Concrete Testing Methods Help Engineers to Design and Build Safe Structures
Concrete is a mixture of cement, aggregates and water which attains strength as it ages. In the initial stage, concrete is fluid and can even be pumped through pipelines, but sets after some time to attain an initial set within minutes, and hardens after a couple of hours.
The final strength of concrete depends on a number of factors, which include the soundness of the aggregates, the composition of the chemicals in the cement, the ratio of the water to cement used during mixing, and effective control of the heat generated by the concrete during its setting process. All these can be controlled by going through a number of concrete testing procedures and final strengths also gauged by destructive and non-destructive test methods.
The strength of the aggregates depends on the natural properties of the stone from which they are produced. The size of the aggregates and their ability to create concrete without voids helps to gain higher strengths. Engineers are able to decide the proportions of aggregates that lead to the densest possible concrete, by various methods like trial mixes. These proportions are then intimated to the persons responsible for producing the concrete.
The proportion of water to cement is very important for concrete to gain its final strength and this is tested by site engineers by judging the slump of the concrete, or its sinking, when it is poured into and then de-moulded in a standard slump cone, just after mixing and before it gains its initial set. These slumps have to be within certain parameters set down by the trial mix results, and where they do not; engineers reduce or increase the quantity of water.
Concrete gains strength over time and certain empirical strengths are determined for various grades of concrete for strength after periods of seven and twenty eight days. Samples in the form of cubes are obtained from batches of concrete, which are tested after 7 and 28 days. This testing is done by crushing these cubes in hydraulic testing machines which indicate the force used, and hence the strength of the concrete. Tests can also be conducted by ultrasonic methods, through this system is used only for older structures, whose strength is being questioned.