Numerical Analysis of SCC Lateral Pressure on Formwork Systems

This essay provides a numerical analysis of the lateral pressure exerted by self-consolidating concrete (SCC) on formwork, examining various methods used to understand and predict this pressure. It discusses the Discrete Element Method (DEM) and its ability to analyze factors like mixing speed, discharge homogeneity, and aggregate size, highlighting its role in preventing formwork collapse. The Volume of Fluid (VOF) method is explored for its use in modeling the interface between SCC and fluids, focusing on the distribution of concrete ingredients and air voids. The Two Fluid Method, treating concrete as a fluid, is presented as a means to demonstrate SCC flow and pressure exertion, emphasizing the interaction between solid, liquid, and gaseous particles. The Multiphase Mixture Model, a simplified Eulerian approach, is examined for determining continuity, momentum, and pressure drop, considering the different phases of SCC. Finally, the Liquid Penetrant Testing (LPT) method is discussed for its role in identifying discontinuities and cracks in the concrete. Each method's strengths and limitations are considered in assessing the overall impact on formwork design and structural integrity. This document is available on Desklib, a platform offering a range of study tools and resources for students.

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NUMERICAL ANALYSIS OF THE LATERAL PRESSURE EXERTED BY THE
FLOWABLE CONCRETE ON FORMWORK
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Numerical Analysis of the Lateral Pressure Exerted by the Flowable Concrete on
Formwork
1. Discrete Element Method
The behavior of self-consolidating concrete (SCC) when it is being mixed, transported
and poured/placed affected numerous properties of the concrete, including the lateral pressure
that it exerts on formwork (Mechtcherine, et al., 2014). There are numerous factors affecting the
lateral pressure exerted on formwork by flowable SCC. Some of them include: speed and time of
mixing the concrete, speed of discharging the concrete, and discharging homogeneity’s oblique
angle. These factors can be measured using discrete element method (DEM), also called distinct
element method. Results from this test show that SCC’s discharge homogeneity increases when
mixing speed increased from up to a certain value after which it starts decreasing with increasing
mixing speed. Also, discharging homogeneity of SCC is inversely proportional to discharging
speed, mixing time and oblique angle (Deng, et al., 2016). Results from DEM also show that the
size of aggregates of SCC affect the ability of the concrete to pass more than the content of
coarse aggregates. Additionally, the ability of SCC to pass when being placed in the form is
affected by the free space available between the reinforcement bars (Cui, et al., 2018). Therefore
DEM demonstrates that lateral pressure exerted on formwork by SCC can be affected by the
ability of the concrete to flow through the reinforcement during concrete pouring/placing. This
implies that the size of aggregates and the spaces between reinforcement bars have to be properly
designed so as to avoid blocking of SCC for equal distribution of lateral pressure on the
formwork, which is useful in preventing collapse of formwork and eventually failure of the
reinforced concrete structure being built.

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Discrete element method is a very reliable and accurate method when analyzing pressure
exerted by reinforced concrete (Lu, et al., 2016). However, this method has some limitations.
Some of the main drawbacks of this method such as indefinite conservation of mass and
restrictions in free surfaces modelling can be overcome using its improved versions such as
smoothed particles hydrodynamics (SPH), an improved Lagrangian particle method (Wu, et al.,
2016). Generally, the results obtained from DEM should be similar to those obtained from
experimental tests. These results show the behavior of SCC, including the factors affecting
lateral pressure exerted on formwork (Gram, 2009). This method creates a discrete element
model that can be used critically analyze how lateral pressure of the SCC is distributed and
exerted on the formwork, and also simulate factors influencing the pressure (Zhang, et al., 2017).
2. Volume of Fluid (VOF) Method
This method is mainly used to establish the development of the interface between SCC
and fluid (air and water) when the formwork is being filled (Tichko, et al., 2014). The main
expected outcome of this method is a model showing distinct phases of the concrete. Concrete
comprises of different ingredients: coarse aggregates, fine aggregates (sand), cement, water and
admixtures. These ingredients have varied densities, sizes and shape and are likely to settle in
layers based on these properties if they are not consolidated properly. However, concrete is
supposed to be homogenous meaning that all the ingredients have to be mixed so that each layer
has equal combination of the ingredients. The distribution of ingredients in layers has a
significant influence on the strength of concrete. That is why it is very important to develop a
volume of fluid model of SCC. This method should therefore provide a model showing the
distinct interfaces between different ingredients of SCC. It has to show the volume fraction of
SCC and volume fraction of air (Khalili, et al., 2016). Volume fraction of SCC is determined by

