Concrete Learning Center

Does strength of capping material (in case of cylindrical specimens) affect the measured strength of concrete?

The capping material should have strength & elastic properties similar to those of the concrete in the specimen. This is required so that there is no enhanced tendency to splitting & also to achieve a reasonably uniform stress distribution over the surface of specimen.

The capping material should not be weaker than the concrete in the specimen. However, if the cap is too strong, there will be apparent increase in strength of concrete due to large lateral restraint produced by strong cap.

The influence of capping material on strength is more for  medium (strength>20MPa)  & high strength concrete (strength>45MPa)   For example, high strength capping of 37M Pa strength leads to 7-11% higher strength than low strength capping  in compression tests carried out on 48M Pa concrete. For 69 M Pa this difference is as high as 17%.

It should be noted that differences are smaller when thickness of the cap is very small.