PERLITE CONCRETE |
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TRANSIT MIX AND READY MIX TRUCKS |
CONSTRUCTION GUIDE |
The Schundler Company 10 Central Street Nahant, MA 01908 732-287-2244 |
TRANSIT MIX PERLITE CONCRETE
GUIDELINES AND PROCEDURES
Describing Perlite Concrete
Perlite concrete aggregate combined with Portland cement, air entraining agent, and water produces an ultra lightweight concrete that is used for insulating roof decks and lightweight floor fills, insulating structural rood decks, curtain wall systems and for a variety of permanent insulating applications. An air-entraining agent is used to improve the workability and to control water content and insulation value. Perlite concrete may be more accurately defined as concrete containing a minimum of 20 cubic feet of perlite concrete aggregate per cubic yard (0.74 m^{3} perlite aggregate per cubic meter concrete.)
Mixing Perlite Concrete
While perlite insulating concrete is mixed in the same equipment and by similar methods as sand-gravel concrete, there are some considerations that must be given to the order of addition of materials and to the time of mixing to assure correct concrete properties and adequate yield. The following mixing information for transit mixing is presented as a guide to the manufacturer to eliminate some of he questions that may arise in the field and to ensure successful construction with perlite concrete. When mixing perlite concrete on-site, in mechanical mixers, please refer to Publication 32-87, Perlite Insulating Concrete, Information for Contractors---available from The Perlite Institute (www.perlite.org).
Transit Mixing
When transit mixing perlite concrete for the first time, it is suggested that the perlite manufacturer be consulted for suggestions as to the correct mixing time and procedure. These may vary with the type and age of locally available equipment.
The mixing procedure used by many transit operations is as follows:
If possible, the drum should be charged with water, air entraining agent and cement at the batching plant, and the perlite aggregate should be added at the job site, mixing at high speed until the desired density and consistency is reached.
Care must be taken to ensure proper mixing time for the perlite insulating concrete. Using the correct amount of water as specified, the perlite concrete should have a slump of approximately 7 inches (18 cm) when properly mixed and may appear too wet by normal concrete practices. However, if the mix appears too dry or too stiff, the mixing time has probably been too short. Continue mixing until the desired plasticity is reached. Extra water and under mixing may reduce the yield.
The first truck load of perlite concrete will usually discharge about one third of a yard sort since this quantity will coat the inner walls of the truck drum. However, this will not occur in subsequent loads because the walls will be coated sufficiently. After discharging the last load, 7-10 gallons (26-38 liters) of water may be added to the revolving drum to wash out this coating and this mixture may be dumped and blended with concrete from the previous load. This will not impair the perlite concrete properties because the excess water bleeds out without loss of cement.
Wet Density
The wet density of perlite insulating concrete as poured is important in the control of the physical properties of the dry concrete and the yield achieved. The strength and the insulating value depend on the wet density. Heavier weight means greater strength and less insulation. Therefore, the architect or engineer usually specifies the wet density of the perlite concrete with a plus or minus 2 lb/ft^{3} (32 kg/m^{3}) range.
Field Control
The wet density can be checked for conformance to the architect’s specifications beginning with the first truckload delivered. Adjustments to the mixing procedure should be made at that time and additional checks made periodically during pouring.
The simplest method of field checking wet density is as follows:
Example:
Weight of Empty Container | 2.0 lbs. |
Weight of Container Filled with Water | 23.0 lbs. |
Net Weight of Water | 21.0 lbs. |
Volume= ^{Net Weight of Water} ÷ _{Density of Water } = ^{21} ÷ _{62.5} = 0.336 ft^{3}
Example: (Using Metric Units)
Weight of Empty Container | .91 kg |
Weight of Container Filled with Water | 10.45 kg |
Net Weight of Water | 9.54 kg |
Volume = ^{ Net Weight of Water} ÷ _{Density of Water } =^{ 9.54 kg }÷ _{1000kg/m3} = 0.00954 m^{3}
Example: (Based on a 1:6 mix)
Weight of Container Filled with Concrete | 15.5 lbs. |
Weight of Empty Container | 2.0 lbs. |
Weight of Perlite Concrete | 13.5 lbs. |
Wet Density = ^{Weight of Perlite Concrete} ÷ _{Volume }= ^{13.5}÷ _{0.336} = 40.2 lbs/ft^{3}
The specified wet density of the 1:6 mix (94 lbs. of Portland cement to 6 ft 3 of perlite aggregate) is 40.5 ± 2.0 lb/ft^{3}. Therefore, the field test wet density is within the specification range.
Example: (Based on a 1:6 mix) (Using metric units)
Weight of Container Filled with Concrete | 7.05 kg |
Weight of Empty Container | .91 kg |
Weight of Perlite Concrete | 6.14 kg |
Wet Density = ^{Weight of Perlite Concrete}÷_{ Volume }= ^{ 6.14}÷ _{0.00954} = 643.6 kg/m^{3}
Therefore, the field test wet density is within the 648± 32 kg/m^{3} specification range.
Air Entraining Agent
The use of the correct amount of air entraining agent of the proper concentration is of extreme importance in successful perlite concrete construction. The air-entraining agent produces countless tiny air bubbles in the concrete which reduces the density, increase the yield and contributes to the insulation value of the dry concrete. Air entrained concrete is also more resistant to water absorption.
