Increase Of Replacement Rate Research Articles

An Analysis of the Flexural Stiffness and Horizontal Bearing Capacity of CFRP Composite Pipe Piles in Marine Environments

Carbon-fiber-reinforced polymer (CFRP) is a composite material consisting of a resin matrix reinforced with carbon fibers. This study focuses on CFRP composite pipe piles as the subject of investigation, exploring the impact of substituting steel bars with CFRP bars on the bending performance of pipe piles through rigorous three-point bending tests. The attenuation of flexural stiffness in CFRP pipe piles under a chloride salt environment was anticipated. The lateral bearing capacity of CFRP pipe piles was calculated by introducing a stiffness degradation coefficient for the piles and utilizing the finite difference method. The findings of the analysis suggest that as the CFRP reinforcement replacement rate increases, the initial bending stiffness of the composite pipe pile experiences a corresponding decrease. After serving for 28.15 years, the steel reinforcement within the pipe pile commences rusting, resulting in a nonlinear decline in the bending stiffness of the composite pipe pile. As the service time of pipe piles increases, a higher replacement rate of CFRP reinforcement results in a slower attenuation of pile stiffness. Consequently, both the horizontal displacement at the top of the pile and the bending moment along the body of the composite pipe pile gradually increase over time. During the same service period, the higher the rate of CFRP reinforcement, the less noticeable the attenuation in the horizontal bearing capacity of the pile shaft.

Fracture behaviors of sustainable recycled aggregate concrete under compression-shear loading: Laboratory test, numerical simulation, and environmental safety analysis

A series of compression-shear tests were carried out to investigate the shear failure of sustainable recycled aggregate concrete, and shear failure surfaces were scanned by a 3D laser scanner. The effect of recycled coarse aggregate (RCA) replacement rates and normal stresses on the shear strength, failure mode, and fracture morphology were analyzed. Meanwhile, discrete element method was used to study shear behaviors at a mesoscale. Finally, the carbon emission was calculated to evaluate the effect of RCA on the environment. The result shows that the shear strength, cohesion c, and internal friction angle φ all decrease as the RCA replacement rate increases. The shear damage of RAC can be aggravated by increasing the RCA replacement rate. Fractal dimension and joint roughness coefficient of shear failure surface tend to increase with increasing RCA replacement rate and normal stress. In addition, more microcracks can be found in coarse aggregate with the increase in RCA replacement rate, and the increasing normal stress can cause more microcracks. Given the nonlinear development of stress-displacement, a modified nonlinear constitutive model is proposed. Finally, the total carbon emissions of recycled aggregate concrete are calculated considering production, transportation, and construction, the carbon emission of 100% sustainable recycled aggregate concrete is 10.2% less than that of 100% natural aggregate concrete.

Durability of Recycled Concrete after Reinforcing the Aggregates with Permeable Crystalline Materials

The utilization of recycled aggregate can significantly mitigate the extraction of natural sand and gravel. However, the practical application of recycled aggregate in engineering is impeded by its inherent characteristics, encompassing high water absorption, high crushing, and low apparent density. This study employed a soaking and air-drying method to enhance the strength of three types of aggregates with varying initial strengths by utilizing permeated crystalline materials. The durability of recycled aggregate concrete (RAC) was studied with three different aggregate replacement rates (0%, 50%, and 100%). The test results demonstrate that the slump, compressive strength, freeze resistance, and carbonation resistance of RAC exhibit a decreasing trend as the aggregate replacement rate increases. The freeze resistance and carbonation resistance of RAC are notably enhanced after incorporating permeated crystalline material. This study contributes to a sustainable and efficient solution for the treatment of construction waste, thereby enhancing the utilization rate of recycled concrete.

