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在荷载和环境因素作用下,混凝土结构产生不同程度的劣化。为了保证结构的安全性和耐久性,需要对损伤水泥基材料进行修复。基体的含水饱和度、界面粗糙度、修补砂浆的水灰比以及试件的养护条件都会影响修补砂浆与基体间的粘结强度。选取四种含水饱和度(0%、30%、70%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,试件密封养护28 d,剪切试验结果表明:当新砂浆水灰比为0.6,旧砂浆含水饱和度按照70%、30%、100%、0%的顺序变化时,界面的剪切强度逐渐减小;当新砂浆水灰比为0.4,旧砂浆含水饱和度按照30%、0%、70%、100%的顺序变化时,界面的剪切强度逐渐减小。同时发现,新砂浆水灰比为0.4时的界面剪切强度普遍大于水灰比为0.6的数值。通过切槽法改变旧砂浆的界面粗糙度,然后浇筑水灰比为0.6的新砂浆,试件标准养护。剪切试验结果表明:当旧砂浆界面粗糙时,界面间的剪切强度是旧砂浆光滑时的1.26倍。选取两种含水饱和度(0%、100%)的旧砂浆作为基体,浇筑水灰比为0.4和0.6的新砂浆,分别进行标准养护和密封养护,剪切试验结果表明:在旧砂浆含水饱和度和新砂浆水灰比相同的情况下,标准养护下的界面剪切强度明显大于密封养护下的界面剪切强度。 相似文献
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混凝土中未水化水泥后期水化的危害研究 总被引:5,自引:0,他引:5
长期以来,水泥混凝土科技发展以提高强度为主,但事实证明高强度不一定就会有高耐久性。提高混凝土强度的首选方法便是降低水灰比,认为降低水灰比能减少结构缺陷,提高混凝土的强度与耐久性。但对于纯水泥混凝土而言,水灰比越低,混凝土的水化程度就越低,其中的未水化水泥量就越大。在混凝土充分硬化后,未水化水泥的后期水化作用,将对纯水泥高强混凝土结构产生破坏作用,而且水灰比越低,这种破坏作用越严重。 相似文献
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在基体上浇筑新拌砂浆是常见的修补与加固措施。当新拌砂浆与基体含水状态差异较大时,会发生水分交换改变修补砂浆配合比,并影响修补砂浆水化进程、微观特征、渗透性以及修补材料与基体间的粘结性能。对此,利用称重法研究了新拌普通砂浆、应变硬化水泥基复合材料(SHCC)与不同初始含水饱和度旧砂浆基体(0、30%、70%和100%)粘结时的水分交换过程,分析了修补砂浆类型和基体初始含水饱和度对水分交换速度、修补砂浆最终水胶比等的影响。通过力学试验、低场核磁共振技术和称重法进一步研究了水分交换对标准养护后修补砂浆与基体粘结强度、修补砂浆微结构和吸水性能的影响规律。结果表明:在水分交换早期,非饱和基体单位面积吸水质量与时间平方根存在良好的线性关系。基体含水饱和度为0时,SHCC或普通砂浆与基体间的界面剪切强度最高。SHCC作为修补材料与基体间的界面剪切强度普遍大于普通砂浆。随着基体饱和度的增大,普通砂浆的孔隙率、小孔体积分数、毛细吸水系数逐渐增大,中孔和大空隙的体积分数逐渐减小。随着基体饱和度的增大,SHCC孔隙率、中孔和大空隙的体积分数逐渐减小,小孔体积分数和毛细吸水系数变化幅度较小。 相似文献
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超高性能混凝土(UHPC)因为其较高的强度和优良的耐久性被认为是极具潜力的结构修补用材料之一。同时,UHPC与普通混凝土(NC)之间的界面黏结性能,是影响UHPC在混凝土加固修复工程中应用可靠性的关键因素。针对严寒环境,本试验对超高性能混凝土与普通混凝土(以下简称UHPC-NC)黏结试件开展-60 ℃的冻融循环试验,分析冻融循环后试件的宏观形态变化、质量变化率。通过黏结强度试验,获得界面的黏结强度以及相应的界面破坏模式。试验主要分析-60 ℃冻融循环对UHPC-NC试件界面黏结性能的影响,以及界面的不同处理方式(钢丝刷刷毛、高压水射流冲毛及劈裂)对抗-60 ℃冻融循环作用的影响,同时,对冻融作用下UHPC-NC试件的界面损伤机理进行初步探索。试验结果表明:-60 ℃冻融循环对UHPC-NC试件黏结强度有较大影响,劈裂组试件的界面黏结强度在经历10次、15次、20次冻融循环后分别下降为界面黏结基准强度的72.94%、55.62%及44.33%,界面黏结强度呈现先急速下降再缓慢下降的趋势;界面粗糙度越高,界面的剩余黏结强度越大,经历20次冻融循环后,劈裂组试件的剩余黏结强度为高压水射流冲毛试件的2.03倍。 相似文献
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混凝土材料的制备与性能优化是建筑3D打印结构化发展与应用的基础。3D打印混凝土材料的宏观力学性能、长期耐久性能均与界面细观结构直接相关。本文明确了3D打印混凝土层间界面水分状态(水膜)的形成机制,测试了不同打印层厚条带的水膜随时间的演化规律,通过CT扫描技术研究了层间间隔时间、打印层厚、环境状态对层间界面孔隙特征的影响,揭示了层间界面水分状态、层间界面孔隙特征及层间黏结性能三者之间的相互影响机制。结果表明:层间界面孔隙率随单位面积上层间界面水分质量的增长而降低,层间界面水分质量是较打印参数而言更直接的层间界面状态影响因素;层间水分状态和界面细观孔隙特征直接影响着3D打印混凝土材料的宏观力学强度。 相似文献
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通过水化热测试、化学结合水含量测试、X射线衍射分析、压汞测试及强度测试研究了合成的纳米水化硅酸钙(n-C-S-H)对水泥水化过程、硬化水泥浆孔结构及混凝土强度的影响。结果表明:n-C-S-H显著加速了水泥早期水化,提升了水泥在12~24 h龄期的水化程度,从而显著提高混凝土12~24 h龄期的抗压强度,24 h以后对强度提升效果逐渐减小。3 d以后n-C-S-H对混凝土强度发展没有明显的促进作用,1.5%掺量下混凝土强度反而较空白样有所降低;加入n-C-S-H的硬化水泥浆在12 h~3 d龄期内相比空白水泥浆临界孔径降低,凝胶孔孔隙率提高,毛细孔孔隙率降低。n-C-S-H改变了C-S-H凝胶的生成方式,使其原本从水泥颗粒表面析出变为了从孔溶液中析出,显著减小了毛细孔孔隙率,同时增加了凝胶间孔的体积。这种多核生长的方式导致水化产物结构疏松,从而导致基体强度略微降低。因此,在相同水化程度时,掺有n-C-S-H的混凝土抗压强度略低于空白混凝土。 相似文献
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硅溶胶对水泥基材料微观结构和力学性能的影响 总被引:2,自引:1,他引:1
用在水泥基材料试件中插入玻璃板的方法进行黏结强度实验,结合 X射线衍射和扫描电子显微镜分析了硅溶胶对水泥基材料微观结构和力学性能的影响.结果表明:随着硅溶胶掺量的增加,水泥硬化浆体强度、水泥硬化浆体与玻璃板界面黏结强度和混凝土强度均随之增加;但当硅溶胶掺量(质量分数)大于1.50%时,各项强度值不再增加.在1.5%硅溶胶掺量和28 d龄期时,掺矿渣的水泥硬化浆体与玻璃板界面黏结强度比不掺硅溶胶时提高了40%;掺矿渣的水泥混凝土抗折强度和抗压强度分别提高了20%和15%.硅溶胶的掺入能有效地降低水泥硬化浆体与玻璃板界面中氢氧化钙晶体的取向程度,可明显减少界面中氢氧化钙晶体的数量并细化其尺寸,减小界面过渡区的厚度. 相似文献