Lateral Pressure by SCC on Formwork 4
dividing volume of the SCC in the formwork (Vscc) by the volume of the formwork (Vf) in which
the concrete sample is placed (Vscc/Vf) (Wallevik & Wallevik, 2017). The volume of the SCC in
the formwork must be less than or equal to the volume of the formwork (Vscc≤Vf) meaning that
the ratio between the two can be one or less than one. In cases where Vscc/Vf = 1, it means that
the formwork is filled with SCC only, while if Vscc/Vf = 0, it means that the formwork is filled
with air only. However, the typical interface is represented by 0 < Vscc/Vf < 1 (Dianat, et al.,
2017). This simply means that the formwork is filled with both SCC and air.
This method is expected to show the free surface profile of SCC and air. SCC
consolidates without use of mechanical devices such as vibrators or compactors. This means that
the strength of SCC is significantly influenced by the ability of the concrete to self-consolidate.
If there is too much air or water in the concrete then it will not achieve the required strength. If
there is too much water, it is likely to settle at the top while the solid components of SCC settle
at the bottom due to differences in their densities. In general, this method is expected to provide
information about distribution of air in the SCC. The information is useful in establishing
whether the air voids present in SCC will affect the strength and stability of the concrete
structure. However, the VOF method has to be customized or modified so as to suit the needed
conditions.
3. Two Fluid Method
This method assumes that the behavior of SCC is similar to that of a fluid. In other
words, two fluid method takes concrete as a fluid. The expected outcome of this method is to
demonstrate how SSC flows to the surface of formwork. This flow causes SCC to exert pressure
on the internal surface of the formwork. In other words, this method will be used to develop a
two-fluid model of the SCC to show the relationship between lateral pressure exerted on the

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formwork by the SCC and space and time. Unlike VOF method, two fluid method does not track
interface of the fluids. This method will demonstrate how the flow of SCC is dispersed. Previous
studies have shown that two fluid method provides results that are very close to the real world
than VOF method results. Therefore two fluid method will provide results that are very close to
actual behavior of SCC in real world.
Two fluid method is used on the fact that SCC comprises of different components i.e.
solid, liquid and gaseous particles. The interaction between these particles creates phases. For
instance, there are gas-solid phase, gas-liquid phase and liquid-solid phase (Chen & Wang,
2014). The flow between these phases is also different depending on how the particles interact.
The two-fluid system basically provides a presentation on how different particles of SCC
ingredients interact. This interaction is important because it influences the amount of lateral
pressure generated. Since the particles are also of different density, the pressure contributed by
each particle is also different (Van Foreest, et al., 2011). Because of their densities, solid
components are likely to settle at the bottom, whereas liquid and gas particles settle on top. This
kind of distribution is undesirable as it will mean that there will be differences in pressure
distribution of the SCC from the top to the bottom. In the long run, lateral pressure exerted on the
formwork will be greater at the bottom than at the top (Spangenberg, et al., 2012). This is likely
to cause failure of the formwork system, starting from the bottom because stress will be very
high at the bottom and low at the top (Xue, et al., 2010).
Generally, two fluid method will be used to predict different flows of the SCC, including
gas-solid flow, gas-liquid flow, and liquid-solid flow. These flows have significant influence on
the amount and distribution of lateral pressure of the SCC that is exerted on the formwork.
Predicting these flow helps engineers to determine the most suitable formwork systems for SCC

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works. The two-fluid model created also helps engineers to determine whether SCC is able to
attain the expected strength level. Fluid-fluid interfaces of the SCC will be generated using this
method. The two-fluid model generated will be used to determine the mass conserved,
momentum and total energy and pressure of the SCC (Herard & Hurisse, 2005).
4. Multiphase Mixture Model
This method is considered to be the simplified version of the Eulerian model and is
mainly used when dispersed phase’s load is small (Shang, et al., 2014). The multiphase mixture
model is expected to be used in determining the continuity, momentum, flow rates, energy, void
fraction, slip velocities and pressure drop of the SCC. This implies that the model will determine
momentum equation, continuity equation, energy equation, slip velocity equation, drift velocity
equation and volume fraction equation, among others. The method will also be used to calculate
the total pressure of solids present in the SCC. The total solid pressure is what makes the largest
percentage of the total lateral pressure exerted by the SCC on the formwork. One of the main
advantages of this method is that it takes into account the different phases of the SCC since the
concrete comprises of different constituents. The multiphase mixture model is different from
VOF model in two main ways. First, the multiphase mixture model allows the different phases of
SCC to be interpenetrating. This means that the ratio between Vscc and Vf can be any value
ranging from 0 to 1. Second, multiphase mixture model allows the different phases of SCC to
move at varied velocities based on the theory of slip velocities.
This method will mainly focus on determining the velocity, momentum, energy and
pressure of different components of the SCC. It is important to note that the individual SCC
constituents have varied properties. When these ingredients are combined to form concrete, they
still maintain their individual properties even though they later form a homogenous compound. It