The effects of the quality of recycled aggregates on the mechanical properties of roller compacted concrete

This study investigates the performance of roller compacted concrete (RCC) made with recycled aggregates derived from crushed demolished concrete with various proportions of natural. The experimental study examines substituting various proportions of natural aggregate (3/8, 8/15, and 15/20) with recycled aggregate. The replacement rates range from 0% to 100% in increments of 25%. Eleven different mixtures have been made by changing the amount of recycled aggregate used, with and without pre-wetting, before being added to concrete. Additionally, 5% of the cement content was substituted with silica fume and slag in each composition. An experiment test was done to see how recycled aggregate-based BCRs' performance changed with the incorporation rate on fresh and hardened concrete's mechanical and physical properties. Physical parameters, including volume masse, vebe time consistency, and mechanical properties such as compression resistance, flexion resistance, and ultrasonic pulse speed, were measured over time. The results found were compared to the control mix made with 100% natural aggregates. Those results show that as the replacement rate increases, the water absorption rate increases with a decrease in mechanical strength. In addition, the pre-wetting treatment did not significantly impact mechanical strength. This can be explained by the characteristics of the recycled aggregate, such as high absorption, low resistance to wear, and low density, which were caused by the residual paste adhered to the recycled aggregate.

Effect of agricultural biomass wastes on thermal insulation and self-cleaning of fired bricks

This research investigates the feasibility of using dry crushed pomegranate peel waste as thermal insulator to produce light clay bricks. Pomegranate peel waste (PW) is used with different substitution levels of 0%, 5%, 7.5%, 10% and 15% of clay weight. The clay bricks were heated at temperatures of 700, 800, and 900 °C, that resulted in the formation of internal pores due to the combustion of PW. The bulk density, water absorption, porosity, shrinkage, and compressive strength are examined to evaluate the effect of using PW on the physical and mechanical properties of thermal insulation bricks. Also, the investigation of the effect of photocatalytic activity of bricks under sunlight irradiation is carried out. The use of PW increased the thermal conductivity up to 21% at 900 °C, water absorption from 22.6% in cold water to 29.1% in boiling water, density from 2.5% at 800 °C to 7.6% at 900 °C, and shrinkage from 4.3% in linear drying shrinkage to 5.4% in linear firing shrinkage. The heated brick samples at 700 °C showed greater photodegradation efficiency than firing clay at 800 °C and 900 °C. Moreover, the compressive strength decreased with the increase in replacement rate, reaching up to 74% for 15 wt% PW. This study confirms that lightweight heated bricks with low thermal conductivity and a reasonable compressive strength can be made using PW as a pore-forming agent.

The Basic Mechanical Properties and Shrinkage Properties of Recycled Micropowder UHPC

Using waste clay brick powder (RBP) to partially replace cement in the preparation of concrete, is one way to recycle construction waste. In order to investigate the physical and mechanical properties and volume stability of recycled micropowder ultra-high-performance concrete (UHPC), the basic mechanical and shrinkage properties of recycled micropowder UHPC were studied at replacement rates of 10%, 20%, 30%, 40% and 50%. The results show that: (1) When the activated recycled brick powder is used to replace the cement, the compressive strength, flexural strength and splitting tensile strength of the UHPC initially increase and then decrease with the increase in the substitution rate. When the substitution rate is 10%, the 28 d compressive strength, flexural strength and splitting tensile strength of the UHPC are the highest; (2) Replacing cement with recycled brick powder can reduce the autogenous shrinkage of the UHPC, and the autogenous shrinkage rate of the UHPC decreases with the increase in the brick powder replacement rate. The drying shrinkage of the UHPC can be reduced by replacing cement with recycled brick powder. The drying shrinkage of the UHPC initially decreases, and then increases, with the increase in the replacement rate of brick powder. When the replacement rate of the brick powder was 30%, the drying shrinkage of the UHPC was the least, and this was 49.7% lower than that in the benchmark group. The prediction models of autogenous shrinkage and drying shrinkage are in good agreement with the experimental results, which can be used to predict the shrinkage development of recycled brick powder UHPC.

