Papers by Keyword: High-Strength Concrete

Abstract: This paper presents a study from an ongoing research project on the bond performance of flexural prisms strengthened using carbon-fiber-reinforced polymer (CFRP) laminates. The primary objective is to evaluate the effect of normal-strength concrete (NSC – 30MPa) and high-strength concrete (HSC - 50MPa) on the bond performance of plain concrete prisms notched at the mid-span and strengthened using CFRP laminates. Six of the twelve plain concrete prisms were strengthened using CFRP laminates, while the remaining prisms were unstrengthened to serve as control specimens. After achieving 28 days of curing in standard lab conditions, all prisms were tested under a four-point bending test. The ultimate mid-span deflection, maximum and ultimate strains at the mid-span, strain distribution at different positions along the length of the laminate, and bond/shear stress versus slip were analyzed to evaluate the bond performance of flexural prisms. The average ultimate load-carrying capacities and mid-span deflection of the NSC and HSC groups were 31.33 and 35.02 kN and 0.55 and 1.54 mm, respectively. The average CFRP strain values at the mid-span corresponding to the ultimate load were 5005 and 3544 με for the NSC and HSC groups, respectively. The maximum attained bond-stress values for NSC and HSC groups were 1.71 and 1.42 MPa, respectively. The corresponding values for slip at maximum bond stress are 0.27 and 0.24 mm for the two groups, respectively. It was concluded from the study that the concrete compressive strength has minimal effect on the flexural bond performance of concrete prisms externally bonded with CFRP laminates.

Abstract: High-strength concretes made with a lot of cement and good quality aggregates added with additives and admixtures causing expensive costs. Conversely, cement manufacturing is not environment friendly due to using many natural raw materials and delivers CO₂ to atmosphere triggering global warming. Moreover, aggregates availability deriving from river reduces over time, almost 60% of civil engineering infrastructures in world are made with concrete. The purpose of this research is to study effectiveness of using cement substitute materials derived from natural geopolymer pozzolanic ash and aggregates substitute derived from palm oil mill waste in high-strength reinforced concrete beams. These local materials are abundantly available in nature but have not been used, which are utilized together to produce hybrid high-strength concrete. The test investigated was shear capacity of reinforced concrete beams in anticipating earthquake-prone areas of Indonesia. Hybrid reinforced concrete beams made with 10% pozzolanic ash as cement substitution, 20% palm oil blast furnace slag as fine aggregates substitution, and 40% palm oil shell chunks as coarse aggregates substitution. Dimensions of beams were 150 x 300 x 2200mm. To ensure shear failure emergence, beams were strengthened with longitudinal tensile reinforcement 4 D 18.9mm, longitudinal compression reinforcement 2 D 15.8mm, and shear reinforcement Ø 6 – 300 mm, resulting in capacity ratio of bending to shear 2.29. Results showed that hybrid high-strength reinforced concrete beam could reach 81.14% of shear capacity of plain beam without material substitutions, but compressive strength could significantly be increased by 130.54% and flexural tensile strength of 122.67% compared to plain high-strength concrete.

Abstract: Given the increasing amount of waste in the world, it is essential not only to reduce waste generation but also to explore potential uses for the waste produced. This includes waste generated in the production of building materials. The construction industry is a significant contributor to global waste and carbon dioxide emissions, making it crucial to address these issues for sustainable development. During the production of CETRIS boards, approximately 7 600 tons of waste are generated annually. One of the waste materials obtained during the board processing is a fine powder. This waste material can potentially be reused in two ways: it can be incorporated back into the process of producing CETRIS boards or utilized in the production of building materials. This research project focuses on examining the possibility of using this waste material as a substitute for fine aggregate in fine-grained concrete. To investigate its viability, the waste material underwent testing for dry density and absorbency. Subsequently, a reference mixture and concretes with different replacement rates (50%, and 100%) of natural fine aggregate were produced to create self-healing concrete mixtures. The study examined the density, and compressive strength of these concrete samples 28 days after concreting. The findings indicated that as the amount of waste material in the concrete increased, the measured properties decreased. However, despite the decrease, the compressive strengths of the concrete remained very high, leading to the classification as high-strength concrete. Further exploration and optimization of the replacement rates could lead to the development of environmentally friendly and sustainable building materials.

Abstract: The present study investigates the effect of incorporating metakaolin and silica fumes in the production of high-strength concrete along with partial replacement of coarse granite aggregates in the high-strength concrete. The higher compressive strength, refined microstructure, and decreased permeability of high-strength concrete are some of the properties responsible for its trending use in the modern construction industry. The main purpose of this research is to evaluate the effect of the replacement of coarse granite aggregates with natural aggregates on the mechanical and durability properties of high-strength concrete. For understanding the effect of metakaolin, silica fume, and granite aggregates on the properties of high-strength concrete, various specimens such as cubes, cylinders, and cylindrical discs were cast and tested after 7, 14, and 28 days of curing. Various concrete mixes were prepared by adding silica fume at 5%, 7.5%, and 10% and metakaolin at 5%, 7.5%, 10%, 12.5%, and 15% in concrete production. Furthermore, High-strength concrete mixes were also prepared by replacing natural coarse aggregates with granite coarse aggregates by 25%, 50%, 75%, and 100% to study the effect of replacement percentage on the concrete properties. Test results indicated that the compressive strength and split tensile strength of the concrete mix increased with the increase in the replacement percentage of granite aggregates, with the highest strength seen at complete replacement with granite aggregate due to the enhanced compressive strength of such aggregates in comparison with the natural coarse aggregates. In various mixes cast using metakaolin and silica fume, the highest compressive strength was seen in a mix containing 10% metakaolin and 7.5% silica fume, and results of other mixes indicated that the use of silica fume and metakaolin are viable options for high-strength concrete production in our experimental study.

