Strength Characteristics Of Concrete Research Articles

Effect of Steel-Nylon Fibre as Reinforcing Material on Strength Characteristics of Concrete

Concrete is reinforced using different kind of admixtures in order to increase its properties and making it cost effective. Fibre is one type of reinforcement, which is a composite material made up of cement or mortar and fragmented, separate, distributed, arbitrarily located, and disconnected reasonable fibres. Concrete is broadly utilized as a part of structural designing with its high compressive strength, minimal effort and bottomless crude material. However, regular cement has a few weaknesses, for instance, low malleability, restricted flexibility, little protection from splitting, weak hardness, high fragility, and other factors limits its use.” The cement may get split because of basic and natural properties; however, a large portion of the breaks are shaped because of inherent inward smaller scale breaks as well as the material’s inherent flaws to oppose ductile powers. Such condition of the structure at the tensile end subjects to the cracks under a certain amount of load. Initially there become small splits or cracks and with due respect of time these cracks gets widened. After drying of cement, Cracks may be developed due to shrinkage. The small-scale splits frame because of drying shrinkage or different reasons for volume change if there should be an occurrence of plain concrete. Along these lines many endeavours have been made to expand the rigidity of cement by method for utilizing traditional strengthened steel bars and furthermore by applying limiting systems.

Strength characteristics of concrete by utilization of metakaolin and steel fibres as partial substitute to binding material

Cement has an unresolved problem of increased utilization of raw materials and energy consumption and also carbon dioxide emission during its production. Metakaolin is utilized as partial substitute to cement. It utilizes lime on hydration and causes an increase in the production of cementitious compounds leading to improved strength. The principal intention of this research activity is to find out the fresh (workability) and hardened properties (compressive, split tensile and flexure) of concrete by using metakaolin at varying percentages from 0%, 5%, 10%, 15% and 20% by weight of cement and again by incorporating various types of steel fibers in the limit of 2%, 2.5%, 3% and 3.5%. Concrete specimens were cast for a M40 grade of concrete. Cube specimens (150 × 150 × 150 mm), cylindrical specimens (300 × 150 mm) and prism specimens (100 × 100 × 500 mm) were tested and evaluated for strengths in direct compression, tension and bending for 7 and 28 days of curing span. The outcomes were compared with normal mix. The results have shown that the increase in compressive, tensile and flexure were 20.29%, 16.13% and 14.4% respectively.

Size effect at testing strength properties of concrete

Various strength characteristics of concrete are considered as fracture parameters. The compressive strength of concrete is of paramount importance when designing concrete structures, whereas tensile strength of concrete is the basic property when estimating cracking resistance of a structure and analysing fracture processes in concrete. When testing the compressive strength of concrete, the results are dependent on the shape and dimensions of used specimens. Some findings reported in the literature suggest that size effect exists also when testing such fracture properties of concrete as tensile strength. Unfortunately this problem is much less recognized and described compared to size effect in compressive test results. In this paper, the experimental investigation is presented on how the length of cylindrical specimens influences the tensile splitting strength of concrete obtained by means of the Brazilian method. Additional variable parameters were: type of aggregate (natural gravel and crushed granite) and cement-water ratio (C/W = 1.8 and C/W = 2.6). In conducted laboratory experiments a higher splitting tensile strength of concrete was noted for all specimens with nominal dimensions of 150×150 mm, compared to specimens 150×300 mm in size, regardless of type of aggregate or cement-water ratio.

ESTIMATION OF VARIABILITY OF STEPS OF ARMATURE IN A MONOLITHIC REINFORCED CONCRETE COVER OF A TOWER INDUSTRIAL CONSTRUCTION

