Mechanical Strength Of Concrete Research Articles

Mechanical properties and damage modeling of hybrid fiber reinforced concrete under freeze-thaw cycles

This study aimed to investigate the mechanical properties of steel-polyacrylonitrile hybrid fiber reinforced concrete and its durability under freeze-thaw damage. Firstly, the mechanical properties of hybrid fiber reinforced concrete were studied by compressive strength and flexural strength tests. Secondly, with the help of rapid freeze-thaw test, the variation rules of mass loss rate and relative dynamic elastic modulus were characterized. Based on the test results and freeze-thaw damage theory, the evolution equation of freeze-thaw damage of hybrid fiber reinforced concrete based on Weibull distribution was established. The results show that the enhancement effect of hybrid fiber on the mechanical strength of concrete is better than that of single mixed fiber, especially in the improvement of flexural strength; Accordingly, compared with the single mixing of steel fibers or single mixing of polyacrylonitrile fibers, hybrid fibers are more effective in improving the durability of concrete against freezing and this improvement effect increases with the increase of steel fiber content; The freeze-thaw damage model of Weibull distribution can better reflect the freeze-thaw damage process of hybrid fiber reinforced concrete .Through the freeze-thaw damage evolution curve, it can be found that after 500 freeze-thaw cycles, the freeze-thaw damage degree of the hybrid fiber reinforced concrete with different steel fiber content has been very close, which means that the influence of steel fiber content on the freeze-resistant performance of hybrid fiber reinforced concrete will be limited. This study provides a theoretical basis and technical basis for the design of concrete structures in alpine regions.

Effect of recycled facemask fabrics on the mechanical strength of concrete

Effect of recycled facemask fabrics on the mechanical strength of concrete

The rheological behavior characterization and prediction of cement concrete containing magnetite (Fe3O4) and/or carbon fiber

The effect of magnetite and carbon fiber (CF) on the rheological properties of concrete was investigated to reflect and affect its engineering performance development. The rheological parameters of concrete were measured. Next, a prediction model was established to predict the change tendency in the rheological properties of concrete. Then, the correlation between rheological and mechanical properties was investigated to explore the mechanism of rheological behavior on its engineering performance. The results showed that magnetite and CF had a significant effect on the rheological behavior of concrete. When the magnetite and CF contents were 50 % and 0.5 wt%, the yield stress and plastic viscosity of concrete increased by 210.77 % and 35.88 %, respectively, compared to the control group. The physical properties of the materials, their interaction with the cement matrix and their effect on the volume fraction of the concrete system are the main factors affecting the rheological properties of concrete. Meanwhile, the prediction model established by using the nonlinear surface fitting function could effectively predict the influence of materials on the rheological behavior of concrete. The R2 between the predicted and measured values of yield stress could be up to 0.99. However, under the condition of large magnetite and CF content, the aggregation effect of the materials had a certain influence on the plastic viscosity of the concrete, resulting in a certain deviation between the predicted and measured values, but the R2 could still be up to 0.89. It indicated that the prediction model had favorable reliability and accuracy. A strong correlation existed between the rheological parameters and mechanical strength of concrete. The effect of magnetite and CF on rheological properties of concrete promoted the internal microstructure characteristics optimization of concrete to affect its mechanical properties.

Effect of Biochar Dosage and Fineness on the Mechanical Properties and Durability of Concrete

Biochar (BC), a byproduct of agricultural waste pyrolysis, shows potential as a sustainable substitute material for ordinary silicate cement (OPC) in concrete production, providing opportunities for environmental sustainability and resource conservation in the construction industry. However, the optimal biochar dosage and fineness for enhancing concrete performance are still unclear. This study investigated the impact of these two factors on the mechanical and durability properties of biochar concrete. Compressive and flexural strength, carbonation resistance, and chloride ion penetration resistance were evaluated by varying biochar dosages (0%, 1%, 3%, 5%, 10%) and fineness dimensions (44.70, 73.28, 750, 1020 μm), with the 0% dosage serving as the control group (CK). The results showed that the addition of 1-3 wt% of biochar could effectively reduce the rapid carbonation depth and chloride diffusion coefficient of concrete. The compressive and flexural strength of BC concrete initially increased and then decreased with the increase in biocarbon content, BC with a fineness of 73.28 μm having the most significant effect on the mechanical strength of concrete. At the dosage of 3 wt%, BC was found to promote the hydration degree of cement, improving the formation of cement hydration products. These findings provide valuable insights for the development of sustainable and high-performance cement-based materials with the appropriate use of biochar as an additive.

