Aquatic Technology Pool & Spa, "Creating Water as Art."™

Aquatic Technology Pool & Spa, "Creating Water as Art."™
Pools as an art form - the way it should be!

Sunday, June 30, 2013

Swimming Pool Designer & Expert Witness

Swimming Pool Design and Watershapes Consulting Expert Paolo Benedetti of Aquatic Technology Pool and Spa discusses concrete basics.

Concrete Strengths

The key to achieving proper concrete strengths is a direct result of the correct mix design and the proper handling of the plastic (fluid) cement.

The project engineer will specify a minimum concrete strength to be utilized.  There is nothing preventing the contractor or project owner from using stronger mix designs.  The added cost is negligible and the resulting performance and benefits are significant.

Mix Design

The project contractor will discuss the project requirements with the ready-mix plant's "Mix Master" when they place an order for the concrete.  They will discuss ultimate strength requirements, weather forecasts, traffic conditions, rate of placement (yards per hour), distance to pump and the pumping equipment.

The Mix Master will discuss the need for water reducers, plasticizers, air entrainment, set retarders or accelerators with the contractor.  The aggregate size should be the largest allowed by the project engineer.  The larger the aggregate the stronger the concrete will be.

Reduce the Water Content

Concrete is weakened by excess water. When water evaporates from concrete, it leaves behind a matrix of microscopic honeycombs.  These voids weaken the concrete.  They also allow ground or rain water to permeated into the concrete.  This can result in corrosion of the reinforcement steel and eventual project failure.

Only that amount of water that is necessary to hydrate the cement particles is required.  To increase the slump (liquidity) of the mix design, water reducers & plasticizers should be used.  Think of these additives a being able to s-t-r-e-t-c-h the water.  The resultant strength will be significant, though the initial concrete will be liquid, workable and pumpable.

A reputable ready-mix plant will even know the moisture content of their sand and aggregates.  They will subtract from the water to be added to the mix, the water inherent in the aggregates.  A load tag will accompany the delivery truck.  The assay of the contents of the truck should be specified, along with the load time and starting count on the truck's rotating drum.

My ready-mix supplier even provides the assay of the aggregate in their mix.  The load tag indicates the psi compressive strength of the rocks in the mix.  

It makes absolutely NO SENSE to use concrete that contains rocks weaker than your objective.  But, there are many ready-mix suppliers who use weak and inferior aggregates (e.g. quartz ).  If they don't volunteer this information - ask.  They are required by the building codes to tell you.

Achieving High Strength Concrete

Higher strength concretes are denser and more durable.  This is achieved by "tightening" the matrix of the concrete.  The increased cost of a higher "sack" mix is minimal (e.g. a 4 sack mix vs a 6 sack mix).  A "sack" is equivalent to 94# of cement powder (about 1 cubic foot).

There are many means to increase concrete's strength.  Many of the methods are used in conjunction with each other:
  • Reduce the water content
  • Increase the aggregate size from 3/8" to 3/4"
  • Add pozzolans (Supplementary Cementitious Materials - SCM)
  • Utilize crystalline or water proof admixes 
  • Corrosion inhibitors 
  • Air entrainment (freeze-thaw conditions)
  • Metakaolis (help reduce efflorescence)
  • Integral color pigments
Some additives are not compatible with others, so be sure to read the labels and warnings (e.g. fly ash is not compatible with some waterproof admixes).

Integrity of the Mix Design

It is the responsibility of the contractor to ensure that the mix design is not adultered by "well meaning" individuals.  Concrete pump operators and ready-mix truck drivers are the worst culprits.  When the truck arrives, the pump operator tells the driver to add water to the mix.  Before the concrete is even out of the truck, the strength is being compromised.

After the truck arrives, if you hear the engine revving and the drum spinning rapidly they are adding and mixing additional water.

Proper Handling

The concrete should not be allowed to sit in a truck, waiting for prior trucks to be unloaded.  The concrete may achieve it's final set while in the truck, rendering it useless (unless set retarders were added).

The truck must achieve a minimum number of rotations prior to off loading.  The dry ingredients are added to the truck at the ready-mix plant.  It is the rotation of the drum and vanes that actually mix the concrete.

Concrete that is to be placed into tall forms, caisson holes, deep trenches or footings should be placed from the bottom up.  It should not be pumped in from the top and allowed to fall to the bottom.  This separates out the aggregate and compromises the strength.  It also creates large voids and air pockets in the finished product.

Proper consolidation (vibration) must also be preformed.  Excessive vibration will also cause the aggregate to settle to the bottom.  The proper mix design can virtually eliminate the need for consolidation.


Concrete does not "dry," it cures.  As the water hydrates the components of the concrete mix, crystalline structures are formed.  These are what give the concrete it's density.  Controlling the rate of water evaporation is critical.  The goal to to have the water leave the concrete as slowly as possible.  This is achieved through proper curing. 

Coverings of burlap, carpet or plastic are the most rudimentary.  This method cause surface discoloration due to trapped moisture under the covering. They are also susceptible to being moved or blown out of position.

Water curing is performed by maintaining the moisture content of the concrete by frequent sprinkling, spraying or flooding with water.  This is not always practical as there may be water restrictions, drought conditions, lack of personnel 24/7, the project is too large or the site may become excessively muddy.

Chemical curing compounds are chemicals that are sprayed onto the finished concrete after it becomes stiff, but is still damp in appearance.  Some chemically penetrate the concrete while others form a surface film.  These are the method preferred by most State Highway Departments because they are the most infallible.

