株洲建宁大桥主体墩大体积承台混凝土浇注工艺

以株洲建宁大桥主体墩承台施工为背景，介绍大体积混凝土施工的浇注工艺及温度控制措施。实践表明，承台施工中有效地进行温控，可减少混凝土内外温差及层间温差，控制温度裂缝的产生。     

超大体积混凝土施工技术例析——以青岛市开发区国际贸易中心为例

高层建筑对基础的整体性要求较高,往往采用大体积混凝土基础承台,但也带来施工及混凝土凝结硬化过程中水泥水化热聚集不易散出,导致混凝土产生极大的内外温差,使混凝土产生裂缝.结合青岛开发区国际贸易中心建设实例,从材料选用、施工现场准备、施工工艺技术及异常情况应急预案等方面,对大体积混凝土施工提出了有效的质量保证措施.     

桥墩承台大体积混凝土施工期温度控制与监测

由于内外温差过大而引起温度裂缝,是大体积混凝土施工过程不可避免的问题.采用水管冷却方法可有效控制大体积混凝土内核温度,防止裂缝产生.并将该方法应用于某刚架桥桥墩承台大体积混凝土的施工中,通过对监测结果的分析,验证了水管冷却方法的有效性.     

基于Midas Civil的承台大体积混凝土温度控制及数值分析

大体积混凝土结构在施工过程中,由于混凝土的水化热反应,易出现内外温差,产生过大的温度应力,进而引起温度裂缝.针对混凝土水化热问题,以兑房河特大桥5#墩为例,提出承台大体积混凝土布设冷却管的温控方案,利用有限元软件Midas Civil进行水化热数值分析,并将理论计算值与现场温度监测结果进行对比分析.实践表明,兑房河特大桥承台在施工过程中采取的温控措施,取得了较好的效果,并为类似工程提供一定的指导意义.     

大体积混凝土温控技术及热工计算

大体积混凝土施工是现代大型土木工程中的特种技术。针对武汉天兴洲长江大桥承台大体积混凝土的特点,提出了切实可行的裂缝控制施工技术措施,并按照规范进行了大体积混凝土裂缝控制的热工计算,计算结果表明承台大体积混凝土浇筑后内外温差满足不超过25℃的规定要求。实践证明所采取的技术措施对裂缝控制效果是明显的,对类似大体积混凝土工程的设计和施工有一定的借鉴作用。     

高寒地区承台水化热有限元分析与裂缝控制

根据高寒地区的气候特点,采用大型有限元软件ANSYS,考虑不同月份中环境温度的变化,对承台混凝土水化热进行了仿真分析,对高寒地区大体积混凝土浇筑季节选择提供了一定的参考,并且针对承台内外温差过大这一问题,采用铺设保温材料进行模拟分析,得出采用保温材料对承台进行表面保温,可以大幅度减少承台内外温差,有效防止温度裂缝的产生.     

桥梁大体积混凝土浇筑过程的温度场及温度应力

桥梁大体积混凝土质量控制的一个重要方面是温度控制,本文通过对宁波甬江特大桥承台大体积混凝土在施工过程中的温度场与温度应力进行仿真分析,计算了大体积混凝土内部温度场及仿真应力场,从而采取了相应温控措施,并对分析计算结果与实测结果进行对比分析,表明该温控措施有效地控制了混凝土的最高温升和内外温差,对类似工程具有一定的借鉴作用.     

桥梁大体积混凝土浇筑过程的温度场及温度应力

桥梁大体积混凝土质量控制的一个重要方面是温度控制,本文通过对宁波甬江特大桥承台大体积混凝土在施工过程中的温度场与温度应力进行仿真分析,计算了大体积混凝土内部温度场及仿真应力场,从而采取了相应温控措施,并对分析计算结果与实测结果进行对比分析,表明该温控措施有效地控制了混凝土的最高温升和内外温差,对类似工程具有一定的借鉴作用．     

大体积混凝土温度裂缝的控制

内外温差引起的裂缝问题是大体积混凝土最主要的工程问题,通过工程实例,对某桥大体积混凝土承台的裂缝进行控制,并通过计算验算措施的可行性,有效地防止裂缝的产生.     

浉河大桥承台大体积混凝土施工与温控分析

河南信阳浉河大桥为独塔双索面斜拉桥,主塔承台混凝土总量为386m^3。分析混凝土裂缝产生的机理,进行了主塔承台大体积混凝土的温度应力计算,提出了防止温度裂缝产生的混凝土施工及温度控制措施。     

Temperature dependency of dynamic mechanical properties of cement asphalt paste by DMTA method

We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis(DMTA) method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of-40 ℃ to 60 ℃, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus(E'), loss modulus(E') and loss factor(tand) is observed. Moreover, the influence of asphalt to cement(A/C) ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.     

