During the mixing and pumping process, the two processes that were originally required need only one operator to complete, which can save 3~4 labors for the construction, which greatly reduces the labor cost.
The mixing and dragging pump is convenient and flexible to move, and has strong maneuverability. It is very suitable for alternate operations in multiple construction sites.
5. Most cities in China have Heavy Branch mixing pump users, the products are well received and trustworthy.
Stirring pump is the best investment choice for entrepreneurs or construction machinery equipment leasing companies. Its investment cost is lower, products are more popular, leasing funds are higher, and the cost recovery period is shorter.
When choosing a method for concrete strength measurement and monitoring, it’s important for project managers to consider the impact each technique will have on their schedule. While some testing processes can be done directly onsite, others require extra time for third-party facilities to deliver strength data. Time is not the only factor that contributes to project managers’ decisions. The accuracy of the testing process is just as important as it directly effects the quality of the concrete structure.
The most common method for monitoring the strength of in-situ concrete is the use of field-cured cylinders. This practice has remained generally unchanged since the early 19th century. These samples are casted and cured according to ASTM C31 and tested for compressive strength by a third-party lab at various stages. Usually, if the slab has reached 75% of its designed strength, engineers will give the go ahead to their team to move on to the next steps in the construction process.
There have been many developments to speed up the curing process since this testing method was first introduced. This includes the use of heating blankets, additives, and vapor retarders, etc. However, contractors still wait three days after their pour before testing for strength, even though their targets are often reached much earlier than that.
Despite knowing that, many project managers prefer to stick to this testing practice because it’s “the way its always been done.” However, that doesn’t mean this technique is the fastest and most accurate method for testing the strength of all their pours. In fact, there are many different practices, aside from cylinder break tests, that can be used. Here are seven different approaches to consider when choosing a method of strength testing:
Methods for Testing Concrete Strength Measurement
Rebound Hammer or Schmidt Hammer (ASTM C805)
Method: A spring release mechanism is used to activate a hammer which impacts a plunger to drive into the surface of the concrete. The rebound distance from the hammer to the surface of the concrete is given a value from 10 to 100. This measurement is then correlated to the concretes’ strength.
Pros: Relatively easy to use and can be done directly onsite.
Cons: Pre-calibration using cored samples is required for accurate measurements. Test results can be skewed by surface conditions and the presence of large aggregates or rebar below the testing location.
Penetration Resistance Test (ASTM C803)
Method: To complete a penetration resistance test, a device drives a small pin or probe into the surface of the concrete. The force used to penetrate the surface, and the depth of the hole, is correlated to the strength of the in-place concrete.
Pros: Relatively easy to use and can be done directly onsite.
Cons: Data is significantly affected by surface conditions as well as the type of form and aggregates used. Requires pre-calibration using multiple concrete samples for accurate strength measurements.
Ultrasonic Pulse Velocity (ASTM C597)
Method: This technique determines the velocity of a pulse of vibrational energy through a slab. The ease at which this energy makes its’ way through the slab provides measurements regarding the concrete’s elasticity, resistance to deformation or stress, and density. This data is then correlated to the slab’s strength.
Pros: This is a non-destructive testing technique which can also be used to detect flaws within the concrete, such as cracks and honeycombing.
Cons: This technique is highly influenced by the presence of reinforcements, aggregates, and moisture in the concrete element. It also requires calibration with multiple samples for accurate testing.
Pullout Test (ASTM C900)
Method: The main principal behind this test is to pull the concrete using a metal rod that is cast-in-place or post-installed in the concrete. The pulled conical shape, in combination with the force required to pull the concrete, is correlated to compressive strength.
Pros: Easy to use and can be performed on both new and old constructions.
Cons: This test involves crushing or damaging the concrete. A large number of test samples are needed at different locations of the slab for accurate results.
Cast-in-place Cylinders (ASTM C873)
Method: Cylinder molds are placed in the location of the pour. Fresh concrete is poured into these molds which remain in the slab. Once hardened, these specimens are removed and compressed for strength.
Pros: Is considered more accurate than field-cured specimens because the concrete is subjected to the same curing conditions of the in-place slab, unlike field-cured specimens.
Cons: This is a destructive technique that requires damaging the structural integrity of the slab. The locations of the holes need to be repaired afterwards. A lab must be used to obtain strength data.
Drilled Core (ASTM C42)
Method: A core drill is used to extract hardened concrete from the slab. These samples are then compressed in a machine to monitor the strength of the in-situ concrete.
Pros: These samples are considered more accurate than field-cured specimens because the concrete that is tested for strength has been subjected to the actual thermal history and curing conditions of the in-place slab.