Care should be taken in mixing perlite concrete to ensure that he proper amount of agent is used. Excess air entraining reduces the strength of the concrete. An even distribution of agent is also essential to produce the desired concrete characteristics. For further information on air entraining, contact the Perlite Institute(www.perlite.org.), your ready mix company, or your local perlite expander.
Placement of Perlite Concrete
Perlite concrete may be placed through the use of crane and bucket or by pumping. The preferred method is by pumping. A progressive cavity pump is recommended, as this type of pump will not place undo pressure on the perlite. In addition, pump hose should be a minimum of 3 inches in diameter. Hose kinking should be avoided. Hoses should be tied off at each joint. For further information on pumping, refer to the Perlite Institute’s (www.perlite.org) literature on "Pumping Equipment and Air Entraining Agents for Perlite Concrete" .
Yield
Yield is defined as the ratio between the volume of the wet perlite concrete as discharged from the mixer and the volume of perlite concrete aggregate used in the mix. The mix proportions included in the specifications are based on extensive field and laboratory tests and are established for 100% yield. If the correct quantities of material and mixing procedure are used, a 100% yield should result. Yield may vary however as it is effected by job site conditions included mixing time, fineness of aggregate, pumping equipment, height to be pumped, length of hose, etc.
Field Check for Yield:
The first step necessary in making a field check for yield is to determine the wet density of the perlite concrete as previously outlined.
The wet density and the weight of total ingredients for the mix being used are then substituted in the following formula:
Consider a 1:6 mix (94 lbs. Of Portland cement to 6 ft^{3} of perlite)
The wet density as determined in Example No. 1 is 40.2 lbs/ft^{3}.
The weight of total ingredients is as follows:
Portland Cement | 94.0 lbs. |
Perlite--6 ft^{3} @ 8.0 lb/ft^{3} | 48.0 lbs. |
Water--12 gallons @8.33 lbs./gal | 99.96 lbs. |
Air Entraining Agent | negligible |
Total | 241.96 lbs. |
Substituting in formula (a): ^{241.46 }÷_{40.2} = 6.0 = Yield
Substituting this value in formula (b):^{ 6.0 }÷ _{6} X 100 = 100%
Consider a mix of 42.73 kg of portland cement to 6 ft^{3} of perlite (0.17 m^{3} of perlite)
The wet density as determined in the Example is 643 kg/m^{3}.
The weight of total ingredients is as follows:
Portland Cement | 42.73 kg |
Perlite--0.17 m^{3} @ 128.0 kg/m^{3} | 21.17 kg. |
Water--45.42 liters | 45.42 kg |
Air Entraining Agent | negligible |
Total | 109.32 kg |
Substituting in formula (a): ^{109.32 }÷_{643.6} = 0.17 = Yield
Substituting this value in formula (b):^{ 0.17 }÷ _{0.17} X 100 = 100%
Loss of Yield:
If the yield as checked by the wet density is less than 100%, a loss of yield is evident. A loss of yield may be attributed to a number of factors as previously noted. However, one or more of the following factors should be checked:
Mix Design Data
The proper proportions of materials for various perlite concrete mixes are shown in the following table. The importance of properly designing and specifiying the mix and the proper use of the air entraining agent cannot be overemphasized.
Materials per Cubic Yard Based on 100% Yield | ||||||
Mix Ratio (Cement/Perlite Aggregate by Volume) | Oven Dry Density (Typical) in lb/ft^{3} | Cement in lbs. | Perlite in ft^{3} | Water in Gallons | Air Entraining Agent | Wet Density Range in lb/ft^{3} |
1:4 | 36 | 635 lbs | 28 | 61 | * | 50.5 ^{+}/- 3.0 |
1:5 | 30.5 | 510 lbs | 28 | 59.5 | * | 45.5 ^{+}/- 3.0 |
1:6 | 27 | 425 lbs | 28 | 54 | * | 40.5 ^{+}/- 3.0 |
1:8 | 22 | 320 lbs | 28 | 54 | * | 36.5 ^{+}/- 3.0 |
Materials per Cubic Meter Based on 100% Yield | ||||||
Mix Ratio (Cement/Perlite Aggregate by Volume) | Oven Dry Density (Typical) in kg/m^{3} | Cement in kg | Perlite in m^{3} | Water in m^{3} | Air Entraining Agent | Wet Density Range in kg/m^{3} |
1:4 | 576 | 376 lbs | 1.0 | .30 | * | 808.0 ^{+}/- 48.0 |
1:5 | 488 | 301 lbs | 1.0 | .29 | * | 728.0 ^{+}/- 48.0 |
1:6 | 432 | 252 lbs | 1.0 | .27 | * | 648.0 ^{+}/- 48.0 |
1:8 | 352 | 188 lbs | 1.0 | .27 | * | 584.0 ^{+}/- 48.0 |
^{*} Consult your transit mix company, air entraining supplier, or perlite manufacturer for recommended type and quantity of air entraining agent. |
For more information, see our page on Perlite Concrete at Schundler Perlite Concrete
The Schundler Company
10 Central Street
Nahant, MA 01908
732-287-2244 or www.schundler.com
email: info@schundler.com
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