The Process and the Concrete Properties Necessary for Pumping - Coursework Example

Pumping Concrete The Process and the Concrete Properties Necessary for Pumping Introduction Concrete has always been used as a necessary material tohelp build structures and its knowledge has been passed on to generations and generations. Its importance second only to wood and stone has made it an important material even today. Ancient civilizations used it for their buildings and structures like Egyptian columns or the Coliseum in Rome. In those days, concrete was a very basic substance made of lime, calcium, rock, sand and shale. With the several ingredients assembled in the proper proportions, its importance was again realized. When sand and rock were added and mixed with water, it hardened and made primitive concrete similar to what we use for our buildings and structures today. [3] Conventional methods of placing concrete posed many problems to the engineers of the buildings. For this purpose the 'concrete pump' was invented to pump concrete from far away distances through tubes. Pumping concrete is more economical rather than transporting concrete from a mixing plant to formwork. A continuous feed of concrete can be placed at high speed with access to every part of the site and with no need of transportation. Concrete pumping is sometimes the only possible placing method where the job is inaccessible or the timescale of the construction work makes slower methods impractical. These days pumping is gaining popularity and the only thing that's holding it back is the number of accidents that have taken place while using concrete pumps. [5] Process of Pumping Concrete The process of pumping concrete involves taking many precautions and following strict codes of conduct since many accidents have occurred in the past due to worker neglect. Before Pumping When starting the pumping operation, the pumpers are met with a common problem. The pumping pipes are dry and are usually covered with a thin layer of cement from previous pumpings. While passing through the dry pipes the concrete will gradually dehydrate, creating a plug before reaching the end of the pipe. To solve this, the pump and pipeline must be grouted with about 500 liters of a cement slurry or rich mortar. And thereon pumping should be started immediately after grouting. This can be described in the following steps: [5] 1. Pour slurry or mortar into hopper while operating the pump slowly; 2. Discharge excess grout to waste, not into formwork; 3. Retain some grout in the hopper to be remixed with the first hopper full of concrete; 4. Fit the protecting grill on the hopper before loading concrete. When pumping is done downhill, tight plugs of damp cement bags or a sponge rubber balls should be placed before the grout to make sure that the walls of the pipe are properly lined. [5] Functionality of the Pumping Device In essence, a concrete pump places the mixed concrete at various sites by pumping the slurry. It comprises of a supporting arm which is projected at an operating position and used for positioning the conduit end of a pump conduit. A supporting arm with segments constitutes a component of the pump conduit. In order to achieve a higher lift, device provides the features that at least one of the supporting arm segments is adapted to be telescoped and can be transferred from a non-extended starting position to at least one extended position. [4] Three different kinds of pumping techniques are available to the manufacturers Boom Pump - Boom trucks are self-contained units consisting of a truck and frame, and the pump itself. Because of their reach, boom trucks often remain in the same place for an entire pour. This allows ready mix trucks to release their loads directly into the pumps hopper at one central location and helps to create a more efficient jobsite traffic flow. [1] Line Pumps - Line pumps are versatile, portable units typically used to pump not only structural concrete, but also grout, wet screeds, mortar, shotcrete, foamed concrete, and sludge. [1] Separate Placing Booms - Separate concrete placing booms can be used when a boom truck is unavailable, or in situations where the boom truck may not be able to conveniently access the pour site. Combined with the right concrete pump, these placing booms provide a systematic method of concrete distribution. [1] How Concrete Moves Through the Pump Line The pump line is separated from the concrete when it is initially pumped by pump line walls by a lubricating layer of water, cement and sand. For this purpose, the concrete mix must be suitable for its particular application and also contain enough water for the mix to move easily through the reducers, bends and hoses found in most basic pipeline setups. It is important to have all concrete mixes specified as "pumpable" prior to any concrete pours or many problems and expenditure has to be incurred to resole the problem. [1] Procedure of Pumping Concrete It is important that a safe and practiced procedure be used every time for concrete pumping. It is advised that when pumping, the concrete must fill the forms uniformly and not too quickly. The voids must be filled along the sides of doorways and windows that continue all the way to the foundation before filling the short ones over the bucking. It is important that before pouring the outside of corner forms is braced in both directions to prevent the cement from trying to push them away from the other walls. [2] The idea should be to let the concrete fill the forms from the bottom up, as evenly as possible. As the concrete begins to set, the wall becomes stronger, so by the time a second pumping is done, the first-pass walls will already be strong enough to take the load of the next pour. [2] Properties of Concrete Required for Pumping