The influence of curing temperature on the strength development of cement-stabilized mud has been well documented in terms of strength-increase rate and ultimate strength.However,the strength development model is not ...The influence of curing temperature on the strength development of cement-stabilized mud has been well documented in terms of strength-increase rate and ultimate strength.However,the strength development model is not mature for the extremely early stages.In addition,there is a lack of studies on quality control methods based on early-stage strength development.This paper presents a strength model for cement-stabilized mud to address these gaps,considering various curing temperatures and early-stage behaviors.In this study,a series of laboratory experiments was conducted on two types of muds treated with Portland blast furnace cement and ordinary Portland cement under four different temperatures.The results indicate that elevated temperatures expedite strength development and lead to higher long-term strength.The proposed model,which combines a three-step conversion process and a hyperbolic model at the reference temperature,enables accurate estimate of the strength development for cement-treated mud with any proportions cured under various temperatures.With this model,a practical early quality control method is introduced for applying cement-stabilized mud in field projects.The back-analysis parameters obtained from a 36-h investigation at temperature of 60C demonstrated a sufficient accuracy in predicting strength levels in practical applications.展开更多
A specially developed ultrasonic measurement apparatus (UMA) was used to in situ monitor the setting process of fly ash blended cement paste. Combined with the results of Vicat Needle tests, isothermal calorimetric me...A specially developed ultrasonic measurement apparatus (UMA) was used to in situ monitor the setting process of fly ash blended cement paste. Combined with the results of Vicat Needle tests, isothermal calorimetric measurement, XRD analysis, SEM morphology and compressive test, the influence of curing temperature (20, 40, 60, and 90 ℃) and fly ash content (0,10%, 20% and 30%) on the setting and hydration process of fly ash blended cement paste was analyzed. The results show that setting and hardening process of fly ash blended cement paste at elevated temperature can be clearly identified into three stages including dormant stage, acceleration stage and deceleration stage. The increasing of curing temperature greatly accelerates the setting and hardening process. However, the content of fly ash does not have significant effect on the setting in condition of 90 ℃. Besides, the initial and final setting time of cement paste is correspondent with the time of duration of dormant stage and the time of UPV value is 1500 m/s (T1500), respectively. Thus, the UMA can be used to determine the initial and final setting time of cementitious material under different curing temperatures. The compressive test results indicate that the paste with 20% fly ash presents higher compressive strength than the plain paste at curing temperatures of 90 ℃. Therefore, appropriate amount of fly ash is beneficial for concrete in the high temperature curing conditions.展开更多
Three different curing temperatures（20 ℃, 40 ℃, and 60 ℃） were set, so that the nonevaporable water（w_n） contents of plain cement pastes cured at these three temperatures were measured to determine the hydratio...Three different curing temperatures（20 ℃, 40 ℃, and 60 ℃） were set, so that the nonevaporable water（w_n） contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree（w_n=15%） or high hydration degree（w_n=16.5%）, elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore（〉100 nm） volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste＇s compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.展开更多
The behaviors of concrete at elevated curing temperature were studied. The test results show that when concrete is cured at elevated temperature, a harmful consequence occurs.The later strength decreases significantly...The behaviors of concrete at elevated curing temperature were studied. The test results show that when concrete is cured at elevated temperature, a harmful consequence occurs.The later strength decreases significantly compared to that under normal curing condition. Incorporating silica fume, fly ash and slag or lowering w/c ratio can effectively alleviate this harmful consequence. Comparatively, incorporation of silica fume is the most efficient means to decrease the later strength reduction. The harmful consequence is not caused by the difference in degree of hydration since the degree of hydration is similar between elevated curing temperature and normal curing condition. The SEM analysis shows that it is the uneven distribution of hydration products caused by elevated curing temperature that leads to the later strength reduction of concrete.展开更多
In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respecti...In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.展开更多
The morphologies and hydration properties of MgO expansive material at different curing temperatures were investigated.When the curing temperature varies from 25℃to 50℃,the conductivity of MgO rises from 40 to 80μs...The morphologies and hydration properties of MgO expansive material at different curing temperatures were investigated.When the curing temperature varies from 25℃to 50℃,the conductivity of MgO rises from 40 to 80μs/cm,the hydration product of MgO expansive material curing in water for 28 days is from 1.5—2 mm to 2—2.5μm in length through SEM observation,and the expansion of pastes with 5%of the magnesium oxide is from 0.36%up to 1.01%,it is increased by 2.78 times.When the content of cement paste increases to 95%and cured in water for 90 days,the brucite forms as hexaflaggy?shaped crystal,which is less than 0.1μm and tends to aggregates.The effect of curing temperature on the hydration of MgO expansive material is obvious.展开更多
