Lithium Ion (Li-Ion) battery technology is one of the fastest-growing trends in the tool community, and certainly for good reason. Lithium Ion batteries have the best energy to weight ratio, meaning they pack the most power with the smallest amount of bulk. They also experience no memory effect or, lazy battery effect. This occurs when a battery can no longer accept a maximum charge for having been repeatedly recharged without being fully used (a common symptom of Nickel Cadmium (NiCad) batteries). Li-Ion batteries, conversely, have absolutely no memory and can continually accept a maximum charge. Additionally, Lithium-Ion batteries have a very slow rate of charge loss while the battery is disengaged.
What is the difference between Lithium Batteries and Lithium Ion Batteries?
The difference is in the chemistry; a Lithium battery is a disposable power source composed of lithium metal compounds – the key word, here, being disposable; Lithium batteries can not be recharged. Lithium Ion batteries, on the other hand, are intercalated, meaning the lithium ion inside the battery moves between two internal electrodes. This movement, or reversibility of the lithium ion accounts for the battery’s rechargeability.
What are the benefits of Lithium Ion Technology?
— Lithium Ion batteries hold a lot of power and are surprisingly light-weight, especially with consideration to other rechargeable batteries.
— Li-Ion batteries combine single cell technology with a greater energy reservoir than Nickel Metal Hydride and Nickel Cadmium batteries. They store more power for their size than both NiCad and NiMH.
— Li-Ion batteries hold their charge for significantly longer than other comparable batteries, and provide steady power until that charge is completely gone. Other batteries gradually and consistently loose power as you work. Li-Ion batteries stay strong until the last push.
Are there disadvantages to using Lithium Ion Batteries?
The disadvantages with using Li-Ion battery technology are generally few and far between, and technological advancements are making them even less so. Manufacturers have recently improved the Lithium Ion recipe to reveal a more reliable battery. Still, every giant has its weaknesses:
— Li-Ion batteries are sensitive to intense hot and cold temperatures. In extreme temperature conditions, the battery will degrade more quickly.
— Li-Ion batteries degrade regardless frequency of use.
— The Li-Ion battery’s built-in computer chip tells the battery to refuse a charge once the batteries power falls below a certain point. If this occurs, the battery is beyond repair.
Although these defects are more applicable to the older Lithium Ion batteries, the possibility of seeing these problems is still worth noting. Fortunately, these said defects are fairly rare, and easily avoided.
— Store Li-Ion batteries (and other batteries as well) in a cool, dry place.
— Use your Li-Ion batteries often.
— Be certain Li-Ion batteries have a full charge before storing them and pull them out every so often to use and recharge. Watch the batteries power level to be sure it doesn’t fall below the charge limit.
General Li-Ion Battery Tips:
— On occasion Lithium-Ion batteries require more than one charge (sometimes 2 to even 10) to accept a full charge. The first time you charge your battery, leave it to charge overnight. This ensures you’ll have maximum power for your first use.
— To maintain proper balance in your battery, leave it to charge over night about once per week for the life of the battery.
— When buying a new Lithium Ion battery, make certain you are buying a fresh one. There’s a chance a battery has been degrading on the shelfs of manufacturers and distributor’s so certain you are buying a new one. Most manufacturers provide a date code on the battery or packaging. Check dates before you purchase, and be confident you are getting a fresh, high-performance battery.
Batteries are an essential part of a vehicle and should not be overlooked. Without a healthy battery, the car stands still. We are responsible for how long they can support our vehicle. To extend their lifespan, we need to properly maintain them. Maintenance free batteries are slowly taking over lead-acid batteries but it is important to understand that the basic principle remains the same. We will discuss all the important aspects of a battery in this article.
How does a battery work?
Lead acid car batteries are energy storing devices made up of lead and lead dioxide plates. These plates are submerged into an electrolyte solution. The percentage of water is 65% and sulphuric acid contributes 35% to this solution. When the battery is used to start the car, it gets discharged. The sulphuric acid in the electrolyte solution gets depleted leaving a higher proportion of water. The sulfate is returned to the acid during the charging process. The battery provides high current required by the starter motor to crank the engine of the car. Once the engine is started, the battery is again recharged by the engine driven charging system. In this process, the alternator takes necessary energy from the rotation of engine through a belt to charge up the battery. When the engine is running, the alternator generates electricity for the electrical equipment of the car.
What makes a battery weak?
When the car is exposed to direct sunlight in summers for longer periods of time, it accelerates the process of corrosion and evaporates the electrolyte. This reduces the life of a battery making it weaker. So, avoid getting your car heated by sunlight by parking in a suitable shade.
A battery must be fitted properly to avoid any sort of vibrations. These vibrations over the time shake the plates around which in turn make the internal connections lose. As a result, the battery would not get properly charged.
Once you start the car, make sure to drive it for enough time for the battery to get recharged again. The alternator takes time to recharge the battery after it has released its energy while starting the engine. Otherwise, the battery will stay undercharged which is not sufficient to provide high current to the starting motor.
Keeping the headlights or music system on while the engine is shut down drains the battery over the time. Avoid plugging in a charger for a longer period of times to prevent the battery from discharging.
Corrosion on battery terminals is as harmful to the battery as anything else. Always clean the battery terminals carefully once or twice in a month. Make sure to wear gloves and eye protection. The white powder on terminals is toxic and should not be allowed to come in contact with the skin.
Signs that indicate battery replacement:
There are a couple of signs that may indicate your battery is getting weak and needs a replacement.
The bright headlights of the car become slightly dim when the engine is turned off.
The starter motor turns slowly when you start the car due to the low current provided by the battery.
There are a few visual signs that indicate the battery needs a replacement.
An internal short circuit or overcharging leads to a swollen battery. If you see signs of bulging anywhere around the battery, replace it.
