18
1735-0522
212
A Geometrical Inclusion-Matrix Model For Concrete
Rasoolan
I.
Sadrnejad
S.A.
Bagheri
A.R.
1
6
2009
7
2
73
82
30
05
2009
11
01
2014
Concrete is a heterogeneous material with a highly non linear behavior, which is mainly caused by theinitiation and propagation of micro cracks within the several components of the material. The damage behavior ofconcrete is usually simulated on the macro scale using complex constitutive models. The direct determination of thehomogenized material parameters is often difficult and sometimes impossible. Furthermore these materials models donot explicitly represent effects and bond behaviors of interfaces between the several components. So in order to predictof concrete behaviors and characteristics, it should be modeled as a three phase composite material consisting ofaggregate, interfacial transition zone (ITZ) and cement paste. The size and distribution of aggregate affects concretecharacteristics. Because of the random distribution and size variation of aggregate in concrete, the modeling ofconcrete behavior based on component in meso structure is difficult and so we must use simple assumption. In thispaper with mixing design and grading curve we developed a simple method to replace real aggregate with equivalentsphere aggregate with effective diameter. So we can use simple methods instead of complex numeral and randomnessor x ray methods to find effective diameter and use it to determine two arrangements with maximum and minimumaggregate volume as a repeatable basical element .As a result we can use this element to modeling the behavior ofsample concrete in meso scale and three phases.
213
The Effect of Rice Husk Ash on Mechanical Properties and Durability of Sustainable Concretes
Ramezanianpour
A.A.
Mahdi khani
M.
Ahmadibeni
Gh.
1
6
2009
7
2
83
91
30
05
2009
11
01
2014
Rice Husk Ash (RHA) is a by-product of the agricultural industry which contains high amount of silicon dioxide (SiO2). In this research, for the first time in the Middle East, in order to supply typical RHA, a special furnace was designed and constructed in Amirkabir University of Technology. Afterwards, XRD and XRF techniques were used to determine the amorphous silica content of the burnt rice husk. Attempts were made to determine the optimum temperature and duration of burning. Results show that temperature of 650 degrees centigrade and 60 minutes burning time are the best combination. Then various experiments were carried out to determine properties of concretes incorporating optimum RHA. Tests include compressive strength, splitting tensile strength, modules of elasticity, water permeability and rapid chloride permeability test. Results show that concrete incorporating RHA had higher compressive strength, splitting tensile strength and modulus of elasticity at various ages compared with that of the control concrete. In addition, results show that RHA as an artificial pozzolanic material has enhanced the durability of RHA concretes and reduced the chloride diffusion.
214
Prediction of Free Shrinkage Strain Related to Internal Moisture Loss
Abbasnia
R.
Kanzadi
M.
Shekarchi Zadeh
M.
Ahmadi
J.
1
6
2009
7
2
92
98
30
05
2009
11
01
2014
Drying shrinkage in concrete, which is caused by drying and the associated decrease in moisture content, is
one of the most important parameters which affects the performance of concrete structures. Therefore, it is necessary
to develop experimental and mathematical models that describe the mechanisms of drying shrinkage and damage build
up in concrete. The main objective of this research is the development of a computational model and an experimental
method for evaluation of concrete free shrinkage strain based on the internal moisture changes. For this purpose and
for modeling of moisture losses in concrete members a computational program based on finite element approach and
the modified version of Fick's second law in which the process of diffusion and convection due to water movement are
taken into account, is developed. Also the modified SDB moisture meter was used to measure the internal moisture
changes in concrete. Based on the obtained results, calculated humidity is in good agreement with measured data when
modified Fick's second law with diffusion coefficient from Bazant method were used, and are very reasonable for
determining the moisture gradient. Also, the predicted value of shrinkage strain from the proposed method is in good
agreement with measured data and also the established relationship can be used for determine the distribution of
shrinkage strains in concrete members.
215
Discharge Estimation by the Aid of Isovel Contours in a Tidal River with Partially Reverse Flow
Givehchi
M.
Maghrebi
M.F.
Kawanisi
K.
1
6
2009
7
2
99
108
30
05
2009
Maghrebi has previously introduced a model for the production of isovel contours in a normalized form,
which can be used for estimation of discharge in artificial and natural channels. The model is applied to a tidal river
with partially reverse flow, which is caused by opening a sluice gate located asymmetrically close to the right bank of
the Ohta floodway in Hiroshima, Japan. An acoustic Doppler current profiler (aDcp) was used to measure the velocity
profiles at different verticals and then discharge was calculated. In addition, the estimated discharge based on each
measured point and the predicted isovels of flow cross section was obtained. The results show that the corresponding
errors for the measured points away from the solid boundaries and the imaginary boundary of the flow between the
two adjacent regions with opposite directions, which are associated with lower absolute values of isovels, are
reasonable.