To further strengthen the protective effect of aerogel cement paste (ACP) coating on self-compacting concrete (SCC) in tunnel fire under the optimal mix proportion,the effect of curing temperature (from 5 to 80 ℃,bas...To further strengthen the protective effect of aerogel cement paste (ACP) coating on self-compacting concrete (SCC) in tunnel fire under the optimal mix proportion,the effect of curing temperature (from 5 to 80 ℃,based on site construction curing temperature and surrounding rock temperature) on fire insulation of ACP was investigated.The mechanical properties,thermal conductivity and porosity of ACP were tested.The microstructure of ACP was characterized by means of SEM,XRD and TG/DTG.The results reveal that 50 ℃ is the optimal curing temperature for ACP with good mechanical properties and fire insulation.Relatively high curing temperature can facilitate hydration and pozzolanic reactions,contributing to the generation of more stable substances (such as C-S-H gels,tobermorite and thenardite,etc).ACP under excessive low curing temperature brings inhomogeneous microstructure with coarse pores,leading to producing wider and longer microcracks when it is exposed to tunnel fire.The microcracks make the heat convection and thermal radiation more significant and thus accelerate the damage of ACP under fire.In case of the less than 7% difference of thermal conductivity,dense microstructure and stable substances are more conducive to strengthening fire insulation of ACP.In practical engineering applications,the thickness of protective layer of ACP can be further optimized when ACP is cured under about 50 ℃.展开更多
Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The ...Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.展开更多
Online monitoring of the curing temperature field is essential to improving the quality and efficiency of the manufacturing process of composite parts.Traditional embedded sensor-based technologies have difficulty mon...Online monitoring of the curing temperature field is essential to improving the quality and efficiency of the manufacturing process of composite parts.Traditional embedded sensor-based technologies have difficulty monitoring the full temperature field or have to introduce heterogeneous items that could have an undesired impact on the part.In this paper,a non-contact,full-field monitoring method based on deep learning that predicts the internal temperature field of composite parts in real time using surface temperature measurements of auxiliary materials is proposed.Using the proposed method,an average temperature monitoring accuracy of 97%is achieved in various heating patterns.In addition,this method also demonstrates satisfying feasibility when a stronger thermal barrier covers the part.This method was experimentally validated during the self-resistance electric heating process,in which the monitoring accuracy reached 93.1%.This method can potentially be applied to automated manufacturing and process control in the composites industry.展开更多
The effects of curing temperature on the expansive effectiveness, strength, hydration degree, and microstructure of shrinkagecompensated binder were studied. The results showed that under the standard curing temperatu...The effects of curing temperature on the expansive effectiveness, strength, hydration degree, and microstructure of shrinkagecompensated binder were studied. The results showed that under the standard curing temperature (20℃), most crystalline ettringite grows in pores, which makes less contribution to the expansion of paste than gelatinous ettringite blended with C-S-H gel. An elevated curing temperature (40℃) promotes the hydration rate of expansive agent and cement. However, quickly developing strength of paste limits its expansion. The pore structure of hardened paste under moderate curing condition is the densest one among all the pastes cured at different temperatures due to the filling effect of crystalline and gelatinous ettringite. Under a high curing temperature (60℃), the formation of massive stick-like ettringite leads to excessive expansion at early hydration age. Some ettringite decomposes at sustainable high temperature, which decreases the restricted expansion rate of paste at a late age. Appropriate volume expansion is benefit to the improvement of pore structure of hardened paste by reducing large pores.展开更多
The effect of curing regime on the distribution ofAl3＋ coordination in hardened cement pastes within 28 d were investigated by 29Si and 27Al magic angle spinning （MAS） nuclear magnetic resonance（NMR） with deconvo...The effect of curing regime on the distribution ofAl3＋ coordination in hardened cement pastes within 28 d were investigated by 29Si and 27Al magic angle spinning （MAS） nuclear magnetic resonance（NMR） with deconvolution technique. The results indicate that the tetrahedral coordination Al3＋ incorporated in C-S-H structure mainly originate from the AP＋ incorporated in the alite and belite phases in the Portland cement. The curing regime of constant temperature of 20 ℃ is beneficial to the octahedral coordination Al3＋ transforming to tetrahedral coordination AP＋ incorporated in C-S-H structure. However, at curing regime of variable temperature, the temperature rising process is more advantageous to the transformation from ettringite to monosulphate, substitution of Al3＋ for Si4＋ in the C-S-H structure and the formation of the third aluminate hydrate （TAH） than that at constant temperature of 20 ℃. The high temperature of 60 ℃ in the holding temperature process promotes the decomposition of ettringite, and enhances the consumption of the Al3＋ incorporated in C-S-H phases and the Al3＋ in TAH for the monosulphate forming. The temperature decreasing promotes the transformation from monosulphate to ettringite, and increases the consumption of the Al3＋ incorporated in C-S-H phases, and then increases the quantity of the TAH.展开更多
