Different properties of Concrete and how to make more knowledgeable decisions based on having it tested.

Concrete testing is typically required for the construction of slabs, sidewalk, grout, and all supporting structures. All concrete testing conforms to CSA A23.1-M94 specifications. This guideline provides directions on regulating concrete testing within Canada. A standard sample includes slump measurement, temperature recording, air entrainment testing, preparation and compressive strength testing of 3 cylinders per set. One concrete cylinder will be tested at 7 days, and the remaining two concrete cylinders will be tested at 28 days. Cast concrete cylinder samples will be stored in temperature-controlled curing boxes on site and retrieved on the following day for delivery to the E2K testing laboratory.

A standard concrete test begins with sampling. A sample must be taken after 10% and before 90% of the load has been discharged. Temperature measurements of the concrete are taken after securing the mix. The thermometer should be accurate and calibrated. The concrete should surround the entire stem in all directions.

Slump tests measure the viscous properties of concrete. Once the concrete sample has been remixed, a slump test can be performed. A cone is filled in three equal layers by volume of concrete, not by height, and rodded each layer 25 times with a round-tipped steel rod for consolidation. After filling and rodding, the cone is raised to allow the concrete to stand freely. The distance the concrete falls – or slumps – is the measurement recorded.

Concrete with air-entrainment is usually specified in areas with freezing temperatures. The purpose of air entrainment is to increase the durability of the hardened concrete. The testing of air content in concrete is performed using a calibrated air meter.  A test for air entrainment begins by filling the air meter in three equal layers and rodding each layer 25 times. The air meter base is struck with a mallet to close any air voids. After completing the three equal layers, the sample is ready for measurement.

A pressure canister is latched on top of the air meter and injected with water to fill any residual pockets of air remaining in the concrete. The meter top is then pressurized with a hand pump. The pressure is released and a final tested value can be reported.

Test cylinders are cast to verify the specified compressive strength of the concrete has been achieved. Cylindrical, non-absorbent molds are used to cast concrete test specimens. E2K uses plastic molds with dimensions of 100 x 200 mm constructed with thick walls. Molds are cleaned and lightly coated with mineral oil or other suitable non-reactive form release materials before each use.

Molds are filled in three equal concrete layers, rodding each layer 25 times. Each layer is tapped to remove any remaining air voids. Once the mold is filled with concrete, the top is levelled and sealed prior to storage.

E2K will provide properly designed, temperature-controlled, storage boxes to secure concrete test cylinders for a period of at least twenty-four (24) hours on site. E2K will provide a maximum and minimum temperature reading thermometer for each storage box in monitoring concrete curing conditions.

Compressive strength of cylindrical concrete specimens is determined at the E2K laboratory. Samples are properly cured in temperature and moisture-controlled tanks until the specified testing break day. Each concrete cylinder sample is mechanically ground for perfectly verified planes at both ends. Perpendicularity and width are measured prior to compressive strength analysis. Each concrete cylinder is crushed in a controlled press which measures the testing force required to break the concrete sample.

Under CSA Standards, a concrete cylinder break is considered to be of low compressive strength when an individual strength test is more than 3.5 MPa below the required expected strength.

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