High-performance Cementitious Materials Research Articles

Preparation of geopolymers from thermally activated lithium slag as sole precursor: Mechanical properties and microstructure

Lithium slag (LS) is a waste residue generated during lithium extraction, posing significant environmental challenge due to its extensive accumulation. This study proposes a method of utilizing thermally activated LS as the sole precursor for geopolymer synthesis. The thermal activation mechanism of LS was investigated using XRD, FTIR, ICP, and SEM techniques, while exploring the optimal composition for LS geopolymers(LSG). The research revealed that heating at 700 °C increased the amorphous content of LS from 15.9 % to 48.1 %, altering the chemical structure of its aluminosilicates and enhancing its leaching capacity in alkaline environments, thereby boosting its reactivity. The activator modulus and alkali equivalent were found to significantly influence the strength and microstructure of LSG. As the modulus increased from 1.0 to 1.4, geopolymer strength initially rose before declining, whereas strength progressively increased with alkali equivalent from 0.10 to 0.16. The geopolymer synthesized with a modulus of 1.2 and alkali equivalent of 0.16 exhibited the highest compressive strength of 53.1 MPa after 28 days. Test results indicated that the internal structure of LSG primarily comprised unreacted particles, N(C)-A-S-H gel, and microcracks. The increased alkali equivalent facilitated the dissolution of Si4+ and Al3+ within LS, intensifying geopolymerization to produce more N(C)-A-S-H gel, thereby densifying the structure and significantly enhancing compressive strength. This study elucidates the mechanism by which high-temperature calcination enhances LS reactivity, as well as the impact of activator on compressive strength and microstructural properties of LSG, offering new insights into the engineering applications of LS in high-performance cementitious materials.

Improvement of the mechanical properties of beta-hemihydrate phosphogypsum by incorporating wet-ground low-calcium fly ash slurries

Beta-hemihydrate phosphogypsum (β-HPG) is a low-carbon cementitious material used in construction. Nevertheless, the poor water resistance and low mechanical strength of β-HPG limit its utilization. In this study, two low-calcium fly ash (FA) slurries with median particle sizes of 1.83 μm and 1.14 μm were prepared using a wet-grinding process for the improvement of β-HPG, and the mechanical strength and softening coefficient were tested to assess the effect. The results show that wet-ground low-calcium FA can significantly enhance the mechanical strength and softening coefficient of β-HPG. Compared with specimens without wet-ground low-calcium FA, the dry compressive strength and softening coefficient of specimens with 30% wet-ground low-calcium FA (D50=1.14 μm) increased by 104.9% and 71.8%, respectively. It is worth noting that the 1 d compressive strength also increased by 11.9%. Specifically, wet-ground low-calcium can increase the pH value and conductivity of the FA slurry, further accelerate the hydration process of FA in β-HPG, forming more ettringite and gels to fill in the pores between dihydrate gypsum (DH) crystal, and reducing the larger pores in the hardened paste. This study can develop a high-performance cementitious material that will enable the effective use of β-HPG.

Mechanical properties of solid waste-based composite cementitious system enhanced by CO2 modification

Utilizing CO2 to modify solid waste and produce high-performance cementitious material is a promising strategy. In this study, circulating fluidized bed fly ash (CFBFA), calcium carbide slag (CS) and flue gas desulphurization gypsum (FGDG) were prepared by mixing CO2 to produce cementitious materials. The impacts of CO2 on mechanical properties and carbonation reaction mechanism of composite materials were investigated. The results shown that the microstructure and mechanical properties of the gelling materials were improved by CO2 modification. When the CO2 mass transfer conditions as followed: CO2 flow rate was 1.5 L/min, stirring rate at 600 r/min, and stirring time at 20 min, compressive strength of modified material was 22 % higher than that of the non-CO2 modified material. Additionally, the density increased by 3.2 %, and porosity was reduced by 34.1 %. Among them, TG/DTG analysis found that the highest effective fixed CO2 rate was 11.1 %. The ultrasonic nondestructive testing also shown that the structure of the CO2-modified cementitious material was significantly better than that of the CFBFA-CS-FGDG composite cementitious system, and the ultrasonic loss rate was reduced by 9.4 %. Therefore, the use of CO2 to modify the composite system was of great significance for the realization of CO2 storage and the improvement of the properties of composite materials. One interesting future possibility is solid waste-based grouting materials production at energy plants: CFBFA, CS and FGDG can be used to capture CO2 from flue gases, thus improving the strength of produced grouting materials.

