Normal High Strength Concrete Research Articles

Mechanical analysis and finite element modeling of FRP-ECC-HSC composite stub column under axial compression

A novel composite column, consisting of an outer fiber-reinforced polymer (FRP) tube, an inner high strength concrete (HSC) core and an engineered cementitious composite (ECC) ring, has been proposed and investigated. Compared with normal FRP-confined HSC column, the FRP-ECC-HSC composite column could exhibit superior deformability performance. In this study, mechanical analysis was firstly conducted on the composite column to investigate the interaction behavior among different components, i.e. HSC core, ECC ring and FRP tube. Modified analysis-oriented models were proposed for HSC and ECC under uniform FRP confinement. Furthermore, finite element (FE) models were also established with the use of accurate concrete damaged plasticity (CDP) model to simulate the behavior of the composite column, especially the ECC ring which is under non-uniform confinement. The material property data used in the FE models were generated by the modified analysis-oriented models. It is shown that the FE models can provide close predictions on the axial load-axial strain behavior and hoop strain-axial strain behavior compared with test results. Meanwhile, stress distribution over the composite column section as well as the influence of ECC ratio were discussed with the validated FE model.

Response of hybrid concrete incorporating eco-friendly waste PET fiber: Experimental and analytical investigations

• Eco-friendly high strength concrete containing waste PET fiber was used as a repair material for deteriorated normal concrete. • Structural and material performance of hybrid RC beams, made with normal concrete and PET fiber HSC, were examined. • Interfacial surface roughened by sand blast technique provided proper bonding between normal concrete and PET fiber HSC. • Analytical solution for the behavior of RC hybrid beams, with PET fiber, was developed considering aspect ratio and content of fiber used. High Strength Concrete (HSC) has the ability to strengthen deteriorated concrete members. The performance of HSC incorporating waste polyethylene terephthalate (PET) fibers as a repair material for concrete structures has not been examined extensively in current literature. Thus, more investigations are considered essential in this direction. This endeavor is devoted to examining the flexural behavior of hybrid reinforced concrete beams (HRCB) made with normal concrete (NC) repaired by or bonded to HSC containing waste PET fibers (FRC). The workability and mechanical properties of fresh and hardened FRC were investigated. Moreover, the efficiency of HSC overlay as a repair material for NC substrate was evaluated through a slant shear test (SST) which considered four modes of roughening of the NC interfacial surface. A third-point load test was used to evaluate the structural behavior of the HRCB. The results of the slant shear and flexural tests indicated that the highest bond strength among all of the members was achieved by employing sandblasted and grooved interfacial surfaces between NC and HSC. The flexural capacity for the beams was also predicted via modification of the ACI 318–19 and Jarquio’s models, using regression analysis of present experimental records. Good matching was observed between the predicted and experimental ultimate load of the hybrid beams. Finally, the testing observations are noteworthy in the direction of using FRC as a repair material.

Experimental investigation on axial compressive behavior of novel FRP-ECC-HSC composite short column

A novel composite column, consisting of an outer fiber reinforced polymer (FRP) tube, an engineered cementitious composite (ECC) ring and an inner high strength concrete (HSC) core, has been proposed and experimentally investigated in this study. Due to the high brittleness of HSC, localized cracks may occur and lead to premature failure for conventional FRP-confined HSC columns. With the excellent tensile and cracking behavior, ECC ring is used to redistribute the hoop stress and strain from HSC core to FRP tube in the proposed novel FRP-ECC-HSC composite column. A total of 12 stub columns with different HSC core strengths and ECC ring thicknesses were tested under axial compression. It is found that FRP-ECC-HSC composite columns can develop larger FRP confining efficiency with more uniform hoop strain distribution in comparison to the corresponding normal FRP-confined HSC columns. The ultimate axial strain is obviously enhanced as well for this composite column, leading to an improved ductile compressive behavior. Based on the test results obtained from this study, design equations are proposed to predict the ultimate loading capacity and ultimate axial strain for the FRP-ECC-HSC composite column.

