compressive strength

This research investigates the influence of synthetic fiber incorporation on the mechanical properties and durability of engineered cementitious composites (ECC) through the examination of four distinct mixtures: a control mixture (fiber-free) and three mixtures containing 10, 20, and 30 kg of synthetic fibers per cubic meter of ECC. The experimental findings revealed that the inclusion of synthetic fibers significantly enhances tensile cracking strength, toughness, and residual strength. Notably, the mixture with 30 kg of synthetic fibers demonstrated the highest tensile cracking strength (10.73 MPa) and toughness (174 N·mm). However, exceeding a fiber content of 10 kg resulted in a decline in compressive strength and modulus of elasticity. Regarding durability, the addition of synthetic fibers exhibited mixed effects: the mixture containing 30 kg of synthetic fibers displayed the lowest water absorption, attributable to reduced surface cracking. Conversely, as the fiber content increased, the depth of water penetration and chloride ion ingress also rose, likely due to the formation of micro-pores around the fibers and an increase in internal permeability. These outcomes suggest that synthetic fibers, by forming a network of strands within the ECC matrix, effectively distribute tensile stresses and inhibit crack propagation through a bridging mechanism. This contributes to enhanced fracture energy and improved mechanical performance of the ECC, albeit with potential trade-offs in certain durability characteristics. In conclusion, this study identifies the mixture containing 10 kg of synthetic fibers as the optimal formulation in terms of compressive strength and modulus of elasticity, while the mixture with 30 kg of synthetic fibers is deemed most effective for improving tensile strength and toughness.

One of the determinants of concrete quality is its compressive strength. One of the factors affecting the compressive strength of concrete is the appearance and diameter of its aggregates, and the shape, size, and granularity of concrete are important factors in concrete production. This paper analyzed part of the relationship and how the size of aggregates affects the compressive strength of concrete, and it seeks to answer the question, what effect does the use of aggregates with the same diameter have on the compressive strength of concrete? In this regard, an experimental method has been used to investigate the effect of the sameness of stone grains on the compressive strength of concrete. This way, after classifying the aggregates based on diameter into nine parts, 81 cubic concrete samples. The results of the investigation showed there is a direct relationship between the diameter of the aggregate and the compressive strength, and when the diameter of the aggregate is between 2.8 and 4 mm, the highest compressive strength is created. As the diameter of the aggregate decreases, the compressive strength increases. In supplementary research, samples were made in which the space between the aggregates was filled with cement paste. The results indicate an inverse relationship between the diameter of the aggregate and the compressive strength of concrete. As the diameter of the aggregates increases, the strength of the concrete decreases and when the diameter of the aggregates is between 22.4 and 25 mm the highest resistance is obtained.

The large volume of cement production includes about 5-8% of CO2 emissions.The adverse environmental effects of CO2 gas as well as the need to increase the strength and durability of concrete led to the introduction of pozzolan. Pozzolan is a substance with a combination of alumina and silica, which will have cement properties if it is amorphous in the vicinity of lime water. In this research, calcined clay was used as pozzolan, first the soil is heated to 700 degrees Celsius to be calcined, then it is replaced with cement with lime powder. In this research, 10 mixed designs were used in 2 ratios of w/c, 0.35 and 0.4. In each proportion of clay at 0, 10 and 20%, limestone powder at 0, 30 and 20%, respectively, and microsilica along with the combination of soil and lime at 0 and 7% by weight as powder materials were replaced by cement. . In order to check the properties of the prepared soil, XRF and XRD tests were performed on it. To investigate and analyze the mechanical properties of concrete from compressive strength tests on 10 cm cube samples at 4 ages of 3, 7, 28 and 90 days, tensile strength on cylindrical samples and flexural strength on prismatic samples at 28 years of age. Fasting was used. over the time and reaching the age of 90 days, designs containing 20% calcined clay and 20% lime Mix3 and Mix8 have more resistance in pozzolanic designs and are introduced as optimal pozzolanic designs.