Investigation of type, size, and dosage effects of superabsorbent polymers on the hydration development of high-performance cementitious materials

The low water-to-binder ratio commonly used for high-performance cementitious materials is known to limit the degree of hydration of their cement particles. This issue often cannot be resolved with conventional external curing methods, primarily because of the low permeability of such materials. Thus, internal curing methods are devised to improve the degree of hydration and maximize the use of cement particles. Focusing on superabsorbent polymers (SAPs) as one of the main internal curing agents, this study investigates the effects of various types, sizes, and dosages of SAPs on the hydration kinetics of high-performance cementitious mixtures. For this purpose, the main performance characteristics of SAPs were characterized first. Paired with monitoring the temperature development patterns in a set of SAP-contained mixtures, thermogravimetric analyses (TGA) and X-ray diffractometry (XRD) investigations were systematically performed to measure the phase consumption of cement particles. Scanning electron microscope (SEM) image analyses were then employed to assess the materials deposited in the remaining SAP voids. By providing original insights into the hydration development process, this study’s outcome guides the use of SAPs with the ultimate goal of maximizing the hydration degree of cement particles, paving the way to minimizing the carbon footprint of high-performance cementitious materials.

Converting sintering red mud to valuable calcium carbonate whiskers via an innovative magnesium-modified wet carbonation

Sintering red mud (SRM) is an industrial alkaline waste residue generated from the sintering process in alumina production, which is often directly discarded and causes environmental issues. In this study, an innovative magnesium-modified wet carbonation method was proposed to convert sintering red mud to valuable calcium carbonate whiskers using CO2-containing flue gas. The effects of carbonation conditions including temperature, MgCl2 concentration, and duration on the composition, microstructure, and morphology of carbonated products were systematically investigated. It was found that a high whisker content of 60% with an aspect ratio of ∼6 could be obtained under the optimal conditions of 80 °C, 0.4 M MgCl2, and 2 h reaction time. Besides the formation of whiskers, amorphous aluminosilicate gel was also generated during SRM carbonation. The effects of the as-prepared whisker-rich materials as partial cement replacement on the mechanical properties of cement paste were evaluated with 5 wt% replacement, the 28 d compressive strength was significantly improved by 20.5% compared to the control specimen. The effective reinforcement was ascribed to the fibrous whiskers and enhanced interfacial bonding. This method enables high-value utilization of SRM waste and CO2 fixation, providing a green and low-cost approach to producing high-performance cementitious materials.

Effects of a novel carbon nanomaterial on hydration, mechanics, and chloride binding of cement composites

Nanomaterials have made significant progress in the field of cementitious materials, but suffer from primary problems of high cost and poor dispersity. Carbon dots (CDs) as a novel low-cost and high-dispersity nanomaterial preliminarily demonstrate their potential for cement. Nevertheless, it lacks systematic research on their effects on cement properties. For the first time, this work comprehensively investigates the effects of CDs on the hydration, mechanics, and chloride binding of cement composites. More importantly, the relevant mechanisms are revealed in depth. Specifically, cost-efficient ($0.013/g) and well-dispersed (dispersed in simulated concrete pore solution for 7 d) CDs are directly prepared by a facile microwave approach. The CDs dramatically retard the early hydration, improve later mechanical performance, and obviously enhance chloride binding. In detail, 0.2 wt% CDs reduce the second exothermic peak value by 75%, but improve the chloride binding capacity of paste by 51%. And 0.1 wt% CDs enhance the compressive/flexural strength of mortar by 17%/21%. Crucially, related influence mechanisms are uncovered. Namely, CDs create a protective barrier to retard hydration through the complexation of their abundant surface groups with Ca2+; While CDs exert the nucleation effect to boost the formation of C–S–H and Friedel's salt, thereby playing a positive impact on chloride binding; Meanwhile, CDs with suitable dosages carry out nucleation effect to counteract their air-entraining effect, thus improving later mechanical properties of cement composites. This study is expected to provide a novel low-cost and high-dispersity CDs nanomaterial to advance the development of high-performance cementitious materials.