The work considers one of the possible reasons for reducing the operational reliability of monolithic thin-walled load-bearing reinforced concrete structures of existing industrial structures in relation to their design solution. As this reason is considered the variability of distances between axes of cores of working inspectedarmature of such designs is quite common.Comparison of design solutions with the qualityof construction and installation work makes it possible to identify the influence of unaccounted factors in the design of monolithic thin-walled reinforced concrete structures, which reduce their serviceability due to variability of concrete strength characteristics and actual longitudinal and transverse reinforcement due to variability of workingsteps. While processing the results of the survey ofmonolithic reinforced concrete thin-walled structures, which perceive the efforts of different levels,the question arises: which step of the working reinforcement, from a large number of actually measured steps, to choose in verified calculations –average or maximum, with extras.In the current norms, an indicator as the averagevalue of concrete strength for the calculation ofreinforced concrete monolithic slab structures doesnot appear, but is used as a statistically reasonablevalue of concrete strength, which takes into account its normalized variability with 95% security.Regulatory documents statistically estimates thevariability of reinforcement strength. At the sametime, they do not take into account the variabilityof the actual reinforcement of monolithic reinforced concrete structures, which is the subject forreconstruction of additional loads, but they aremade without observing the design distances between the reinforcement in these structures.When performing verified calculations of suchstructures for different design situations, to develop working designs for overhaul, reinforcement,reconstruction or dismantling, it is necessary todetermine which actual step of the working reinforcement should be taken with other defined design parameters of the structure.The authors instrumentally investigated and statistically analyzed the data of reinforcement of themonolithic reinforced concrete shell of the towerstructure, which made it possible to reasonablyaccept the values of the reinforcement steps in thetest calculations.

STRENGTH OF CONCRETE UNDER LOCAL COMPRESSION TAKING INTO ACCOUNT THE RELATIONSHIP OF THE ELEMENT HEIGHT TO THE SIZE OF THE LOADING AREA

Formulation of the problem. Reliability of buildings and structures from reinforced concrete largely depends on efficiency of construction solutions of supporting areas and joins of elements of bearing systems. At the same time, an important place is given to the issues of ensuring their bearing capacity. One of the ways to solve this problem is to increase the strength characteristics of concrete, in particular by using basalt fiber. The purpose of the article is to improve the method of calculating the strength of concrete elements under the local compression on a general theoretical basis and to clarify the impact on the strength of determining factors. Conclusion. To calculate the strength of concrete elements under the local compression, the theory of concrete plasticity is promising. The application of the variational method and the principle of virtual velocities is proposed. According to research, the strength of concrete, in addition to the ratio of the area of application of the load and the cross-sectional area, is affected by the ratio of the height of the element to the width of the stamp and both characteristics of concrete strength. The proposed kinematic failure schemes have found experimental confirmation. Analysis of test results of concrete elements and assessment of their strength on the basis of the theory of plasticity allowed making the program of experimental research of fibroconcrete on basalt fibers under local compression.

Analysis of Dowel Action in Reinforced Concrete Beams with Shear Reinforcement

Abstract The shear transfer mechanism was examined to view the contributions of different components of shear transfer such as aggregate interlocking, dowel force and uncracked compression zone. Understanding the role of various shear transfer components with transverse reinforcement provided was complex due to traditional difficulties involved in detail assessment of accompanying kinematics during the failure. In the present paper, the issue was addressed by employing sixteen specimens and grouped under two categories representing conventional beams and beams with preformed cracks and were tested under four - point bending load with a shear span to depth ratio of 1.26 by increasing the characteristic strength of concrete. From the results obtained, empirical formulas proposed were also evaluated and it was concluded that the results were consistent and contribution of shear transfer across uncracked compression zone was maximum in shear resistance with transverse reinforcement provided. Later structural behaviour was also assessed and it was concluded that beams with preformed cracks had exhibited greater stiffness thus nullifying the effect of aggregate interlocking in shear transfer.

Strength Characteristics of Concrete with Waste Polypropylene as Modifier for Pavement Construction

