محمد شکرچی زاده

With the development of the human community and increasing number of treatment plants, the treatment and disposal of high volume of sludge requires efficient management. Nowadays, due to the lack of land for burying sludge and environmental limitations of using sludge in agriculture, incineration is considered as a proper solution for sludge disposal. Sewage sludge ash is one of the materials that has been used in recent years as a substitute for cement and stone materials in concrete and construction materials.The quality of the resulting ash depends heavily on the origin of the sludge and its incineration process. Regarding this, there is no codified information about the content of the sludge of Tehran wastewater treatment plants, with considering its usage in construction materials. Also, there are many discrepancies in the heating process and the optimal incineration temperature of sewage sludge ash in the sources. In the first step, by examining the sludge of Tehran wastewater treatment plants and performing chemical analyzes such as XRF and XRD, the best treatment plant in terms of constituent content was selected. Then, by burning sewage sludge at 700 to 1000 C and re-analyzing XRF and XRD, as well as calculating the percentage of pozzolanic activity of the resulted ash, the most optimal heating process was selected.The obtained results of this study indicated that heating the Shahrake Gharb wastewater treatment plant's sludge at 800°C produced the most desirable sludge ash in case of chemical composition and pozzolanic activity. So, in general, it can be seen that although sludge ash could not be classified as one of the types of strong pozzolans, but this ash can be used as a raw material for Portland cement production and also as a weak pozzolan in reactions. Therefore, it is possible to replace the sewage sludge ash in optimal percentages in the mortar and concrete with Specified applications and as an alternative to cement, fine aggregate and filler.

The necessity of attention to the sustainable development in civil engineering for the progress of modern societies has highlighted concrete as the most widely used construction material for researchers. In this way, Ultra High Performance Concrete (UHPC) has been highly appreciated as one of the newest inventions in the field of concrete technology. The purpose of this article is to: 1- depict outstanding properties of UHPC that make its utilization in construction, rehabilitation and strengthening projects efficient and 2- promote the application of UHPC in bridge engineering in the national scale relying on extensive domestic studies in order to localize it. Much effort has been made to present a comprehensive report on innovations and gained experiences in the field of using UHPC in the bridge industry during the last two decades in all parts of the world and investigate the main direction of future research pointing to the key constraints of the widespread use of this material for constructing and maintaining bridges.

The durability-based design of reinforced concrete structures especially in hot marine environment of Bandar-Abbas became extensively important during the last few years. It has been known that the durability of concrete mainly depends on how easily seawater containing chloride ions can ingress into an unsaturated concrete (Sabir et al., 1998; Hubert et al., 2003; Prabakar et al., 2010; Yoo et al., 2011). Chloride-induced corrosion of embedded reinforcement is more severe in tidal condition because of more ingress of chloride due to moisture convection phenomena. (Broomfield, 1997; Olajumok et al., 2009; Akindahunsi et al., 2010). In is necessary to approximate the moisture distribution in concrete due to wetting and drying cycles for determination of the moisture convection zone. The moisture transfer coefficient (MTC) is one of the most important parameters for prediction of moisture distribution. The moisture distribution is often influenced by environmental conditions such as temperature. The changes of the depth of convection zone can be assessed if MTC is available in various temperatures. In this research, six concrete mixtures were prepared in which four plain concrete mixtures were proportioned with water to cementitious materials (w/cm) ratios of 0.40, 0.45, 0.50, and 0.55. In addition to the plain concretes, one silica fume and one natural zeolite blended concrete mixtures with cement replacement levels of 7.5, and 10% and a w/cm ratio of 0.45 were considered. The moisture loss or water absorption of specimens exposed to wetting and drying were measured using the gravimetric method at temperatures of 23, 43, and 63 ºC. A finite element analysis was performed afterward to fit the experimental data to the governing equations of moisture transfer to determine the MTC. The moisture distribution of concrete exposed to wetting and drying and then the depth of convection zone (DCZ) are determined using approximated MTC and finite element-based model. The amount of water entered (AWE) to concrete surface subjected to tidal condition is also calculated.