Cons: This is a destructive technique that requires damaging the structural integrity of the slab. The locations of the cores need to be repaired afterwards. A lab must be used to obtain strength data.
Wireless Maturity Sensors (ASTM C1074)
Method: This technique is based on the principle that concrete strength is directly related to its hydration temperature history. Wireless sensors are placed within the concrete formwork, secured on the rebar, before pouring. Temperature data is collected by the sensor and uploaded to any smart device within an app using a wireless connection. This information is used to calculate the compressive strength of the in-situ concrete element based on the maturity equation that is set up in the app.
Pros: Compressive strength data is given in real-time and updated every 15 minutes. As a result, the data is considered more accurate and reliable as the sensors are embedded directly in the formwork, meaning they are subject to the same curing conditions as the in-situ concrete element. This also means no time is wasted onsite waiting for results from a third-party lab.
Cons: Requires a one-time calibration for each concrete mix to establish a maturity curve using cylinder break tests.
A combination of these methods for measuring the compressive strength is sometimes used to ensure quality control and quality assurance of a concrete structure. A combined method results in a more comprehensive overview of your slab, allowing you to confirm strength data by using more than one testing method. The accuracy of your strength data will also increase as using multiple methods will help account for influencing factors, such as cement type, aggregate size, and curing conditions. For example, a combination of the ultrasonic pulse velocity method and the rebound hammer test has been studied. Similarly, when using the maturity method on your jobsite to test compressive strength, it is recommended to perform cylinder break tests on day-28 of your concrete’s lifecycle for acceptance purposes and to confirm the strength of your in-situ slab.
How to Decide Which Concrete Strength Measurement Method to Use for Your Next Pour
Tests like the rebound hammer and penetration resistance technique, while easy to perform, are considered less accurate than other testing methods (Science Direct). This is because they do not examine the center of the concrete element, only the curing conditions directly below the surface of the slab. Practices, such as the ultrasonic pulse velocity method and the pullout test, are more difficult to perform as their calibration process is lengthy, requiring a large number of sample specimens in order to obtain accurate data.
As destructive testing techniques, the drilled core and cast-in-place cylinder methods need third-party labs to perform break tests in order to get data. As a result, more time is needed in your project schedule when using either of these methods. Comparatively, with the maturity method, you can get strength data in real-time directly on site, allowing for well-informed and quick decision-making. By reducing your reliance on break tests, you can also avoid inaccuracies associated with testing labs.
Learn more about wireless concrete sensors, like SmartRock™,
Your decision in choosing a testing method may simply come down to what you know and are used to. However, the accuracy of these tests and the time they take to obtain strength data, are significant factors that are not always taken into consideration as heavily as they should. Think about where all of your time and money goes during the construction of a project. How much of that is spent on repairs, fees for testing labs, and extra labor to make sure your project finishes on time? The accuracy of the technique you choose can lead to future durability and performance issues of your concrete structure. Furthermore, choosing a technique that takes additional time to receive strength data can be detrimental to your project deadlines, negatively impacting productivity on your jobsite. Conversely, choosing the right tool can positively impact project timelines and allow you to finish the project below budget. How do you decide which strength testing method to use?
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Reinforced concrete structures have shaped our cities for thousands of years, from historical buildings stretching as far back as the Romans to present day, such as the 3-story parking garage adjacent to the mega shopping mall a few miles from your home. As individuals living in the 21st century, experiencing historical buildings is a blessing and something we are all grateful for – success of architects’ past. These magnificent, sometimes intimidating, structures continue to be built. This includes large spanning bridges, government buildings, multi-use high rises, and much more.
However, behind the photogenic façade lies an engineered system of reinforcement – steel reinforcement. Carefully designed, steel reinforcement is an important part of a multi-functioning system that ensures the structures’ integrity. Each reinforced concrete structure has a designed service-life – “the assumed period for which a structure is to be used for its intended purpose with anticipated maintenance but without major repair being necessary” (1).
The initial construction, specifically concrete pouring, curing, and the concrete mix design, are essential to reach or surpass its designed service-life. Further, it is important to inspect the reinforced concrete structure over time to observe any signs of deterioration, and if required, perform remediation.
Methods of Inspecting Service-Life of Reinforced Structures
The most common method for inspecting reinforced concrete structures is visual inspection. This method includes, but is not limited to, checking for cracks, delamination, disintegration, dusting, leakage, and scaling. Further details can be found in “ACI 201: Guide for Conducting a Visual Inspection of Concrete in Service”. Visual inspection reports, gathered over time, provide valuable information on the structure’s health.