Experimental study on heat transfer enhancement of heat storage material for energy pile

As a kind of clean and renewable energy, shallow geothermal energy has the characteristics of wide distribution and huge reserves. The use of pile foundation heat exchange for building heating is a new technology to realize the effective utilization of geothermal energy. Improving the mechanical properties of the pile body material and improving the heat exchange efficiency of the pile foundation concrete will effectively promote the application of concrete in building structures. In this paper, the effect of steel fiber content on the thermal conductivity and mechanical strength of concrete is discussed by carrying out physical and mechanical properties test of concrete material of pile body. It is proposed to incorporate steel fibers into the concrete of the pile body to improve its thermal conductivity, thereby improving its heat transfer efficiency per unit time. At the same time, the role of steel fiber in enhancing heat transfer performance in pile material is analyzed from the microscopic mechanism, which provides theoretical support for the optimization process of concrete ratio of pile foundation in practical engineering.

Synergistic influence of SiO<sub>2</sub> nanoparticles and carbon nanotubes on the properties of concrete

carbon nanotubes (MWCNTs) in the range of 0.00004–0.000006 wt. % of the mass of cement on the structure and mechanical properties of concrete was demonstrated. A correlation was found between an increase in the mechanical strength of concrete by 56 % with changes in the structure of the cement stone, at which the proportion of crystals of calcium hydroaluminate, calcium hydrosulfoaluminate and type 14A tobermorite increases significantly. The results obtained lay the foundations for the development of a technology for the industrial production of complex additives in concrete with a combination of nanoparticles (MWCNT + SiO2), which make it possible to improve the mechanical and physical characteristics of concrete and increase its durability.

Experimental investigations on mechanical strength of concrete using nano-alumina and nano-clay

The current work aims to advance the mechanical characteristics of concrete by replacing cement with a low volume fraction of nano-alumina particles and fine aggregate with nano-clay. The initial tests had piloted on the conventional concrete using varying fractions of nano-alumina particles in order to determine the optimal nano-alumina proportions for various curing times (1 week, 4 weeks, and 8 weeks). Then, the accompanying experiments using varied volume fractions of nano-clay with the determined optimal proportion of concrete nano-mixture were conducted. The results indicated that the optical volume percentage in the concrete nano-mixture should be 2.0 percent nano-alumina particles and 3.0 percent nano-clay in order to achieve the greatest splitting tensile strength, and compressive strength. With the assistance of nano-alumina particles and nano-clay, the mechanical characteristics of the concrete were improved by around 30% effectively.

Mechanical Performance of Steam-Cured Self-Compacting Concrete Incorporating Silica Fume and Limestone Powder

In this paper, influence of heat treatment on evolution of mechanical strengths at early age, less than 24hours of self-compacting concretes containing limestone powder and silica fume as fine materials was investigated experimentally. Two compositions of self-compacting concrete have been studied; the first is elaborated with silica fume addition and the second with limestone powder, each mixture were prepared with a constant water/binder ratio of 0.39. Concrete samples were either cured in water at (23±1°C), or steam cured at 65°C maximum temperature over six hours (6h) curing period. Tests of mechanical strengths were performed on specimens cooled down slowly to room temperature after heating.The obtained results show that all self-compacting mixtures exhibited satisfying fresh properties and check EFNARC specifications of self-compacting concrete (slump flow diameter higher than 650mm, L-box ratio higher than 80% and sieve stability less than 17%).Mechanical strengths of concrete containing limestone addition are slightly lower than those of concrete based on silica fume at all ages. Moreover, heat treatment generates an improvement of compressive and flexural strength. Interesting compressive strengths are obtained. At 24 hours, after heat treatment, the strengths are already greater than 35 MPa. The values ​​are 37 MPa and 40 MPa for self-compacting concrete containing limestone powder and silica fume respectively compared to 40 MPa and 46 MPa obtained at 7 days for the corresponding non-heat treated concretes. Compressive strength gain of SCCs mixtures with limestone powder and with silica fume, undergoing heat treatment at the age of 24hours is 85% and 75% respectively compared to SCCs mixtures cured in water.

