Tao Chengcheng, Massoudi Mehrdad
School of Construction Management Technology, Purdue University, West Lafayette, IN 47907, USA.
National Energy Technology Laboratory (NETL), U. S. Department of Energy, Pittsburgh, PA 15236, USA.
Materials (Basel). 2024 Mar 26;17(7):1504. doi: 10.3390/ma17071504.
Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection-diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry.
纳米二氧化硅和粉煤灰等添加剂广泛应用于水泥和混凝土材料中，以改善新拌水泥和混凝土的流变性能以及硬化材料的性能，并通过减少波特兰水泥的用量来提高水泥和混凝土行业的可持续性。因此，研究这些添加剂对新拌水泥流变行为的影响具有重要意义。在本文中，我们通过考虑两种不同的添加剂及其组合（纳米二氧化硅、粉煤灰、纳米二氧化硅与粉煤灰的组合），研究了水平管道中新鲜水泥的脉动泊肃叶流动。为了模拟新鲜水泥悬浮液，我们使用了幂律模型的修正形式来证明水泥粘度与水泥和添加剂颗粒的剪切速率及体积分数之间的依赖关系。对流扩散方程用于求解体积分数。在以无量纲形式求解方程后，我们进行了参数研究，以分析纳米二氧化硅、粉煤灰以及纳米二氧化硅与粉煤灰的组合添加剂对水泥悬浮液速度和体积分数分布的影响。根据本文提出的参数研究，较高的纳米二氧化硅含量会导致水泥悬浮液的中心线速度较低，且体积分数的不均匀性较大。与纳米二氧化硅相比，粉煤灰对速度的影响相反。较高的粉煤灰含量会导致中心线速度较高，而粉煤灰对体积分数的影响不明显。对于含有纳米二氧化硅与粉煤灰组合添加剂的水泥悬浮液，纳米二氧化硅在悬浮液的流动行为中起主导作用。该研究结果有助于3D打印行业中新拌水泥砂浆和混凝土脉动流动的设计与操作。
