浅谈消除清水混凝土桥梁柱子表面气泡的措施

混凝土结构物表面的气泡问题是混凝土外观质量常见的问题，成因非常复杂，如何消除混凝土表面气泡是很多施工技术人员感到棘手的问题。昌乐永昌路桥项目桥梁工程柱子要求使用清水混凝土，如果表面气泡问题得不到解决，就会影响外观质量。为此，施工方采取调整混凝土的施工浇筑技术、使用水溶性脱模剂等措施，同时混凝土生产企业通过调整混凝土配合比，采取改变减水剂用量、掺合料品种和掺加量等措施，取得满意效果。     

高层建筑使用泵送混凝土楼板裂缝产生浅析

从设计、材料、施工角度进行分析,提出采取控制混凝土的收缩应力及温差应力,控制混凝土坍落度,以达到控制混凝土的收缩,控制高层建筑泵送混凝土裂缝的目的。     

混凝土凝结时间偏长问题的分析及解决措施

从水泥质量、混凝土用料以及配比等方面分析了某混凝土搅拌站混凝土凝结时间偏长的原因,最终发现凝结时间偏长是由于混凝土用砂受到了醇类物质污染所致.采取相应措施后,混凝土凝结时间恢复正常.     

泵送商品混凝土结构的防裂措施

混凝土裂缝问题是混凝土工程中普遍存在的技术问题，引起了建筑工程界的广泛注视，尤其是商品混凝土(特别是泵送混凝土)防裂问题。其中控制泵送商品混凝土裂缝，应从商品混凝土的生产和施工及设计等几个方面采取相应的技术措施。     

粉煤灰高强钢纤维混凝土的试验研究

采取"低水灰比,用优质粉煤灰替代部分水泥,加入一定量的钢纤维,掺人适量高减水率、低坍落度损失的减水剂",可配制出施工性能优良的高强钢纤维混凝土.     

浅谈水泥混凝土施工的几个问题

分析水泥混凝土的浇筑产生裂缝的原因,采取相应措施,防止因温度变化而导致的裂缝,降低水泥混凝土的局部温差,保证混凝土结构质量.     

提高混凝土高温性能措施的研究

混凝土在受热时、受热后,性能会发生变化。为了提高混凝土的高温性能,本文对国内外的相关研究进行了总结、分析,得知提高混凝土的高温性能可以采取：加入钢纤维、聚丙烯纤维、粉煤灰以减少混凝土的微裂纹的产生、扩展,提高混凝土高温力学性能。     

用科学发展观指导预拌砼产业发展

一发展预拌混凝土的必要性1.商品混凝土的生产采取集中搅拌的方式,实现了混凝土生产的专业化、商品化和社会化商品混凝土生产由粗放型生产向集约型生产的转变是实现建筑工业化的一项重要改革。广泛地使用商品混凝土可以大大地减少城市噪音、粉尘、道路污染等问题。改变施工现场脏、乱、差等现象。2.商品混凝土的发展将带来建筑工程领域的一次新的技术革命在反复的科研实践中人们逐渐认识到,决定混凝土强度和耐久性的是水灰比,而不是水泥的标号和用量。高效减水剂和矿物掺和料的开发和应用,可以使混凝土在水灰比非常低的条件下,浇注成型,强度…     

粉煤灰的掺入量对混凝土性能影响的试验研究

本文研究了粉煤灰不同掺入量对混凝土性能的影响。试验结果表明:对于强度而言普通混凝土一般掺量在25%以内为宜;粉煤灰混凝土应增加钢筋保护层厚度;掺粉煤灰混凝土具有良好的抗冻融性能和抗氯离子渗透能力;粉煤灰混凝土收缩性能在不同的时间段有所不同;养护应采取即时塑料薄膜养护而不宜采取直接蓄水养护。     

低温条件下大体积混凝土温控与防裂措施

为有效防止调蓄池底板混凝土产生裂缝,本文以某流域治理一期工程为实例,根据工程的结构特点,采取分层、分块浇筑措施对混凝土进行浇筑,在浇筑后采取措施对混凝土进行养护。结果表明：在低温条件下,通过节约水泥用量来优化混凝土配合比可有效降低混凝土内部最高温度。在进行混凝土浇筑时,对浇筑区域进行合理分块、分层浇筑,在混凝土浇筑后12～18 h内,及时采取养护措施能有效的将混凝土内外温差控制在25 ℃以内,从而降低裂缝产生的可能性。通过研究结果提出低温条件下大体积混凝土温控与防裂措施,对各施工企业在低温条件下进行大体积混凝土浇筑和养护具有借鉴意义。     

