A strength model for cement-stabilized mud subjected to various curing temperatures and its early-stage quality control

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.

Influence of Elevated Curing Temperature on the Properties of Cement Paste and Concrete at the Same Hydration Degree

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.

Early Hydration and Setting Process of Fly Ash-blended Cement Paste under Different Curing Temperatures

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.

Performances of Concrete under Elevated Curing Temperature

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.

Effect of Curing Temperature on Intermediate Temperature Properties of Calcium Aluminate Cement Bonded Corundum Castables

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.

Effect of Curing Temperature on the Morphology and Hydration of MgO Expansive Material in Paste

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.

Effect of Curing Temperature on Tunnel Fire Insulation of Aerogel Cement Paste Coatings

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 ℃.

Influence of CaO-based expansive agent,superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

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.

Optimum Calcination Condition of Waste Stabilized Adobe for Alkali Activated High Volume Adobe-Slag Binder Cured at Room Temperature

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.

Hydrophilicity Modification of Addition-cured Room Temperature Vulcanization Silicone Rubber

Allyl terminated polyether was used to improve the hydrophilicity of addition-cured room temperature vulcanization silicone rubber. With the increasing of the polyether, both the hydrophilicity and water absorbed of the vulcanizates were increased. The mechanical properties were also improved by adding the polyether. The result showed that 1.5wt% of the polyether provided the silicone rubber with proper hydrophilicity.

Risk Regionalization of Low-temperature Disasters for Flue-cured Tobacco Planting in Qujing Area Based on GIS

There is a prominent,complex and diverse three-dimensional climate and a variety of meteorological disasters in Qujing area. The risk zoning of low-temperature disasters for flue-cured tobacco planting in Qujing area was studied to provide reference for drawing on advantages and avoiding disadvantages in flue-cured tobacco planting,disaster reduction,and disaster relief services. According to the production practice of fluecured tobacco and local climate analysis,it was determined that flue-cured tobacco in Qujing area was very vulnerable to low temperature during the seedling stage（ from early February to middle April） and in the mature period（ from early July to early September）. Based on the quantitative analysis and evaluation of risk of disaster-causing factors,sensitivity of disaster-breeding environment,vulnerability of carriers,and disaster prevention and reduction capability,a risk assessment model of meteorological disasters was established to precisely evaluate and zone the risk of low-temperature disasters for flue-cured tobacco planting in allusion to the seedling and mature stage in Qujing area by using GIS technology. The risk of lowtemperature disasters for flue-cured tobacco planting during the two periods was divided into four grades,namely low,medium,high and very high risk.

修正硫化效应法制定厚制品橡胶硫化时间

测试了混炼胶不同温度下的硫化曲线,研究了硫化温度对不同混炼胶交联程度的影响;以天然橡胶(NR)/顺丁橡胶(BR)硫化胶为研究对象,进一步测试了其不同硫化温度下的硫化曲线,进行硫化程度修正系数P和硫化温度系数K拟合,采用预埋热电偶法测试了厚制品橡胶中心处的升温曲线,采用修正以及传统硫化效应法分别进行二者工程硫化时间计算。结果表明,硫化温度对不同橡胶硫化程度会产生较大影响,采用修正硫化效应法硫化的厚制品与标准试片更加接近,而传统硫化效应法硫化程度偏低。

温度和相对湿度对CO_(2)养护钢渣制品性能的影响

通过响应面法(RSM)研究了温度和相对湿度对CO_(2)养护钢渣制品(以下简称钢渣制品)性能的影响.结果表明:温度和相对湿度的相互作用对钢渣制品碳化过程的影响在不同碳化阶段有所不同.CO_(2)养护初期,CO_(2)的扩散是关键因素,但该阶段碳化不充分;CO_(2)养护后期,钢渣制品的抗压强度和碳化程度受Ca^(2+)和CO_(2)溶解度的影响较大.当相对湿度低于30%时,尽管CO_(2)扩散较快,但其溶解度低,限制了CO_(3)^(2-)与Ca^(2+)的反应,导致钢渣制品无法达到理想的强度和碳化水平.将温度和相对湿度分别提至70℃和64%,可以促进更多纳米级CaCO3形成,填充了40~180 nm孔隙,有效减小了钢渣的孔径和孔体积,从而改善了材料性能.

