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Abstract This study investigated the effectiveness and limitations of newly developed biological mortars regarding chloride ion diffusion resistance. Through several tests on the glycocalyx production capacity and growth potentials of bacteria cells under marine environments, Bacillus licheniformis was isolated and immobilized in the expanded vermiculites together with a bacterial culture medium for producing biological mortars. The chloride ion diffusion coefficient of the mortars up to 91 days was determined through natural diffusion cell tests. Subsequently, the service life of RC structure repaired with biological mortars under chloride attack was evaluated considering multilayer theory and time-dependent diffusion. The addition of expanded vermiculites immobilizing Bacillus licheniformis significantly reduced the chloride ion diffusion coefficient. When its addition increased from 10 to 30%, the chloride ion diffusion coefficient decreased by 50–90% compared to that of mortars without bacteria. The service life of reinforced concrete structures repaired with biological mortars containing 30% expanded vermiculite concentration and thickness of 50 mm was evaluated to be six times longer than that of repaired with conventional mortar. Overall, this novel approach holds significant potential in addressing the salt-induced deterioration challenges faced by RC structures.

Polydimethylsiloxane (PDMS) is a highly reliable thermosetting polymer with exceptional chemical and mechanical resistance, as well as remarkable water repellency and adhesive performance. Its unique features make it the preferred choice for fluorine-free hydrophobic coatings. However, the use of PDMS requires organic solvents that are toxic and environmentally hazardous. In this study, an emulsion composed of amine-terminated polydimethylsiloxane (PDMS-NH2) in an environmentally friendly solvent, water, was prepared. Subsequently, glutaraldehyde (GA) was added and crosslinked to generate a hydrophobic PDMS–GA emulsion. The PDMS–GA emulsion is a low-viscosity solution that can infiltrate different types of fabrics (cotton, nylon, and polyester) or paper with numerous intertwined fibers. After dipping the fabrics and paper into the prepared PDMS–GA emulsion, they were washed in an aqueous solution containing dispersed kaolin particles and dried to yield a rough structure. As a result, a hydrophobic surface with a water contact angle of 151.2° was achieved. Furthermore, after exposure to strongly acidic or alkaline solutions (pH 1–13) and washing six times with water, the hydrophobic fabric remained chemically stable. Additionally, it withstood ten tape peeling tests, proving its mechanical durability. Crucially, the hydrophobic treatment method does not involve fluorine and uses eco-friendly water as the solvent. Therefore, this is a convenient way to apply waterproof coatings to functional textiles that require water resistance and are expected to have great industrial applications.

Abstract The objective of the present study is to examine the effects of different types and content of steel fibers on the workability, mechanical properties, and ductility enhancement of lightweight aggregate concrete (LWAC). Thirteen LWAC mixtures were prepared using different types of steel fibers including conventional hooked-end macro steel fibers (SF(H)), straight (CSF(S)), crimp-shaped (CSF(C)), and hooked-end (CSF(H)) copper-coated micro steel fibers at the designed compressive strength of 40 MPa. The fiber volume fraction varied from 0% to 1.5% at an interval of 0.5%. Test results showed that CSF(H) type possesses a better potential than the other types in enhancing the tensile resistance and toughness at the post-peak branch of the load–deflection curve of beams. The bond characteristics of fibers with cement matrix were one of critical parameters that needs to be considered in designing the fiber reinforced concrete. Thus, the splitting strength, modulus of rupture, and modulus of elasticity of fiber reinforced LWAC were formulated as a function of volume fraction, aspect ratio, and bond strength of fibers from the regression analysis using the present test data.

Abstract The mechanical properties of lightweight aggregate concrete developed with the use of bottom ash aggregate (LWAC-BA) as a partial or full replacement of lightweight aggregate differ from those of general lightweight concrete made using natural fine and/or coarse aggregates. The mechanical properties of LWAC-BA are difficult to predict using the existing equations proposed by codes or researchers. Therefore, in this study, empirical equations using nonlinear regression analysis are proposed to predict the mechanical properties of lightweight concrete mixed with bottom ash aggregate, based on the collected measured values from other studies (Yang "Development of replacement technology for ready mixed concrete with bottom ash aggregates", 2020; Kim et al. Appl Sci, 10: e8016, 2020; Constr Build Mater 273: e121998, 2021). The collected data include density, compressive strength, elastic modulus, modulus of rupture, splitting tensile strength, and stress–strain relation of LWAC-BA featuring varying amounts of bottom ash fine aggregate and/or coarse aggregate. The proposed empirical equations for each mechanical characteristic are developed considering the replacement volume of bottom ash fine/coarse aggregates. The mean values of the ratios of the measured to predicted values obtained using the proposed equation range from 1.00 to 1.05, with a standard deviation ranging from 0.002 to 0.013, indicating a reasonably positive agreement.

Abstract Concrete sewage structures are difficult to maintain since they are constructed under the ground and their surfaces inside are exposed to various deteriorations such as acid and sulfate ingress. In this study, their repair costs were evaluated both deterministically and probabilistically considering the extended service life through repairing of conventional repair mortar and a newly developed bacteria repair material. Unlike the conventional deterministic method, the probabilistic manner evaluates repair cost continuously, taking into account variations in the initial service life and extended service life through repair. For the work, variations in the sulfate ion diffusion coefficient and protection parameters (cover depth and repair layer thickness) were obtained experimentally. Based on the target service life (60 years), the repair cost increased to 123% as the maintenance-free period (MFP) decreased by half, and decreased to 77% as the MFP increased to 1.5 times. As the extended service life through repair decreased by half, the repair cost increased to 180% due to the increasing repair frequency. When the repair-extended service life increased to 1.5 times, the repair cost decreased to 73%. Considering exterior sulfate concentrations (120 and 200 ppm) and entire sewage pipelines (3268 m), the bacteria repair material showed the lowest repair cost (1376 K$ and 1498 K$ with the deterministic and probabilistic method, respectively) since the repair-service life increased from 10.4 to 25.3 years and the number of repairs decreased from 9 to 4 due to the low diffusion coefficient of the bacteria repair material.

Halochromic sensors, which allow users to visually recognize exposure to acid/base chemicals that are harmful to the human body, are routinely used in a wide range of industries, such as pharmaceuticals, biotechnology, cosmetics, and environmental/human monitoring systems. In this study, halochromic fibers that operate stably, even when exposed to rain or sweat and repeated stretching–releasing, were investigated. While the halochromic mesoporous silica was synthesized using tetraethylorthosilicate and cetyltrimethylammonium bromide, methyl yellow (MY) and bromothymol blue (BTB) as halochromic dyes were added so that MY and BTB were chemically or physically immobilized on the siloxane network structure of the halochromic mesoporous silica. Using the swelling and shrinking properties of the polymer, the halochromic mesoporous silica was embedded in a highly elastic spandex fiber composed of multiple strands. Because of the strong ionic and hydrogen bonding between the dye and the silica matrix, the dyes can be immobilized even in an aqueous solution without the leaching of the dyes. The stretchable halochromic fiber reversibly changed its color even after repeated exposure to acidic/basic conditions five times and could sense acid/base concentrations in the range of 0.5–10 wt %. In addition, because the halochromic mesoporous silica is tightly adhered between the stands of spandex fibers, stable color conversion properties were maintained even after stretching to 150% of the fibers and repeated 100 times. Because the halochromic fiber can be applied to lab coats, work clothes, and gloves, it is expected to be used as a wearable colorimetric sensor for daily life and industrial applications.