216
An Iterative Penalty Method for the Optimal Design of Pipe Networks
Afshar
M.H.
Afshar
A.
MariĆ±o
M. A.
ASCE
Hon. M.
1
6
2009
7
2
109
123
30
05
2009
This paper presents the application of an iterative penalty method for the design of water distribution pipe
networks. The optimal design of pipe networks is first recasted into an unconstrained minimization problem via the use
of the penalty method, which is then solved by a global mathematical optimization tool. The difficulty of using a trial
and error procedure to select the proper value of the penalty parameter is overcome by an iterative use of the penalty
parameter. The proposed method reduces the original problem with a priori unknown penalty parameter to a series of
similar optimization problems with known and increasing value of the penalty parameters. An iterative use of the
penalty parameter is then implemented and its effect on the final solution is investigated. Two different methods of
fitting, namely least squares and cubic splines, are used to continuously approximate the discrete pipe cost function
and are tested by numerical examples. The method is applied to some benchmark examples and the results are
compared with other global optimization approaches. The proposed method is shown to be comparable to existing
global optimization methods.
217
Effect of Plasticity Index and Reinforcement on the CBR Value of Soft Clay
Naeini
S.A.
Ziaie_Moayed
R.
1
6
2009
7
2
124
130
30
05
2009
11
01
2014
In recent years, soil reinforcement is considered of great importance in many different civil projects. One of
the most significant applications of soil reinforcement is in road construction. Sub grade soil and its properties are
very important in the design of road pavement structure. Its main function is to give adequate support to the pavement
from beneath. Therefore, it should have a sufficient load carrying capacity. The use of geosynthetics in road and
airfield construction has shown the potential to increase the soil bearing capacity. One category of geosynthetics to
particular, geogrid, has gained increasing acceptance in road construction. A geogrid is a geosynthetic material
consisting of connected parallel sets of tensile ribs with apertures of sufficient size to allow strike-through of
surrounding soil, stone, or other geotechnical material. Geogrid reinforcement of sub grade soil is achieved through
the increase of frictional interaction between the soil and the reinforcement. Geogrid have been successfully used to
provide a construction platform over subgrades. In this application, the geogrid improves the ability to obtain
compaction in overlying aggregates, while reducing the amount of material required be removing and replacing.
Relative agreement exists that substantial benefits can be achieved from the inclusion of geogrids within the pavement
systems however, the quantity of the improvement is in relative disagreement. This paper presents the effects of
plasticity index and also reinforcing of soft clay on CBR values. Three samples of clay with different plasticity index
(PI) values are selected and tested without reinforcement. Then by placing one and two layer of geogrid at certain
depth within sample height, the effects of reinforcement and PI on CBR values are investigated in both soaked and
unsoaked conditions. The results shows that as the PI increase the CBR value decreases and reinforcing clay with
geogrid will increase the CBR value.
218
Effects of Geosynthetic Reinforcement on the Propagation of Reflection Cracking in Asphalt Overlays
Khodaii
A.
Fallah
Sh.
1
6
2009
7
2
131
140
30
05
2009
11
01
2014
An experimental program was conducted to determine the effects of geosynthetic reinforcement on mitigating
reflection cracking in asphalt overlays. The objectives of this study were to asses the effects of geosynthetics inclusion
and its placement location on the accumulation of permanent deformation. To simulate an asphalt pavement overlaid
on top of a crack in a concrete or asphalt pavement, an asphalt mixture specimen was placed on top of two
discontinuous concrete or asphalt concrete blocks with 100 mm height. Four types of specimens were prepared with
respect to the location of geogrid: (I) Unreinforced samples, which served as control specimen, (II) Samples with
geogrid embedded on the concrete or asphalt concrete block, (III) Samples with geogrid embeded one-thired depth of
asphalt concrete from bottom, (IV) Samples with geogrid embedded in the middle of the asphalt beam. Each specimen
was then placed on the rubber foundation in order to be tested. Simulated- repeated loading was applied to the asphalt
mixture specimens using a hydraulic dynamic loading frame. Each experiment was recorded in its entirety by a video
camera to allow the physical observation of reflection crack formation and propagation. This study revealed that
geosynthetic reinforced specimens exhibited resistance to reflection cracking. Placing the geogrid at the one- third
depth of overlay thickness had the maximum predicted service life. Results indicate a significant reduction in the rate
of crack propagation and rutting in reinforced samples compared to unreinforced samples.