Strength Of Concrete Increases Research Articles

Seismic Behaviors of Concrete Beams Reinforced with Steel-FRP Composite Bars under Quasi-Static Loading

Steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a new composite material with good corrosion resistance and designable post-yield stiffness. Substitution of steel bar with SFCB can greatly increase the durability and ultimate capacity associated with seismic performance. First, the method and main results of the experiment are briefly introduced, then a simplified constitutive model of composite bar material was applied to simulate the seismic behaviors of the concrete beams reinforced with SFCBs by fiber element modeling. The simulation results were found to be in good agreement with test results, indicating that the finite element model is reasonable and accurate in simulating the seismic behaviors of beams reinforced with SFCB. Based on the numerical simulation method, a parametric study was then conducted. The main variable parameters were the FRP type in composite bars (i.e., basalt, carbon FRP and E-glass FRP), the concrete strength, basalt FRP (BFRP) content in SFCBs and shear span ratio. Seismic behaviors such as load-displacement pushover curves, seismic ultimate capacity and its corresponding drift ratio of the SFCBs reinforced concrete beams were also evaluated. The results showed that (1) the fiber type of the composite bar had a great impact on the mechanical properties of the beam, among which the beam reinforced with BFRP composite bar has higher seismic ultimate capacity and better ductility. With the increase of the fiber bundle in the composite bar, the post-yield stiffness and ultimate capacity of the component increase and the ductility is better; (2) at the pre-yield stage, concrete strength has little influence on the seismic performance of concrete beams while after yielding, the seismic ultimate capacity and post-yielding stiffness of specimens increased slowly with the increase in concrete strength, however, the ductility was reduced accordingly; (3) as the shear span ratio of beams increased from 3.5 to 5.5, the seismic ultimate capacity decreased gradually while the ultimate drift ratio increased by more than 50%. Through judicious setting of the fiber content and shear span ratio of the composite bar reinforced concrete beam, concrete beams reinforced with composite bars can have good ductility while maintaining high seismic ultimate capacity.

Parametric Study of EWECS (Engineering Wood Encased Concrete-Steel) Columns Using 3D FE Modelling

This paper presents an analytical study on the behavior of composite column that consist of an exterior wood panel with concrete encased steel (CES) core, hereafter referred to as Engineering Wood Encased Concrete-Steel (EWECS) columns. A detailed three-dimensional (3D) nonlinear finite element model is developed to study the response and predict the seismic performance of EWECS columns subjected to both axial and cyclic loads by using finite element program, ANSYS APDL v.14. A reference model is validated with previous test results and is used as a reference for the parametric study. The parameters considered in the parametric study are the thickness of the wood panel and the compressive strength of concrete. The analytical results obtained from the finite element analysis can accurately simulate the behavior of the EWECS column on the experimental study. The results show that the EWECS column has excellent seismic performance. Moreover, the results of the parametric study show that the thickness of wood panel has the greatest influence on the seismic behavior of the EWECS columns, with the increment of flexural capacity of 15% by addition of 10 mm thickness of the wood panel. Meanwhile, the increase of concrete strength has not much influence on the flexural capacity of the EWECS columns, in which the flexural capacity of the EWECS column only increases around 3% with the increase of concrete strength from 35 to 60 MPa.

Predictive model for compressive strength of concrete made from recycled concrete coarse aggregates

