Strength Of Concrete Specimens Research Articles

Specimen size and shape effect on the compressive strength of concrete

The results of the investigation of the specimen size and shape effect on concrete strength indicators are presented in this paper. Research on the strength of concrete specimens in the form of cubes (150x150x150 mm) and cylinders of different diameters (50 mm, 100 mm and 150 mm) and heights (100 mm, 200 mm and 300 mm), under compression are carried out on Matest testing machine with Servo-Plus Evolution servo-drive control unit. Three specimens of each type are tested. Control specimens are made according to such ratios of materials that concrete corresponds to the strength class C16/20. All specimens are visually inspected for the presence of any defects, such as large pores, chips, or shrinkage cracks. After that, the actual measurements of all specimens are carried out. They showed minimal deviations from the planned size, which is considered acceptable. In order to check the reliability of the results, after the research of each type of specimen, calculations are carried out to determine the actual strength and the concrete grade. The actual dimensions of the faces and the results of the certain batch research are taken. The data obtained from the concrete specimens research on the test press are analyzed. Due to the formulas and data obtained after the investigation, the actual strength class of concrete for all specimens is determined. According to the results of the research, fracture graphs of all types of control specimens are constructed. The results show that the laboratory measurements are consistent with the literature results, namely that the compressive strength decreases with the specimen size increase. In the case of the smallest, non-standardized specimens (cylinders with 100 mm height and 50 mm diameter), the deviation of compressive strength tests is higher compared to other specimens. The graph is presented for visualizing the specimen type and size effect on concrete strength.

Prediction of Concrete Compressive Strength Using a Back-Propagation Neural Network Optimized by a Genetic Algorithm and Response Surface Analysis Considering the Appearance of Aggregates and Curing Conditions

In the present research, the authors have attempted to examine the compressive strength of conventional concrete, which is made using different aggregate sizes and geometries considering various curing temperatures. To this end, different aggregate geometries (rounded and angular) were utilized in various aggregate sizes (10, 20, and 30 mm) to prepare 108 rectangular cubic specimens. Then, the curing process was carried out in the vicinity of wind at different temperatures (5 °C < T < 30 °C). Next, the static compression experiments were performed on 28-day concrete specimens. Additionally, each test was repeated three times to check the repeatability of the results. Finally, the mean results were reported as the strength of concrete specimens. Response Surface Analysis (RSA) was utilized to determine the interaction effects of different parameters including the appearance of aggregates (shape and size) and curing temperature on the concrete strength. Afterwards, the optimum values of parameters were reported based on the RSA results to achieve maximum compressive strength. Moreover, to estimate concrete strength, a back-propagation neural network (OBPNN) optimized by a genetic algorithm (GA) was used. The findings of this study indicated that the developed neural network approach is greatly consistent with the experimental ones. Additionally, the compressive strength of concrete can be significantly increased (about 30%) by controlling the curing temperature in the range of 5–15 °C.

Concrete Overstrength: Assessment of Field Strength Seeking Insights for Overdesign Optimization

This study investigates the high contents of cementitious materials in Portland cement concrete and assesses the required (f’cr) and actual (σ) compressive strength of concrete specimens. A linear optimization technique identifies the required binder content to reach f’cr. Standard specifications have required concrete overdesign (OD) for decades, but few studies have evaluated the actual magnitude of OD from field data. The compressive strength of 958 cylinders prepared in the field represented 8200 m3 of ready-mixed concrete with 300 and 450 kg/m3 of cementitious are analyzed. The actual OD appears to be 7 to 21% higher than required. The required 28-day compressive strength of concrete was achieved in less than seven days. Therefore, the content of the cementitious materials could be reduced by 6 and 17% so that concrete could reach f’cr without cementitious overconsumption. Reducing cementitious content is recommended to improve construction quality and optimize resource utilization. Among the main reasons for this recommendation are the estimated substantial long-term savings, increased concrete durability and more rational use of natural resources required to build the structures.