高温下钢筋与混凝土粘结锚固性能试验研究

为研究温度对钢筋与混凝土粘结性能的影响,通过制作30个标准立方体试块、8个温度场试件及15个中心拉拔试件,分别完成了室温(20℃)、100℃、200℃、400℃、600℃下标准立方体试块抗压试验与抗拉劈裂试验、拉拔试件温度场试验及中心拉拔试验.分析了高温作用对混凝土抗压强度与抗拉强度的影响,根据温度场试验研究结果,提出一种简易的高温下中心拉拔试验方法,在此基础上研究了高温下钢筋与混凝土粘结性能退化规律.基于Harajli模型综合考虑温度对粘结强度、峰值滑移及试件破坏模式的影响,提出了高温下钢筋与混凝土粘结-滑移本构模型.试验结果表明:高温下混凝土强度、钢筋与混凝土的粘结强度随温度升高整体呈下降趋势,但在100℃时发生陡降现象,高温下钢筋与混凝土的粘结强度变化趋势与混凝土抗拉强度相近.最后提出了高温下钢筋与混凝土的粘结-滑移本构模型,并验证了模型的适用性.     

Prediction of creep of polymer concrete

Polymer concrete possesses viscoelastic properties conditioned by relaxation processes in the polymer binder. Their acceleration with an increase of temperature (principle of time–temperature equivalence) is used in predicting the long‐term creep of polymer concrete. Physical aging of the polymer binder influences the creep of polymer concrete. To predict the long‐term creep accounting for the aging process, an attempt to improve the time–temperature equivalence principle was undertaken. As a result of the experimental study of polyester resin‐based concrete and its structural components (a resin unfilled and filled with diabase flour), it has been established that the changes in the creep compliance of the material follow according to the principle of the time–aging time equivalence with the reduction function depending on aging temperature. To predict the long‐term creep of polymer concrete, a function of the time–temperature–aging time reduction was applied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1949–1952, 1999     

Scaling and corrosion resistance of steam-cured concrete

In this paper, effects of various factors such as steam temperature, precuring time, air content, and fly ash (FA) on the deicer-scaling resistance and corrosion resistance of steam-cured concrete were investigated. Results showed that the deicer-scaling resistance and corrosion resistance of steam-cured concrete without FA were much lower than those of concrete cured in 20 °C under the same condition, and became worse with the increase in steam temperature and with the reduction of precuring time. The deicer-scaling resistance of steam-cured concrete was also improved with the increase in the air content, but the corrosion resistance of steam-cured concrete with 4.5% air content was a little lower than that of steam-cured concrete without SJ-2. The deicer-scaling and corrosion resistances of steam-cured concrete with FA were better than those without FA. Moreover, these results are discussed by analysing air-void parameters, 3-day-intake evaporable water, and compressive strength of concrete.     

盐冻融与干湿作用下沥青混凝土的高低温力学性能分析

制备了沥青混凝土样品,并进行了不同次数的盐冻融干湿循环试验。在此基础上,测试了沥青混凝土的高温车辙深度、动稳定度和低温抗弯拉强度,得到了车辙深度、动稳定度和抗弯拉强度随盐冻融干湿循环次和盐浓度的变化规律,研究了盐冻融与干湿作用下沥青混凝土的高低温力学性能。研究结果表明:(1)沥青混凝土60min车辙深度随盐浓度的增加和冻融循环次数的增多而呈线性增长的趋势;(2)沥青混凝土的抗高温变形能力随盐冻融干湿循环次数的增多而逐渐弱化;(3)沥青混凝土的抗弯拉强度经历9次和15次盐冻融干湿循环后分别下降22%~26.4%和42.6%~51.5%;(4)冻融干湿循环次数一定时,沥青混凝土的抗弯拉强度随盐浓度的增加而缓慢下降,并且当盐浓度达到12%时,沥青混凝土的抗弯拉强度减小就很不明显。     

