Ordinary Concrete Structures Research Articles

Exploring Ultimate Flexural Strengths of Ultra-High-Performance Concrete (UHPC) Samples through Experimental Analysis in Comparison with Ordinary Concrete Structures

Exploring Ultimate Flexural Strengths of Ultra-High-Performance Concrete (UHPC) Samples through Experimental Analysis in Comparison with Ordinary Concrete Structures

Finite Element Method Simulation Study on the Temperature Field of Mass Concrete with Phase Change Material

Phase change materials can be converted between solid, liquid, and gaseous states, absorbing or releasing a large amount of heat. PCM is incorporated into concrete to adjust the temperature difference between inside and outside of concrete, which can reduce cracking. In this paper, the finite element analysis method is used to establish the model of an ordinary concrete structure, doped with phase change materials, on the basis of mechanical properties and a temperature regulation test performed by calculating the adiabatic temperature rise of concrete with different contents of composite phase change material, comparing the experimental and simulation results of the ordinary concrete structures with phase change materials, and analyzing the change in temperature field of the concrete structure with the content of self-prepared composite phase change materials. It is found that the addition of self-prepared composite phase change materials reduces the temperature peak of the concrete structure in the stage of hydration heat and delays the time taken to reach the temperature peak. Then, the temperature field of the phase change mass concrete structure is established, and the influence law of composite phase change material admixture on the temperature field of mass concrete is summarized through the time–temperature curves of different admixture amounts and positions so as to predict the possibility of cracks in mass concrete.

The flexural strength of high-ductile concrete in saline-alkali area

Sulfate corrosion is an important cause of accelerated structural failure in concrete structures in coastal and saline alkali areas. High ductility concrete has good tensile and durability properties, and is therefore widely used for the repair and reinforcement of damaged structures. To investigate the flexural performance of high ductility concrete on ordinary concrete structures in saline alkali environments, experimental methods were used to test it. The experimental data validated that the bearing capacity of the 10 mm specimen reinforced with high ductility concrete before and after corrosion is 125 kN and 117 k, respectively. After reinforcement and corrosion, the bearing capacities of the specimens were 115 kN, 129 kN, and 139 kN, respectively. In addition, sodium sulfate reduced the deformation capacity of the original specimen by 13.9 %, but after reinforcement, the deformation capacity of the specimen increased by at least 97.1 %. Compared to reinforced specimens in non saline alkali environments, the deformation capacity of reinforced specimens in saline alkali environments decreases by no more than 23 %. Compared to unreinforced specimens, the strain capacity of reinforced concrete and longitudinal bars in sulfate environments increased by at least 28.1 % and 34.5 %, respectively. However, compared to reinforced specimens in conventional environments, the strain capacity of reinforced specimens in sulfate environments decreased by no more than 19 %. The above results indicate that high ductility concrete can effectively improve the bending resistance of specimens, while also slowing down the corrosion of sulfates on specimens and effectively extending the service life of concrete structures.

Integration of Java Programming-Based Pert and Earned Value Management Methods Based on Residential Precast Case Study to Improve Project Cost Efficiency

The need for residential houses is still high for property and construction commodities. The availability of land and market prices for residential houses continue to increase yearly. Only 45.04% of Jakarta residents had a home ownership status in 2020. 2021 is the precast building mode. It is justified that precast construction structures can save 35% on construction costs and are 27.33% more reliable than ordinary concrete structures. The research examines the integration of the PERT method and earned value management (EVM) based on Java programming in residential precast case studies. The results of this study are that the implementation of the PERT method can increase the efficiency of project duration by 6%, and the implementation of the EVM method can increase project cost efficiency by 7% with the indicators Schedule Performance Index (SPI) = 1.01 (under schedule) and Cost Performance Index = 1, 07 (Under Budget)

Experimental and numerical study on seismic performance of prefabricated new fly ash foam concrete structure