High performance inorganic fullerene cage WS2 enhanced cement

An original cement based material enhanced with inorganic fullerene tungsten disulfide (IF-WS2) nanoparticles has been engineered with superb shock absorbing properties. Physical properties were attributed to the IF-WS2 nano-hollow multiple layered onion-like structure. The effect of IF-WS2 concentration at 0.1 wt%, 1 wt% and 5 wt% on the hydration kinetics of ordinary Portland cement (CEM1), electrical impedance, thermal stability, rheology and strength development was thoroughly evaluated. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies confirmed the formation of the new phase, calcium tungstate (CaWO4), at the nano-particle/cement matrix interface during early hydration. 1 wt% IF-WS2 additions enhanced the impact energy of CEM1 by 89% compared to the control. An IF-WS2 cementitious mixture was developed for 3D printing based on the 1% WS2-CEM composition. The mix exhibited excellent workability and buildability enabling the creation of a layer-by-layer printed component. Intimate interlayer adhesion minimized the presence of voids leading to a high flexural strength of 6.7 MPa, which equated to an over 86% improvement compared to plain CEM1 printed components. This study showcases IF-WS2 nanoparticles as a new ground-breaking additive enabling the production of high-performance cementitious construction materials, for use under extreme environments demanding high strength and impact resistance.

Preparation and Performance Improvement Mechanism Investigation of High-Performance Cementitious Grout Material for Semi-Flexible Pavement.

Semi-flexible pavement material (SFPM) combines the advantages and avoids the disadvantages of asphalt concrete flexible pavement and cement concrete rigid pavement. However, due to the problem of interfacial strength of composite materials, SFPM is prone to cracking diseases, which limits the further application of SFPM. Hence, it is necessary to optimize the composition design of SFPM and improve its road performance. In this study, the effects of cationic emulsified asphalt, silane coupling agent and styrene-butadiene latex on the improvement of SFPM performance were compared and analyzed. The influence of modifier dosage and preparation parameters on the road performance of SFPM was investigated by an orthogonal experimental design combined with principal component analysis (PCA). The best modifier and the corresponding preparation process were selected. On this basis, the mechanism of SFPM road performance improvement was further analyzed by scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) spectral analysis. The results show that adding modifiers can significantly enhance the road performance of SFPM. Compared to silane coupling agents and styrene-butadiene latex, cationic emulsified asphalt changes the internal structure of cement-based grouting material and increases the interfacial modulus of SFPM by 242%, allowing cationic emulsified asphalt-SFPM (C-SFPM) to exhibit better road performance. According to the results of the principal component analysis, C-SFPM has the best overall performance compared to other SFPMs. Therefore, cationic emulsified asphalt is the most effective modifier for SFPM. The optimal amount of cationic emulsified asphalt is 5%, and the best preparation process involves vibration at a frequency of 60 Hz for 10 min and 28 days of maintenance. The study provides a method and basis for improving the road performance of SFPM and a reference for designing the material composition of SFPM mixes.

