Impact of the initial moisture level and pre-wetting history of recycled concrete aggregates on their water absorption

Initial moisture and pre-wetting method influence on the water absorption of recycled concrete aggregates (RCA) have been studied experimentally. For this purpose, RCA were pre-wetted by three methods: soaking under partial vacuum (simulating long term wetting), soaking under atmospheric pressure, and spraying (simulating short term wetting). The results show that the same initial amount of water in two samples of RCA do not lead to the same total amount of water absorbed by RCA during 5–120 min. The latter depends on the way they have been pre-wetted (either long term or short term). It is suggested that this phenomenon is related to the accessibility filled pores in the different pre-wetting methods. So, the pre-wetting history of RCA could change the amount of total water absorbed by the RCA up to 1%. When mixing and casting concrete are produced with RCA, the corresponding error in the determination of the effective water should have adverse effects on the fresh and hardened concrete characteristics. In this study real applications on mixtures of recycled concrete have been carried out, where the influence of initial moisture content and pre-wetting history of RCA on fresh recycled concrete properties (slump) have been investigated.     

Slow release somatotropin in dairy heifers and cows fed two levels of energy concentrate. 2. Plasma hormones and metabolites

Fifty Holstein dairy cows (26 primiparous) were used to evaluate effects of level of concentrate and of slow release recombinant bST on plasma hormones and metabolites. Blood was sampled at wk 14 and 20 of lactation, which was 5 and 11 wk after the first bST injection. In addition, at d 3 and 10 after the third bST injection, diurnal profiles of somatotropin and metabolites were studied in 7 bST cows and 5 control cows by blood sampling every 20 min over 6 h. Supplementation by bST enhanced plasma somatotropin and insulin-like growth factor-I but did not significantly affect plasma concentrations of triiodothyronin and insulin. The bST supplementation increased plasma NEFA at wk 14 and reduced uremia at wk 20. Primiparous cows showed higher plasma NEFA and triiodothyronin than multiparous cows at both sampling periods, higher insulin-like growth factor I, and lower beta-hydroxybutyrate at wk 14, and higher glucose and lower insulin at wk 20. In the diurnal kinetic study, bST supplementation did not alter bST spike frequency and duration but increased spike magnitude, the area under the curve above the baseline, and the baseline mean. Sixty-one to 56% of the increase over controls in plasma bST total area was due to increase in the area under the curve above baseline. Preprandial NEFA were increased by bST at d 10.     

PWR steam generator R&D in France: thermal-hydraulic and vibratory aspects

Concomitant with the launching of the French pressurized water reactor (PWR) nuclear power program, a large research and development (R&D) effort was initiated, devoted to the steam generators (SGs). This program, managed cooperatively by Framatome, the SG designer and manufacturer; Electricité de France (EDF), the French electrical utility; and the Commissariat à l'Energie Atomique (CEA), the French Atomic Energy Commission, primarily responsible for nuclear research; was focused on four main objectives:

1. (1) To obtain a better understanding of the physical phenomena existing in these steam generators and leading to SG performance alterations or operating life reductions.

2. (2) To test and validate improved design solutions for the model 51 Framatome steam generator, which was the first one designed under Westinghouse license.

3. (3) To test and validate new Framatome SG designs.

4. (4) To test and validate new, high-performance design tools.

This vast R&D program covers the following theses:

• - SG thermal-hydraulics,

• - SG tube vibration and wear,

• - SG materials (production, corrosion, etc.),

• - Primary and secondary fluid chemistry,

• - SG technology (manufacturing processes, NDT, etc.),

• - SG in-service inspection, and

• - SG maintenance.

These themes are too numerous to be dealt with in a single article. Consequently, the present article will focus on only the first two themes.     

Slow release somatotropin in dairy heifers and cows fed two levels of energy concentrate. 1. Performance and body condition.

