Abbas Nezhad Hassan

Two-Phase Numerical Modeling of Fresh Concrete, Using SPH Method

Abstract

Concrete is one of the most practical structural materials. Concrete is consist of aggregates that cohesived by cement mortar. Some of characteristics of proper harden concrete are; complete filling of molds, good cohesions to bars, homogeneous paste, aggregates and hollows are distributed uniformly and smooth finished surfaces without hollows. Most of durability problems of concrete structures are made by improper concrete mostly caused by leaving holes, high porosity, aggregate segregation, bleeding caused by capillarity, concentrating or settlement of aggregates, or dense reinforcement. These problems could be predicted by computer simulation of fresh concrete flow using numerical methods incorporated with experimental and analytical results. These methods are used together to decrease probable problems. This investigation is conducted to predicate concrete flow during form filling of concrete using two-phase of concrete (cement paste and aggregate).

In this study, concrete flow is simulated in two phases (liquid and solid) using SPH numerical method (Smoothed Particle Hydrodynamics). Liquid phase assumed to be a non-newtonian fluid. Interaction forces between solid and fluid phases are estimated using two different points of view. First, solids are simulated with accurate boundaries. Second, solids are simulated as a particle. Results of some problems verification are demonstrated in chapter 4. At first some examples of newtonian and non-newtonian homogenous fluid of flow between two parallel plates, flow through pipe, dam break, and falling suspended solid in fluid are solved by SPH method to verify the presented methods. Then example of contact between solids and boundaries are investigated to verify proposed methods for solids contact. Finally, some problems of two-phase concrete flow are investigated. These problems are consist of, concrete flow during form filling of concrete in I-shape beam, calculating of exerted force to sphere dragging viscometer and comparison to other numerical investigations, and estimating spreading diameter of slump test during time pass and comparison to other numerical investigations.

Based of conducted study, if could be conclude that first point of view in simulation of solid has a good estimation of flow field around substances and good accuracy in calculating of forces, contact and friction between solids are accurately modeled in the first point of view. Results of this investigation showed that presented methods are able to predict concrete form filling problems and these methods are reliable in problem with mold or reinforcement complexity. Some of results in this investigation were predictable that could a reason for some of results are validated base on expectation. Increasing sharpness of aggregate, decreases segregation and settlement of aggregates and distribution of aggregates are more uniform. Increasing in aggregates size, increases probability of blocking flow by reinforcement. Increasing in aggregates sharpness, increases viscosity and yield stress of concrete. Also, this study shows that the second point of view in solid simulation (simulating as particle)  does not demonstrate proper results.