Cement Hydration Products Research Articles

Mutual Activation Mechanism of Cement–GGBS–Steel Slag Ternary System Excited by Sodium Sulfate

To promote the large-scale recycling of solid waste, the hydration characteristics of blended cement with different amounts of GGBS (ground granulated blast-furnace slag) and SS (steel slag) were investigated. The optimum blending amounts of GGBS and SS in cement were 40% and 10% by mass, and the optimum dosage of Na2SO4 in the C50-S40-SS10 (50 wt.% cement–40 wt.% slag–10 wt.% steel slag) system was 2 wt.%. The flexural and compressive strengths of the C50-S40-SS10 system after adding 2 wt.% Na2SO4 are 57.95% and 9.28% higher than that of pure cement at 28 d. XRD, FT-IR and Ca(OH)2 content analysis were chosen to investigate the hydration products of pure cement and blended cement. The results show that GGBS enhanced the hydration of both cement and SS. And GGBS contributed to the generation of calcium silicoaluminate hydrate (C–A–S–H) in the blended cement system. The addition of Na2SO4 promoted the hydration reaction and contributed to the generation of ettringite (AFt) in the ternary system. The hydration heat evolution results showed that GGBS and SS can reduce the hydration heat of cement. Na2SO4 had similar effects and delayed the time of AFt conversion to monosulfide calcium sulphoaluminate (AFm). A mutual activation mechanism of cement–GGBS–SS ternary system mixed with Na2SO4 was proposed in this study.

Influence of iron substitution on the microstructure and properties of ettringite in calcium sulfoaluminate cement: A comprehensive study on the Al/(Fe+Al) ratios

Ettringite, as the dominant hydration product of calcium sulfoaluminate cement, significantly contributes to cement strength. Its formation is closely related to the Fe and Al ratio in raw materials. During cement hydration, Fe present in ferrite can replace some of the Al in ettringite, which notably affects the microstructure and properties of the latter. To understand the relationship between the Al/(Fe + Al) ratios and the ettringite phase, we synthesized ettringite with varying Al/(Fe + Al) ratios using a chemical synthesis method. The microstructure was then characterized to determine the formation process of this phase. Various analysis methods, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), and N2 adsorption-Brunauer Emmett Teller (BET), were used to study the solid phases. For aqueous solutions, inductively coupled plasma emission spectroscopy (ICP-OES) was employed. Our results reveal that Fe replacing Al leads to regular changes in the ettringite crystal's microstructure. As the Al/(Fe + Al) ratio decreases, there is a reduction in the ettringite unit cell parameter a, an increase in c, and an enlargement of the unit cell volume. Concurrently, Fe substitution shrinks the crystallinity and grain size of ettringite crystals. SEM-TEM and BET demonstrate that Fe substitution boosts ettringite's particle size and aspect ratio, while the specific surface area contracts with a decreasing Al/(Fe + Al) ratio. Moreover, Fe substitution tends to lower ettringite's thermal stability and OH group binding ability. When the Al/(Fe + Al) ratio reached 80%, the ettringite crystal exhibited optimal thermal stability.

Phase and microstructure evolution of the hydration products of magnesium phosphate cements under sulfuric acid environments

Magnesium phosphate cement is a good canditate of repairing material served under harsh environments and its acid resistivity has drawn a lot of interest, but rare detailed research on the evolution of its physiochemical features has been reported. In this work, the impacts of sulfuric acid solution (pH = 2 – 7) on the hydration products of magnesium potassium phosphate cement and magnesium ammonium phosphate cement. Results showed that the main hydration products, struvite/struvite–K, experienced partial corrosion in the absence of the sulfuric acid solution replacement. The phase transition of struvite–K is clearly visible, leading to the formation of the new crystalline hydration product Mg3(PO4)2•22 H2O. The initial blossoms cluster microstructure transformed into a diffused dispersion that resembled a plate. When the solution was replaced, struvite/struvite–K underwent significant corrosion and even complete decomposition in more acidic (pH = 2, 3) solutions.

