Cast-In-Place Concrete Vs. Shotcrete: What's The Difference?
Wednesday, March 13, 2019
Today, the pool shell of a commercial swimming pool can be constructed in several ways. Two of the most commonly used methods are cast in place concrete and shotcrete. The major difference between the two is quite simply the method of placement. At the end of the day, both systems, with proper design and construction, will provide a rock solid pool shell which can last for more than 40 years.
Cast in place concrete construction can be a costly and very labour intensive process. This type of construction requires additional excavation to allow workers room to install an extensive forming system for both the inside and outside of the pool walls, which is used to contain the concrete and shape the pool structure. This working room behind the forming system requires backfilling when the concrete work is complete.
Once the formwork is in place, concrete is discharged from a ready-mix truck, and transferred to the work area by way of boom pump, line pump, buggy, or down the chute directly off the back of the truck. Next, concrete is placed on the ground or in the form work, and then must be vibrated for consolidation & compaction.
Cast in place concrete forming system.
Pouring cast in place concrete.
It’s the most common type of concrete construction.
Cast-in-place concrete will result in a strong and waterproof structure with compressive strengths of 4,000 to 5,000 psi.
When properly designed and constructed, cast in place concrete results in a relatively smooth surface that will require very little surface preparation for the use of epoxy-based pool paint, tile and plaster finishes.
Cast-in-place concrete results in the most uniform surfaces possible.
Over excavation is required to allow working area behind the forming system.
Very labour intensive to form the walls.
Backfilling of the formed walls is required.
It’s harder and much more complicated to form shapes.
Generally more expensive to construct in comparison to a shotcrete pool.
The quality of a shotcrete pool can be comparable to a cast in place pool with one exception. Typically, they do not require extensive forming which often results in cost and time savings. Although the hardened properties of shotcrete are similar to conventional cast-in-place concrete, the nature of the placement process provides additional benefits, such as very fast erection, particularly on complex forms and shapes, including curved walls. Due to the speed of construction and the minimal equipment requirements, shotcrete is a very cost effective building method.
The shotcrete method utilizes concrete that is discharged from a ready-mix truck into a shotcrete pump and then pneumatically “shot” in place against a wood or earth form. To increase the velocity of the material which improves the control of the “shooting” process, accelerators and other admixtures can be added to the nozzle along with air under pressure. Because shotcrete is "shot" up against wood forms or earth, there is generally very little backfilling required.
Pool form ready for shotcrete.
Shotcrete being "shot" into place.
No over excavation required. As a result there is very little to no backfilling required.
The ability to build in very tight spaces and “free form” applications make it very simple to build pools of any shape.
Higher compressive strengths than cast-in-place concrete. Typical compressive strengths of shotcrete are in the 6,000 to 7,500 psi range
Lower construction costs.
There are fewer trained and skilled in the use of shotcrete than that of cast-in-place concrete.
The finished surface of shotcrete is rougher than a finished surface of a cast-in-place concrete pool. Additional surface preparation is required before the application of epoxy paint. As a result most shotcrete pools have a plaster finish.
Swimming pools are an excellent way to stay active and have fun in the summer, but if you live or operate a swimming pool in a colder climate, there comes a time at the end of the swimming season when pools must be winterized. Not winterizing a pool in a colder climate is simply not an option, unless you want a hefty repair bill come spring.
The power of water when it freezes and thaws is absolutely amazing. In colder climates, like Canada for instance, pools that are not properly winterized will experience all kinds of damage, such as cracked and broken pipes, pumps and filters.
In addition to winterizing the entire mechanical system for the pool, the pool shell itself requires protection against frost. The simplest way to protect a pool shell is to leave it full of water for the winter. When filling the pool for a winter hibernation, care should be taken to allow room for the water to rise with rain and snow. Typically the water level in a pool is left 12-18" from normal operating level at the time of winterizing.
To complete the winterizing, the pool should be completely drained, and compressed air used to blow out water from the recirculation piping. All returns, water inlets, drains, etc. need to be capped or plugged to keep water out. Play features in pools also need to have all the water removed from them and in some cases some water features will need to have antifreeze introduced into them to prevent low lying fittings from collecting water and freezing. Items such as skimmers should also have expansion devices installed to prevent these items from damage due to freezing expansion. Once all of the piping has been cleared of water and properly sealed up, the pool shell can then be filled and chemicals added. Items such as pumps, filters and heaters in the mechanical room also need to have all drain ports opened up and drain plugs removed.