In view of the current situation of solid waste resource utilization and the introduction of exterior wall insulation limit policy, this paper proposes a new type of assembled fly ash foam concrete structure for rural areas. After that, a 1:3 scaled specimen model was designed for the proposed static test with three actuators loaded synchronously, and the seismic performance of each floor of the structure was investigated by hysteresis curves, skeleton curves, ductility coefficients, equivalent damping ratios, and stiffness degradation curves, and compared with that of ordinary concrete structures. Finally, ABAQUS was used to establish the structural model with different porosity, and the effects of different porosity on the seismic performance of the structure were determined by comparing the results of tests and finite elements. The results show that the peak load of the assembled new fly ash foam concrete structure model is 84.9 kN, the ultimate displacement is 49.5 mm, the equivalent damping ratio is increased by 24.0 %, and the ductility coefficient is 2.15 compared with that of the ordinary concrete structure, with the increase of the pore rate, the damage location is mainly concentrated from the surface of the specimen to the corners of the doors and windows. The pore rate of 0.101 can simultaneously meet the requirements of structural lighting, economy, and load-bearing capacity. The proposal of an assembled new fly ash foam concrete structure enriches the structural form and lays the foundation for the design and application of this structure in the future.

Towards enhancing the anti-progressive collapse performance of concrete beam-column structures via ECC and BFRP: Experiments and mechanisms

To investigate the beneficial effects of engineered cementitious composite (ECC) and basalt fiber reinforced polymer (BFRP) bars on the anti-progressive collapse robustness of concrete structures, three high-performance material composite specimens strengthened with ECC, hybrid reinforcements (BFRP bars and steel bars) or their combination and one ordinary concrete beam-column specimen were tested and simulated based on the pushdown method. Moreover, the influence relationships and improvement mechanisms of ECC, hybrid reinforcements, and their combination on structural robustness were revealed. The results demonstrated that all three composite specimens underwent typical flexural action (FA), compressive arch action (CAA), and catenary action (CA) stages and had enhanced capacities for structural dissipation of energy. In particular, their bearing capacity and ductility were dramatically distinguished from those of ordinary concrete structures. In comparison with the ordinary concrete specimen, ECC delayed the displacement of the initial fracture for longitudinal bars (33.7%) and the ultimate displacement (7.6%). The hybrid reinforcements with BFRP bars and steel bars increased the CAA capacity by 60% due to secondary stiffness action plus CAA mechanisms. More importantly, the combination of ECC and hybrid reinforcements exhibited a combined strengthening and toughening mechanism that resulted in a significant synergetic effect. The increase in the maximum load of the quasi-static or pseudo-static response owing to the combined strengthening and toughening mechanism surpassed the sum of individual load increase by the ECC and BFRP bars. Finally, based on the research findings, a design strategy for combining ECC (beam bottom) and hybrid reinforcements with BFRP bars and steel bars in a beam was recommended to enhance structural robustness.

A time-variant model of chloride diffusion in prestressed concrete cylinder pipe (PCCP) considering the effects of curing age

Chloride penetration is considered as the most responsibility to steel corrosion for PCCP during service. Compared with ordinary concrete structures, the curing method of PCCP is generally steam-curing. Despite numerous contributions have shown that curing age has significant effect on the resistance to chloride penetration of concrete. There is still a lack of critical understanding of the curing age effect on the chloride migration in steam-cured concrete. For this reason, this paper aims to establish a chloride diffusion model suitable for PCCP. In this study, the non-steady-state chloride diffusion coefficient and chloride concentration of steam-cured concrete are measured through RCM test and chloride diffusion simulated test, respectively. The apparent chloride diffusion coefficient and surface chloride concentration are calculated based on Fick’s second law. Moreover, the instantaneous chloride diffusion coefficient was estimated. It is found that the steam-cured concrete cannot ignore the influence of curing age on the chloride penetration resistance, according to RCM test results, the non-steady-state chloride diffusion coefficient of 28 days decreased by 33 % compared with that of 3 days, while the chloride diffusion coefficient of 90 days decreased by 15 % compared with 28 days under steam curing. The larger the curing age, the smaller the chloride concentration at each depth, as well as the chloride diffusion coefficient and surface chloride concentration. In addition, it can be concluded that with the increase of exposure time, the chloride diffusion coefficient decreases gradually, while the surface chloride concentration increases gradually. Thus, the two kinds of test results and theoretical analysis were combined to establish the time-variant models of instantaneous chloride diffusion coefficient and surface chloride concentration of steam-cured concrete considering the effects of curing age and exposure time. On this basis, a new chloride diffusion model considering the effects of curing age, exposure time, the time-variant chloride diffusion coefficient and time dependence surface chloride concentration was established, which plays an important role in durability evaluation of PCCP.