Reaction molecular dynamics study of calcium alumino-silicate hydrate gel in the hydration deposition process at the calcium silicate hydrate interface: The influence of Al/Si

Supplementary cementitious materials (SCMs) can partially replace cement in concrete production, forming calcium alumino-silicate hydrate (C-A-S-H). This enhances concrete durability while recycling waste. However, the early hydration reaction process of C-A-S-H and its deposition and aggregation behavior at the interface with the primary hydration product of cement, calcium silicate hydrate (C–S–H), remain unknown. Therefore, this study utilizes reactive molecular dynamics to model the deposition and growth behaviors of C-A-S-H precursors with different Al/Si ratios on C–S–H, and discusses the effects of the Al/Si ratio on C-A-S-H gel aggregation behavior and structural evolution at the C–S–H interface. The results show that increasing Al content significantly promotes the early hydration reaction rate of C-A-S-H gel, the degree of polymerization of silicate chains, and the amount of Qn(n ≥ 2) species. Moreover, higher Al content leads to the precursors aggregating among themselves rather than depositing on the C–S–H substrate surface. The incorporation of Al–O polyhedra can effectively bridge silicate chains on the C–S–H surface and alter the growth patterns of hydration products from linear chains to three-dimensional networks. This work provides molecular-level insights into the influences of the Al/Si ratio on the early hydration reaction process and interfacial deposition behaviors of C-A-S-H gel.

Effect of coarse calcareous aggregates on corrosion of steel reinforcement in marine concretes

Finely ground limestone, perhaps as part cement replacement, has been shown to reduce concrete permeability and enhance strength. Whether this holds also for coarse limestone aggregates is of both practical and environmental interest, particularly the effect on corrosion of steel reinforcement. This is confirmed herein with exposure tests over 14 years for a range of concretes exposed to a high chloride environment. Importantly, these concretes also showed delayed initiation of reinforcement corrosion and lower long-term corrosion losses compared with similar concretes made with coarse igneous or siliceous aggregates. The observations are attributed to enhanced bonding between cement-hydration products and the limestone aggregate surfaces. These findings are important both for reducing environmental impacts and greenhouse gasses and for extending the durability of reinforced concrete structures.

Effect of the Side-Chain Length in Polycarboxylic Superplasticizer on the Competition Adsorption in the Presence of Montmorillonite: A Density Functional Theory Study.

Polycarboxylic superplasticizers (PCEs) exhibit numerous advantages as concrete additives, effectively improving the stability and strength of concrete. However, competitive adsorption of PCEs occurs in the presence of clay, which may affect the cement dispersion and water-reducing performance. Extensive research has been conducted on the physical and mechanical properties of PCEs; however, the effect of the diverse structures of PCEs on the competitive adsorption on clay and cement hydration products has been rarely studied. This study employs Ca-montmorillonite (CaMMT) as a clay representative, by constructing adsorption models of PCEs on CaMMT and cement hydration products. A comparison of the adsorption energies considering different side-chain lengths of PCEs is included. Typically, the adsorption energy on CaMMT is lower than that on hydration products, leading PCEs to preferentially adsorb on the clay, thereby reducing its effective dosage in the cement particles. The challenge of PCE adsorption on CaMMT increases with the polymerization degree, and methylallyl polyoxyethylene ether (HPEG) exhibits lower adsorption energies on CaMMT. The density of states (DOS) analysis indicated the highest peak values of allyl polyethylene ether (APEG) as well as the peak area at n (polymerization degree) = 1. The total number of transferred electrons for APEG was 0.648, surpassing those of other PCEs. The interaction mechanism of PCEs with clay and hydration products is further elucidated through electronic gain/loss analysis, also providing a basis for the theoretical analysis on how to reduce the adsorption of PCEs on clay and the structural design of mud-resistant PCEs.

Durability Improvement of Pumice Lightweight Aggregate Concrete by Incorporating Modified Rubber Powder with Sodium Silicate.

