slag inherently lacks reductive properties and cannot remove NOx through traditional calcium cycle methods. Doping with reducing substances, such as copper, iron, and other metal oxides, can enable NOx reduction by promoting reactions that convert NOx into harmless nitrogen and oxygen.
The future of calcium carbide slag modification technology is expected to move towards systematic and refined strategies. These strategies can leverage the synergistic effects of multiple modification techniques to optimize performance across different reaction stages. As research progresses, the multifaceted applications of calcium carbide slag will gain increasing recognition. Beyond its role in CO2 capture, it holds significant potential for processes such as desulfurization and nitrogen removal.
From an environmental perspective, utilizing calcium carbide slag addresses resource wastage while aiding the cement industry in achieving a green transformation by reducing greenhouse gases and pollutants such as CO2, SO2, and NOx. Continuous innovation in modification technology will ensure that calcium carbide slag not only plays a pivotal role in CO2 capture but also in mitigating pollutants, contributing to the attainment of global emission reduction goals. The enhanced versatility and cyclic stability of modified calcium carbide slag will further support the green transition of the cement industry and other high-emission sectors, contributing to efforts toward a sustainable future.
The status of scientific research projects in the inorganic non-metallic materials discipline (E02) under the Department of Engineering and Materials Sciences of the National Natural Science Foundation of China (NSFC) in 2024 has been statistically analyzed. Taking key programs as examples, the discipline's management of these funded projects is introduced. Representative initiatives and their implementation effects in deepening and implementing the reform tasks of scientific funding for the discipline in this year are elaborated in detail. Furthermore, the priority funding areas, key funding directions for the discipline in 2025, as well as reflections on future work are presented.
The use of steel slag as a cementitious material is the most likely field to achieve large-scale engineering utilization. However, the inherent defects of low activity and poor grindability caused by the high iron oxide content of steel slag limit its dosage in cement. One important direction to improve the activity and grindability of steel slag is to obtain a product similar to granulated blast furnace slag (GBFS), mainly composed of glass, by melting and reducing iron oxides in steel slag. This GBFS-like residue exhibits lower early activity due to its lower alkalinity coefficient (K=n(CaO)+ n(MgO)/n(SiO2)+ n(Al2O3)). In order to improve the early activity of the residue, this paper focuses on the effect of CaO content on the formation of clinker minerals. Coal gangue is used as a reducing agent to reduce iron oxides in steel slag for making full use of industrial solid waste.
Based on the principle of complete reduction of iron oxides in steel slag and coal gangue, the appropriate ratio of coal gangue and steel slag is calculated according to the chemical composition of steel slag and the fixed carbon content of coal gangue. CaO was obtained by calcining and analytical reagent CaCO3 at 1500 ℃. Different amounts of resultant CaO (10, 20, 30, 40 g) were incorporated into 100 g mixture of steel slag and coal gangue, respectively. The reference sample without CaO and the above four samples are named as C0, C10, C20, C30 and C40, and the K of samples are 1.05, 1.33, 1.61, 1.89, 2.17, respectively. After thoroughly mixing each sample, 200 g mixture containing CaO was placed into a corundum crucible and calcined at 1500 ℃ for 30 min. After calcination, the crucible was take out from the high temperature furnace for water quenching. Iron alloy particles are obtained by crushing, peeling, and magnetic separation from water quenched slag. The remaining water quenched residue (WQR) is used for mineral phase analysis, cement mortar strength, soundness, and other tests.
Iron alloy particles in C0, C10, C20, C30 sample can be easily peeled off. But it is difficult for C40 sample and some small metal particles can be observed at the crucible bottom. This is because the increase of K leads to an increase in the viscosity of the melt, making it difficult for iron particles to sedimentation and aggregation.
The analysis of the chemical composition of the WQR after stripping iron particles shows that the reduction rate δ and recovery rate η of the reference sample C0 are about 92%. For C10 (K=1.33), the η and δ of Fe reach maximum values. As the CaO content continues to increase, the η and δ gradually decrease. But, these two parameters of C20 still exceed that of C0. The f-CaO content and soundness of the WQR meet the requirements of relevant national standards, although these two values will slightly increase with the increase of dosage of CaO.