Although the anchorage location of longitudinal reinforcing bars is a significant design element for flexural behavior, the conventional anchorage method of using longitudinal reinforcing bars has limited applications in new types of structures, such as composite structures. Therefore, this study examined the effect of the anchorage location of longitudinal reinforcing bars on the flexural behavior of slabs at the junctions of developed composite basement walls (SCBW) under monotonic loads at the top free end of the slab. The test results showed that the slab with longitudinal reinforcing bars anchored to the cast-in-place pile (CIP) in the composite basement wall exhibited ductile behavior accompanied by the yielding of the longitudinal reinforcing bars, a relatively wide area of vertical cracks propagating along the slab length, and a plastic plateau flow in the load–deflection relationships. In particular, the slab with longitudinal reinforcing bars anchored to the basement wall experienced severe crack concentration localized at the junction of the composite basement walls and concrete spalling in the basement walls, which resulted in no yielding of the longitudinal reinforcing bars and no cracks in the slab. Consequently, in a slab, it is recommended that longitudinal reinforcing bars be anchored into the CIP by penetrating the steel plate.

This experimental study was conducted to evaluate the deflection performance of wire-integrated steel deck plates with various end details subjected to cumulative gravity loads. In general, when deck plates are installed in the Republic of Korea, vertical bars are mounted at the ends of the wire-integrated deck plates. However, this process can extend the construction time, thus incurring additional costs. Consequently, this study aimed to examine the structural performance of a deck plate when a lattice foot—rather than a vertical bar—is installed at the end of it. A total of nine specimens were prepared; the experimental variables included the end details, height of the lattice truss girder, and structure type. To evaluate the deflection performance, the cumulative gravity load (as a construction load) and a concrete self-weight were applied to the specimens, and the deflections of each specimen were measured. In the experimental results, the deflection values of the specimen with vertical bars were 0.9~6.1 mm, while those for the specimen without vertical bars were 0.8~5.0 mm. This means that a lattice foot exhibits better deflection performance than conventional end details. Additionally, the deflection of the specimens satisfied the deflection limits required in the relevant standards.

A halochromic sensor that can visually and quickly monitor the information regarding the exposure of harmful chemicals to the human body is highly valuable in the safety and industrial fields. A general halochromic sensor uses a hydrophilic matrix to increase its detection sensitivity by promoting the diffusion of foreign materials. However, it is difficult to maintain the reversibility, durability, and stability of the color change in the halochromic sensor due to the loss of halochromic dyes under continuous exposure to chemicals. This study investigates a hydrophobic halochromic aerogel sensor that is stable even when exposed to various external environments and reacts to both acids and bases. By embedding halochromic dyes in silica aerogels with a porous structure and hydrophobicity, the leaching of halochromic dyes can be prevented even when the aerogels are placed in aqueous solutions. Hydrophobic halochromic aerogels can detect vapors generated in acidic and basic solutions, and the color change in hydrophobic halochromic aerogels reacts stably even with repeated acid and base environmental changes, enabling accurate acid or base concentration detection. In addition, halochromic aerogels can be easily applied to various platforms because they can be combined with fabric, concrete blocks, pipes, and polymers such as polydimethylsiloxane to create composites. The halochromic aerogels derived in this study are expected to contribute to the development of color change sensors applicable to various work environments by greatly improving the color change reversibility, durability, and stability that are the most important characteristics of robust halochromic sensors.

Concrete structures are considered as durable construction material, but corrosion of the embedded steel reinforcement occurs under chloride exposure as concrete has porous properties. Herein, a cyclic drying–wetting test was performed for two years using saltwater to accelerate steel corrosion in a reinforced concrete (RC) member. The open-circuit potential (OCP) was measured using a newly developed and replaceable agar sensor. The corrosion potential was measured considering the chloride concentration, water-to-cement (w/c) ratio, and cover depth at three levels. Furthermore, its relationships with influential parameters were evaluated using averaged OCP results. The measured OCP showed a linear relationship with the cover depth, and this tendency was more distinct with increasing retention period and higher chloride concentration. For the highest w/c ratio (0.6), values below −100 mV were monitored after only six months regardless of the cover depth, and values below the critical potential level (−450 mV) were evaluated at lower cover depths (30 and 45 mm). The results of regression analysis considering the exposure environment showed a clear relationship in the case of high chloride concentration (7.0%). A linear relationship between cover depth and OCP was derived with a reasonable determination coefficient ranging from 0.614 to 0.771.

With the increased interest in the inherent fire resistance of organic insulators, various precast concrete insulation panels have been developed. However, precast concrete insulation panels still have structural and fire resistance problems resulting from a low composite action and unclosed cross-sectional details. To improve composite action and fire resistance, this study proposes the closed cross-sectional details of insulator panels with lightweight aggregate concrete, insulation material, and wire mesh. The objective of this study is to examine the flexural–shear performance of precast lightweight concrete panels with closed cross-sectional details developed for exterior cladding with high insulation capacity. Six full-sized insulation panels were tested under two-point top loadings. The main investigated test parameters to vary the moment–shear ratio of the insulation panels were the amount of the shear reinforcement and shear span–effective depth ratio. Test results indicate that the insulation panels with moment–shear ratios of 2.60 or higher were governed by shear, indicating that the longitudinal bars remained in an elastic state until the peak load of the insulation panels was reached. Thus, an increase in the moment–shear ratio of the insulation panels led to more brittle failure characteristics. Meanwhile, the insulation panels governed by flexure exhibited plastic flow performance in the applied load–deflection curve and well-distributed cracks. In particular, the maximal flexural moments of insulation panels with moment–shear ratios of 0.75 or less were higher than those calculated from the equations specified in ACI 318-19, indicating that the composite action was fully exerted. Overall, the developed insulation panels with cross-sectional details must be designed to a have moment–shear ratio of 0.75 or less to fulfil the ductile response under extreme lateral loads and exert full composite action.

This study investigated the axial and shear behaviors of a seismic damping isolation unit (SDI) developed to improve the seismic resistance of suspended ceiling structures. To enhance the energy dissipation of the SDI, it was composed of a spring, embossed rubbers, and prestressed bolts. Twelve specimens were prepared and tested for failure under axial and shear loading. The main parameters were the presence or absence of a spring, loading type, and magnitude of the prestressed force introduced to the bolts to connect the embossed rubbers. The test results showed that in the relationship of axial or shear load–displacement of the SDI, the post-peak behavior tended to be more ductile for specimens with a spring or higher prestressed force magnitude. Consequently, the ductility ratio and equivalent damping coefficient of the SDI with the spring and 0.1fby were 3.81 and 0.166, which was 1.06 and 1.20 times higher than the specimens without spring and prestressed force. In addition, the ductility ratio was approximately 1.07 times higher for the SDI specimens subjected to monotonic loading than for those subjected to cyclic loading. Meanwhile, the JIS B 2704−1 and AISC specifications estimated the tensile strength of the SDI specimens subjected to monotonic loading well, but overestimated that of the specimens subjected to cyclic loading. Hence, the JIS B 2704−1 and AISC specifications should be underestimated by 15.7% and 81.7%, respectively, when estimating the tensile and shear loads of the SDI subjected to cyclic loading.