Behavior of GFRP-concrete double tube composite columns

A novel glass fiber-reinforced polymer (GFRP) — concrete double tube composite column, which consists of an outer filament winding GFRP tube, an inner pultruded GFRP tube and infilled core concrete and ring concrete, is proposed in this study. A total of 20 specimens were tested to investigate the structural behavior of the composite column. High strength concrete (HSC) was used as the core concrete filled in the inner pultruded GFRP tube, while engineered cementitious composite (ECC) or normal concrete (NC) with medium compressive strength was used as the ring concrete. Different outer and inner GFRP tube thicknesses were considered. Test results reveal that overall performance of the GFRP-concrete double tube composite columns, especially the deformability, is effectively enhanced in comparison to the corresponding normal GFRP-confined HSC columns. Axial load–strain responses and dilation behavior of the composite column were carefully analyzed. Based on the test results, equations are developed to predict the ultimate load carrying capacity and ultimate axial strain for the proposed GFRP-concrete double tube composite column.

Kajian Parametrik Balok Beton Memadat Mandiri Menggunakan Analisis Nonlinier Elemen Hingga

Self-compacting concrete has self-flowing, viscous and compact properties that minimize mechanical compaction. This concrete is suitable for solving the concrete pouring in the narrow and congested reinforcement. Beams made of both self-compacting concrete and normal high-strength concrete are analyzed by MSC Marc / Mentat software. Steel is modeled by being embedded in concrete. The failure criterion of Linear Mohr-Coulomb is used for concrete and Von Mises for reinforcing steel, respectively. Concrete and the plate support are modelled by 3D solid elements. For the steel, the truss element is used. The contact analysis is implemented between beam and both steel plate and steel supports. The load-deflection curve for both concrete are almost the same as the results of the experimental curve. The results of the contact analysis also showed that there were contact and separation in the contact area. The shear retention factor value close to one meaning will restrain greater loads. The results of the study on the reinforcement ratio also showed a reduction of 70% and an increase of 70% when using minimum and maximum reinforcement, respectively. The larger concrete cover also reduces the load that the beams can restrain.

Effect of Elevated Temperatures on Microstructure of High Strength Concrete Based-Metakaolin

The present experimental study evaluates the residual mechanical properties and the microstructure evolution of high-strength concrete (HSC) after the exposure to elevated temperatures. Metakaolin (MK) is used as supplementary material that is expectable to produce fire-resistant HSC and environmentally friendly. Three major groups of testing have been carried out herein. First, testing six mixes of hardened cement paste (HCP) using different ratios of MK replacements. Second, evaluating the optimum MK dosages at both ambient and after elevated temperatures in three concrete mixes. Finally, an attempt to define the correlation between the residual properties of HCP and HSC after elevated temperatures carried out as well. Results indicated that the influence of aggregate on concrete in the presence of MK is relatively less significant after elevated temperatures exposure. Inclusion of MK has shown beneficial changes on the interfacial transition zone (ITZ) of aggregate with HCP, in which ITZ between aggregate and mortar are clearly merged in the bond region, and the joints observed in the normal HSC are eliminated in the presence of MK. In addition, thermogravimetric and microscopy investigations demonstrated the high pozzolanic activity and microstructure development of HCP and of concrete. Finally, general equations are proposed for the residual compressive strength and flexural strength correlation of HSC after elevated temperature.

Performance comparison of beam-column joints with different concretes

With the development of concrete materials, high strength concrete (HSC) and fiber reinforced concrete (FRC) are more and more used in reinforced concrete frame structures. This paper collected the test results of normal concrete (NC), HSC and reactive power concrete (RPC) beam joints. The performances of different concrete joints were compared and analyzed from two aspects of failure process and characteristics and shear deformation. The results showed that the ratio of through-crack load to shear capacity of NC joints is about 0.75-0.80, while that of RPC joints through-crack is close to shear capacity. The randomly distributed steel fibers of RPC like dispersed steel bars can effectively restrain the development of oblique cracks in the core area of joints. When the ultimate load is reached, the average shear angle of NC joints is much larger than that of RPC and steel fiber reinforced concrete joints. The small deformation of joints ensures the stiffness of RPC and steel fiber reinforced concrete joints. However, because there is no coarse aggregate in RPC, the occlusal interaction between the two sides of oblique cracks in the core area of RPC beam-column joints is obviously lower than that of NC joints.