The objective of the study is to replace coarse natural aggregate with recycled concrete coarse aggregate (RCCA) for concrete production in order to determine the compressive strength of such concrete for different percentages of partial replacement using different water/cement ratios. Thereafter develop a predictive model for the compressive strength using different percentages of partial replacement and water/cement ratios. The polynomial regression model was applied to examine the correlation between the compressive strength of concrete, water cement ratio and %RCCA. The following regression models were established for 28 days at 0.4, 0.45 and 0.50 water cement ratio,f 28,0.4 = -0.000(%RCCA)²- 0.192(%RCCA) + 49.79 with R² = 1,f 28.0.45 = 0.000(%RCA )² - 0.371(%RCCA) + 44.29 with R² = 1, and f 28,0.50 = -0.001(%RCCA)² - 0.386(%RCA) + 41.91 with R² = 1. At 28days test for water cement ratios of 0.55, 0.6 and 0.65 as f 28,0.55 = -0.0001(%RCCA)² - 0.158(%RCCA ) + 38.26 with coefficient of determination of R² = 1, f 28,0.60 = 0.010(%RCCA )² - 0.1954 (%RCCA) + 28.29 with R² = 1, while for W/C ratio of 0.65 is given as f 28,0.65 = -0.001(%RCCA )² + 0.222(%RCCA) + 18.37 with coefficient of determination, R² = 1. It was concluded that the increase or decrease in compressive strength of concrete was dependent on percentage replacement ratio of natural aggregate to recycled concrete aggregate (%RCCA) and the amount of water to cement ratio (w/c) ratio of the mix. The significance of the study is that the compressive strength of concrete made with RCCA which is a waste product can be predicted by using the predictive model developed. Keywords : Concrete, Compressive strength, natural aggregate, Predictive model,Recycled concrete aggregate, Water/ cement ratio.

The Effect of Pre-Damaged Level on Repair Damaged Columns by Using Steel Straps Tensioning Technique

To date, repair of damaged columns has become increasingly more significant. The failure of columns structure contributes to the serious consequences in structural stability. Most of the existing repairing techniques are based on lateral passive confining pressure. However, this passive-type of confinement is ineffective in restoring the performance of damaged concrete columns. In this regards, active confinement was selected in this study to repair damaged concrete columns which can actively confine concrete in this study. Steel strapping tensioning technique (SSTT) allows pre-tensioning low-cost recycled steel straps around the damaged column was chosen herein to represent active confinement. A total of 12 columns were prepared and loaded axially to certain degree of their respective ultimate strength. Hence, a pre-damage level of the columns was developed. Then, the damaged columns repaired by using mortar and confined with SSTT. Finally, the repaired columns were then tested under monotonic uniaxial load. The structural performances of the confined repaired columns were compared with those of the repaired columns without confinement. It is expected that as the concrete compressive strength increases, the effectiveness in restoring the load carrying capacity of the damaged column becomes more significant.

LOAD-MOMENT INTERACTION DIAGRAMS OF SLENDER PARTIALLY ENCASED COMPOSITE COLUMNS

Partially Encased Composite (PEC) Columns consist of thin-walled built-up H-shaped steel sections with links welded near the flange tips and concrete cast between the flanges. To predict the strength and ductility of slender PEC columns, Newmark’s numerical iterative procedure is implemented. Overall column slenderness ratio, flange plate slenderness ratio and concrete strength are the selected parameters to observe the variation of strength and ductility of slender PEC column. Bending of column about both the strong and weak axis is considered to observe the significance of the selected parameters. In strong axis bending, a decrease in strength is found with the increase of overall slenderness ratio and flange plate slenderness ratio. Again, failure envelope of column strength curve becomes smaller with the increase of overall slenderness ratio. It implies the ductility of slender PEC column decreases with the increase of the overall slenderness ratio. Moreover, similar behaviour is observed with the increase of flange plate slenderness ratio. As the strength of concrete increases, strength of slender PEC column is observed to increase by significant amount. Similar behaviour is observed in weak axis bending along with some drop in strength