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is for these differences that heavier constituents settle at the bottom while heavier ones at the top
when the concrete is not consolidated properly (Yu & Qin, 2009). Therefore the velocity,
momentum and pressure of these constituents should be determined so as to establish the most
appropriate conditions that will facilitate proper self-consolidation of the concrete.
The basic principle of multiphase mixture model is the fact that SCC is made up of
different particles. When these particles are combined, they form varied phases. These phases
have unique properties that affect the overall strength of concrete. One of the properties affected
is lateral pressure. Depending on how the phases are formed, the lateral pressure can either be
evenly or unevenly distributed.
5. LPT Method
Liquid penetrant testing (LPT) is one of the commonly and widely used non-destructive
testing techniques in concrete (Bentzley, 2010). The main expected outcome of this method is to
determine any discontinuities that are present in the SCC after it has been poured. Since concrete
has a liquid with surface wetting properties, this method comes in handy to establish the ability
of the liquid in concrete to rise when it is confined in the formwork. Typically, when concrete is
poured in the formwork, water tends to climb up and float on top of the solid aggregates of
concrete. One of the reasons why water rises is because it is less dense than the solid particles of
the concrete. Therefore when water rises through the concrete, it shows that there are existing
cracks in the concrete.
Cracks are undesirable in concrete because they create channels through which water can
penetrate into concrete, corrode the reinforcement and deteriorate the strength of the reinforced
concrete (Zhou, et al., 2008). The exposure of concrete deterioration is directly proportional to

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the extent or depth of the cracks (the deeper the cracks the higher the deterioration and vice
versa). LPT method will therefore be used to determine the extent or depth of cracks present in
the concrete. Besides cracks, LPT method is also used to determine the presence of voids in fresh
concrete. This automatically means that cracks are determined in old structures or in concrete
that has already been placed. In this project, LPT method will mainly be used to determine voids
in fresh concrete. The presence of voids can also mean that there are cracks in the concrete at the
time of placing. Using this method, it will be possible to determine the width and depth of
cracks, and the proportion of voids present in the concrete. This data will be used to determine
the need for corrective or improve strategies aimed at remediating or covering the cracks/voids.
Additionally, this method will be used to determine the compatibility of the concrete ingredients,
the effectiveness of mixing and pouring methods, porosity of the concrete ingredients, and any of
defects related to the mixing and pouring of concrete.
Conclusion
Use of SCC is becoming widespread and has resulted to development of new pouring
techniques. One of such techniques is bottom-up pouring of concrete in formworks. However,
these new techniques have raised one major concern: the lateral pressures exerted by the SCC on
the formwork. It is important for engineers to determine the lateral pressures so as to select and
use appropriate formwork systems. If the formwork used is not adequate then the concrete will
not attain the desired strength and the structure may fail prematurely. This is because the
formwork will not sustain the lateral pressure exerted by SCC hence it will fail. The distribution
of the lateral pressure is also important. Typically, the lateral pressure has to be evenly
distributed on the formwork surfaces. It means that the pressure acting at the top, middle and
bottom of the formwork should be equal so as to prevent excessive stress on one part of the

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formwork resulting to failure. For all these conditions to be achieve, the above five methods will
be used to measure necessary parameters and create proper models. Discrete element method
will be used to demonstrate the behavior of SCC together with various factors affecting lateral
pressure produced by the concrete. The data collected will be used to create a discrete element
model that will provide a better representation of the distribution of lateral pressure of the SCC
on the formwork, and also simulate factors affecting this pressure. Volume of fluid method will
demonstrate the free surface profile of SCC and air. The test will show how solid, liquid and gas
particles of the concrete are distributed, and how this distribution affects lateral pressure exerted
on the formwork by the concrete.
Two fluid method will be used to predict different flows of SCC, which has a significant
effect on the amount of lateral pressure generated by the SCC. From this method, a two-fluid
model will be generated and used to determine the mass conserved, momentum and total energy
and pressure of the SCC. Multiphase mixture phase model will be used to determine the
continuity, momentum, flow rates, energy, void fraction, slip velocities and pressure drop of the
SCC. Last but not least, LPT method will be used to determine the presence and extent of voids
and cracks in the concrete. All these methods will be used to estimate the lateral pressure exerted
by SCC on the formwork systems.

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