Papers by Keyword: Particle Packing

Abstract: The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al₂O₃-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( > 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm^-3, permanent linear change < 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (I_c = 22.4%) and penetration (I_p = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

Abstract: The continued growth of the world construction sectors has resulted in high demand for concrete materials. The innovation of using filler as a replacement for cement is becoming a trend in order to reduce the cement consumption and provide benefit in various ways. Hence forth, 10% of cement was replaced by the calcium carbonate (CaCO₃) in this study. CaCO₃ is a natural material, which has a finer particles size as compared to the cement particles. This improves particle packing of concrete and give spacer effect. The concrete with CaCO₃ replacement possess a higher slump, which increased the workability. The specimens were prepared in 150mm x 150mm x 150mm mould. At 28 days, the water absorbed by hardened concrete was lower for CaCO₃ as microscopy analysis indicates very low porosity in CaCO₃ concrete. Mechanical properties tests were conducted in 3, 7 and 28 days. The CaCO₃ helps to increase the early strength, due to the accelerator effect and high rate of hydration which hardens the concrete quicker. At matured age, the concrete with the CaCO₃ addition exhibits lower strength as compared with concrete without CaCO₃, but still within the target strength.

Abstract: This paper discusses the particle packing background of cementitious materials. On micro-level the Portland cement and eventually the mineral admixture grains can be considered packed in the watery environment. Particularly for (super) high performance materials, the packing density can be quite significant. An economic and due to fast computer developments reliable way to study packing of the binder, is by modern discrete element modeling (DEM) approach. In this paper use is made of a concurrent algorithm-based dynamic system, HADES. Hydration is simulated based on spherical grains. Thereupon strength can be studied on the basis of packing density. For durability issues, the complex and tortuous 3D pore structure has to be investigated. This paper uses for the assessment of pore characteristics the robotics-inspired DraMuTS system. Hydrated Portland cement is compared with gap-graded rice husk ash-(RHA)-blended (green) Portland cement. Experiments on gap-graded RHA-blended PC concrete are used as reference. Packing density is shown improved by gap-graded packing. What is more spectacular are the effects of gap-grading with RHA on the pore characteristics obtained on the DEM-produced virtual materials. This paper discusses the expected positive effects on transport-based durability issues due to gap-graded packing-induced changes in the pore system

Abstract: Cementitious material can be considered consisting of particulate elements on the levels of the microstructure and mesostructure. HADES is a concurrent algorithm-based program, designed to simulate the mixing or flow of granular material encompassed arbitrary particle shapes. In this paper, a specific technology is employed to generate the single aggregate particle of arbitrary shape in HADES. Then with the HADES toolbox materials structure can be formed. Based on these work, concrete is taken as an example of a typical cementitious material. With the simulated meso-structure of concrete from HADES, interfacial transition zone (ITZ) is enriched and a special tool is employed for the meshing of aggregates, cement paste and ITZ. After that finite element method is used for the analysis of stress and strain within the meso-structure. The calculation results show that the approach to simulate cementitious material, of HADES packing, then meshing and finally finite elements analysis, is feasible and effective and the numerical prediction of elastic modulus of concrete consisting of three-phase material is in agreement with effective.