For example, the strength parameters of concrete test specimens of any grade of concrete.
Colonel Sudhir Mudigere Rangappa, There are several reasons why experimental values of concrete parameters occasionally fall 5 to 10% below the recommendations provided by international code equations. Firstly, the inherent variability in concrete mixes plays a pivotal role; concrete is a composite material comprising various components such as cement, aggregates, water, and admixtures, and variations in their quality and proportions can significantly influence the overall strength and durability of the concrete.
Secondly, the curing conditions exert a substantial impact on concrete strength. Concrete cured in ideal conditions, like a controlled environment with adequate moisture and temperature, generally exhibits higher strength compared to concrete exposed to less favorable conditions, such as a dry and hot environment.
Additionally, the testing methods employed to measure concrete parameters can introduce slight discrepancies in results, even when examining the same concrete mix. International code equations tend to rely on conservative estimates of concrete strength and durability to ensure that structures can withstand expected loads and environmental conditions. Consequently, these code values are often higher than what's observed experimentally.
It's crucial to recognize that the divergence between experimental and code values need not be a cause for alarm. Concrete structures are designed with a safety margin to accommodate the variability in concrete properties and uncertainties surrounding loads and environmental factors they may encounter.
However, if a consistent trend of experimental values consistently falling below code values emerges, further investigation becomes necessary. This might entail concrete mix testing to ensure compliance with specifications and a review of curing conditions to optimize them.
If you are comparing the US practices and Indian then the difference is in terms of cylinder and cube testing practices. Secondly the standard of quality control will also have its impact on the final value being considered.
If mix design of concrete is done properly considering target strength based on quality control parameter ( Standard deviation) , normally experimental values of compressive strength are more than Grade of concrete. Of course it should be slightly greater ( 5 t0 10 %) than target strength. However , same concrete if implemented at field ( site) , actual strength of concrete at field must be slightly more than expected strength (grade of concrete ), If desired quality of material and concrete operations are not maintained, expected strength at field (site) will be less. Strength Equations mentioned in codes may be different for lab concrete specimens and field concrete specimens, based on the research data.
Do you compare the mean (average) value from your tests to the standard concrete class? Because (at least according to EN 206 standard) as the class of concrete there are given characteristic values of compressive strength, not the mean values. And characteristic strength is the strength value below which there is only 5% of all possible strength determinations for a given batch of concrete. This means that 95% of the tested specimens have a strength greater than the characteristic value.
- Badges
- Science topic