Interfacial bond-slip behaviour between reinforced high-strength concrete and built-in steel plate with studs

Steel-plate-reinforced concrete composite shear walls have been widely used in high-rise and super-high-rise buildings. To improve the bond behaviour between the steel plate and high-strength concrete (HSC) in shear walls, 13 steel-plate HSC shear wall (SPHSCSW) specimens with group studs were designed for push-out tests. Specimens were constructed using HSC or high-strength recycled aggregate concrete (HSRAC). Concrete strength, concrete type, stud length-to-diameter ratio, and replacement of studs with tie bar connectors are considered. The influence of different parameters on the interfacial bond behaviour of specimens is discussed by analysing the load-slip curves, bond strength, and interface damage energy dissipation. The equations for the shearing capacity of studs and the interfacial bond-slip constitutive relationship under different connectors were obtained. Results show that the influence of concrete strength on the bond strength of SPHSCSWs is positively correlated, and the bond behaviour with HSRAC is similar to that of normal HSC. When the stud length-to-diameter ratio exceeds four, increasing the ratio has little effect on improving the shearing capacity, and a further increase reduces the residual bond strength. Replacing some studs with tie bars can significantly improve the residual bond strength and interfacial bond energy dissipation capacity. The proposed equations for the shearing capacity of studs in SPHSCSWs and the bond-slip constitutive relationship agree well with the test results, which can be used for engineering applications and further research.

Failure Patterns and Energy Analysis of Shaft Lining Concrete in Simulated Deep Underground Environments

The failure patterns and energy evolution of three types of shaft lining concrete subjected to static and dynamic loading were reported. The energy and damage characteristics of concrete were determined by means of a uniaxial hydraulic servo machine, acoustic emission (AE) equipment, a split Hopkinson pressure bar (SHPB) and an ultrasonic wave analyser. The experimental results indicate that the confluence of multiple cracks forms a penetrating cross section in normal high-strength concrete (NHSC) under the condition of static loading, while the elastic energy that surges out at failure can cause tremendous damage when subjected to dynamic loading. A single crack was split into multiple propagation directions due to the presence of fibres in steel fibre-reinforced concrete (SFRC); adding fibre to concrete should be an effective way to dissipate energy. The non-steam-cured reactive powder concrete (NSC-RPC) designed in this paper can store and dissipate more energy than normal concrete, as NSC-RPC exhibits a strong ability to resist impact. Applying NSC-RPC to the long-service material of a shaft lining structure in deep underground engineering is quite effective.

Ultimate stress increase in unbonded tendons in post-tensioned indeterminate I-beams cast with high strength normal and self compacting concrete

The use of un-bonded tendons is prevalent in post-tensioned concrete structures. Equations for prediction of stress in un-bonded tendons of post-tensioned normal (vibrating) concrete flexural members have been given in various codes. They are based on experience and don’t account all of important parameters such as concrete strength (normal and high strength) and its type (vibrating and non-vibrating concrete). Since self-compacting concrete (SCC) is nearly a new innovation therefore, understanding the implementation of this type of non-vibrating concrete on the ultimate unbonded tendon stress is critical. For this aim, in this paper there are presented experimental results of six continuous un-bonded post-tensioned I-beams in two groups were casted and monitored by different electrical strain gauges. In the first tested group, the beams (UPN1-12, UPN1-18, UPN1-22) were consisting of high strength normal concrete (HSNC) where as in the second group (UPS1-12, UPS1-18, UPS1-22) high strength self-compacting concrete (HSSCC) were tested. The variables included the type of concrete and percentage of bounded non-prestressed steel. Experimental monitored results of ultimate stress increase in unbonded tendons are compared with predicted equations of different researchers and standards. It was found that, the proposed equation is in better agreement with the test results. The results of standard error of estimate Sy/x, indicates that for two types of HSCs, the ACI 318-2011 provides better estimates than AASHTO-2010 model whereas this model provides better estimates than BS 8110-97.

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.