The results of XRD Rietveld refinement for quantification indicate that C0 and C10 samples are mainly consist of glass and contain a small amounts of Gehlenite, spinel et al. With the increase of CaO content, the diffraction peak of the crystalline phase gradually increases, while the amorphous envelope peak gradually weakens. For C20, the main crystalline phases are C2S and bredigite, and diffraction peaks of periclase can be observed. In the C30 sample, the main mineral phases are C2S, C3A, iron, and periclase. Meanwhile, C3S diffraction peak is relatively low. The C3S diffraction peak in the C40 sample is significantly enhanced, with a content of 50%. FTIR shows that as the CaO content increases from 20 g to 40 g, the absorption band of β-C2S decreases, while the absorption band of M3 C3S gradually increases.
BSE image show that the C10 sample is mainly composed of glass matrix, with a small amount of C2S grain, serrated-like fine stuff formed at the edge of C2S grains, snowflake like or dendritic substance surrounding the C2S, and iron particles. EDS results show that the order of Al content in several phases is C2S < fine stuff < dendritic substance < matrix. The order of Ca and Si content is C2S >fine stuff > dendritic substance > matrix.
In the C30 sample, sharp edged plate-like particles with a Ca/Si of about 3 formed, indicating that C2S has begun to transform into C3S. The formation of C3S and C2S not only significantly reduces the Si content in the matrix, but also leads to an increase in the relative content of Al in the intermediate matrix. When the dosage reaches 40%, C3S has already formed in large quantities. The Ca/Al ratio of the intermediate phase is about 1.53, indicating the formation of C3A.
The main conclusions of this paper are summarized as following. When K value of WQR is less than 1.6, increasing the CaO content appropriately can improve the reduction rate and recovery rate of iron. The C10 sample is mainly composed of glass. When K is 1.3, a small amount of β-C2S is formed in the WQR, which gradually grows by absorbing CaO and SiO2 from the glass matrix. With the increase of K, Periclase begins to form in the zone where silicate minerals are more abundant. When the CaO dosage reaches 40 g, the amount of C3S continues to increase to 50%, and C3A form simultaneously. Although high alkalinity leads to the formation of C3S and C2S minerals in the system, it also results in the formation of periclase. To avoid the potential long-term unsoundness, it is more appropriate to control K value at around 1.3.
The remediation of tailings sand requires improving both mechanical properties and the stabilization of heavy metals. Practical engineering applications must also consider cost and feasibility. Microbially Induced Carbonate Precipitation (MICP) is an innovative technique that uses microorganisms to enhance soil properties and immobilize heavy metals. However, the traditional MICP method using Bacillus pasteurii has several limitations: reduced activity in high concentrations of heavy metals, calcium carbonate buildup on the soil surface that clogs and limits solidification depth, risks of introducing invasive species, and high costs associated with bacterial cultivation and transport. These factors make it unsuitable for large-scale applications.
In situ stimulation of indigenous urease-producing microorganisms in the soil offers a solution. This approach avoids species invasion, eliminates the need for bacterial cultivation and injection, reduces costs, and minimizes clogging. Developing a cost-effective and feasible in situ stimulation strategy for tailings sand solidification is essential for applying this technology in practical engineering.
The tailings sand used in this study was sourced from the tailings reservoir of Fujian Makeng Mining Co., Ltd., moderately contaminated with cadmium and slightly with zinc. An initial stimulation solution was designed to screen and enrich urease-producing microorganisms in the tailings sand, considering the necessary carbon source, nitrogen source, urea, and other growth factors. Since urease activity is key to the effectiveness of MICP solidification, the urease activity of tailings sand suspensions after in situ stimulation was used as the evaluation metric for optimization.