Study on Mechanical Properties and Action Mechanism of Leather Industrial Sludge Aggregate Baking-Free Bricks

Taking an industrial sludge and its preparation of sludge wrap shell aggregates (WSAs) instead of sand to prepare baking-free brick as the research object, the development law of mechanical properties and the influence mechanism of macro and micro characteristic parameters of the bricks under different sludge and WSAs replacement rates were studied through the macroscopic mechanical properties test, with the help of nuclear magnetic resonance (NMR), transmission electron microscopy-energy spectrum and other testing technology and pores and cracks analysis system (PCAS) software. The results showed that the compressive strength of each sample decreased with the increase of sludge content. When the sludge content was less than 30%, it was mainly affected by the water-binder ratio. When the sludge content was more than 30%, it was mainly affected by the sludge content. At the age of 7 days, with the increase in replacement rate of WSAs, the compressive strength of the S10 and S30 groups was higher than that of the control group. The compressive strength of the S50 experimental group was 30.38 MPa, and the loss of compressive strength was slight compared with the control group. The water absorption rate of the 28 days S100 experimental group increased by 10.71% compared with the control group. When the content of WSAs was less than 50%, the holes above 0.1 μm in the brick can be reduced and transformed into smaller holes, with a decreasing trend of the plane porosity of the brick. The microscopic results of the baking-free brick showed that the three-phase system of WSAs-interface transition area-mortar was poorly bonded and delaminated compared with the gravel aggregate-interface transition area-mortar system, and damage was more likely to occur in the WSAs and interface transition area. The above results show that it is feasible to use sludge and WSAs instead of sand for the preparation of baking-free bricks. This technology not only solves the problem of sludge disposal, but also protects the over-exploitation of mineral resources, and the technology has a broad application prospect and market value.

Mechanical Performance and Durability of Mortar Based on Slag Cement and NaOH-Activated Slag

This paper investigates the valorization of slag in cement production in order to obtain a sustainable mortar and participate in protecting the environment. The study evaluated the setting time, hydration heat, mechanical strengths, drying shrinkage, sulfuric acid and sulfate attack of mortars. These mortars are based on Portland cement (PC), slag cements containing 10%, 30% and 50% slag and alkali-activated slag (AAS) using 6% and 9% of sodium hydroxide (NaOH). The results show that the increase in slag replacement rate increases the setting time accompanied by a drop in initial mechanical strength such that the compressive strength decreased by 30% at two days for a 50% slag substitution; also, it considerably reduces the shrinkage and hydration heat. The resistance to sulfate and sulfuric acid attack increases with the slag replacement rate. NaOH-activated slag mortar is the most resistant binder to sulfate attack and sulfuric acid, but it develops a lower mechanical strength and a more significant shrinkage than PC mortar. X-ray diffraction (XRD) analysis carried out on binder paste shows the formation of the same main hydration products in PC and slag cement with a small amount of portlandite in the last binder. Calcium silicate hydrate (CSH) and Hydrotalcite are the main hydration products of AAS.

The effects of adding molybdenum tailings as cementitious paste replacement on the fluidity, mechanical properties and micro-structure of concrete

To reduce the land occupation and environmental pollution caused by the accumulation of molybdenum tailings (MT), MT has been used as cement or fine aggregate replacement to produce concrete. Molybdenum tailings concrete (MTC) was prepared by replacing cement paste with MT of equal mass in this study in order to offer one more option for the adding of MT into concrete. The workability of the concrete mixture and the mechanical properties of the hardened concrete were investigated. The internal pore structure characteristics and micro-morphology of MTC were analyzed by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), respectively. The results showed that, as the MT replacement rate increases, the slump of the concrete mixture decreases, the air content increases firstly and then decreases, the compressive strength and splitting tensile strength decreases firstly and then increase with the optimum MT replacement rate at 10%; the total porosity of concrete increases and then decreases, both the compressive strength and splitting tensile strength are inversely proportional to the porosity. When the MT replacement rate is 7.5% and 10%, the number of medium capillary pores (0–100 nm) decreases significantly, while the number of capillary pores (100–1000 nm) and air pores (>1000 nm) gradually increases.

