摘要
从可持续发展的观点出发,将废弃混凝土循环再生骨料与粉煤灰、磨细矿渣粉等一起配制高性能再生骨料混凝土可以很好地解决资源和环境的协调发展问题。因此,本文以试验研究为主,对高性能再生骨料混凝土的基本性能和微观结构进行了研究,主要内容如下:
首先,对高性能再生骨料混凝土的基本力学性能进行了试验研究,试验结果显示高性能再生骨料混凝土的立方体抗压强度、轴心抗压强度和劈裂抗拉强度均稍低于同强度等级的高性能天然骨料混凝土,而其弹性模量明显低于高性能天然骨料混凝土,随着强度的提高,高性能再生骨料混凝土的弹性模量提高,且高性能再生骨料混凝土的破坏都是界面破坏。
第二,提出了在新旧水泥石之间和旧水泥石与原天然骨料之间存在一个双层界面的观点,并运用扫描电镜、偏光镜和显微硬度计对高性能再生骨料混凝土的水化产物形貌、界面过渡区缺陷和界面显微硬度进行了测试。试验表明在再生骨料与新水泥石之间的界面过渡区内存在一些孔洞、微裂纹以及疏松的Ca(OH)2晶体且界面硬度低,从再生骨料表面到水泥石本体,界面弱区的特点逐渐变弱;随着强度的提高和水化龄期的增长,界面过渡区的显微硬度增大。试验还表明粉煤灰、矿渣等微细矿粉可以改善再生骨料混凝土界面过渡区的性能,提高再生骨料混凝土的密实性。
第三,通过试验获取了高性能再生骨料混凝土的应力-应变全曲线,试验发现高性能再生骨料混凝土的峰值应力稍低于同强度等级的高性能天然骨料混凝土,而峰值应变则明显高于高性能天然骨料混凝土;高性能再生骨料混凝土峰值应力和峰值应变都随强度的提高而提高;建立了高性能再生骨料混凝土的应力-应变本构模型,且根据该模型拟合的理论曲线与试验曲线吻合较好;定义和计算了高性能再生骨料混凝土的“压缩应变能”和“脆性指数”,计算结果表明随着强度的提高,高性能再生骨料混凝土的压缩应变能增大,脆性指数增大。
最后,对高性能再生骨料混凝土的抗氯离子渗透性展开了试验研究。试验表明随着强度的提高和龄期的增长,高性能再生骨料混凝土的抗氯离子渗透性显著增强,矿粉、粉煤灰等微细矿物质大大改善了再生骨料混凝土抗氯离子侵蚀性。试验还表明高性能再生骨料混凝土的抗氯离子渗透性较高性能天然骨料混凝土差,但其仍具有很好的抗氯离子渗透性,能满足工程耐久性要求。
本文的研究为再生混凝土的破坏机理和再生混凝土结构的非线性分析提供了研究基础,为制定再生混凝土应用的技术规范提供了重要的参考。
In consistent with sustaining development, the recycled high performance concrete that is made from recycled concrete aggregates, fly ash, granulated blast-furnace slag and so on, could be a perfect solution to resource and environment preservation. Therefore, on the basis of experimental research, the basic behaviors and microstructure of recycled high performance concrete are studied in this thesis. The main contents of this thesis are introduced as follows:
Firstly, the basic mechanical behaviors of high performance concrete are tested and the results indicate: the cubic compressive strength, axial compressive strength and tensile splitting strength of recycled high performance concrete are just a little lower than those of common high performance concrete. At the same time, the elastic modulus of recycled high performance concrete is evidently lower than that of common high performance concrete.
When the concrete’s strength enhanced, the elastic modulus of recycled high performance concrete increases, and moreover, the failure of the recycled high performance concrete is often broken by the interface between the recycled aggregates and the new mortar matrix. Secondly, the viewpoint of a two-layer interface of recycled concrete aggregates is put forward in this thesis, one interface is between the original aggregate and the old adhesive mortar, the other interface is between the old adhesive mortar and the new mortar matrix. And the morphology of concrete’s hydrates, the defects and the microhardness values in the Interfacial Transition Zone(ITZ) of recycled high performance concrete are tested by using scanning electro microscopy, polarizing microscope and microhardness testing machine. The test results indicate: some voids, microcracks and loose hydrates of Ca(OH)2 crystal are existed in the recycled aggregate-matrix ITZ, and the microhardness values in the ITZ are lower than those of the mortar matrix body, but those disadvantageous features in ITZ gradually weaken and the ITZ become much stronger from the recycled aggregate to the mortar matrix body; as well the microhardness values in the ITZ increase with the concrete’s strength enhanced and the growth of hydration ages of the recycled high performance concrete. However, the mineral fumes, such as fly ash, granulated blast-furnace slag and so on, can improve the performances of the ITZ of recycled high performance concrete and make the recycled aggregates concrete become much denser.
Thirdly, the complete stress-strain curves of recycled high performance concrete are obtained from the test. It is found that the peak stress of recycled high performance concrete is just a little lower than that of common high performance concrete,while, on the contrary, its peak strain is obviously higher than that of common high performance concrete. Furthermore, both the peak stress and peak strain of recycled high performance concrete increase companying with the concrete’s strength enhanced. Then a stress-strain relation model of recycled high performance concrete is constructed, and the theoretical curve is faithfully accord with the test curve; moreover, the“compressive strain energy”and the“brittle index”of recycled high performance concrete are defined and calculated, and the results indicate that both the compressive strain energy and brittle indexes of recycled high performance concrete increase with the concrete’s strength enhanced.
Finally, Chloride ion penetration of recycled high performance concrete has been tested in the study. The test results indicate that the resistance of chloride ion penetration of recycled high performance concrete has evidently intensified as the concrete’s strength enhanced and the growth of hydration ages. As well the mineral fumes, such as granulated blast-furnace slag, fly ash and so on, can greatly improve the resistance of chloride ion penetration of recycled aggregates concrete, and the resistance of chloride ion penetration of recycled high performance concrete is lower than that of common high performance concrete. However, the resistance of chloride ion penetration of the recycled high performance concrete remains good, and it is satisfied with the durability of the engineering.
The researches in the thesis would establish basis for studying the failure mechanism of recycled aggregates concrete and the non-linear analysis of recycled aggregates concrete structure, and the test results would also provide important references for constituting technical specification of the recycled aggregates concrete.
引文
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