The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of 29Si with magic angle spinning （MAS）...The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of 29Si with magic angle spinning （MAS） nuclear magnetic resonance （NMR） and by analyzing the 29Si NMR spectra with deconvolution technique. The experimental results indicate that, at curing regime of constant temperature of 20℃, the polymerization of C-S-H increases and then decreases with curing age, and the A1/Si ratio increases gradually with curing age, furthermore, the two non-bridging oxygen bonds of bridging silicate tetrahedra in C-S-H structure mainly bond to H＋. At curing regime of variable temperature, the polymerization of C-S-H firstly increases then changes slightly and subsequently decreases with the temperature from low to high and then to low, and the A1/Si ratio firstly increases then keeps invariant and subsequently slightly decreases. Moreover, the temperature decreasing is advantageous for the Ca2＋ to be bonded to the bridging silicate tetrahedra and entering into the interlayer of C-S-H structure. The polymerization of C-S-H at curing regime of variable temperature is higher than that cured at constant temperature, but the curing regime of constant temperature is more beneficial to the substitution of AP for Si4＋ than that of variable temperature.展开更多
In order to lower the imidization temperature of polyamic acids（PAA）, the catalytic activities of the curing agents p-hydroxybenzoic acid（PHA）, quinoline（QL）, benzimidazole（BI）, benzotriazole（BTA）, triethyla...In order to lower the imidization temperature of polyamic acids（PAA）, the catalytic activities of the curing agents p-hydroxybenzoic acid（PHA）, quinoline（QL）, benzimidazole（BI）, benzotriazole（BTA）, triethylamine（Et_3N） and 1, 8-diazabicyclo [5.4.0]undec-7-ene（DBU） were investigated in the process of thermal imidization of PAA. In addition, the effect of these various curing agents on the thermal stabilities and mechanical properties of the resultant polyimide（PI） films was determined. Quinoline was found to be an effective curing accelerator in the use of two-step method for synthesizing PI. Due to its moderate base strength, low steric crowding effect and moderate boiling point, quinoline could not only accelerate PAA to achieve imidization completely at 180 ℃, but also maintain the mechanical properties and thermal stability of the ordinary PI film. Any residual quinoline could be removed from PI films by heating at 250 ℃ for 4 h.展开更多
This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaC...This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaCO3 as a stabilizer,and straw(for strengthening).The availability of raw materials for making Adobe presents the waste-stabilized Adobe as a potential product for a new alkali-activated binder.Waste-stabilized Adobe collected from an abandoned damaged building in the village of Inonu in Northern Cyprus,ground and calcined at the following temperatures:450,550,650,750,850,and 950℃.The calcination at each temperature was held for different durations 1,3,5,and 7 h.Raw and calcined waste stabilized Adobe structures were investigated using XRF,TGA-DTA,XRD,FTIR,and SEM.Considering technical and environmental views related to energy consumption,waste stabilized Adobe calcined at 750℃ for 1 h presented the most promising results regarding the production of a new precursor for alkali-activated binder.This study also presents the effect of ground granulated blast furnace slag(GGBFS)usage on the fresh and hardened properties of optimum calcined AB-based alkali-activated pastes cured at room temperature.GGBFS was used to partially replace AB to form a binary composite raw material system and seven experimental groups were designed according to replacement levels of 0%,5%,10%,15%,20%,25%and 30%(by mass).Alkali-activated high volume waste-stabilized Adobe-slag pastes prepared using Na2SiO3-to-NaOH ratio of 2 and 12 M concentration of Sodium Hydroxide.The fresh property as flowability and the hardened property as the compressive strength of the alkali-activated pastes with different GGBFS contents were investigated.The results indicated that the incorporation of GGBFS increased the flowability of fresh alkali-activated pastes.A 28-day compressive strength of 43.75 MPa can be obtained by a 30%replacement level of GGBFS.展开更多