To improve the durability of pumice lightweight aggregate concrete applied in cold and drought areas, sodium silicate-modified waste tire rubber powder is used to treat the pumice lightweight aggregate concrete. The pumice lightweight aggregate concrete studied is mainly used in river lining structures. It will be eroded by water flow and the impact of ice and other injuries, resulting in reduced durability, and the addition of modified rubber will reduce the damage. The durability, including mass loss rate and relative dynamic elastic modulus of pumice lightweight aggregate concrete with different sodium silicate dosages and rubber power particle sizes, is analyzed under freeze-thaw cycles, and the microstructure is further characterized by using microscopic test methods such as nuclear magnetic resonance tests, ultra-depth 3D microscope tests, and scanning electron microscopy tests. The results showed that the durability of pumice lightweight aggregate concrete is significantly improved by the addition of modified waste tire rubber powder, and the optimum durability is achieved when using 2 wt% sodium silicate modified rubber power with a particle size of 20, and then the mass loss rate decreased from 4.54% to 0.77% and the relative dynamic elastic modulus increased from 50.34% to 64.87% after 300 freeze-thaw cycles compared with other samples. The scanning electron microscopy test result showed that the surface of rubber power is cleaner after the modification of sodium silicate, so the bonding ability between rubber power and cement hydration products is improved, which further improved the durability of concrete under the freeze-thaw cycle. The results of the nuclear magnetic resonance test showed that the pore area increased with the number of freeze-thaw cycles, and the small pores gradually evolved into large pores. The effect of sodium silicate on the modification of rubber power with different particle sizes is different. After the treatment of 2 wt% sodium silicate, the relationship between the increased rate of pore area and the number of freezing-thawing cycles is 23.8/times for the pumice lightweight aggregate concrete containing rubber power with a particle size of 20 and 35.3/times for the pumice lightweight aggregate concrete containing a particle size of 80 rubber power, respectively.

Study on Mechanical Properties and Microscopic Mechanism of PVA-Modified Recycled Brick Aggregate Concrete

This paper addresses a range of environmental issues stemming from the improper disposal of construction waste and its low recycling rate by examining the effects and mechanisms of polyvinyl alcohol (PVA) solution in modifying recycled aggregates. Basic physical properties, energy-dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to study these effects and mechanisms. Tests on basic mechanical properties were performed to assess the impact of aggregate modification and the brick-concrete ratio on recycled brick-aggregate concrete’s mechanical characteristics. Nuclear magnetic resonance and microhardness tests were performed to analyze the influence exerted by PVA modification on the interfacial transition zone (ITZ), microstructure, and pore structure, thus exploring the connection between modified recycled-brick-aggregate concrete’s microstructure and its icromechanical properties. The findings show that the water absorption and crushing index of recycled aggregates (RA) immersed in a 10% PVA solution for 24 h decrease significantly, while the apparent density increases most notably. This phenomenon can be ascribed to the development of a PVA coating on the exterior of the reused aggregates. The optimal mechanical properties for recycled brick aggregate concrete (RAC) occur when the replacement rate is 30% and the brick-concrete ratio is 1:1. The compressive strength is 44.2 MPa, the bending strength is 15.6 MPa, and the splitting tensile strength is 3.85 MPa. Additionally, the modification with PVA results in a higher percentage of transition pores, while simultaneously reducing the percentage of macropores. There is an uptick in the frequency of harmless and less harmful pores, and a declining proportion of harmful and more harmful pores. The ITZ’s structural morphology in the RAC is effectively improved by the coating structure formed through the bonding of the polymer with cement hydration products, and PVA modification reduces the thickness of this zone.

Study on the Effect of Ultra-fine Limestone Powder on the Resistance of Cement-slag Powder System to Chloride Ion Permeability

The effect of different limestone powder fineness on the chloride ion migration coefficient of the cement paste was tested using the Rapid Chloride Migration (RCM) method. The changes in the phase composition and pore structure of the paste were studied using hydration kinetics analysis, XRD and pore structure analysis. The results showed that before the chloride ion erosion, the limestone powder mainly exhibited filling effect, microcrystalline nucleation effect, and chemical activity effect. It reacted with the hydration products of cement to form calcium aluminate carbonate, which improved the strength of the hardened paste. After chloride ion erosion, the diffraction peak of calcium aluminate carbonate weakened, and Friedel’s salt was formed. With the increase of the specific surface area of limestone powder, the chemical activity of the powder became more obvious, and the generation of Friedel’s salt increased, leading to stronger resistance to chloride ion penetration. Limestone powder can reduce the porosity of the hardened paste and optimize the pore structure. When the particle size of the powder increased from 800 to 5000 mesh, the total porosity of the hardened paste decreased from 20.7% to 14.7%, and the most probable pore size decreased from 450nm to 75nm. Limestone powder with a particle size larger than 1500 mesh can fully exert its activity and play a role in solidifying chloride ions, thus improving the resistance to chloride ion penetration of limestone powder cement-based materials.