Abstract The objective of this study is to assess the shear friction characteristics of lightweight aggregate concrete (LWAC) prepared using artificially expanded bottom ash and dredged soil granules. A total of 37 concrete mixtures were prepared under the classification of three series. In the first and second series, the natural sand content for replacing lightweight fine aggregates and the water-to-cement ratio varied to obtain different densities and compressive strengths of concrete. The third series was designed to estimate the effect of the maximum aggregate size on the friction resistance along the shear crack plane of the monolithic interfaces. The frictional angle of the LWAC tested was formulated as a function of the ratio of the effective tensile and compressive strengths of concrete through the expansion of the integrated mathematical models proposed by Kwon et al., based on the upper-bound theorem of concrete plasticity. When predicting the shear friction strength of LWAC, the present mathematical model exhibits relatively good accuracy, yielding the mean and standard deviation of the ratios between experiments and predictions of 1.06 and 0.14, respectively, whereas the empirical equations proposed by the AASHTO provision and Mattock underestimated the results. Ultimately, an advanced modification factor for shear design of LWAC is proposed as a function of the density and compressive strength of concrete and the maximum size of aggregates.

Abstract In this study repeated cyclic loading tests were carried out on seven shear wall specimens, which were fabricated in a real scale. The purpose of these experiments is to investigate the difference on the seismic performance of the wall depending on two methods of confining longitudinal bars at the wall boundaries and propose relaxed bar arrangement details that could be used in a moderate to high seismicity zone. The results showed that the seismic performance of special shear walls using overlapping loops as transverse reinforcement of the boundary element was similar to that of special shear walls using a closed hoop in strength, stiffness, and energy dissipation. This means the former can serve as an alternative for rational seismic design for moderate to high seismicity zones using overlapping hoops.

Abstract The objective of this study is to examine the workability and various mechanical properties of concrete using artificial lightweight aggregates produced from expanded bottom ash and dredged soil. Fifteen concrete mixes were classified into three groups with regard to the designed compressive strengths corresponding to 18 MPa, 24 MPa, and 35 MPa. In each group, lightweight fine aggregates were replaced by using natural sand from 0 to 100% at an interval of 25%. Thus, the density of concrete ranged between 1455 and 1860 kg/m3. Based on the regression analysis using test data, a reliable model was proposed to clarify lower early-age strength and higher long-term strength gains of lightweight aggregate concrete (LWAC) when compared with the predictions of the fib model. The proposed model also indicates that a lower water-to-cement ratio is required with the decrease in the natural sand content to achieve the designed compressive strength of concrete. The partial use natural sand is favorable for enhancing the tensile resistance capacity, shear friction strength, and bond behavior with a reinforcing bar of LWAC. The fib model overestimates direct tensile strength, bond strength and the amount of slip at the peak bond stress of LWAC. Therefore, it is necessary to consider the density of concrete as a critical factor in conjunction with its compressive strength to rationally evaluate the various mechanical properties of LWAC.

Abstract Chloride attack is one of the most critical deterioration due to rapid corrosion initiation and propagation which can cause structural safety problem. Extended service life through repairing is very important for determination of maintenance strategy. Conventionally adopted models for estimation of life cycle cost have shown step-shaped elevation of cost, however the extension of service life is much affected by quality of construction and repairing materials, which means engineering uncertainties in residual service life. In the paper, reinforced concrete column with three different mix proportions exposed to chloride attack are considered, and repairing numbers with related costs are evaluated through probabilistic technique for maintenance. With a given exposure condition, service lives with normal probabilistic distribution are considered, and the effect of design parameters such as coefficient of variation of service life and 1st repairing timing are investigated. The comparison of results from conventional approach (step-function) and probabilistic approach are performed. When calculating repair frequency for intended service life through probabilistic model, the required repair frequency is evaluated to be 6.71 times for OPC, 4.09 times for SG30, and 2.95 times for SG50, respectively. The probabilistic model for repairing cost is evaluated to be effective for reducing the repair frequency reasonably with changing the intended service life and design parameters.

Since a concrete structure exposed to a sulfate environment is subject to surface ion ingress that yields cracking due to concrete swelling, its service life evaluation with an engineering modeling is very important. In this paper, cementitious repair materials containing bacteria, Rhodobacter capsulatus, and porous spores for immobilization were developed, and the service life of RC (Reinforced Concrete) structures with a developed bacteria-coating was evaluated through deterministic and probabilistic methods. Design parameters such protective coating thickness, diffusion coefficient, surface roughness, and exterior sulfate ion concentration were considered, and the service life was evaluated with the changing mean and coefficient of variation (COV) of each factor. From service life evaluation, more conservative results were evaluated with the probabilistic method than the deterministic method, and as a result of the analysis, coating thickness and surface roughness were derived as key design parameters for ensuring service life. In an environment exposed to an exterior sulfate concentration of 200 ppm, using the deterministic method, the service life was 17.3 years without repair, 19.7 years with normal repair mortar, and 29.6 years with the application of bacteria-coating. Additionally, when the probabilistic method is applied in the same environment, the service life was changed to 9.2–16.0 years, 10.5–18.2 years, and 15.4–27.4 years, respectively, depending on the variation of design parameters. The developed bacteria-coating technique showed a 1.47–1.50 times higher service life than the application of normal repair mortar, and the effect was much improved when it had a low COV of around 0.1.

In recent years, many studies have been performed on the crack repairing technique in concrete or the protection of the concrete surface against sulfate ions. Bacterial immobilization and survival rate are the dominant influencing factors for the repair of concrete. In this study, a negative pressure method (NPM) was developed to forcibly remove air in the porous materials of concrete, which was applied for surface repair through bio-coating using Rhodobacter capsualtus. For normal repair—repair using the conventional simple soaking method (SSM) and repair through NPM—various evaluations of the concrete strength and durability were performed. Since a reinforced concrete (RC) structure for the application of these repair methods is a sewer pipe exposed to sulfate ingress, variations in concrete mass and strength were analyzed by the accelerated sulfate resistance test. The diffusion coefficient of the sulfate ion in the repair materials and the bacterial count after the accelerating test were also measured. In order to investigate the changes in the properties of the concrete hydrates, surface analyses with SEM, XRD, and TGA were carried out on the concrete under the repair layer after the tests. In all the experimental results, the bacterial immobilization rate was evaluated, and the high immobilization rate indicates the excellent shielding of sulfate ions as well as improves the survival rate of bacteria. This not only improves the service life of the coating repair but also extends the service life of the structure itself. As a result of analyzing the composition of concrete protected by different types of repair, the results most similar to the general concrete composition without sulfate attack were obtained in the case of applying NPM, which shows the least damage from sulfate attack.