Extensive researches have been carried out on the conventional sulfate attack, while it has been found that the thaumasite form of sulfate attack（TSA）, sulfate attack at low temperature, has just been discovered and...Extensive researches have been carried out on the conventional sulfate attack, while it has been found that the thaumasite form of sulfate attack（TSA）, sulfate attack at low temperature, has just been discovered and its mechanism is not well understood so far. In this study, the sulfate attack of cement paste incorporating 30% mass of limestone powder was investigated. After 20 ℃ water cured for 7, 14, and 28 days,respectively, 20 mm cube specimens were exposed in a 5% magnesium sulfate solution at（6 ±1） ℃ for periods up to 240 days. Their appearance change, compressive strength development were examined at different storage time, and selected paste samples were examined by X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results indicate that all Portland-limstone cement pastes suffer from appearance deterioration to some extent. The compressive strength of cement paste initially increases and after 120 days decreases with increasing exposed period. In addition, the cement paste with short curing time is more susceptible to sulfate attack, which directly leads to the formation of non-binder thaumasite crystal accompanied by the formation of ettringite, gypsum and brucite, and becomes a white, mushy, and incohesive matrix. Additionally, the extent of sulfate attack is greater and the formation of thaumasite is observed earlier for shorter curing time.展开更多
Superhydrophobic materials are severely limited in their applications due to their weak mechanical properties and complex preparation process.In this paper,polystyrene/fluorinated silica(PS/SiO_(2))superhydrophobic co...Superhydrophobic materials are severely limited in their applications due to their weak mechanical properties and complex preparation process.In this paper,polystyrene/fluorinated silica(PS/SiO_(2))superhydrophobic composite coatings were prepared on the surface of 304 stainless steel using a simple one-step spraying method.The effects of different PS contents on the wettability as well as the wear properties of the samples were investigated.SiO_(2) was encapsulated in polystyrene to form a structure similar to cement encapsulated stones.With the addition of PS,a mound-like structure was formed on the sample surface,and a more optimized micro–nano structure was obtained when the content of PS was 0.6 g.At this time,the sample exhibited excellent wettability with a contact angle of 157.86°and a sliding angle of 0.84°.In addition,the contact angle of 151.09°was achieved after 180 cm of friction under a 100 g load and the composite coating prepared by this method also has excellent chemical stability,water impact resistance,corrosion resistance,and self-cleaning properties.This opens up new possibilities for the development of simple and robust superhydrophobic materials.展开更多
Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for ...Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for microsilica-gel bonded no-cement castable systems to control flow properties and setting characteristics.Three mixing and curing temperatures were applied：5℃,20℃and 35℃.The results show that setting-behaviour and mechanical properties strongly vary with the type of dispersant and the curing temperature.However,both setting and strength are less temperature dependent in the castables with Siox X-Zero.Furthermore,the drying and firing of microsilica-gel bonded NCCs were investigated.Since microsilica-gel bond system contains only a small amount of bound water,the castables can be fired at very high heating rates,once the free water has been removed.展开更多
This study has been conducted to evaluate the application of silver nanoparticles(NPs)in Electrically Conductive Adhesives(ECAs),filled with hybrid silver flakes and NPs,and silver flakes as a control sample,at a fill...This study has been conducted to evaluate the application of silver nanoparticles(NPs)in Electrically Conductive Adhesives(ECAs),filled with hybrid silver flakes and NPs,and silver flakes as a control sample,at a filler loading of 78 wt.%,83 wt.%and 88 wt.%and cured at 150℃and 180℃,respectively.The results show that the electrical and thermal conductivities of ECAs were improved with the increasing of filler loading and curing temperature.Adding silver NPs in silver flakes negatively affected the electrical and thermal conductivities of ECAs at a low filler mass fraction of 78 wt.%,because the segregation of NPs enlarged the average distance of silver flakes;while it positively influenced the electrical and thermal conductivities of ECAs at a loading ratio of 88 wt.%,probably due to NPs filling in the gaps between silver flakes or even sintering together with each other or with silver flakes,especially when curing at high temperature of 180℃.展开更多
The fly ash based geopolymer has emerged as a capable and sustainable binder material in construction industry.Ultrasonic pulse velocity(UPV)method is a non-destructive technique for investigating the mechanical perfo...The fly ash based geopolymer has emerged as a capable and sustainable binder material in construction industry.Ultrasonic pulse velocity(UPV)method is a non-destructive technique for investigating the mechanical performance of concrete.Experimental investigation was performed for studying the effect of NaOH Molarity,Na2SiO3/NaOH and curing temperature on the ultrasonic pulse velocity of geopolymer mortar.Experiments were designed based on central composite design(CCD)technique of response surface methodology(RSM).Statistical model was developed and statistically validated and found significant as the difference between adjustable R-squared and predicted R-squared less than 0.2.Finally,the optimized mix proportion was assessed for maximized value of UPV.Experimental validation on the optimized mix reveals the close agreement between experimental and predicted values of UPV with significance level of more than 95%.The proposed technique improves the yield,the reliability of the product and the processes.展开更多
基金supported by funding from the National Natural Science Foundation of China (Grant Nos.51978303 and 52208367)the Fundamental Research Funds for the Central Universities (Grant No.2042023kfyq03).