Water Penetration Resistance of Fly Ash Concrete Incorporating with Quarry Wastes

Slump of fresh concrete, compressive strength and water penetration depth under pressure of fly ash concrete incorporate with quarry waste as fine aggregate were investigated. The cementitious materials of the concrete includes ordinary Portland cement 80% and fly ash 20% by weight of cementitious. The mix proportions of the concrete were set into two classes of compressive strength. The results show that fly ash enhances workability of both concretes (normal concrete and concrete incorporate with quarry waste). Increasing the percentage of quarry dusts as fine aggregate in concrete seem negligible effect on the compressive strength whereas adding fly ash shows a slightly improve the compressive strength in the case of cohesive concrete mixture. Besides, adding the suitable amount of fly ash could improve the permeability of concrete. Therefore, fly ash could be a good admixture to improve the water resistant of normal strength concrete and also could be a supplemental material to improve the compressive strength of normal high strength concrete.

Ultimate Unbonded Tendon Stress in CFRP Strengthened Post-Tensioned Indeterminate I-Beams Cast with HSCs

Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the analysis of the stress increment of unbonded tendons is monitored in the loading process. Since self-compacting concrete (SCC) is a suitable innovation,, understanding the implementation of this type of concrete on the ultimate unbonded tendon stress is critical. For these aims, results of four continuous un-bonded post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges andare presented here. In the first group, the beams (UPN1-12, SUPN1-12) consisted of high strength normal concrete (HSNC), while in the second group (UPS1-12, SUPS1-12) high strength self-compacting concrete (HSSCC) were tested. The beams are made which are compared with the theory proposed by different codes, and a preliminary modification is given for each code equation. The results of standard error of estimate Sy/x , indicates that for two types of HSCs (strengthened and non-strengthened beams), the ACI 318-2011 provides better estimates than AASHTO-2010 model, whereas this model provides better estimates as compared toBS 8110-97.Comparison of increase in experimental ultimate tendon stress of beams indicates that the increase in tendon stress at ultimate state in strengthened beams is lower than that in non-strengthened beams cast with HSCs.

Monitoring and theoretical losses of post-tensioned indeterminate I-beams

Self-consolidating concrete is a desirable achievement in reinforced concrete structures. This non-vibrating concrete has had a significant impact on the prestressed concrete industry because it increases productivity in the casting of durable prestressed or precast members without mechanical vibration. In the design of prestressed concrete structures, the immediate and time-dependent losses in tendon stresses are important. The main objective of this study is to investigate the losses in tendon stresses of indeterminate (continuous) post-tensioned unbonded beams consisting of two different types of concrete (high-strength self-consolidating concrete (HSSCC) and high-strength normal concrete (HSNC)). Six continuous, unbounded, post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges for a duration of 60 d and the losses were measured. Results were compared with the Association of State Highway and Transportation Officials (Aashto) third and fourth edition methods, the Precast/Prestressed Concrete Institute (PCI) method and the Eurocode 2 model. It was found that the Aashto third edition, PCI and Eurocode 2 methods were conservative and the Aashto fourth edition method was non-conservative for estimating time-dependent losses in post-tensioned beams cast with high-strength concretes. The amount of experimental time-dependent losses in beams consisting of HSSCC was slightly lower than that of beams prepared using HSNC with almost the same concrete strength.

Ultra Durable Concrete for Sustainable Construction

With the rapid consumption of natural resources, there is a growing concern about sustainable development. More than 6 billion tons of concrete are produced annually for various construction purposes with limited life expectancy. In addition, increasing cost of construction and demolition of concrete structures in densely populated areas is a great concern for the future. One of the best solutions to tackle these challenges is to increase the life expectancy of the structures. Residential structures and important civil structures are typically designed for a life span of 50 and 100 years respectively. However, the life expectancy of structures can be increased to several hundred years with careful planning and proper design. Cost of the concrete materials is not a considerable amount compared to the total cost for construction of reinforced concrete structures. Doubling the concrete materials cost may only increase the total construction cost by few percent but it can increase the life expectancy of structures significantly. In this work, a comparison between ultra durable concrete mixes with normal high strength concrete in terms of cost, mechanical and durability aspects is presented. Ultra durable concrete has superior qualities which makes it a favourable construction material for future structures.

