Effects of Curing Conditions on Strength Development of High Strength Concrete

This paper presents the results of a series of studies on the influence of curing conditions on the strength development of high strength concrete. The 1-, 3-, 7-, 14- and 28-day strengths of four different mixes of Grade 75 similar to 80 concrete, with or without pulverized fuel ash and/or condensed silica fume, under five different curing regimes were investigated. It is revealed that the curing conditions have significant influence on both the short term and long term strength development of the concrete and that concrete mixes of the same grade but containing different mineral admixtures show distinct favour for a curing regime. These results will be helpful for evaluating suitable curing methods for high strength concrete with different mix proportions.

Strength Development of Cement-Slag Mortars

In this experimental work, three groups of cement-slag mortars namely OPC, OPC-slag, and slag mortars were made. All were cured in both water and air under room temperature. Strength development was studied up to 90 days. The mortars were prepared using 0%, 50%, and 100% replacement with slag. The sensitivity for all groups was obtained against the curing regime with the highest being attributed to the slag mortars. The highest and lowest strengths at early ages were attributed to OPC and slag mortars when both were cured in water. The highest and lowest strengths were attributed to OPC-slag and slag mortars at later ages, respectively. The highest strengths for OPC-slag, OPC, and slag mortars were as 72.0, 64.0, and 21.5 MPa at 90 days when the specimens cured in water, respectively. Strength loss was observed for all groups at later ages when cured in air under room temperature. The maximum and minimum, of about 8.0% and 1.3%, occurred at 56 and 90 days for slag and OPC-slag mortars, respectively.

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.

Modification of nanoparticles for the strength enhancing of cementstabilized dredged sludge

This paper investigates the effectiveness of nano-modification on the strength enhancement of cementstabilized dredged sludge(CDS).Three types of nanoparticles including nano-SiO2(NS),nano-Al2O3(NA)and nano-MgO(NM)were used as cement admixtures for dredged sludge stabilization.Effects of single nanoparticle content,mass ratio of composite nanoparticles and curing time on the strength development of CDS were evaluated via a series of unconfined compressive strength(UCS)tests.The pH evolutions of CDS caused by nanoparticles were also examined by a range of pH tests.Furthermore,micromechanisms reflecting the strength evolutions were analyzed by performing scanning electron microscopy(SEM)and X-ray diffraction(XRD)tests.The results indicated that adding nanoparticles can significantly improve the UCS of CDS.For single nano-modification,the optimum contents of NS,NA and NM were 4%e6%,6%and 8%,which can increase the 7-and 28-d UCSs of CDS by 38%and 50%,17%and 35%,65%and 67%,respectively.Compared with single nano-modification,composite nano-modifications were more effective in improving the strength gain of CDS.The optimum mass ratios of composite nanoparticles,namely NS/NA,NS/NM and NA/NM,were 9/1,3/7 and 3/7,respectively.Based on the strength growth rate,the composite nanoparticles with NS/NM of 3/7 were highly recommended.The addition of nanoparticles obviously affected the pH evolution of CDS,which was mainly determined by the difference of OHproduction and consumption inside nano-modified CDS.The microstructural analysis revealed that C-S-H and C-A-H gels are the main cementitious products,and the addition of nanoparticles can obviously contribute to a denser and more homogenous microstructure of CDS.

High-Volume Fly Ash Concrete-A Relevant Step to Sustainable Development

HVFA （high-volume fly ash） concrete could be a sustainable way for by-product utilization to conserve natural resources and protect environment. HVFA concrete can play the role of a high-performance material that may be comparable to the conventional Portland cement concrete. The results of the research programme concerning the relationships between the composition of concrete （w/b ratio, fly ash content and type of cement） and their physical and mechanical properties are presented and discussed in the paper. It is found that the introduction of high-volume fly ash into concrete has caused a decrease in compressive strength at the early age of storage. The significant increase in strength was observed between 28 days and 90 days of curing. The high-volume fly ash concretes were characterized with lower water absorbability and sorptivity than control concrete.