The synergistic hydration mechanism and environmental safety of multiple solid wastes in red mud-based cementitious materials

Red mud (RM) is a solid waste material with high alkalinity and low cementing activity component. The low activity of RM makes it difficult to prepare high-performance cementitious materials from RM alone. Five groups of RM-based cementitious samples were prepared by adding steel slag (SS), grade 42.5 ordinary Portland cement (OPC), blast furnace slag cement (BFSC), flue gas desulfurization gypsum (FGDG), and fly ash (FA). The effects of different solid waste additives on the hydration mechanisms, mechanical properties, and environmental safety of RM-based cementitious materials were discussed and analyzed. The results showed that the samples prepared from different solid waste materials and RM formed similar hydration products, and the main products were C–S–H, tobermorite, and Ca(OH)2. The mechanical properties of the samples met the single flexural strength criterion (≥ 3.0 MPa) for first-grade pavement brick in the Industry Standard of Building Materials of the People's Republic of China-Concrete Pavement Brick. The alkali substances in the samples existed stably, and the leaching concentrations of the heavy metals reached class III of the surface water environmental quality standards. The radioactivity level was in the unrestricted range for main building materials and decorative materials. The results manifest that RM-based cementitious materials have the characteristics of environmentally friendly materials and possess the potential to partially or fully replace traditional cement in the development of engineering and construction applications and it provides innovative guidance for combined utilization of multi-solid waste materials and RM resources.

Semi-Flexible Pavement: A Review of Design and Performance Evaluation

It is known to researchers in the field of road construction and development. Three types of pavement are rigid, flexible, and composite paving. The composite pavement consists of a layer of flexible pavement on top of which a layer of rigid pavement is placed or vice versa. All of these types have advantages in addition to disadvantages that affect road performance on the one hand and user convenience on the other. About 50 years ago, work began establishing a type of pavement characterized by its semi-flexible performance, which combines rigid pavement's rigidity and flexible pavement's flexibility. It is called semi-flexible pavement and grouted macadam in some sources. It consists mainly of an open-graded asphalt mixture in which the percentage of air voids ranges from (25 to 35%), and in some sources, it is mentioned that it ranges between (20 to 28%) grouted with a high-performance cementitious material. Work began on this type of pavement in the sixties of the last century. However, there is no approved specification for its design, as its design methods differ according to the researcher's vision. This scientific paper aims to facilitate the way for new researchers in this field by knowing the basic stages of semi-flexible pavement design and presenting the existing design methods and what is required for laboratory tests to evaluate the performance of the completed pavement design. It was found that the performance of semi-flexible paving depends mainly on the bonding between its components, as it is considered a composite material. For this reason, the direction in the future may be to study the bonding between asphalt and cement, in particular, as they are two basic materials in their composition.

Optimal design of a low-cost high-performance hybrid fiber engineered cementitious composites

Engineered cementitious composites (ECC) is a fiber reinforced high-performance cementitious material with an ultra-high tensile strain capacity (above 3%) and excellent durability. However, such excellent strain capacity far exceeds some engineering requirements and is usually not fully utilized. Meanwhile, its high cost limits it application only in local engineering. In this study, a low-cost high-performance hybrid fiber ECC (HF-ECC) with both polypropylene (PP) fiber and polyethylene (PE) fiber was manufactured. Both macroscopic and microscopic mechanism analyses were conducted to investigate the effect of fiber characteristics and proportions on the performance of HF-ECC. The results show that the ultimate tensile strain of HF-ECC can reach 5% even the volume fraction of PP and PE fibers account for 1%, respectively. Its fiber cost is 43.8% lower than that of pure PE-ECC, which reduces the corresponding total cost by 27.5%. This paper presents an in-depth investigation of the characteristics of HF-ECC, direct tension, compression, fiber-bridging, pore structure, fiber distribution, and fiber dispersion. Finally, the optimal design of the HF-ECC is conducted through pseudo-strain-hardening indices and multi-criteria evaluation.

Mechanical properties and material characterization of cement mortar incorporating CNT-engineered polyvinyl alcohol latex

