Search

Abstract In order to control urban dust pollution and to improve the utilization of agricultural and forestry straw solid waste, this paper prepared an environmentally friendly dust suppressant with plant straw using nine different types of waste straw as raw materials with environmentally friendly additives. By the single factor experiment, the composition of each component reagent and the effect of mass concentration on its properties under single factor were determined. Multi-factor interaction tests were designed by response surface method. Three independent variables including wheat straw based superabsorbent polymers (SAP), hydroxyethyl cellulose (HEC10S) and octyl glucopyranoside (APG0810) were selected. Viscosity (Y1), anti-evaporation rate (Y2) and surface tension (Y3) were determined as response values. Meanwhile, the functional relationship between the fitting factors and the response values is established by regression analysis. The results showed that the predicted values are in good agreement with the experimental values. The plant straw-based dust suppressant with 1.93% SAP, 0.10% HEC10S and 0.80% APG0810 exhibited good bonding performance, wettability and anti-evaporation rate.

The early-age cracking of concrete is one of the most critical parameters affecting the performance of concrete structures. It is attributed to both the internal and external influences such as early age restrained shrinkage, thermal deformation as well as the applied load. In this paper, a detailed review of the causes of early-age cracking is first presented, followed by the factors affecting the concrete cracking including raw materials quality problems, improper construction measures, external environmental influences and structural design flaws. Then the preventive measures for concrete cracking are summarized. The potential for the application and development of structural health monitoring and artificial intelligence techniques for early-age cracking of concrete is also discussed. Through the comprehensive review of the early-age cracking of concrete, the research direction for the subsequent research on early-age cracking of concrete is pointed out. The current problems and concerns of concrete cracking are also prospected.

Abstract Prepacked aggregate concrete (PAC) is made by placing coarse aggregates of various sizes into a formwork and then filling the voids between coarse aggregate and grout. The mechanical performance of PAC is dominated by the compactness due to grout filling, but few study considered the pouring methods and grout performance synchronously. The coupled effect of pouring methods and grout performance on the compactness of PAC is investigated in this study. The results show that the gravity pouring method is only suitable for grouts with good flowability. The pump pouring method is more widely used. It can be adapted to grout with poorer fluidity and coarse aggregate with greater apparent density. The ultrasonic pulse velocity test method provides a relatively accurate evaluation of the compactness of PAC. Furthermore, due to the enhanced mechanical properties of PAC, the filed application potential in the preparation of steel tube concrete columns has also been confirmed, where the results exhibited that PAC based steel tube concrete contributed to an enhanced ductility and autogenous shrinkage.

With the increasing use of concrete-filled steel tubular (CFST) structures, exposed steel tubes are highly susceptible to corrosion, posing potential safety hazards. This study innovatively proposes the use of stainless-steel tubes instead of traditional carbon-steel ones and introduces coarse aggregates into ultra-high-performance concrete (UHPC), forming a coarse aggregate-incorporated ultra-high-performance concrete-filled stainless-steel tube (CA-UFSST). The inclusion of coarse aggregates not only compensates for the shortcomings of UHPC but also enhances the overall mechanical performance of the composite structure. Twenty sets of specimens were designed to analyze the influence of four parameters, including the coarse aggregate content, compressive strength, stainless-steel-tube thickness, and stainless-steel type on the axial compression performance of UHPC. The experimental results indicate that the failure mode of UHPC is related to the confinement ratio. As the confinement ratio increases, the failure mode transitions from shear failure to bulging failure. The addition of coarse aggregates enhances the stiffness of the specimens. Furthermore, this paper discusses the applicability of six current codes in predicting the bearing capacity of CA-UFSST and finds that the European code exhibits the best prediction performance. However, as the confinement ratio increases, the prediction accuracy becomes notably insufficient. Therefore, it is necessary to establish a more accurate calculation model for the axial compression bearing capacity.

The treatment and disposal of sewage sludge ash (SSA) have emerged as crucial environmental concerns. This study delves into the profound impact of substituting SSA for sand in cement mortar, examining fresh and mechanical properties, drying shrinkage, and high-temperature resistance. Analyzing the SSA-modified mortar through X-ray diffraction (XRD) and scanning electron microscopy (SEM), the research reveals that the porous nature of sludge ash marginally influences the hydration rate and degree by adsorbing ions or encapsulating cement particles. While the SSA leaching solution has only a neglectable impact on the hydration rate. The workability is enhanced with the increase of the addition of excess water. Meanwhile, although the presence of excess water indirectly increases the w/c ratio of mortar, mortar with 5 % and 10 % SSA exhibit superior mechanical performance due to denser microstructure. Porous structures of SSA and more excess water in higher SSA content result in the rise of mortar drying shrinkage. When the sintering temperature reaches 800 °C, the high-temperature resistance of mortar with 20 % SSA is greater than that of the control group. The rough surface of SSA effectively fills cracks induced by elevated temperatures and improves the friction reaction, contributing to enhanced performance.

Abstract Supplementary cementitious materials (SCMs) such as fly ash and ground granulated blast furnace slag (GGBFS) are found to control the maximum temperature and the accompanying thermal gradients effectively. However, SCMs also lead to low early age strength development. Thus, it is crucial to understand the cracking behaviour of SCMs-based concrete affected by the mix design parameters. In this paper, the thermal cracking resistance was evaluated using a rigid cracking frame (RCF) with a computer-controlled temperature profile. The temperature profile was determined using the software ConcreteWorks by assuming the centre point of the mass concrete. The free shrinkage frame (FSF) and match-curing oven follow the same temperature profile as RCF to measure the free total deformation and time-dependent mechanical properties of concrete, respectively. An analytical model was proposed to calculate the autogenous shrinkage and the thermal stress separately. A time-dependent cracking risk coefficient allowing to estimate the risk of early age cracking of concrete was also proposed.

The extensive usage of concrete and ordinary Portland cement has generated 5~8% of annual global CO2 emissions, causing serious environmental problems. To reduce such environmental impact, researchers have made significant efforts to develop alternative materials that may partially or entirely replace the ordinary Portland cement, such as limestone calcined clay cement (LC3). LC3 has not been commonly adopted in reality because of uncertain setting times during the transportation and construction processes. Comprehensive investigation and understanding of the setting times of LC3 has great significance to industrial upgrading. As a result, this study is committed to comprehensively reviewing the hydration process and the setting time of LC3 materials.

The application of reinforced concrete has been used in various engineering and architecture fields. Stress relaxation and creep are two crucial time-dependent behaviours of concrete. The influence of two behaviours is closely related to the service life of the reinforced concrete structure. However, the research on experimental relaxation behaviour has rarely been extensively studied because of the complicated procedures. Meanwhile, fly ash is commonly utilised to partially replace cement to reduce the greenhouse effect. As a result, this study is committed to examining the creep and relaxation behaviour of fly ash concrete. The concrete creep and relaxation tests were designed to maintain a constant stress and strain levels, respectively. The creep and relaxation tests were conducted at the same time to minimise the shrinkage and ageing effects. The stress and strain levels were selected as 20% and 60% of concrete compressive strength to investigate creep and relaxation in linear and nonlinear cases. By comparing computed values of relaxation from the inverse of the compliance function, the estimated relaxation function showed good agreement using the inverse of the compliance function. However, the existing creep model showed a difference in predicting the creep of fly ash concrete. As a result, the existing model is amended to improve the estimation of creep and relaxation of fly ash concrete.