Mechanical behavior of PVC tube confined concrete and PVC-FRP confined concrete: A review

This paper presents a summary review of research focused on the mechanical behaviors of the PVC tube confined concrete (PTCC) and PVC-FRP confined concrete (PFCC). Using the PVC tube and prefabricated PVC-FRP tube as the confinement materials and protective jacket, these two new composite structures behave greater bearing capacity, higher ductility and better durability than ordinary concrete structures. This paper starts with an introduction of research findings on the behaviors of the PTCC members with respect to the static behaviors, the seismic behaviors and the long-term behaviors. Then, the research progress made on the PFCC is introduced with the same routine for discussing the PTCC. Followed with concluding the references focused on the PTCC and PFCC members, the development of the joint for connection of the PFCC column and RC beam is further described. Finally, some recommendations for future research of the PFCC structures are proposed for design and application of this composite system. This paper can help readers to better understand the PTCC and PFCC and provide meaningful information for their application in structural engineering.

Freeze-thaw resistance of recycled aggregate concrete damaged by simulated acid rain

Acid rain severely decreases the durability of ordinary concrete structures; however, the effect of acid rain on recycled aggregate concrete (RAC) remains unclear. To fill this gap, this study investigated the freeze-thaw resistance of RAC in response to simulated acid rain spraying. The effects of replacement ratios of recycled coarse aggregate (20%, 35%, and 50% by mass), acidity of simulated solutions (pH of 2.5 and 3.5), erosion time (0, 20 d, and 40 d), and the number of freeze-thaw cycles on the apparent state, quality loss, and relative dynamic elastic modulus (RDEM) of RAC were evaluated. The results demonstrate that the freeze-thaw resistance of RAC with different replacement ratios is unsatisfactory in comparison to ordinary concrete. Acid rain attack has no obvious effect on the mass loss rate of RAC, but it significantly influences the RDEM. The RDEM results indicate that acid rain attack weakens the capacity of RAC to resist freezing and thawing. Moreover, the freeze-thaw resistance of RAC decreases strongly with prolonged acid rain spraying time or with increased acidity of acid rain. These test results indicate several theoretical suggestions and potential implications for government and industry to increase energy conservation, pollution reduction, and recycling of resources.

FIBER REINFORCED SAND BACKFILL FOR UNDERGROUND PEDESTRIAN CROSSINGS

Crosswalk is an essential element of the transport system of any city. A priority assignment in any such crossing is to ensure the safety of pedestrians. Underground pedestrian crossings are much safer than crossings at another level, but they lose in attraction when it comes to cost. The cost of the construction of an underground pedestrian crossing often leads to project abandonment. The cost of construction can be reduced through the use of flexible corrugated metal structures instead of ordinary concrete structures. The stress-strain state of the structural shells need to be known to facilitate their rational design. The stress-strain state of flexible corrugated metal shells largely depends on the strength and deformation characteristics of the surrounding soil. Therefore, improving the characteristics of backfill soil is an urgent task in reducing the cost of construction for such tunnels. One way to improve the strength and deformation characteristics of soils is the use of reinforcement. Currently, there are a large number of reinforcement schemes and also associated reinforcing materials. One of the most prospective methods of soil reinforcement is the use of fibre filaments. Fibre reinforced soils have significantly higher strength and deformation characteristics in comparison with unreinforced soils. Numerical modelling of a tunnel shell made out of a corrugated metal structure was undertaken to evaluate the effectiveness of using fibre reinforced sand. Ordinary sand and sand reinforced with polypropylene fibres have been used as soil backfill. The calculation results for a pedestrian tunnel structure involving different strength and deformation characteristics of the backfill soil are presented in this article.