When winterizing a pool, it is imperative that the time is taken to do it properly, in order to avoid any future damage and additional repair costs to the facility. Taking the proper steps can not only help preserve the condition of the pool tank and the mechanical equipement, but these simple steps can also help increase the longevity of the grounds, building, and deck equipment. Here are some tips to closing a swimming pool, recommended by the National Swimming Pool Foundation.
Adjust the chemical balance of the pool water to the recommended levels.
Treat Facility water with appropriate products to minimize algae, bacteria, or damage to surfaces.
Clean and vacuum the pool.
Empty and store skimmer baskets and hair and lint traps for the winter.
Backwash the filter thoroughly and clean the filter media or elements.
Drain sand filters. Remove cartridges or D.E. filter elements, inspect for tears or excessive wear, and store.
Lower the water level to below the skimmers and return lines for plaster pools. If needed, remove the remaining water from the recirculation lines using an air compressor or industrial type tank vacuum cleaner.
Open all pump room valves and loosen the lid from the hair and lint skimmer. However, if the filter is below pool water level, close the valves leading from the pool to the filter.
Grease all plugs and threads.
Add antifreeze formulated specifically for recreational water applications to the pipes to prevent bursting. Do not use automotive antifreeze.
Plug the skimmer or gutter lines. Winterize with antifreeze and expansion blocks. Secure the skimmer lids to the deck to prevent their loss. Plug wall return lines and the main drain.
Make sure the hydrostatic relief valve is operational.
Drain and protect pumps. If a pump and motor will be exposed to sever weather, disconnect, lubricate, perform seasonal maintenance of the pump, and store. Add antifreeze to help protect pumps and seals from any residual water left after draining.
Clean surge pits or balancing tanks.
Disconnect all fuses and open circuit breakers.
If underwater wet niche lights are exposed to the elements, remove them from their niches and lower them to the bottom of the pool.
Drain the pool water heater. Grease the drain plugs and store for the winter.
Turn off the heater gas supply, gas valves, and pilot lights.
Install the winter safety cover.
Properly store any unused chemicals as described on their labels to prevent containers from breaking and the mixing of potentially incompatible chemicals. Dispose of test reagents, disinfectants, and other chemicals that will lose their potency over the winter.
Disconnect, clean and store the chemical feeder, (Remember - Only Water can be used to clean out the chemical feeders) controllers, and other chemical feed pumps. Store controller electrodes in liquid and in a warm environment.
Clean and protect pressure gauges, flow meters, thermometers and humidity meters.
Store all deck furniture (chairs, lounges, tables, umbrellas, etc.) Identify and separate all furniture in need of repair.
Remove deck equipment, hardware, and non-permanent objects such as ladders, rails, slides, guard chairs, starting blocks, drinking fountains, handicapped lifts, portable ramps, clocks, weird, and safety equipment to prevent vandalism. Store in a clearly marked, identifiable, weather-protected location. Cap all exposed deck sockets.
Remove the diving boards. Store the boards indoors, upside down and flat so they will not warp.
Turn off the water supply to restroom showers, sinks, and toilets. Drain the pipes and add antifreeze.
Remove shower heads and drinking fountain handles. Open hose bibs and fill spouts.
Inventory all supplies and equipment. Make suggestions for preventative maintenance and repair, upgrading, and needed equipment purchases.
** ALL COMMERCIAL POOLS ARE DIFFERENT – ENSURE YOUR PERSONAL CLOSING PROCEDURES FOR YOUR POOL PRIOR TO COMMENCING WORK.
Every year people die by electrocution, and some of these incidents are associated with pools. In fact, In September 2016, a young girl working as a lifeguard at a swimming pool in North Carolina lost her life when she was electrocuted as she entered the water. So let’s talk a little bit about this, and how we might reduce the risk of electrical injury associated with pools.
Electrical energy acts a lot like other sources of energy in that it moves (flows) from one area to another when there is a “potential difference” in the voltage of those areas. Like a waterfall plummeting from a high point to a low point, so does electricity from a higher voltage (a live wire or battery terminal for example) to a lower voltage (ground).