养护温度与沙漠砂替代率对机制砂混凝土抗压强度与孔结构的影响

为探究不同养护温度下沙漠砂替代率对机制砂混凝土抗压强度及孔结构的影响规律,试验选用不同比例的沙漠砂替代机制砂用作细骨料配制C40混凝土.测试不同沙漠砂替代率下混凝土的抗压强度,借助SEM,XRD、核磁共振等测试手段分析不同养护温度下,混凝土水化产物、微观形貌及孔结构.结果表明:标准养护下沙漠砂体积替代率为30%时,混凝土抗压强度最高;沙漠砂替代机制砂降低了混凝土低温养护下7 d强度损失率,减缓了高温水泥水化的速率;30%的沙漠砂替代机制砂,改善了骨料的颗粒级配,优化了混凝土内部的孔隙结构,从而提高了体系的密实性;考虑到混凝土孔隙结构的复杂性,引入分形维数间接评价混凝土的孔隙特征,其分形维数具有分段性;将分形维数与孔径分布进行线性拟合,分形维数与无害孔呈正比关系,与多害孔呈反比关系.该研究可为10~30℃养护下混合砂混凝土的研究与实践提供一定的参考.

有机荧光材料对光敏聚酰亚胺性能的影响

以2,2-二(3-氨基-4-羟基苯基)六氟丙烷、5-氨基-2-(4-氨基苯基)苯并咪唑、3,3′,4,4′-二苯酮四酸二酐为主要原料合成了光敏聚酰亚胺(PSPI)预聚物,再将预聚物与自制的含有二硫代水杨酸的4种不同荧光材料充分混合涂膜并紫外光固化,得到加上对照组共5组的PSPI薄膜样品。利用傅里叶变换红外光谱仪、万能拉力试验机、差示扫描量热仪,接触角测量仪等对各组PSPI薄膜进行性能表征,并对PSPI薄膜的水接触角和吸水率进行了研究。结果表明,虽成功合成出含有聚酰亚胺特征官能团的PSPI薄膜,但加入荧光材料的PSPI薄膜相较于未加入荧光材料的PSPI薄膜,拉伸强度略有降低,玻璃化转变温度升高,说明荧光剂的加入,会使PSPI分子侧基体积增大并改变其对称性,降低分子柔性;荧光材料会增大PSPI分子的结构空隙,从而表现出更好的亲水性和吸水性。

氧化石墨烯增强硅烷丙烯酸复合防腐涂料的制备及性能

[目的]水性丙烯酸乳液涂层在力学性能、耐久性和附着力方面有待提高。[方法]将改性后的硅氧烷基丙烯酸乳液与氧化石墨烯等功能性填料进行混合,制备出一种具有高力学性能、高耐久性和良好附着力的常温固化型硅烷复合丙烯酸涂料。选用镀锌钢板作为基材,对涂料进行施工,并对其性能进行了测试。[结果]添加氧化石墨烯后,丙烯酸涂料的附着力达到0级,铅笔硬度达到6H,并且在耐水性、耐碱性、耐盐雾性等方面均有显著提升。[结论]该涂料满足了接地引下线与接地体之间腐蚀防护的技术要求。

Non-contact and full-field online monitoring of curing temperature during the in-situ heating process based on deep learning

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.

固化温度对蓄电池极板成分影响的研究

铅酸蓄电池极板的固化干燥是一个物相变化非常复杂的过程,对最终电池的容量及使用寿命具有直接的影响。因此,了解极板固化过程中铅膏成分的变化非常重要。通过X射线衍射(XRD)和电子扫描电镜(SEM)研究不同固化温度对极板铅膏中3BS和4BS的影响,同时对采用不同固化温度的极板组装的电池在循环寿命性能方面进行检测,探究极板成分对电池性能的影响。

Effect of double-layer formwork curing on the early temperature field and properties of precast concrete components in environments with large diurnal temperature variations

An efficient double-layer formwork curing method using an“inner supporting formwork+outer insulation formwork”was proposed in this study to address the early cracking of precast concrete components in high altitude regions.Steel and plywood formwork were designed as inner support formwork,while polystyrene(PS)and polyurethane(PU)were used as outer insulation formwork.Indoor experiments and two finite element methods(The complete simulation method focuses on computational accuracy,and the equivalent simulation method emphasizes computational efficiency)were employed to analyze the evolution of the concrete temperature field under different double-layer formwork curing methods throughout the curing period,combined with compressive strength and pore structures testing.The results show that steel+5-mm-thick PU insulation formwork curing method can significantly mitigate the impact of large diurnal temperature variations on the internal temperature of concrete.Unlike traditional steam-curing,this method does not deteriorate the pore structure or compressive strength of the concrete.This study is of great significance in addressing the problem of early cracking of precast concrete components exposed to large diurnal temperature vriations in high altitude regions.