南京市城区5～6岁儿童握力的研究

目的探讨儿童握力发育水平并调查握力在性别、年龄、左右手及生理手型方面的发育规律及特征。方法采用随机抽样方法,使用握力计对南京市主城区485名儿童进行握力测试,并同时进行生理手型的测量,分析握力在年龄、性别、左右手及生理手型方面的发育规律及特征。结果 (1)男生握力始终大于同龄女生,男生、女生左右手的差异不明显;男生右手握力每半年增长1.7～3.8 LB(1 LB=0.453 kg),男生左手握力每半年增长1.7～4.5 LB;女生右手握力每半年增长2.3～2.5 LB,女生左手握力每半年增长1.5～3.2 LB;(2)获得南京市城区5～6岁儿童握力的P_5、P_(25)、P_(50)和P_(75)百分位数参考值;(3)握力与生理手型有密切联系。结论通过对儿童握力的测量,初步了解南京市城区5～6岁儿童握力发育过程中的年龄、性别及双手之间的发育规律及特征,为进一步的临床和科研工作提供参考依据。

新疆区域经济发展实力评价与分类研究

本文从经济发展水平和经济增长贡献两个层面界定了区域经济发展实力,并在此基础上采用了基于主成分分析的多指标综合评价法对新疆区域经济发展实力进行了分析、评价与分类,最后得出一些结论和启示。

提升西安文化软实力的战略思考

城市文化软实力,就是指一个城市的文化所具有的凝聚力、生命力、创新力和传播力以及由此而产生的感召力和影响力。提升文化软实力,对于建设"人文西安、活力西安、和谐西安",实现西安科学发展、率先发展和西安"文化名市"的宏伟目标,有着重要的现实意义。进一步提升西安文化软实力,必须转变发展理念,强化科学决策,必须明确城市定位和文化发展目标,着力于关键领域,实施重点突破。

何为发展性评价及如何实施——一个案例引发的沉思

本文由一个案例的角度针对新课程实施中学生评价中的一些问题进行了探讨,提出了一个新的视角:即针对学生长处的评价,或者是落脚点是学生长处的评价这样一个观点,并在各类别的学校进行了小部分的试验,得出了一个结论:针对长处的评价是能促进对方发展的评价,或者说,促进对方发展的评价就是针对对方长处的评价,即使不针对长处,但落脚点也必须是在对方长处的评价。

体育强市背景下宁波市体育产业发展对策研究

本文以宁波市体育产业为研究对象,采用文献资料法、数理统计法专家访谈法和逻辑分析等方法,对宁波市体育产业进行现状分析,并对宁波市体育产业结构升级与产业合理布局进行全面系统的探讨。以此来规划宁波市体育产业的发展,促进宁波市体育产业全面的振兴。

Activation of Rejected Fly Ash Using Flue Gas Desulphurization (FGD) Sludge

Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon content and large particle size (>45μm).But it is thought that the rejected ash may have potential uses in chemical stabilization/solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity.Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum.As there is no effective usage of both of these two materials,it is of interest to research on the possible activation of rFA using FGD.This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes.Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes.The results show that FGD takes effect as an activator only at late curing ages.Adding Ca(OH) 2 enhances the effect of FGD on activating the hydration of rFA.Also,10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes.The results of the compressive strength measurements correlate well with the porosity results.

南京市城区5～6岁儿童捏力的研究

目的探讨儿童捏力发育水平并调查捏力在性别、年龄、左右手、生理手型方面的发育特征与规律。方法采用随机抽样方法,使用捏力计对南京市主城区485名儿童进行捏力测试,同时进行生理手型的测量,并分析捏力在年龄、性别、左右手、生理手型方面的发育特征与规律。结果 (1)南京市城区5～6岁儿童三指捏力:男女左右手的差异不明显;男生始终大于同龄女生;男生右手三指捏力每半年增长0. 2～1. 2 LB(1 LB=0. 453 kg),男生左手三指捏力每半年增长0. 1～1. 2 LB;女生右手三指捏力每半年增长0. 5～0. 6 LB,女生左手三指捏力每半年增长0. 3～0. 8 LB。(2)南京市城区5～6岁儿童指尖捏力:男女左右手的差异不明显;男生始终大于同龄女生;男生右手指尖捏力每半年增长0. 3～0. 5 LB,男生左手指尖捏力每半年增长0. 1～0. 5 LB;女生右手指尖捏力每半年增长0. 3～0. 4 LB,女生左手指尖捏力每半年增长0. 1～0. 4 LB。(3)获得南京市城区5～6岁儿童三指捏力、指尖捏力的P_5、P_(25)、P_(50)、P_(75)百分位数参考值。(4)三指捏力、指尖捏力与生理手型有密切联系。结论通过对儿童捏力的测量,初步了解南京市城区5～6儿童捏力发育过程中的年龄、性别及双手之间的发育特征及规律等。