In this study, a stress-strain model for unconfined concrete with the consideration of the size effect was proposed. The compressive strength model that is based on the function of specimen width and aspect ratio was used for determining the maximum stress. In addition, in stress-strain relationship, a strain at the maximum stress was formulated as a function of compressive strength considering the size effect using the nonlinear regression analysis of data records compiled from a wide variety of specimens. The descending branch after the maximum stress was formulated with the consideration of the effect of decreasing area of fracture energy with the increase in equivalent diameter and aspect ratio of the specimen in the compression damage zone (CDZ) model. The key parameter for the slope of the descending branch was formulated as a function of equivalent diameter and aspect ratio of the specimen, concrete density, and compressive strength of concrete. Consequently, a rational stress-strain model for unconfined concrete was proposed. This model reflects trends that the maximum stress and strain at the peak stress decrease and the slope of the descending branch increases, when the equivalent diameter and aspect ratio of the specimen increase. The proposed model agrees well with the test results, irrespective of the compressive strength of concrete, concrete type, equivalent diameter, and aspect ratio of the specimen.

This study proposes a simple and rational stress-strain relationship model applicable to brick masonry under compression. The brick prism compression tests were conducted with different mortar strengths and with constant brick strength. From the observation of the test results, shape of the stress-strain curve is assumed to be parabola. In developing the stress-strain model, the modulus of elasticity, the strain at peak stress, and the strain at 50% of the peak stress on the descending branch were formulated from regression analysis using test data. Numerical and statistical analyses were then performed to derive equations for the key parameter to determine the slopes at the ascending and descending branches of the stress-strain curve shape. The reliability of the proposed model was examined by comparisons with actual stress-strain curves obtained from the tests and the existing model. The proposed model in this study turned out to be more accurate and easier to handle than previous models so that it is expected to contribute towards the mathematical simplicity of analytical modeling.

This study aims to predict the compressive strength of concrete using a machine-learning algorithm with linear regression analysis and to evaluate its accuracy. The open-source software library TensorFlow was used to develop the machine-learning algorithm. In the machine-earning algorithm, a total of seven variables were set: water, cement, fly ash, blast furnace slag, sand, coarse aggregate, and coarse aggregate size. A total of 4297 concrete mixtures with measured compressive strengths were employed to train and testing the machine-learning algorithm. Of these, 70% were used for training, and 30% were utilized for verification. For verification, the research was conducted by classifying the mixtures into three cases: the case where the machine-learning algorithm was trained using all the data (Case-1), the case where the machine-learning algorithm was trained while maintaining the same number of training dataset for each strength range (Case-2), and the case where the machine-learning algorithm was trained after making the subcase of each strength range (Case-3). The results indicated that the error percentages of Case-1 and Case-2 did not differ significantly. The error percentage of Case-3 was far smaller than those of Case-1 and Case-2. Therefore, it was concluded that the range of training dataset of the concrete compressive strength is as important as the amount of training dataset for accurately predicting the concrete compressive strength using the machine-learning algorithm.

Plastics are used in cover substrates for billboards, windows, large LED signboards, lighting devices, and solar panels because they are transparent and can be colored and shaped as desired. However, when plastic cover substrates installed in outdoor environments are constantly exposed to harsh conditions such as snow, rain, dust, and wind, their transparency deteriorates owing to watermarks and dust contamination. Herein, we investigated a simple dipping-press coating method that can impart hydrophobicity while maintaining the transparency, regardless of the plastic substrate type. A highly transparent and hydrophobic coating film was formed on a plastic substrate by a two-step process, as follows: (1) application of a polydimethylsiloxane–octadecylamine coating by a dipping process, and (2) embedding (1H,1H,2H,2H-heptadecafluorodec-1-yl) phosphonic acid–aluminum oxide nanoparticles by a thermal press process. The plastic substrates on which the highly transparent and hydrophobic coating film was formed showed 150° or higher hydrophobicity and 80% or higher visible light transparency. The coating method proposed herein can easily impart hydrophobicity and is compatible with any plastic substrate that must maintain prolonged transparency without contamination when exposed to adverse conditions.

The purpose of this study is to evaluate the workability and mechanical properties of concrete containing bottom ash, which is an industrial byproduct, as an aggregate. Twelve concrete mixtures, including concrete containing bottom ash aggregate (CCBA), are classified into three groups of W/C 0.45, 0.375, and 0.3 according to the target strength. Each group includes four mixtures in which natural aggregate and bottom ash are applied as fine and coarse aggregates according to particular ratios. On the basis of the test results, a reliable model to predict the 28-day compressive strength of CCBA is proposed by applying regression analysis. The proposed model points out that when applying bottom ash as aggregate, the concrete density is lowered, and W/C should be reduced to offset the lowered compressive strength. As a result of comparing experimental values with the existing design code models, it is found that while the fib model accurately predicts compressive strength development and tensile resistance capacity in general, the ACI 318 code overestimates the elastic modulus at the oven-dried density (ρc) range of 1840 kg/m3 and above. Accurate prediction of the mechanical properties of CCBA requires the measurement of additional experimental data that consider W/C and ρc as important parameters.

An effective dipping method for coating of textile fabrics with porous materials is proposed on the basis of the use of epoxy solution consisted of resins, crosslinkers, and dilution solutions. The removal rates of nitrogen oxides (NOx), sulfur oxides (SOx), and fine dust particles in the coated textile fabrics are accessed. The textile fabrics made of polyester are used to effectively reduce fine dust particles through static electricity. Zeolite and coconut shell activated carbon are used as porous material to reduce SOx and NOx, respectively. The effects of the epoxy content and dilution solution types on the SOx removal rate of textile fabrics coated with zeolite are evaluated to determine the optimum coating conditions. In addition, the effects of external environmental conditions, such as washing and freeze thawing, on the SOx and NOx removal rates of the textile fabrics coated with porous materials using the optimum coating conditions are examined. The test results show that the SOx removal rate of textile fabrics coated with zeolite decreases with the increase in the epoxy content. The decrease is 2.9 times larger for textile fabrics coated using deionized water than those coated using isopropyl alcohol. After one wash, the SOx removal rate decreases dramatically. However, the decrease is reduced by 16% when the epoxy content ratio is increased by 0.5%. The effects of washing and freeze thawing on the SOx and NOx removal rates of textile fabrics coated using the deionized water diluted with the epoxy content ratio of 2% are minimal. Consequently, to maintain stable SOx and NOx removal rates under external environmental conditions such as washing and freeze thawing, 98% deionized water dilution and 2% epoxy content ratio are required for the optimum coating of textile fabrics with zeolite and coconut shell activated carbon.

With the increasing trend of high-rise, large-scale, and functional modern architectural structures, lightweight aggregate (LWA) concrete that exhibits excellent strength and high functionality has garnered active research attention. In particular, as the properties of concrete vary considerably with the raw materials and the proportions of aggregates in the mix, in-depth research on weight reduction, strength improvement, and functional enhancements of aggregates is crucial. This study used the negative pressure coating of a mixed solution comprising epoxy (mixture of epoxy resin and crosslinker), hyper-crosslinked polymer, and titanium oxide (TiO2) nanoparticles on the LWA, and achieved an improvement in the strength of the LWA as well as a reduction in air pollutants such as NOx and SOx. Compared to a normal LWA with an aggregate impact value (AIV) of 38.7%, the AIV of the proposed epoxy–TiO2-embedded high-strength functional LWA was reduced by approximately half to 21.1%. In addition, the reduction rates of NOx and SOx gases resulting from the photocatalytic properties of TiO2 nanoparticles coated with epoxy were approximately 90.9% and 92.8%, respectively. Epoxy–TiO2, embedded in LWAs through a mixture, exhibited stability, high strength, and a reduction in air pollutant characteristics, despite repeated water washing. The LWA proposed herein offers excellent structural and functional properties and is expected to be used in functional lightweight concrete that can be practically applied in high-rise and large-scale architectural structures.