To overcome the highly brittle nature of cementitious materials, our study aims to explore the potential of incorporating nano-engineered polyvinyl alcohol (PVA) latex in cement mortars. Hydroxyl carbon nanotubes (CNT-OH) were used to enhance the mechanical properties of PVA latex, and the resulting CNT-OH/PVA latex was used to improve the mechanical properties of cement mortars. The morphology and microstructure of CNT-OH/PVA latex and resulting mortars were characterized by SEM, FTIR and XRD. Results showed that incorporating 10 wt% of CNT-OH increased the tensile strength and modulus of solidified PVA latex by 1.56 times and 16.6 times, respectively. CNT-OH/PVA latex increased the compressive strength, flexural strength, fracture toughness and fracture energy of cement mortars by 14.3%, 39.4%, 55.4 % and 134.7%, respectively. The positive effect of CNT-OH/PVA latex on mechanical properties of cement mortars attributed to 1) uniform dispersion of CNT-OH/PVA latex in mortars, 2) acceleration of hydration, 3) chemical and hydrogen bonds between CNT-OH/PVA latex and cementitious matrix; and 4) prevention of cracking and refinement of microstructure in mortars. These findings can provide new insights into the design of high-performance cementitious materials.

The Influence of Drop Panel's Dimensions on the Punching Shear Resistance in Ultra-High-Performance Fiber-Reinforced Concrete Flat Slabs

Ultra-high performance fiber reinforced concrete (UHPFRC) is a high-performance cementitious material with enhanced tension, compression, and toughness, strengths in the post crack region with high ductility, toughness, and durability. The companies prefer to use it to construct highly durable structures such as high-rise buildings, towers, and bridges. In addition, the thickness of the flat slab produced by UHPFRC might be thinner than the conventional concrete. One problem that has always been a concern in a flat slab is the punching shear failure since this failure is brittle and occurs suddenly without any previous notice. Besides, the position of the critical section for punching shear could be changed based on the thickness of the drop panel and the inclusion of fiber in the concrete. This paper highlights the effect of drop panels dimension on the punching shear resistance in UHPFRC flat slabs. The four two-way interior UHPFRC supported flat slab panels, consisting of one control flat slab without drop panels and three-flat slabs with different sizes of drop panels (10.5%,14.5%, and 19%) of the total area of slab drop panels, tested under punching load. Results indicated that the covered area of flat slabs by drop panel around 10.5% improved punching load up to %20 and 37% at the crack and ultimate loads. Furthermore, the test results show that the efficient covered area for resisting punching was 10.5% of the total area of the tested slab. Besides, the deflection values, strain in reinforcement and concrete, rotation at supports, and the inclination angles of cracks were improved due to the stiffness enhancement in the flat slabs.

A Review on the Use of Self-Curing Agents and Its Mechanism in High-Performance Cementitious Materials

Self-cured concrete is a type of cement-based material that has the unique ability to mitigate the loss rate of water and increase the capacity of concrete to retain water compared to conventional concrete. The technique allows a water-filled internal curing agent to be added to the concrete mixture and then slowly releases water during the hydration process. Many researchers have studied the composition of self-curing concrete using different materials such as artificial lightweight aggregate (LWA), porous superfine powders, superabsorbent polymers (SAP), polyethylene glycol (PEG), natural fibers, and artificial normal-weight aggregate (ANWA) as curing agents. Likewise, physical, mechanical, and microstructure properties, including the mechanisms of curing agents toward self-curing cement-based, were discussed. It was suggested that adopting self-curing agents in concrete has a beneficial effect on hydration, improving the mechanical properties, durability, cracking susceptibility behavior, and mitigating autogenous and drying shrinkage. The interfacial transition zone (ITZ) between the curing agent and the cement paste matrix also improved, and the permeability is reduced.

Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete

Integration of fiber reinforcement in high-performance cementitious materials has become widely applied in many fields of construction. One of the most investigated advantages of steel fiber reinforced concrete (SFRC) is the deceleration of crack growth and hence its improved sustainability. Additional benefits are associated with its structural properties, as fibers can significantly increase the ductility and the tensile strength of concrete. In some applications it is even possible to entirely replace the conventional reinforcement, leading to significant logistical and environmental benefits. Fiber reinforcement can, however, have critical disadvantages and even hinder the performance of concrete, since it can induce an anisotropic material behavior of the mixture if the fibers are not appropriately oriented. For a safe use of SFRC in the future, reliable non-destructive testing (NDT) methods need to be identified to assess the fibers’ orientation in hardened concrete. In this study, ultrasonic material testing, electrical impedance testing, and X-ray computed tomography have been investigated for this purpose using specially produced samples with biased or random fiber orientations. We demonstrate the capabilities of each of these NDT techniques for fiber orientation measurements and draw conclusions based on these results about the most promising areas for future research and development.