Strength development and self-desiccation of saline cemented paste backfill.

Given that many mines around the world are located in areas where fresh water is scarce, and companies are being held to increasingly stringent sustainability and environmental responsibility standards, many mines are looking to use locally available saline groundwater or seawater as mixing water in cemented paste backfill (CPB). However, the impacts of this decision on key engineering properties of CPB (e.g. strength and self-desiccation) that affect its mechanical stability need to be better understood to allow confident selection of this practical and more sustainable solution. Thus, the effect of mixing water salinity and binder type on the strength (unconfined compressive strength, UCS) development and self-desiccation (measured by suction and volumetric water content) of CPB is explored in this research. NaCl concentrations from 0 to 300g/L were used in CPB made with silica tailings and Portland cement type I (PC). Concentrations of 10 and 35g/L were found to moderately increase UCS, while a concentration of 100g/L had comparable UCS to non-saline CPB and a concentration of 300g/L was found to significantly decrease UCS over all curing times. The overall trend is 10g/L > 35g/L > 0g/L > 100g/L > 300g/L. The UCS of the 60-day-old CPB with a NaCl of 300g/L is significantly lower, registering a 26% decrease compared to the UCS of the 60-day-old CPB without salt. In contrast, the UCS of the 60-day-old CPBs containing 10g/L and 35g/L of salt exhibits a notable improvement, being 15% and 10% higher, respectively, than the UCS of the 60-day-old CPB without salt. Water content and suction monitoring were conducted up to 28days of curing time, and it was found that suction only slightly contributed to UCS gain of the saline CPB, and high salt contents (100 and 300g/L) significantly inhibited the self-desiccation ability of CPB due to inhibition of cement hydration by the excessive amount of salt. The increase in strength of both saline and non-saline samples was attributed primarily to the increase in cement hydration products, while the increased strength of the samples with salinities of 10 and 35g/L was mainly attributed to the enhancement of the binder hydration due to the low amount of salt and the presence of Friedel's salt in the pores. The effect of PC replacement by 25 to 75% with slag on CPB with 35g/L mixing water salinity was also studied. Slag replacement of 50% and higher resulted in significantly higher UCS over most curing times. Suction likely moderately contributed to UCS of the saline CPB with slag, in addition to the presence of Friedel's salt in the pores and the acceleration of cement and slag hydration by the presence of NaCl.

Fabricating hydrophobic silica fume to improve mechanical strength and anti-corrosion of integral hydrophobic cement mortar and its carbon emission assessment

Integral hydrophobic concrete possesses superior waterproof performance and can prevent internal concrete and steel bar from erosive ions attacking in marine environment. However, the low mechanical strength limits its application. Silica fume (SF) and stearic acid (SA) were used to prepare hydrophobic SF by ball milling. Further, the prepared hydrophobic SF was added to cement mortar to fabricate integral hydrophobic cement mortar. Effects of hydrophobic SF on compressive strength, water resistance and anti-corrosion performance of integral hydrophobic cement mortar were investigated. Besides, the cement hydration products and morphology were analyzed after the addition of hydrophobic SF. The results showed the compressive strength of integral hydrophobic cement mortar reached 48.3 MPa. The contact angle of integral hydrophobic cement mortar surface arrived 151.5–152.7°. The capillary absorption coefficient also reduced by 93.06 %–93.67 % compared with the control group. Electrochemical test results showed the integral hydrophobic cement mortar provided a long-term protection for the embedded steel bar. The hydrophobicity and pozzolanic effect of the hydrophobic SF made cement mortar a high strength, good water resistance and corrosion resistance. Additionally, the global warming potential (GWP) of hydrophobic cement mortar was calculated based on life cycle assessment (LCA). It showed that the GWP and environmental impacts of hydrophobic cement mortar reduced.