This study examined the effectiveness of zeolite addition to reduce the autogenous shrinkage of high-performance cement-based concrete (HPC). The zeolites were replaced up to 15% of the cement content by weight and their mean particle size varied from 5.6 to 16.7 µm. To evaluate the crack resistance of HPC containing zeolites, the ring tests and internal relative humidity measurements were performed at different ages. The compressive strengths were determined at 3, 7, 28 and 90 days of curing. Test results confirmed that the addition of zeolite was promising and favourable in enhancing the compressive strength, crack resistance and reducing the autogenous shrinkage of HPC due to synergistic pozzolanic and internal curing effects. The autogenous shrinkage tended to decrease with the increase in zeolite content and its particle size. In addition, the extent of the autogenous shrinkage development at the early ages decreased with higher zeolite content replaced. Furthermore, to predict the autogenous shrinkage of HPC containing zeolite, an improved model has been proposed, in which the conventional ultimate autogenous shrinkage strain and time function were modified by introducing new parameters accounting for the zeolite content and its particle size. It appeared that the proposed model was able to capture the autogenous shrinkage behaviour of HPC with or without zeolite, while the fib 2010 model underestimated the autogenous shrinkage of HPC containing less than 10% zeolite replacement.

The service life of concretes exposed to sulfate decreases as the concrete body expands due to the formation of gypsum and ettringite. Bacteria-based repair coating layers, which have been studied lately, are aerobic and very effective on the sulfate attack. In this study, bio-slime repair coating layers were fabricated using bacteria, and chloride diffusion experiments were performed. In addition, the service life of concrete under sulfate attack was evaluated using time-dependent diffusivity and a multi-layer technique. Chloride diffusivity was compared with sulfate diffusivity based on literature review, and the results were used to consider the reduction in the diffusion coefficient. In the analysis results, the service life of concrete was evaluated to be 38.5 years without bio-slime coating layer, but it was increased to 41.5−54.3 years using it. In addition, when the thickness of the bio-slime coating layer is 2.0 mm, the service life can be increased by 1.31−2.15 times if the sulfate diffusion coefficient of the layer is controlled at a level of 0.1 ~ 0.3 × 10−12 m2/s. Eco-friendly and aerobic bio-slime coating layers are expected to effectively resist sulfate under appropriate construction conditions.

This study examined the reliability and limitations of code equations for determining the shear friction strength of a concrete interface with construction joints. This was achieved by examining the code equations (ACI 318-14, AASHTO, and fib 2010) and comparing the results predicted by equations with experimental data compiled from 207 push-off specimens (133 rough and 74 smooth construction joints). The integrated mechanical model for the monolithic interface, derived from the upper-bound theorem of concrete plasticity, was also modified to estimate the shear friction strength of the construction joints. The upper limit for shear friction strength was formulated from a concrete crushing failure limit on the strut-and-tie action along the interfacial plane, to avoid overestimating the shear transfer capacity of transverse reinforcement with a high clamping force. Code equations are highly conservative and dispersive in predicting the shear friction strength of rough construction joints and yield large scattering in the data for the ratios between the measured and predicted shear friction strengths. The predictions obtained using the proposed model agreed well with test results, indicating correlating trends with the test results for evaluating the effects of various parameters on the shear friction strength of rough construction joints. According to the proposed model, the values of cohesion and coefficient of friction for concrete could be determined as 0.11 fc′0.65 and 0.64, respectively, for smooth construction joints and 0.27 fc′0.65 and 0.95, respectively, for rough construction joints, where fc′ is the compressive strength of concrete.

This study proposed a new binder as an alternative to conventional cement to reduce the heat of hydration in mass concrete elements. As a main cementitious material, low-heat cement (LHC) was considered, and then fly ash (FA), modified FA (MFA) by vibrator mill, and limestone powder (LP) were used as a partial replacement of LHC. The addition of FA delayed the induction period at the hydration heat curve and the maximum heat flow value (qmax) increased compared with the LHC based binder. As the proportion and fineness of the FA increased, the induction period of the hydration heat curve was extended, and the qmax increased. The hydration production of Ca(OH)2 was independent of the addition of FA or MFA up to an age of 7 days, beyond which the amount of Ca(OH)2 gradually decreased owing to their pozzolanic reaction. In the case of LP being used as a supplementary cementitious material, the induction period of the hydration heat curve was reduced by comparison with the case of LHC based binder, and monocarboaluminate was observed as a hydration product. The average pore size measured at an age of 28 days was smaller for LHC with FA or MFA than for 100% LHC.

The objective of this study is to examine the effect of the poor anchorage length of glass fiber reinforced polymer (GFRP) bars used for longitudinal reinforcement on the flexural and shear performances of beam elements in exterior beam⁻column connections made using high-strength materials. Six exterior beam⁻column connection specimens were tested under reversal cyclic loads applied at the free-end of the beam. The selected strength categories of materials in the beam element were as follows: 35 MPa and 70 MPa for the design compressive strength of concrete, 400 MPa and 600 MPa for the yield strength of conventional longitudinal steel bars, and 800 MPa for the tensile strength of the GFRP bar. All the longitudinal steel bars of the beams satisfied the minimum requirements of the provisions of ACI 318⁻14, whereas all the longitudinal GFRP bars of the beam were linearly anchored into the column section, resulting in poor anchorage length, especially for the beam with the concrete compressive strength of 35 MPa. The flexure-governed beams with GFRP bars exhibited a greater increasing rate in displacement at the pre-peak state and did not display the plastic flow characteristic after the peak load when compared with companion beams with steel bars. The beams with GFRP bars possessed lower diagonal cracking strengths and shear capacities than the companion beams with steel bars although the shear capacities of the beams with GFRP bars could be conservatively predicted using the design equation of ACI 440.1R⁻15 provision. The low elastic modulus and elongation capacity of GFRP bars resulted in large displacements and brittle post-peak beam performances. Furthermore, the lack of anchorage length of GFRP bars in exterior beam⁻column connection significantly reduced the flexural strength and ductility of the beam element.

This study develops a simple and rational shear stress-relative slip model of concrete interfaces with monolithic castings or smooth construction joints. In developing the model, the initial shear cracking stress and relative slip amount at peak stress were formulated from a nonlinear regression analysis using test data for push-off specimens. The shear friction strength was determined from the generalized equations on the basis of the upper-bound theorem of concrete plasticity. Then, a parametric fitting analysis was performed to derive equations for the key parameters determining the shapes of the ascending and descending branches of the shear stress-relative slip curve. The comparisons of predictions and measurements obtained from push-off tests confirmed that the proposed model provides superior accuracy in predicting the shear stress-relative slip relationship of interfacial shear planes. This was evidenced by the lower normalized root mean square error than those in Xu et al.’s model and the CEB-FIB model, which have many limitations in terms of the roughness of the substrate surface along an interface and the magnitude of equivalent normal stress.