The optimization process involved three steps: 1) Starting with the initial stimulation solution formula, single-factor experiments were conducted to vary carbon and nitrogen sources to identify those yielding the highest urease activity. 2) Using the selected optimal carbon and nitrogen sources, along with other components and pH, a Plackett-Burman (PB) design was employed to identify key factors affecting urease activity. Single-factor tests were then conducted to determine the optimal concentration range for each key factor. 3) A Central Composite Design (CCD) response surface analysis was performed, using urease activity as the response value, to calculate the optimal concentration of each key factor. This resulted in the most effective stimulation solution for tailings sand.
Different concentrations of cementation solution and numbers of solidification rounds were tested to compare the effects of indigenous urease-producing bacteria and Bacillus pasteurii on tailings sand in terms of surface strength, cementation thickness, permeability, raindrop erosion resistance, heavy metal leachate toxicity, and heavy metal morphological changes. Microbial community analysis, combined with scanning electron microscopy (SEM) and X-ray diffraction (XRD), was conducted to explore how in situ stimulation enhances mechanical properties and immobilizes heavy metals.
1) The optimal in situ activation formula for tailings sand includes sodium acetate at 35.85 mmol/L, ammonium sulfate at 53.59 mmol/L, urea at 481.0 mmol/L, yeast extract (YE) at 0.2 g/L, nickel chloride at 0.01 mmol/L, and a pH value of 8.70, achieving a urease activity 1.944 times higher than that before optimization. 2) The best cementation solution concentration for in situ solidification of tailings sand is 1 mol/L. In situ activation demonstrated better heavy metal immobilization, deeper solidification, and more uniformity compared to Bacillus pasteurii at the same round count. Although the mechanical properties of in situ-treated sand were lower after the same number of rounds, 15 rounds of in situ treatment achieved comparable properties to 10 rounds with Bacillus pasteurii. 3) The cost per round of in situ activation is only one-fifth that of Bacillus pasteurii. Achieving similar mechanical properties, the total cost of 15 rounds of in situ treatment is only one-third of 10 rounds with Bacillus pasteurii. In situ activation eliminates the need for bacterial culture or transportation and avoids the risk of introducing non-native species, providing superior economic and environmental benefits. 4) The optimized activation solution effectively enriched previously low-abundance urease-producing bacteria, making them the dominant group (70%-90% relative abundance) by inhibiting other microorganisms. This also increased the abundance of the urease accessory protein COG0830. 5) The final product of MICP is calcite. Compared to Bacillus pasteurii, in situ activation produced smaller, fewer, and more scattered calcite crystals under the same conditions. Calcite crystal nucleation and growth were influenced by cementation solution concentration. 6) The urease-producing bacteria in tailings sand exhibited good tolerance to heavy metals and had a long survival time, continuously converting exchangeable heavy metals into stable forms. After in situ activation, the cation exchange capacity (CEC) of the tailings sand increased, effectively enhancing soil fertility for mine site revegetation after heavy metal fixation.
1) In situ activation of urease-producing microbes offers stronger heavy metal immobilization and deeper, more uniform solidification compared to traditional MICP methods. 2) After 15 rounds of treatment, tailings sand solidified using native urease-producing bacteria achieved mechanical properties comparable to those treated with Bacillus pasteurii after 10 rounds, while reducing costs by two-thirds. 3) In situ activation altered the microbial community in the tailings sand, making urease-producing bacteria dominant. These bacteria induced calcium carbonate precipitation, filling sand particle pores, and converting exchangeable heavy metals into stable forms such as metal carbonates, metal-calcium carbonate co-precipitates, or adsorbed forms on iron and aluminum oxides. This improved both mechanical properties and heavy metal immobilization. 4) By increasing the cation exchange capacity, this method enhanced soil fertility, facilitating mine site revegetation. It is an economically and environmentally viable approach for engineering applications.