Mechanical properties and microstructure of waterborne polyurethane-modified cement composites as concrete repair mortar

With the increase in service life, the durability of a large number of concrete structures deteriorates year by year under the influence of the external environment, requiring urgent repair and reinforcement. Ordinary cement concrete materials have disadvantages such as high brittleness, low tensile strength, poor bonding ability, and insufficient durability, making it difficult to meet the repair needs of high-quality building structures. Therefore, self-synthesized anion WPU was used to study its effect on the mechanical properties of cement-based repair mortar. The research found that waterborne polyurethane (WPU)-modified cementitious composite repair materials exhibit better bonding strength with old concrete substrates compared to traditional cement-based materials. Additionally, the incorporation of WPU significantly reduces the brittleness of the repair material, ensuring enhanced efficiency in the repair process. However, according to the hydration heat test results, the addition of WPU delays the hydration process of the composite repair materials. In addition, the addition of WPU enhances the flexibility and bonding ability of the materials, with flexural strength and tensile strength at the age of 28 days reaching 13 MPa and 6 MPa, respectively. Through stress‒strain curve analysis, it was found that the maximum strain amplification of WPU cement mortar can reach 134 %. Combined with SEM testing, it was observed that cured WPU films were present in specimens aged 28 days with P/C ratios of 10 % and 15 %. WPU and cement hydration products permeate each other, forming a three-dimensional polymer network structure, improving the pore structure, and fully exerting the flexibility of WPU. This also validates the experimental results of increased ultimate tensile strain. WPU cement-based composite repair materials have higher bonding strength at a high P/C ratio (15 %), and WPU alone, used as an interface agent for pretreating the interface of old concrete, can improve the interface bonding strength, up to twice that of the group without the surface agent.

MSWIFA and cement cooperate in the disposal of soft soil - experimental study on silty sand and silty clay.

Municipal solid waste incineration fly ash (MSWIFA) can be reused as a positive additive to strengthen soft soil. In this study, MSWIFA was initially used as a supplementary solidification material in combination with ordinary Portland cement to prepare fly ash cement-stabilized soil (FACS) with silty sand and silty clay, respectively. The ratio of MWSIFA to total mass was 5%, 10%, and 15%, and the cement content was set as 10% and 15%. The mechanical properties of FACS were evaluated by unconfined compressive strength test. The heavy metal-leaching test was conducted to estimate the environmental risk of FACS. The scanning electron microscope was used to test the micro-structure of FACS. The X-ray diffraction was performed to analyze material composition of FACS. The result indicates that the collaborative solidification of soft soil with MSWIFA and cement is feasible. Regarding the silty clay, the FA had positive effects on the silty clay in the service age (between 50 and 100% with 15% MSWIFA), as the MSWIFA reformulated the initial silty clay structure, resulting in interconnection and pore fill between particles. It can be founded that C-S-H and ettringite are the main products of MSWIFA and cement hydration, which are formed by the hydration of C3S and C2S. Regarding the silty sand, the MSWIFA decreased the peak strength (between 35 and 48% with 15% MSWIFA) but increased the ductility of the stabilized cement. Under the same mix proportions, the leaching toxicities of Zn and Pb in FACS of silty clay were obviously lower than were those of silty sand. Generally, the leaching concentrations of tested metals under all the mix proportions were well below the limit value set by GB 18598-2019 for hazardous waste landfill. Thus, the reuse of MSWIFA in cement-stabilized soil would be one of the effective methods in soft soil treatment and solid waste reduction.

Physico-chemical research of the processes of hydration of cements

The activating effect of phosphoanhydrite on cement hydration is strongly supported by the results obtained from various physico-chemical analyses, including IR spectroscopy, X-ray phase analysis, and differential thermal analysis. IR spectroscopy revealed significant differences in the hydration products of cement with and without phosphoanhydrite. The presence of phosphoanhydrite led to distinct absorption bands in the IR spectra, indicating a higher concentration of Portland cement hydrate compounds and calcium the activated cement. This observation suggests that hydrosilicates in phosphoanhydrite plays a vital role in promoting the formation of these hydration products, leading to enhanced cement activation.X-ray phase analysis further confirmed the activating effect of phosphoanhydrite. The diffraction patterns of the hydrated cements showed a remarkable increase in the analytical lines corresponding to Ca(OH)2 when phosphoanhydrite was present. This indicates a higher content of this phase in the activated cement, reinforcing the notion that phosphoanhydrite contributes to the accelerated hydration process.Differential thermal analysis provided additional evidence of the activating effect of phosphoanhydrite. The DTA curves exhibited higher hydration levels for the cement activated with phosphoanhydrite compared to the control cement. This was indicated by an increased percentage of bound water and a greater mass loss at 140°C, demonstrating the more extensive hydration of the activated cement.Taken these physico-chemical analyses consistently demonstrate the activating effect of phosphoanhydrite on cement hydration. The unique properties of phosphoanhydrite facilitate the formation of hydration products, such as Portland cement hydrate compounds and calcium hydrosilicates, leading to an accelerated and more efficient hydration process.