The demand for a better performing pavement and the need to convert the ever-growing polymer waste into beneficial use necessitated the need to develop and characterize a polypropylene modified concrete for use in pavement construction. This research focuses on characterizing the strength of concrete produced with waste polypropylene waste as modifiers for pavement construction. The materials used in this research are fine and coarse aggregates, cement and polypropylene waste chairs (PWC). Tests were performed on the aggregate and fresh concrete to determine their suitability and characteristics for use in concrete for pavement. Two concrete grades 1:2:4 and 1:3:6 was produced into 200 mm, 400 mm and 500 mm long paving stones on which compressive and flexural tests were performed. Results obtained showed that 400 mm 1:2:4 grade concrete has the highest compressive strength of 27.36 N/mm2 at 10% polypropylene composition. The 200 mm 1:2:4 concrete grade paving stone with 10% polyprpopylene composition has the highest flexural strength of 12.90 N/mm2. The 200 mm at 10% polypropylene composition correlation coefficient has that the highest value of 0.98 which better explains the compression-flexural strength relationship and validates the 200 mm length at 10% polypropylene composition paving stone as the most adequate length of paving stone for pavement construction. It was concluded that the 200 mm long 1:2:4 concrete grade paving stone at 10% polypropylene composition is the best length of paving stone that can give an adequate flexural strength which is the most important requirent in concrete pavement requirement.

Relationship Between Compressive Strength and Splitting Tensile Strength of Palm Kernel Shell Concrete

The use of palm kernel shell (PKS) has gained acceptance in the production of concrete. Compressive strength is the mostly used strength characteristics of concrete. The compressive strength CS of concrete should provide a good basis for predicting the splitting tensile strength STS. The aim of this study is to establish a mathematical relationship between the CS and STS of concrete produced with PKS. In this study, coarse aggregates was fully replaced with PKS at varying water-cement ratios (w/c) for concrete mix ratios 1:1½:3 and 1:2:4. Unit weigth of the PKS, slump, compressive and splitting tesnsile strength were determined. A relationship between CS and STS was developed for the different w/c ratios using exponential function aproximation. Physical property tests carried out on the PKS characterized it as lightweight aggregate with saturated surface dry unit weight of 1.27. The slump revealed that PKS concrete at 0.3 and 0.4 w/c is stiff and not workable. CS and STS at 28day for mix ratio of 1:1½:3 at w/c of 0.3, 0.4, 0.5 and 0.6 were respectively 3.2 and 1.2; 9.4 and 2.1; 10.8 and 2.6; 9.0 and 2.4 N/mm2. The corresponding values obtained for mix ratio 1:2:4 were 3.0 and 1.0, 1.7 and 1.3, 4.5 and 1.6, 7.7 and 1.9N/mm2, respectively. Equations relating CS and STS at 0.3, 0.4, 0.5 and 0.6 w/c were established. It was concluded that PKS concrete produced with mix ratios 1:1½:3 and 1:2:4 performed better in compression and splitting tensile strength at w/c of 0.5 and 0.6.

Evaluation of Strength Characteristics of Concrete by Glass Fibre Reinforced Polymer (GFRP) And Carbon Fibre Reinforced Polymer (CFRP) Wrapping

The construction material mainly reinforced concrete is being used extensively for various type of construction projects. However, deterioration of RC structures is recognized as a major problem worldwide. Extension of the structures’ life is an inevitable need for a healthy planet. Any deficiency caused to the members of the structure may affect the life of structure. Therefore, it is important that the members should provide adequate strength (for which it is designed) throughout its operational life. But, it has been observed that due to alteration in purpose of use of structure (very common in mega cities), improper design and deficiency caused due to earthquake, blast and impacts in structural members and as a result in the members structure can possibly be subjected to loads which have higher magnitude compared to its design loads. This study is based on experimental investigation to assess the behavior of CFRP & GFRP wrapped concrete under compressive loads. For this purpose, M30 grade concrete specimens have been casted and wrapped it with Glass and Carbon FRP and its strength against compressive loads have been found.

A mathematical optimisation model for the design and detailing of reinforced concrete beams

An evolutionary metaheuristic optimization model for sizing reinforced concrete beams is presented. The proposed optimization model transcends ones in the literature as it is able to consider characteristic concrete strength (fck), cross-section area and reinforcement bars' diameters as discrete design variables, thus representing a more realistic model. The goal is to minimize construction costs via configuring cross-sectional dimensions, determining reinforcement layouts, and defining fck. The design constraints formulated in the mathematical model proposed are related to structural integrity, considering ultimate limit state, serviceability limit state, and good construction practices. A finite element method program was developed to obtain the stresses and strains of beams, geometries, and load forces. Additionally, a longitudinal reinforcement database generator was developed, ensuring that the reinforcement layouts generated are within codes of practice. A Genetic Algorithm was adopted to solve the resulting optimisation problem. Results of case studies demonstrate that the cost variance implications are directly related to the reinforcement detailing arrangements, with 3.63% to 17.07% improvements in costs that are achieved when compared with other studies in the literature.