Role of carbon nanotube in reinforcing cementitious materials: An experimental and coarse-grained molecular dynamics study

One-dimensional carbon-based nanomaterials, such as carbon nanotube (CNT) or carbon nanofiber (CNF) have been regarded as ideal candidates to form nanocomposites for the fabrication of high-performance cementitious materials. Although CNT, CNF and nanocellulose possess different mechanical properties, the mechanical enhancement of CNT, CNF or nanocellulose reinforced cementitious falls in a similar magnitude compared with plain cement paste, which should be highly related to the interaction between the nanomaterials and cement hydration products. In this study, CNT has been chosen as a representative nanomaterial to investigate the role in reinforcing cementitious materials in the nanocomposite system through an experimental and coarse-grained molecular dynamics approach. The findings suggest that the CNT changes the fracture process in cement matrix when the microcracks initiate with the significantly improved fracture energy, leading to the improved global mechanical properties, and a nanoscale interfacial transition zone is found that governs the failure of the nanocomposite system.

Effect of Styrene-Acrylic Emulsion on Crack Resistance of Cement-Based Materials

In this paper, the brittleness coefficient, elastic modulus-to-strength ratio, drying shrinkage and autogenous shrinkage and cracking sensitivity were used to investigate the effect of styrene-acrylic emulsion (SAE) on crack resistance of cement-based materials under ultralow water binder ratio (0.22). Then the pore structures, hydration products and surface morphology were also studied to explore the mechanism of SAE on improving the crack resistance of cement-based materials. Results show that, the addition of SAE significantly reduces the elastic modulus, brittleness coefficient, elastic strength ratio, drying shrinkage and autogenous shrinkage of the specimen. The cracking susceptibility is also decreased by the incorporation of SAE and when the dosage of SAE was 5%, the initial cracking time would be extended by 43 hours. In addition, incorporation of SAE can reduce the amount of pores that have an adverse effect on shrinkage, refine the microstructure and decrease the calcium hydroxide formation and microcracks of cement-based materials. Such results would be expected to provide guidance on enhancing the anti-cracking ability of high-performance cementitious materials by the dosage of SAE under low water-binder ratio in practical engineering.

Nanoscale Construction Biotechnology for Cementitious Materials: A Prospectus

Climate change, infrastructure resilience, and resource recovery from waste have emerged as grand challenges for civil engineers in the 21st century. Wicked problems associated with these global grand challenges are necessitating innovative, multidisciplinary thinking and multiscale, integrated solutions that are spurring the development of a new field—construction biotechnology. While the field of construction biotechnology spans multiple scales, this review highlights the promise and potential of nanoscale (<100 nm) biotechnological applications to civil engineering. While the field of nanotechnology has revolutionized other industries, applications of nanotechnology in civil engineering have remained limited due to techno-economic and environmental barriers. Biological production of functional nanoparticles (NPs), however, offers new economical routes to develop resilient, high-performance cementitious materials while simultaneously addressing critical needs related to wastewater and air-pollution treatment. Recent research has elucidated that biological production of NPs exhibit preferred—and genetically controllable—morphological characteristics that could tailor the structure-property relationships of civil engineering materials. The natural ability as well as the programmability via synthetic biology allow microorganisms to immobilize heavy metals (e.g., Hg, Cr, Zn, Cd, Cu, Ag) and interact with greenhouse gases and volatile organic compounds, therefore affording civil engineers a grand opportunity to treat wastewater and recover rare earth elements, and remove air pollutions. In addition to featuring state-of-the-art research in the field, this review summarizes the opportunities and challenges of nanoscale biotechnology and proposes a roadmap of research for civil engineers of the 21st century.