The unique properties and characteristics of ultra-high performance concrete as a new material in civil engineering have brought exciting new horizons to the designers. One of these design horizons that could be very applicable in the future is the idea of a composite of ultra-high performance and usual concrete, which has been put forward to make maximum use of the material capacity. This idea is useable in both of the new construction and repair (improvement) of existing structures. As studies and practical applications have shown, composite of usual and ultra-high performance concrete than original concrete structures will be stronger and durable. However, in any composite structures, the integrated performance of the materials is very important and this integrated performance will make through the interconnection resistance between materials. Also, as regards to the newness of composite the ultra-high performance and usual concrete, limited studies were conducted about to continuity strength between these materials. Therefore, the present research is one of a part in the collection studies related to applicable ultra-high performance concrete in faculty of engineering of Tehran University, continuity strength between usual and ultra-high performance concrete with using ordinary tests in a different mode of base concrete preparation has been studied. According to the results of this study, the continuity of the strength between the two materials is highly dependent on the basic concrete level preparation conditions and, if proper level preparation is carried out, will result in better conditions than even the reference standards

In order to repair a concrete structure, it is currently necessary to have appropriate recognition of repair materials to achieve an effective and efficient repair. Therefore, the repair materials should be selected in a manner that different properties such as modulus of elasticity and thermal compatibility of the modified mortar be close to the substrate concrete of the structure. Styrene acrylate (SA) is a latex in a cement-based repair mortar, which has a good thermal compatibility with the substrate concrete. So, in this study, five mixtures of repair mortars have been prepared with different ratios of SA to cement materials (0, 5, 10, 15 and 20%) and their physical and mechanical properties including density, consistency and compressive, flexural and tensile strength have been investigated under two curing conditions In the first curing condition, the specimens are immerged in water for 24 hours after demolded and then maintained in the specific temperature and humidity. (Combined curing condition). In the second curing condition, the specimens are immerged in water up to the age of the test. The first curing condition, comparing with the second one, showed the better mechanical properties for the all test ages due to cement hydration at an early age and the formation of the polymeric film. The use of SA increased the flow and reduced the density. Moreover, the use of SA in repair mortar, in polymer to cement material ratio of 20%, reduced the compressive strength by 49% under combined curing condition at 28 days; SA, however, increased the flexural and tensile strength by 21% and 19%, respectively, in the polymer to cement materials ratio of 10% under combined curing condition at 28 days.

Chloride penetration into concrete and consequently corrosion of reinforcing steel is one of the main causes of concrete deterioration in Persian Gulf and Sea of Oman. Concrete deterioration exposed to tidal condition is very severe when compared to the atmospheric exposure condition. Therefore, it is necessary to accurately model the simultaneous moisture and chloride ingress into concrete for durability-based design of reinforced concrete structures. In this study, a finite element model was developed to numerically solve the governing differential equations of moisture and chloride transfer. Comparison of the model output with the ones obtained from experimental works in Bandar Abbas and Qeshm research sites showed that the proposed model can predict the chloride profile with good accuracy. By using the test results, the model output showed that the maximum chloride concentration decreased with increasing in water to cement ratio (w/c) from 0.40 to 0.45 and then slowly increased with increasing in w/c up to 0.55. Although, the total chloride concentration, which ingress into concrete, increased up to 50 %.

Today, concrete structures have a crucial role in the infrastructure of society. The conditions and performance of these structures are important. In recent years, due to corrosion phenomenon, a number of concrete structures in Southern areas of Iran have suffered damage or premature failure. Concrete damage in the chloride environments is the most common failure of reinforced concrete structures and an important problem for civil engineers which today they are faced with the maintenance of them. Recent societal shift toward sustainable consumption and growth applied to civil infrastructure systems requires the construction materials to be designed and used with utmost attention to their durability and long term response. Pozzolanic materials including silica fume, fly ash, slag, and metakaolin have been used in recent decades for developing high performance concrete with improved workability, strength and durability. Metakaolin has been used as a pozzolan for high performance concrete applications. This material is a thermally activated alumino-silicate which is mostly manufactured by calcinations of kaolin clay at the temperature range of 500-850°C [1].