As mentioned before, the concrete has to be specified as pumpable before pumping is commenced. However minor variations in the concrete mix can make an un-pumpable mix pumpable. The sand grading is particularly important and variations in grading can rapidly cause un-pumpability. Even if only a small part of the mix in the hopper proves to be un-pumpable, the pump may become blocked, leading to a time-consuming and expensive delay while the pump is stripped down, and the blockage removed. Certain considerations such as pre-saturation of lightweight aggregates, use of admixtures and minimum cement content may be necessary. Here are some of those considerations Slump The slump is critical for the mix to flow correctly into the voids of the wall. A thick mixture makes it harder to pump therefore the addition of water provides the moisture necessary for cement hydration which creates the necessary fluidity for pumping the concrete. The more cement, the easier it should be to pump. It not only is stronger due to more bonding ability, cement acts as the lubricant that allows the mixture to slide through a pipe. It will be sticky also from more powder and less water. There must be sufficient cement mortar to bind the rock and there must be enough sand to fill and contain the rock to provide strength. Too many rocks can be a problem in pumping because the sand and cement must support or carry the rock in the pipeline. Too little rock will result in limited strength. [3] PSI Generally a 3000 PSI Tested Compressive Strength will be sufficient, however for multi story structures or for special loads this figure may vary. So as a precaution it is advisable to conduct concrete samples for strength testing during placement. [3] Aggregate The aggregate (the rock) can vary according to the needs of the final product. Most common are rock sizes in the pea rock to 1.5" area. This is the typical pumpable aggregate size that can be used in the pumping industry. Any size rock can be a problem if the remainders of the ingredients are out of proportion. Number 3 pea gravel is a good option. It is advised that crushed rock or large aggregates should not be used since the jagged edges will get caught on the rough surfaces as it tries to flow through the forms. Pea gravel is naturally smoother and it is this difference that makes the formula work and easier for pumping. [2] [3] Gradation Gradation is the most important aspect for pumpability. No matter what the rock size, there must be a little of everything in order for a mix to pump well, and to provide the maximum strength. It is recommended to void voids or 'gap graded' aggregates. When a rock size is specified, that should be the maximum aggregate size with smaller rock always present. [3] Accelerators An accelerator such as calcium chloride is used to quick set the concrete. It is used whenever temperature is too low and/or there is a lack of natural sunlight to permit the natural chemical reaction of cement and water to take place. However it is fairly unpredictable when used in all but the smallest amounts and can "flash" set in minutes. Pumping can become a big issue if the concrete sets in the pipe due to over use of calcium. [3] Colour Additives Colours are added to concrete sometimes for styling purposes. The problem with them is that they are all fairly inert making the load set faster because of the color powder itself absorbs much of the available water before the water can become part of the chemical reaction. [3] Air Entraining Agents Adding air into a mix is a careful balance of necessity and requirement, as air decreases the strength in concrete. Air is not a problem for pumping unless it is of such a quantity that pumping the material actually becomes difficult because the air will compress when pressure is applied by the pump and the material will not pump because all the force of the pump is being absorbed by the air content. This is easily resolved by reducing the air in the mix design. [3] Plasticizers Superplasticizers or High Range Water Reducers are plant added water-reducing admixtures which produces a high slump, flowing concrete. They are ideal and usually necessary for pumping concrete, producing high strength concrete, and enabling concrete to flow around tightly matted rebar. [6] Conclusion Concrete has been used since times immemorial and its importance can be judged by the fact that it is still being used today as a primary agent in constructing buildings and structures. But as time is passing by, newer technology is shaping new paths for us to follow. Pumping concrete is the path for today and it very successful. Concrete pumps can be used to pump concrete from far distances, it saves the time and it is cost effective. However several safety precautions must be taken before hand. Further more the concrete needs to be made pumpable by adding certain admixtures to allow the free flow of concrete through the pipes. Following the instructions given in the above text is important to understand the process and the requirements of concrete properties for utilizing this rewarding technology. Works Cited 1. "Concrete Pumping", 2007, [Internet], Concrete Network, Available at , Accessed on August 7, 2007 2. "Construction > Pumping the Concrete", [Internet], Amazon Gridwall, Available at , Accessed on August 7, 2007 3. Horton, Lee. "What is concrete", [Internet], Available at , Accessed on August 7, 2007 4. Hudelmaier, Gerhard. "Device and method for pumping concrete", 1996 [Internet] Wiki Patents, Available at , Accessed on August 7, 2007 5. "Lubricating suspension for pumping concrete", 1994, [Internet] US Patent, Available at , Accessed on August 7, 2007 6. "What is Concrete By Residential Concrete", [Internet], Residential Mixture, Available at , Accessed on August 7, 2007 Read More