Nondestructive maturity testing can help yield important information about concrete strength in critical places while accounting for variances in field conditions, writes Scott Grumski, vice president of platform development at Forney. While it cannot replace traditional testing, it can enhance it.
The construction materials testing (CMT) industry is excited by the possibilities of estimating concrete strength via the non-destructive maturity method. This method provides a number of enhancements to the traditional laboratory compression test method. But the maturity method is not an alternative or replacement. Indeed, maturity testing relies completely on the traditional compression test method.
Maturity testing exploits this known warming phenomenon to estimate the early strength of poured concrete based on its temperature. The temperature is measured with devices embedded in the concrete when it is placed at site. Done properly, the temperature can then be cross-referenced against the laboratory developed strength-maturity relationship for the concrete mix in question.
So, before you can use the temperature of the in-place concrete, you need to know how the temperature correlates with strength—and that is done under laboratory conditions. To do this:
- Prepare a batch of concrete test cylinders according to traditional strength testing protocol and of the same mix design that will be used in the field;
- Place temperature sensors in at least two of the concrete cylinders;
- Compute the Maturity Index by recording temperatures at prescribed time intervals;
- At prescribed intervals of elapsed time, break the remaining cylinders according to the traditional compression strength test regimen;
- Record compression strength, corresponding temperatures and elapsed time; and,
- Calculate and generate the maturity curve by plotting the average compressive strength versus the average Maturity Index to reveal the strength-maturity relationship
You can then embed temperature sensors in newly poured concrete and—armed with the data that reveals the relationship between time, temperature and strength—begin to make informed decisions about your project.