Ultra-High Performance Concrete (UHPC) is widely recognized for its exceptional mechanical properties and durability, making it a cornerstone material in modern infrastructure projects. However, the long-term service performance of UHPC structures with initial cracks under freeze-thaw (F-T) cycling remains a safety concern, particularly in harsh environments such as cold regions and coastal zones. While extensive research has focused on the properties of uncracked UHPC, the study on degradation of cracked UHPC under coupled F-T cycling and self-healing conditions is limited. Existing studies highlight UHPC's intrinsic self-healing potential through secondary hydration and carbonation reactions, yet the interplay between these healing mechanisms and cyclic F-T-induced deterioration remains unclear. To address this, the present study investigates the tensile performance evolution of pre-cracked UHPC under F-T cycling and water-curing conditions. By integrating macroscopic mechanical tests with microscopic analyses, this work aims to unravel the dual effects of self-healing and F-T-induced damage on UHPC's structural integrity.
UHPC specimens were prepared using white cement, silica fume, quartz powder/sand, steel fibers (2% by volume), and a polycarboxylate superplasticizer. The mix design followed a water-to-binder ratio of 0.22. After casting and demolding, specimens underwent 48 h hot-water curing at 90 ℃. Dog-bone-shaped specimens (30 mm×13 mm×80 mm) were pre-notched and subjected to pre-tensioning to introduce controlled initial cracks (100 μm width) via displacement-controlled loading. Pre-cracked specimens were divided into two groups, including 1) F-T cycling groups: Exposed to 100, 200, or 300 F-T cycles (-17 ℃ to 8 ℃ per cycle); 2) water-curing groups: immersed in 20 ℃ water for 14, 30 d, or 60 d. Secondary tensile tests were conducted to evaluate residual strength and crack recovery. Single-fiber pull-out tests assessed interfacial bond performance, while scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) characterized microstructural evolution and hydration products.
Water-cured specimens exhibited remarkable mechanical recovery. After 60 d, tensile strength exceeded the undamaged control group by 32%, attributed to C-S-H gel and Ca(OH)2 filling microcracks. SEM revealed dense microstructures with nearly closed cracks, confirming the role of secondary hydration in enhancing matrix integrity. Single-fiber pull-out tests showed interfacial bond strength fully recovered within 30 d, though prolonged immersion led to steel fiber corrosion, reducing post-peak ductility. F-T cycling initially promoted low-temperature self-healing. After 200 cycles, tensile strength increased by 14% due to partial crack closure via hydration. However, beyond 300 cycles, cumulative damage dominated: surface spalling, fiber corrosion, and interfacial debonding caused a 7.1% decline in tensile strength. TGA confirmed reduced Ca(OH)2 and CaCO3 content under F-T conditions, indicating suppressed hydration and carbonation compared to water curing. Progressive densification of the matrix with crystalline hydration products sealing cracks. Initial healing at 100-200 F-T cycles was counteracted by interfacial microcrack propagation and fiber-matrix debonding at 300 cycles. EDS analysis highlighted localized CaCO3 precipitation at crack surfaces, insufficient to offset F-T-induced damage. The study revealed a critical threshold (200 F-T cycles) where self-healing and deterioration mechanisms compete. While water ingress facilitates secondary hydration, prolonged F-T exposure disrupts the healing process through ice crystallization pressure and moisture redistribution, exacerbating matrix degradation.
Water curing significantly enhances UHPC's self-healing capacity, with complete tensile strength recovery, which was driven by continuous secondary hydration and carbonation, forming dense, crack-resistant matrices. Freeze-thaw cycling exhibited a dual role: healing occurred at early stages (≤200 cycles), but 300 cycles led to irreversible strength loss. Microstructural analysis underscored the importance of hydration products (C-S-H, CaCO3) in healing cracks, while F-T cycling disrupts interfacial bonding and accelerates matrix spalling. For UHPC structures in cold climates, proactive crack sealing and controlled curing are essential to maximize self-healing benefits before F-T damage accumulates. Future work should explore hybrid curing regimes and corrosion-resistant fibers to extend service life.
In light of the policy of 'carbon peaking and carbon neutrality' and the advent of artificial intelligence, there is an urgent need for research and development in the field of cementitious materials to advance low-carbon alternatives. Given the lengthy research periods associated with traditional experimental methods, digital research and development has recently emerged as a dominant trend in the field. Currently, digital models are being developed for purposes such as performance prediction, composition optimization, and low-carbon innovation, with a primary focus on algorithm optimization. However, the success of these models relies heavily on the availability of accurate, high-quality databases, which serve as the foundation for model implementation. Utilizing such databases can significantly simplify model construction and reduce the need for extensive optimization procedures. Consequently, building comprehensive databases for cementitious materials research and development has become a key objective in this field.