Numerical Analyses of Caisson Breakwaters on Soft Foundations Under Wave Cyclic Loading

A caisson breakwater is built on soft foundations after replacing the upper soft layer with sand. This paper presents a dynamic finite element method to investigate the strength degradation and associated pore pressure development of the intercalated soft layer under wave cyclic loading. By combining the undrained shear strength with the empirical formula of overconsolidation clay produced by unloading and the development model of pore pressure, the dynamic degradation law that describes the undrained shear strength as a function of cycle number and stress level is derived. Based on the proposed dynamic degradation law and M-C yield criterion, a dynamic finite element method is numerically implemented to predict changes in undrained shear strength of the intercalated soft layer by using the general-purpose FEM software ABAQUS, and the accuracy of the method is verified. The effects of cycle number and amplitude of the wave force on the degradation of the undrained shear strength of the intercalated soft layer and the associated excess pore pressure response are investigated by analyzing an overall distribution and three typical sections underneath the breakwater. By comparing the undrained shear strength distributions obtained by the static method and the quasi-static method with the undrained shear strength distributions obtained by the dynamic finite element method in the three typical sections, the superiority of the dynamic finite element method in predicting changes in undrained shear strength is demonstrated.

徐州地区农业产业化发展的优劣势及对策分析

结合统计数据、运用SWOT分析法分析徐州地区农业发展的现状,得出徐州地区农业产业化具有区位优势明显、资源优势突出、市场空间广阔和科技优势较强等优势,也存在人地矛盾突出、环境污染严重与人工成本提高等劣势。指出实施科技兴农战略、把握农业经营的市场导向、因地制宜地合理规划农业生产、推进农村剩余劳动力转移、实施农产品品牌战略和深加工以及坚持生态型农业产业化道路是徐州农业产业化发展的方向和措施。

上级发展性反馈对民航机务人员安全绩效的影响机制研究

为提升民航机务人员的安全作业水平,保障民航领域的安全生产运行,从社会交换理论和社会认知理论双视角出发,建立了以工作嵌入和安全效能感为中介变量、基于优势的心理氛围为调节变量的上级发展性反馈对安全绩效影响机制的理论模型。通过对来自多个民航组织的296位民航机务人员进行问卷调查,并采用多元层次回归分析法开展假设检验。结果表明:上级发展性反馈显著正向影响民航机务人员的安全绩效;工作嵌入和安全效能感在上级发展性反馈和民航机务人员安全绩效之间发挥平行中介作用;基于优势的心理氛围分别正向调节工作嵌入和安全效能感在上级发展性反馈与安全绩效之间的中介作用。研究揭示了上级发展性反馈对安全绩效的影响机制,可为民航机务人员的安全绩效管理提供指导基础。

Curing Reaction Model of Epoxy Asphalt Binder

In order to understand the strength developing law of the epoxy asphalt mixture,a curing reaction model of the epoxy asphalt binder was proposed based upon the thermokinetic analysis.Given some assumptions,the model was developed by applying the Kissinger law as well as Arrhenius equation,and the differential scanning calorimetry was performed for estimating the model parameters.To monitor the strength development of the epoxy asphalt mixture,a strength test program was employed and then results were compared to those produced from the proposed model.The comparative evaluation shows that a good consistency exists between the outputs from test program and the proposed model,indicating that the proposed model can be used effectively for simulating the curing reaction process for the epoxy asphalt binder and predicting the strength development for the epoxy asphalt mixture.

Application of New Calcium Aluminate Cement CA-670 in Low Cement Castables

A new calcium aluminate cement CA-670 was studied in the system of tabular alumina, white fused alumina （WFA）, and bauxite based low cement castables. The flow ability, strength development, and hot strength （ HMOR ） were investigated. Different types of additives were used for the CA-670 bonded castables. The results show CA-670 provides a good workability for each type of＂ castables. CA-670 displays a good compatibility with different types of additives. Testing on different batches of CA-670 shows good reproducible properties in each castable, which manifests good consistency and reliability of CA-670.

