Curing Ages Research Articles

Enhancing Sustainability in Unsaturated Polyester Resin: A Way to Use Biobased Curing Agents for Reduced Styrene Content and Improved Recyclability Properties

Enhancing Sustainability in Unsaturated Polyester Resin: A Way to Use Biobased Curing Agents for Reduced Styrene Content and Improved Recyclability Properties

Preparation, physicochemical analyses, and comparative evaluation studies of deep eutectic solvents (DES) from non-conventional precursor materials applied as catalytic curing agents for epoxy resin

Curing agents for epoxy resins play a significant role in initiating crosslinking reactions resulting in the hardened and durable material with enhanced properties as per end-user applications. The industrial world still lacks efficient, environmentally friendly, and cheap curing agents for epoxy resins. Here, we report the development of deep eutectic solvents (DESs) based on N, N’-Bis(2-aminoethyl)ethane-1,2-diamine (commonly known as triethylenetetramine, TETA) as hydrogen bond donor (HBD), and salicylic acid (SA) and choline chloride (CC) as hydrogen bond acceptor (HBA). The formulated DESs are suggested to be relatively safe, affordable, and eco-friendly and the active groups in the DESs are capable of initiating crosslinking reactions. The physical stability of the formulated deep eutectic solvents was examined by polarizing optical microscopic (POM) analysis, which confirmed the absence of any crystals or residues. The purity was ensured by 13C nmr spectroscopy. Additionally, supportive evidence for the hydrogen bond formation between the constituents was gained from the outcomes of FTIR, 1H nmr, and mass spectrometry. Deep depression in melting points was confirmed from DSC studies, and TGA suggested better thermal stability for DESs than its constituents. Density functional theory (DFT) at B3LYP6-31G* of Gaussian computational framework was applied to energetically optimize the isolated structure and determine the bond lengths in angstroms. The structural characteristics and nonbonding interactions of DESs were investigated by the same. In addition, the density and rheological characteristics were assessed for the ideal utilization of the formulated DESs as epoxy resin curing agents. The detailed comparative studies demonstrated the advantages of deep eutectic solvents over conventional curing agents. The efficacy of the formulations as a curing agent was primarily confirmed from FTIR analysis and the curing behavior was investigated by DSC studies.

Mitigating autogenous shrinkage of cement with carbon nanotube sponge

Autogenous shrinkage can be mitigated by the addition of superabsorbent polymer (SAP), however, typically at the cost of a significant strength loss. To overcome such dilemma, hydrophilic carbon nanotube sponge (H-CNTSP) was proposed in this study as a novel internal curing agent. Due to the high porosity and enriched hydrophilic functional groups, H-CNTSP can absorb pore solution at 72 g/g driven by the capillary force, which is 176%–620 % higher than the commercial SAPs. The autogenous shrinkage of cement can be reduced or mitigated with the addition of 0.05–0.2 wt% H-CNTSP due to the continuous water release after final setting. Interestingly, the compressive strength loss resulting from the addition of H-CNTSP can be greatly diminished and even be overcompensated by the formation of CNT/hydrate nanocomposite shell with a higher modulus. This study illustrates the great potential to optimize concrete performance through proper design of assembly structures with chemically functionalized nanomaterials.

EXPERIMENTAL INVESTIGATION OF THE DURABILITY PROPERTIES OF CONCRETE PRODUCED WITH METAKAOLIN AS PARTIAL REPLACEMENT OF CEMENT

The research investigates the durability properties of concrete produced with metakaolin (MTK) as partial replacement of cement. Cement was partially replaced by metakaolin at 5% to 30% at an interval of 5%. Physical properties of materials were tested. A 100 x 100 x 100mm cube was used for density, compressive strength, water absorption and abrasion resistant test, while, 100mm x 200mm cylinder was used for split tensile strength, at a mix ratio of 1:2:4 with 0.5 w/c ratio, and cured at 7, 14, 28, 56 and 90 days under different curing conditions. Result shows that the density of concrete increase as the curing ages of concrete increases. The highest compressive strength of concrete at 28days was at 0% control which achieved 28.2 N/mm2 and 27.6 N/mm2, while, 10% has the highest strength of 32.1 N/mm2 and 31.1 N/mm2 at 90 days for concrete cured in H2SO4 and MgSO4 respectively. 10% MTK concrete has reduce absorption capacity of 11.34, 11.17% and 6.57% in H2O, H2SO4 and MgSO4 respectively, as compared to that of control concrete, and has improve resistance to abrasion in aggressive environment. Chemicals significantly affect the strength of concrete. MgSO4 is more deleterious to concrete than H2SO4. In conclusion, metakaolin is a suitable pozzolana for use in the production of concrete, at lower volume of replacement will enhance the reduction of cement usage in concretes, thereby reducing the production cost and environmental pollution from exploration and production of cement. 10% MTK is the optimum percentage in concrete, therefore,...