Strength Characteristics of Concrete with Partial Replacement of Cement by Waste Glass Powder

: In this examination an endeavor is made to contemplate the impact of waste glass power in Concrete utilizing waste glass, which is non biodegradable and not reasonable to landfill. This examination is done to utilize such waste materials into development enterprises with the goal that our current circumstance is free to one of the significant contamination created by the assembling ventures. The primary point of this investigation is to use of waste glass power as a halfway substitution of fine total. In this examination the point is to decide the level of glass substitution, bringing about ideal compressive strength. Substantial ostensible blend of M20 with various rates of Glass power has been assessed according to IS 2386(part IV) and IS 383. Squander glass powder was supplant with fine total in different rates, for example, 5%,10%,15%. Reference substantial blend is likewise made for relative reasons.

Changes in the structural and phase composition and strength characteristics of concrete during liquid corrosion in chloride-containing media

The results of physico-chemical studies that allow us to judge the changes occurring in the cement stone under the influence of liquid chloride-containing media are analysed. Samples of CEM I 42,5N Portland cement with a water-cement ratio of W/C = 0,3 were exposed to solutions of 2 % MgCl 2, 0,001 % HCl and 0,1 % CaCl 2 for 150 days. Changes in the strength characteristics of CEM I 42,5N Portland cement samples under the influence of chloride-containing media were studied. It is established that the 2 % MgCl 2 solution is an extremely aggressive medium in the conditions of liquid corrosion of concrete, its action causes a deterioration in the strength characteristics of concrete by 1,5 times. The changes in the structural and phase composition of concrete that occur under the influence of chloride-containing media are studied. The relationship between the characteristics of the cement stone structure and the strength parameters of the cement stone is established. The decrease in the strength of cement concrete is associated with the decomposition of calcium hydrosilicate C 2SH under the influence of liquid aggressive chloride-containing media, as evidenced by the decrease in intensity and the disappearance of the lines corresponding to this compound on X-ray images.

Strength Characteristics of Concrete by Partial Replacement of Coarse Aggregate with Coconut Shells & Cement with Glass Powder

In this study coarse aggregates and cement are partially replaced in the concrete with similar materials like coconut shells and glass powder. While production of the cement there is a lot of pollution to the environment and which causes health issues to the society. In the same way while production of the course aggregates which releases lot of dust into the atmosphere which causes damage to human lives. We can obtain some advantages by partially replacing the coarse aggregates and cement in the concrete. As we all know that the Cement and the coarse aggregates are the main ingredients in the concrete. The cost of these materials is getting increased day by day. There are some of the materials proposed by many researchers to lesser the cost of the concrete and to improve the strength characteristics of the concrete. For coarse aggregates, the coconut shell is the most preferable and it has more potential to the partial replacement of the coarse aggregates in concrete. As well as there is a similar material which used to partially replacement of the cement is waste glass powder. As we observe at many places there is a lot of wastage of glass will produce throughout the year. Mainly glass is the composition of silica. When the glass is crushed into very small size as powder it experienced to the pozzolanic reactions with hydrates in the cement, and calcium silicate hydrate will be formed. The main aim of this research is utilization of the waste material in the concrete as well as decreasing the cost of the construction by using these waste materials in the concrete, by performing all these things we can easily reduce the pollution of the environment and clean the environment by using these waste materials in the concrete..

