Before placement of concrete in its casting location, several tests are conducted to fresh concrete to assess its properties and workability as per the project requirements. It will help the troubleshooting investigator to respond any problems that ensue, such as low strength or cracking of concrete.
Some of the common tests on fresh concrete are as follows:
1. Slump Test - Slump test is a laboratory or at site test used to measure the consistency of concrete. Slump test shows an indication of the uniformity of concrete in different batches. The shape of the concrete slumps shows the information on the workability and quality of concrete. The characteristics of concrete with respect to the tendency of segregation can be also judged by making a few tamping or blows by tapping rod on the base plate.
The slump value of concrete is just a principle of gravity flow of surface of the concrete cone that indicates the amount of water added to it, which means how much this concrete mix is in workable condition.
2. Concrete Temperature - The heat produced by concrete during concrete curing is called heat of hydration. This exothermic reaction occurs when water and cement react. The amount of heat produced during the reaction is mostly related to the composition and fineness of the cement.
The temperature measurement is typically done to make sure the concrete is in compliance with certain specifications that define a certain allowable temperature range. Typical specifications require the temperature of the concrete during placement to be within a range of 10°C to 32°C.
3. Air Content - Air Content is the volume of air voids in concrete, exclusive of pore space in aggregate particles; usually expressed as a percentage of total volume of the mixture.
A sample of concrete is placed in the cylinder of an air meter in three layers, each being fully compacted by hand or by vibration. The cylinder is filled level with the top. The cover, which has a sealed graduated cylinder fitted, is clamped to the cylinder. The assembly is filled with water and any air is allowed to escape through a valve. The valve is closed and an air pump is used to increase the internal pressure. As the pressure rises the concrete becomes compressed and the water level in the graduated cylinder falls. When the pressure has reached a specified level, the reading of the water level is recorded. The pressure is then released and the water level rises. The difference in the two levels is the apparent air content. Various adjustments are made to give the true air content.
4. Unit Weight of Fresh Concrete – The unit weight of concrete (density) varies depending on the amount and density of the aggregate, the amount of entrained air (and entrapped air), and the water and cement content.
The unit weight is a useful tool in determining the concrete batch yield and air content.
To get the unit weight of a sample of concrete, you must get the weight of a full container of concrete, subtract the weight of the empty container, and divide that by the volume of the container.
5. Setting Time of Concrete - Concrete setting time testing is beneficial to identify various stages of the concrete's hardening process. Measuring the concrete with set time tools determines various effects such as: temperature, mixture proportions, hardening of concrete and additions to the settings.
Knowing the set time will help to determine when the concrete has fully hardened. The term “initial set” is the semi-hardened, partially hydrated condition of the concrete beyond which it can no longer be worked.
Reference:
theconstructor.org
humboldtmfg.com
civiconcepts.com
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