自密实高性能轻骨料混凝土力学性能与粘结锚固性能研究

发布时间：2018-12-15 22:49

【摘要】：轻骨料混凝土(lightweight concrete,LWC)具有轻质高强、保温隔热、耐火抗冻等特点,能够显著改善结构的抗震性能和耐久性。但破坏发生在骨料处,导致弹性模量低,延性问题突出,且施工过程中存在骨料上浮,引起粗细骨料分层现象严重。采用纤维增韧的自密实轻骨料混凝土(self-compacting lightweight concrete,SCLC)兼具轻骨料混凝土和自密实混凝土的优势,能够显著提高延性和改善轻骨料混凝土的施工工艺,但国内外在该方面开展研究较少。因此,本文结合现有研究进展,对自密实高性能轻骨料混凝土的配合比设计、工作性能、破坏机理、微观结构特征、粘结滑移等进行了系统的研究,主要包括以下几方面:(1)配合比设计与工作性能。以固定砂石体积法和全计算法为理论依据,选用合适的原材料,通过调整水胶比、外加剂含量,经过多次试配,设计了强度等级为LC40、LC50的SCLC及四种纤维改性自密实高性能轻骨料混凝土;开展了流动扩展度试验、V型漏斗试验、L型槽试验及U型槽试验并通过混凝土断面图观察骨料的分布情况。研究表明:设计的六组SCLC的工作性能良好,能够满足实际工作要求;(2)基本力学性能。通过试验,系统的对立方体抗压强度、劈裂抗拉强、抗折强度等力学性能进行了研究,深入分析了纤维对其力学性能的影响。研究表明:SCLC中粗骨料的剪切破坏是导致其呈现明显脆性破坏的重要原因,纤维的加入能够显著提高SCLC的劈裂抗拉强度、抗折强度,提高其韧性,改善脆性破坏特征,提高延性;(3)微观结构特征。采用电镜扫描技术对微观试验试样中不同龄期、不同外掺矿物的粗骨料—浆体界面、纤维—浆体界面等进行了多倍数的观察分析。结果显示:SCLC的界面过渡区非常致密,粘结性能优于普通自密实混凝土,纤维的掺入增加了浆体与骨料界面处的连接,提高了延性;(4)与变形钢筋的粘结锚固性能。设计了10组中心拉拔试验试件,分析了混凝土强度等级、钢筋直径、钢筋锚固长度、不同纤维掺量对SCLC与钢筋粘结锚固的影响规律及原因,提出了SCLC粘结强度的计算模型,建立了自密实高性能轻骨料混凝土与钢筋的应力-滑移本构关系模型。研究表明:SCLC中浆体强度和骨料强度共同决定黏结强度,且浆体强度影响大于粗骨料,建议的滑移本构关系模型与试验结果吻合较好。论文研究成果可为轻骨料混凝土的工程实际应用提供理论基础,能够为改善LWC的延性提供思路,具有重要理论意义和实际价值。
[Abstract]:Lightweight aggregate concrete (lightweight concrete,LWC) has the characteristics of light weight and high strength, heat insulation, fire resistance and freezing resistance, which can improve the seismic performance and durability of the structure. However, the failure occurs at the aggregate, which leads to the low elastic modulus, prominent ductility problem, and the floatation of aggregate in the construction process, which results in serious stratification of coarse aggregate. Fiber toughened lightweight aggregate concrete (self-compacting lightweight concrete,SCLC) has the advantages of both lightweight aggregate concrete and self-compacting concrete, which can significantly improve ductility and construction technology of lightweight aggregate concrete. But there are few researches in this field at home and abroad. Therefore, combined with the existing research progress, this paper systematically studies the mix ratio design, working performance, failure mechanism, microstructure characteristics, bond-slip and so on of self-compacting high performance lightweight aggregate concrete. Mainly include the following aspects: (1) mix ratio design and performance. Based on the theory of fixed sand volume method and total calculation method, choosing suitable raw materials, through adjusting water / binder ratio, admixture content, after many tests, the strength grade is designed as LC40,. SCLC of LC50 and four kinds of fiber modified self-compacting high performance lightweight aggregate concrete; The flow expansion test, V-shaped funnel test, L-groove test and U-groove test were carried out, and the distribution of aggregate was observed through the concrete sectional diagram. The results show that the six groups of SCLC have good performance and can meet the practical requirements. (2) basic mechanical properties. The mechanical properties such as cube compressive strength splitting tensile strength and flexural strength were systematically studied and the effect of fiber on mechanical properties was analyzed. The results show that the shear failure of coarse aggregate in SCLC is an important reason for its obvious brittle failure. The addition of fiber can significantly improve the splitting tensile strength, flexural strength, toughness and brittle failure characteristics of SCLC. Improving ductility; (3) microstructure characteristics. The scanning electron microscopy (SEM) technique was used to observe and analyze the coarse aggregate / slurry interface and fiber / slurry interface of different ages and different mineral admixtures in the microcosmic test samples. The results show that the interfacial transition zone of SCLC is very compact, and the bond property is better than that of ordinary self-compacting concrete. The addition of fiber increases the connection between the slurry and aggregate interface, and improves the ductility. (4) the bond and anchoring properties of SCLC with deformed steel bar are improved. Ten groups of central drawing test specimens were designed. The influence of concrete strength grade, steel bar diameter, reinforcement Anchorage length and different fiber content on bond anchoring between SCLC and steel bar was analyzed. The calculation model of SCLC bond strength was put forward. The stress-slip constitutive model of self-compacting high performance lightweight aggregate concrete and steel bar is established. The results show that the bond strength is determined by the strength of paste and aggregate in SCLC, and the influence of the strength of slurry is greater than that of coarse aggregate. The suggested slip constitutive model is in good agreement with the experimental results. The research results can provide a theoretical basis for the practical application of lightweight aggregate concrete and provide ideas for improving the ductility of LWC. It has important theoretical significance and practical value.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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