Workability, placeability, strength, durability, economy--these are among the words that are always heard when concrete mixes are discussed. Whether or not these qualities will actually be present on the job may already be determined when the materials are being batched into the truck mixer.
TESTING OF CONCRETE IN THE FIELD
There are four field tests that relate directly to the quality of the concrete mix and to the control of the batching and proportioning of the materials in the mix. They involve measures of workability, strength, yield and air content.
Slump Test (ASTM C 143)--The slump test is an indicator of the workability or plasticity of the concrete. Concrete test cylinders (ASTM C 31 or ASTM C 39)--Concrete cylinders are made and tested for two different purposes: to determine the quality of the concrete as delivered to the job; and to indicate the strength of concrete in place at a given time.
Yield test (ASTM C 138)--Yield describes the volume of concrete that will be produced by combining a given quantity of each of the materials. To be able to design a mix for a cubic yard of concrete, it is necessary to know the volume that will be occupied by each material in the mix.
Tests for air entrainment (ASTM C 231, C 173)--There are two types of standard field tests for air content in the plastic concrete that are made with two types of air meters. One tests for air by the pressure method and the other by the volumetric method.
MIX DESIGN AND ADJUSTMENTS
Mix adjustments are made based on several factors: water content in the aggregates; water reducers; fly ash; and admixtures.