不同水胶比的橡胶混凝土低温力学性能试验研究

在3种水胶比0.35、0.40、0.45下,分别配制含4种橡胶掺量的混凝土,在低温-30 ℃、常温20 ℃和0 ℃进行立方体抗压强度、劈裂抗拉强度试验研究.结果表明,低温条件下,不同水胶比的橡胶混凝土抗压和抗拉强度均有所提高,但强度变化有明显差异,水胶比越大,受低温的影响程度越显著.在0 ℃时,基准混凝土的强度较常温略有下降,随着橡胶掺量的增加,强度由减小转变为增大趋势.低温-30 ℃时,水胶比为0.35时,橡胶混凝土力学性能相对优越.     

Dynamic compressive behavior of basalt fiber reinforced concrete after exposure to elevated temperatures

This paper investigated the dynamic behavior of basalt fiber reinforced concrete (BFRC) after elevated temperatures by using a 100‐mm‐diameter split Hopkinson pressure bar apparatus. Changes in weight and ultrasonic pulse velocity (UPV) were also studied. The results indicate that the weight losses of BFRC before cooling increase with temperature, while a reduction in weight loss value is observed after water cooling. The UPV values of BFRC decrease constantly as temperature increases, and the measured velocities under the same temperature increase with fiber content as temperature exceeds 200 °C. For a given temperature, the strain rate, dynamic strength, critical strain, and impact toughness of BFRC increase with impact velocity. For a given impact velocity, the increasing temperature generally leads to an increase in strain rate and critical strain and results in a decrease in dynamic strength and impact toughness except in the case of 200 °C. At 200 °C, however, a marginal reduction, even an improvement in dynamic strength is observed, and the impact toughness initially decreases, then increases with loading rate when compared with that at room temperature. Basalt fiber is effective in improving the strength performance, deformation capacity, and energy absorption property of concrete after high temperature. Copyright © 2015 John Wiley & Sons, Ltd.     

低温冻融循环对陶粒混凝土动态力学性能的影响

为了研究冻融循环温度和循环周次对陶粒混凝土动态力学性能的影响,开展了冻融循环试验和Hopkinson束杆动态压缩试验.冻融循环温度上限取+10℃,下限取为-20～-60℃,间隔-10℃,试样尺寸150 mm×150 mm×100 mm,对冻融循环后的试样进行动态压缩试验.结果表明,增加冻融循环周次和降低冻融循环温度,均...     

南海石化项目储罐基础大体积混凝土保温测试方法

建设施工中往往涉及到大体积混凝土施工,如高层楼房基础、大型设备基础等。大体积混凝土施工除了要考虑混凝土的制作与浇筑之外,还要注重混凝土养护阶段的温度控制工作。如何对大体积混凝土进行养护阶段的温度控制,确保混凝土不产生温度裂缝,至关重要。     

The effect of high temperature on the residual mechanical performance of concrete made with recycled ceramic coarse aggregates

This paper presents an experimental study on the residual mechanical properties of concrete with recycled ceramic coarse aggregate (RCCA) after exposure to elevated temperatures. Four concrete mixes were produced: a control concrete and three concrete mixes with replacement ratios of 20, 50 and 100% of natural aggregate (NA) by RCCA. The specimens were subjected to temperatures of 200, 400 and 600°C, for a period of 60 min. After cooling down to room temperature, the following concrete properties were evaluated: (i) compressive strength; (ii) splitting tensile strength; (iii) modulus of elasticity; (iv) ultrasonic pulse velocity (UPV); and (v) water absorption by immersion. At ambient temperature, as expected, the replacement of NA by RCCA resulted in a performance reduction of concrete. After exposure to elevated temperature, in general, the results obtained indicated an improvement of the residual relative mechanical properties of the mixes with RCCA, particularly after exposure to 400 and 600°C. However, exposure to the highest temperature (600°C) tended to cause spalling in concrete mixes containing RCCA. Significant linear correlations were observed between the residual compressive strength of all concrete mixes and both the UPV and the water absorption by immersion. Copyright © 2014 John Wiley & Sons, Ltd.     

超长钢筋混凝土结构无缝设计实践

通过分段浇筑补偿收缩混凝土抵抗干缩变形,同时通过温差应力计算,确保使用过程中混凝土温差应力不超过抗拉强度,实现超长混凝土结构的无缝设计.