08-17-2017, 12:25 AM
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Abstract
This study aims to determine the influence of the content of water and cement, water binder ratio, and
the replacement of fly ash and silica fume on the durability of high performance concrete (HPC) by using
artificial neural networks (ANNs). To achieve this, an ANNs model is developed to predict the durability of
high performance concrete which is expressed in terms of chloride ions permeability in accordance with
ASTM C1202-97 or AASHTO T277. The model is developed, trained and tested by using 86 data sets from
experiments as well as previous researches. To verify the model, regression equations are carried out and
compared with the trained neural network. The results indicate that the developed model is reliable and
accurate. Based on the simulating durability model built using trained neural networks, the optimum
cement content for designing HPC in terms of durability is in the range of 450 500 kg/m3. The results also
revealed that the durability of concrete expressed in terms of total charge passed over a 6-h period can be
significantly improved by using at least 20% fly ash to replace cement. Furthermore, it can be concluded
that increasing silica fume results in reducing the chloride ions penetrability to a higher degree than fly
ash. This study also illustrates how ANNs can be used to beneficially predict durability in terms of chloride
ions permeability across a wide range of mix proportion parameters of HPC.
1. Introduction
The use of concrete possessing both high strength and durability,
hereinafter called high performance concrete (HPC), has been
increasing all over the world. The factors which justify its popularity
are high workability, high strength, and high durability for various
structural purposes. Although the definitions of HPC are
varied, the essence of HPC emphasizes three main characteristics.
Apart from the three basic ingredients, i.e. cement, aggregates
and water in conventional concrete, active mineral additives like
fly ash, silica fume, and superplasticizer have been incorporated
to make highly workable, high-strength and durable concrete [1
3]. HPC mix design seems to be complicated because HPC includes
more ingredients. In addition, maintaining a low water binder ratio
with adequate workability makes the design process more complicated.
Traditionally, expert civil engineers can produce HPC mix
proportions by using empirical results from previous research plus
their experience to achieve the required performance [4]. However,
available results are often of limited value because some types of
ingredients and some properties have not been investigated. Nowadays,
concrete can be made with about 10 different components.
The number of properties to be adjusted has also increased, so
empirical methods are no longer sufficient in concrete mix design
[5]. Compressive strength, workability, and durability of concrete
are fundamentals of concrete properties. Most research has focused
on properties of normal concrete. Many mathematical models
have been suggested to describe the relationship between
components and materials behavior. The traditional approach used
in modeling HPC properties starts with an assumed form of analytical
equation and is followed by regression analysis employing
experimental data to determine unknown coefficients in the equations.
Unfortunately, rational and easy-to-use equations are not yet
available in design codes to accurately predict the properties of
HPC. Furthermore, with the aforementioned models, the evaluation
of the effect of each parameter on the properties of concrete
is almost impossible [6 8].
Durability is a fundamental property of concrete based on its
impermeability, and it can be explicated by electrical conductivity
in accordance with ASTM C1202-97 and AASHTO T277 [9,10]. If the
6-h period charge passed of concrete is lower than 1000 C, the concrete
is said to possess very high impermeability and durability.
The permeability of concrete depends on the pore structure of concrete,
while the electrical conductivity of concrete is determined by
both pore structure and the chemistry of the pore solution. Many
researchers have found that the microstructure of concrete can
be improved and charge passed can be decreased by adding supplementary
cementing materials such as fly ash, silica fume, and
blast furnace slag. Since high performance concrete is a highly heterogeneous
material, the modeling of its behavior is a very difficult
task. However, there are no guidelines or specifications for durability
of high performance concrete