APLIKASI MODIFIED PROCTOR PADA ROLLER COMPACTED NO-FINES CONCRETE DENGAN AGREGAT 5-10 mm

The usage of no-fines concrete as pavement currently was being utilized. It was constituted by diversity effort of concrete cement pavement construction material, besides no-fines concrete pavement having benefit that reduce water pond on pavement surface rapidly because of its pervious. Permeability character of no-fines concrete will recharge groundwater deposit therefore more environmental friendly. Problem faced is low strength of no-fines concrete as compared to conventional concrete. Therefore it is required the effort of increasing the strength of no-fines concrete by increase concrete density that is done by roller machine. No-fines concrete that is compacted by roller machine is called Roller Compacted No-fines Concrete (RCNC). 
 This research analyzed the increase of concrete properties especially compression strength and split tensile strength effected by external compaction using modified proctor in creating the laboratory specimen. Materials of no-fines concrete utilized Clereng coarse aggregate with size 5-10 mm, Gresik Portland cement and the aggregate cement ratio is 4 and 6. To accelerating the hardening concrete utilized admixture type C which is sikaset accelerator with 20% of total water volume. The blow variation of modified Proctor per layer is 28, 42 and 56. Compression test and split tensile test been done at the age of 1 and 28 days. 
 Result of research showed the increase of concrete specific gravity and compression strength in line with the increase of blow variation. RCNC specific gravity acquired ranging between 1,544 and 1,788. Compression strength at the age of 28 days acquired were (1) aggregate cement ratio 4 with 28, 42, 56 blows per layer were 21,47 MPa, 22,92 MPa, 26,55 MPa (2) aggregate cement ratio 6 each were 8,48 MPa, 10,51 MPa, 14,82 MPa. Split tensile strength at the age of 28 days were (1) aggregate cement ratio 4 with 28, 42, 56 blows per layer each were 2,27 MPa, 2,92 MPa, 3,13 MPa (2) aggregate cement ratio 6 each were 1,63 MPa, 1,83 MPa, 2,08 MPa.

Influence of activation of fly ash on the mechanical properties of concrete

The use of high volume fly ash as a partial replacement of cement in concrete reduces environmental pollution and conserves natural resources. This study presents the results of an experimental investigation to find out the effect of chemical activation of class F fly ash to overcome the low early strength problem. The replacement ratio of Portland cement with fly ash was 40%. Four different chemical activators were used in the study; 2.5% Na2SO4, 2.5% NaOH, 3.0% (Na2SiO3 and CaO) by ratio (1:8) and 4% Aquis Na2SiO3. Concrete strength was investigated at room temperature and after exposure to elevated temperature. Glass fibers were added by ratio 0.7% to improve concrete ductility. Test results indicated that aquis Na2SiO3 activator is the superior activator for fly ash in view of enhancing concrete compressive, splitting tensile and flexural strengths at early ages. Besides, a significant increase in concrete strength was obtained at elevated temperatures. Adding glass fibers in the ratio of 0.7% by weight of cementitious material with activated FA by using aquis Na2SiO3 greatly enhances the splitting tensile and flexural strengths at normal and elevated temperature.

Influence of synthetic calcium silicates on the strength properties of fine-grained concrete

The effect of additives based on acicular calcium hydrosilicates (xonotlite and tobermorite) and wollastonite, obtained from boric acid production waste in autoclave synthesis at a temperature of 220 °C, on the strength of fine-grained concrete, has been studied in this paper. It was shown that when the calcium hydrosilicates and wollastonite are introduced, an increase in the strength characteristics of concrete is observed. After heat and moisture treatment, the maximum increase in strength is observed with the addition of 4% of mass content of calcium hydrosilicates and 6% of mass content of wollastonite. After 28 days of hardening under normal conditions, the maximum increase in strength of concrete is observed with the addition of 4% of mass content of both types of additives. It was shown that the water absorption of concrete decreases with a maximum when 4% of mass content is added, as in the case of the introduction of calcium hydrosilicates, and wollastonite. With a further increase in the number of additives, the amount of water absorption increases, but these values remain below the values for the control sample without additives.

Performance assessment and design of ultra-high performance concrete (UHPC) structures incorporating life-cycle cost and environmental impacts

Ultra-high performance concrete (UHPC) as a novel concrete material is associated with very high strength and low permeability to aggressive environment. There have been many studies focusing on the development of UHPC materials. More studies are needed to implement the knowledge obtained from material level into the structural design and construction level. This paper emphasizes on the structural modeling and performance assessment of bridge girders made of UHPC considering the major improvements in terms of structural performance, durability, environmental impacts, and cost-effectiveness in a long-time interval. Additionally, the effect of the concrete strength increase on the life-cycle environmental impact and cost is assessed on a structural scale. An illustrative example is established to demonstrate the use of UHPC within precast-prestressed girder bridge. It is found that the use of UHPC can result in a significant reduction of concrete volume and CO2 emissions compared with conventional bridge with the same span length. Additionally, the life-cycle cost and equivalent annual cost associated with these two bridges are compared. This study aims to aid the development and adaptation of novel materials within civil engineering to make optimal use of the favorable material properties.

