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The tensile creep of concrete with supplementary cementitious materials (SCMs) such as fly ash (FA) and ground granulated blast furnace slag (GGBFS) is investigated in this paper. A total of 21 series of tensile creep tests using dog-bone specimens under uniaxial tensile loading have been carried out. The cement replacement rates considered were 30% fly ash, 40% and 60% GGBFS. The characteristic compressive strength of concrete was ranging from 25 to 100 MPa. The tests were conducted from the age of 2 days until 28 days. It is observed that the tensile creep of fly ash concretes was slightly lower than that of the reference mixtures without SCM. For GGBFS concrete, the higher the GGBFS content, the higher the tensile creep. Existing creep models, originally developed for creep in compression, could not predict the experimental tensile creep results. Thus, a new tensile creep model was proposed including creep prediction for concrete with fly ash and GGBFS. The new model was calibrated only for controlled environmental conditions (23°C and 50% RH) and has been validated by analyzing the development of concrete tensile stress in the restrained ring test.

This study investigates the shrinkage of two sustainable aluminosilicate blends with fly ash or limestone-calcined clay (LC3). Paste and concrete were prepared using these SCMs for the highest possible replacement of binder without compromising the strength. The chemical and autogenous shrinkage were assessed for paste samples and further investigation were conducted on hydration by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Opting for an engineering approach, comparison among different segments of shrinkage i.e., autogenous, drying and total shrinkage of concrete having a specific compressive strength were considered. The initial investigation on paste samples highlighted the dissimilarities in shrinkage and hydration of fly ash and calcined clay. LC3 hydrated faster compared to fly ash leading to greater autogenous shrinkage. The high autogenous shrinkage in the LC3 blend was compensated by a low drying shrinkage for a specific compressive strength. Considering the replacement level of cement, shrinkage, and ecological impact, LC3 proved to be a more sustainable and eco-friendly concrete compared to fly ash.

The load-bearing capacity of perfobond Leisten (PBL) shear connectors in hybrid structures is represented by the shear-friction effect between the shear surfaces caused by the interlocking of aggregates when the fracture surface of the concrete dowel slips under an external load. To carry out an accurate numerical simulation of the bearing capacity and shear transmission mechanism of the PBL shear connectors, based on the secondary development function of the user subroutine, user-defined field variable subroutine (USDFLD), the effective simulation of the transverse shear expansion effect of the concrete dowel is achieved. A comparison with the results of the test data shows that the concrete damage plasticity (CDP) model demonstrates good robustness and convergence for the prediction and simulation of the damage characteristics of concrete structures. Based on the user subroutine USDFLD's automatic update function of material points and element integration points to field variables, this model effectively simulated the functional gradient model of the concrete dilatancy angle, the load on the shear connectors is always transmitted from the near load end to the far one, and the bearing capacity is clearly affected by the boundary conditions.

Supplementary cementitious materials (SCMs) are widely used to reduce the cement content to achieve economic and environmental objectives. As a result, understanding the shrinkage of blended cement-based concrete is essential. In total, 21 concrete mixes were produced with type general purpose cement and with cement replacements of 30% by fly ash, 40% and 60% by ground granulated blast furnace slag (GGBFS). The concrete compressive strength ranged from 25 MPa to 100 MPa. Experimental results were also compared with the predictions by models. Additional tests on pastes with the same SCM content were conducted to investigate both autogenous and chemical shrinkage in relation to their time-dependent pore structure refinement. For concretes with strength below 50 MPa, no significant difference in autogenous shrinkage could be observed between the different blends up to 28 days. However, the autogenous shrinkage of GGBFS concrete increased significantly after 28 days, being about 50% higher than all other concretes at 100 days. This late increase in autogenous shrinkage between 28 and 100 days can be attributed to pore refinement processes. No clear difference was observed for GGBFS concretes with strength greater than 50 MPa. Autogenous shrinkage of fly ash concretes was overall equivalent to that of reference concretes.

Nowadays, light emitting diode (LED) lamps have been widely utilized for lighting system due to its low-energy consumption. The harmonic emission standard is ignored by most of the manufacturers, high harmonic current will increase harmonic injection and cause fire risk. Existing research focuses on investigating harmonic emissions from several specific LED drivers, but a systematic evaluation approach is not given. The contribution of this paper proposed a LED harmonic evaluation in the management view, which can evaluate the harmonics of the LED lamps, accelerate the elimination of inferior LED lamps, and improve the power quality of distribution network. The evaluation approach combines G1 method and entropy method, which can make the weighting more scientific and rational. An evaluation model is established by collecting data, then the G1-entropy method is used to calculate the weights of harmonic characteristics in this model. Finally, we analyze and discuss the results, a specific evaluation approach is proposed, which can thoroughly and accurately represent the harmonic characteristics of LED lamps.

