Contribution on the Use of Household Waste as Bio-Admixture

In the civil engineering field, the incorporation of chemical admixtures is now a practical technics' used for improving the properties of concrete, such as improved workability, decreasing the water demand, increasing strength, etc. However, chemical admixtures have some disadvantages such as environmental pollution during both their manufacture and their use, else, there are rare somewhere. Because of this background, bio-admixtures appear principally useful, due to their environmental effect and friendly properties, bio-admixtures are substances obtained from a biodegradable product also resulting from the methanisation. The objective of this research is the valorization of household waste used as a bio-admixture. Moreover studying its effect on cement path workability, start/end of the cement setting.

A Coupled Model of Temperature and Pressure for Managed Pressure Cementing in Deep-Water Region

The narrow density window in deep-water environment brought great challenges to well drilling and completion by causing well control issues. Managed Pressure Cementing (MPC) is a new technology developed from Manage Pressure Drilling (MPD), which can precisely control the annular fluid pressure profile. Accurate calculation of wellbore temperature and pressure is the key to MPC. This paper focus on coupled models of temperature and pressure for MPC in deep-water region. The well cementing process can be divided into two stages: fluid displacement stage and cement setting stage, which displays different characteristics. During the cementing displacement stage, the cement is in a flowable slurry state and is circulated into the annulus. During this process, the rheology of fluids if effected by temperature in wellbore. On basis of the fluid rheology model, a coupled model of temperature and pressure in wellbore is established considering the transient flow characteristics during cementing displacement stage. During cement setting stage, the cement slurry stops flowing and the significant cement hydration reaction starts. A large amount of hydration heat and obvious pressure reduction can be observed. On basis of the cement hydration kinetics model, a coupled model of temperature and pressure in wellbore during cementing setting stage is established. Based on the models established in this paper, a series of numerical simulations are conducted using a deep-water well. Simulation results show that neglecting the complicated interactions between temperature and pressure can cause a big error. During the cementing displacement stage, higher temperature in the deep part of wellbore reduces the fluid viscosity, which leads to a smaller friction. On the contrary, larger friction is observed near seabed as a result of the low temperature in deep-water environment. The pressure in wellbore changes frequently due to the coexistence of multiple fluids in wellbore. Therefore, a frequent control of annular fluid pressure is required using the MPC technology. During the cement setting stage, an obvious temperature increase is observed as a result of cement hydration heat. The pressure decreases with the depending of cement hydration. An addition back pressure at wellhead has to be added using the MPC technology. The transient temperature and pressure have impact on the rate of cement hydration in turn. Cement in the deep part of wellbore have a faster rate of cement hydration. The low temperature at mudline slows the cement hydration process. Considering the complicated interactions between temperature, pressure, cement hydration and fluid rheology, coupled models between temperature and pressure based on hydration kinetics during well cementing in deep-water region is established in the manuscript. The new model established in this paper plays an important role in the MPC technology.

Solidification Effect and Mechanism of Marine Muck Treated with Ionic Soil Stabilizer and Cement

In this study, an environmentally friendly ionic soil stabilizer (ISS) was adopted with combination of Portland cement to stabilize a marine muck. The macro and micro tests results demonstrated that the ISS was an effective stabilizer to improve the strength of marine muck when it was used combined with cement after adding the alkalizer NaOH. Except for the reduction in interlayer distance of clay minerals by ISS, Ca2+ and SO42− dissolved from ISS promoted the production of ettringite (AFt), pozzolanic and carbonation reactions of Portland cement in the presence of NaOH. Meanwhile, the hydration products of curing reaction notably agglomerated soil particles, which caused an obvious decrease of pores and a high increase of strength for solidified soils. Furthermore, this combination of stabilizers can not only save the dosage of cement, but also accelerate the solidification speed, decrease the cement setting time within 7 days to meet the curing requirements, and enhance the strength of solidified soils.

A Feasibility Study on Production of Concrete Blocks Using Treated Municipal Solid Waste Leachate

Population growth and development have increased the need for drinking water all over the world. Hence, it is required to find an alternative to water in different industries. Concrete represents a remarkable water-consuming industry. The present study investigates whether the treated leachate of municipal landfills can be employed as a substitute for water in the concrete mixing scheme. For this purpose, concrete samples fabricated at different concentrations of treated leachates were compared to the control sample containing distilled water in terms of unconfined compressive strength (UCS) at the ages of 7 and 28 days. The experimental results revealed treated leachate accelerated the cement setting time by nearly 15 min and increased concrete slumping by 16%. The complete replacement of distilled water with treated leachate decreased UCS by 25% (from 50 to 38 MPa). The scanning electron microscope (SEM) and ultrasonic results showed that a rise in the treated leachate content of concrete increased porosity. Increased porosity would reduce UCS. The presence of heavy metals and leaching from the cement matrix are important characteristics of leachates. The toxicity characteristic leaching procedure (TCLP) revealed that the leaching of heavy metals in all the samples was in the acceptable range.

Fellows and Observers Are Not a Problem for Infection in the Operating Rooms of Teaching Centers

Purpose: The aim of the present study was to determine whether the risk of complications increases with the number of people in the operating room (OR). Several studies have stated that an increased number of people in the OR increases not only the risk of infection but also the risk of intraoperative complications due to distractions during the surgery. Materials and Methods: This retrospective study included all patients who had surgery between January 2017 and January 2018 in an OR with the usual surgical team and three or more observers. Patient demographic data, surgical details (duration of the surgery, the surgery being open or arthroscopic, and whether a graft was used), and intraoperative and postoperative complications were recorded. Results: A total of 165 surgeries were recorded, with a mean operating time of 70 min (40% open surgeries, 37% arthroscopic surgeries, and 23% combined open and arthroscopic procedures). The main intraoperative complications were vessel damage, nerve damage, premature cement setting, and leg-length discrepancy, with 1 case each. The main postoperative complications were rigidity (8 cases), unexplained pain (11 cases), failed meniscal suturing (3 cases), a postoperative stress fracture (1 case), correction loss in osteotomy (1 case), and wound problems not related to infection (1 case). There were no cases of infection. Discussion: The present study shows that the complication rate when having observers in the OR is comparable to the reported data. The key to avoiding complications is for everyone to comply with basic OR behavior.

Alternative methods of delivering concrete and mortar mixes to low-rise construction projects

Concrete mixes are usually delivered to construction projects with the help of special vehicles. Depending on its fluidity, cement setting rate, temperature and relative humidity of carriage conditions, as well as a distance and road condition, transportation of a concrete mix may be done in concrete mixer trucks and ready-mix delivery trucks, also in buckets and hoppers mounted on vehicles (bucket trucks). At the same time, it is necessary to reduce the number of transship operations as much as possible and, wherever practicable, unload a mix directly into the structure to be concreted. Each method of transportation has its rational areas of application. For low-rise construction characterized by small volumes, scattered construction sites, insufficient coverage by a good-quality road system, and a long distance from concrete factories, it is expedient to use alternative, non-dedicated to concrete mix transportation, types of vehicles equipped with their own lifting devices. The issues of application of drop-side lorries with crane manipulators and gantry hopper trucks for transportation of ready-mix buckets are discussed. The technical characteristics of general purpose vehicles and lifting equipment are described. Recommendations concerning fitting of various types of vehicles with portable hoppers are given.