Experimental Study on Consolidation Characteristics of Concentrated Full Tailings and Research on Pore Water Relief Methods of Piles

Surface harmless storage of concentrated full tailings (CFTs) involves the technology of adding a curing agent to the tailings slurry discharged from the thickener to realize the modification of the tailings and centralized storage of the tailings on the surface to realize the harmless treatment of the tailings. High water content of tailings is still the key technical problem that restricts the harmless storage of piles at present. Regarding the above problems, we implemented the consolidation test and numerical simulation of seepage-stress coupling consolidation of CFT, clarified the consolidation characteristics and parameters of CFT under different curing ages, and conducted a comparative analysis of pore water pressure in the whole cross-section of piles with different drainage schemes based on the results of the test. In addition, we also clarified the drainage effect of interlayer drainage on reducing the excess pore water pressure of piles and compared the simulation results of the pore water pressure of piles under different permeability coefficients. The results show that as the permeability coefficient of the concentrated tailings material decreases, the pore pressure accumulation inside piles under the same drainage scheme is more serious, and the length of time for consolidation and stabilization becomes longer. Therefore, it is recommended that the excess porous water pressure be relieved by means of increased drainage facilities under a small permeability coefficient.

Effect Of Quarry Dust On Mechanical Properties Of Rice Husk Ash-Based Concrete For Sustainable Environment

As the global population has continued to grow, the costs and environmental issues associated with traditional construction materials like cement and river sand have become increasingly problematic. This research aimed to explore an alternative and eco-friendly approach to traditional building materials. The researchers conducted an experimental program to assess the mechanical properties of the rice husk ash-based concrete at different curing ages 7, 14, 21, and 28 days. Following the mix design, the concrete was produced using water to binder ratio of 0.5. A series of experiments were conducted on both fresh and hardened states to investigate the impact of quarry dust on rice husk ash-based concrete. It was observed from the experimental results that when 40% of the quarry dust was used as a replacement for fine aggregates, the concrete exhibited the highest strength. After 28 days of curing, the compressive strength showed a 0.65% improvement, while the splitting tensile strength displayed a 1.77% enhancement compared to the reference mix. To ensure the reliability of the experimental findings, a statistical analysis was conducted. The study concluded that certain factors, such as quarry dust, curing duration, and rice husk ash, interacted synergistically to influence the compressive and splitting tensile strengths of the concrete. The researchers also proposed equations to predict these strengths based on the aforementioned parameters.

Evaluating the Potential of Vegetable Powders as Nitrite Replacements in Cured Pork Sausages: Effects of Different Processing Methods to Produce Chinese Cabbage and Radish Powders.

This study investigated the potential of Chinese cabbage and radish powders as natural sources of nitrite in ground pork sausages. Four vegetable powders from Chinese cabbage and radish, depending on the processing method, were prepared for evaluation: filtered Chinese cabbage juice powder (FCJP), crushed Chinese cabbage powder (CCP), filtered radish juice powder (FRJP), and crushed radish powder (CRP). Both FCJP and FRJP from filtered juice of Chinese cabbages and radishes had higher total soluble solids and water soluble index compared to CCP and CRP from crushed Chinese cabbages and radishes. Additionally, FRJP and CRP showed a higher nitrate content than CCP and FCJP. The evaluation of vegetable powders against products containing sodium nitrite (control) or commercial vegetable powder in ground pork sausages showed that the use of FRJP and CRP resulted in similar levels of CIE a* compared to the control, whereas those cured with FCJP or CCP resulted in lower CIE a* values. However, regardless of the type and processing method of vegetables, all sausages treated with vegetable powders were similar in terms of cured pigment, total pigment, curing efficiency, and lipid oxidation compared with the control. Although lower hardness was observed in sausages treated with FRJP, no other treatments affected textural attributes. These results indicate that FRJP and CRP have great potential as natural curing agents for replacing nitrite in cured sausages. The use of powders obtained from filtered juices may provide extended utility as vegetable-based curing methods for other meat products.