Understanding erosion resistance mechanisms of sodium aluminate silicate hydrate in erosion environments: a molecular dynamics study.

Sodium-aluminate-silicate-hydrate (NASH) gel, as the primary reaction product stimulated by alkali in silica-aluminum-rich minerals, influences the mechanical and durability properties of geopolymers. In erosion environments, NASH demonstrates superior compressive strength and erosion resistance compared to hydration products of ordinary Portland cement. However, the underlying erosion resistance mechanism of NASH under such conditions remains unclear. Therefore, this study employs molecular dynamics research methodology to investigate the alteration in performance and deterioration mechanism of NASH in erosive environments. The findings reveal that in Na2SO4 solution, the infiltration of H2O molecules and Na+ ions into the three-dimensional mesh structure of NASH results in slight expansion and reduced tensile strength. Although H2O intrusion induces hydrolysis of the three-dimensional skeleton, the adsorption sites within NASH possess the capability to capture externally introduced Na+ ions. During tensile loading, Na+ ions can interact with reactive oxygen species produced through stretching or H2O molecule-induced decomposition of the internal framework, facilitating the repair of fractured structures. Consequently, this process partially alleviates tensile rupture, modifies the fracture damage mode, enhances overall toughness, and improves resistance against sulfate attack.

Influences of Graphene Oxide on Mechanical Properties and Mesoscopic Deformation and Failure Process of Concrete

In this research, graphene oxide (GO) was integrated into concrete to assess its effectiveness as an additive. Triaxial compression permeability experiments, variable‐angle (30°, 45°, and 60°) shear experiments, and dynamic compression experiments were conducted on graphene oxide concrete (GOC) and normal concrete (NC). The Holmquist–Johnson–Cook model and LS‐DYNA software were utilized to simulate the mesoscopic failure of NC and GOC under impact loading. The mechanism of GO was examined through scanning electron microscope (SEM) microscopic scanning and energy dispersive spectroscopy (EDS) energy spectrum testing. The findings demonstrate that the contain of GO significantly enhances the destruction resistance of concrete under triaxial compression. The permeability of both NC and GOC exhibits a negative exponential decrease with increasing confining pressure, and carbon fiber reduces concrete permeability by 17.79%–60.9%. Compared to NC, the cohesion and internal friction angle of GOC increased by 7.80% and 8.55%, respectively. GO also improves energy conversion and storage capacity during the elastic stage of concrete, reducing inelastic energy loss during shear processes. Although, both NC and GOC exhibit strain rate sensitivity, the DIF value of GOC surpasses that of NC and the disparity between the two intensifies with increasing impact pressure. Simulation results indicate that the number of crushing units in GOC is significantly lower than in NC, maintaining integrity. Analysis of SEM microscopic test results reveals that the distribution of cement hydration products in NC is uniform, whereas in GOC, it displays regional characteristics, a phenomenon corroborated by EDS energy spectrum test results.

Formulation development of metakaolin geopolymer with good workability for strength improvement and shrinkage reduction

This study aims to optimize formulation and preparation of metakaolin based geopolymer for good workability, high compressive strength, and reduced drying shrinkage by considering alkaline activator composition, liquid to solid mass ratio, curing condition, and admixtures. The optimized geopolymer paste was further modified by granulated blast furnace steel slag (GBFS) and ordinary Portland cement (OPC) as calcium sources and carbon fibers as reinforcing additive for further strength improvement and shrinkage alleviation, in which the improvement mechanisms were manifested through mechanical strengths and microstructure observations. An optimized combination of modifiers and curing condition was obtained by Orthogonal Array Testing method. Experimental results indicate that sodium silicate is essential in the synthesis of alkali activator with nominal composition of Na2O·1.3SiO2·10.8H2O for strength development and cracking prevention. Good workability and high compressive strength of paste specimens could be attained by liquid to solid mass ratio of 1.21 between alkaline activator and metakaolin with ambient curing. The modified geopolymer pastes presented further improved compressive strength and reduced drying shrinkage. The microstructure images showed that the formation of cement hydration products, ettringite crystals, and more condensed matrix structure by using OPC as additive in geopolymer. The optimized geopolymer paste was made with 2% carbon fiber, 33% Portland cement and 10% GBFS and cured at ambient temperature achieved ultimate compressive strength of 73 MPa with reduced drying shrinkage. This ultimate compressive strength was 55% and 65% higher than non-modified geopolymer and ordinary Portland cement pastes, respectively, and was higher than 80% values in related studies.

