جستجوی مقالات مرتبط با کلیدواژه "concrete compressive strength" در نشریات گروه "عمران"

The role of compressive strength of standard sand-cement mortar in the undeniable strength of concrete is crucial. Additionally, the Blaine of cement is one of the key factors in the compressive strength of cement mortar and concrete. In this research, the Artificial Neural Network (ANN) and Gene Expression Programming (GEP) methods are employed as comprehensive processes to predict the compressive strength of concrete based on the compressive strength of corresponding cement mortar. To achieve this goal, 286 mixed designs of sand-cement mortar with consistent ratios of raw materials were introduced into the cement kiln, focusing on Type 2 cement (32.5 MPa strength). The results of compressive strength tests on standard sand-cement mortar samples (3 specimens) and concrete produced with consistent mix designs (3 specimens) at the age of 28 days were obtained. Based on these results, the developed model can accurately and effectively predict the compressive strength of concrete based on the compressive strength of corresponding mortar, emphasizing the role of cement Blaine.

Beam-to-column joints in reinforced concrete structures play an essential role in the overall behavior of the structure. Therefore, it seems necessary to strengthen joints that have been damaged over time under various loads or designed only based on gravity loads. Nowadays, shear retrofitting of joints with fiber-reinforced-polymers (FRP) has attracted the attention of researchers. Since the shear force applied to the joint is transferred by the truss mechanism formed by horizontal and vertical bars and also the compressive strength of the concrete, so the concrete of the joint plays the main role in the shear capacity before retrofitting by FRP materials. In this study, 7 reinforced concrete external joint specimens were designed and constructed on a scale of 2/3 and in two concrete compressive strength groups of 30 and 42 MPa. Seismic criteria were not considered in these joints. Two specimens were damaged up to 1.5% drift and the other two specimens up to 3% drift, and then retrofitted with FRP materials by Near Surface Mounted (NSM) method. Of the other three specimens, one with and two without considering seismic criteria as control specimens were subjected to cyclic loading at two levels of concrete strength. The purpose of considering two different levels of concrete strength was to investigate the effect of increasing concrete strength within the normal range of engineering on the performance of the NSM-retrofitted joint. As the results show, damaged retrofitted specimens with concrete compressive strength of 42 MPa were able to increase the bearing capacity of the joint by 12% compared to the seismic control specimen with concrete compressive strength of 30 MPa. Also, the increase in concrete strength by 12 MPa caused a 20, 40, and 65 percent increase in the bearing capacity, hardness, and energy dissipation ability of the NSM retrofitted specimens, respectively.

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.

Today, staying in economic markets depends on maintaining the quality and cost of production due to the intense competition of producers. It has also led governments to take tougher approaches to improve the environmental situation of industries. Therefore, the use of new technologies that leads to maintaining or increasing product quality and reducing costs without harming the environment will be desirable. Today, the use of high-power ultrasonic waves, due to the lack of noise pollution, has been highly regarded by various industries to improve engineering processes. The effectiveness of these waves in the manufacturing and production industries, such as reducing machinery, increasing surface smoothness, grinding metals during freezing, etc., can also be the motivation for its use in the construction industry. Therefore, the widespread use of high-power ultrasonic waves in various fields of engineering and the identification of the positive effects of these waves on the properties of materials and materials is the reason for the present study. For this purpose, for the first time in this study, the use of high ultrasonic power waves with different powers, different times, and a frequency of 20 kHz in concrete compaction and its effect on concrete compressive strength has been investigated. The results of this study show that the use of ultrasonic high-power waves as a complementary process in the compaction of fresh concrete will increase the compressive strength of concrete by up to 10%.

Chloride ions cause the most common corrosion, so chloride ions can enter the concrete through contaminated aggregates and additive materials or infiltration from external sources, such as seawater. If the concrete is exposed to the aforementioned ions, there will be severe loss of durability and expansion of corrosion. In this case, there will be a tangible effect on the development process of resistance reducing the concrete's strength. Therefore, the extant study was conducted to compare the effect of fly ash and micro silica on the development, compressive strength, and electrical resistance of concretes exposed to chlorinated waters. The plans of this study included two types of ordinary concretes and concretes containing pozzolanic material. Concrete mixing plans in chloride medium were divided into 11 groups, which included 8 plans with substitution of micro silica and fly ash powders with different percentages in exchange for cement. The first group included no additive material as a cement substitute and included one plan as the base plan. Accordingly, 81 plans that each consisted of 4 samples were constructed and examined to test compressive strength in 7, 14, 28, and 42-days ages (N=324 plans). According to the results of laboratory samples in chloride medium, there was an increase in the development process of compressive strength, and electrical resistance of concrete while using concrete with standard aggregates reinforced with micro silica and fly ash by selecting the optimal mixing plan and lower cost. The above mentioned case was cost-effective for project implementation.

During the construction of concrete structures, delay time and improper casting sequence may lead to the creation of cold joints that would consequently affect the concrete strength. In this research, the effect of orientation angle and delay time characteristics of the cold joints on the concrete strength was investigated experimentally. Experiments were conducted on concrete cubic samples with the compressive strength, water to cement ratio and slump values equal to 30 MPa, 0.5 and 7 cm respectively. In this experiments, the orientation angle of cold joints with respect to horizontal were considered as 0o, 30o, 45o, 60o and 90o and delay times were considered as 15, 30, 60, 90 and 120 minutes. Then, the uniaxial compressive strengths and corresponding strains of the produced samples were measured. Based on the experiments, the results, a significant relationship between the compressive strength of concrete and angle and delay time of cold joints was identified, with the most suitable angle of the cold joint being at 0o and the most unsuitable angle being at 45o, providing the highest and the least compressive strengths respectively.

Due to the critical situation of environmental issues, waste materials recycling and their reusing has been a research interest for many researchers. Recycled Asphalt Pavement (RAP) is a waste material which may have unfavorable influence on its surrounding environment. Considering the reported characteristics of these materials, different strategies to reuse RAP’s have been introduced. One of these applications recently noticed by the researchers is using RAP’s in cement mixtures such as concrete. As RAP is mainly collected from roadsides and highways, so it is desirable to use it in common mixtures for roads pavements. Hence, Roller Compacted Concrete - a concrete mixture with unique featues such as ease of application and low cost- was selected as the basic mixture. In this research, replacing a part of aggregates with RAPs in three states was carried out: 1- with fine and coarse aggregates, 2- with just fine aggregates, and 3- with just coarse aggregates, with ratios of 0, 10, 20, 40, and 80 percentages. Tests results indicated that use of RAPs as a part of aggregates in pavement Roller Compacted Concrete has no effect on the consistency of concrete compressibility, and cement and water batches; however, the compressive strength is reduced by increased quantity of RAP aggregates.