This paper reviews the current status of databases for cementitious materials, including those related to clinker, cement, concrete, mineral admixtures, and construction mortar. The types of data, application methods, and scope of application encompassed by these databases are summarized. Databases for clinker were among the earliest to be developed, primarily cataloging diverse mineral properties, including hydration products. They include crystallographic data, thermodynamic data, and force field data, with some databases integrating models for analyzing cement hydration. Cement databases, while recording thermodynamic properties, cement types, and characteristics, have largely been focused on production control in cement plants. Moreover, the construction of databases for concrete and related materials has often been driven by specific research objectives, such as studying chemical composition, strength, and durability. Some researchers have also conducted property predictions based on their collected datasets.
Despite the existence of numerous databases on cementitious materials, a significant volume of relevant data within scientific literature remains underutilized. The advancement of artificial intelligence in natural language processing has enabled the adaptation of data extraction algorithms across various domains, including metals, medicine, and biology. Named entity recognition and textual relationship extraction—two critical components of literature data mining—can be implemented through AI algorithms such as ChemDataExtractor and BERT. ChemDataExtractor and related algorithms have demonstrated accurate chemical data extraction from compounds and semi-supervised relationship extraction. Similarly, BERT, like ChatGPT, is a state-of-the-art language model developed using the Transformer architecture and has been successfully applied in automated text data extraction. However, the complex mineralogical and chemical composition, multi-scale particle characteristics, and hydration processes of cementitious materials pose challenges to the direct application of these algorithms.
The construction of comprehensive databases represents the cornerstone of the digital transformation of low-carbon cementitious material research and development. Although existing databases contain extensive datasets on cementitious materials, several challenges persist, such as non-standardized database structures, insufficiently considered data categories, and incomplete material coverage. To address these issues, future database development should prioritize unifying data formats and linking upstream and downstream processes to create a cohesive and interconnected database. Such a unified database would enable the establishment of a fully connected data chain for cementitious materials, enhancing the accuracy of predictions, supporting reverse design processes, and saving time on data cleaning.
Particular emphasis should also be placed on refining databases for related materials, such as mineral admixtures. These refined databases would provide critical data for improving the durability of cementitious materials and reducing their carbon emissions. Furthermore, combining artificial intelligence algorithms, such as ChemDataExtractor and BERT, with domain expert knowledge holds significant potential for advancing literature mining techniques tailored to cementitious materials. This process could begin by focusing on individual performance attributes and gradually expand to encompass the comprehensive extraction of data for all cementitious materials.
The future of cementitious materials database development is promising, with the potential to drive innovations in low-carbon materials research and development, ultimately contributing to achieving global carbon neutrality goals.
There are many methods to test the water content, pore water distribution and pore structure characteristics of cement-based materials, and they are different in the measurement principle, accuracy, ease of use and reliability. As a non-destructive testing method, low-field nuclear magnetic resonance (LF-NMR) relaxation technology uses hydrogen and 1H nuclei in water as a probe. By testing the relaxation signal of 1H nuclei, it can accurately detect the content of hydrogen protons and the interaction with the pore wall, thereby indirectly obtaining features such as water content, water distribution in pores of different sizes and pore size distribution. They can be tracked and monitored over time and through other physical and chemical processes. Compared to traditional methods such as weighing method for water content and mercury intrusion porosimetry or nitrogen adsorption for porous structure measurement, LF-NMR relaxation technology can perform non-destructive testing without drying. It avoids the destruction of the abundant nanopore structure caused by drying pretreatment, and the pore measurement range covers the nanometer and micron scale pores. These significant technical advantages are very key to the study of the properties of cement-based materials. Because of the undisturbed, non-destructive and accurate characteristics of LF-NMR relaxation technology, it is precise, and thus more and more widely used in the field of cement-based materials, especially the hydration of cement, volume stability, actions of drying-wetting and freezing-thawing cycles, and durability performance. Since almost all these studies are closely related to water content and pore structure, LF-NMR plays an increasingly key role.