Service Life Prediction of Bagasse ash Blended Concrete in Marine Splash Zone

Supplementary cementitious materials are commonly used in concrete due to their superior performance such as higher strength and low heat of hydration when compared to ordinary Portland concrete. In addition to pozzolanic benefits, utilization of these materials leads to durable and sustainable concrete. Although several pozzolanic materials are available including industrial by-products for use in concrete, their utilization is considerably restricted due to inadequate performance evaluation in concrete. Sugarcane bagasse ash is a by-product from the sugar industries that is directly disposed as a waste material which leads to significant environmental degradation. Pozzolanic characteristics of sugarcane bagasse ash have been evidently reported in the previous research studies. However, durability of bagasse ash blended concrete and its service life prediction are not reported in the existing literature. In the study, sugarcane bagasse ash was processed based on appropriate characterization scheme and bagasse ash blended cements were produced. Permeability of bagasse ash blended concrete was investigated and compared with Portland cement concrete and fly ash blended concrete. Moreover, influence of cover depth on service life of concrete structure was investigated. Results of accelerated durability test were correlated with the parameters influencing the long term performance of the concrete. The service life of bagasse ash concrete structures was found to be higher than the ordinary concrete structure in the same exposure conditions.

Passive film formation and corrosion initiation in lightweight concrete structures as compared to self compacting and ordinary concrete structures at elevated temperature in chloride rich marine environment

Corrosion of reinforced concrete is one of the most critical durability concerns in the construction field. Researchers and engineers are examining and determining the performance of various types of reinforced concrete in saline and under various environmental conditions. This research is also a contribution to such corrosion studies and it aims at investigating passive film formation and the corresponding corrosion and its extent in the ordinary (OC), self-compacting (SSC) and lightweight concrete (LWC) structures at normal and elevated temperature. For this purpose total of 18 specimen including 6 specimens of each OC, SCC and LWC were prepared with 5% and 3% total chloride, respectively and kept in environmental chambers at 30, 40 and 50°C. After six months of corrosion observations i.e., corrosion potentials, currents and gravimetric mass loss, interesting and novel results were obtained on comparing the corrosion observations of all the above types of concrete.

Theoretical analysis and experimental investigation on flexural performance of steel reinforced ultrahigh toughness cementitious composite (RUHTCC) beams

UHTCC (ultrahigh toughness cementitious composite), which is a kind of ultrahigh toughness cementitious composites material, exhibits pseudo strain hardening feature when subjected to tension load, and has enormous ductility and prominent crack dispersal ability. Accordingly, UHTCC can improve mechanical behavior of ordinary concrete structure especially its durability, and has been regarded as historical breakthrough to traditional cementitious materials. In this paper, the study focuses on flexure behavior of steel reinforced beam made of UHTCC. Based on the plane section assumption, along with two equilibrium equations of force and moment, the formulae to calculate the flexural load capability for the reinforced ultrahigh toughness cementitious composite (RUHTCC) beam were developed under the assumption that the compression stress-strain relationship in the UHTCC material is a bilinear model. Following this, the simplified formulae were further evolved by effective rectangle stress distribution approach in order to facilitate design of practical engineering. Two effective parameters introduced in effective rectangle approach were determined. The mathematical expressions to evaluate limited reinforcement ratio, flexural stiffness as well as ductility index were proposed, too. Last, two series of different reinforcement ratios of the RUHTCC beams were tested in four-point flexure loading. For comparison purposes, ordinary RC (reinforced concrete) beams also were prepared. Both moment curvature curves and load mid-span displacement curves were recorded and compared with the theoretical calculations. A good agreement between them was found, which validates the proposed theoretical formulae. For ductility index, a slightly big difference between the experimental values and the calculated ones exists. The experimental results show that, compared to control RC beams, the RUHTCC beam can improve both flexural capacity and ductility index, and the degree of improvement will decrease with the increase in the reinforcement ratio. Particularly, the results also reveal that lager crack width in control beams can be greatly reduced by formation of tightly-spaced fine cracks in UHTCC, which offers more durable structures.

When plasticity?

