نشریه مصالح و سازه های بتنی
سال هشتم شماره 1 (پیاپی 15، بهار و تابستان 1402)

Clinker phases have a significant effect on the technical characteristics of cement and its performance in concrete, but sufficient information is not available to determine the effect of each of these phases on the optimal performance of concrete. Therefore, in this practical essay, it was studied and a laboratory operation was designed. In the first stage, regular sampling of clinker from 2 kiln of Tehran cement factory was done in 3 months. Then 11 clinker samples (Portland type II) were selected which their phase values were different from each other. During the second stage, laboratory cementing was done in completely identical conditions using 11 clinker samples. A super plasticizer additive sample was also prepared. In the third stage, physical and chemical analysis was done on laboratory cement samples. During the fourth stage, 22 concrete mixes were prepared with 11 cement samples, and their slump were fixed (8cm in the first group and 12cm in the second group) so that 11 mixtures were labeled "without additives" and 11 mixtures were labeled "with additives". Slump loss tests within 1 hour, determination of density, determination of air content of fresh mixed concrete, compressive strength of 7, 28 and 90 days in hardened concrete were performed on concrete mixtures. Based on the results, the comparison of the effect of C3S amount of clinker on the compressive strength of standard mortar and concrete showed that the direct relationship between C3S amount and compressive strength (mortar and concrete) is not favorable; but it can be said that with each increase of C3S percentage of clinker, the 7 and 28 days strength of concrete increases by about 1.5 units (kg/cm2) and with the increase of C3S from about 57% onwards, a drop in concrete strength can be observed. These points out the negative effect of excessive increase of C3S phase. Based on the results of the tests which determine the percentage of air in fresh concrete mixes containing additives and its decrease after 30 minutes, it was determined that the optimal amount of C3A was about 5-6%.

Today, various types of industrial waste are used as sustainable mineral materials to replace part of cement in concrete production with an economic approach. The main purpose of this study is to compare and evaluate the effect of using two types of slag from Isfahan Steel Plant and Esfarayen Steel Plant as a replacement of different percentages of cement in ordinary concrete, which was done in three phases. Concrete samples with mixing design and different percentages of two types of slag with water-cement ratios equal to 0.54 and 0.43 were made in the first phase and after being placed in the water pool, at the ages of 28, 56 and 90 days. were tested for compressive strength. In the second phase, concrete samples with optimal percentages of slag were made to measure the samples. Reinforced concrete beams with dimensions of 1000 × 150 × 150 mm with 3 different mixing designs in the third phase and to check the structural performance of concretes containing optimal percentages of slag were made and a four-point bending beam test was performed to obtain the Ultimate capacity. became. The results of the tests showed that although the strength of concrete samples containing different percentages of slag at the age of 28 days was lower than that of normal concrete, but the strength of concrete samples containing 30% of Isfahan slag and 20% of Esfarayen slag at the age of 56 and 90 days was almost equal to normal concrete. And resistance was the goal. The results of the durability tests in the second phase showed that the durability of samples containing slag in sulfate environment was more than normal concrete. Also, the ultimate bending capacity of reinforced concrete beams containing 30% of Isfahan slag and 30% of Esfarayen slag showed a 10% increase and a 3% decrease, respectively, compared to the beam without slag.

Using different additives in order to increase the durability and mechanical resistance of concrete is one of the new approaches in concrete technology. In recent years, graphene has attracted attention due to its unique properties. However, the phenomenon of graphene accumulation in cement mixtures and high production costs have challenged its application in the concrete industry. For this purpose, it is necessary to use a graphene dispersing agent in the cement structure. This research used surfactants to spread graphene sheets in cement structures. This method has resulted in producing a cheap solution compared to typical methods, which can be used as an additive. The results of this research showed that the surfactant solution can increase mechanical properties at early ages. Detailed microstructure examination by FESEM analysis showed that the compounds containing 0.56 g/l of surfactant have a denser structure than the control sample, and also the compressive strength of the cement paste increased by 28.66% compared to the control sample at the age of 7 days. TGA and XRD analyses show that graphene played an effective role in nucleation and produced CH and C-S-H products in the cement structure. This solution can be used as a new additive in many construction projects.

Cement-based materials that are used in construction today, require the extraction of natural sand and gravel on a very large scale, which is still increasing. On the other hand, with the ever-increasing production of plastics, especially PET polymer, which is one of the examples of its uses is in mineral water bottles, and the release of these bottles after consumption in nature, a new challenge in the field of environmental destruction has been created. In this research, with the aim of recycling PET and reducing the consumption of natural aggregates in the production of cement and concrete mortars, fine particles of PET (WPLA) were replaced with sand in different percentages, and factors such as weight and compressive strength of the manufactured composites were evaluated. The results showed that these materials have less weight than the samples without WPLA, but their compressive strength has decreased and according to the standards in this field, they are placed in the category of non-load bearing materials and in the section of non-structural parts can be used.

