Effect of Linkage Bond between Backbone and Side Chain in Comb-Like Copolymer Dispersants on Early Properties of Concentrated Cement Suspensions

AbstractComb-like copolymer, consists of backbone with ionizable group and charge neutral poly(ethylene oxide)-based “teeth” side chain grafted onto the backbone at frequent intervals, has been widely used as superplasticizer in concrete industry due to its unique properties compared to traditional polyelectrolyte dispersants, such as lower dosages, outstanding water reduction, excellent workability retention and lower shrinkage. It is easy to modify and adapt this molecular structure in order to maximize the targeted properties and also meet specific properties for different applications. However, modification attempts usually focused on the side-chain length and charge density. In fact, the linkage bond between backbone and side chain has greatly influence on the early behavior of cement suspensions due to copolymers with different linkage bond have different structure stability under the strong basic environment. In this study, two comb-like copolymer dispersants with different linkage group (ester and ether) were produced. The effects of the type of linkage bond in comb-like copolymers on the adsorption characteristics and hydration behavior of concentrated cement suspensions, were investigated by means of Total organic carbon analyzer(TOC),DSC-TG and calorimetric device and Environmental Scanning Electron Microscope(ESEM). Test results showed that the comb-like copolymer with ester linkage bond, has lower initial adsorbed amount, and thus not only accelerate the hydration rate, but also change its crystal shape of hydrated cement. This will help in the understanding of the structure-property relationship of comb-like copolymer and in the designing the molecular structure of new functional superplasticizer

Behaviour of a FRP anchor for seismic strengthening of clay brick masonry walls

Fibre reinforced polymer (FRP) anchors made from rolled or folded fibres have been shown to be an effective technology for delaying or even preventing premature debonding failure in concrete structures strengthened with externally bonded FRP. It would naturally be expected that the use of FRP anchors can improve the earthquakeresistance of FRP strengthened structures by increasing its loading capacity and ductility especially the latter. This study explores the application of FRP anchors in seismic strengthening of clay brick walls. One unique feature of such a system is that the brick unit has smaller dimensions compared to common concrete specimens. This paper reports an experimental pull out study of these FRP anchors. Test parameters included anchor construction, the diameter of the anchor, and the size of predrilled holes in clay brick. The experimental results indicate that FRP anchors can be designed to achieve high loading capacities and hence can be effectively used to prevent or delay FRP debonding failure. The results also indicate that the geometry of the anchor system has a significant effect on its loading capacity

Carbon Stocks across a Fifty Year Chronosequence of Rubber Plantations in Tropical China

Transition from forest to rubber (Hevea brasiliensis Muell. Arg.) plantation has occurred in tropical China for decades. Rubber has been planted on 1 million ha to provide raw materials to the rubber industry. The role of various-aged rubber plantations in carbon (C) sequestration remains unclear. The biomass C accumulation including latex C and C distribution in soil of five different-aged stands (7, 13, 19, 25 and 47 years old) were examined. The total biomass C stock (TBC) and total net primary productivity (NPPtotal), whether with or without latex C, had a close quadratic relationship with stand age. Regardless of stand age, around 68% of the C was stored in aboveground biomass, and NPPlatex contributed to approximately 18% of C sequestration. Soil organic carbon stock in the 100-cm depth remained relatively stable, but it lost about 16.8 Mg ha−1 with stand age. The total ecosystem C stock (TEC) across stands averaged 159.6, 174.4, 229.6, 238.1 and 291.9 Mg ha−1, respectively, of which more than 45% was stored in the soil. However, biomass would become the major C sink rather than soil over a maximal rubber life expectancy. Regression analysis showed that TEC for rubber plantation at 22 years is comparable to a baseline of 230.4 Mg ha−1 for tropical forest in China, and would reach the maximum value at around 54 years. Therefore, rubber plantation can be considered as alternative land use without affecting net forest ecosystem C storage. In addition to the potential C gains, a full set of ecosystem and economic properties have to be quantified in order to assess the trade-offs associated with forest-to-rubber transition

On the Data Freshness for Industrial Internet of Things With Mobile-Edge Computing