This study examined the relative strength-maturity relationship of high-strength concrete (HSC) specifically developed for nuclear facility structures while considering the economic efficiency and durability of the concrete. Two types of mixture proportions with water-to-binder ratios of 0.4 and 0.28 were tested under different temperature histories including (1) isothermal curing conditions of 5°C, 20°C, and 40°C and (2) terraced temperature histories of 20°C for an initial age of individual 1, 3, or 7 days and a constant temperature of 5°C for the subsequent ages. On the basis of the test results, the traditional maturity function of an equivalent age was modified to consider the offset maturity and the insignificance of subsequent curing temperature after an age of 3 days on later strength of concrete. To determine the key parameters in the maturity function, the setting behavior, apparent activation energy, and rate constant of the prepared mixtures were also measured. This study reveals that the compressive strength development of HSC cured at the reference temperature for an early age of 3 days is insignificantly affected by the subsequent curing temperature histories. The proposed maturity approach with the modified equivalent age accurately predicts the strength development of HSC.

This study examined the stress-strain behavior of 10 calcium hydroxide (Ca(OH)2)-activated Hwangtoh concrete mixes. The volumetric ratio of the coarse aggregate (Vagg) and the water-to-binder (W/B) ratio were selected as the main test variables. Two W/B ratios (25% and 40%) were used and the value of Vagg varied between 0% and 40.0%, and 0% and 46.5% for W/B ratios of 25% and 40%, respectively. The test results demonstrated that the slope of the ascending branch of the stress-strain curve of Ca(OH)2-activated Hwangtoh concrete was smaller, and it displayed a steeper drop in stress in the descending branch, compared with those of ordinary Portland cement (OPC) concrete with the same compressive strength. This trend was more pronounced with the increase in the W/B ratio and decrease in Vagg. Based on the experimental observations, a simple and rational stress-strain model was established mathematically. Furthermore, the modulus of elasticity and strain at peak stress of the Ca(OH)2-activated Hwangtoh concrete were formulated as a function of its compressive strength and Vagg. The proposed stress-strain model predicted the actual behavior accurately, whereas the previous models formulated using OPC concrete data were limited in their applicability to Ca(OH)2-activated Hwangtoh concrete.

The objective of this study is to examine the compressive strength and durability of very high-volume SCM concrete. The prepared 36 concrete specimens were classified into two groups according to their designed 28-day compressive strength. For the high-volume SCM, the FA level was fixed at a weight ratio of 0.4 and the GGBS level varied between the weight ratio of 0.3 and 0.5, which resulted in 70–90% replacement of OPC. To enhance the compressive strength of very high-volume SCM concrete at an early age, the unit water content was controlled to be less than 150 kg/m3, and a specially modified polycarboxylate-based water-reducing agent was added. Test results showed that as SCM ratio (RSCM) increased, the strength gain ratio at an early age relative to the 28-day strength tended to decrease, whereas that at a long-term age increased up to RSCM of 0.8, beyond which it decreased. In addition, the beneficial effect of SCMs on the freezing-and-thawing and chloride resistances of the concrete decreased at RSCM of 0.9. Hence, it is recommended that RSCM needs to be restricted to less than 0.8–0.85 in order to obtain a consistent positive influence on the compressive strength and durability of SCM concrete.

Alkali-activated ground granulated blast-slag (AAS) is the most obvious alternative material for ordinary Portland cement (OPC). However, to use it as a structural material requires the assessment and verification of its durability. The most important factor for a durability evaluation is the degree of carbonation resistance, and AAS is known to show lower performance than OPC. A series of experiments was conducted with a view to investigate the carbonation characteristics of AAS binder. As a consequence, it was found that the major hydration product of AAS was calcium silicate hydrate (CSH), with almost no portlandite, unlike the products of OPC. After carbonation, the CSH of AAS turned into amorphous silica gel which was most likely why the compressive strength of AAS became weaker after carbonation. An increase of the activator dosage leads AAS to react more quickly and produce more CSH, increasing the compaction, compressive strength, and carbonation resistance of the microstructure.

The objective of the present study is to assess the flexural residual strengths of lightweight aggregate concrete (LWAC) reinforced with micro-steel fibers. Further, the material class of such concrete was examined through comparison with the fiber-reinforced concrete classification specified in the provisions of fib 2010. Fourteen beam specimens were classified into L (21 MPa [3.05 ksi]) and H (40 MPa [5.80 ksi]) groups according to the design compressive strength of LWAC. The volume fraction of micro-steel fibers varied from 0 to 1.5% at a spacing of 0.25% in each beam group. From the beam test results under the three-point loading condition, flexural stress-crack mouth opening displacement (CMOD) curves were measured and then discussed as a function of the fiber reinforcing index (βf). The flexural residual strengths corresponding to four different CMOD values (0.5, 1.5, 2.5, and 3.5 mm [0.02, 0.06, 0.1, and 0.14 in.]) were compared with previous empirical equations and fib 2010 classification. The various analyses of the measured results indicate that βf can be regarded as a critical factor in directly determining the magnitude of flexural residual strengths and assessing material classification. The proposed refined equations improve the accuracy in predicting the flexural residual strengths of concrete beams with different densities and reinforced with different types of steel fibers. Consequently, microsteel fibers are a promising partial replacement for conventional steel reinforcing bars to enhance the ductility of LWAC elements. [ABSTRACT FROM AUTHOR]

A reliable compressive stress-strain model was established for concrete with varying densities reinforced with either steel fibers alone, or a combination of steel fibers and micro-synthetic fibers. Moreover, a simple equation was presented to determine the compressive toughness index of fiber-reinforced concrete in a straightforward manner. The fiber reinforcing index was introduced to explain the effect of various parameter conditions of fibers on the enhancement of the concrete properties under compression. Numerical and regression analyses were performed to derive equations to determine the key parameter associated with the slope at the pre- and post-peak branches and compressive toughness index through extensive parametric studies. The proposed models are promising tools to accurately predict the stress-strain relationships of fiber-reinforced concrete with different densities, resulting in less-scattered values between experiments and predictions, and reasonably assess the efficiency of fiber reinforcements in enhancing the compressive response of concrete. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the effect of steel fiber content and type on the compressive and flexural ductility capacities of lightweight aggregate concrete (LWAC). Fiber-reinforced LWAC specimens were divided into four groups according to the type of fibers, such as conventional macrosteel fibers (SFs) with hooked ends, straight copper-coated microsteel fibers (CMSFs), crimping-shaped CMSFs, and hooked-end CMSFs. The fibervolume fractions (Vf) were 0.5, 1.0, and 1.5%. This study also modifies the ASTM C1018 method by using the initial crack point calculated from the elastic theorem to save a tedious and elaborated effort in determining the reference point at the load-deflection curve, particularly for beams with a strong hardening response. The test results revealed that the hooked-end CMSFs were better than SFs and crimping-shaped CMSFs with the same shape and length at decreasing the slope of the applied loads at descending branches of the compressive stress-strain and flexural loaddeflection curves for the LWAC. Compressive and flexural toughness indexes were derived as functions of the fiber reinforcing index based on the regression analysis of test data to assess the ductility improvement of LWAC with steel fibers. [ABSTRACT FROM AUTHOR]