文摘The influence of curing temperature on the strength development of cement-stabilized mud has been well documented in terms of strength-increase rate and ultimate strength.However,the strength development model is not mature for the extremely early stages.In addition,there is a lack of studies on quality control methods based on early-stage strength development.This paper presents a strength model for cement-stabilized mud to address these gaps,considering various curing temperatures and early-stage behaviors.In this study,a series of laboratory experiments was conducted on two types of muds treated with Portland blast furnace cement and ordinary Portland cement under four different temperatures.The results indicate that elevated temperatures expedite strength development and lead to higher long-term strength.The proposed model,which combines a three-step conversion process and a hyperbolic model at the reference temperature,enables accurate estimate of the strength development for cement-treated mud with any proportions cured under various temperatures.With this model,a practical early quality control method is introduced for applying cement-stabilized mud in field projects.The back-analysis parameters obtained from a 36-h investigation at temperature of 60C demonstrated a sufficient accuracy in predicting strength levels in practical applications.
基金Funded by the National Natural Science Foundation of China (Nos.51678309,51978339)973 Program (No.2015CB655102)+4 种基金Natural Science Foundation of Jiangsu Province of China (No.BK20161529)China Postdoctoral Science Foundation (No.2016M600351)Jiangsu Province Postdoctoral Science Foundation (No.1601028B)State Key Laboratory of Silicate Materials for Architectures (Wuhan University of Technology)Priority Academic Program Development Jiangsu Higher Education Institutions (PDPA)
文摘A specially developed ultrasonic measurement apparatus (UMA) was used to in situ monitor the setting process of fly ash blended cement paste. Combined with the results of Vicat Needle tests, isothermal calorimetric measurement, XRD analysis, SEM morphology and compressive test, the influence of curing temperature (20, 40, 60, and 90 ℃) and fly ash content (0,10%, 20% and 30%) on the setting and hydration process of fly ash blended cement paste was analyzed. The results show that setting and hardening process of fly ash blended cement paste at elevated temperature can be clearly identified into three stages including dormant stage, acceleration stage and deceleration stage. The increasing of curing temperature greatly accelerates the setting and hardening process. However, the content of fly ash does not have significant effect on the setting in condition of 90 ℃. Besides, the initial and final setting time of cement paste is correspondent with the time of duration of dormant stage and the time of UPV value is 1500 m/s (T1500), respectively. Thus, the UMA can be used to determine the initial and final setting time of cementitious material under different curing temperatures. The compressive test results indicate that the paste with 20% fly ash presents higher compressive strength than the plain paste at curing temperatures of 90 ℃. Therefore, appropriate amount of fly ash is beneficial for concrete in the high temperature curing conditions.
基金Funded by the National Natural Science Foundation of China(No.51478248)the Tsinghua University Initiative Scientific Research Program(20131089239)the Jiangsu Key Laboratory of Construction Materials(No.CM2016-02)
文摘Three different curing temperatures（20 ℃, 40 ℃, and 60 ℃） were set, so that the nonevaporable water（w_n） contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree（w_n=15%） or high hydration degree（w_n=16.5%）, elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore（〉100 nm） volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste＇s compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.
文摘The behaviors of concrete at elevated curing temperature were studied. The test results show that when concrete is cured at elevated temperature, a harmful consequence occurs.The later strength decreases significantly compared to that under normal curing condition. Incorporating silica fume, fly ash and slag or lowering w/c ratio can effectively alleviate this harmful consequence. Comparatively, incorporation of silica fume is the most efficient means to decrease the later strength reduction. The harmful consequence is not caused by the difference in degree of hydration since the degree of hydration is similar between elevated curing temperature and normal curing condition. The SEM analysis shows that it is the uneven distribution of hydration products caused by elevated curing temperature that leads to the later strength reduction of concrete.
基金The authors appreciate the financial support from National Natural Science Foundation of China(No.5157244,U1604252 and 5167225).
文摘In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.
基金the Research Center on Levee Safety Disaster Prevention, MWR (No. 2019004)High-level Talent Project Funding Scheme of Jiangsu (No. XCL-CXTD-007)+3 种基金China Postdoctoral Science Foundation (No. 2018M630559)the National Natural Science Foundation of China (No. 51908285)the Fundamental Research Nantong Metro Group Co., Ltdthe traffic construction science and technology project of Shanxi (No. 16-2-08) for its financial support in this project
文摘The morphologies and hydration properties of MgO expansive material at different curing temperatures were investigated.When the curing temperature varies from 25℃to 50℃,the conductivity of MgO rises from 40 to 80μs/cm,the hydration product of MgO expansive material curing in water for 28 days is from 1.5—2 mm to 2—2.5μm in length through SEM observation,and the expansion of pastes with 5%of the magnesium oxide is from 0.36%up to 1.01%,it is increased by 2.78 times.When the content of cement paste increases to 95%and cured in water for 90 days,the brucite forms as hexaflaggy?shaped crystal,which is less than 0.1μm and tends to aggregates.The effect of curing temperature on the hydration of MgO expansive material is obvious.