However, visual inspection is just that – visual. These inspections are often supplemented with non-destructive tests, destructive tests, and other investigative techniques. The goal of these tests is to understand the condition of the concrete and steel reinforcement, thus, allowing the inspector to conclude on the structures health after interpreting the data. Defects found during visual inspection may require immediate action.
Destructive tests may include concrete coring to help determine compressive strength, carbonation depths, the presence of sulfates and chlorides, and the concrete’s pH level. These tests, especially when performed simultaneously, can provide a substantial amount of data on the concrete’s durability and the condition of the structure. Carbonation and pH tests assess the loss of alkalinity (the steel reinforcements natural protector). Sulfate and chloride sampling provide visibility on harmful agents that may exist in the concrete cover, the amount in which they exist, and their depth. The latter, chloride ingress, is the most prominent cause of deterioration in reinforced concrete in North America and many parts of the world.
Given the significant affect of chlorides on a structure’s durability, inspectors are interested in a multitude of corrosion parameters. Figure 1 shows a representation of service-life stages for structures exposed to chloride-induced corrosion risk.
Figure 1: Schematic Representation of Service-Life Stages for Structures Exposed to Chloride-Induced Corrosion Risk
Further, correctly understanding the time for chloride-induced corrosion to occur is an important step to assess a structures remaining life. The end of service-life can be generalized as the time to cracking resulting from corrosion products formation.
What is Corrosion Rate?
The main challenges of concrete structure inspections are to understand the severity of the corrosion, in other words where in the structure service-life are we located and when the onset of the steel corrosion started. One parameter that is very useful to know is the corrosion rate. Corrosion rate can be defined as the speed at which any metal in specific environments deteriorate (3). Figure 2 illustrates the service-life model of a concrete structure exposed to chlorides.
Figure 2: Service-Life Model of a Concrete Structure Exposed to Chlorides (2)
There are different techniques on the market to measure the corrosion rate of reinforcing steel, however, they all utilize the Stern-Geary equation (shown in the equation below).
Stern-Geary Equation for Determining the Corrosion Rate of Metals
The Stern-Geary equation calculates the corrosion rate by measuring the polarization resistance (Rp), which is the slope of a current-voltage plot, generally from an applied current, and the measured change in potential of the metal in an electrolyte (concrete). Aprepresents the area of polarization. B is a corrosion constant calculated from the anodic and cathodic Tafel slopes (4).
The objective of corrosion rate measurement devices, such as the iCOR®, is to measure the corrosion current on the surface of the rebar due to the transfer of electrons from anode to cathode. This is illustrated in Figure 3. Corrosion rate values are typically outputted in two units: corrosion density (uA/cm2) and corrosion rate (um/year). It’s important to note that the value being measured is the corrosion current occurring on the rebar at that point in time. It can be understood as a snapshot of the corrosion activity at a certain point in time in the structure’s service life.
Figure 3: The Electrochemical Process of Corroding Steel in Concrete
What Can I Do with Corrosion Rate Values?
Generally, as an inspector, the more analysis techniques at your disposal the better. Other techniques such as half-cell potential and concrete resistivity are often used in conjunction with corrosion rate measurements. The higher frequency of testing (within reason) the better. Performing measurements over time is critical when understanding the state of the structure and estimating its remaining service-life.
A 6-year study conducted on a highway-bridge pillar exposed to de-icing salts in Copenhagen illustrates a great example on the importance of corrosion rate testing, factors that influence measurements, and how to interpret the results (5). A portion of the study took corrosion rate measurements at the same locations over a 6-year span as seen in Figure 4. It can clearly be observed when the corrosion propagation period started.
Figure 4: Corrosion Rate Values Measured with the Galvanostatic Pulse Technique
Humidity and temperature will affect the corrosion rate results. Dryer and warmer months are going to slow down corrosion activity, where seasons of heavy rain are more conducive for corrosion activity, as seen in Figure 5. Based on the factors that can impact corrosion rate values, the increase in corrosion rate over time will not always be linear. Figure 5 shows how corrosion activity can change at different time in the year.
Figure 5: Corrosion Rate Values Determined via Post Mounted Sensors
The goal of the corrosion rate testing is to understand the speed at which the rebar is corroding and also to understand how much reinforcement diameter has been lost over time, where 20% of mass loss is a critical threshold for structural failure. In order to understand the total mass loss, it is important to know the corrosion rate activity over time. The integral of the corrosion measurements can be calculated to provide an approximation of the mass lost. It is also important to understand the time at which corrosion started to provide a good estimation.
Lastly, with this data, the inspector can predict the service life of a structure. One way of interpretation can follow the guidance of K.C. Clear (6), whose model is based on the combination of outdoor exposure, laboratory, and field studies.
