Amir Hossein Vakili

Effects of Using Pozzolan and Portland Cement in the Treatment of Dispersive Clay

Use of dispersive clay as construction material requires treatment such as by chemical addition. Treatments to dispersive clay using pozzolan and Portland cement, singly and simultaneously, were carried out in this study. When used alone, the optimum amount of pozzolan required to treat a fully dispersive clay sample was 5%, but the curing time to reduce dispersion potential, from 100% to 30% or less, was 3 month long. On the other hand, also when used alone, a 3% cement content was capable of reducing dispersion potential to almost zero percent in only 7 days; and a 2% cement content was capable of achieving similar result in 14 days. However, treatment by cement alone is costly and could jeopardize the long term performance. Thus, a combined 5% pozzolan and 1.5% cement content was found capable of reducing dispersion potential from 100% to zero percent in 14 days. The results indicate that although simultaneous treatment with pozzolan and cement would extend the required curing time in comparison to treatment by cement alone of a higher content, the task could still be carried out in a reasonable period of curing time while avoiding the drawbacks of using either pozzolan or cement alone.

Filtration of Broadly Graded Cohesive Dispersive Base Soils

AbstractDispersive soils are highly susceptible to erosion, particularly when they are used as a base soil for the core of an earth dam. To prevent migration of the core material, the required filter must be designed and properly positioned in the structure. A study was carried out to assess the adequacy of the existing filter design criteria in controlling core materials that are not only dispersive but also broadly graded and are commonly available for use in the construction industry. The criteria of D15f/d85≤5.5 and D15f≤0.28  mm, each with a reasonable factor of safety, were found to be applicable for the broadly graded, highly dispersive soils from Group 1 and Group 2, respectively. The criteria of D15f/d85reduced≤9 for the soils of Group 1, D15f/d85reduced≤7 for the soils of Group 2 with significant clay content, and D15f/d85reduced≤2 for the soils of Group 2 with significant silt content were also found to be acceptable. Thus, the required D15f size of a filter reduces with the increasing dispersi...

Investigating the Effect of Lignosulfonate on Erosion Rate of the Embankments Constructed with Clayey Sand

Internal erosion is known as the most important cause of dam failure after overtopping. It is important to improve the erosion resistance of the erodible soil by selecting an effective technique along with the reasonable costs. To prevent internal erosion of embankment dams the use of chemical stabilizers that reduce the soil erodibility potential is highly recommended. In the present study, a lignin-based chemical, known as lignosulfonate, is used to improve the erodibility of clayey sand specimen. The clayey sand was tested in various hydraulic heads in terms of internal erosion in its natural state as well as when it is mixed with the different percentages of lignosulfonate. The results show that erodibility of collected clayey sand is very high and is dramatically reduced by adding lignosulfonate. Adding 3% of lignosulfonate to clayey sand can reduce the coefficient of soil erosion from 0.01020 to 0.000017. It is also found that the qualitative erodibility of stabilized soil with 3% lignosulfonate is altered from the group of extremely rapid to the group of moderately slow.

A Critical Review on Filter Design Criteria for Dispersive Base Soils

Dispersive soils have become common materials for the construction industry. Highly susceptible to internal erosion and piping, dispersive soils must only be used with specific engineering measure in order to avoid failures that were often catastrophic. In an earth dam, clayey soils are used for the core and sandy materials are used for the filter to retain the eroded core soils and prevent their migration. In the absence of first-rate core material, dispersive soils have been used instead. This paper provides a review of the current knowledge and experiences regarding filtration of core soils, particularly the dispersive ones. The engineering problems associated with the use of dispersive soils are discussed and significant findings from previous studies on protective filters are summarized. It is worthy to note that the current review considers both, the conventional, rather empirical filter design criteria based on particle sizes and the current, quite theoretical state-of-the-art filter design criteria based on constriction sizes, with discussion given on the advantages and disadvantages of both. The information provided by this review should be handy for the study, design, construction, and operation of related geotechnical and geo-environmental projects.