Abstract: This paper presents the study results of the nonlinear stress-strain diagrams of concrete based on the local materials of Central Yakutia. The results of comparing the obtained data with the requirements of normative documents of the Russian Federation, European countries, India and China are presented. The calculation results for bending bearing elements with concrete nonlinear deformation taken into account obtained using the Ansys software are given. The reliability of the calculated data was verified using the proposed diagrams, using the example of the results of a survey of characteristic failures of bending concrete and reinforced concrete elements in the Republic of Sakha (Yakutia).

Abstract: Nowadays the great attention of scientists and engineers is attracted by applying 3D-additive technologies for obtaining high-strength fine-grain concrete by using technogenic raw materials. It is distinguished from the conventional concrete by the increased content of cement stone, lower grain size, multicomponent composition and the increased specific surface of the aggregate [1-3]. The performance characteristics of such concrete mostly depend on its aggregate’s properties and water content.The paper considers the problem of improving fine-grain concretes production technologies. For this purpose the opportunities of 3D-additive technologies, which improve the efficiency of fine-grain concretes production technology due to using concrete compositions with natural and technogenic raw materials of various chemical and mineral formulas, were studied. The opportunity of increasing the economic feasibility of high-strength fine-grain concretes, produced by means of 3D-additive technology, with preserving their performance characteristics, has been demonstrated

Abstract: The mechanical properties of a cementitious composite are strongly affected by interfacial transition zone (ITZ) between the matrix and the aggregates, mainly by its strength and thickness. A micromechanical model based on Mori-Tanaka scheme coupled with an estimation of deviatoric stress in ITZ was developed for evaluation of the effect of selected secondary cementitious materials (SCMs – silica fume, fly ash and metakaolin) on the properties of ITZ in high-strength concrete (HSC). The model was validated by means of comparison of predicted ITZ thickness with direct ITZ thickness measurements performed by a combination of scanning electron microscopy and grid nanoindentation. Very good agreement between the theoretical and experimental results was reached, therefore the developed micromechanical model can be used for further research and optimization of HSC containing SCMs. Silica fume was determined to be the most efficient supplementary cementitious material from the point of view of ITZ thickness reduction.

Abstract: An experimental investigation on square and circular high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets was conducted in this study. Fiber Bragg grating sensors have been applied successfully in monitoring of the strains of the AFRP-confined square and circular concrete columns. The experimental results demonstrate that two types of axial force-strain curves were observed depending on the form of the column. Results show fiber Bragg grating sensors have good repeatability and the ultimate load of the circular concrete column is larger than that of the square concrete column. The interlaminar strains of AFRP and high-strength concrete have also been attained. It helps to analyze the constraint effect of the concrete column and compute the ultimate load of the square and circular concrete column.

Abstract: Prestressed concrete pipe pile with high bearing capacity, the advantages of convenient construction, low cost and widely used in practical engineering, because of the prestressed high strength concrete in use process is in complex stress state, both are under a lot of vertical load, and horizontal seismic action needs to be considered at the same time, it is necessary under the condition of considering the vertical load bearing capacity of prestressed high strength concrete level and considering the loading level, the horizontal bearing capacity. Scholars at home and abroad based on the simple hypothesis, puts forward the calculation method of a lot of interaction with soil, in the future will be adopted in calculation, using ABAQUS finite element analysis, this paper established the three-dimensional finite element model of prestressed concrete pipe pile, respectively under different vertical pressure (P = 4000 kn, P = 4800 kn, P = 6000 kn) one-way load and calculated the horizontal bearing capacity, and under repeated load, respectively to study the size of the different vertical pressure and different reinforcement stirrup ratio on its bearing capacity and seismic performance. The results show that the stiffness of pipe pile decreases significantly with the increase of vertical pressure under different vertical loads. With the increase of vertical load, the ductility and energy dissipation capacity of the components decrease gradually. The horizontal bearing capacity of prestressed high strength concrete pipe decreases with the increase of vertical pressure. However, its amplitude decreases with the increase of vertical pressure value.

Abstract: Conditional quantitative criteria characterizing the shrinkage crack resistance of various concretes and a model describing the change in the proposed criteria depending on the magnitude of shrinkage deformation, creep coefficient, tensile strength kinetics and shrinkage strain kinetics for ordinary concrete and self-compacting concrete are proposed. The proposed criteria for the class C40/50 concrete have been calculated and it was shown that self-compacting concrete can potentially have higher crack resistance during shrinkage. To ensure high cracking resistance during shrinkage when choosing superplasticizers and mineral additives, attention should be paid to their effect on shrinkage, creep and E-modulus of the cement stone. It should exclude additives that increase the shrinkage and E-modulus and reduce creep of cement stone.