The atmospheric purification capacity of concrete has not been adequately investigated. This study examines the feasibility of using sustainable foam-concrete granules as a porous material for reducing air pollutants in concrete. To enable the removal of nitrogen oxide (NOx) and sulfur oxide (SOx) using titanium dioxide (TiO2) nanoparticles, foam concrete was crushed into granules with porosity exceeding 30%. Ordinary portland cement (OPC), fly ash (FA), and slag cement were used as source cementitious materials. OPC was replaced with 0 to 40% FA and 0 or 40% slag cement by weight. Test results indicate that 30% FA and unit cementitious materials content exceeding 500 kg/m³ (31.2 lb/ft³) are optimal for replacing cement and foam-concrete granules, respectively. Considering the particle-size distribution and specific surface area, 6 to 13 mm (0.24 to 0.51 in.) and 6 to 9 mm (0.24 to 0.35 in.), were selected as optimal granule sizes. The coating procedures yielded improved SOx and NOx removal, with the removal rates reaching 83.8 and 45% using granules of 6 to 9 mm (0.24 to 0.35 in.), respectively. Consequently, the foam-concrete granules coated with TiO2 nanoparticles are promising in developing porous concrete with the reduction capability of air pollutants. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine the effect of different wall-to-base connections on the flexural performance of precast alllightweight aggregate concrete (ALWAC) shear walls. The wall-to-base connection techniques considered the practical construction joint and seismic resistance of precast shear walls by using the conventional spliced sleeve, one-touch coupler, welded steel plate, and bolted steel plate approaches. The precast shear walls were tested under constant axial loads and cyclic lateral loads. The backbone curves determined from the lateral load-displacement relationship of the precast shear walls are compared with the predictions using the two-dimensional (2-D) nonlinear laminar approach procedure under the assumption that the connections are performed as a perfectly rigid joint. The displacement ductility ratios of the precast shear walls were also compared with the predictions calculated from the design equations proposed for conventional monolithic shear walls. The precast shear wall connected by the one-touch coupler technique exhibited poor flexural performance with lower moment capacity and flexural ductility than the other wall specimens. Meanwhile, the precast shear walls with the welded steel plate or bolted steel plate connection displayed very close flexural performance to the conventional monolithic shear wall, although their displacement ductility ratio and work damage indicator were slightly lower than those of the conventional monolithic shear wall. Consequently, the lateral load-displacement backbone curves of the precast shear walls with the welded steel plate or bolted steel plate connection are in good agreement with the predictions. [ABSTRACT FROM AUTHOR]

This study aims to examine the axial performance and confinement effect in reinforced concrete columns with different concrete unit weights (ρc). Eleven columns, classified into all-lightweight aggregate concrete (ALWAC), sand-LWAC (SLWAC), and normalweight concrete (NWC) groups, were tested under concentric axial loads. The existing data compiled from the previous NWC and LWAC column specimens are also used to compare the confinement effect in LWAC columns with those of NWC columns at similar levels of the transverse reinforcement index (ωsh). Test results show that the lateral confining pressure by the transverse reinforcement tends to decrease with the decrease in ρc. Hence, the strength gain factors, strains corresponding to the peak stress of the stress-strain performance, and axial ductility ratio of columns are lower for LWAC columns compared with those for the counterpart NWC columns. The decreasing rates of the axial ductility ratio with the decrease in ρc were more conspicuous in columns with more transverse reinforcement. The increasing rate in the tensile strains of hoops owing to the increase in the applied axial loads is lower for columns with a lower ρc. Hence, modification factors as a function of ρc in the stress-strain model of confined concrete proposed by Razvi and Saatcioglu are introduced herein to account for the reduced confinement effectiveness due to the crack and failure characteristics of LWAC. [ABSTRACT FROM AUTHOR]

This study investigated the reliability and limitation of the minimum and maximum longitudinal reinforcement ratios specified in code provisions regarding the flexural ductility of lightweight aggregate concrete (LWAC) beams. From the load-displacement curves of beams computed using a two-dimensional (2-D) nonlinear analysis approach, displacement ductility ratio was simply formulated and validated through comparisons with test data compiled from 29 normalweight concrete (NWC) and 47 LWAC beam specimens. The 2-D analysis revealed that the displacement ductility ratio of beams decreases with the decrease in the unit weight of concrete. In addition, the ductility of concrete beams rather decreases with the decrease in the longitudinal tensile reinforcement ratio (ρs) when the latter varies within the ranges not exceeding the minimum requirements. Therefore, based on the proposed displacement ductility ratio model, compensation factors are generalized for LWAC beams to adjust the minimum and maximum longitudinal reinforcement ratios specified in code provisions with respect to retaining a flexural ductility equivalent to that of their counterpart NWC beams. To achieve flexural ductility comparable to that of NWC beams, LWAC beams require more minimum amount and less maximum amount of longitudinal tensile reinforcement when compared with those specified in code provisions. Consequently, the proposed compensation factors can be implemented by examining the reliable ranges for longitudinal reinforcement ratios in LWAC beams. [ABSTRACT FROM AUTHOR]

Ultra-High-Performance Concrete (UHPC) has been increasingly widely applied in civil and infrastructure engineering because of its outstanding properties in strength and durability. In particular, the research and application of UHPC in structures requiring high load-bearing capacity and high impact resistance, such as manhole covers, will have great practical significance. This paper presents experimental results of some properties of UHPC and uses the finite element method (FEM) to analyze and design two types of UHPC manhole covers according to the requirements for BS EN 124 classes A15 and B125. The research results show that the UHPC manhole covers need only 30 mm thickness without steel bar can ensure class A15. However, to meet the requirements of class B125, the UHPC manhole covers with a thickness of 60 mm need a steel mesh of diameter size 10 mm reinforcement. The test results prove that the load-bearing capacity of the UHPC manhole covers from the experiments is consistent with the theory. [ABSTRACT FROM AUTHOR]

The primary objective of the present study is to examine the effectiveness of previously developed prefabricated bar units with seismic details in the jacket section in improving the flexural performance of columns jacketed with reinforced concrete (RC) sections. One non-seismic existing column, two bonded-type laminate-jacketed columns, and six RC-jacketed columns were tested under constant axial load and cyclic lateral loads. The flexural strength of the columns was examined by comparing with predictions obtained using the ACI 318-14 procedure and nonlinear section lamina analysis considering the confinement effect provided by the jacket. The flexural ductility of RC jacketed columns was assessed by using the work damage indicator and the performance-based approach proposed by Sheikh and Khoury for seismic virgin columns. The test results revealed that the proposed RC jacketing approach using prefabricated bar units has the potential to enhance the flexural stiffness, strength, and ductility of deficient columns by providing a reliable confinement. The flexural capacity of jacketed columns can be conservatively estimated by the ACI 318-14 procedure and predicted more accurately by the section lamina analysis. In addition, RC-jacketed columns with prefabricated bar units can be designed to possess moderate ductility performance by adjusting the amount of transverse reinforcement in the jacketed section. [ABSTRACT FROM AUTHOR]