Study on Mechanical Properties and Mechanism of Recycled Brick Powder UHPC

Recycled brick powder (RBP) is a kind of solid waste material with pozzolanic activity, which can partially replace cement as a cementitious material to prepare concrete. In this paper, ultra-high-performance concrete (UHPC) was prepared by RBP. The effects of different RBP contents as a mineral admixture on the mechanical properties and microstructure of UHPC were studied by experiments. The results show that RBP has a certain weakening effect on the compressive strength development of UHPC. The compressive strength of UHPC decreases with the increase in the replacement rate of RBP, but the 28 d compressive strength of each group of specimens is not less than 140 MPa. The flexural toughness and tensile strain of RBP UHPC increased first and then decreased with the increase in brick powder replacement rate and reached the maximum at 40% and 30%, respectively. The material exhibits good strain-hardening characteristics. In addition, the incorporation of RBP can improve the bond strength between steel fiber and matrix and the ultimate bond strength reaches the maximum when the substitution rate is 40%. From the perspective of nano-scale characteristics, the RBP not only fills the pores as micro-aggregate, but also participates in the secondary hydration reaction to further optimize the pore structure of UHPC.

Influence of nano-attapulgite on compressive strength and microstructure of recycled aggregate concrete

In order to solve the problem of waste concrete caused by demolition of old buildings, calcined nano-attapulgite (CNAT) was added into recycled aggregate concrete (RAC) to form nano-attapulgite recycled concrete. In this paper, the experiment was divided into two stages. Stage 1: The influence of activity of nano-attapulgite (NAT) which is calcined at different temperatures was analyzed by thermo-gravimetric analysis (TGA), scanning electron microscope (SEM) and X-ray diffraction (XRD) to find out the optimal activation temperature. Stage 2: The influence of different CNAT content and replacement rate of recycled coarse aggregate (RA) on the compressive strength of RAC were investigated, and the microstructure was analyzed by SEM, XRD and Barret-Joyner-Halenda (BJH) method. The results showed that when the calcination temperature is 500 °C, NAT has the highest activity; the compressive strength of RAC decreases gradually with the increase of replacement rate of RA. When the replacement rate of RA were 30 wt% and 50 wt% and the content of CNAT was 6 wt%, the compressive strength of concrete were the largest and the compressive strength is 13.2% and 16.1% higher than that without CNAT, respectively. Because of its filling effect, surface effect and pozzolanic activity, CNAT can fill the pores and cracks in the old mortar, new mortars and the interfacial transition zone (ITZ) of RAC. The harmful pores of RAC is refined, and the concrete is more dense. Above all, CNAT can increase the macroscopic mechanical properties of RAC by improving its microstructure effectively, which provides a theoretical basis for the further study of RAC.

Experimental Study and Theoretical Analysis on the Compression-Shear Multiaxial Mechanical Properties of Recycled Concrete.

Recycled concrete, which is formed by replacing coarse aggregates in ordinary concrete with recycled aggregates (RA), is of great significance for the secondary utilization of waste building resources. In civil engineering, concrete structures are sometimes subjected to a compression–shear multiaxial stress state. Therefore, research on the compression–shear multiaxial mechanical properties of recycled concrete plays an important role in engineering practice. To explore the effect of RA replacement rate on the compression–shear properties of recycled concrete, an experimental study was carried out using a compression–shear testing machine and considering five RA replacement rates and five axial compression ratios. Consequently, the failure modes and mechanical property parameters under different working conditions were obtained and were used to analyze the effects of RA replacement rate and axial compression ratio on the shear stress of recycled concrete. Eventually, the following conclusions were reached: With the growth of axial compression ratio, the shear cracks exhibit a developing trend along the oblique direction, and the friction traces on the shear surface are gradually deepened. As the replacement rate increases, the number of shear cracks is gradually increased, accompanied by increasing broken fragments falling off from the shear interface. Since the action of the axial compression ratio can effectively improve the mechanical bite force and friction on the shear interface of recycled concrete, as the axial compression ratio increases, the shear stress is gradually increased. On the other hand, due to the initial damage of RA and its weak adhesion with cement mortar, the shear stress is gradually reduced with the increase of RA replacement rate. Meanwhile, the increase in shear stress shows a gradually decreasing trend with the growth of axial compression ratio. Specifically, for the RA replacement rates of 0% and 100%, the shear stress increased by 4.06 times and 3.21 times, respectively, under the influence of the axial compression ratio. Under different axial compression ratios, the shear stress was reduced by 43~46%, due to the increase of RA replacement rate. In addition, based on the octahedral stress space and the principal stress space, a compression–shear multiaxial failure criterion and shear stress calculation model for recycled concrete were proposed, by considering the effect of the RA replacement rate. The outcomes of this research are of great significance for engineering applications and the development of recycled concrete.