Examine the battery case carefully for any damage to the battery case.
How to start an engine with a weak battery?
It is not recommended to use a weak battery. However, in an emergency case, jumper cables can be used when you are stuck during your trip along the roadside. Always keep a set of jumper cables in your car if you think the battery is not in a supreme condition. Jumper cables let you jump start your vehicle with the help of another car. Although it is a very simple technique but safety measures must be taken to avoid any danger. Following steps will guide you to jump-start the vehicle:
Make sure both batteries have the same voltage rating i.e. 12 V
Turn off the ignition switch after parking it close enough to the other car in neutral position.
Never jump a frozen battery. It can easily explode.
Wear rubber gloves and safety glasses.
Carefully identify and connect the positive terminals of both batteries to each other.
Make sure the other end does not touch car’s body to avoid any dangerous spark.
Clamp the negative cable to the negative terminal of the good battery.
Connect the other end of the negative cable to a metal part of the car with a weak battery.
Now start the ignition of the car with a weak battery.
Carefully remove the cables in reverse order. Remove the negative cables first followed by removing the positive cable from the car with the good battery. In the end, remove the positive cable from the car with a weak battery.
How to check battery’s health?
For proper maintenance of battery, schedule once a month to check the status of the battery. Nowadays there are tools that can help measure the present condition of the battery. Following are the most commonly used tools for this purpose:
Battery load tester:
Battery load tester is used to check the voltage rating of the running battery. It has a display meter with voltage readings up to 16V along with the battery health indicator. It has positive and negative probes. Inside, there is a high current capacity coil which provides the necessary load with a toggle switch. Battery voltage can be tested easily by following these steps:
Turn off the car engine.
Connect the positive probe of load tester with the positive terminal of the battery.
Similarly, connect the negative probe with the negative terminal.
Make sure both probes are properly connected with the battery terminals.
The meter will show a voltage reading in accordance with the health of the battery.
Now, turn on the load toggle switch for 05-07 seconds to measure the battery voltage on load.
A healthy battery ideally shows 12.5 volts.
If the meter needle deflects anywhere near the “weak” indication, immediately replace the battery.
Safely remove the probes in reverse order.
Hydrometer:
The hydrometer is another tool to measure the battery health. It measures the specific gravity of electrolyte but can only be used on batteries with removable caps. Hydrometers usually have a built-in thermometer. Follow these easy steps to measure the remaining battery life:
Start with removing caps from the top of the battery.
Dip the tip of the hydrometer in the first cell of the battery.
Squeeze and release it from behind to let the electrolyte enter into the cylinder of the hydrometer.
Read the specific gravity of electrolyte as indicated.
Note the reading for all cells one by one.
Make a comparison of readings with those one given on hydrometer.
Usually, readings between 1.265 and 1.299 indicate towards a charged battery. Any reading under this bracket show signs of a weak battery.
Another method to examine battery health is to use a multimeter. This process is similar to the one we used for the battery load tester.
How to replace a battery?
A car battery can be easily replaced at home without any complication by following these simple steps:
Removing the old battery:
Start with removing negative terminal of battery usually marked as black or with (-) symbol to avoid any arcing with the wrench.
Disconnect the positive terminal usually marked as red or with (+) symbol.
Remove the “hold down clamp” of battery
Batteries are heavy in weight so lift it up carefully.
Clean the battery tray if it is corroded.
Connecting new battery:
Carefully lift in the new battery in its position.
Properly connect the “hold down clamp” first.
Connect the battery terminals in reverse order by connecting the positive terminal first.
Connect the negative terminal of the battery.
Make sure the connections are not loose.
Battery must be fixed properly to avoid any vibrations.
Terminals must be in a clean condition.
Add some petroleum jelly on both terminals as it reduces the process of corrosion.
The old battery can be sold to a battery shop from where you have purchased the new one. These car batteries are also recycled to prevent dangerous chemicals from getting into the atmosphere. Old lead plates can also be recycled into various other products.
How to maintain your battery?
To extend the battery life, it should be well maintained. Schedule the maintenance of battery every month. It includes following few things:
Cleaning battery and its terminals:
Cleaning of a battery involves removing the corrosion or any white powder from the terminals and the surface of the battery. For this purpose, use warm water and add a tablespoon of baking soda to it. Carefully remove the battery (as mentioned in replacement section) Make sure the removable caps are properly tight. Always use rubber gloves because the white powder is toxic and should not be allowed to come in contact with the skin. Thoroughly apply the solution over the battery case. Clean the terminals properly. Use a brush to reach narrow spaces. Let the solution for a couple of minutes and then wash it with cold water. The terminals will be corrosion free after this practice. Install the battery back to its position with care.
Inspection of Electrolyte level:
Electrolyte level inside a battery can be examined visually by removing the caps on top of the battery. The lead plates must be dipped properly into the electrolyte solution. If you see a decreased level of electrolyte in any of the cells, add some water into it. Let the solution get mixed properly.
Using a battery charger/maintainer:
If your car is idle for a long period, use a battery charger to keep the battery properly charged. Batteries soon become dead if you don’t charge them. A battery charger can be of great help to keep the desired voltage output from the battery. Usually, it comes in different modes as per requirement i.e. charging, boost charging and maintainer. It can also be used to maintain battery voltage. Carefully plug in the charger into a socket. Connect the positive cable with the positive terminal of the battery and negative cable to the negative terminal. Turn on the switch and let the battery charge properly.
Always inspect the battery before leaving on a trip. Overlooking the condition of battery might bring you trouble in the middle of nowhere. A 10-15 minutes inspection might help you save a lot of time during your journey. If you know any other important aspect related to batteries, do mention in the comments section below.
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
