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.
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.
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.
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.
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.
The evaluation of steel-fiber reinforced concrete using the maturity method was investigated in this study. There were four different volume fractions of fibers (0, 0.5, 1 and 1.5 by volume of concrete) and three different curing temperatures (8°C, 22°C and 32°C) considered. The compressive strength and flexural strength were tested at 1, 3, 7, 10, 14 and 28 days for all of the volume fractions of fibers and at the different curing temperatures. The results show that as the volume fraction of fiber increased from 0 to 1.5%, the compressive and flexural strengths increased by 14% and 35%, respectively, compared to plain concrete. The maturity method was used to predict the compressive and flexural strengths. Four different equations (linear hyperbolic, parabolic hyperbolic, logarithmic and exponential) were used to predict the compressive and flexural strengths. All of the predicted models have good correlations with the experimental results for both compressive and flexural strengths. Moreover, to predict the compressive and flexural strengths using the maturity method, the apparent activation energies were calculated.
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.
A simple, economical, and practical drop-weight impact testing machine was developed to determine the impact resistance for high-strength fiber-reinforced concrete (HSFRC) composite. Impact and compression tests were carried out on concrete cylinders reinforced with three different aspect ratios of hooked-end steel fibers l/d (length/diameter): 60, 75, and 83 (30/0.50, 60/0.80, and 50/0.60 mm/mm), and four different percentages of steel fibers 0.5%, 1.0%, 1.5% and 2.0% by volume of concrete. For each aspect ratio and volume of fibers, complete stress–strain curves of HSFRC were generated in order to determine the total energy absorbed for each cylindrical specimen in compression. The addition of steel fibres to concrete has improved impact resistance and also the compression toughness. The test results showed that a logarithmic relation exists between compression toughness energy (E Ct) by means of the generated stress–stress curves from the compressive tests and the impact energy (EI) by means of the modified impact machine for HSFRC at different l/d ratio of 60, 75, and 83.
In this study, two grades of concrete namely C30 and C50 were investigated for the direct shear behavior of plain and steel fiber reinforced concrete. Shear tests were performed on concrete beams, 100 × 100 × 300 mm, reinforced with two different aspect ratios (l/d) of steel hooked-end fibers 65 and 80 and three percentages of fibers 0.5, 1.0 and 1.5 % by volume of concrete. The water/cement ratios (w/c) used were 0.5 and 0.43. The main objective of this study was to study the shear behavior of plain and fiber reinforced concrete at different aspect ratios and at different volume fractions of steel fibers. Test results for C30 and C50 concretes showed that, as the volume fraction of fibers increased from 0 to 1.5%, the shear strength increased about 2.15 and 2.46 times that of plain concrete, respectively. Also, test results showed that the aspect ratio of steel fibers has no clear effect on the shear strength. Relationships between shear strength and volume of fibers were determined, and a relationship obtained in terms of fiber factor and compressive strength to estimate the shear strength of fiber reinforced concrete. The obtained equations give good correlation with the experimental results.
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.
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.
Commodity plastics are being used in many applications due to their low density, high durability, and relatively low cost. Their wide usage and degradable nature create environmental problems. Polyethylene terephthalate (PET) is the one of most used plastics and the second largest contributor to the global plastic waste. The scientific literature suggests a global effort for utilizing PET waste in building materials including concrete, mortars, and cementitious composites, in the form of granules, powder or fibres. This study aims to contribute to the knowledge about the material behavior of Recycled PET Fibre Reinforced Mortars (RPFRMs) by investigating the influence of fibres on some physical and mechanical properties of a cementitious render mortar.
