Development of Flotation Device for Removing Unburnt Carbon in Fly Ash for Use in Hardened Cementitious Materials

The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15–30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible.

Technological Capabilities of Well Cementing

Cementing of casing string is a final operation before the next stage of well construction; it provides maximum operational life of the well. Cementing of casing string is carried out with the use of technology, based on squeezing of the whole volume of drilling mud by special grouting composition. The main purposes of cementing include isolation of water-bearing horizon, strengthening of borehole walls in unconsolidated and unstable rocks. Well cementing process is divided into five subsequent operations. Firstly, grouting mixture is prepared in concrete mixers (cementing units) with necessary water-to-cement ratio and additives. Secondly, prepared grouting solution is injected in a well. Thirdly, the solution is squeezed into the space between the casing pipes and wellbore walls. Then it is necessary to wait until the cement sheath is hardened. And at last, quality control is carried out. For convenient transportation, the equipment for well cementing is installed on the truck chassis (KAMAZ, URAL and etc.). All components are poured in concrete mixer, then the water is added and everything is being mixed until formation of uniform mass, which is later pumped in a well. Oil and Gas Industry Safety Regulations say that «calculated endurance of casing string cementing should not exceed 75% of time of cement thickening, established by laboratory tests». Therefore, it is necessary to carry out all operations of injection of fluids into the well as soon as possible without any incompliances of the cementing technology. With cementing material used and its water-to-cement ratio of 0.5, the average time of cement thickening is 120 minutes, according to laboratory tests. Therefore, a set of operations of injection of fluids should not exceed 90 minutes.

Experimental Study on Fly-Ash Aggregate as a Lightweight Filler in a Structural Element

Light-weight structures are widely used in the construction field. Light-weight fillers such as aggregates can be used to improve weightless structures. Generally, standard aggregates cannot be used to attain the desired weight for light-weight structures. To determine a light-weight filler, the aggregates are made by using fly-ash along with cement mortar. Fly ash was collected from the Mettur Thermal power plant. Cement and fly-ash were mixed in a concrete mixer in a proportion of 30:70 with a water-cement ratio of 0.3 and it is mixed until the pellets are formed. The aggregates are replaced at different percentages such as 0%, 10%, 20%, and 30% respectively to the coarse aggregate. The properties such as compressive strength, split tensile strength and flexural strength were taken. The maximum strength was attained at 30% of fly-ash aggregate with a compressive strength of 46.47 N/mm2, split tensile strength of 14.85 N/mm2 and flexural strength of 3.80 N/mm2.

Development of High-Strength Foamed Concrete Compositions

Unlike traditional materials, the development of high-performance foamed concrete with a compressive strength of up to 20 MPa and a density of up to 1400 kg/m3 allows the use of foamed concrete as a constructive material with additional functions including good thermal insulation properties, sound insulation and capillary porosity needed to ensure hydrothermal conditions. Unlike autoclaved aerated concrete, foamed concrete can also be used in monolithic construction.The studies of high strength foamed concrete were performed by using mostly local mineral components and mixing technology by using planetary activator which provides a fundamentally new mixing mode that combines intensive mixing, foaming and activation of components. To realize the experimental part of the research, turbulence type foamed concrete mixer SPBU-LUKS was used.

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.