Effect of calcium sulfoaluminate and MgO expansive agent on the mechanical strength and crack resistance of concrete

This work explored effects of calcium sulfoaluminate (CSA) and MgO blended expansive agent on the mechanical strength and deformation of concrete. What’s more, the mechanism was investigated using SEM and XRD analysis. Results show that the addition of MgO is beneficial to improve the later strength of concrete. When the MgO content exceeds 2%, the mechanical strength of concrete at the later stage increases significantly; however, it begins to reduce when the MgO content is more than 5%. All results illustrate that the optimum mass ratio of CSA and MgO is 2:1, and the concrete shows a certain expansion at all stages, which also reduces the drying shrinkage at the later stage. Meanwhile, with the optimum mass ratio of CSA and MgO, the crack resistance of concrete can be improved by 97–127 % compared with a single expansive agent.

Preparation and heat insulation of Gemini-halloysite aerogel/concrete composites

Abstract In our previous research, the utilization of Gemini surfactants to control the dispersion and interaction of HNTs aerogels (HCAs) in the concrete matrix had obtained positive research results. In order to further deepen the research in this field, in this work, a Gemini surfactant with a new structure was synthesized, the surface modification characteristics of HCAs in a series of concrete systems were also investigated. Microstructures and properties of the composites were characterized by using scanning electron microscope (SEM), Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), and so on. The results showed that the newly synthesized Gemini surfactants had an ideal modification effect on the surface of HCAs. Compared with other traditional surfactants, Gemini had better hydrophobic and mechanical properties. Different molecular layers with hydrophilicity or hydrophobicity were constructed on the HCAs surface. The introduction of the modified HCAs could significantly improve the heat insulation performance and mechanical strength of concrete. The improvement of the above comprehensive properties could not have significant difference due to the different types of concrete matrix.

Properties of Concrete with Eggshell Powder and Tyre Rubber Crumb

Solid waste management is one the leading problems in Malaysia. Rapid development and population growth have prompted researches to improve the recycling and reusing of waste material for sustainable development. Chicken eggshell is discarded in Malaysia as municipal waste, while waste tyre is a waste that is difficult to handle and often ends up in the landfill. This paper presents the properties of high performance concrete with eggshell powder and tyre rubber crumb as partial replacement of cement and sand. Grade 45 concrete was prepared with 5% tyre rubber crumb as sand replacement and up to 15% of eggshell powder as cement replacement. The mechanical strength of concrete was investigated for up to 90 days while durability properties were studied through water absorption and carbonation test. Results show that concrete with 5% eggshell powder is optimal for high mechanical properties, lower water absorption and low carbonation depth. X-Ray Diffraction of concrete shows increase of calcite compound which contributes to the gain of strength. Microstructure analysis with SEM and EDX provides insight of the improved performance, which is attributed to a denser C-H-S gels and finer pore structure.

Density and Mechanical Strength of Gum Arabic-Sawdust Ash Concrete.

The density and mechanical strengths of concrete are important properties in the study of concrete structures. An experimental study was mounted to study these concrete properties and the effects of using sawdust ash (SDA) and gum Arabic (GA). In studying these effects four concrete mixtures designated as C/00SDA:GA-00, C/00-SDA:GA-0.5, C/10-SDA:GA-0.5, and C/30-SDA:GA-0.5, respectively. The Mix with C/00-SDA:GA-00, is the control (containing zero percent SDA and GA), with a mix proportion of 1: 2.24: 2.71. The cement content was 370 kg/m3 with a water-cement ratio of 0.5. The other mixes contain either 0.5 % GA (only), or 0.5 % GA with 10 % SDA or 30 % SDA replacement by wt. % of cement, as the case may be. The results showed that the addition of GA and SDA to concrete have various degrees of effects on the concrete parameters. The effect of 0.5 % GA decreased the density of the cube sample but increased the beam and the cylinder samples. On the other hand, the mechanical strengths were increased for all the samples. Using GA with SDA reduced the mechanical strengths of all the concrete samples. However, Ca (OH) 2 was reduced by 54 % by the addition of 10 % SDA and 12 % by 30 % SDA addition by wt. % of cement. The empirical models developed on the density and mechanical strengths showed good predictive values with relative predictive errors (RPE) ranging from 0.00% to 0.045 %.