应用DSR评价沥青胶浆路用性能的研究

沥青胶浆是沥青混合料的重要组成部分,但是由于试验条件与手段的限制,我国对沥青胶浆的研究不多,针对这一问题,利用动态剪切流变仪（DSR）,研究沥青胶浆性能以及胶浆中矿粉和纤维对它的路用性能的影响,研究结果表明,矿粉与纤维可以显著提高沥青胶浆的高温性能,但是,不适当的增加矿粉与纤维用量将损伤沥青胶浆的疲劳性能。     

Effects of Curing Temperature on Rheological Behaviour and Compressive Strength of Cement Containing GGBFS

The viscoplasticity and compressive strength of cement with high erosion performance were studied. The influences of curing temperature and content of ground granulated blast furnace slag(GGBFS) on these performances of the medium heat cement(including high iron and low calcium phase) were also investigated. The results indicate that the medium heat cement with high iron phase can maintain better fluidity and low temperature sensitivity than that of ordinary Portland cement at high temperature. GGBFS can play an important role in improving the fluidity and stability of the slurry, and avoid the cement setting and hardening prematurely at high temperatures. The microstructure analysis shows that a large amount of CH with layer shape appear in the slurry. The amount of this gel layer in the slurry increased as the curing temperature elevated. The layer can make the cement stone structure more denser, so that the compressive strength of samples are enhanced in the later stage. When the medium heat cement contains 40% GGBFS, the system has the best flow performance and stability under high temperature environment, and can be applied to mass concrete with excessive internal temperature.     

磷石膏分解特性对磷石膏制硫酸联产水泥新工艺的影响研究

磷石膏预分解制硫酸联产水泥技术的关键是对磷石膏分解特性的深入了解,结合水泥新型干法预分解窑的特点,采用热分析及相关试验对磷石膏的热分解性能进行了研究.结果表明,磷石膏完全分解温度在1 300℃以上,在还原条件下其分解温度也在1200℃以上.结果还表明,由于磷石膏的分解温度往往高于该系统的最低共熔点温度,其对预热器分解炉的适应性较差,易对窑系统造成粘结堵塞问题.利用水泥新型干法技术分解磷石膏制酸并联产水泥的实施会有较大难度.     

水泥细度与成分对混凝土温升的影响

大体积混凝土的绝热温升影响因素众多,其中水泥细度与组成成分的影响研究较少。分别测试了不同水泥细度及碱含量、粉煤灰掺量与石膏含量等对混凝土温升的影响规律。研究结果表明,随着水泥比表面积的增加,混凝土绝热温升值与温升速率随着水泥细度增加而增大;水泥碱含量在0．4％～1．2％范围内,水泥碱含量增加,其最大温升值减小,水泥碱含量过高或过低都会延长混凝土温升时间;粉煤灰的掺入有利于降低混凝土最大温升值;石膏含量增加也对控制混凝土温升有利。     

Comparison of temperature field distribution between cement preclinkering technology and cement precalcining technology

Through the comparison of calcination conditions between cement preclinkering technology and cement precalcining technology,we studied the characteristics of temperature field distribution of cement preclinkering technology systems including cyclone preheater,preclinkering furnace,and rotary kiln.We used numericalsimulation method to obtain data of temperature field distribution.Some results are found by system study.The ratio of tailcoalof cement preclinkering technology is about 70%,and raw mealtemperature can reach 1070 ℃.Shorter L/D kiln type of preclinkering technology can obtain more stable calcining zone temperature.The highest solid temperature of cement preclinkering technology is higher than 80 ℃,and high temperature region(1450 ℃)length is 2 times,which is beneficialfor calcining clinker and higher clinker quality.So cement preclinkering technology can obtain more performance temperature filed,which improves both the solid-phase reaction and liquid-phase reaction.     

磁铁矿对超高密度水泥浆体系性能的影响

针对钻探深井超深井过程中的高温高压固井问题,研制一套抗高温超高密度水泥浆体系。该水泥浆体系由磁铁矿粉、降失水剂FS-23L、分散剂SXY-2、缓凝剂HX-31L配制而成。通过对超高密度水泥浆流变性、流动度、沉降稳定性和抗压强度等的评价,得到磁铁矿加重剂的优选加量范围,以及适应循环温度150℃的综合性能良好的水泥浆配方。     

现浇大体积混凝土的裂缝控制技术

高层建筑基础大体积混凝土施工,一般使用低水化热的矿渣水泥,而本工程因混凝土设计标号高,必须使用高水化热的普通硅酸盐水泥．在本文,合理选用原材料,用ＵＥＡ外加剂代替相应水泥用量并调整配合比,对混凝土温度进行了估算,根据工程实际合理设置后浇带,不仅实现了温度控制的目标,也解决了高标号大体积混凝土使用普通硅酸盐水泥的裂缝控制技术问题．     

Determination of the apparent activation energy of concrete carbonation

Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy E _a of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35–0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1–1.69 times as temperature increase every 10 °C at the temperature range of 10 to 60 °C.     

聚羧酸减水剂在水泥和泥土表面的吸附行为

采用有机碳测定仪研究了水泥、泥土和水体系中聚羧酸减水剂吸附量与吸附时间、减水剂浓度、体系温度的关系。同时,对减水剂吸附模型和吸附热进行了分析,探讨了聚羧酸减水剂在水泥、泥土颗粒表面的吸附特性。结果表明:水泥和泥土对聚羧酸减水剂的吸附量随时间延长不断增加,最后达到平衡,同时,泥土比水泥对减水剂的吸附量要大,泥土的掺入量为0.5%就会大大降低水泥净浆的流动度;聚羧酸减水剂的吸附基本符合Langmuir等温吸附模型,水泥和泥土对减水剂的饱和吸附量分别为3.7mg/g和10.1mg/g;水泥和泥土对聚羧酸减水剂的吸附量随温度的增大而减小,其吸附是一个放热过程。