内侧突出技术对成人发育性髋关节发育不良患者全髋关节置换术后髋关节外展肌力恢复的影响

目的评价内侧突出技术对成人发育性髋关节发育不良(developmental dysplasia of the hip,DDH)患者THA术后外展肌力恢复的影响。方法回顾性分析2012年1月至2021年12月于武汉大学人民医院因DDH、股骨颈骨折、股骨头坏死及髋关节骨性关节炎行单侧髋关节置换116例患者,将患者分为DDH组(52例)及非DDH组(64例)。在术前,术后1、4、24及48周进行临床数据采集,具体包括Harris评分、VAS疼痛评分、双侧髋关节外展肌肌力矩比(HAMMR)。通过骨盆正位平片测量髋关节旋转中心内移距离,比较两组间外展肌力矩差异。结果患者随访时间12~18个月,平均随访时间14.3个月,其中DDH组52例患者髋关节Harris评分从术前(39.6±7.9)分改善至术后12个月(85.1±6.2)分,差异具有统计学意义(P<0.05)。DDH组52例患者髋关节旋转中心内移距离平均(15.5±6.0)mm,最小内移距离8 mm,最大内移距离24.4 mm,其中CroweⅠ型24例,CroweⅡ型19例,CroweⅢ型9例,DDH组患者术后6个月及12个月HAMMR分别为(85.3±7.4)%及(93.9±3.6)%,较术前显著改善(P<0.05),提示患侧外展肌力恢复接近对侧水平(100%)。通过皮尔逊相关性分析,旋转中心内移距离与HAMMR无明显相关性(r=-0.061,P=0.665>0.05)。对DDH组与非DDH组间HAMMR进行独立样本t检验发现,在术后1、5、12个月HAMMR比较,差异均无统计学意义(P>0.05)。结论DDH患者行THA术应用内侧突出技术,在有限范围内移旋转中心(内移距离不超过24.4 mm),对术后6个月后髋关节外展肌力的恢复无明显影响,术后髋关节功能及外展肌力得到明显改善。

高位髋关节旋转中心对髋臼发育不良髋关节置换术后外展肌力及早期康复的影响

目的探讨高位髋关节旋转中心对髋臼发育不良(DDH)患者人工全髋关节置换术(THA)后髋关节外展肌力恢复及早期康复的影响。方法选取我院2010年1月至2020年12月接受初次单侧THA手术治疗的CroweⅠ~Ⅳ型DDH病例142例,回顾分析其术前及术后3、6、12个月时Harris评分和Trendelenburg征;记录相关并发症;检测双侧髋关节外展肌力矩比(HAMMR);采用Adobe illustrator CC 201822.0软件在标准骨盆正位片上测量外展肌力臂、股骨头水平旋转中心距(HRC)、股骨头垂直旋转中心距(VRC)、股骨头垂直移位(V-shift)。结果142例患者DDH-THA术前双下肢长度短缩差为(31.2±20.1)mm,术后为(3.6±3.5)mm;髋关节Harris评分术前为(43.4±13.4)分,术后为(79.8±21.7)分;CroweⅠ~Ⅲ型DDH的136例患者术后HRC较术前显著改善(P<0.05);DDH-THA术后6个月HAMMR为(85.5±8.6)%,而术后12个月为(94.3±4.8)%,均较手术前显著升高(P<0.05);V-shift>4~8 mm患者DDH-THA术后获得HAMMR的明显改善,术后6~12个月患者的髋关节外展肌力恢复明显;而V-shift>12 mm患者HAMMR的恢复有延迟现象(P<0.05)。结论DDH伴髋关节骨性关节炎患者THA术后髋关节旋转中心的有限高位(V-shift≤12 mm)不影响髋关节外展肌力的的恢复,配合THA手术后早期的康复训练,可有效改善DDH-THA患者的髋关节功能。

三峡库区发展乡村旅游优劣势分析与对策研究

发展乡村旅游是三峡库区改善城乡二元经济结构,推动农村经济社会发展和加快新农村建设强有力的手段.在对三峡库区发展乡村旅游的优劣势进行全面分析的基础上,提出乡村旅游发展对策,以期为库区乡村旅游的发展提供科学依据.