Optimization of Ratio and Hydration Mechanism of Titanium-Extracted Residual Slag-Based Filling Cementitious Materials

Using metallurgical solid waste Titanium-extracted Residual Slag (TRS) as mine-filling cementitious material is crucial to reduce the filling cost and promote the utilization of solid waste resources. In this paper, taking the strength of the backfill at different curing ages as the response target, the Design-expert mixing design was used to optimize the proportioning experiment of titanium-extracted residual slag, titanium gypsum, silicate cement, and total tailings, to analyze the interactions and influences of the materials on the strength of the backfill, and to analyze the hydration mechanism of the titanium-extracted residual slag-based filling cementitious materials under the optimal proportioning. The results show that: (1) the order of the sensitivity of each component to the strength of backfill is: composite activator > cement > titanium gypsum > titanium-extracted residual slag, and there are different degrees of interaction between them; (2) the optimal ratio of titanium-extracted residual slag-based filling cementitious materials is TRS:titanium gypsum:cement:composite activator = 55:25:17:3; (3) early strength formation of backfill is mainly related to its hydration products ettringite and C-S-H, the rapid nucleation and cross-growth of ettringite in the early stage forms an effective physical filling effect, which is the main reason for the formation of high early strength, and the later strength of backfill benefited from the continuous accumulation of C-S-H encapsulation and bonding, which further densified its internal structure; (4) the use of titanium-extracted residual slag-based filling cementitious materials contributes to safe, green, and economic mining.

Alternative Concepts for Extruded Power Cable Insulation: from Thermosets to Thermoplastics.

The most common type of insulation of extruded high-voltage power cables is composed of low-density polyethylene (LDPE), which must be crosslinked to adjust its thermomechanical properties. A major drawback is the need for hazardous curing agents and the release of harmful curing byproducts during cable production, while the thermoset nature complicates reprocessing of the insulation material. This perspective explores recent progress in the development of alternative concepts that allow to avoid byproducts through either click chemistry type curing of polyethylene-based copolymers or the use of polyolefin blends or copolymers, which entirely removes the need for crosslinking. Moreover, polypropylene-based thermoplastic formulations enable the design of insulation materials that can withstand higher cable operating temperatures and facilitate reprocessing by remelting once the cable reaches the end of its lifetime. Finally, polyethylene-based covalent and non-covalent adaptable networks are explored, which may allow to combine the advantages of thermoset and thermoplastic insulation materials in terms of thermomechanical properties and reprocessability.

Thioester-Based Latent Curing Agent for Thermally Conductive Epoxy Composites

Thioester-Based Latent Curing Agent for Thermally Conductive Epoxy Composites

Compressive performance and analytical modeling of early strength seawater sea sand engineered cementitious composites

Early strength seawater and sea sand engineered cementitious composites (ESSECC) are novel fiber-reinforced cementitious composites that exhibit strain-hardening behavior and a high early strength. The compressive properties of ESSECC with different polyvinyl alcohol (PVA) fiber content, carbon nanotubes (CNTs) content, and water–binder ratios were investigated at different curing ages in this study. Experimental evaluations were conducted to assess compressive strength, elastic modulus, Poisson's ratio, peak strain, energy dissipation capacity, toughness index, and stress-strain curves. The experimental results showed that early strength of ESSECC reached 58.0 %, 81.6 %, and 86.7 % of its 28-day compressive strength after 2 h, 3 days, and 7 days of curing, respectively. An increase in the PVA fiber volume fraction from 0 to 2 % resulted in a 32.8 % increase in average peak strain. Incorporating 0.15 % CNTs into ESSECC led to an average enhancement of compressive strength by 7.2 %. Based on these experimental results, an analytical model considering the effects of curing age and the addition of PVA fibers and CNTs was developed to describe the compressive stress–strain behavior of ESSECC. This model showed strong consistency with the experimental results.

Mechanical performance and structural application of a novel basalt‐fiber‐reinforced ultra‐high‐performance seawater‐sea‐sand concrete (UHPSSC) with basalt coarse aggregate