Effect of the number and arrangement of inclusions on the strength of concrete specimens

In concrete structures, we identify deformation fields of nodes with applied concentrated stress, which are accompanied by a change in the density and shape of force trajectories. These changes are caused by the presence of large grains of aggregate and/or reinforcing bars (inclusions) in the concrete, clumps of grains of normal size, or the presence of a cavern around the grain of the aggregate. These internal imperfections are among the important parameters that affect the failure process of concrete test specimens, and thus the initiation and development of cracks in concrete and can have a negative impact on the strength of concrete elements. This paper deals with the influence of the number of inclusions in their symmetrical arrangement on a series of test specimens of three different sizes, which are subjected to uniaxial compression. Attention is paid to the selection of a suitable standardization parameter, which will consider the different quality of concrete test specimens

MSFEM을 적용한 콘크리트 공시체의 압축강도에 대한 크기효과

이 연구에서는 중규모크기 유한요소법을 이용하여 콘크리트 원주공시체와 입방체의 압축강도의 크기효과에 관한 연구를 수행하였다. 해석에 앞서 콘크리트를 중규모크기의 다상의 복합체로 정의하는 방법에 관하여 기술하였다. 즉, 콘크리트를 골재, 시멘트 매트릭스, 그리고 ITZ 3가지 상태를 가지는 복합체로 가정하였고, 이후 각각의 상에 대한 재료특성을 부여하였다. 구축된 해석모형을 이용하여 콘크리트의 압축파괴거동에 대한 해석을 수행하였고, 이를 통하여 크기효과와 균열의 발생 및 진전도 확인하였다. 또한 비표준형 원주공시체에 대하여 ASTM C42에서 제시하는 에 따른 강도보정계수도 비교하였다. 기 수행된 연구결과와 이 연구에서 얻은 결과는 충분히 신뢰할 만한 수준의 결과를 나타내었다. 최종적으로 중규모크기 유한요소법을 이용해서도 원주공시체와 입방체의 압축강도 및 크기효과를 충분히 예측 가능함을 확인하였다.

Influence mechanisms under different immersion methods and different strengths of concrete in corrosive environments, and verification via long‐term field test

AbstractThis paper is to study the influence of sulphate corrosion on the mechanical behaviors of concrete, especially concrete corrosion under actual corrosion environment. This study investigated different immersion methods for concrete in a corrosion environment, and different strengths of concrete specimens with contents of sodium sulphate and magnesium chloride of 10.36% and 12.00%, respectively. Strength tests were performed on the specimens for the different immersion methods of full immersion, half‐immersion, and dry‐wet cycles, and with different strengths for the concrete of C20, C35, and C50. To study the internal mechanisms of the corrosion of concrete with different immersion methods and different strengths, a microscopic pore structure test was conducted. The field tests were performed after 12 years to evaluate the long term performance of the concrete under the actual environmental conditions. The test results show that full immersion mainly led to chemical corrosion, half immersion led to double damage from salt crystallization and chemical corrosion, and dry‐wet cycles accelerated the corrosions of the salt crystallization and chemical corrosion. The higher the strength of concrete, the better its resistance to the sulphate corrosion. In comparison with the strength of the concrete before corrosion, field test results show that the strength of uncorroded concrete after 12 years is increased by 9.5% and the strength of corroded concrete after 12 years is reduced by 56.2%. The results of the strength tests and pore structure tests show that sulphate has a significant impact on concrete strength after 12 years of field tests. This study will contribute to improve long‐term performance of the concrete, provide guidance for concrete structure design in corroded areas, and suggested that increasing attention should be paid to the effects of sulphate on concrete performance.

Experimental investigation on the compressive strength of PFGP-covered concretes exposed to high temperature

Purpose This study aims to investigate the effect of high temperature (600°C) on the compressive strength of concrete covered with a mixture of polypropylene fiber and gypsum plaster (PFGP). Design/methodology/approach To study the compressive strength of concrete specimens exposed to temperature, 16 cubic specimens (size: 150 mm × 150 mm × 150 mm) were made. After 28 days of processing and gaining the required strength of specimens, first, polypropylene fiber was mixed with gypsum plaster (CaSO4.2H2O) and then the concrete specimens were covered with this mixture. To cover the concrete specimens with the PFGP, the used PFGP thickness was 15 mm or 25 mm. The polypropylene rates mixed with the gypsum plaster were 1, 3 and 5 per cent. A total of 14 specimens, 12 of which were covered with PFGP, were exposed to high temperature in two target times of 90 and 180 min. Findings The results show that the PFGP as covering materials can improve the compressive strength lost because of the heating of the concrete specimens. The results also show that the presence of polypropylene fiber in gypsum plaster has the effect on the compressive strength lost because of the heating of the PFGP-covered concrete. The cover of PFGP having 3 per cent polypropylene fiber had the best effect on remained strength of the specimens. Originality/value The cover of PFGP having 3 per cent polypropylene fiber has the best effect on remained strength of the PFGP covered specimens exposed to temperature.

