Seismic retrofitting and/or the strengthening of RC columns has been a popular area of research for decades. Currently, reinforced concrete jacketing is considered as the most common technique for repairing and strengthening of deficient and/or damaged RC columns. In general, this technique is a practical solution to recover and improve the load-carrying capacity and stiffness of reinforced concrete columns in earthquake-prone countries. It is a simple method that can be applied to any column cross section for rehabilitating structural elements by encasing the old member in a stiff jacket. The importance of this approach comes from its ability to improve the load-carrying capacity, strength, and stiffness of any column section significantly without the need for experienced labor or complicated installations process. This paper summarizes and compares general conclusions of recent investigations on columns retrofitting using reinforced concrete jacketing. As a part of this study, experimental, analytical, and numerical studies were reviewed and their findings were collected and discussed.
Polyethylene terephthalate bottles production has drastically increased year after year due to high versatility of polyethylene terephthalate plastics and considerable consumption of beverages. In tandem with that increase, the major concern of society has been the improper disposal of this non-biodegradable material to the environment. To deal with this concern, recycled polyethylene terephthalate bottles were incorporated in concrete as fibre reinforcements in this study. The objective of this research is to evaluate the mechanical properties of recycled polyethylene terephthalate fibre reinforced concrete (RPFRC) in comparison with control concrete without fibres. polyethylene terephthalate fibres with three different diameters (0.45, 0.65, and 1.0 mm) and two lengths (20 and 30 mm) were added at various proportions (0.5%, 1.0%, 1.5% and 2.0%) by volume of concrete in order to determine the effect of fibres initially on compressive, flexural and splitting tensile strengths of concrete. The results revealed that none of the fibres have detrimental effects up to 1 % volume fraction, however further addition caused slight reductions on mechanical properties in some conditions. Plastic shrinkage resistance and impact resistance tests were also performed according to related standards. Polyethylene terephthalate fibres were observed to have marked improvements on those properties. Such a good performance could be attributed primarily to the bridging effect of fibres.
Nowadays, many researchers are focused on studying the behavior of rubberized concrete as a structural material due to its enhanced properties such as ductility, energy dissipation, and damping ratio and its role in sustainable development by recycling non-biodegradable wastes and reducing the amount of natural aggregates in concrete mixture. Previously, it was suggested that fine rubber particles should be used instead of coarse ones when the intention is to achieve high strength concrete; however, incorporating coarse rubber particles provides better energy dissipation, damping ratio, and vibration behavior. This study aims to develop high strength rubberized concrete by utilizing large amounts of fine materials and replacing 15% and 25% of the natural aggregates by volume with a well graded mix of coarse and fine rubber particles. As a part of the study, mechanical, and dynamic tests were performed to address the properties of the produced concrete with different rubber replacement percentages. In general, the results of the experiments have shown that it is possible to produce high strength concrete with superior vibration behavior when 25% of the natural aggregates is replaced.
Natural building cut (NBC) stones are being used in Cyprus for ages to build masonry structures because of being abundant, relatively easy to cut and shape and good performance in many applications. Almost all of the historical buildings in Cyprus are made of these NBC stones. Although these stones are low cost construction materials, they are not widely used in these days. This is due to lack of knowledge causing incorrect construction methods and highly skilled labour requirement. For this study two quarries are selected and samples obtained were tested for some physical and mechanical properties. Traditional names of these NBC stones are Meluşa Stone and Karpaz Stone (or Bouri Stone). The physical properties such as bulk density, water absorption, specific gravity and porosity were measured. The mechanical properties such as compressive strength, flexural strength, direct tensile strength, splitting tensile strength, point load strength, fire resistance, abrasion resistance and freeze-thaw resistance were measured. From the results obtained it can be said that Meluşa stone behaved better than Karpaz stone. A regression analysis also provided a polynomial relation between compressive strength and burning temperature and flexural strength and burning temperature.
This study develops empirical models for the prediction of the bond strength of uncorroded and corroded reinforcement bars. The effects of hooked reinforcement on the bar’s development length when covered fully and partially are examined. An accelerated corrosion method is used to corrode the reinforcement bars embedded in concrete specimens. Pull-out tests are performed to investigate the ultimate bond strength of the concrete specimens. The effects of two different geometries of reinforcement bars are discussed by considering two different concrete strength levels and concrete cover depths. It is found that partly covered hooked reinforcement bars increase the radial stress on the concrete surface and reduce the bond strength. Increases in the bond strength due to the increased roughness of the steel bar caused by the confined corrosion products are less for hooked bars. The results reveal that the developed models show good relationships with the experimentally computed test results.