Lightweight and low thermal conducted face-centered-cubic cementitious lattice materials (FCLMs)

Lightweight and thermal insulative cementitious materials with large porous structures for improving energy efficiency have rapid development currently. However, the design of cementitious materials for energy-efficient building system in terms of low thermal conductivity, excellent mechanical properties and lightweight remains a crucial challenge in construction & building fields. Recently, the polymer-based lattice-inspired structures fabricated by 3D printing technology (3DPT) show a rapid development that achieves a balance of thermal and mechanical properties due to their ordered and large-scale cellular architecture. In this work, a novel category of lattice-inspired cementitious lattice materials was first proposed for applying in the energy-efficient building systems by integrating the 3DPT and traditional casting technology. Taking face-centered cubic (FCC) lattice as an example, the advantages of the proposed fabrication technology and FCLMs are follows: (i) ultralight weight; (ii) enhanced ductility of brittle cementitious materials; (iii) low thermal conductivity. Through the structural and material design, the proposed fabrication technology could effectively overcome the current issues of 3DPT, such as the weakness of interlayer performance and low accuracy (Extrusion-based 3DPT) as well as limited feasible materials (Powder-bed-based 3DPT), in the civil engineering. Statement of SignificanceHow to design cementitious materials for energy-efficient building system in terms of thermal conductivity, mechanical properties and lightweight requirement remains a crucial challenge in construction & building fields. Inspired by the low thermal conductivity and lightweight structure of metamaterials in the previous researches (Song et al., Materials & Design, 2019. 173: 107773-86; Nicholas et al. Nano letter, 2018. 18: 4755-61), here a novel category of lattice-inspired cementitious materials with ordered porous structures has been proposed for energy-efficient building materials with lightweight, low thermal conductivity and good mechanical properties characteristics.Additionally, recently there is increased interest to use 3D concrete printing technology (3DCPT) to automatically manufacture complicated and customized structure. However, currently, 3DCPT encounters many sticky issues, involving that (i) weak interlayer performance induced by cold joints between layers; (ii) deformation under self-weight due to the low yield stress of fresh mix; (iii) probable shrinkage under the low water/cement ratios typically used in printed mortars; (iv) geometrical instability owing to creating suspended structures. It is not a trivial to directly print cementitious porous materials, and therefore this work also achieved a breakthrough in developing cementitious porous materials combining advanced SLA 3D printing and traditional casting technology for the first time. It is worth mention that compared to Extrusion-based 3DCPT and Powder-bed-based 3DCPT, the advantages of the manufacture technology include that (i) automatically printing 3D complex structure; (ii) Optional cementitious materials; (iii) Good interlayer performances of prepared materials.We expect that the proposed design idea and novel manufacture strategy could serve as the guideline to develop material-structural-functional integrated energy-efficient building materials combining 3D printing technology, advanced structure design and high-performance cementitious materials.

A molecular dynamics study of calcium silicate hydrates-aggregate interfacial interactions and influence of moisture

The interface properties between hydrated cement paste (hcp) and aggregates largely determine the various performances of concrete. In this work, molecular dynamics simulations were employed to explore the atomistic interaction mechanisms between the commonly used aggregate phase calcite/silica and calcium silicate hydrates (C-S-H), as well as the effect of moisture. The results suggest that the C-S-H/calcite interface is relatively strong and stable under both dry and moist conditions, which is caused by the high-strength interfacial connections formed between calcium ions from calcite and high-polarity non-bridging oxygen atoms from the C-S-H surface. Silica can be also adsorbed on the dry C-S-H surface by the H-bonds; however, the presence of water molecules on the interface may substantially decrease the affinities. Furthermore, the dynamics interface separation tests of C-S-H/aggregates were also implemented by molecular dynamics. The shape of the calculated stress-separation distance curves obeys the quasi-static cohesive law obtained experimentally. The moisture conditions and strain rates were found to affect the separation process of C-S-H/silica. A wetter interface and smaller loading rate may lead to a lower adhesion strength. The mechanisms interpreted here may shed new lights on the understandings of hcp/aggregate interactions at a nano-length scale and creation of high performance cementitious materials.