Electricity generally speaking, needs a “conductor” to move or "flow" through. This flow of electricity is expressed in terms of Amperes or Amps. Some things are better conductors than others. Copper, aluminum and gold are excellent conductors and pass electricity, while things like the human body are less apt as conductors, but can certainly still pass electricity. Other substances like some (but not all) polymers and glass are insulators. Still others are classified as semiconductors (like doped / contaminated silicon). Uncontaminated water is actually an insulator when pure (distilled), but becomes sort of a semiconductor most of the time. In pools, it is usually a pretty fair conductor having been “contaminated” with minerals, chlorine and sometimes salt. The human body is a mediocre conductor, but also a poor insulator. Being that we are largely made up of contaminated water, electricity from a source will pass through our bodies on the way to ground…the lower voltage. On the way through it can interfere with nerve impulses including those activating the heart, and cause damage, seizure or in the worst case death by cardiac arrest.
So how can we make the seemingly unsuitable bed partners of pools and electricity less…shocking?
BONDING AND GROUNDING
Bonding refers to bringing all of the conductors around the pool (the reinforcing steel, handrails, light fixtures, pump cases etc.) to the same electrical potential by connecting them all together with a conductor (a ground wire). This eliminates the possibility of any potential difference between these various items; whatever voltage one item is at, the same voltage will be seen at all of the other items. But bonding alone does not render the items safe. You can’t get a shock between one item and another, but what if a stray voltage is energizing the bonding wire to some higher voltage? Then any of the items could give you a shock if your body is grounded (for example, being barefoot on the deck). To ensure the items are a zero volts, the bonded items have to be grounded. This simply involves running a wire from the bonded loop to the ground lug in the distribution panel.
KEEP ELECTRICAL ITEMS AWAY FROM THE POOL
It is never a good idea to have an electrically powered item near a swimming pool. Things like radios, blenders (for those summer margaritas) if dropped into the pool, can electrically charge the water and potentially shock bathers. Even if the device is away from the pool on the deck somewhere, someone who has recently been in the pool could drip water into the device and create a conductive path with the water from the device, through them to ground…not fun!
USE GFCI DEVICES AND BREAKERS
Ground Fault Circuit Interrupting (GFCI) devices work by comparing the current flow in the hot (supply) wire to the current flow in the neutral (return to ground) wire. In any circuit, the current flow should be the same in both ‘legs’. If it isn’t, it means the current is going somewhere else - like through you! The GFCI device will trip to disconnect the power supply if there is a difference of 6mA (that’s 6/1000 Amps), and does so in a fraction of a second to protect us from being shocked. GFCI devices are a great way to protect people from any electrical device, but are particularly appropriate for things like underwater pool lights where electricity is so close to the water.
PERFORM REGULAR ELECTRICAL REVIEWS
It’s a fact of life on this planet of ours that things change, materials degrade, corrode, erode, oxidize and just plain wear out. Your electrical system is no exception. Electrical distribution boxes and the breakers within become corroded and fail. Plastic wire insulation dries out and cracks, ground points become corroded. Corrosion is exacerbated by exposure to salt water because of its electrolytic properties. Having a reputable electrical contractor visit the site periodically may flag some of these issues before they become a health and safety concern. In addition to a visual inspection, they can perform tests (like high voltage meggering) to assess the condition of various electrical insulators in the system.
Today, technology is all around us. It makes our lives easier and allows us to connect to anything from anywhere at anytime. Having a smart phone, access to the internet, and heck - even a personal computer, is a staple in this day and age. The internet is about to become classified as a utility because we are so dependent on it for our everyday life. When I was growing up, technology was nowhere near where it is today. There was no such thing as an iPhone, an Android phone, or a Blackberry. I remember the days when a telephone was attached to the wall, it had a rotary dial and a cord, and it meant running half way across the house to answer it when someone called! The extent of modern technology in my house as a kid was a microwave, a television, a VCR and an Atari game system. If I wanted to communicate with friends I had to either call them on the old rotary phone or walk down the street to their house.