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预养护对二氧化碳养护混凝土过程及显微结构的影响 总被引:1,自引:0,他引:1
研究了干硬性混凝土经干燥环境预养护后的剩余水灰比对其二氧化碳养护过程及显微结构发展的影响。用热重分析和Fourier红外光谱等方法对二氧化碳养护砂浆过程中形成的产物进行了定性和定量分析,并利用压汞测孔仪分别测试了二氧化碳养护3h和自然养护5h的砂浆的孔径分布。结果表明:剩余水灰比为0.16~0.20时二氧化碳养护程度及抗压强度最高;养护过程中反应物为水泥颗粒及少量水化产物,生成方解石及硅胶;养护程度较高的试件生成的碳酸钙结晶度较高;二氧化碳养护后混凝土孔隙率明显降低,50~1 000nm的毛细孔含量降低,养护程度越高的混凝土,孔结构改善程度越高。 相似文献
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An experimental and analytical study was performed to evaluate the adhesion between concrete and overlays using five different substrate surfaces and six different mixtures of self-compacting concrete and mortar. Saw cut surfaces of high strength concrete slabs were used as substrate. After the application of self-compacting concrete or mortar layers to dry, saturated surface dry, saturated surface wet, dry with bonding grout, and saturated with bonding grout surfaces of concrete slabs, they were covered with wet hessian and polythene sheets for curing. At the age of 28 days, friction-transfer tests were performed to evaluate the adhesion. The results indicate that while dry and saturated wet surfaces produced the lowest bond strength, the application of cement bonding grout improved the bond strength significantly. The results also showed that despite the noticeable correlations between the adhesion and the results of different flow tests, aggregate/cement ratio, fly ash/cement ratio, compressive strength, and water/powder ratio, the effect of the other constituents of the employed self-compacting overlays on their adhesion were not so significant. In order to predict the adhesion of self-compacting mixtures applied to concrete substrates, a fuzzy logic model was also devised. The results obtained from the fuzzy logic prediction model were compared with the average results of the friction-transfer method and found to be in very close agreement. The results show that fuzzy logic can be used to predict adhesion of self-compacting overlays. 相似文献
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This paper presents the results of an experimental study on the effect of curing on the degree of cement hydration and capillary porosity of concrete in a tropical environment. It provides basic information for the estimation of w/c of hardened concrete using petrographic methods. Concrete with w/c ratios of 0.30 to 0.70 with an increment of 0.05 was investigated. The concrete was cured at 20 and 35 °C and exposed to various durations of moist curing. The results indicated that the concrete cured at 20 °C water for 28 days had a higher degree of cement hydration and lower capillary porosity than did the concrete cured in water of the same temperature for 7 days followed by exposure to outdoor air for 21 days, but had an opposite trend compared to the concrete cured in 35 °C water for 7 days followed by exposure to outdoor air. However, the differences on the degree of cement hydration and capillary porosity for the concrete cured in these different conditions were not significant. 相似文献