This paper presents the results of a study investigating the consistency, hardened and toxic metal immobilization properties of concretes containing copper tailings as an additive. To compare the effects of copper tailings on strength and strength related properties across two concrete classes, two series of concretes with 0.57 and 0.50 water-to-binder ratios are used. For each series, three mixtures incorporating copper tailings at 0%, 5%, and 10% addition levels by mass are prepared. Copper tailings have a slight negative impact on the slump, setting time and porosity of mixtures. However, improved mechanical strengths and abrasion resistance, and reduced chloride penetration compared to the control specimens are observed in mixtures incorporating copper tailings. Toxicity characteristic leaching test results revealed that the release of heavy metals from mixtures containing copper tailings is considerably lower than the United States Code of Regulations limits. Overall, it seems that there is a potential for the use of copper tailings as a zero-cost, environmentally-friendly additive in concrete, especially at a 5% addition level.
Increasing demands for copper and copper allied products have made the processing of low grade ores with high volume waste output unavoidable. Presently, billions of tons of copper tailings can be found in major copper producing countries. The impact of copper tailings at 0%, 5% and 10% addition level by mass of cement on the fresh and hardened properties of mortars were determined. Results showed that dry copper tailings affect mixture consistency negatively. However, the use of pre-wetted tailings reduced this drawback. Copper tailings blended mortars showed higher strength and abrasion resistance. Similarly, rate of water absorption, acid and chloride resistance higher than those of the control mixture were observed. The use of pre-wetted tailings at 5% addition level seems to be the best reuse approach.
This paper provides the result of experimental and statistical modeling study on modulus of elasticity of Ultra High Performance Asphalt Concrete Pavement consisting different level of silica fume, superplastisizer, steel fiber, cement, and water binder ratio. Number of experiments designed by using design of experiment (DOE) in two levels, results modeled by using analysis of variance (ANOVA), and monitored using response surface methodology. This study clearly revealed the effect of each variable and their interactions on modulus of elasticity of Ultra High Performance Asphalt Concrete Pavement. This study is valid for the mixes of UHPC with 0.18–0.32 water binder ratio, 0.04–0.08 steel fibre, 0.7–1.3 cement, 0.15–0.30 silica fume, and 0.04–0.08 superplasticiser by aggregate mass.
Utilisation of recycled Polyethylene Terephthalate (PET) waste in construction materials contributes towards the environmental sustainability by reducing the accumulation of non-degradable waste into the nature. This study aims to contribute to the knowledge about the material behaviour of recycled PET fibre reinforced concrete (RPFRC). The present work investigates the influence of recycled PET fibres on the physical properties of concrete, with a focus on the durability, acoustic properties, and the mechanical response to heat exposure. Mixtures with varying fibre dimensions and fibre volumes were prepared. Fibre addition reduced the bulk density, increased the permeable void volume, and decreased the ultrasonic pulse velocity (UPV) of concrete, suggesting possible porosity formations within. Water permeability of RPFRC samples was substantially higher than the concrete without fibres and the findings were in agreement with rapid chloride permeability test results. Sound permeability was slightly reduced by fibre addition. RPFRC samples were heated at three different temperatures and tested for compressive and flexural strengths. At room temperature, fibre addition caused negligible variations in compressive strength but notable increase in flexural strength. Strength values were reduced slightly with fibre addition when samples were exposed to 100 °C and 200 °C, indicating possible response of PET fibres to high-temperature exposure.
This paper describes an experimental study conducted to investigate the properties of concretes produced with recycled aggregates and normal aggregates for two different concrete classes (C20/25, C30/37). Tests of compressive strength, splitting tensile strength, ultrasonic pulse velocity, rebound hammer, wet and dry density and freeze-thaw resistance were conducted on specimens of the concretes. Moreover slump test was conducted on fresh concrete. The results showed that the slump of recycled aggregate concrete (RAC) was less than that of normal aggregate concrete (NAC). For class C20/25, the average compressive strength, rebound hammer and density of the RAC were 26%, 17% and 16.6% less, respectively, than those of NAC. The splitting tensile strength of RAC was 3.5% greater that of NAC. Moreover for C30/37 the average compressive strength, splitting tensile strength, rebound hammer and density of the RAC were 32.5%, 12%, 21% and30% less, respectively, than those of NAC. For class C20/25 and class C30/37 the ultrasonic pulse velocity of RAC was 17% and 18% smaller than that of NAC, respectively. RAC for C20/25 lost 2.5% more weight than NAC in freeze-thaw resistance tests and RAC for C30/37 lost 29% more weight than NAC in this test.