Fracture properties of normal and lightweight high-strength concrete

This paper presents the results of a comparative study on the fracture properties of high-strength concrete (HSC) with normal aggregate (crushed limestone) and lightweight aggregate (sintered fly ash). The compressive strengths of the normal and lightweight HSC were about 115 and 90 MPa respectively. The fracture properties, namely the critical stress intensity factor [Formula: see text] and critical crack tip opening displacement (CTODC) for the two-parameter model, and the fracture energy (GF) for the fictitious crack model were examined. A three-point bending test on notched beams was carried out on specimens of varying sizes to examine the size effect on the measured properties and flexural behaviour. The experimental findings indicated that the [Formula: see text] and GF values of normal aggregate HSC were more size-sensitive than that of lightweight HSC while the CTODC of both types of HSC seemed to be size-independent. Compared with the normal aggregate HSC, the lightweight HSC had a considerably lower [Formula: see text] but had a similar GF and more ductile flexural behaviour.

Autogenous shrinkage of high strength lightweight aggregate concrete

The characteristic of autogenous shrinkage (AS) and its effect on high strength lightweight aggregate concrete (HSIAC) were studied. The experimental results show that the main shrinkage of high strength concrete is AS and the amount of cement can affect the AS of HSLAC remarkably. At the early stage the AS of HSIAC is lower than that of high strength normal concrete, but it has a large growth at the later stage. The AS of high strength normal concrete becomes stable at 90 d age, but HSIAC still has a high AS growth. It is found that adjusting the volume rate of lightweight aggregate, mixing with a proper dosage of fly ash and raising the water saturation degree of lightweight aggregate can markedly reduce the AS rate of HSIAC.

Residual strength of hybrid-fiber-reinforced high-strength concrete after exposure to high temperatures

Residual strengths of high-strength concrete (HSC) and hybrid-fiber-reinforced high-strength concrete (HFRHSC) after exposure to high temperatures were investigated in the paper. The results showed that normal HSC is prone to spalling after exposure to high temperatures, and its first spalling occurs when the temperature approaches 400 °C. For HSC reinforced by high melting point fibers, the first spalling occurs when the temperature reaches to approximately 800 °C, while there is no spalling during exposing to high temperatures for HSC reinforced by polypropylene (PP) fiber with a low melting point. Mixing high melting point fiber (i.e., carbon or steel fiber) with low melting point fiber (i.e., PP fiber) HSC greatly improves the properties of HSC after exposure to high temperatures.

Size effect on flexural, splitting tensile, and torsional strengths of high-strength concrete

This paper presents the results of an investigation into the size effect on flexural, splitting tensile, and torsional strengths of high-strength concrete (HSC) with normal aggregate (crushed limestone) and lightweight aggregate (sintered fly ash). The Bazant’s size effect law gives a very good fit to the flexural strengths of both normal and lightweight aggregate HSC measured from beams of different sizes. As observed in the size effect curve, the fracture behavior of the lightweight HSC seems more brittle than that of the normal HSC. Linear elastic fracture mechanics may still be less applicable to HSC in the normal size range than nonlinear fracture mechanics. A reverse size effect is observed in the prism splitting tensile strengths of both normal and lightweight HSC and possible mechanisms of the reverse size effect are discussed. The torsional strength of the lightweight HSC appears to have a stronger size dependency than that of the normal HSC.

Behavior of Tension Splices for Reinforcing Bars Embedded in High-Strength Concrete

Safety concerns and a lack of test data on bond capacity of deformed reinforcing bars embedded in high-strength concrete (HSC) have been reasons that the American Concrete Institute (ACI) 318 building code has imposed an arbitrary limitation of 69 MPa (10,000 psi) in the calculation of tension development and splice lengths. This limitation was first introduced in the 1989 revision of the ACI 318 building code. In an attempt to evaluate the impact of this limitation and develop provisions for its removal, a two-phase investigation was carried out at the University of Nebraska-Lincoln. During both phases of the investigation, 70 beam splices were tested. The parameters studied included diameter, length, and deformation type of the reinforcing bars; amount of transverse reinforcement over the splice length; casting position; and concrete compressive strength. Results of the investigation are used to discuss the differences that exist between normal concrete and HSC, develop hypotheses to explain these observed differences, and suggest alternatives for removal of the current concrete compressive strength limitations existing in the ACI 318 building code for calculating tension development and splice lengths.