Influence of ion erosion on RHPB strength in brine environment

In order to study the change of dynamic elastic modulus, compressive strength and flexural strength of recycled coarse aggregate high performance concrete (RHPB) specimens during one-year corrosion period in Salt Lake brine, and to explore the failure mechanism of its physical and mechanical behavior, the dynamic elastic modulus and strength of concrete specimens and beam members under the corrosion age of RHPB were studied. Research on the influence of degree and so on. The experimental results show that the longer the corrosion time of RHPB specimens is, the higher the chloride ion content is, the stronger the corrosion strength will become; the coexistence of ions can also affect the corrosion rate; the loss of dynamic elastic modulus will increase with the extension of the corrosion time under 0a-1.0a erosion; and under the same replacement rate of recycled coarse aggregate (RG), R. When the corrosion time of HPB is 0-1.0a, the flexural strength increases continuously with the extension of service time. The compressive strength of specimens with different RG replacement rates decreases as a whole under corrosion. At 1.0a, the compressive strength decreases most obviously with the increase of RG replacement rate, and the strength decreases the most, RG substitution rate of 40% is the best.

Investigation of Strength and Cracking Behaviour of ZnCo2O4 Nanoparticles Incorporated Porous Concrete

In this study, the effect of limewater on strength assessments and percentage of water absorption of zinc cobaltate (ZnCo2O4) nanoparticles incorporated porous concrete has been investigated. Portland cement was partially replaced by ZnCo2O4 nanoparticles with the average particle size of 50 nm. The results indicated that the incorporation of nanoparticles could transform concrete with improved strength and water permeability when the specimens are cured in saturated water. The strength of concrete specimens without nanoparticles are relatively low compared to the specimen with ZnCo2O4 nanoparticles. The results show that the strengthening of nanoparticles incorporated specimens resulted from improved permeability together with high strength. Microstructure and morphology of the specimen after compressing test was observed by scanning electron microscopy (SEM). In addition, ZnCo2O4 nanoparticles are able to act as nanofillers and recovered the pore structure of the specimens by decreasing damaging pores.

Research on hysteretic behaviour of high-strength concrete shear wall plate for steel tube in building construction

For the problem of insufficient analysis of the hysteretic behaviour of the traditional concrete shear wall, the research method of hysteretic behaviour of high-strength concrete shear wall for steel tube in building construction is proposed in paper. Based on the OpenSee platform, the displacement of the base was recorded by the displacement metre installed on the base, and the load displacement curve is plotted, and the shear bearing capacity of the model was analysed. The failure modes, axial compression ratio and concrete strength parameters of the specimens were studied to obtain the following conclusions. Higher the axial compression ratio and the wall shaft pressure, the higher the load capacity of the specimen. By comparing the hysteretic behaviour of different steel tube high strength concrete shear strength specimens, this paper analyses the performance of steel tube high strength concrete shear wall panels, which provides data and reference for future construction.

Biocalcification by Piezotolerant Bacillus sp. NIOTVJ5 Isolated from Deep Sea Sediment and its Influence on the Strength of Concrete Specimens.

Biocalcification or microbially induced carbonate precipitation (MICP) is gaining attention from the research fraternity, primarily ascribed to their eco-friendly applications. Bacterial strains have been isolated from various sources and their ability to precipitate carbonate has been studied extensively. In spite of the fact that the deep-sea environment is a potential source for bioprospecting, meager reports exist on the isolation of biocalcifying bacterial strains from deep-sea. In this study, a deep-sea sediment sample obtained from off-Barren Island coast in the Andaman Sea was investigated for biocalcifying strains. Based on the urease activity and the ability to produce calcite crystals, the strain NIOTVJ5 was chosen for further investigations. The strain showed a similarity to Bacillus thuringiensis through 16S rRNA sequencing and was shown to possess positive urease, protease, amylase, catalase, and oxidase activities. The isolate was found to be piezotolerant as it was able to survive at 100bar pressure with significant changes in the spore morphology. The strain was able to produce strong monoxenic biofilms as well. Maximum urease activity was 554.03U/mL and it precipitated 1.80g/L of carbonate crystals. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy confirmed the presence of calcium carbonate. The carbonate polymorph was identified as calcite using X-ray powder diffraction. The impact of biocalcification by NIOTVJ5 on concrete specimens indicated an increase of 30.91% in their compressive strength. This is the first report of a biocalcifying strain from a deep-sea sediment around the Indian subcontinent region. This study indicates the potential of the strain NIOTVJ5, which can be employed for various biotechnological applications.