In light of the adverse ecological outcomes of cement production, researchers are exploring alternative materials that can replace cement in construction while maintaining environmental compatibility. An alternative strategy is the use of soil base materials containing aluminum silicate with alkaline activators and industrial waste. This study aims to evaluate the strength and durability properties of geopolymer mortar relative to cement and clay-based mortars. Eight mixing designs were employed, including two for cement and clay-based mortars for comparison, and six for geopolymer mortars. The geopolymer mortars tested comprised 0%, 30%, and 40% slag, with 0.1% polypropylene fibers used in three designs. A 12 M concentration of sodium hydroxide solution and a sodium silicate to sodium hydroxide ratio of 2.5 were utilized in this study. The samples were subjected to compressive and tensile strength evaluations at 7, 28, 54, and 90-day intervals. Additionally, water absorption, capillary water absorption, and impact resistance tests were performed after 28 days. The compressive strength test conducted after 28 days revealed that geopolymer mortars that contained either 30% or 40% slag, along with polypropylene fibers, achieved 53% and 73% of the compressive strength of the cement sample, respectively. This increase represented a 3.6 to 9-fold improvement over clay-based samples. The tensile strength of the geopolymer samples was found to be 53% and 63% of the strength of the cement, but 5 and 9.5 times higher than the clay-based sample, respectively. The results showed that the use of polypropylene fibers in geopolymer samples containing 30 and 40% slag reduced water absorption, but compared to cement samples, they absorbed 95 and 72% more water after 72 hours. The coefficient of capillary absorption in all geopolymer samples was high, but the use of fibers in the sample containing 40% slag resulted in a 1% reduction in this coefficient compared to the non-fiber sample. Cracking resistance tests were conducted on the geopolymer samples, which showed that the samples containing 30 and 40% slag with fibers achieved 40 and 73% of the cracking resistance of the cement sample, respectively. The destruction resistance of the sample containing 30% slag with fibers was approximately 46% of the cement resistance, while the model containing 40% slag with fibers exhibited a 15% improvement relative to the cement sample.

Using steel shear walls is one way to increase the lateral load-carrying capacity of reinforced concrete moment-resisting frames and have been gaining the interest of researchers due to their excellent performance in earthquakes and ease of construction. In these shear walls, connection to the frame and force transfer between the wall and the frame are of particular interest. In this study, the connection type of these walls and transfer of forces between them and the frame via bolts were examined and controlled using the ABAQUS software. For this purpose, a two-story concrete frame equipped with steel shear walls was evaluated after verifying the numerical model. The frame was assessed under two connection conditions: the ideal state, in which the shear wall is fixed to the beam, and the realistic state, in which these shear walls are attached to the beam using connecting plates on the beams and bolts at the top and bottom of the beam. To design the bolts, first, the prestressing force needed to prevent sliding should be calculated, according to which the prestressing force and the bolts can be designed. Also, the simultaneous effect of tension and shear should be taken into account in the bolts design. .After designing the bolt diameter and prestressing force, the behaviors of the frame were compared in both cases. The numerical analysis revealed that the load-displacement behaviors in both cases were almost identical. Furthermore, the stress in the bolts in the second state was found to be lower than their strength, indicating that the bolt design method is safe and suitable for transferring forces between the shear wall and the reinforced concrete structural frame in floors. Also, by designing the bolt and its prestressing force according to the method of this paper, it is ensured that no slippage between the concrete and the connection plates occurs until the end of loading.

Today, the issue of environment in Iran has become one of the critical problems. The production of pollutants and the release of carbon dioxide gas in the air and on the other hand the production of garbage and construction waste in the past years have caused a lot of damage to the environment and imposed a lot of costs on the municipalities. According to statistics, cement factories are the second producer of CO2 gas, which accounts for more than 5% of all pollution in the world. Also, the high volume of construction waste production due to the destruction of dilapidated buildings is very high. Therefore, recycling construction materials can be a good way to reduce construction costs and prevent environmental degradation. In this research, with the aim of producing environmentally friendly concrete to reduce the use of cement, reduce costs, recycle materials and reduce environmental pollution, the behavior of concrete was investigated using waste brick waste. For this purpose, waste brick from the destruction of the building was collected and pulverized to the size of 150 microns and used in weight amounts of 5%, 10%, 15% and 20% instead of part of cement in concrete. Further, slump tests, compressive strength, water absorption and freezing durability were conducted to investigate the behavior of this concrete. Also, to determine the chemical structure of the recycled brick powder, an XRD test was performed and an XRF test was performed to identify its phases. The results of this research showed that the use of 5% recycled brick powder in concrete only reduces the 90-day compressive strength by 2.4%, and its use in non-structural elements is justified.