Strength characteristics of concrete using coconut shell as a coarse aggregate – A sustainable approach

Many researchers have carried out works on use of various agricultural and industrial by-products to enrich the performance and strength characteristics of concrete. The study here reports and captures the use of coconut shell (CS) as partial replacement to coarse aggregate (CA). CS is a naturally available abundant agricultural waste material, which can be used as an alternate to CA. For this research, authors considered M20 grade concrete to investigate the rheological and strength characteristics of concrete incorporating CS as an alternate material for CA in varying percentages like 0%, 5%, 10%, 15%, 20%, 25%, and 30%. The study aims to find the optimum dosage of coconut shell that can be replaced partially in concrete to enhance the strength characteristics and to make concrete lightweight by overcoming the disposal challenges of agricultural waste. Total of seven mixes are considered for this investigation to attempt CS a substitute for CA. The rheological properties like slump & compaction factor tests are conducted for fresh properties. Similarly, strength characteristics of concrete like compressive, split tensile and flexural strength tests are performed to measure the structural performance of CS as a CA. Test outcomes of this investigation exhibits that, CS can be replaced up to 20% by weight of CA, without compromising the strength characteristics and rheological properties of concrete. Use of CS as a CA in concrete production not only contributes to performance and strength of concrete but also solves the solid waste disposal problem and helps in conserving natural resources.

Высокоэффективный тяжелый бетон с использованием углеродсодержащего модификатора

Reducing the consumption of cement in the production of concrete mixtures has been a topical issue in the construction industry. The study aims to optimise the structure of concrete stone by selecting the particle size distribution of the components to nanoscale values. Such microfillers include silica fume, metakaolin, ashes, nanographite/graphene, etc. Thus, producing additives of complex action having a plasticising ability, as well as containing finely dispersed fillers forming binding material, is promising. Expandable graphite was dispersed in an aqueous medium and subjected to ultrasonic treatment using an ultrasonic bath with an 80 W generator. The particle size distribution in the graph-ite-containing suspension was studied using a laser diffraction particle analyser FritschNanoTeс with a wet dispersion system (measuring range of 0.01 to 2100 μm). Microscopic examination was carried out using a scanning electron microscope TESCAN Mira 3 with a magnification range of up to 1,000,000 times. In the present work, the physical-mechanical properties of heavyweight concrete containing modified oxidised expandable graphite were investigated. The results of microscopy and particle size distribution analysis of the graphite-containing suspension are presented. The research indicates the efficiency of ultrasonic treatment of a graphite-containing suspension and its effect on the strength characteristics of concrete. The presented results demonstrate the potential of ultrasonic treatment for additional disintegration of graphite particles in a graphite-containing suspension improving the physi-cal and mechanical characteristics of a concrete stone by adding this suspension to its composition.

EFFECT OF HUMAN HAIR FIBRES ON STRENGTH CHARACTERISTICS OF CONCRETE

Human hair fibres (HHFs) are made of non-degradable matter. These fibres possess high tensile strength and are available in abundance at very low cost. The use of HHFs in concrete structures may increase its capacity to resist tensile stresses which are caused by bending moments. This paper presents a study to investigate the effects of HHFs on concrete strength characteristics. Experiments were conducted on concrete cylinders to measure the compressive strength and split tensile strength while prisms were used to calculate the modulus of rupture. Three percentages of HHFs (one percent, 1.5 percent and two percent by weight of cement) were mixed to prepare the concrete samples. Mixes without HHFs were employed as control mixes. The obtained results indicated that with the addition of 1.5 percent HHFs, concrete compressive and split tensile strengths were increased by twenty-nine percent and fourteen percent, respectively. The same amount of HHFs increased the modulus of rupture and modulus of elasticity by twenty-three percent and nine percent, respectively.

МОДЕЛЬ КРИТЕРИЯ ТРЕЩИНОСТОЙКОСТИ И ПРОЧНОСТИ ПЛОСОКНАПРЯЖЕННЫХ КОНСТРУКЦИЙ ИЗ ВЫСОКОПРОЧНОГО ФИБРОБЕТОНА И ФИБРОЖЕЛЕЗОБЕТОНА

A variant of the crack resistance criterion and the strength criterion of plane-stressed structures made of high-strength fiber-reinforced concrete, fiber-reinforced concrete is proposed. The criteria are based on the theory of plasticity of concrete and reinforced concrete G.A. Genieva. In general, the condition for crack resistance of a plane-stressed fiber-reinforced concrete element is presented in the form of an ellipse with jumps on the coordinate axes of the main reduced stresses. The strength condition of a fiber-reinforced concrete element is described by a complex figure that takes into account cracking in the element under a plane stress state. The characteristic points on the coordinate axes are calculated from the physical and mechanical characteristics of concrete strength, obtained as a result of testing high-strength fiber-reinforced concrete for uniaxial compression and uniaxial tension with “dissolved” fiber in the concrete body and reinforcement reduced to concrete. The results of a comparative analysis of the criteria for crack resistance and strength of high-strength concrete and high-strength fiber-reinforced concrete are given, depending on the percentage of fiber in the concrete body and the type of fiber used. The proposed analytical dependences can be used to analyze the crack resistance and strength of plane-stressed reinforced concrete beams-walls reinforced with fiber, corner zones of shallow shells and other plane-stressed structures made of high-strength fiber-reinforced concrete and fiber-reinforced concrete.

