The high strength concrete has been extensively used in the past decades for several construction projects such as high-rise buildings, bridge construction, sports arenas etc. The prominent ...difference between strength concrete (HSC) and conventional concrete is the lower water-to-binder ratio, which imparts an overall better strength and durability to the concrete. However, certain undesirable characteristics, such as high shrinkage, high hydration heat, and early age cracking, can also be found in such concrete and therefore, require special consideration. The curing of high strength concrete therefore becomes an utmost important factor to minimise the effect of the aforementioned problems. This review article aims to outline the outcomes of various curing techniques and establish a systematic framework for evaluating their effect on high strength concrete. The curing methods for high strength concrete presented in the study include steam curing, oven curing, autoclave curing, dry curing, burlap curing, high and low temperature curing, vacuum curing and internal curing. The performance of the concrete depends on several factors and quantifying them simultaneously may not be feasible; however, summarising one of the major factors, i.e., curing, would provide valuable addition to the overall discussion.
•A detailed review of various curing techniques employed for high strength concrete is presented.•Merits and demerits of different curing methods are compared.•Effect of curing methods on strength and durability of high strength concrete are compared.•Proposed mathematical models for internal curing are discussed.
•E53/E20/BICP features a long shelf life of ∼40 days.•E53/E20/BICP can be cured rapidly within 35 min at 120°C.•E53/E20/BICP shows satisfactory flame retardancy and thermal stability.
This work ...reported a flame-retardant single-component epoxy resin via the integration of two bisphenol-A-type epoxy resins (E20 and E53) and benzimidazolyl-substituted cyclotriphosphazene (BICP). The differential scanning calorimetry (DSC) tests showed that the onset curing temperature of E53/E20/BICP was 30°C lower than that of E53/BICP due to the catalytic decomposition effect of E20 towards BICP under heating. Besides, the shelf life of E53/E20/BICP at room temperature reached ∼40 days, demonstrating good storage stability. E53/E20/BICP maintained satisfactory thermal properties and showed outstanding flame retardancy with a UL-94 V-0 classification. Compared with the unmodified EP sample, the peak heat release rate (PHRR) and total heat release (THR) of E53/E20/BICP were decreased by ∼64.1% and ∼39.0%, respectively. Hence, this flame-retardant single-component EP with satisfactory comprehensive properties exhibited great potential for versatile industrial applications.
Ultra-high-performance concrete (UHPC) is a distinguishing material used in new construction and conjunction with conventional concrete. However, some issues limit the wider application of UHPC, such ...as high autogenous shrinkage, low workability for large-volume production, high cost, and unpredictable peak curing method. This comprehensive study aims to clarify the different effects of curing methods on the strength development of normal concrete and UHPC. The present article reviews studies that used microwave curing, autoclave curing, carbon curing, steam curing, electric curing, ambient and air curing and water to determine their effect on compressive strength. All the curing methods achieved satisfactory values of compressive strength. However, it is not practical to specify the peak curing regimes for concrete or UHPC since the best results need critical monitoring of curing parameters. The time when the samples are demolded and subjected to hydrothermal and thermal treatments varies in the literature since it depends on the binder setting time. That time should be carefully selected to avoid adverse effects and to maximise output. A combination of these curing regimes could be used together or with pressure or heat to further improve the compressive strength. In addition to the type of materials used, the curing temperature and duration significantly affect the overall performance of concrete. This review is expected to guide future research and provide an overview of the research field.