AbstractAs unlimited resources, seawater and sea sand (SS) could be used as alternatives for fresh water and river sand in concrete constructions in areas with limited resources, such as mega‐cities and islands. To further improve the material efficiency, SS have been used to fabricate the ultra‐high‐performance seawater‐sea‐sand concrete (UHPSSC) in the literature. This work proposes a new type of UHPSSC, which incorporates basalt fibers to enhance the tensile property and coarse aggregate (CA) to improve the modulus. To investigate the contributing factors to the mechanical performance, 12 mixes of different fiber lengths, fiber volumes, and CA contents were designed and tested under compression and flexure. To verify the validity of the proposed UHPSSC in structural elements, six beam specimens reinforced with basalt‐fiber‐reinforced polymer (BFRP) bars were designed and tested. The influence of the tensile properties of the proposed UHPSSC and BFRP flexural reinforcement designs was analyzed. This research shows that with a proper mix design, the proposed UHPSSC has a maximum compressive strength of 140 MPa, exceeding the benchmark strength of 120 MPa for ultra‐high‐performance concrete. With different mix designs, the compressive strength of the proposed UHPSSC varies from 101.5 to 140.5 MPa and the flexural strength varies from 10.8 to 15.4 MPa at 28 days. At different curing ages, the basalt fiber length and volume have more significant impacts on the flexural strength but have limited impact on the compressive strength. Although an optimal CA content of 400 kg/m3 was found for the compressive strength and the CA content could amplify the influences of the fiber length and volume on the flexural strength. With the flexural reinforcement ratio varying from 0.58% to 1.29%, the UHPSSC beam specimens failed with expected flexural failure and the ultimate capacities varying from 118 to 183 kN, showing a predictable manner. Improving the tensile strength of the proposed UHPSSC could effectively enhance the cracking load and expand the stiffness degradation phase.

Strength characteristics of self-compacting concrete with alkali-activated fly ash

The primary goal of this study is to examine the impact of sodium hydroxide (NaOH)/alkali-activated fly ash on the fresh properties and mechanical properties of self-compacting concrete (SCC). The fresh properties, known as the workability of SCC characteristics, were determined using the U-box, V-funnel, J-ring, and L-box tests. The M30 grade SCC containing superplasticizer of 0.86 wt. % of cement is replaced with 10%, 15%, 20%, 25%, 30%, and 40% of alkali-activated fly ash. On days 7, 14, and 28 after curing, the compressive strength and the splitting tensile strength of the SCC were examined. The study was further extended to evaluate the behavior of reinforced concrete beams containing fly ash and ground granulated blast furnace slag, whose size was 1200 × 100 × 150 mm3, under flexure loading. Based on the test results, it was found that the increase in the replacement of cement with alkali-activated fly ash increased the workability in the SCC. With the addition of superplasticizers, the SCC gained much more workability than conventional concrete containing no superplasticizer. The mechanical properties of 10% and 15% activated fly ash in Portland cement provided the maximum strength for the SCC at different ages of curing. The maximum first crack load and maximum ultimate flexure loading of the reinforced concrete beam containing 10% activated fly ash by weight of cement were greater than those of the control concrete beam. The microstructural scanning electron microscope observations confirmed that the alkali-activated fly ash increased the strength properties of the self-compacting concrete.

Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement (RMC) method for dredged sludge stabilization using the urea pre-hydrolysis strategy. Based on unconfined compression strength (UCS), pickling-drainage, and scanning electron microscopy (SEM) tests, the effects of pre-hydrolysis duration (T), urease activity (UA) and curing age (CA) on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed. The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80% high water content. A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing, which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples. Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield, but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates (HMCs), which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples. The optimum formula was determined to be the case of T = 24 h and UA = 10 U/mL for dredged sludge stabilization. A 7-day CA was enough for bio-carbonized samples to obtain stable strength, albeit slightly affected by UA. The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization. This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil, such as dredged sludge.

Effect of early damage on the mechanical properties, localized deformation and damage failure of cemented tailings backfill

To investigate the effect of early damage on the mechanical properties of cemented tailings backfill (CTB) in the later stage, different degrees of stress damage were applied to CTB at different curing age. Unconfined compressive strength (UCS) and ultrasonic testing were conducted on CTB. The acoustic emission (AE) and digital speckle correlation methods were used to analyze the AE response characteristics and localized deformation patterns of CTB. The results show that when the damage age (DA) is short and the damage degree (DD) is low, a smaller compressive stress can improve the internal density of CTB and enhance its UCS and wave velocity. A high compressive stress has a deteriorating effect on the UCS and wave velocity of CTB. When DA is 14 d, the amount of hydration products generated inside the CTB has decreased, and it is not enough to fill the cracks caused by stress damage, reducing the UCS and wave velocity of the CTB. An increase in DD can enhance the elastic modulus of CTB at various curing age. As DD increases, the failure mode of CTB transitions from shear failure to splitting tensile failure and then to composite failure via shear and splitting tensile failure. The AE counts and energy peak values of CTB increase continuously with increasing DD. When the DD is 40%, 60%, or 80%, there is a significant sudden increase in the AE count and energy near the peak stress point, which can be used as a precursor to CTB instability and failure.