Hybrid confinement of high strength concrete using shape memory alloys and fiber-reinforced polymers

This exploratory study investigates an innovative hybrid confinement technique for high-strength concrete (HSC) which combines traditional passive confinement applied using fiber-reinforced polymer (FRP) sheets with active confinement applied using thermally pre-stressed shape memory alloy (SMA) spirals. Normal strength concrete (NSC) and HSC cylinder specimens, confined either with traditional FRP confinement or hybrid confinement, are tested under uniaxial cyclic compression. Test results indicate that the application of hybrid confinement on HSC with a small active component results in a significantly higher ductility in comparison to passively confined HSC. The experimental test results are then used to carry out pushover analysis of high strength concrete-filled fiber tube (CFFT) bridge columns wrapped with SMA spirals. The pushover analyses show that the application of active confinement improves the ultimate drift ratio of high strength CFFT columns.

COMPRESSIVE STRENGTH OF CONCRETE WITH FIBRES AT ELEVATED TEMPERATURE

Concrete, when exposed to high temperature, can cause spalling, cracking, and severe damage, which could lead to a sudden collapse of a building. One of the solutions for overcoming this weakness of concrete is by incorporating fibres in the concrete mix. Concrete incorporated with more than one type of fibres is often known as hybrid concrete. In this paper, the compressive strength of the hybrid concrete when exposed to elevated temperature is studied. The result is compared to concrete mixed with a single type of fibre of polypropylene or steel fibres. An observation of spalling is also carried out to verify the compressive strength test. The test results showed that both the single fibre specimens with steel fibre and hybrid specimen improved by 23.34% and 24.60% in residual strength compared with other residual strengths of concrete specimens.

Size Effect Studies on Concrete Made of Natural and Artificial Sand

Objective : An experimental investigation was carried out to study the size effect on concrete specimens. Methods : In order to study the size effect compressive and split tensile test were conducted on standard and high strength concrete (M 30 and M 60 ) specimens of two different sizes of cubes (150 x 150 x 150 mm and 100 x 100 x 100 mm) and cylinders (150 x 300 mm and 100 x 200 mm) made of natural and artificial sand. In addition to this, the flexural strength test was also conducted for beam (500 x 100 x 100 mm) to compare the flexural strength of the beams made of natural and artificial sand. Findings: The result showed that the larger size concrete specimen fails at a lower stress than a smaller one and it was also observed that there was no significant variation in the strength with two sizes considered. The mechanical properties obtained with natural sand and artificial sand indicates that strength obtained for artificial sand was higher than that of natural sand for both M 30 and M 60 grade of concrete. Applications/Improvements: From this study, it was concluded that the standard cube of 150 x 150 x 150 mm and 100 x 100 x 100 mm can be used interchangeably for the test purpose. Similarly, for split tensile strength, standard cylinder of 150 x 300 mm and 100 x 200 mm can be used interchangeably.

현장타설말뚝 콘크리트 공시체 압축강도 데이터 분석을 통한 강도 영향인자 분석

현장타설말뚝 콘크리트 공시체 압축강도 데이터 분석을 통한 강도 영향인자 분석

Fresh Water Savings Through the Use of Municipal Effluents in Concrete Pavement

Wastewater reuse presents a promising solution to the growing pressure on the world’s water resources. The use of municipal wastewater effluents for concrete production in the construction industry would result in energy and water savings leading to conservation and sustainability of our water resources. In this research, to promote and increase the reuse of wastewater in construction industry, both chemical and bacteria analyses were performed to ensure the recommended quality for concrete mixing water and the compressive strength of concrete specimens made with wastewater effluents was investigated and compared to specimens made with fresh water. Statistical analysis of the strength results showed that at 95% confidence interval, the compressive strengths of the control specimens and those of test specimens are not statistically different.