Based on the relaxation mechanism of 1H nuclei and the commonly used relaxation measurement methods, this paper systematically describes the transverse relaxation mechanism of pore fluid and the inversion algorithm of transverse relaxation data. The determination methods of surface relaxivity and quantitative calibration of transverse relaxation signal and continuous/discrete relaxation time spectrum into water content and continuous/discrete pore size distribution are described in detail. In addition, the application status of LF-NMR is summarized and prospected from 5 different perspectives: quantitative characterization of cement hydration process, pore structure at saturation, pore-scale water distribution at unsaturated state, imaging of water spatial distribution, and freezing-thawing damage process analysis.
First of all, by testing relaxation magnetization and transverse relaxation time spectrum, LF-NMR resonance technology can non-destructively monitor the moisture content and its physical constraint state in the hydration process of cement at real time, so as to analyze the time-varying process of pores, especially nanopores, and apprehend the development history of microstructure, so as to realize the undisturbed characterization and analysis of cement hydration process. Secondly, the porosity and pore size distribution of hardened cement-based materials can be obtained according to the relaxation magnetization and relaxation time spectrum, allowing for qualitative and quantitative investigation of the relationship between pore structure and macroscopic properties. Thirdly, the pore classification method based on discrete or distinct peak T2 spectrum can monitor the distribution of water in pores of different sizes at real time and continuously under unsaturated conditions, which can be used to study the macroscopic properties of cement-based materials such as moisture shrinkage. Fourthly, the water content and relaxation time spectra of different locations can be obtained by one-dimensional imaging, which can directly characterize the internal water migration process of cement-based materials. Finally, since the LF-NMR relaxation technique can only monitor the 1H nuclear signal in evaporable water other than in solid phase such as ice and calcium hydroxide, it can be used to detect the phase transition of liquid water into ice.
It is found after literature reviewing that the LF-NMR relaxation technique using 1H nuclei in pore fluid as a probe is especially suitable for characterizing cement hydration, pore structure evolution and pore-scale water allocation and spatial distribution of cement-based materials. On the basis of reasonable selection of hardware platform, test method, test parameters, inversion algorithm and accurate calibration of relaxation magnetization and transverse relaxation time, LF-NMR technology can help accurately measure important information closely related to pore structure and pore-scale water allocation of cement-based materials, such as hydration degree, pore size distribution and unsaturated pore water distribution non-destructively.
Due to the influence of ferromagnetic substances, current LF-NMR analysis is mainly recommended to use white cement as the principal cementitious material. In future, it is necessary to fully consider the influence of ferromagnetic materials on transverse and longitudinal relaxation, to establish LF-NMR relaxation test method suitable for ordinary Portland cement, and to improve the signal-to-noise ratio of relaxation signals, to reduce the dead time of the probe, and to develop an inversion algorithm with good accuracy and precision. The probe diameter (sample chamber size) should be increased to support the test analysis of concrete specimen.
LF-NMR relaxation technology is the promising characterization method that can detect the multi-scale pore structure and unsaturated pore water allocation and other key information of cement-based materials without any pretreatment. Since most of the key properties of cement-based materials, such as volume stability and durability, are closely related to pore structure and pore-scale water allocation, LF-NMR relaxation technology is expected to be able to drive breakthroughs and promote the development of modern concrete science and technology, similar to the encouraging role of magnetic resonance imaging in clinical diagnosis.
From the initiation of hydration when water is added to cement until the end of service life of cement-based materials, the influence of water permeates almost the entire lifecycle, comprehensively affecting both the development and degradation of their properties. Water transport is a critical fundamental factor determining the durability of cement-based materials (CBMs) and service life of structures. Since most concrete structures under service are unsaturated, capillary water absorption is the primary and efficient mechanism for water transport in concrete. An in-depth analysis of capillary water absorption process and sorptivity is of great significance for quantitatively studying and improving the durability of CBMs.