Fifty-two Holstein dairy cows (27 primiparous) were used in a 2 x 2 factorial design during wk 9 to 39 of lactation to assess the effects of slow release recombinant bST (500 mg injected at 14-d intervals) and the effects of the level of energy concentrate in the diet on dairy performance. After a winter period, cows were turned out to pasture at wk 24 of lactation. During winter, cows given low concentrate (2.5 vs. 5.4 kg DM/d) ate significantly more corn silage (13.9 vs. 11.9 kg DM/d), so that treatment had no significant effect on any measured parameter. The milk yield of bST-supplemented cows increased by 2.1 kg/d (11.0%) throughout the total experimental period. The response did not differ according to parity. Milk fat content and SCC were not altered, but milk protein was lower (.8 g/kg) from cows receiving bST during winter, and lactose increased (.5 g/kg). Lactation curves of bST-supplemented cows showed a cyclic response in milk production. Gross efficiency of milk yield was improved (.18 units) by bST administration without change in diet digestibility. No difference due to bST was found in the health or reproduction of cows. Live weight change did not differ among the groups. Multiparous cows gained body condition (bST-supplemented animals gained less than controls: .1 vs. .7 point on a five-point scale; NS). Control primiparous cows gained body condition (.1 point) but bST-supplemented cows significantly lost body condition (1.4 point).     

Statistical continuum theory for the effective conductivity of fiber filled polymer composites: Effect of orientation distribution and aspect ratio

Effective conductivity of polymer composites, filled with conducting fibers such as carbon nanotubes, is studied using statistical continuum theory. The fiber orientation distribution in the matrix plays a very important role on their effective properties. To take into account their orientation, shape and distribution, two-point and three-point probability distribution functions are used. The effect of fibers orientation is illustrated by comparing the effective conductivity of microstructures with oriented and non-oriented fibers. The randomly oriented fibers result in an isotropic effective conductivity. The increased fiber orientation distribution can lead to higher anisotropy in conductivity. The effect of fiber’s aspect ratio on the effective conductivity is studied by comparing microstructures with varying degrees of fiber orientation distribution. Results show that the increase in anisotropy leads to higher conductivity in the maximum fiber orientation distribution direction and lower conductivity in the transverse direction. These results are in agreement with various models from the literature that show the increase of the aspect ratio of fibers improves the electrical and thermal conductivity.     

Cooperative viscoplasticity theory based on the overstress approach for modeling large deformation behavior of amorphous polymers

A micromechanically based formulation of the cooperative model is incorporated into the viscoplasticity theory based on overstress (VBO) model. The plastic shear strain rate given by the cooperative model is used as a flow function which is responsible for rate and temperature dependence in the VBO model. In this way, thermomechanical analysis can be performed under different loading rates and temperatures of amorphous polymers. Introducing strain softening, the temperature‐ and strain‐rate‐dependent elasticity moduli are two other modifications of the VBO formulation. The validity of the newly proposed cooperative VBO model is demonstrated by modeling the uniaxial compression behavior of poly(methyl methacrylate) under different temperatures and strain rates. © 2013 Society of Chemical Industry     

High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties

This paper presents an experimental study on the properties of self-compacting concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete mixture were tested. These concrete mixtures come from the French National Project B@P. The specimens of each concrete mixture were heated at a rate of 1 °C/min up to different temperatures (150, 300, 450 and 600 °C). In order to ensure a uniform temperature throughout the specimens, the temperature was held constant at the maximum temperature for 1 h before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. In this paper, the physicochemical properties and the microstuctural characteristics are presented. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and SEM observations were used. The aim of these studies was in particular to explain the observed residual compressive strength increase between 150 and 300 °C.     

Three-dimensional transient finite element analysis of the selective laser sintering process

A transient three-dimensional finite element model is developed to simulate the phase transformation during the selective laser sintering process; taking into account the thermal and sintering phenomena involved in this process. A bi-level structure integration procedure is chosen, in which the temperature dependent thermal conductivity, specific heat, and density are integrated at the outer level then used as material constants for the integration of the heat equation in the inner level. Results for temperature and density distribution, using a polycarbonate powder, are presented and discussed.