Concrete is known as the most globally used construction material, but it releases a huge amount of greenhouse gases due to cement production. Recently, Supplementary Cementitious Materials (SCMs) such as fly ash and Ground Granulated Blast Furnace Slag (GGBFS) have been widely used in concrete to reduce the cement content. However, SCMs can alter the mechanical properties and time-dependent behaviors of concrete and the early age mechanical properties of concrete significantly affect the concrete cracking in the engineering field. Therefore, evaluation of the development of the mechanical properties of SCMs-based concrete is vital. In this paper, the time development of mechanical properties of concrete mixes with various fly ash and GGBFS was experimentally investigated. Four different cement replacement levels including 0%, 20%, 30%, and 40% by fly ash and GGBFS as well as ternary binders were considered. Compressive strength, splitting tensile strength, flexural strength, and elastic modulus of concrete were measured until 28 days. Three additional concrete mixes with ternary binders were also cast to investigate the early-age autogenous shrinkage development until 28 days. In addition, prediction models in existing standards were used and compared to experimental results. The comparison results showed that the prediction models overestimated the compressive strength but underestimated the splitting tensile strength development and autogenous shrinkage. As a result, a model capturing the effect of fly ash and GGBFS on the development of compressive and splitting tensile strength is proposed to improve the prediction accuracy for current standards and empirical models.

This work investigates the autogenous shrinkage of pastes and concretes prepared using General Purpose cement and GGBFS (40% and 60%) up to 100 days. To determine the underlying factors influencing autogenous shrinkage, hydration progression and evolution of microstructure were investigated. Results showed that autogenous shrinkage of GGBFS blends continuously increased after 28 days (until 100 days) whereas the control samples reached a plateau after about 28 days. Late reaction between limestone from the General Purpose cement and alumina from GGBFS progressed untill 90 days forming a high amount of monocarboaluminates. General Purpose cement blends with high GGBFS content can behave as ternary blends and not as binary blends due to the small amount of limestone usually added to General Purpose cements. These long term reactions lead to a significant refinement of the pore structure which is responsible of the late autogenous shrinkage in GGBFS blends.

Cracking induced by early age restrained shrinkage can lead to durability issues in concrete structures and premature deterioration that reduce service life of reinforced concrete members. Despite the increasing demand for using Supplementary Cementitious Materials (SCMs) in concrete, the effect of binders and strength grades on early-age restrained concrete cracking has not been fully understood. This study investigated 21 concrete mixes with 30 % fly ash, 40 % and 60 % slag having compressive strengths ranging between 25 MPa and 100 MPa using a restrained ring test. Their cracking potential was evaluated by considering three different methods. The results showed that the time to cracking was short for high grade concretes and concretes with slag. Fly ash delayed the cracking for all strength grades. Though all cracking estimators used in this study did not outstandingly predict the potential of early-age cracking in concrete, the stress rate method performed the best. The cracking strain method and the R ratio method were significantly influenced by the supplementary cementitious materials. The most dominant factor governing the cracking potential of concrete was the rate of stress or strain development for all strength grade and binder types.

Concrete structures may experience unexpected cracking at an early age. Early age cracking can be induced by restrained deformations where tensile stress generated in concrete exceeds its tensile strength. The restrained concrete ring test is often used to evaluate the ability of concrete to resist early age cracking induced by shrinkage. This paper proposed an analytical model of the restrained ring test by capturing the effect of both restrained shrinkage and tensile creep based on the age-adjusted effective modulus theory. The analytical model allows for accurately predicting the tensile stress of the restrained concrete ring based on the experimental measurements of the time-dependent development of elastic modulus, total free shrinkage, and tensile creep of concrete. A numerical finite element simulation was also successfully carried out to validate the new analytical model. Importantly, the model was validated considering a total of 21 concretes consisting of 6 strength grades ranging from 25 MPa to 100 MPa. For each grade, one fly ash blend (30%), two GGBFS blends (40% and 60%) and a reference mix without supplementary cementitious materials were tested.

In this study, the developments of autogenous and total shrinkage of limestone calcined clay cement (LC3) concretes were investigated. Three concrete grades including 25 MPa, 32 MPa and 45 MPa of both LC3 and general purpose cement (GPC) concretes were considered. Compressive strength and tensile strength were measured until curing of 28 days. In addition, pore size distribution of cementitious pastes was evaluated by using nitrogen adsorption. Several models were used to assess their applicability for LC3 concretes in predicting mechanical properties and shrinkage development. The LC3 concretes showed higher autogenous shrinkage at a later age up to 100 days due to continuous refinement of the pore structure whilst the development of total shrinkage was similar between LC3 and OPC concretes. All models underestimated LC3 concrete autogenous shrinkage and the Bazant B4 model provided the best prediction of total shrinkage development.

The battery swap station is an important centralized charging infrastructure, and it has broad application prospects utilizing V2G technology, but it will make great influence on protection system and automated configuration of a distribution system. This paper first analyzes the impact of a battery swap station on feeder automation based on FTU, and then proposes a new control strategy. The proposed strategy comprises not only the fault identification and response strategy, but also the coordinated control strategy of all the bi-directional battery chargers. In the end, a feeder automation simulation model is built using PSCAD, and the impact of a battery swap station utilizing the proposed control strategy on feeder automation system is simulated. The simulation results show that the proposed control strategy can effectively reduce the negative impact.