Sep 2019 HOW TO TEST THE STRENGTH OF CONCRETE
While strength testing your concrete installation may not be a critical consideration for small to medium sized construction, for entrepreneurs and contractors, this added step may save you unforeseen problems and huge costs later in your project. Sephaku Cement discusses different types of concrete strength testing and simple steps to test the durability of any concrete application large or small. The assumption that strength testing concrete is a costly process is an incorrect one and not nearly as costly as having to replace installations compromised due to inadequate load bearing qualities or poor durability.
Adding a step to assess the strength of fresh concrete assures both contractors and clients of a quality installation and peace of mind that their project will pass safety compliance testing.
While testing the slump or volume of air in wet concrete may seem to be the obvious and more commonly exercised method to measure strength and durability, from field test sampling to testing the temperatures and measuring the density of concrete there are a number of alternative ways to evaluate the strength of freshly placed concrete.
When working frequently with cement, the chemical reaction that takes place when cement becomes wet should come as no surprise, as a result, this chemical reaction gives off heat (heat of hydration) and offers a good indication of what can be expected from the strength of the concrete once cured. The process of measuring the temperature of concrete is a simple one beginning with your first measurement taken 5 minutes after pouring.
Insert your thermometer between 5 and 10 cm into the wet concrete taking the temperature for around two minutes, because the temperature of concrete can influence a number of variables that take place during curing, measuring the temperature of wet concrete will help contractors to respond to ambient conditions which in turn can influence a stable curing process. Concrete with a high internal temperature can be vulnerable to cracking due to the fast evaporation of water during the curing process as well as due to temperature differential between the temperature inside the concrete and the surface of the concrete (expansion and contraction). Concrete that cures at too cold temperatures may be prone to freezing which negatively impacts the compressive strength resulting in a brittle final product. With temperature information available on site, concrete should not be placed at temperatures 5oC and falling, building contractors can respond to the varying curing conditions and temperatures and positively influence a favourable curing process by closing/covering newly casted concrete to allow temperature built-up.
Concrete Density Testing
Testing the density of concrete takes specialised skills and equipment including the need for a Type B pressure meter or a calibrated scale to measure mass per volume. Although an added technical requirement to your project, this process offers valuable insight that could end up saving you more than the cost of conducting the test itself. Relaying information that will indicate the relative yield of your concrete, this test will not only pinpoint the air content of the concrete mix which is directly related to the strength measurement of the concrete, but will also help determine the exact volume of concrete required for the project ensuring the correct quantities of materials are used.
Outside of confirming the yield and relative yield of the volume of concrete, density testing will also confirm results that may come out of a slump and air content test where if the slump of concrete is high and the air content is high the density of concrete will measures low. As a rule of thumb an air content of 1% above the normal air content relates to a reduction of 5 MPa strength. E.g. a concrete designed for 25 MPa with an additional 2% air can measure strength of as low as 15 MPa. This strength reduction not only may render a sub-strength concrete by the air voids will greatly reduce its durability.
Ensuring the use of an excellent quality cement product such as the Sephaku Cement range, as well as the correct ratio proportioning of building materials have been measured, curing conditions are favourable and care and attention paid during placing, regardless of the test type conducted there should be no reason to doubt that test results will measure near perfect when testing the strength of concrete