Concrete Mix Design

Compressive Strength of Cylindrical Concrete Specimens

Molded or cored concrete specimens are tested in compression and the strength is reported on a pounds/square inch basis.

Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)

Concrete beams are cast or sawn from hardened specimens. Specimens are placed on the third-point loading apparatus with an appropriate span, and are subsequently loaded to failure. The load, fracture location, and specimen dimensions are evaluated to determine the flexural strength (modulus of rupture) is reported on a pounds/square inch basis.

Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete

Performed on freshly cast material only. Wet concrete is consolidated in a calibrated unit weight container and weighed to determine the actual unit weight per volume of the material vs the theoretical properties.

Slump of Hydraulic Cement Concrete

Performed on freshly cast material only. Wet concrete is consolidated in a calibrated “slump cone”. The cone is removed, and the consistency (slump) of the material is determined by measuring the change in height of the cone of concrete.

Length Change of Hardened Hydraulic-Cement Mortar and Concrete

Mortar or concrete is cast into beams and cured per ASTM C157 procedures. The lengths of the beams are measured, and the beams are allowed to cure in standard conditions (either lime water or laboratory air) for a period of up to 64 weeks. Intermetent readings are taken to determine the length change of the material.

Bleeding of Concrete

Fresh concrete is consolidated in an appropriate container. The sample is kept in standard laboratory conditions, with the bleed water periodically removed per ASTM C232 methods. The total bleed water is expressed as a percent of the net mixing water in the test specimen.

Time of Setting of Concrete Mixtures by Penetration Resistance

Performed on freshly cast material only. The coarse material in fresh concrete is removed, with the remaining material collected in an appropriate container. Material is allowed to cure, and is periodically penetrated with a calibrated concrete penetrometer. A curve of penetration resistance over time is used to calculate initial and final setting times of the material.

Resistance of Concrete Beams to Rapid Freezing and Thawing

Concrete prisms are exposed to 300 cycles of rapid freezing and thawing. The fundamental transverse frequency is determined at 30 cycle intervals, and this is used to determine the durability factor rating (out of 100).