基金Funded by the National Natural Science Foundation of China(No.51678081)Natural Science Foundation of the Jiangsu Higher Education Institution of China(No.18KJB560001)。
文摘To further strengthen the protective effect of aerogel cement paste (ACP) coating on self-compacting concrete (SCC) in tunnel fire under the optimal mix proportion,the effect of curing temperature (from 5 to 80 ℃,based on site construction curing temperature and surrounding rock temperature) on fire insulation of ACP was investigated.The mechanical properties,thermal conductivity and porosity of ACP were tested.The microstructure of ACP was characterized by means of SEM,XRD and TG/DTG.The results reveal that 50 ℃ is the optimal curing temperature for ACP with good mechanical properties and fire insulation.Relatively high curing temperature can facilitate hydration and pozzolanic reactions,contributing to the generation of more stable substances (such as C-S-H gels,tobermorite and thenardite,etc).ACP under excessive low curing temperature brings inhomogeneous microstructure with coarse pores,leading to producing wider and longer microcracks when it is exposed to tunnel fire.The microcracks make the heat convection and thermal radiation more significant and thus accelerate the damage of ACP under fire.In case of the less than 7% difference of thermal conductivity,dense microstructure and stable substances are more conducive to strengthening fire insulation of ACP.In practical engineering applications,the thickness of protective layer of ACP can be further optimized when ACP is cured under about 50 ℃.
基金Projects(51878245,U1965105)supported by the National Natural Science Foundation of ChinaProject(2019GSF110006)supported by the Key Research and Development Program of Shandong Province,China+2 种基金Project(2020Z035)supported by the Ningbo 2025 Science and Technology Major Project,ChinaProject(KJ2017B01)supported by the Scientific Research Project of Department of Education of Anhui Province,ChinaProject(2019CEM001)supported by the State Key Laboratory of High Performance Civil Engineering Materials,China。
文摘Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.
基金supported by the Major Program of National Natural Science Foundation of China(Grant No.52090052)General Program of National Natural Science Foundation of China(Grant No.51875288)the authors sincerely appreciate the continuous support provided by their industrial collaborators.
文摘Online monitoring of the curing temperature field is essential to improving the quality and efficiency of the manufacturing process of composite parts.Traditional embedded sensor-based technologies have difficulty monitoring the full temperature field or have to introduce heterogeneous items that could have an undesired impact on the part.In this paper,a non-contact,full-field monitoring method based on deep learning that predicts the internal temperature field of composite parts in real time using surface temperature measurements of auxiliary materials is proposed.Using the proposed method,an average temperature monitoring accuracy of 97%is achieved in various heating patterns.In addition,this method also demonstrates satisfying feasibility when a stronger thermal barrier covers the part.This method was experimentally validated during the self-resistance electric heating process,in which the monitoring accuracy reached 93.1%.This method can potentially be applied to automated manufacturing and process control in the composites industry.
基金supported by the National Basic Research Program of China ("973"Project) (Grant No. 2009CB623106)
文摘The effects of curing temperature on the expansive effectiveness, strength, hydration degree, and microstructure of shrinkagecompensated binder were studied. The results showed that under the standard curing temperature (20℃), most crystalline ettringite grows in pores, which makes less contribution to the expansion of paste than gelatinous ettringite blended with C-S-H gel. An elevated curing temperature (40℃) promotes the hydration rate of expansive agent and cement. However, quickly developing strength of paste limits its expansion. The pore structure of hardened paste under moderate curing condition is the densest one among all the pastes cured at different temperatures due to the filling effect of crystalline and gelatinous ettringite. Under a high curing temperature (60℃), the formation of massive stick-like ettringite leads to excessive expansion at early hydration age. Some ettringite decomposes at sustainable high temperature, which decreases the restricted expansion rate of paste at a late age. Appropriate volume expansion is benefit to the improvement of pore structure of hardened paste by reducing large pores.