Vpliv dodatka recikliranih polimernih šiber na mehansko trdnost betona

Vpliv dodatka recikliranih polimernih šiber na mehansko trdnost betona

Improved bond behavior between FRP reinforcing bars and concrete with carbon nanotubes

This study investigates the pullout bond behavior between fiber reinforced polymer (FRP) reinforcing bars and concrete with carbon nanotubes (CNTs). Fifty four pullout specimens were prepared and tested to investigate the effect of CNTs content (0%, 0.05%, 0.1%, and 0.2% by weight of cement), FRP bar diameter (10 mm and 12 mm), embedded length (100 mm, 150 mm, and 200 mm), and type of FRP bar on the bond behavior. The development length was calculated based on both experimental results and ACI standards. Effect of CNTs on the mechanical strengths of concrete was also investigated. The results showed that adding 0.2% CNTs significantly enhanced the compressive and splitting tensile strengths of concrete. During the pullout bond test, three main failure modes were observed: splitting, pullout, and bar fracture. The failure mode was affected by the bar diameter but not by the CNTs content or the embedded length. Experimental results revealed that CNTs enhanced the bond strength and reduced the development length. The enhancement increased with increasing the CNTs content. Scanning electron microscopic images showed the CNTs well distributed within the concrete at the interfacial zone with the FRP bars.

Effect of Combination of Steel Fibre and Silica Fume on the Mechanical Strength of Concrete

Concrete currently consists of several types. Among them are Fibrous Concrete, Lightweight Concrete, SCC Concrete, Hollow Concrete etc. All have advantages and disadvantages to each. The use of various types of concrete is adjusted to the needs of construction. In this research, fibrous steel concrete with a combination of silica fume will be the main object to be studied. So far, fibrous concrete has been actively studied in various countries. From the results of previous studies, fibrous concrete can improve the quality of concrete, especially reducing the brittle nature and initial cracking in concrete. While Silica Fume can increase the compressive strength of concrete. The main objective of this study to determine and understand the mechanical properties of concrete with a combination of steel fibre and silica fume such as compressive strength and split tensile strength. The percentage of steel fibre percentage used in this study is from 0 to 3 per cent, while the percentage of silica fume used is l0 per cent by weight of cement. The results of a study are the optimum compressive strength is in the DFl variation with the percentage of silica fume l0 per cent and 0 per cent steel fibre. The use of steel fibre combined with silica fume does not significantly affect the compressive strength. Although it tends to decrease the compressive strength. The strength of tensile strength obtained ranges from 11 to 14 per cent of the compressive strength.

The Influence of Thermo-Mechanical Activation of Bentonite on the Mechanical and Durability Performance of Concrete

Despite presenting a very high global warming toll, Portland cement concrete is the most widely used construction material in the world. The eco-efficiency, economy, and the overall mechanical and durability performances of concrete can be improved by incorporating supplementary cementitious materials (SCMs) as partial substitutions to ordinary Portland cement (OPC). Naturally found bentonite possesses pozzolanic properties and has very low carbon footprint compared to OPC. By applying activation techniques, the reactivity of bentonite can be improved, and its incorporation levels can be maximized. In this study, the influence of mechanical and thermo-mechanical activation of bentonite is investigated on properties of concrete. Bentonite was used for 0%, 10%, 15%, 20%, 25%, 30%, and 35% mass replacements of OPC. Mechanical (compressive strength and split tensile strength) and durability (water absorption, sorptivity coefficient, and acid attack resistance) properties were studied. Results of experimental testing revealed that, concrete containing bentonite showed good mechanical performance, while durability was significantly improved relative to control mix. Application of thermo-mechanical activation can enhance the incorporation levels of bentonite in concrete. At 15% and 25%, bentonite produced optimum results for mechanical and thermo-mechanical activation, respectively. Bentonite inclusion is more beneficial to the durability than the mechanical strength of concrete.