Study on flexural behavior of graphene oxide recycled concrete beams

Abstract In order to study the flexural behavior of graphene oxide (GO) recycled concrete beams, 6 GO recycled concrete beams were studied, and observe its failure mode and process. The effects of GO content, oxygen content of GO and replacement rate of recycled aggregate on the flexural behavior of the test beams, including cracking load and ultimate load, concrete strain and steel strain, mid-span deflection, were analyzed. The test results show that the cracking load and ultimate load of recycled concrete beams with GO increase to a certain extent with the increase of GO content. And the higher the oxygen content of GO, the higher the ultimate bearing capacity of GO recycled concrete beams. With the increase of replacement rate of recycled aggregate, the cracking load and ultimate load of the test beams decrease.

Experimental study on the influence of recycled aggregates on the mechanical properties of concrete

Construction solid waste has become an important environmental pollution source in the city, and the treatment and application of construction solid waste has become the focus of attention. Construction waste recycled aggregates have defects such as high water absorption and micro cracks, which affect its extensive application. In order to improve the utilization rate of recycled aggregates, the influence of different replacement rates of recycled aggregates on the mechanical properties of concrete is studied in this paper. The results show that with the increase of replacement rate of recycled aggregates, the 3-day, 7-day and 28-day compressive strength, splitting strength and cohesive force of concrete decrease gradually, but the mechanical properties of concrete decrease slowly at 3 days and 7 days, and decrease obviously at 28 days. Moreover, with the increase of replacement rate of recycled aggregates, the decline trend of mechanical properties is not obvious. Compared with natural aggregate concrete, the 28-day compressive strength, splitting strength and cohesive force of 100% recycled aggregate concrete are reduced by 16.1%, 20.1% and 18.1% respectively, but the mechanical properties meet the requirements of C30 concrete, which provides a reference for engineering application.

Triaxial compressive strength experiment study of recycled aggregate concrete after high temperatures

To study the triaxial compressive properties of recycled aggregate concrete (RAC) after high temperature, 100 Ф100mm×200mm cylindrical RAC specimens with different replacement rate (0%, 30%, 70%, 100%) were fabricated to the conventional triaxial experiment (with the lateral confining stress of 0MPa, 5MPa, 10MPa, 15MPa and 20MPa) after exposure to different high temperatures (20°C, 200°C, 300°C, 400°C, 500°C). The results show that the specimens present longitudinal splitting failure form when under uniaxial stress condition and inclined plane shear or flake splitting failure form when under triaxial stress condition. The triaxial compressive strength presents the trend of decreasing→increasing→decreasing with the increase of replacement rate. Improving lateral confining stress can effectively improve the compressive strength of RAC. The triaxial strength of specimens is almost equal to each other when the temperatures do not exceed 400°C. After 500°C high temperature, the triaxial strength will gradually decrease, but the decrease amplitude is far less than that of uniaxial strength. Based on test data and some related theories, the triaxial strength calculation formula of RAC with different replacement rate after high temperatures was given. And it can provide some references for the related research and practical engineering application of RAC.

The Effect of Unemployment Benefit Generosity on Unemployment Duration: Quasi-Experimental Evidence from Slovenia

The paper analyses the effects of a 2011 increase in the unemployment benefit replacement rate on the job-finding rate of Slovenian benefit recipients. Using registry data on the universe of Slovenian unemployment benefit recipients, we exploit legislative changes that selectively increased the replacement rates for certain groups of workers while leaving them unchanged for others. Applying this quasi-experimental approach, we find that increasing the replacement rate significantly decreases the hazard rate of the transition from unemployment to employment, with an implied elasticity of the hazard rate with respect to benefit replacement rate being 0.7 to 0.9. The results also show that increase of the unemployment benefit replacement rate does not affect the job-finding probability of jobseekers whose reason for unemployment is employer exit, and that the effects of the increase of replacement rate are present only upon exit to employment and not to inactivity.