Coagulation of the Suspended Organic Colloids Using the Electroflocculation Technique

Electroflotation is an unconventional separation process owing its name to the bubbles generation method (i.e., electrolysis of the aqueous medium) caused by the hydrogen and hydroxide development. Collecting the colloidal particles in surface water has been a long-term issue all over the world, because of their adverse influence. In the present research, the electroflocculation technique have been use to collect the humus particles throughout the polluted wastewater. The uses of different chemical additives namely, Al2(SO4)3, Al(OH)3, CaCl2, CaO, and Na2SiO3 were also successfully examined and enhanced the electroflocculation technique. Although high negatively surface electrical charge of humus causes difficulties in the conventional flocculation and coagulation technique, it enhances the flocculation process when the electroflocculation techniques have been used. The results of both Jar test and electroflocculation technique are further compared. It can be concluded that the polluted water were fully decontaminated (i.e., all of the suspended colloids through the water were removed) by using the electroflocculation technique. The removal rate after electroflocculation test were 91.8%, 98%, 93.5%, 85.3%, 95.4%, and 94% for neutral, Al2(SO4)3, Al(OH)3, CaCl2, CaO, and Na2SiO3, respectively. While the removal rate after Jar test were 84.8%, 83.79%, 71.44%, 84.83%, 77.09%, and 77.09% for neutral, Al2(SO4)3, Al(OH)3, CaCl2, CaO, and Na2SiO3, respectively.

The Rheology Properties of Peat Treated with Sodium Silicate System Grouts

In the present study, the effect of sodium silicate stabilizers on the flowability and soil volume reduction are investigated. Two secondary additives are also admixed in order to assess their effects. Accordingly, a series of viscosity, shrinkage limit, and pH tests were performed to assess the effects of the mentioned cationic reagents as a suitable grout. It is observed that the sodium silicate grout has a viscosity higher than water and causes a very high soil volume reduction during the air curing. The reduction in the soil’s volume was reduced significantly when secondary additives were used. The microstructure analysis performed to help understanding the reason of highly soil’s volume reduction due to presence of sodium silicate reagent.

Stabilization treatment of Na-montmorillonite with binary mixtures of lime and steelmaking slag

Abstract This paper reports the influence of lime-slag mixtures and curing on stabilization of Na-montmorillonite clays that have greater water holding capacity than other soils studied previously. For this purpose, different amounts of hydrated lime and two types of steelmaking slag including Granulated Blast Furnace Slag (GBFS) and Basic Oxygen Furnace Slag (BOFS) were added in a ratio of 1:1 to the soil and finally the investigation was carried out at 25 °C. The efficiency of soil-additive mixtures was measured using different laboratory tests such as plasticity index, pH, electrical conductivity, swelling potential and unconfined compressive strength. The results showed that blends containing 5% additive, particularly in LG (Lime:GBFS = 1:1), significantly reduced swelling potential of highly expansive soil at one day curing. Furthermore, addition of 20% LB (Lime:BOFS = 1:1) to the samples after 1 and 90 days of treatment increased their compressive strength by 8 and 13 times, respectively.

Damage source identification of reinforced concrete structure using acoustic emission technique.

Acoustic emission (AE) technique is one of the nondestructive evaluation (NDE) techniques that have been considered as the prime candidate for structural health and damage monitoring in loaded structures. This technique was employed for investigation process of damage in reinforced concrete (RC) frame specimens. A number of reinforced concrete RC frames were tested under loading cycle and were simultaneously monitored using AE. The AE test data were analyzed using the AE source location analysis method. The results showed that AE technique is suitable to identify the sources location of damage in RC structures.

Fracture Formation Evaluation of Reinforced Concrete Structure Using Acoustic Emission Technique

Acoustic emission (AE) is an important nondestructive evaluation (NDE) technique used in the field of structural engineering for both case local and global monitoring. In this study AE technique with a new approach was employed to investigate the process of fracture formation in reinforced concrete structure. A number of reinforced concrete (RC) one story frames were tested under loading cycle and were simultaneously monitored using AE. The AE test data was analyzed using the relaxation ratio and calm and load ratio method. Also, the relaxation ratio was dominated with approaching load to 58% of the ultimate load. In addition three levels of damage using calm and load ratio were distinguished. The trend of relaxation ratio and calm and load ratio method during loading and unloading showed that these methods are strongly sensitive with cracks growth in RC frame specimens and were able to indicate the levels of damage. Also, results showed that AE can be considered as a viable method to predict the remaining service life of reinforced concrete. In addition, with respect to the results obtained from relaxation ratio and, load and calm ratio indicated, a new chart is proposed.

The Surface Electrical and Microstructure Analysis of Peat Treated with Cement

Peat usually undergo large secondary settlements depending on the amount of organic content present in the soil. This is because of its special microstructure. The microstructure of peat has interdependence with mechanical and physical characteristics, such as compressive and tensile strength, and water retention. In the present research, peat samples were admixed with different concentrations of cement to enhance its physical, chemical, electrical, and microstructural properties. As a result, the surface electrical of the peat colloids influence the rate of flocculation, and in turn further strength achievement. The results is in contrary with the microstructural analysis that performed by SEM and EDX on the treated peat.