The present research investigates the feasibility of manufacturing masonry mortars with recycled sand. The primary aim is to study the effect of fine recycled aggregates on fresh and hardened states with properties. Two series of mortars were designed by substituting natural sand with recycled sand, with variable sand replacement ratios ranging from 0% to 100%. One series, named variable workability series, has variable workability with constant water to cement ratio (W/C), while the other series, called constant workability series, has a constant workability with variable W/C. The density, air content, and slump of mortars in fresh state were measured with a special attention devoted to the effect of pre-saturation of recycled sand on the slump. In the hardened state, the microstructure was studied by means of water accessible porosity test and mercury intrusion porosimetry test. Flexural and compressive strength as well as the dynamic modulus of elasticity were also examined and the correlations between these properties and the microstructure have been established. It was found that the properties of mortars with recycled sand are lower than those obtained for the natural sand mortar (−20% for variable workability series and −45% for constant workability series at the age of 28 days). For the series with variable workability, mechanical properties decrease to a step starting from 30% replacement ratio, while linearly decrease for the mortars with constant workability. The difference between the two series lies in the difference in total porosities and the pore size distribution.

中文翻译：

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配方参数对不同再生砂配比混凝土等效砂浆性能的影响

本研究调查了用再生砂制造砌筑砂浆的可行性。主要目的是研究细再生骨料对具有特性的新鲜和硬化状态的影响。用再生砂替代天然砂设计了两个系列的砂浆，砂替代率从0%到100%不等。一个系列称为可变和易性系列，具有恒定水灰比 (W/C) 的可变和易性，而另一个系列称为恒定和易性系列，具有恒定的和易性和可变水灰比。测量新砂浆的密度、空气含量和坍落度，特别注意再生砂的预饱和对坍落度的影响。在硬化状态下，通过水可及孔隙率试验和压汞孔隙率试验研究了微观结构。还检查了弯曲和压缩强度以及动态弹性模量，并建立了这些特性与微观结构之间的相关性。结果表明，再生砂砂浆的性能低于天然砂砂浆的性能（28 天龄期可变和易性系列为 -20%，恒定和易性系列为 -45%）。对于可变和易性系列，机械性能从30%替代率开始下降，而对于恒定和易性的砂浆则线性下降。两个系列的区别在于总孔隙率和孔径分布的不同。