This study systematically investigates the capillary water absorption process and its anomalies in CBMs. While existing theories attribute sorptivity anomalies to factors such as gravitational effects, material heterogeneity, and secondary hydration of unhydrated cement particles, certain experimental phenomena remain inadequately explained. Through macro- and micro-scale testing combined with theoretical modeling, it is hypothesized that the unique physicochemical interactions between water and C-S-H gel may underpin these critical anomalies.
Although sorptivity testing is operationally simple, its results are highly sensitive to experimental conditions (e.g., temperature, humidity, and initial saturation). The moisture state of specimens plays a decisive role in sorptivity measurements, while inconsistencies in testing protocols can lead to disparate outcomes. Consequently, adopting a scientifically rigorous and practical testing methodology is imperative. This paper reviews international standards for sorptivity testing, including the widely recognized and scientifically reliable ASTM C1585—20 and ISO 15148:2002. However, these standards exhibit limitations, such as short testing durations that overlook the significance of secondary sorptivity. Given the anomalous long-term absorption behavior of CBMs, a systematic consideration of the two-stage sorptivity process is essential. Furthermore, China urgently requires the development of a national testing standard tailored to its specific material and environmental conditions.
To elucidate the influencing factors of sorptivity, this study compiles and analyzes experimental data from diverse studies. The results reveal that cement content, water-to-cement ratio, and the dosage of supplementary cementitious materials profoundly alter hydration kinetics, hydration products, and pore structure, thereby significantly affecting sorptivity. Beyond material composition, variations in pretreatment methods (e.g., drying protocols) also induce substantial discrepancies in test results due to differing moisture states. Moreover, the coupling effects of these factors further complicate the interpretation of sorptivity behavior. Therefore, during the sorptivity test, it is crucial to adopt a scientific pretreatment protocol to minimize the impact of drying, equilibration, and moisture content on the test results.
The study also explores correlations between sorptivity and other macroscopic performance indicators. Sorptivity demonstrates strong linkages with transport properties such as permeability and electrical flux, as these metrics are fundamentally governed by pore structure. Additionally, sorptivity exhibits predictive potential for mechanical properties and durability outcomes, including carbonation resistance, freeze-thaw durability, and sulfate attack resistance. Compared to other durability indicators, sorptivity not only boasts a relatively straightforward testing process, but its primary advantage lies in its high sensitivity to durability changes in long-age concrete. It also provides highly accurate assessments of the carbonation resistance of cement-based materials. Furthermore, it contributes effectively to evaluating frost resistance and sulfate erosion resistance. When used in conjunction with other durability indicators, sorptivity enables a comprehensive assessment of the durability performance of cement-based materials. As a durability indicator, sorptivity shows promise in forecasting the service life of cement-based materials.
In conclusion, this work underscores the need for refined theoretical models, standardized testing protocols, and comprehensive investigations into the coupling mechanisms governing sorptivity. Addressing these challenges will enhance the reliability of sorptivity as a critical parameter for optimizing material design and durability assessment in cement-based systems.
Cement-based materials exhibit water sensitivity due to their unique physicochemical interactions with water. Current understanding and quantitative characterization of capillary water absorption (sorptivity) require further refinement through integrated theoretical and practical studies. Notably, the two-stage sorptivity mechanism, particularly the physical significance and engineering implications of the secondary sorptivity, demands deeper exploration to enhance its practical application.
Critical anomalies observed in sorptivity evolution highlight the urgent need to develop more scientifically robust testing protocols. A standardized framework for evaluating concrete quality based on sorptivity should subsequently be established.
The measured sorptivity is significantly influenced by material composition and mix design parameters, including cement type, supplementary cementitious materials, water-to-binder ratio, curing conditions (temperature and humidity), aging, and drying pretreatment. Systematic investigations into the correlations between sorptivity and material composition are essential to optimize mix designs for improved durability.