In recent years, metakaolin is used in concrete to improve the short-term and long-term properties of concrete. Considering the importance of compressive strength and bonding between concrete and rebar in reinforced concrete structures, a new method for evaluating bonding strength between concrete and reinforcement is presented in this research. Also, the optimal percentage of metakaolin along with steel fibers has been determined in order to achieve maximum bonding and compressive strength. In this research, 20 different mixing designs with four different percentages of metakaolin (0%, 10%, 15% and 20%) and five different percentages of steel fibers (0%, 0.75%, 1%, 1.5% and 2%) were considered and slump test on fresh concrete and compressive strength and bonding strength tests on 28-day samples were conducted. The results showed that the new method presented for measuring the bonding strength between concrete and rebar is very practical. Also, minor addition of metakaolin and steel fibers significantly reduced the compressive strength, and by increasing the percentage of fibers, the compressive strength was increased and then decreased. Also, adding metakaolin up to 15% significantly increased the bonding strength of concrete, but by increasing the amount of metakaolin up to 20%, bonding strength of concrete was decreased. On the other hand, both metakaolin and steel fiber reduced the flowability of fresh concrete. Finally, the sample containing 15% metakaolin and 1.5% steel fibers showed the highest bonding strength.

Weak soils with unfavorable geotechnical characteristics cause many technical and economic problems in construction projects such as road construction. One of the solutions to the problem is soil improvement (Asgari et al., 2015; Bayat et al., 2021; Eshaghzadeh et al., 2021; Hadi Sahlabadi et al., 2021; Hakimelahi et al., 2023; Rezaei-Hosseinabadi et al., 2022, 2022; Saadat and Bayat, 2022; Tavakol et al., 2023). Many materials such as fiber, cement, lime, nanomaterials etc. have been used to improve of soils. On the other hand, previous studies indicate that freeze-thaw cycles have an important effect on the mechanical behavior of geomaterials (Hadi Sahlabadi et al., 2021; Noroozi et al., 2022; Roustaei, 2021).

Rheological properties of Self-compacting concrete are important in saving time and cost. The aim of this research was to investigate the effect of adding iron slag with two different specific surfaces (the first type was normal iron slag with a specific surface of 3800 blaine and the second type was fine iron slag with a specific surface of 6000 blaine) on the rheological and strength properties of self-compacting concrete. Ten concrete mixes including control mix and nine mixes containing three compositions of iron slag were designed with proportions of (20-30-40) percent of cement weight. The first composition of slag consists was 100% normal slag, the second was 75% normal slag and 25% fine slag, and the third one was 50% normal slag and 50% fine slag. The J-ring test (to measure the flow diameter, T50 time, and the height difference of the concrete in the middle and outside of the ring ) and the V-funnel test (to measure the V-funnel time) were performed for fresh concrete. The compressive and tensile split strengths were performed to measure the strength properties of hardened concrete. The results of the J-ring test indicated that the flow diameter was decreased for concretes with each composition of slag, the mixtures containing 30 and 40% of third composition of slag had a decrease of 2.5 and 3.1%, respectively, while the T50 results compared to the control mix showed an improvement and the mixtures containing 20 and 30% of first composition of slag had a decrease of 53 and 47%, respectively. Regarding the difference in height of the concrete between the middle and outside of the ring, the results indicated an increase in height when adding any composition of slag and the mixtures containing 30 and 40% of third composition slag were increased by 76 and 69%, respectively. The V-funnel test showed variation in the results that the addition of 20 and 40% of first composition of slag resulted in a reduction of the V-funnel time by 12 and 11%, respectively. The two different slags with specific surfaces had different effects on flow diameter, T50, Δh and V-funnel time. The results of the 28-day compressive strength test indicated an increase in compressive strength when 30 and 40% of third composition of slag were added, with a ratio of 12 and 15%, respectively. However, the results of the 28-day tensile split strength test have shown that the addition of 30% of third composition of slag leads to an increase in tensile strength by 8%. The second and third compositions contain slag with a specific surface of 6000 blaine respectively 25 and 50% of the weight of each composition, this leads to an increase in the rate of hydration reaction more than that in the first composition. Therefore, the compressive and tensile strengths increases compared to the first combination.

The use of mineral waste to produce new concrete is one of the important issues in the construction industry, which can have many environmental benefits and economic savings. Today, excessive production of cement has become a crisis in human societies, especially in iran. Because the production of cement will cause the release of carbon dioxide gas and the production of pollutants in the air of cities, which has irreparable consequences. On the other hand, the supply of electricity or gas energy for the fuel cycle of cement factories faces many challenges in some days of the year, which will cause a shortage of cement and an increase in the price of cement and, of course, an increase in the price of housing. In this research, calcium carbonate oxide powder was used in different weight ratios of 5%, 10%, 15% and 20% to reduce the amount of white cement used to make white concrete. The tests performed include slump, compressive strength, tensile strength, water absorption and checking the durability of concrete against the melting and freezing cycle. The results of this research showed that the use of calcium carbonate oxide will increase the compressive and tensile strength of concrete due to the increase in the production of calcium hydroxide in cement But using 15% calcium carbonate will increase the compressive strength of concrete by 20%. Due to the increased water absorption of calcium carbonate, the durability of concrete against frost decreases. The use of 20% calcium carbonate can reduce the durability of concrete by 11.7% against the cycle of melting and freezing.