One of the influential factors on concrete compressive strength results, which is often neglected in construction and research projects, is the quality of specimen molds. In this study, the effect of six types of 150 mm×150 mm×150 mm cubic molds, including two types of steel molds and four types of plastic molds, on compressive strength (17 MPa to 67 MPa) results of fifteen concrete mixtures at different ages were investigated. It was found that using the worst of the studied molds led to an 18% reduction of the measured compressive strength compared to the best one. These results show that the effect of mold on compressive strength of concrete can be very considerable. This issue can result in incorrect mixture design and an inaccurate measurement of concrete strength produced in construction projects and hence, legal and technical disputes among the sides involved in construction projects. In addition, in this paper, to quantify the quality of the studied molds, two parameters of flatness and perpendicularity deviation were defined. Through applying a linear regression for the obtained results, an empirical formula with high accuracy was presented to predict the effect of the two parameters of molds on the concrete compressive strength reduction factor. This formula indicates that the reduction factor decreases when perpendicularity deviation and flatness deviation values increase.

Today, with the expansion of urban life and the increase in the number of cars, the accumulation of a large amount of worn tires has become one of the urban and environmental problems. One of the proposed solutions to deal with this problem is the use of recycled materials from worn tires in the concrete mix. Undoubtedly, the use of these recycled materials in concrete can affect the mechanical properties and durability of concrete. On the other hand, roller concrete is also one of the developing methods of concrete implementation, especially in road construction. In this research, the effect of the combined additive of worn tire recycled materials, including rubber crumb, rubber cotton fibers and rubber metal fibers, on the durability properties of rolled concrete has been investigated. After the mixing plan, the samples made with the combination of recycled rubber crumb materials were processed for 28 and 90 days. The results of the tests showed that in the best case, with the addition of 3% of rubber crumb and 5% of rubber metal fibers in rolled concrete, the compressive strength increased by 1.9% compared to the control sample. Also, the compressive strength of rolled concrete in sulfated environment has increased by 7.14% compared to the control sample by adding 3% of rubber crumb and adding 5% of metal fibers. The wear percentage of roller concrete has also decreased by 1.8% compared to the control sample by adding 3% of rubber crumb and adding 10% of rubber metal fibers. In the case of rolled concrete containing cotton rubber fibers, despite the problems of mixing these fibers in concrete, we have only seen an increase in relative abrasion resistance in concrete, and no particular improvement was observed in other characteristics of concrete samples.

A b s t r a c tConsidering cement as the main constituent material of concrete, in recent years, it has received significant attention from researchers and scientists in the construction industry due to high direct and indirect costs. Non-burnt black soil, which is extracted as waste material from ceramic tile factories, is a recognized problem, and its utilization in other industries can have a positive impact on environmental preservation. In this study, 216 samples were prepared in the form of 24 mix ratios and at ages of 7, 28, and 90 days. After conducting compressive strength and slump tests, as well as electron microscopy imaging, it can be observed that the optimal utilization of non-burnt black soil waste can bring about changes in the compressive strength of concrete at higher ages, indicating the potential use of this waste as a substitute for cement in concrete to reduce the cost of the final product and promote environmental preservation towards sustainable development. In this study, it was observed that a replacement percentage of 5% and 10% of black soil with cement at 28 days and a replacement percentage of 15% at 90 days can be introduced as the optimal substitution percentage.

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.

Generally, elevated tanks of liquid storage are designed for higher seismic forces than buildings due to their ductility and low energy absorption capacity. So that for a tank with low ductitlity, its base shear coefficient is about 6 to 7 times larger than the base shear coefficient of a ductile building and for a tank with high ductility, this ratio is about 3 to 4 times higher than all standards. In standard 2800, the fourth edition for elevated tanks of liquid storage behavior coefficient 2 and 3 is considered. In standard 2800, the fourth edition for air tanks of liquid storage behavior coefficient 2 and 3 is considered. In the publication, No. 38 coefficients of behavior for elevated tanks are presented in accordance with the standard 2800. The results showed that in standard 2800, the ratio of the base shear coefficient of the tank to the base shear coefficient of the ductile building in the relatively high risk zone for tanks with behavior coefficients of 3 and 2 in short periods was 3.5 and 5,25, respectively, while this value was obtained in No. 38 publications 4 and 6, respectively. The results also showed that the ratio of base shear coefficient of tanks to buildings in short periods for both behavior coefficients and four soil types in publication No. 38 was 14% higher than the results of the fourth edition of standard 2800