Nonlinear stress growth and failure characteristics of gangue-cemented backfill

The stability of a filling body is the main control index of the filling effect, which is significantly affected by the strength and damage characteristics, and its stress increases nonlinearly with damage evolution. In this study, the uniaxial compression test and digital image correlation (DIC) method were used to investigate the stress and damage characteristics of a gangue-cemented backfill, and the stress–strain characteristics and crack propagation laws of the backfill under different curing ages were analyzed. A modified damage model of the gangue-cemented backfill based on the Weibull distribution characteristics of the microelement damage of the backfill and pore closure characteristics in the compression stage was constructed. Through numerical simulations, the nonlinear growth characteristics of stress in the specimen were revealed from the perspective of energy dissipation. The results showed that the nonlinear increase in stress originated mainly from pore closure and crack extension. The crack propagation in the backfill was divided into intermediate crack budding and symmetric crack propagation at the corners. The key signs of the peak stress and fracture of the specimen are the connection of the surface cracks and fracture surfaces on both sides. The proposed modified damage model was proven to be in relatively close agreement with the experimental results. The stress growth in the backfill exhibited a nonlinear-linear-nonlinear growth pattern before the peak stress. This study provides a theoretical basis for studying the strength characteristics and damage evolution of backfill, which is important for optimizing the material proportions and analyzing the stability of the quarry and other aspects.

Enhancing Cement Paste Properties with Biochar: Mechanical and Rheological Insights

Biochar, the solid sub-product of biomass pyrolysis, is widely considered an effective water retention material thanks to its porous microstructure and high specific surface area. This study investigates the possibility of improving both mechanical and rheological properties of cement pastes on a micro-scale. The results show that using biochar as a reinforcement at low percentages (1% to 5% by weight of cement) results in an increase in compressive strength of 13% and the flexural strength of 30%. A high fracture energy was demonstrated by the tortuous crack path of the sample at an early age of curing. A preliminary study on the rheological properties has indicated that the yield stress value is in line with that of self-compacting concrete.

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.

Influence of Accelerators on Cement Mortars Using Fluid Catalytic Cracking Catalyst Residue (FCC): Enhanced Mechanical Properties at Early Curing Ages.

Supplementary cementitious materials (SCMs) have been used in the construction industry to mainly reduce the greenhouse gas emissions associated with Portland cement. Of SCMs, the petrochemical industry waste known as fluid catalytic cracking catalyst residue (FCC) is recognized for its high reactivity. Nevertheless, the binders produced using SCMs usually present low mechanical strength at early curing ages. This study aims to assess the effect of different accelerating additives (KOH, sodium silicate SIL, commercial additive SKR) on the mechanical strength of mortars containing FCC. The results show that after only 8 curing hours, the compressive strength gain of the FCC mortars containing SKR was over 100% compared to the FCC mortar with no additive (26.0 vs. 12.8 MPa). Comparing the compressive strength of FCC mortar containing SKR to the control mortar, the enhancement is spetacular (6.85 vs. 26.03 MPa). The effectiveness of the tested accelerators at 8-24 curing hours was KOH ≈ SIL < SKR, whereas it was KOH < SIL < SKR for 48 h-28 days. The thermogravimetric data confirmed the good compatibility of FCC and the commercial accelerator.

Aggregate Type and Concrete Age Effects on Anchor Breakout Performance: Large Database and Insights

This contribution summarizes the largest available literature data collection on tensile and shear loaded anchor tests, obtained in two independent studies and performed by two different research groups. It was the objective of the two studies to investigate a possible effect that petrographically different coarse aggregate types may have on the tensile and shear load capacity for concrete breakout failure modes. In total, seven normal-strength and four high-strength concretes were tested at two different ages. Structural tests were performed on cast-in (tensile and shear tests) and post-installed adhesive anchors (shear tests). Parallel to the structural tests, each concrete was characterized in terms of compressive and tensile strength. Finally, the combined experimental data offer novel insights into the predictive quality of available design models for concrete cone capacity in tension and edge breakout in shear with respect to a potential aggregate effect. Systematic analyses indicate only minor aggregate effects after normalization by compressive strength (less than 7% difference between normalized values). However, the study reveals potential curing and concrete age effects where a 9% increase in predicted values is shown when concrete cures longer. The predictive equations remain conservative in comparison to all the investigated properties and their validity is shown in this study.