Figure 6: Estimating Service-Life Based on Corrosion Rate Values
A concrete pump is an extremely vital piece of equipment utilized in huge construction tasks. This is one of the most reliable methods to transfer concrete to a fluid building and construction website. In some building and construction tasks, the positioning of concrete by the pump is the only acceptable technique of supplying the concrete.
Furthermore, the rate of work efficiency when making use of a concrete pump plus their ease of use of the pump implies it is the most cost-effective option for supplying the concrete. The concrete pump is typically made use of on large jobs as well as gives the fastest feasible use of concrete as well as reduces complete cost, power, and workforce.
ehicle Mounted Concrete Pump
The system is set up in a truck as well as has actually a pump affixed to the back of the truck and regulates the positioning of the concrete making use of a push-button control robot( robot de control de botón). Their capacity to pump huge quantities of concrete quickly suggests efficiency and also budget-friendly specifically while carrying out huge building tasks such as large overpasses. Keep in mind that the boosted innovation such as mechanized and also computerized robotic arms allows exact control when clearing liquid concrete.
Keep in mind truck-mounted ( mente montada en camión )concrete pump can stand up to 100 cubic meters of volume in the piping and various accessories, enabling you to work in reasonably cross countries as well as in position where Conveyors may not function. Their sizes can be specified according to the clients requires to satisfy their certain concrete needs needs. The location as well as the functioning area of the site additionally establish the size of concrete pumps required.
A lot of truck-mounted concrete pumps have a large extension therefore making them run in a fixed put on the job site. This is beneficial because that the concrete ingredients transport carts can quickly dump concrete elements straight into the pump tank in a main setting. This simultaneous job implementation makes certain the work is done reasonably quicker which subsequently makes the building and construction price very cost-effective.
Fixed Concrete Pump.
A stationary concrete pump is an unique unit with a trailer-like configuration ( configuración tipo remolque ) and the vehicle is required to draw the pump to the building website. It has rubber pipes made use of to apply fluid concrete to the preferred location area. These rubber pipe systems are often linked by hand either to adjust their dimension by increasing their length to get to a longer distance of at some times they are detached to lower their size for the precise discharge of liquid concrete.
Their rate of discharging the liquid concrete is reasonably much less than that mounted in a vehicle as well as is, for that reason, a preferred system for little installments. such as concrete pieces, sidewalks or swimming pools. They typically pump concrete in much less amount than truck-mounted concrete pumps though they are are a lot more versatile so they can be utilized in places where the truck-mounted concrete pumps can not get to.
Special concrete pump.
The objective of an Unique concrete pump is to operate in the most difficult conditions, such as tunnels or mines. They have special expansions as well as devices such as automatic stress evaluates that enable them to effectively regulate the amount of concrete called for at various periods hence smooth efficiency in such situations.
Advantages of concrete pumps
In the case of pumping concrete, the advantage is that the concrete is transferred faster to the construction website than by the conveyor. This works if you have a large task that calls for a continual supply of concrete such as building slaps and also wall surfaces that requires really details supply rate of the concrete.
It likewise inimizes the time it requires to unload concrete, so you can save on labor costs. Because of the likely rapid positioning of concrete, it lowers and also possibly quality concessions such as cool joints as well as castings.
Concrete can be supplied to the building site outside the concrete mixer, as an example in salt water or across the roads.T his is made possible as a result of the rubber pipe pipelines being adjustable to numerous lengths and diameters in these devices.
When using a concrete pump, there are lots of ways to choose a particular place to apply the concrete hence decreasing wastage. Keep in mind using a concrete pump, much less water is included, which considerably reduces contraction cracks as well as loss of concrete strength. The concrete pump also reduces office website traffic therefore decreasing spreading dust across the workplace.
In some construction tasks, the positioning of concrete by the pump is the only appropriate method of delivering the concrete.
A stationary concrete pump is a distinct unit with a trailer-like setup and also the vehicle is called for to pull the pump to the building website. They typically pump concrete in much less amount than truck-mounted concrete pumps though they are are a lot more flexible so they can be used in places where the truck-mounted concrete pumps can not reach.
When utilizing a concrete pump, there are lots of means to choose a specific area to use the concrete thus reducing wastefulness. Note making use of a concrete pump, less water is added, which significantly reduces contraction cracks and loss of concrete strength.
Stationary Pump had the following main technical parameters such as conveying displacement, export pressure, motor power and distribution valve form. According to the new national standards, these main parameters from the concrete pump model can be learned.
