The porous lightweight aggregates adversely affect fresh properties of concrete, including slump and disruption of pumping concrete. Besides, this type of concrete is very susceptible to shrinkage cracking. In this study, two types of lightweight aggregates were used with a combination of two types of coating, including hydrophobic polymers -polyvinyl acetate and styrene-butadiene rubber coatings. The coatings were applied in single and double layers. For the fresh concrete, the fresh properties of concrete, including slump flow, T₅₀, flow time, and L-Box were evaluated and for the hardened concrete, compressive strength, flexural strength, tensile strength, water absorption and shrinkage was studied. It was seen that the slump flow of coated lightweight aggregates increased by 10%, and also coating process reduced the water absorption of the aggregates up to 82%. The compressive strength increased by up to 21% for the coated aggregates. Scanning electron microscopy was also used to investigate the microstructure of the mortar-aggregate interface. Microstructural images showed a uniform and dense interfacial zone of cementitious matrix-aggregate for coated lightweight aggregates. Moreover, an improvement of 50–150 μm in the interfacial zone's thickness was seen for coated aggregates compared to uncoated aggregates.

中文翻译：

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预涂轻骨料对自密实混凝土的影响

多孔轻质骨料对混凝土的新鲜性能产生不利影响，包括坍落度和泵送混凝土的破坏。此外，这种类型的混凝土很容易出现收缩开裂。在这项研究中，两种类型的轻质骨料与两种类型的涂层组合使用，包括疏水聚合物 - 聚醋酸乙烯酯和丁苯橡胶涂层。涂层以单层和双层形式施加。对于新拌混凝土，混凝土的新拌性能，包括坍落度，T ₅₀、流动时间和 L-Box 进行了评估，并对硬化混凝土进行了抗压强度、抗弯强度、抗拉强度、吸水率和收缩率的研究。可以看出，涂层轻骨料的坍落度增加了 10%，并且涂层工艺使骨料的吸水率降低了 82%。涂层骨料的抗压强度提高了 21%。扫描电子显微镜也用于研究砂浆-骨料界面的微观结构。显微结构图像显示用于涂层轻质骨料的水泥基骨料界面区域均匀且致密。此外，与未涂覆的骨料相比，涂层骨料的界面区厚度增加了 50-150 μm。