The present study examined the flexural performance of continuous two-span lightweight aggregate concrete (LWAC) T-beams. A total of 12 two-span beams were prepared considering full-scale dimensions that can be typically observed in beams of mid- to low-rise buildings. The test parameters for each group of all-LWAC and sand-LWAC beams were the compressive strength of concrete (fc ') and amount of longitudinal tensile reinforcement (As) in accordance with the minimum and maximum amounts specified in the ACI 318-14 code provisions. The reliability of the equivalent rectangular stress block and degree of moment redistribution (ß) recommended in the code provisions was ascertained for the present beams through a comparison of the measured ultimate load capacity and moment redistribution. The test results showed that the ACI equivalent stress block gives a conservative result for all the beams in estimating the ultimate load capacity of two-span LWAC beams, although this conservatism decreases as As increases. The present two-span LWAC T-beams exhibited a lower displacement ductility ratio than simply supported normal weight concrete (NWC) beams of the same longitudinal reinforcement index (s). Thus, the fib model and ACI 318-14 equations overestimated the ß values of the LWAC T-beams. Overall, the maximum As specified in the ACI 318-14 provision for preventing brittle failure of beams needs to be reduced for LWAC beams to achieve design requirements equivalent to those of NWC beams. [ABSTRACT FROM AUTHOR]

This paper presents a new section enlargement strengthening technique based on prefabricated steel arrangement approach employing V-ties as a supplementary transverse reinforcement in the jacket section to enhance the structural performance of nonseismic or deteriorated columns. Nine full-scale columns were tested to failure under concentric axial loads to explore the significance and shortcomings of the proposed strengthening technique. The test parameters included the arrangement method of closed peripheral hoops and amount of transverse reinforcement in the jacket section. Thus, the strengthened columns were classified into two groups as follows: 1) the L-group for overlapped channel-shape bar hoops; and 2) the P-group for prefabricated bar unit hoops. The test results confirmed that the axial strength of the strengthened columns is conservatively determined using the nominal design equation of the ACI 318-14 provision. The supplementary V-ties are effective in preventing the premature failure of longitudinal bars in the jacket section and the sudden decreases in the load-transfer capacity of the strengthened columns, indicating that the strengthened P-group columns had an axial ductility more than 1.39 times higher than that of the existing column. Therefore, the developed technique exhibits significant potential for seismic section enlargement strengthening of columns by providing core concrete with a high lateral confinement and preventing the premature buckling of longitudinal bars. [ABSTRACT FROM AUTHOR]

The objective of the present study is to provide a databank and comprehensible design equations of the mechanical properties of concrete prepared using different expanded lightweight aggregates. For the statistical database, 25 lightweight aggregate concrete (LWAC) mixtures using expanded bottom ash and dredged soil granules were tested under design compressive strengths of 18, 24, and 35 MPa (2.61, 3.48, and 5.08 ksi) and targeted ovendried densities between 1300 and 1800 kg/m3 (81.6 and 112.4 lb/ ft3). Wherever feasible, the mechanical properties measured in the present concrete specimens were compared with those data compiled from LWAC specimens made of expanded clay and/or fly ash granules. The mechanical properties including the moduli of elasticity and rupture, stress-strain relationship, splitting and direct tensile strengths, shear friction strength, and bond strength were proposed as power functions of the compressive strength and oven-dried density of concrete. The mechanical properties predicted using the proposed equations closely agreed with the test results; the coefficient of variation of the ratios between the experiments and predictions was mostly less than 0.18. In addition, the proposed formulae for the compressive strength development and stress-strain relationship corresponded adequately with the experimental response of LWAC. Meanwhile, the design equations of the fib model resulted in overestimations while predicting the earlystrength gain, direct tensile strength, and bond strength of LWAC. Overall, the proposed equations possessed adequate potential to properly evaluate the different mechanical properties of concrete prepared using expanded lightweight aggregates. [ABSTRACT FROM AUTHOR]

RC (Reinforced Concrete) members are always subjected to loading conditions and have construction joints when constructed on a big scale. Service life for RC structure exposed to chloride attack is usually estimated through chloride diffusion test in sound concrete, however the test is performed without consideration of effect of loading and joint. In the present work, chloride diffusion coefficient is measured in concrete cured for 1 year. In order to evaluate the effect of applied load, cold joint, and mineral admixtures, OPC (Ordinary Portland Cement) and 40%-replaced GGBFS (Ground Granulated Blast Furnace Slag) concrete are prepared. The diffusion test is performed under loading conditions for concrete containing cold joint. Investigating the previous test results for 91 days-cured condition and the present work, changing diffusion coefficients with applied stress are normalized considering material type and cold joint. For evaluation of service life in RC continuous beam with 2 spans, nonlinear analytical model is adopted, and service life in each location is evaluated considering the effects of applied stress, cold joint, and GGBFS. From the work, varying service life is simulated under various loading conditions, and the reduced results due to cold joint and tensile zone are quantitatively evaluated. The effect of various conditions on diffusion can provide more quantitative evaluation of chloride behavior and the related service life. [ABSTRACT FROM AUTHOR]

This study proposed a practical strengthening technique for enhancing the seismic behavior of reinforced concrete shear walls using prestressed wire ropes as a lateral reinforcement at the wall boundary elements. An unstrengthened wall and six strengthened walls were tested under constant axial load and cyclic lateral loads to explore the significance and feasibility of the developed seismic-strengthening procedure. The main variables investigated were the amount of wire rope and height of the jacket section for strengthening. Test results revealed that the shear walls strengthened with wire ropes in their boundary elements had better buckling resistance of longitudinal reinforcement and ductility behavior than the non-seismic shear wall. Unlike the brittle behavior of the unstrengthened wall, the strengthened walls exhibited a highly enhanced ductile pattern in a lateral load--lateral displacement relationship. Thus, the strengthened walls achieved the displacement ductility ratio capacity required for the design of a medium ductility shear wall. In particular, the strengthened wall with a lateral reinforcement index of 0.174 met the minimum displacement ductility ratio requirement for a highly ductile shear wall. Considering the enhanced flexural behavior, including the strength, stiffness, and ductility, along with the construction efficiency, a recommendation could be made that the height of the jacket section when strengthening shear walls not exceed 0.76 times the wall height. Ultimately, the developed strengthening approach showed significant potential in enhancing the flexural stiffness, strength, and ductility of existing non-seismic shear walls. [ABSTRACT FROM AUTHOR]

This study examined the flexural behavior of reinforced concrete (RC) columns with V-shaped ties as an alternative to the conventional crossties specified in ACI 318-14. Ten columns were tested to failure under constant axial loads and reversed cyclic lateral loads with the aim of exploring the potential for practical application of the proposed V-tie arrangement for enhancing column ductility. The parameters investigated were the axial load level, the compressive strength of concrete, and the column section size. The backbone curves of columns obtained from the reversed lateral load-displacement relationship were compared with predictions derived using a nonlinear two-dimensional (2-D) lamina method. Test results ascertained that the conventional crossties with a 90-degree hook are unfavorable to the enhancement of the flexural ductility of columns and prevention of the premature buckling of longitudinal bars, particularly under high axial load levels, owing to the opening of their 90-degree hooks. Meanwhile, the extraction of V-tie legs from the core concrete was not observed until the columns failed. As a result, higher displacement ductility ratio and work damage indicator were obtained for V-tie columns than for crosstie columns, indicating that the superiority of the V-ties to the conventional crossties in enhancing the flexural ductility of columns becomes more pronounced as the axial load level and concrete compressive strength increase. The flexural behavior of RC columns with V-ties could be accurately evaluated using the proposed 2-D lamina approach. However, the slope at the descending branch of the lateral load-displacement curve of the crosstie columns was lower than the corresponding prediction results owing to the opening of the 90-degree hooks. [ABSTRACT FROM AUTHOR]