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Structural Lightweight Concrete

Structural lightweight concrete made with Buildex aggregate solves weight and durability problems in buildings and exposed structures. Buildex concrete has strengths comparable to normal weight concrete, yet is typically 25% to 35% lighter. Buildex offers design flexibility and substantial cost savings by providing less dead load, improved seismic structural response, longer spans, better fire ratings, thinner sections, decreased story height, smaller size structural members, less reinforcing steel, and lower foundation costs. The excellent durability performance of Buildex is a result of the ceramic nature of the aggregate and its exceptional bond to, and elastic compatibility with, the cementitious matrix.

Much of the structural lightweight concrete used in building floors is pumped into place. Buildex has developed pumping guidelines outlining the steps needed to achieve problem free pumpable structural lightweight concrete using our aggregate, specific to Buildex from each plant. These guidelines can be viewed and downloaded in pdf format using the links that follow. 

Buildex New Market VS Aggregate Pump Guidelines

Buildex Marquette Aggregate Pump Guidelines

New information has recently been published on Floor Drying of both normal weight and lighthtweight concrete floors. The report is authored by well known flooring industry consultant Peter Craig, and contains important insight on the differences in drying characteristics between lightweight and normal weight elevated concrete slabs.

Our Guilde Specification that follows below has been revised to include recent changes to ASTM C 567. The traditional "28 day unit weight" has been replaced by "calculated equilibrium density" which can be determined by calculation at the time the concrete is batched and placed. More information is included in the commentary that follows the Density section below. 

Guide Specification (Short Form): Sec 03300:

Revised March 9, 2009

Materials:

Expanded shale lightweight coarse aggregate shall be Buildex or approved equal, manufactured by the rotary kiln process, and shall meet ASTM C 330. Grading shall be 1/2" x No. 4 (12.5 mm to 4.75 mm) as detailed in ASTM C 330. Coarse lightweight aggregate shall be pre-wetted prior to mixing if placement is to be made using a concrete pump. Follow the lightweight aggregate manufacturer's recommendations for pre-wetting procedures. Normal weight fine aggregate shall meet ASTM C 33.

Concrete Properties:

Strength:
Proportion materials to produce concrete with a minimum compressive strength of ___ psi at 28 days.

Comment: Commonly specified compressive strengths are 3000 psi and 4000 psi, but higher strengths, up to 9000 psi, are attainable with special mixes.

Density:
Proportion materials to produce concrete with a calculated equilibrium density of 100 to 110 lb/cu ft, as determined by ASTM C 567 "Standard Test Method for Determining Density of Structural Lightweight Concrete".

Comment: Concrete proportioned for a fresh pumped in place density of approximately 116.5 lb/cu ft correlates to a calculated equilibrium density of approximately 105 lb/cu ft. Fresh density is specified for job acceptance in Field Control below. The equilibrium density is calculated per ASTM C 567 Section 9, and represents the point at which the concrete in place reaches its air dry equilibrium density. Mixes with this density have shown good pumpability, performance and economy. Other design densities are attainable if needed; contact our sales office for details. 

Note: The estimated 28 day air dry density will be 108 - 115 lb/cu ft but this property is no longer defined by ASTM so is no longer used in specification.

Slump: Slump at point of placement shall be 2 - 3 inches if placed conventionally and 3 - 5 inches if placed by concrete pump.

Comment: Design pump mixes so that the mix attains the desired strength with the higher slump needed for pumpability.

Air Entrainment: The air content shall be 6 percent, plus or minus 1.5 percent.

Comment: Typical pumped mixes will lose 2 inches of slump and 1% entrained air during pumping.

Field Control:  Perform all quality control tests on lightweight concrete at the point of placement. Fresh bulk density shall be between ___ and ___ lb/cu ft. Adjust material proportions as needed to maintain proper slump, air content, fresh density and yield. 

Comment: Normally the fresh bulk density will need to be between 112 and 122 lb/cu ft to achieve calculated equilibrium density of 100 to 110 lb/cu ft. 
 
Review /Download in pdf format:  Buildex Guide Specification

Buildex Structural Lightweight Concrete
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