Abstract Objectives To evaluate the effect of photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths. Methods Model ...resin-based composites were associated with diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) or camphorquinone (CQ) associated with 2-(dimethylamino) ethyl methacrylate (DMAEMA), ethyl 4-(dimethyamino) benzoate (EDMAB) or 4-( N , N -dimethylamino) phenethyl alcohol (DMPOH). A narrow (Smartlite, Dentisply) and a broad spectrum (Bluephase G2, Ivoclar Vivadent) LEDs were used for photo-activation (20 J/cm2 ). Fourier transform infrared spectroscopy (FT-IR) was used to evaluate the cure efficiency for each composite, and CIELab parameters to evaluated color stability (Δ E00 ) after aging. The UV–vis absorption spectrophotometric analysis of each photoinitiator and reducing agent was determined. Data were analyzed using two-way ANOVA and Tukey’s test for multiple comparisons ( α = 0.05). Results Higher cure efficiency was found for type-I photoinitiators photo-activated with a broad spectrum light, and for CQ-systems with a narrow band spectrum light, except when combined with an aliphatic amine (DMAEMA). Also, when combined with aromatic amines (EDMAB and DMPOH), similar cure efficiency with both wavelength LEDs was found. TPO had no cure efficiency when light-cured exclusively with a blue narrowband spectrum. CQ-systems presented higher color stability than type-I photoinitiators, especially when combined with DMPOH. Conclusions After aging, CQ-based composites became more yellow and BAPO and TPO lighter and less yellow. However, CQ-systems presented higher color stability than type-I photoinitiators, as BAPO- and TPO-, despite their higher cure efficiency when photo-activated with corresponding wavelength range. Clinical Significance Color matching is initially important, but color change over time will be one of the major reasons for replacing esthetic restorations; despite the less yellowing of these alternative photoinitiators, camphorquinone presented higher color stability.
UV‐curing of adhesive areas often requires planar light exposure. Users of UV‐light sources, e.g. deuterium lamps, often use liquid light guides or optical fiber bundles for that purpose, but had to ...accept drawbacks in either case previously. End‐fused fiber bundles now provide a component solution which opens the entire spectrum for UV‐curing.
•A review of recent advances on the effect of different curing regimes on properties of AAMs is presented.•Common curing regimes for AAMs include air, water, sealing, oven, and microwave ...curing.•Adopting suitable curing regime for AAMs depends on the type, content and concentration of activator and precursor.•No specific curing regime is found to address all the durability (e.g., shrinkage) issues of AAMs.
Alkali-activated materials (AAMs) refer to a group of alternative materials to ordinary Portland cement concrete with reduced environmental footprint. Despite several benefits of AAMs, due to certain shortcomings such as the variation in mechano-durability properties through the adaptation of different curing regimes, their use in large scale construction has been limited. This tendency, however, can be enhanced through the use of proper curing techniques adopted in accordance with the mixture’s overall materials' ratio and chemical composition. In this regard, the most commonly used curing regimes for AAMs are conducted in thermal or ambient temperature environments, adopted in the form of immersion of the AAMs in water, ambient and high humidity, sealing, oven and, more recently, microwave curing. In that respect, this article aims to review and discuss the recent advances in understanding and optimizing the mechanical, durability and microstructural properties of AAMs in different curing regimes. On this basis, sealing and microwave curing are found to be the most suitable curing regimes used in both one-part and two-part AAMs (especially for high calcium system). The favorable physico-mechanical and microstructural properties of AAMs can be attributed to the enhanced polymerization and avoidance of significant moisture loss in sealing and microwave curing. In contrast, instant immersion in water (water curing) and continued thermal curing is found to be the least favorable curing regime for AAMs due to the dilution of the activator and an increase in free-water within air-void pores, versus that of vaporizing microstructural water content, respectively. At the end, the challenges, solutions and recommendations for future studies on the curing regime of AAMs are provided to discuss the future potentials within this area of research.
This study investigated the influence of different curing conditions on the compressive strength (CS) of the different alkali activated concrete (AAC) specimens at the ages of 2, 28, and 90 days for ...the structural utilization and standardization process of AAC instead of OPC concrete. For this aim, 100% slag (S100), 75% slag and 25% fly ash (S75FA25), and 50% slag and 50% fly ash based (S50FA50) AAC specimens were produced. Based on the oven-curing (O), water-curing (W), and ambient-curing (A) methods, the influence of 2O for 2 days, 26A2O, 2O26A, 28A, 28W, 26W2O, and 2O26W for 28 days, and 88A2O, 2O88A, 90A, 88W2O, 2O88W, 90W for 90 days on the CS of the AAC were examined in details. In addition, the influence of delayed oven-curing conditions on CS development was also investigated. The results indicated that curing conditions significantly affected on the CS and the water-curing condition could provide a better CS for those of AAC at 90 days. Although, the oven-curing enhanced CS of the S100 specimens at initial ages (first oven-curing applied), delayed oven-curing (oven-curing applied later) was found significant for S75FA25 and S50FA50 specimens. The delayed oven-curing affected more on the CS of the AAC when fly ash content increased. The most of AAC specimens with oven-curing had significantly enhanced the CS at 28 days, but S50FA50 at the age of 90 days decreased. Different curing regimes were proposed for the superior compressive strength values for each AAC specimens at the ages of 28 and 90 days.