Evaluation of the durability of concrete made with crushed glass aggregates

Contrasting with previous studies that aimed to evaluate the mechanical properties of concrete made with glass, this one focuses on their durability performance. For this, water absorption by capillarity and immersion, carbonation resistance, chloride penetration and shrinkage tests were performed. Mixes containing 0%, 5%, 10% and 20% of glass aggregates (GA) as replacement of natural aggregates (NA) were prepared. Also analysed is the influence of the size of the replaced aggregates (fine and coarse, separately or simultaneously), in a total of 10 concrete mixes. It was found that the particle size strongly affects the workability of concrete. Due to the lower density of the glass aggregates, the mixes made with glass had a lighter fresh density than the reference concrete. Although there is a decrease in the compressive strength as the replacement rate increases, mixes with GA are totally feasible, even though there are some differences in performance as a function of the particle size of the GA used to replace the NA. It was found that in most cases the GA do not significantly alter the durability-related properties of concrete. In a few instances there is a variation from the reference concrete of ±15%, which is well within the expectable scatter of the results from experimental research.

풍쇄슬래그 잔골재를 사용한 콘크리트의 공학적 특성에 관한 실험적 연구

In this study, the experiment was carried out to investigate and analyze the engineering properties of concrete using fine aggregate of PS bal slagl. The main experimental variables were water/cement ratio 30, 40, 50(%), water content <TEX>$170kg/m^3$</TEX>, replacement ratio of slag fine aggregate 0, 25, 50, 75(%) in experiment I and water/cement ratio 30, 40, 50(%), water content 165, 170, 175(<TEX>$kg/m^3$</TEX>), replacement ratio of fine aggregate of PS ball 0, 50 in experiment II. According to the test results, the principle conclusions are summarized as follows (1) The workability of slag fine aggregate-mixed concrete tends to improve, as the replacement rate increases. (2) The air content of slag fine aggregate-mixed concrete tends to decrease, as the replacement rate increases. (3) The unit volume weight of slag fine aggregate-mixed concrete tends to significantly increase, as the replacement rate increases. (4) The compressive strength of slag fine aggregate-mixed concrete tends to show more increasing propensity, in case the curing period is relatively long, as the replacement rate increases.

The Wage Replacement Rate and Benefit Utilization in Workers' Compensation Insurance

Both indemnity claims and costs are affected by the rate at which wages are replaced in the workers' compensation program. This article examines the magnitude of these effects in the state of Texas. The research indicates that there are sizeable increases in the relative frequency of indemnity claims and costs as the replacement rate increases. Failure to recognize these increases could lead to serious underestimates of the cost of benefit changes.

Replacement policy in dairy herds on farms where heifers compete with cows for grassland—Part 3: A revised hypothesis

A preliminary investigation of replacement policy on dairy farms where heifers compete with cows for grassland suggested that profitability falls as replacement rate increases, because the number of cows able to be milked and the maturity of the herd override the gains in milk yield per cow due to genetic improvement by culling for insufficient yield and by the greater use of a sire of high genetic merit. This hypothesis was inadequate to cover all the situations investigated in two factorial experiments involving changes in herd health status, replacement rate, age at first calving, calving index and the merit of AI sires used in the herd from an initial state for these variables of 0·22, 36 months, 13 months and Standard, respectively. Overall, these was a clear indication that the major influence on profitability was the number of cows in the herd. An increase in replacement rate was not always associated with a fall in profitability, nor was an improvement in yield per cow always associated with a rise in profitability relative to the performance of a control herd after 15 simulated years. The manipulation of replacement rate and age at first calving to achieve an increase in the number of cows in the herd was not necessarily incompatible with a desire for herd improvement either phenotypically (yield per cow) or genetically (herd and heifer genotype), particularly if premium bulls were used.