基金Funded by the Major State Basic Research Development Program of China(973 Program)(No.2009CB623201)
文摘The effect of curing regime on the distribution ofAl3＋ coordination in hardened cement pastes within 28 d were investigated by 29Si and 27Al magic angle spinning （MAS） nuclear magnetic resonance（NMR） with deconvolution technique. The results indicate that the tetrahedral coordination Al3＋ incorporated in C-S-H structure mainly originate from the AP＋ incorporated in the alite and belite phases in the Portland cement. The curing regime of constant temperature of 20 ℃ is beneficial to the octahedral coordination Al3＋ transforming to tetrahedral coordination AP＋ incorporated in C-S-H structure. However, at curing regime of variable temperature, the temperature rising process is more advantageous to the transformation from ettringite to monosulphate, substitution of Al3＋ for Si4＋ in the C-S-H structure and the formation of the third aluminate hydrate （TAH） than that at constant temperature of 20 ℃. The high temperature of 60 ℃ in the holding temperature process promotes the decomposition of ettringite, and enhances the consumption of the Al3＋ incorporated in C-S-H phases and the Al3＋ in TAH for the monosulphate forming. The temperature decreasing promotes the transformation from monosulphate to ettringite, and increases the consumption of the Al3＋ incorporated in C-S-H phases, and then increases the quantity of the TAH.
基金Funded by the Major State Basic Research Development Program of China(973Program)(No.2009CB623201)
文摘The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of 29Si with magic angle spinning （MAS） nuclear magnetic resonance （NMR） and by analyzing the 29Si NMR spectra with deconvolution technique. The experimental results indicate that, at curing regime of constant temperature of 20℃, the polymerization of C-S-H increases and then decreases with curing age, and the A1/Si ratio increases gradually with curing age, furthermore, the two non-bridging oxygen bonds of bridging silicate tetrahedra in C-S-H structure mainly bond to H＋. At curing regime of variable temperature, the polymerization of C-S-H firstly increases then changes slightly and subsequently decreases with the temperature from low to high and then to low, and the A1/Si ratio firstly increases then keeps invariant and subsequently slightly decreases. Moreover, the temperature decreasing is advantageous for the Ca2＋ to be bonded to the bridging silicate tetrahedra and entering into the interlayer of C-S-H structure. The polymerization of C-S-H at curing regime of variable temperature is higher than that cured at constant temperature, but the curing regime of constant temperature is more beneficial to the substitution of AP for Si4＋ than that of variable temperature.
文摘In order to lower the imidization temperature of polyamic acids（PAA）, the catalytic activities of the curing agents p-hydroxybenzoic acid（PHA）, quinoline（QL）, benzimidazole（BI）, benzotriazole（BTA）, triethylamine（Et_3N） and 1, 8-diazabicyclo [5.4.0]undec-7-ene（DBU） were investigated in the process of thermal imidization of PAA. In addition, the effect of these various curing agents on the thermal stabilities and mechanical properties of the resultant polyimide（PI） films was determined. Quinoline was found to be an effective curing accelerator in the use of two-step method for synthesizing PI. Due to its moderate base strength, low steric crowding effect and moderate boiling point, quinoline could not only accelerate PAA to achieve imidization completely at 180 ℃, but also maintain the mechanical properties and thermal stability of the ordinary PI film. Any residual quinoline could be removed from PI films by heating at 250 ℃ for 4 h.
文摘This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaCO3 as a stabilizer,and straw(for strengthening).The availability of raw materials for making Adobe presents the waste-stabilized Adobe as a potential product for a new alkali-activated binder.Waste-stabilized Adobe collected from an abandoned damaged building in the village of Inonu in Northern Cyprus,ground and calcined at the following temperatures:450,550,650,750,850,and 950℃.The calcination at each temperature was held for different durations 1,3,5,and 7 h.Raw and calcined waste stabilized Adobe structures were investigated using XRF,TGA-DTA,XRD,FTIR,and SEM.Considering technical and environmental views related to energy consumption,waste stabilized Adobe calcined at 750℃ for 1 h presented the most promising results regarding the production of a new precursor for alkali-activated binder.This study also presents the effect of ground granulated blast furnace slag(GGBFS)usage on the fresh and hardened properties of optimum calcined AB-based alkali-activated pastes cured at room temperature.GGBFS was used to partially replace AB to form a binary composite raw material system and seven experimental groups were designed according to replacement levels of 0%,5%,10%,15%,20%,25%and 30%(by mass).Alkali-activated high volume waste-stabilized Adobe-slag pastes prepared using Na2SiO3-to-NaOH ratio of 2 and 12 M concentration of Sodium Hydroxide.The fresh property as flowability and the hardened property as the compressive strength of the alkali-activated pastes with different GGBFS contents were investigated.The results indicated that the incorporation of GGBFS increased the flowability of fresh alkali-activated pastes.A 28-day compressive strength of 43.75 MPa can be obtained by a 30%replacement level of GGBFS.