This article studies the freshness of information with the aid of Age of Information (AoI) in the Industrial Internet of Things (IIoT), which plays a vital role to ensure quality and timely delivery of data services. To reduce the AoI, we leverage mobile-edge computing (MEC) to partially offload information to the mobile edge server. Aiming to cope with the packet error in the setting of short packet communication (SPC) in IIoT, we consider the standard automatic repeat request (ARQ) protocol with two policies, i.e., either retransmitting an out-of-date packet (RO) or transmitting a freshest packet (TF), when a packet error occurs. We derive the closed form of average AoI under these two policies, respectively, and then formulate the average AoI minimization problem by jointly optimizing the short packet blocklength and MEC offloading ratio. Due to the nonconvexity nature of the problem, we tackle it by employing block coordinate descent (BCD) and successive convex approximation (SCA) methods and then prove their convergence. Our extensive numerical results show that the optimal average AoI yielded by our proposed approach is almost identical to that from the high-complexity exhaustive search method, and has significant improvement over the benchmark methods. From the AoI perspective, it is revealed that the optimal strategy tends to offload all information to mobile edge server when the computing capacity of local device is less than a threshold. Furthermore, it is found that the RO policy is suitable for the relatively small bandwidth and large local computing capability scenario, whilst the TF policy is better for the large bandwidth and small local computing capability case

Flow-Field Characteristics of High-Temperature Annular Buoyant Jets and Their Development Laws Influenced by Ventilation System

The flow-field characteristics of high-temperature annular buoyant jets as well as the development laws influenced by ventilation system were studied using numerical methods to eliminate the pollutants effectively in this paper. The development laws of high-temperature annular buoyant jets were analyzed and compared with previous studies, including radial velocity distribution, axial velocity and temperature decay, reattachment position, cross-section diameter, volumetric flow rate, and velocity field characteristics with different pressures at the exhaust hood inlet. The results showed that when the ratio of outer diameter to inner diameter of the annulus was smaller than 5/2, the flow-field characteristics had significant difference compared to circular buoyant jets with the same outer diameter. For similar diameter ratios, reattachment in this paper occurred further downstream in contrast to previous study. Besides, the development laws of volumetric flow rate and cross-section diameter were given with different initial parameters. In addition, through analyzing air distribution characteristics under the coupling effect of high-temperature annular buoyant jets and ventilation system, it could be found that the position where maximum axial velocity occurred was changing gradually when the pressure at the exhaust hood inlet changed from 0 Pa to −5 Pa

Coordination contracts of dual-channel with cooperation advertising in closed-loop supply chains

On the background of an online/offline dual channel, this paper studies contract coordination of centralized and decentralized dual-channel closed-loop supply chains. With the feature of recycle rate fluctuation, we develop a revenue-sharing mechanism by taking the relationship between the recycle rate and the recycle revenue sharing ratio into consideration. After comparing of centralized decision and the manufacturing led decentralized decision, the optimal online/offline price, wholesale price and advertising investment are derived. The influence of revenue sharing ratio in forward and reverse channels on the online/offline prices and wholesale prices is discussed. The numeric example is used for observing the relationship between variables, and between the optimal profit and variables through analysis of changing parameter valuations

Modifying Cement Hydration with NS@PCE Core-Shell Nanoparticles

It is generally accepted that fine particles could accelerate cement hydration process, or, more specifically, this accelerating effect can be attributed to additional surface area introduced by fine particles. In addition to this view, the surface state of fine particles is also an important factor, especially for nanoparticles. In the previous study, a series of nano-SiO2-polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized, which have a similar particle size distribution but different surface properties. In this study, the impact of NS@PCE on cement hydration was investigated by heat flow calorimetry, mechanical property measurement, XRD, and SEM. Results show that, among a series of NS@PCE, NS@PCE-2 with a moderate shell-core ratio appeared to be more effective in accelerating cement hydration. As dosage increases, the efficiency of NS@PCE-2 would reach a plateau which is quantified by various characteristic values. Compressive strength results indicate that strength has a linear correlation with cumulative heat release. A hypothesis was proposed to explain the modification effect of NS@PCE, which highlights a balance between initial dispersion and pozzolanic reactivity. This paper provides a new understanding for the surface modification of supplementary cementitious materials and their application and also sheds a new light on nano-SiO2 for optimizing cement-based materials