A Short Review on Chondroitin Sulphate and Its Based Nanomaterials for Bone Repair and Bone Remodelling Applications

Joint damage is a major symptom of osteoarthritis, a degenerative disease that worsens over time. The purpose of this review was to assess the effectiveness and safety of nanomaterials as an alternative to the widely used methods. Due to its poor regenerative and self-healing properties, cartilage repair after lesions or debilitating disease is a major clinical issue. Here, we use the organometallic chemistry identity of chondroitin sulphate to repair cartilage lesions by creating a nano-elemental particle through electrostatic interactions. As an integral part of the extracellular matrix, chondroitin sulphate (CS) is shown to improve osteogenesis in this review. The injectability of hydrated cement products was greatly improved by the addition of CS, but there was no discernible change in their phase, morphology, apparent porosity, or compressive strength. This review article provides a thorough analysis of the results from the use of nanocomposites in orthopaedic drug delivery and bone remodelling engineering.

Recycle Option for Municipal Solid Waste Incineration Fly Ash (MSWIFA) as a Partial Replacement for Cement in Mortars Containing Calcium Sulfoaluminate Cement (CSA) and Portland Cement to Save the Environment and Natural Resources.

Reduction of emissions, energy consumption, and use of substitutes for natural resources is an element of sustainable development and the circular economy. Cement production is a process with a high carbon footprint; therefore, minimizing the use of this material has a significant impact on reducing environmental costs. A substitute for cement is municipal solid waste incineration fly ash (MSWIFA). The article presents a method of making an eco-concrete with the use of municipal solid waste incineration hazardous fly ash. The use of secondary waste for the production of building materials additionally contributes to achieving climate neutrality established by the European Union and China. The article analyzes the physicochemical properties of various MSWIFAs, the amount and leachability of heavy metals, and selected elements from MSWIFA and concrete properties. The technical properties of mortars containing MSWIFA were investigated. Consistency is not affected by MSWIFA content, although the workability time is prolonged. Air entraining admixture efficiency is lowered, but the effect lasts longer. The initial setting time is prolonged, and the flexural and compressive strengths are decreased in early terms because of the zinc presence in MSWIFA. MSWIFA does not influence the water demand, volume stability of mortars, or microstructure of cement's hydration products.

Preparation of cellulose fibre-sheets and its impact on pore connectivity of cement paste during early hydration

This study was aimed at evaluating the size and microstructure of cellulose fibres modified via ultrafine ball-milling methods and investigated the effects of these fibres on the rheological properties, compressive strength, hydration behaviour, and pore structure of cement paste in the early stage of hydration by scanning electron microscopy (SEM), isothermal calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TG), low-field nuclear magnetic resonance (LF NMR) and electrical resistivity. The results showed that the ultrafine ball-milling method with a velocity of 500 r/min effectively produced cellulose fibre-sheets (CFS) by rupturing intermolecular hydrogen bonds. And their microstructure was transformed from a “fibrous structure” to a “fibre-sheet structure”, which improved the rheological properties and early compressive strength of cement by bridging effect between the cement particles, hydration products, and CFS. Meanwhile, CFS provided more nucleation sites for hydration products accelerating the early hydration rate without changing the structure of hydration products. Compared to pure cement paste, the cumulative heat released from the CFS-cement paste with 0.3% CFS increased by 14%, reaching 113.34 J/g over 20 h. Besides, CFS altered hydration product distribution and increased product content, thus rapidly decreasing the pore connectivity of cement paste. Hydrating for 12 h, the cement paste containing 0.3% CFS had a reduction in pore connectivity from 0.25 to 0.07, which decreased by 72% in contrast with that of pure cement paste.