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Showing 4 results for Ghoddousi

P. Ghoddousi, A.m. Raiss Ghasemi, T. Parhizkar,
Volume 5, Issue 4 (December 2007)

Plastic shrinkage is one of the most important parameter which must be considered in hot weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especialy if silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity, temperature and wind velocity, sun rediation also is very important factor in evaporation rate. It is found that under solar radition condition, the evaporation was much larger than the estimated value in ACI 305 Nomogram. The rate of evaporaion under solar radiation was about two folds of evaporation rate under shade condition. The results showed that in terms of crack initiation time, crack width and total cracking area, concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water cement ratio in concrete with silica fume makes the concrete more sensitive in cracking. The results of this project also showed that the severity of the cracking is not related only to rate of bleeding but all environmental factors including like sun radiation or shading and also mix compositions have important roles.
P. Ghoddousi, R. Ahmadi, Mahdi Sharifi,
Volume 8, Issue 4 (December 2010)

 Superior performances of Self-Compacting Concrete (SCC) in fresh state to achieve a more uniform distribution encourage the addition of fibers in concrete which is a motivation for structural application of fiberreinforced concrete. Fiber addition reduces the workability of Self-Compacting Fiber Reinforced Concrete (SCFRC). To provide required workability of the SCFRC, more paste is needed in the mixture. Therefore, the coarse aggregate content shall be adjusted to maintain its workability. The purpose of this study is to drive a model for estimating the aggregate contents for SCFRC. This model is based on constant covering mortar thickness theory. In this paper, all parameters which are participated in coarse aggregate content are discussed and presented in a relation. Then another relation is developed for predicting the void volume in the fibrous concrete. These relations are combined and a mathematical relation is deduced for predicting the coarse volume content in the function of the fiber factors. Proposed model is validated by conducting a rheological test. The result shows that the proposed model is simple, applicable and can be used as starting point in practical project.      Finally in order to complete the proposed model, another relation has been derived that can show the interaction of parameters involved in SCFRC rheology behavior. 

R. Ahmadii, P. Ghoddousi, M. Sharifi,
Volume 10, Issue 4 (December 2012)

The main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (SFRC) behavior

under four point bending test (FPBT). In this model all the force components at the beam section (before and after cracking)

are formulated by applying these assumptions: a bilinear elastic-perfectly plastic stress-strain response for concrete behavior

in compression, a linear response for the un-cracked tension region in a concrete constitutive model, and an exponential

relationship for stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical

cracked section is calculated by applying these assumptions and satisfying equilibrium lawat critical cracked section. After that,

parametric studies have been done on the behavior of SFRC to assess the sensitively of model. Finally the proposed model has

been validated with some existing experimental tests.The result shows that the proposed solution is able to estimate the behavior

of SFRC under FPBT with simplicity and proper accuracy.

Parviz Ghoddousi, Amir Masoud Salehi,
Volume 15, Issue 8 (Transaction A: Civil Engineering 2017)

The fresh properties of Self Compacting Concrete (SCC) might be more susceptible to quality and quantity changes of ingredients than conventional concrete because of a combination of detailed requirements, more complex mix design, and inherent low yield stress and viscosity. In spit of the low robustness of SCC, there are a few methods available to assess the SCC robustness that the accuracy of these methods has not been fully agreed. The current study provides an index for SCC robustness based on the rheology parameters. Thus, an experimental program was undertaken to evaluate the robustness of eight selected SCCs. For doing this, water content of each SCC was changed slightly and their fresh and hardened properties were measured. The results indicated that the length of rheology parameters curve due to variation of mixing water is able to assess the SCC robustness that is comparable with combined performance based on the workability tests changes. According to this index, the robustness of SCC increases about 10% by using air-entraining admixture (AEA) and decreases considerably by reduction the paste volume (up to about 5 times). Also, the most appropriate single workability test to assess the robustness is sieve segregation test. Moreover, the scattering of compressive strength results show that there is a level of robustness in fresh state that after that the scattering of results in hardened state can be affected.

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