The primary objectives of this study was to investigate the effects of default hinge properties based on FEMA-356 (FEMA-356, 2000) and user-defined hinge properties on the timedependent seismic performance levels of corroded RC buildings. An assumed corrosion rate was used to predict the capacity curve of the buildings by using default and user-defined plastic hinge properties as a function of time (t: 25 years, and t: 50 years). Two, four and seven stories of RC buildings were considered to represent the effects of default and user- defined hinge properties on story levels. For the modelling of user-defined hinge properties, the time-dependent moment-curvature relationships of structural members were predicted as a function of corrosion rate for two different time periods in order to perform push-over analyses, while default hinge properties were used for the other case based on the ready documents by FEMA-356 (FEMA-356, 2000). Then, the nonlinear time-history analyses for both corroded and non-corroded buildings were performed by using 20 individual earthquake motion records. Seismic performance levels of non-corroded buildings and predicted time-dependent seismic performance levels of corroded buildings were compared based on their story levels as a result of user-defined and default hinge properties. Limit–states at each performance levels (e.i. immediate occupancy, life safety, collapse prevention and collapse) were obtained. The obtained results were summarized to compare the differences in the results of seismic response of the buildings due to user-defined and default hinge properties for both corroded and non-corroded cases.
Abstract Now, it is widely accepted by civil engineers and architects that walls and masonry building units, which are made of pumice, can insulate buildings against both heat and sound, and also reduce the dead load of the building compared to traditional buildings. In this study, pumice was used as a fine aggregate in mortar and plaster instead of traditional crushed limestone sand. This study shows that the properties of pumice mortars indicate lower values compared to limestone mortars for workability durations, time of settings, and fresh and hardened unit weights. Other properties of pumice mortars indicate higher values compared to limestone mortars, such as water absorption, coefficient of capillary water absorption, drying shrinkage, flexural strength, and compressive strength. Also, wall systems made with pumice mortar and plaster show significant benefits in terms of thermal conductivity.
This study investigates the effect of steel fibres on the physical and mechanical properties of Self-compacting concrete (SCC). Six mixes of steel fibre reinforced self-compacting concrete (SFR-SCC) were prepared with two different steel fibre aspect ratios (l/d) of 60 and 80 at three-volume fractions (Vf) of 0.35%, 0.45% and 0.55%, in addition to a control mix. All specimens were cast with a constant water-binder ratio of 0.34 and 2% silica fume (SF) of cement content as additive. The performance of different SCC specimens was characterized for compressive strength, ultrasonic pulse velocity, rebound hammer, permeability, flexural strength, toughness, splitting tensile strength and impact resistance of SCC. With the increase of steel fibre aspect ratio, (1) the workability and rheology decrease; (2) the compressive strength of different SCC mixes shows slight variations; (3) the flexural strength increases the toughness, split tensile strength and impact resistance; (4) the ultrasonic velocity results increase (5) the permeability results decrease.
One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.
This study investigates potential effects of the vertical-component-of-ground-motion (VCGM) on the maximum-inelastic-horizontal-response (MIHR) of single-degree-of-freedom (SDOF) systems. The effects of VCGM can be considered in two categories. First, it may initiate some modes of failure, like over-compression, and second, it might adversely influence the horizontal response through altering the P-delta effect. The latter is a result of variation of the gravitational acceleration, and hence, seismic weight, upon action of the VCGM. This study uses time-history analysis to compare the response of SDOFs in presence and absence of the VCGM. In both cases, the P-delta effect is inherent in analyses and period-dependent feature of the stability-coefficient, which is essential for reliable treatment of the P-delta effect, is explicitly reflected. Since available record selection and scaling strategies use uncoupled vibrators in vertical and horizontal directions, this research follows two steps to avoid undesirable bias. The first step, which focuses on examining the influence of some important parameters, adopts an event-based record selection scheme. Results indicate that for certain combinations of the strength reduction factor and initial period of vibration the effect of the VCGM on the MIHR is significant. Specifically, the systems with initial periods between 1.0 and 2.0 s are found most vulnerable. Moreover, the mentioned effect is not limited to near source regions. The second step evaluates capability of the VCGM to initiate dynamic instability. In this step, a set of 26 records, which resembles an assumed target spectrum at a near field site, is used. Results show that under action of some of the examined records, the presence of the VCGM leads to dynamic instability; hence, this study suggests consideration of the VCGM for collapse evaluation.