Care must be taken in selecting the proper curing solution.  Some of them create a "bond breaker" that inhibits the bonding of subsequent surfaces.  Subsequent decorative finishes of plaster, stucco, paint or stone work may not bond to the concrete.  

Then why do they even make those types?  Contractors who pour roadways, bridges, sidewalks and other high traffic surfaces are the largest consumers of these type of curing compounds.  They are also the most inexpensive.  Most contain some type of waxy substance.  The curing film often dries white (or has a dye), to indicate areas of coverage and proper application.  Over time, the film will eventually wear away from traffic, abrasion and weather.  

Remember, they are concerned with lifetime performance of their structure (as should you!)

Paolo Benedetti - Aquatic Artist 
"Creating water as art."™ 
Aquatic Technology Pool and Spa 

Saturday, June 15, 2013

Swimming Pool Expert Witness & International Watershape Consulting Engineer

Forms of Chlorine Sanitization

Large residential and commercial aquatic facilities need to perform a complete evaluation of the various form of chlorine sanitization available, before committing to a method.

Calcium Hypochlorite - Cal Hypo

It has the word "hype" in it's name for a reason.  While it provides the most inexpensive forms of chlorine, is carries with it a lot of hidden expenses.

Maintenance - the high levels of calcium in the compound cause clogging of the feeders, injectors and in severe cases even the plumbing.  The only way to remove these deposits is to physically chip them off or to saturate the deposits with muriatic acid.  DANGER: soaking these deposits in muriatic acid may cause an explosion and will form deadly mustard gas (chlorine gas).  Mustard gas will permanently burn and scar the lungs and sear the eyes.

Maintenance of the feeders is both dangerous and time consuming.  There is NO EASY way to keep the feeders clean.  The salesman is looking at his commission from reoccurring sales of calcium tablets... ad nauseam.

Water Balance - The high levels of calcium are also placed into solution within the pool water.  Very quickly the water become over saturated with calcium and the pool becomes difficult to balance.  The water gets a cloudy appearance.  Late in the day, the water appears murky and milk like.  The only way to reduce the calcium content is to DUMP precious water - that's right, drain the pool & dilute the water with fresh water.  

If the make up water (fill water) is ran through a water softener prior to entering the pool, then this ZERO calcium water will dilute calcium laden water, slowing the build-up - that will still occur (just slower).

Financial Interest - Most firms that specify calcium hypochlorite, sell the erosion feeders.  Most will also gladly contract for the supply (sell) of the cal-hypo briquets.  The equipment that they sell, states that the warranty is void, if another brand of briquets is used in their feeder.  This guarantees the specifier will have a client for life - or until the client wises up.

DiChlor or Trichlor Powdered Chlorine

Dichlor..... and Trichlor.... Chlorine are stabilized forms of granular chlorine.  Trichlor... has a low pH and is slow dissolving, and Dichlor... has a neutral pH and is fast dissolving.  

Both contain cynauric acid as a part of their compound.  This is also know as "stabilizer" as it protects the chlorine in the pool from the degradation effects of UV rays.  Too much stabilizer in the pool water can reduce the effectiveness of the chlorine.  Again, the only means to reduce it, is do DUMP precious water from the pool.

Sodium Hypochlorite

Salt Chlorinator
A "salt water pool" is sanitized with chlorine, regardless of what people are told or think.  Liquid Chlorine (Bleach - Sodium Hypochlorite) is produced at the pool equipment pad, as the salt water passes through electrolytic plates.

This is the same means used to create liquid bleach (sodium hypochlorite).  The only difference is that the chlorine is not injected or poured into the pool, instead it is made within the plumbing.

Sodium hypochlorite has a high pH.  Regardless of what the manufacturers of salt chlorinators say, the chlorine generated has a pH of about 13.  The miniscule amount of sodium hydroxide generated, in no way negates this high pH.  During a week, a pool with salt chlorinators will consume 4-8 times the quantity of acid (to buffer the 13 pH), as a pool utilizing liquid sodium hypochlorite.

Liquid Bleach
Another method to utilize sodium hypochlorite, is to store a barrel of it and meter it into the pool.  It is injected into the plumbing using a peristaltic pump.  Of course an acid solution is also injected to maintain the proper pH.  These peristaltic pumps are best controlled by an ORP/pH Controller (water chemistry controller) that monitors and feeds the chemicals as needed.  Periodic deliveries of liquid chlorine and acid are used to refill the barrels.  This relies upon a reliable local source of liquid bleach and acid.

On-Site Generation
In remote corners of the world, there is no reliable source of liquid chlorine.  Large users of liquid chlorine or remote locations find it economically feasible to manufacture their own liquid chlorine bleach on-site.  The key ingredients are available around the world - electricity, salt and water.  A free standing skid mounted system creates liquid chlorine which is then stored in a large barrel.  This ensures a readily available and steady supply. 

In resorts or hotels, these units are over-sized, so that extra liquid chlorine can be used to mop floors, sanitize showers, clean dishes in the commercial kitchens and to wash laundry.  Since the freight to import cleaning solutions is cost prohibitive, utilizing on-site chlorine bleach become economically feasible and environmentally friendly.

Liquid acid is still utilized to buffer the higher pH.  A water chemistry computer (ORP/pH controller) meters the bleach and acid solution as needed, guaranteeing a perfectly balanced pool, regardless of the weather conditions or bather loads.  Powdered or granular acid can be mixed with water to create acid solutions on site, if local sources of liquid acid are not available.

Paolo Benedetti - Aquatic Artist 
"Creating water as art."™ 
Aquatic Technology Pool and Spa