Wet-mix or dry-mix it's all shotcrete - steel reinforced concrete pools, per the American Concrete Institute (ACI) and American Shotcrete Association (ASA).
Wet-mix vs. Dry-mix
The process of pneumatically applying concrete is called shotcrete.
The differences between the two processes, is the moisture content of the material as it travels through the hose to the nozzle.
Wet-mix shotcrete is delivered pre-mixed with water from a ready mix plant in a cement truck. Dry-mix shotcrete is blown through the hose dry and water is added at the nozzle.
Though both effectively deliver high strength concrete, the dry-mix process has the potential to deliver stronger psi strengths. Why?
Less water is utilized to hydrate the cement particles. Less water equates to greater yield strengths.
Experienced Nozzleman
To achieve a structurally sound shell and high compression strengths, the nozzleman must be experienced. Not just experienced in holding the hose, but in the application of the material and the science of the process being utilized.
The dry-mix method requires that the nozzleman not add too much water, as this will result in a weaker finished product.
The term is Shotcrete, not Gunite
Gunite is a company that makes equipment for the dry-mix process. Like all tissues are not Kleenex, dry-mix shotcrete is not called gunite.
Air Lance
An air lance, also referred to as a blow-pipe, must be utilized during the dry-mix process. Since the material is drier, the air lance it used to disperse any unsound material from the area where the shotcrete is being placed. Build up of loose material will result in horizontal stratification voids within the shotcrete. This loose material is often referred to as rebound, though technically not all of it is actually rebound.
These voids are oftentimes called sand lenses, though they are actually incompetent material that was allowed to accumulate within the wall. It may be unhydrated cement, sand or aggregate. Any way you slice it, it is a hollow void that will allow the entrance of water and the eventual corrosion of the reinforcing steel.
Why isn't an air lance always employed, since it is required by the ACI/ASA specifications? Laziness - the shotcrete crews do not want to employ an additional man to operate the air lance. It also requires that they have to unroll, clean and roll up an extra hose at the end of the day.
Achieving High PSI Strengths
Either process can yield 7,000 - 9,000 PSI strengths. It has to do with the mix design, skill of the applicator, supervision of the crew, quantity of mix water and the curing of the finished product. Per the ACI/ASA standards, the minimum allowable strengths are 4,000 PSI. Since the ASI 318 and ACI 506 standards are incorporated into the International Building Code (IBC), they ARE THE SHOTCRETE CODES across the United States (except Minnesota, that has yet to adopt the IBC).
Without proper curing of the material, complete hydration of the cement particles will not occur. The purpose of curing is to keep the water within the concrete, so that the chemical process of hydration can occur. Keeping moisture in the concrete also helps control the heat that is generated from this process.
Curing can be accomplished through frequent and constant soaking (water curing), covering the shotcrete with a physical barrier (plastic, carpet, burlap, etc.) or the application of a chemical curing compound ( a chemical membrane). The process utilized is not critical, so long as it is performed per the ACI/ASA standards and the project structural engineers recommendations.
Remember, which ever method is used to cure the structure must also be utilized to cure the test panels. For example, is not a fair test to apply a chemical curing compound to the structure and then to water cure the samples in a submerged water bath.
Regardless of the shotcrete process employed, high compression strengths are easily achieved when using either process. It is the skill and knowledge of the applicator and their crew that makes all of the difference. Nozzleman are certified for either wet-mix or dry-mix processes. Really competent nozzlemen are certified in both processes.
Insist that only a ASA Certified Nozzleman operate the nozzle on your project.
Paolo Benedetti
Aquatic Artist, Watershape Consultant, Expert Witness
"Creating water as art."™
Aquatic Technology Pool and Spa
©www.aquatictechnology.com
Wet-mix vs. Dry-mix
The process of pneumatically applying concrete is called shotcrete.
The differences between the two processes, is the moisture content of the material as it travels through the hose to the nozzle.
Wet-mix shotcrete is delivered pre-mixed with water from a ready mix plant in a cement truck. Dry-mix shotcrete is blown through the hose dry and water is added at the nozzle.
Though both effectively deliver high strength concrete, the dry-mix process has the potential to deliver stronger psi strengths. Why?
Less water is utilized to hydrate the cement particles. Less water equates to greater yield strengths.
Experienced Nozzleman
To achieve a structurally sound shell and high compression strengths, the nozzleman must be experienced. Not just experienced in holding the hose, but in the application of the material and the science of the process being utilized.
The dry-mix method requires that the nozzleman not add too much water, as this will result in a weaker finished product.
The term is Shotcrete, not Gunite
Gunite is a company that makes equipment for the dry-mix process. Like all tissues are not Kleenex, dry-mix shotcrete is not called gunite.
Air Lance
An air lance, also referred to as a blow-pipe, must be utilized during the dry-mix process. Since the material is drier, the air lance it used to disperse any unsound material from the area where the shotcrete is being placed. Build up of loose material will result in horizontal stratification voids within the shotcrete. This loose material is often referred to as rebound, though technically not all of it is actually rebound.
These voids are oftentimes called sand lenses, though they are actually incompetent material that was allowed to accumulate within the wall. It may be unhydrated cement, sand or aggregate. Any way you slice it, it is a hollow void that will allow the entrance of water and the eventual corrosion of the reinforcing steel.
Why isn't an air lance always employed, since it is required by the ACI/ASA specifications? Laziness - the shotcrete crews do not want to employ an additional man to operate the air lance. It also requires that they have to unroll, clean and roll up an extra hose at the end of the day.
Achieving High PSI Strengths
Either process can yield 7,000 - 9,000 PSI strengths. It has to do with the mix design, skill of the applicator, supervision of the crew, quantity of mix water and the curing of the finished product. Per the ACI/ASA standards, the minimum allowable strengths are 4,000 PSI. Since the ASI 318 and ACI 506 standards are incorporated into the International Building Code (IBC), they ARE THE SHOTCRETE CODES across the United States (except Minnesota, that has yet to adopt the IBC).
Without proper curing of the material, complete hydration of the cement particles will not occur. The purpose of curing is to keep the water within the concrete, so that the chemical process of hydration can occur. Keeping moisture in the concrete also helps control the heat that is generated from this process.
Curing can be accomplished through frequent and constant soaking (water curing), covering the shotcrete with a physical barrier (plastic, carpet, burlap, etc.) or the application of a chemical curing compound ( a chemical membrane). The process utilized is not critical, so long as it is performed per the ACI/ASA standards and the project structural engineers recommendations.
Remember, which ever method is used to cure the structure must also be utilized to cure the test panels. For example, is not a fair test to apply a chemical curing compound to the structure and then to water cure the samples in a submerged water bath.
Regardless of the shotcrete process employed, high compression strengths are easily achieved when using either process. It is the skill and knowledge of the applicator and their crew that makes all of the difference. Nozzleman are certified for either wet-mix or dry-mix processes. Really competent nozzlemen are certified in both processes.
Insist that only a ASA Certified Nozzleman operate the nozzle on your project.
Paolo Benedetti
Aquatic Artist, Watershape Consultant, Expert Witness
"Creating water as art."™
Aquatic Technology Pool and Spa
©www.aquatictechnology.com
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