Hydration, mechanical properties and durability of high-strength concrete under different curing conditions

The properties of high-strength concrete under standard curing condition (20 °C, 95% RH), high-temperature curing condition (50 °C) and temperature match curing condition were comparatively investigated. The cumulative hydration heat of composite binder containing fly ash and silica fume is lower than that of composite binder containing the same amount of slag. Addition of fly ash and silica fume clearly reduces the adiabatic temperature rise of concrete, but adding slag leads to higher adiabatic temperature rise than Portland cement concrete. High-temperature curing condition and temperature match curing condition lead to the sustainable increase in compressive strength of concrete containing mineral admixture, but they hinder the later-age strength development of Portland cement concrete. For cement–slag paste and cement–fly ash–silica fume paste, the non-evaporable water contents increase significantly and the pore structures are much finer under high-temperature curing condition and temperature match curing condition, which negatively affect the pore structure of Portland cement paste. The differences in properties of concrete among three curing conditions become smaller with time. The properties obtained under standard curing condition can approximately reflect the long-term properties of high-strength concrete in the real structure. The concrete prepared with cement–fly ash–silica fume composite binder has the highest compressive strength, finest pore structure and best resistance to chloride permeability under any curing condition. This composite binder is very suitable to prepare the high-strength concrete with large volume.

Experimental investigation on the durability performances of concrete using cathode ray tube glass as fine aggregate under chloride ion penetration or sulfate attack

Cathode ray tube (CRT) funnel glass has been used to partially or totally replace natural sand as fine aggregate in concrete. It is an effective and environmentally friendly method of recycling the increasing number of discarded CRT in the electronic industry. However, little research has been performed on its durability performance under environmental attacks, in particular in the areas of chloride ion penetration and sulfate attack, the two major environmental attacks on reinforced concrete structures. This study presents an experimental investigation on the durability performances of concrete using CRT funnel glass as fine aggregate in 8% sodium chloride solution, 5% sodium sulfate solution and 10% sodium sulfate solution. Four volume replacement ratios (the ratio of CRT glass to natural sand), i.e. 0%, 30%, 60%, 100%, are considered. The chloride ion content along concrete depth direction, compressive strength and elastic modulus of concrete was measured with attack time. The test results show that although the compressive strength and elastic modulus decrease with increasing content of CRT funnel glass in concrete, the long-term resistance to chloride ion penetration is enhanced by using CRT funnel glass as fine aggregate. Furthermore, the compressive strength, rather than dynamic elastic modulus of concrete containing CRT glass, is more sensitive to sulfate attack. The relative increase in strength of CRT glass concrete is obviously larger than that of control concrete under sulfate attack. This study also provides a reference for the durability design of concrete structures using CRT funnel glass as fine aggregate.

Mechanical Properties and Service Life Prediction of Modified Concrete Attacked by Sulfate Corrosion

Under the condition of drying and wetting circulation, ordinary concrete, modified concrete containing fly ash, and double-admixture concrete containing fly ash and polypropylene fiber were corroded in the solution of Na2SO4 and (NH4)2SO4. The sulfate concentration of the solution was designed to be 1000 g/L. The compressive strength and splitting tensile strength of the concrete were tested after different number of drying and wetting cycles (0, 2, 4, 6, 8, and 10). The results indicate that the strength of concrete increases in the early stages of corrosion and decreases gradually later. The admixture significantly improves the resistance to sulfate erosion of the modified concrete, while polypropylene fiber plays a less important role on anticorrosion properties. When suffered 10 times of drying and wetting cycle, the compressive strength and splitting tensile strength of modified concrete increase by 28% and 19%, respectively. Based on the test results, the service life of the modified concrete corroded by sulfate was predicted.