An Influence of Basalt Fiber on Mechanical Properties of Concrete

The efficacy of fiber reinforced concrete in various application of civil engineering is unassailable. It is a heterogeneous material that includes the fibrous substance which increases its structural integrity and cohesion. In recent years, continuous basalt fibers extruded from naturally basalt rock are attracted attention due to its high temperature and abrasion resistance. Basalt fibers has emerged as a contender in fiber reinforcement composites. This paper aims to evaluate the outcome of basalt fiber on the mechanical strength of concrete and also identify the content that have a optimum influence on concrete. Compressive, split tensile and flexural strength of basalt fiber reinforced concrete is increased than the control concrete. The experimental study shows that the mechanical strength of concrete is increased up to 0.9% of basalt fiber in volume fraction. From the result it is observed that the optimum content of Basalt fiber is 0.9% and the ability of basalt fiber to arrest the cracks area indicated as reason for escalation in mechanical properties.

Synergetic effect of MEA and SAP on the deformation and mechanical properties of concrete

This paper presents an experimental investigation on the synergetic effect of magnesium oxide expansion additive (MEA) and superabsorbent polymer (SAP) on the long-term drying shrinkage, autogenous shrinkage, internal humidity and mechanical strength of concrete. Concrete with varying dosages of MEA (0, 4, 6, 8 and 10%) and SAP dosage (0, 0·2, 0·4 and 0·8%) was studied to assess the synergetic effect of MEA and SAP on concrete. The results revealed that the long-term drying shrinkage of concrete could be effectively inhibited by a hybrid system based on SAP and MEA addition. SAP had a significant effect on maintaining the internal relative humidity of concrete. The hybrid system of 0·4% SAP and 6% MEA not only eliminated autogenous shrinkage but also controlled the deformation of expansion to a minimum. The addition of SAP and MEA generally resulted in a reduction in the cube strength of concrete. Scanning electron microscopy and stereomicroscopy results showed that larger voids were formed by desorbed SAP, which had a negative effect on the cube strength of concrete.

Karakterizacija dodajanja novih polnil, ki vplivajo na mehansko trdnost betona

Karakterizacija dodajanja novih polnil, ki vplivajo na mehansko trdnost betona

Effects of using chemical admixture with nanosilica in the consistency and mechanical strength of concrete

Abstract The concrete’s performance depends on its behavior in the fresh and hardened states, since the workability corroborates for the transport and application processes of the material, while the mechanical strength guarantees structural effectiveness and functionality. Generally, studies of nanosilica (nS) are focused on performance analysis in the hardened state and they are founded on the use of the mineral admixture in dry grains. Thus, this article aims to evaluate the effects of superplasticizer admixture use with nanosilica in colloidal suspension in the consistency and mechanical strength of the concrete. Two concrete mixtures were produced with the same materials and identical proportions, however with different superplasticizes, one with nanosilica (CnS) and the other without nanosilica (CC) used as reference to analyse the effects of the presence of mineral admixture in the development of the consistency and the mechanical strength of the concrete. For evaluation of these properties were carried slump tests as a function of time and compressive strength at 28 days, according to ABNT NBR 10342 and NBR 5739, respectively. The results showed that the concrete without nanosilica presented longer time available for handling, achieving 135 minutes, extending its period of slump loss for fifteen minutes besides the concrete with nanosilica, which reached 120 minutes; and, also presented higher slump values throughout the test, reaching up to 60.0 mm above at 75 minutes after the beginning of test. However, the CnS presented better performance in the hardened state, achieving the C70 high performance concrete class with 70.92 MPa; while the CC reached 65.57 Mpa, fitting within the C60 class.