Compressive and Flexural Behaviour of Unstressed Concrete Substructure in Cassava Effluent Contaminated Soils

Concrete research is gradually shifting from the conventional strength-based approach to durability-centred in the past decade. Durability is the measure of the robustness of constructed facilities against deterioration tendencies. The rate of deterioration is affected by the loading condition, and more importantly the physical and chemical nature of the host environments. This paper reports the experimental investigation of unstressed concrete substructure in the natural (uncontaminated) and cassava’s hydrocyanide effluent-polluted soils on the compressive and flexural strengths of buried concrete specimens for a maximum of 84 days. The compressive strengths of the cubes were tested every 7 days until the 84th day, while the beams were only subjected to third-point loading flexural tests at age 84 days. The compressive strength of concrete specimens in the two soil environments increased, though the trend was lower in the polluted soil. The strength reduced by 2.50% to 9.47% between the 7th and 28th days, but steadily between the 28th and 84th days with strength loss of 9.95% (COV = 2.64%). The load-deflection curves were quadratic for the beams in the two geo-environments. The beams in cyanide-polluted soil lost 34.5% of its flexural stiffness, while its loss of load-carrying capacities at the first crack and ultimate failure was 15.8% and 20% respectively. Higher degree of deterioration is certain for loaded concrete substructures in similar conditions. Hence, prior knowledge of soil chemistry is crucial to determining suitable concrete grade and nominal cover for durable substructural elements.

Advances in experimental assessment of dynamic tensile strength of concrete by the spalling technique

An experimental method to test concrete in dynamic tension by spalling with a Hopkinson bar as loading and measuring tool was developed in 1999. The dynamic strength of concrete specimen and strain rate were indirectly derived from an accurate data processing of the signals measured on the Hopkinson bar surface. This method suggested by late Prof. Klepaczko, allowed for reaching the highest strain rate reported in literature for which an intriguing tensile strength increase was highlighted. This simple and efficient technique has been adopted by many researchers around the world. Some significant improvements in terms of definition and reproducibility of the incident loading pulse travelling along the bar and direct and/or contactless measurements on concrete specimens have been introduced. The very high rate sensitivity of concrete tensile strength was corroborated by the additional experimental data obtained with this experimental technique during the last fifteen years.

Test Research on Strength of Concrete Shaft Lining under Salt Disaster Corrosion

In order to study the strength change of high strength concrete shaft lining structure in underground complex environment resisting composite salt damage erosion, C70 high strength concrete test specimens were made and composite salt disaster solutions of different concentrations were compounded. The test results show that the coefficient of compressive strength and flexural strength of high strength concrete increase in early corrosion and then decline. The strength of specimen declines more quickly in higher corrosion solution concentration in latter time. The change law of the flexural strength is more complex than the compressive strength. Composite salt disaster solutions have little effect for no damage high strength concrete.

Recycling MSTP Sludge as an Admixture in Concrete

One of the main objectives of this study was to activate the pozzolanic activity of sludge, produced by municipal sewage treatment plants (MSTP), make it become an admixture to replace a part of cement in concrete. Nowadays, a significant quantity of MSTP sludge is obtained in China. That is why this paper examines the possibility of adding this waste product to plain concrete with Portland cement. Preliminary studies are carried out on using MSTP sludge as an admixture by thermal (calcining) and mechanical (grinding) treatment. The pozzolanic activity of the calcined sludge ash (CSA) evaluated by Cement Mortar test. The CSA-blended cement concrete was formed into specimens of cubic concrete with 100 mm×100 mm×100 mm. They are with 30 wt. % cement replaced by CSA, which was prepared by the optimal activation conditions. The Cement Mortar test results revealed that the optimal activation conditions of CSA were as follows: calcined at 800°C for 2.5 hours followed by fast cooling in air and then ground until 60 minutes. Besides, the compressive strengths of concrete specimens with added 30% CSA were 103.6% and 105.3% of those of the ordinary Portland cement concrete specimens at 7 and 28 days, respectively. These results demonstrate the feasibility of recycling MSTP sludge as an admixture in concrete for construction engineering.