As an important thermosetting resin, epoxy resin (EP) is widely used in the field of composite materials. Long storage time, rapid curing and low viscosity of one‐component EP is ideal for preparing ...composite materials by vacuum assisted resin transfer molding (VARTM). For this sake, we developed and synthesized a new imidazole thermal latent curing agent, 4,7‐diimidazol‐2,1,3‐benzothiadiazole (BTD‐MZ2) with a yield of about 75%. The curing behavior, thermal stability and storage time of the prepared EP system was studied by differential scanning calorimeter (DSC), thermal gravimetric analyzer (TGA), modular compact rheometer (MCR), respectively. DSC results showed that EP/17.5 wt% BTD‐MZ2 had a good latent period at low temperature, and can rapidly cure EP when heated to 150°C. TGA results show that BTD‐MZ2 promoted the formation of carbon residue and the residual carbon rate of EP/17.5 wt% BTD‐MZ2 is as high as 37.9%. MCR results show that the storage time of EP/17.5 wt% BTD‐MZ2 at 60°C can reach 850 min. In addition, it could play a role of catalyst used as co‐curing agents with aromatic amines for EP. DSC test showed that the addition of 5 wt% BTD‐MZ2 reduced the activation energy of EP/4,4′‐diaminodiphenylmethane (DDM) and promoted the curing reaction.
This study aims to investigate the effects of further water curing on the compressive strength and microstructure of CO2-cured concrete. The results showed that concrete with a residual w/c ratio of ...0.25 showed the most rapid strength development rate upon further water curing due to hydration of uncarbonated cement particles. Thermogravimetric, IR-spectrophotometric and scanning electron microscope examinations indicated that further hydration of the cement particles could form C-S-H gel and ettringite crystals. The results showed that the calcite formed during the initial CO2 curing was consumed during the further hydration of C3A, and produced calcium monocarbonaluminate hydrate. Also, Ca(OH)2 was not detected due to its reaction with the formed silica gel. Mercury intrusion porosimetry test results indicated that the porosity and pore size of the CO2 cured mortar decreased further after water curing.
In this study, a CO2 curing process was adopted in order to promote rapid strength development of concrete blocks containing recycled aggregates. The influence of several factors associated with the ...curing conditions on the curing degree and compressive strength of the concrete blocks were investigated, including curing time, temperature, relative humidity, pressure and post-water curing after the pressurized CO2 curing (PCC) process. In addition a flow-through CO2 curing (FCC) method at ambient pressure was also used. The results of the PCC experiments showed that, considerable curing degree and compressive strength were attained during the first 2 h of CO2 curing, and a prolonged curing time yielded slower gains. The variations of temperature from 20 °C to 80 °C and relative humidity from 50% to 80% had limited impacts on PCC; but the effects of CO2 gas pressure on the curing degree and compressive strength were more pronounced. The post-water curing after pressurized CO2 curing allowed the concrete blocks to attain further strength gain but its effectiveness was inversely proportional to the CO2 curing degree already attained. The FCC experimental results indicated that although a lower curing degree and slower strength development at the early age were observed, after 24 h of curing duration, they were comparable to those obtained by the PCC method. To assess the thermal stability of the concrete blocks, the optimum CO2 curing regime was adopted for preparing the concrete blocks with recycled aggregates, and the CO2 cured specimens exhibited better fire resistance than the water-cured ones at 800 °C.
PDF