Seismic behavior of SFRC shear wall with CFST columns

The use of reinforced concrete (RC) shear wall with concrete filled steel tube (CFST) columns and steel fiber reinforced concrete (SFRC) shear wall has aroused widespread attention in recent years. A new shear wall, named SFRC shear wall with CFST columns, is proposed in this paper, which makes use of CFST column and SFRC shear wall. Six SFRC shear wall with CFST columns specimens were tested under cyclic loading. The effects of test parameters including steel fiber volume fraction and concrete strength on the failure mode, strength, ductility, rigidity and dissipated energy of shear wall specimens were investigated. The results showed that all tested shear wall specimens exhibited a distinct shear failure mode. Steel fibers could effectively control the crack width and improve the distribution of cracks. The load carrying and energy dissipation capacities of specimens increased with the increase of steel fiber volume fraction and concrete strength, whilst the ductility of specimens increased with the increase of steel fiber volume fraction and the decrease of concrete strength.

Compressive strength improvement for recycled concrete aggregate

Increasing amount of construction waste and, concrete remnants, in particular pose a serious problem. Concrete waste exist in large amounts, do not decay and need long time for disintegration. Therefore, in this work old demolished concrete is crashed and recycled to produce recycled concrete aggregate which can be reused in new concrete production. The effect of using recycled aggregate on concrete compressive strength has been experimentally investigated; silica fume admixture also is used to improve recycled concrete aggregate compressive strength. The main parameters in this study are recycled aggregate and silica fume admixture. The percent of recycled aggregate ranged from (0-100) %. While the silica fume ranged from (0-10) %. The experimental results show that the average concrete compressive strength decreases from 30.85 MPa to 17.58 MPa when the recycled aggregate percentage increased from 0% to 100%. While, when silica fume is used the concrete compressive strength increase again to 29.2 MPa for samples with 100% of recycled aggregate.

Study of Confinement Index of High-Strength Concrete Columns Reinforced with High-Strength Steel Bars

Nowadays, the need of mega structures such high-rise buildings and long-span bridges due to the rapid growth of population is becoming increasingly urgent. The bigger the structures the higher the load should be carried by their structural members. To resist higher load, it normally requires larger size members. In reinforced concrete members, the capacity enhancement can be attained by either increasing the element size, the grade of materials used (concrete and steel bars), or the number or size of the steel bars used. However, higher-strength materials such as concrete and steel typically have more brittle properties. To improve the ductility of the concrete, it can be achieved by providing confining steel through transverse reinforcement. For higher-strength steel bars, a chemical based research has been conducted in recent years to come up with the high strength yet ductile steel material. This paper focuses on the analysis of various strengths of concrete columns 30 MPa and to 60 MPa reinforced and confined with high-strength reinforcing steel bars 550 MPa (Grade 80) with variety cross section of columns. From the study, it can be concluded that the confinement index decreases significantly with the increase of concrete strength. The use of higher-strength transverse steel increases the confinement index. The greater strengths of concrete used, the confinement ratio will be smaller at the same spacing.

Shear behavior of large-diameter concrete filled tube (CFT)

Circular concrete filled tube (CFT) is composite structure to fill concrete in steel tube as formwork. By combining advantage of steel tube and concrete, CFT has more superior deformation capacity and strength than reinforced concrete and steel structure, since bond stress between steel tube and concrete has influence on prevention of local buckling and increase in strength of concrete. For such a reason, CFT has been applied to as columns in buildings, and pile and drilled shaft foundations. CFT drilled shaft is designed to large diameter due to large local shear strength by seismic load, liquefaction and lateral spreading of soil layer. However, it brings uneconomical design by the conservative shear equation of current design provision. Until today, shear studies of circular CFT to improve shear equation have been rarely conducted and they are limited to small scale test. In this research, the numerical and experimental results are compared to current shear design equations, with the ultimate goal to serve as an initial analytical study that aids in planning further experimental and analytical research on shear resistance and behavior of circular CFT, which leads to improved shear design equations.