Although sorptivity demonstrates varying degrees of correlation with mechanical properties, other transport indices (e.g., chloride diffusion), and accelerated durability test results, it exhibits unique potential as a complementary indicator for assessing concrete durability. Integrating sorptivity with conventional metrics could enhance the accuracy of service life prediction models for concrete structures. However, further theoretical, experimental, and field studies are imperative to validate its application in engineering practice.
In summary, advancing research—spanning mechanistic interpretation, standardized testing, material optimization, and durability assessment—will provide critical insights into the performance and longevity of cement-based materials in real-world environments.
As an energy-intensive industry, cement manufacturing is a significant contributor to CO2 emissions. Simultaneously, the increasing volume of construction waste has also exerted significant pressure on the environment. Recycling demolished concrete has been proposed as a strategy to address the depletion of aggregate resources. In addition, it facilitates the disposal of construction waste and reduce carbon emissions. A particularly promising approach is the recycling of waste concrete powders (WCP) as a supplementary cementitious material (SCM), which has garnered significant attention. However, the high absorption and low reactivity of WCP pose a challenge to its direct use as SCM. Accelerated carbonation of WCP produces calcium carbonate (CaCO3) and amorphous silica gel. These products enhance the reactivity of WCP and facilitate the effective sequestration of CO2. This process not only promotes the high-quality utilization of WCP but also helps to mitigate the environmental and energy burdens associated with cement production.
This study reviews the properties of carbonated waste concrete powder (cWCP) and provides an in-depth analysis of the carbonation process of WCP. It covers various carbonation methods, the regulation of carbonation degree and the prperties of carbonation products. Furthermore, the review evaluates the influence of cWCP on the performances of cement-based materials, including rheology, hydration behavior, mechanical properties, and impermeability.
The carbonation products of cWCP are influenced by the carbonation conditions. In turn, cWCP influences the properties of cement-based materials through the properties of these carbonation products. The primary products of cWCP are CaCO3 and amorphous silica gel. Their composition, morphological characteristics, chemical properties, and relative distribution depend significantly on the carbonation method and conditions used. The reaction environments and carbonation kinetics of dry and wet carbonation processes differ significantly, resulting in variations in both the degree of carbonation and the polymorphs of products. By optimizing these carbonation conditions, it is possible to improve the degree of carbonation of cWCP while also controlling the polymorphs of CaCO3 and polymerization degree of silica gel. Furthermore, the influence exerted by these carbonation products on cement-based materials primarily stems from their surface characteristics combined with various effects. Surface properties include both geometrical and surface electrochemical characteristics of CaCO3 in diverse polymorphs, as well as the hydrophilicity of the silica gel. The effects of carbonation products include the filler effect, nucleation effect, chemical reaction with C3A, and the pozzolanic effect attributed to silica gel. Notably, improvements in rheological properties are not significantly influenced by either the filler effect or surface electrochemical characteristics of CaCO3. Instead, more pronounced negative influences arise from the hydrophilicity of silica gel and the fibrous geometry of aragonite. These factors contribute to a significant deterioration in rheological properties, with hydrophilicity being the primary mechanism behind this deterioration. When the degree of carbonation is sufficiently high, the combined positive effects of the filler effect, nucleation effect, chemical reaction, and pozzolanic effect can surpass the negative influence of dilution effect. As a result, the incorporation of cWCP accelerates the hydration, improves the microstructure, and enhances the compressive strength and impermeability.
Existing studies have shown that the incorporation of cWCP accelerates cement hydration, improves microstructure, enhances compressive strength, and strengthens mortar impermeability. However, it may also result in a degradation in rheology.
Base on these findings, further advancements are essential to fully understand the properties of cWCP-based cementitious materials and to support their widespread application. Key areas for development include: 1) establishing a model that correlates carbonation conditions with carbonation products to precisely control their performance, 2) addressing the contradiction between compressive strength and rheological properties, 3) deepening our understanding of the durability of cement-based materials containing cWCP, particularly concerning corrosion of steel reinforcement, and 4) overcoming challenges related to improving the degree of carbonation in cWCP due to an accumulation of carbonation products. These efforts will lay the groundwork for the industrial adoption of cWCP and drive the concrete industry toward more sustainable and environmentally friendly practices.
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