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This paper reviews the basic nature of the cement-aggregate bond and its effect on concrete performance. The bond is a result of mechanical interlocking provided by epitaxic growth of cement hydration products on the aggregate surface and of chemical reactions between the cement paste and aggregate. The degree to which the bond results from each of these processes is not known. The effect of the bond on concrete performance is a subject of controversy; however, there seems to be a relationship between concrete strength and bond strength, and it is suggested that the quality of the bond affects concrete durability. 相似文献
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Characterization of concrete properties from dielectric properties using ground penetrating radar 总被引:1,自引:0,他引:1
This paper presents the experimental results of a study of the relationships between light-weight (LWAC) and normal aggregate concrete (NAC) properties, as well as radar wave properties that are derived by using ground penetrating radar (GPR). The former (LWAC) refers to compressive strength, apparent porosity and saturated density, while the latter (NAC) refers to real part of dielectric permittivity (ε' or real permittivity) and wave energy level (E). Throughout the test period of the newly cast concrete cured for 90 days, the above mentioned material properties gradually changed which can be attributed to the effects of cement hydration, different types of aggregates and initial water to binder ratios. A number of plots describing various properties of concrete such as dielectric, strength and porosity perspectives were established. From these plots, we compare the characteristics of how much and how fast free water was turned to absorbed water in LWAC and NAC. The underlying mechanisms and a mechanistic model are then developed. 相似文献
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A numerical model for the thermo-hygral (TH) behaviour of cementitious materials is presented. The model includes a new approach to the evaluation of porosity during hydration in which a colloid model and stoichiometry are used to evaluate the volume of bound and unbound water forms. The advantage of the proposed porosity function is that it accounts for different cement types and concrete mixes and it gives a porosity evolution consistent with the moisture mass balance equation. Sink/source terms are introduced for the capillary water that account for the moisture entering/exiting the gel pores and the aggregate, whilst the standard capillary curve is modified to account for temperature and changing porosity with hydration. The numerical model considers as the primary variables the water degree of saturation of capillary pores and the temperature and is validated using several drying experiments. The results are generally in good agreement with experimental measurements. 相似文献
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以不同配比的水胶比和矿渣粉掺量为影响因素,配制混凝土试件进行抗压强度正交试验,深入系统的研究其对高性能混凝土力学性能的影响。在此基础上,通过电镜观测,从微观机理角度对宏观性能进行分析解释。研究表明,混凝土的抗压强度均随着水化龄期的延长而增大。水化早期,掺有矿渣粉的高性能混凝土强度都较低;水化后期,矿渣粉活性效应发挥显著。在水胶比不变时,随着矿渣粉掺量的增加混凝土的强度是在逐渐降低的。使用42.5R普通水泥,控制水胶比在0.40—0.20,掺加矿渣粉,可配制出C45~C65的高性能混凝土。微观机理研究显示矿渣粉的存在使混凝土中孔隙减少,孔径变小,结构变密实,起到了很好的填充和微集料作用。 相似文献