2. Power of electric motor（diesel engine is the same）
The motor power of concrete pump trailer is the precondition to determine the outlet pressure and the amount of conveyor. Under the condition of a certain motor power, the increase of the pressure will reduce the amount of conveyor. On the contrary, reducing the outlet pressure will increase the throughput. In order to ensure that the concrete conveying pump not only has a large amount of conveying, but also has a certain outlet pressure and economic power to match, in the design of concrete conveying pump, the constant power plunger pump is mostly used. That is, after the constant power value is selected, when the outlet pressure rises, the output displacement of the oil pump will automatically decrease to the value corresponding to the power design. If both of them want to achieve high export pressure, and want to get the purpose of large throughput. The only way is to increase the motor power. Therefore, in the new national standard, the concept of capacity index of concrete conveying pump is introduced (taking MPa·m3/h as the measurement unit). the product of the actual outlet pressure of concrete conveying pump and the actual throughput per hour are identified. The larger the value is, the larger the capacity index will be, and the larger the motor power will be. Thus, the purpose of large displacement and high lift can be realized.
Use skills of stationary pump
Operators and relevant equipment management personnel shall carefully read the operating instructions and master the relevant knowledge of its structural principle, operation and maintenance as well as pumping concrete operations; The operation of concrete pump should be strictly in accordance with the operating instructions. Since there is required processes for the operator to fully master the mechanical properties, the instruction manual should be prepared at random. At the same time, it should be based on the use of the manual to develop special operating points, to be able to effectively control some variable factors in the pumping technology, such as pump position, pipeline layout.
The ground supporting theStationary Pump should be flat and solid; The whole machine should be placed horizontally and should not be tilted in the working process. The supporting leg should be able to support the whole machine stably and lock or fix reliably. The pump location should not only be convenient for the concrete mixing truck to enter and exit and feed to the hopper, but also be conducive to the pumping distribution pipe and reduce the pumping pressure loss. At the same time, it should be close to the pouring site and convenient for power supply and water supply.
Stationary Pumpshould be based on the characteristics of the construction site and concrete pouring scheme for piping, piping design to check whether the horizontal conversion distance of the pipeline and concrete pump pumping distance.Piping should be as short as possible, less elbow and hose. Pipeline laying should facilitate pipeline cleaning, troubleshooting and disassembly and maintenance.When the new pipe is mixed with the old one, the new pipe should be arranged at the place with high pumping pressure. In the process of piping, a pipe layout diagram shall be drawn, and the specifications and quantities of various pipe fittings, pipe clips, elbow pipes and hoses shall be listed, and a list shall be provided.
In the process of concrete pumping, with the increment of pump pressure, pumping impact will force pipe moves back and forth, it was not only the pumping pressure loss, and was the connection between pump pipe area was in a state of shock and discontinuous tension, which can lead to the pipe clamp and aprons premature damage, water mud overflow, so the pump must be fixed.
After the connection of theStationary Pump with the conveying pipe, the concrete pump shall be fully inspected in accordance with the operating instructions of the concrete pump, and the machine shall not be started for empty operation until it meets the requirements.After no-load operation for 10min, check again whether all institutions or systems work normally.
During construction in hot season, it was advisable to cover the concrete conveying pipe with wet straw bag, wet cover cloth and other materials to avoid direct sunlight, so as to prevent the concrete from blocking the pipe due to the rapid loss of collapse.When vertical upward piping was required, with the increase of height, namely the increase of potential energy, there is trend of back flow of concrete. Therefore, horizontal pipes of a certain length should be laid between the concrete pump and the vertical piping to ensure sufficient resistance to prevent back flow of concrete. When pumping concrete in high-rise buildings, pipes shall be arranged vertically upward. At this time, the length of horizontal pipes on the ground shall not be less than 1/4 of the length of vertical pipes.If the required length of water pipe cannot be placed due to the limitation of the site, elbow pipe or hose can be used instead.
7. During the stationary pump in the cold region in winter, appropriate insulation measures shall be taken, and the concrete conveying pipe shall be wrapped with insulation materials to prevent the concrete inside the pipe from freezing.When vertical upward piping was required, with the increase of height, namely the increase of potential energy, there is trend of back flow of concrete. Therefore, horizontal pipes of a certain length should be laid between the concrete pump and the vertical piping to ensure sufficient resistance to prevent back flow of concrete. When pumping concrete in high-rise buildings, pipes shall be arranged vertically upward. At this time, the length of horizontal pipes on the ground shall not be less than 1/4 of the length of vertical pipes. If the required length of water pipe cannot be placed due to the limitation of the site, elbow pipe or hose can be used instead.more information please click here