The paper considers the broad question of when and to what extent the theory of plasticity is useful in the analysis and design of reinforced concrete structures at the ultimate limit state of collapse. It covers early lower- and upper-bound approaches to design, and discusses various objections to the application of plasticity theory to concrete, concentrating on the need for adequate ductility – nowadays perhaps provided by fibre rather than bar reinforcement – and the crucial matter of size effect. It concludes that plasticity theory can be useful for the design of ordinary concrete structures known to have ductile failure modes, but that great care and wariness are needed when attempting to extrapolate its use to unusual structures and particularly to structures of large size without adequate ductility.

Influence of Electrochemical Chloride Extraction on the Performance of Prestressed Concrete under Dynamic Loading Conditions

One of the major causes of corrosion of reinforced concrete structures worldwide is chloride. With progressing corrosion, the integrity of the structure is at stake and repair measures are necessary. In recent years electrochemical repair methods such as chloride extraction or cathodic protection have become increasingly popular. Chloride extraction is less expensive as compared to traditional patch repair methods due to its short duration. It is accepted for application on ordinary concrete structures with mild steel reinforcement. Its application on prestressed concrete, however, has been ruled out because of the danger of hydrogen embrittlement. Contradicting results of research on the subject have suggested that chloride extraction might be a feasible repair option for prestressed concrete structures, thus leading to major cost savings for bridge owners. This study investigated the feasibility of chloride extraction on prestressed concrete structures. A distinction was made between hydrogen embrittlement, which temporarily reduces the ductility of steel, and hydrogen-induced stress corrosion cracking, which leads to sudden and unexpected collapse of the structure. The most commonly accepted test methods for hydrogen embrittlement are constant extension rate tests, but they give little indication of the performance of the prestressed tendons under serviceability conditions. In this study, along with constant extension rate tests, 22 prestressed concrete specimens were also tested using a fatigue test program. The fractured surfaces were carefully investigated to identify signs of hydrogen embrittlement and to rule out any other causes of failure. The results of the study suggest that chloride extraction temporarily reduces the fatigue life of prestressed steel. Although hydrogen-induced stress corrosion cracking was not observed for the type of steel investigated in the main study, it occurred for a different type of steel. Statistic analysis of the fatigue tests also suggested the possibility of hydrogen-induced stress corrosion cracking for the investigated steel; therefore, chloride extraction should not be applied to prestressed concrete structures.

着色材の添加量がコンクリートの表面色彩に及ぼす影響

Ordinary concrete structures are colorless and monotony. Therefore, they give an artificial and dreary impression. Many approaches for harmonizing concrete with surrounding landscape have been investigated. The coloring concrete is an approach to provide concrete with a favorable impression. The various highlights and contrasts of the scene may enable to readily distinguish elements from one another and to pick those that are most important to us at the moment. The pigment for coloring concrete, whose main component is iron oxide, can give any color without white and blue. The pigment whose main component is chrome oxide makes the color of concrete blue. The pigment whose main component is titanium oxide makes the color of concrete white. Furthermore, carbon black gives black color. When some types of pigment are mixed, the variation of concrete color is expected to be spread much more. In this paper, the effect of the dosage and the type of pigment on the color of concrete is discussed. The method to estimate the lightness and color shade of the color-conditioned concrete is proposed. The proposed method can be also available for the estimation of the color-conditioned concrete with several types of pigments. Normal Portland cement concrete and high volume blast furnace slag cement concrete were used for test.

The investigation of aggregate grain size effect on fracture toughness of ordinary concrete structures

The material under investigation was ordinary conerete of B 20 class, different in the sizes of coarse aggregate and water-cement ratio of the same value w/c=0.55. It was found during the tests that there were two kinds of sample cracking mechanisms. Some samples cracked at the moment of the initiation of slit (when PQ=Pmax); in others the decohesion force Pmax exceeded PQ, which was identified as a minor deflection or relative extremum of the curve. The frequency of the second type of cracking increased with the growing size of coarse aggregate grains. Together with the growth of the grain size, the angle of curve inclination also became smaller. This phenomenon can be explained by the fact that, in the process of decohesion, the aggregate grains are relocated and the system of contact between them changes, so the KHc depends on coarse aggregate.