基金Funded by National Natural Science Foundation of China(No.51378499)China Railway Corporation(No.2014G004-R)Science and Technology of China(No.2010G004-E)
文摘Extensive researches have been carried out on the conventional sulfate attack, while it has been found that the thaumasite form of sulfate attack（TSA）, sulfate attack at low temperature, has just been discovered and its mechanism is not well understood so far. In this study, the sulfate attack of cement paste incorporating 30% mass of limestone powder was investigated. After 20 ℃ water cured for 7, 14, and 28 days,respectively, 20 mm cube specimens were exposed in a 5% magnesium sulfate solution at（6 ±1） ℃ for periods up to 240 days. Their appearance change, compressive strength development were examined at different storage time, and selected paste samples were examined by X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results indicate that all Portland-limstone cement pastes suffer from appearance deterioration to some extent. The compressive strength of cement paste initially increases and after 120 days decreases with increasing exposed period. In addition, the cement paste with short curing time is more susceptible to sulfate attack, which directly leads to the formation of non-binder thaumasite crystal accompanied by the formation of ettringite, gypsum and brucite, and becomes a white, mushy, and incohesive matrix. Additionally, the extent of sulfate attack is greater and the formation of thaumasite is observed earlier for shorter curing time.
基金This study was supported by the National Natural Science Foundation of China(Grant Number 52172090 and 52071159).
文摘Superhydrophobic materials are severely limited in their applications due to their weak mechanical properties and complex preparation process.In this paper,polystyrene/fluorinated silica(PS/SiO_(2))superhydrophobic composite coatings were prepared on the surface of 304 stainless steel using a simple one-step spraying method.The effects of different PS contents on the wettability as well as the wear properties of the samples were investigated.SiO_(2) was encapsulated in polystyrene to form a structure similar to cement encapsulated stones.With the addition of PS,a mound-like structure was formed on the sample surface,and a more optimized micro–nano structure was obtained when the content of PS was 0.6 g.At this time,the sample exhibited excellent wettability with a contact angle of 157.86°and a sliding angle of 0.84°.In addition,the contact angle of 151.09°was achieved after 180 cm of friction under a 100 g load and the composite coating prepared by this method also has excellent chemical stability,water impact resistance,corrosion resistance,and self-cleaning properties.This opens up new possibilities for the development of simple and robust superhydrophobic materials.
文摘Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for microsilica-gel bonded no-cement castable systems to control flow properties and setting characteristics.Three mixing and curing temperatures were applied：5℃,20℃and 35℃.The results show that setting-behaviour and mechanical properties strongly vary with the type of dispersant and the curing temperature.However,both setting and strength are less temperature dependent in the castables with Siox X-Zero.Furthermore,the drying and firing of microsilica-gel bonded NCCs were investigated.Since microsilica-gel bond system contains only a small amount of bound water,the castables can be fired at very high heating rates,once the free water has been removed.
基金Project was supported by the Natural Science Foundation of Guangdong Province(No.2019A1515011844)the Opening Project of Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory(ZHD201801 and 31512050201).
文摘This study has been conducted to evaluate the application of silver nanoparticles(NPs)in Electrically Conductive Adhesives(ECAs),filled with hybrid silver flakes and NPs,and silver flakes as a control sample,at a filler loading of 78 wt.%,83 wt.%and 88 wt.%and cured at 150℃and 180℃,respectively.The results show that the electrical and thermal conductivities of ECAs were improved with the increasing of filler loading and curing temperature.Adding silver NPs in silver flakes negatively affected the electrical and thermal conductivities of ECAs at a low filler mass fraction of 78 wt.%,because the segregation of NPs enlarged the average distance of silver flakes;while it positively influenced the electrical and thermal conductivities of ECAs at a loading ratio of 88 wt.%,probably due to NPs filling in the gaps between silver flakes or even sintering together with each other or with silver flakes,especially when curing at high temperature of 180℃.
文摘The fly ash based geopolymer has emerged as a capable and sustainable binder material in construction industry.Ultrasonic pulse velocity(UPV)method is a non-destructive technique for investigating the mechanical performance of concrete.Experimental investigation was performed for studying the effect of NaOH Molarity,Na2SiO3/NaOH and curing temperature on the ultrasonic pulse velocity of geopolymer mortar.Experiments were designed based on central composite design(CCD)technique of response surface methodology(RSM).Statistical model was developed and statistically validated and found significant as the difference between adjustable R-squared and predicted R-squared less than 0.2.Finally,the optimized mix proportion was assessed for maximized value of UPV.Experimental validation on the optimized mix reveals the close agreement between experimental and predicted values of UPV with significance level of more than 95%.The proposed technique improves the yield,the reliability of the product and the processes.