Concrete containing recycled waste glass: strength and resistance to freeze–thaw action

The mechanical strength, mass loss and dynamic elastic modulus of Portland cement concrete incorporating recycled glass powder (GP) as a cement replacement material or crushed glass aggregate (GA) as a fine aggregate replacement material subjected to different cycles of freezing and thawing were investigated. A series of 11 concrete mixing proportions was designed with a constant water/cement ratio of 0·5 including fractions of GP or GA. Tests were conducted on 100 × 100 × 100 mm cubes, 100 × 200 mm cylinders and 100 × 100 × 500 mm prisms. The tests of compressive strength, flexural strength and indirect tension were used to examine the impact of the inclusion of different percentages of glass (GP or GA) on the mechanical properties of concrete cured for 7, 28 and 60 d. Two non-destructive testing approaches (ultrasonic pulse velocity and resonance frequency) were used in the freezing and thawing test. The test results indicated that, compared with conventional concrete, the mechanical strength characteristics of concrete containing GP or GA were more enhanced. The use of GP decreased the deterioration of the concrete under the effect of frost action, whereas the use of GA had an adverse influence on the frost resistance of the concrete.

Stress assessment in reinforcement for columns with concrete creep and shrinkage through Brazilian technical normative

In this paper, the induced stress in longitudinal reinforcement bars with cross sections subjected to concrete creep and shrinkage was evaluated. The study was performed for a reinforced concrete column, with loading varying from zero—in which the structure is exclusively subjected to self-weight—to forces close to the loss of stability by bifurcation of equilibrium. A real precast concrete pole, extremely slender, with geometry varying lengthwise, was the structure chosen for the analysis. The aspects related to the material nonlinearity, as well as creep, shrinkage and the development of characteristic concrete strength, were taken into account following Brazilian normative recommendations in NBR 6118:2014 (Design of structural concrete—Procedure) by the Brazilian Association of Technical Standards (ABNT). The critical buckling load was defined according to the structural frequency by using particularly nonlinear formulations. The results were obtained for different instants without exceeding the expected time for convergence of results. The maximum relative value found for the reinforcement stress was 1.24% of the steel yield strength, eliminating the possibility of yielding material.

Feasibility of Construction Demolition waste in Concrete as a Coarse Aggregate

Concrete is an efficient and versatile material for construction. The rapid urbanization results in huge increase in new construction activities which ends with exploitation of natural resources, whereas demolition of structure ends up in the generation of Construction & Demolition wastes (CDW) in a huge amount that causes solid waste disposal issues. This research reveals utilization of CDW effectively in Concrete, to attain the property of natural aggregates as well as to reduce the solid waste disposal issues. Initially, the debris from the building waste is collected, crushed, and separated as C-Coarse and C-Sand. The M40 concrete specimens is done by using the cultivated aggregates in 25, 50, 75 and 100 % replacement with that of the natural aggregates. From the test result the 50% replacement of cultivated aggregate is optimum and M3 mix is a suitable mix. The effective depth of beam is also almost similar with M3 mix makes the use of CDW as a feasible one. Use of CDW will save about 12.075 m3 of fine aggregate and 21.625 m3 of coarse aggregate for every 100 m3 of concreting work makes it as a suitable alternative for the conventional aggregates. Thus, the 50% replacement of CDW for aggregates is feasible in terms of strength characteristics of concrete that makes it as best material for natural aggregates and may decrease its requirement. Further, the rise in the use of CDW will reduce the volume of solid waste generated and corresponding environmental pollution which leads to achieving the sustainability of natural resources.