Flexural behavior of ECC-concrete composite beams reinforced with steel bars

This paper presents analytical technique and simplified formulas for the calculations of cracking, yield and ultimate moments of different cases as well as deflections of ECC-concrete composite beams reinforced with steel bars. The technique is based on the simplified constitutive models of materials, strain compatibility, perforce bond of materials and equilibrium of internal forces and moment. Experimental testing of eleven ECC-concrete composite beams reinforced with steel bars is also presented. All beams tested had the same geometrical dimensions but different steel reinforcement strength and ECC thickness. The proposed formulas showed good agreement with the experimental results of various moment values and deflections. A parametric analysis shows that yield and ultimate moments increase with the increase of concrete strength in case of compression failure but, essentially, remain unchanged in case of tensile failure. With increasing the tensile resistance, for example by increasing ECC height replacement ratio, reinforcement ratio, strength of steel reinforcement and ECC, ultimate curvature and energy dissipation increase in case of tensile failure and decrease in case of compressive failure. On the other hand, ductility and energy dissipation ratio decrease with the increase of reinforcement ratio and strength, but, essentially, remain unchanged with increasing the height replacement ratio and strength of ECC.

Structuring in Cement Systems with Introduction of Graphene Nano-Additives

At present, one of the most promising areas in the field of concrete research is the study of the effect of nano-additives for the production of highly effective concretes. Many authors have already obtained primary results which testify to the very effective role of nanoadditives based on carbon in modifying concrete. In this paper, the influence of a nano-additive of graphene on the phase composition and microstructure of the cement stone was studied. It has been found that, when a nano-additive of graphene is introduced, low-basic calcium hydrosilicates are mainly formed. This leads to an increase in the compressive strength of concrete. The results of the study of the microstructure of cement stone with nano-additive graphene showed that the high compressive strength of concrete modified with nano-additive graphene is explained by the cement stone dense structure. Thus, it was found that the nanoadditive of graphene contributes to the formation of a dense structure of cement stone, composed mainly of low-basic calcium hydrosilicates, and due to this, the physical and mechanical characteristics of concrete and its resistance to frost and other forms of aggression.

Effect of the iron-containing filler on the strength of concrete

The purpose of present research is to determine the impact of a mixture of river and technogenic sand containing iron compounds in the presence of plasticizers on the strength of fine-grained concretes. As a result of the performed research it was established that the technogenic sand, representing mineral complexes containing iron compounds, interacts with Portland cement minerals and the products of their hydration. The studies we conducted showed the possibility of targeted regulation of the processes of formation of structure of fine-grained concretes by joint application of mineral complex with iron ions, river sand and surface-active substances that are substantially different in the structure of molecules. It was established that using a mixture of river and technogenic sand containing iron compounds in the form of a fine aggregate leads to a significant increase in concrete strength. There is a certain ratio between river sand and the technogenic sand containing iron compounds, which provides concrete with the largest strength. An optimal content of the technogenic sand in a fine aggregate depends on the type and amount of minerals within its structure, and the content of particles with different size. It is demonstrated that the effectiveness of using modern superplasticizers in fine-grained concretes increases considerably with the introduction of mineral complexes containing ions of iron to the compositions of concrete.

Numerical Modeling of the Behavior of the Steel-Concrete Interface Contribution by Extended Finite Element Method (X/FEM)

In the reinforced concrete study, the concrete steel connection is a key element» in the behavior of this composite because it will allow the transfer of forces between steel and concrete. The understanding of this phenomenon and its inclusion in the numerical analysis of reinforced concrete structures are the main objects of this research work; the approach suggested for modeling this problem is the extended finite element method (X FEM) that allows the introduction of the interface independently by the mesh. Steel and concrete bond has been studied through a pull-out test as recommended by RILEM. This work provides some ideas about the adhesion’s behavior, thus an experimental campaign was carreid out, measuring the concrete’s andsteel’s constraints and sliding over concrete. The bond stress –slip curve shows a similar behavior between experimental and theoretical results. The obtained results show the improvement of the adhesion constraint according to the increase of concrete compressive strength. Indeed, the transmission of forces between reinforcement and concrete enclosing it gives rise to a relatively complex state of stress. This paper presents a stabilized formulation for 3D contact problems, in the framework of X-FEM. It is shown that the choice of a simple algorithm and the type of mesh (concrete - steel bond) is a good solution for the determination of the adhesion behavior.