Fast forward to 2016 and just imagine your life without technology. With app’s like Twitter, all of the day’s news is waiting for us in the palm of our hand each morning. With Facebook and Instagram, we don’t even need to call our friends to know what’s happening in their lives. Technology has so much to offer and it has reached out into most areas of our everyday lives making completing daunting tasks more efficient and less time consuming. If you look around, how many people do you see without a form of technology, whether it be a mobile phone, a tablet or a personal computer?
Well the modern day swimming pool is no different. Technology, automation, and computer controls play a very important role in today’s pools. Gone are the days of having to manually adjust the chemistry in a swimming pool by hand on a regular basis. Swings and spikes in pool chemistry were difficult to control when adjusting manually, but with the help of technology, computer controls keep the chemistry in check and allow your pool to virtually run on auto pilot.
These improved chemical controllers also add an additional level of safety to the modern pool. Given that the chemical controller controls the feed of chemicals into the system, it also has the ability to lock out the feed if chemical levels get to high or too low. For example, if the PH level in a pool drops too low, the water will become very acidic and can cause damage to the pool/spa, and can also cause irritation to a swimmers body. If the body of water is very small, such as in a spa, and PH levels are drastically low, it can even cause acid burns. When the controller sees a low PH condition it will put the controller into alarm and prevent additional feeding of muriatic acid, keeping bathers safe and alerting the operator through on screen displays, texts or email notifications. The controller can also do the same thing when it comes to chlorine levels. If the chlorine levels in a pool or spa become too high, it can lock out the chlorine feed until the levels come within an acceptable range. The controllers can be set to a proportional feed, pumping in smaller amounts of chemicals to prevent “over shooting” or “spiking” chemical feed.
Behind the scenes of every swimming pool is a mechanical room; the mission control of a pool. The mechanical room is full of pumps, filters, piping, heaters, controls, UV’s, and a small computer control center called the chemical controller. The chemical controller is the brain of the entire operation, but what does it do and what are the differences between the different manufacturers?
The chemical controller constantly monitors the water through a sample line and sample cell which is fed water via the filter pump. The basic controller is checking the chlorine or bromine levels and PH with ORP and PH probes. Higher end controllers also have the ability to check free chlorine, total chlorine and stabilizer levels. What’s more, they can also connect to and control UV units, start and stop filtration systems, automatically control backwashing of the filters and they can even communicate with variable frequency drives (VFD’s) and building automation systems.
The days of worrying about your pool while you’re off duty or away from your facility are long gone. With new technology, most chemical controllers now have the ability to send a text or email notification directly to your smart phone if the controller senses a problem! You can even connect to them over the internet through HTML or smart phone apps to monitor and control the complete system from anywhere in the world. Talk about a technological advancement for a swimming pool!
Imagine being a pool operator of a commercial facility and having an issue with the pool in the middle of the night, or worse, while you are away on vacation. You could come back to a real mess, and the pool chemistry could be completely out of balance. Depending on the size of the pool, this mess could take a couple of days to get back inline. A pool with a modern chemical controller will notify you of the problem and then automatically start to chemically treat the water to keep it in balance, before you come back to a big mess.
But what are the big differences between different manufacturers? Is one better than the other? In my opinion, there really aren’t any “big” differences; they all come down to budget, options, and operator preference. All name brand controllers come with the basic ORP and PH monitors and controls, and just like a new car you can get them with options. For example; if monitoring the chlorine levels and bromine levels by ORP is not your thing, add on a PPM probe. Some operators are not familiar with ORP levels, but they are very familiar with PPM levels because this is what they commonly record in their books. Is the ability to log in and control your pool using your smart phone from anywhere in the world important to you? No problem! Just add an HTML interface. Today, most chemical controller manufacturers are seeing the importance of being connected all the time and this option is now becoming a standard hardware option and just requires setup at the time of commissioning. Are you looking to monitor the cyanuric acid level of your outdoor pool? No problem! Simply add on the probe. Free chlorine and total chlorine are an easy add-on to any system with the simple addition of monitor probes. All of these options can be added to any chemical controller.
No matter what brand you choose, at the end of the day all will ultimately do the same thing. How much it will do depends on how much you want to invest and what options you want to include.
So next time you are staying up to date with your friends on Twitter and Facebook, or checking the news on your CNN app, take a few minutes to click the pool app on your phone and see how things are operating on your swimming pool.