The Alkali-silica reaction (ASR) is one of the most significant concerns in the concrete life cycle. It reduces the serviceability and increases the expense of maintaining structures. In addition, the occurrence of ASR impacts the internal structure of concrete and decreases its integrity. Thus, the mechanical properties of concrete can be significantly affected by ASR. Different researchers have mentioned this issue, and most of the results have proved the reduction of the mechanical properties of concrete due to ASR. In this study, in addition to examining the length changes of mortar and concrete samples, the effect of ASR on three main mechanical properties of concrete (compressive strength, bending strength and tensile strength) was also investigated. In order to evaluate the aforementioned parameters, mixtures with and without Trass containing aggregates with varying degrees of reactivity were prepared and cured under various conditions. The results showed all studied properties decreased under ASR conditions (accelerated ASTM C1293 at 60 ºC). However, this reduction depended on the reactivity degree of the used aggregates. Furthermore, using the Trass as a partial replacement for cement could reduce ASR's destructive effects. In addition, a significant relationship can be established between the results of the length changes and the changes of the studied mechanical characteristics.

Self-compacting concrete is concrete that, due to its fluidity and fluidity, can fill all corners of the mold and rebars only under the influence of gravity and without the need for any mechanical pressure, without causing separation or shedding water, and it compacts automatically. Self-compacting concrete has been increasingly targeted by engineers and researchers in the construction industry. Plastic bottles are one of the major parts of solid waste. One of the plastic recycling materials that are prepared based on plastic bottles are recycled polyethylene terephthalate fibers. The main goal of this research is to use polyethylene terephthalate fibers in the self-compacting concrete mixing plan to increase the tensile strength and reduce the permeability of the samples. In this way, the fibers are cut with a length of 3 to 4 cm and used in self-compacting concrete with different percentages (0, 0.5, 1, 1.5, 2 percent compared to the weight of cement) as a cheap and accessible additive. became. Slump flow tests, V funnel, L box, J ring, compressive strength, tensile strength, ultrasonic pulse speed, Schmidt hammer and permeability tests were tested for the fresh and hardened properties of self-compacting concrete with fibers. The results of the experiments showed that with the increase in the percentage of polyethylene terephthalate fibers in self-compacting concrete, the tensile strength during 7 and 28 days of curing in the range of 14.35-58.35 and 21.9-72.57 percent increased compared to self-compacting concrete without fibers. The compressive strength was in the range of 3.02-12.64 and 3.97-12.88 percent of the strength reduction compared to self-compacting concrete without fibers, and also the permeability test in 72 hours was in the range of 8.13-47.67 percent of permeability compared to concrete The self-density without fibers decreased.

Rice husk as an agricultural waste material has a large amount of amorphous silica, adding its ash to concrete increases the pozzolanic property of concrete and consequently increases the strength and durability of reinforced concrete structures. The quality and method of rice husk ash preparation greatly influence the final properties of the concrete prepared from it. In this article, rice husk ash has been burned in controlled, semi-controlled, and uncontrolled conditions in terms of temperature conditions, and the resulting ash has been used as a 10% substitute for cement in self-compacting concrete. Properties related to concrete performance and compressive strength of samples containing rice husk ash at different ages have been evaluated. The properties of rice husk ash powder have been determined through XRF, FESEM, and the determination of grain size range. The results show that in all cases the sum of SiO2, Al2O3 and Fe2O3 is higher than 70%; which indicates being within the standard range of pozzolanic cement materials. In the semi-controlled state, the amorphous silica is more than 8%. Based on the results, adding rice husk ash increases the long-term compressive strength (90 days) and decreases the short-term compressive strength of self-compacting concrete. The increase in long-term strength for samples with ash produced in controlled conditions was more and up to 18%. The reduction of short-term compressive strength for samples with uncontrolled ash has been obtained up to 25%.