Concrete Maturity Method

The concrete maturity method is a technique for predicting concrete strength in real time based on the actual thermal history of the concrete. There are three steps required to carry out the maturity method:

1. Establish the strength-maturity relationship for the specific mix that will be used in construction.
2. Estimate the in-situ strength of the concrete using the maturity index.
3. Verify the strength-maturity relationship (E4-15, page 10).

This research pilot project indicates that the concrete maturity method using sacrificial sensors is an efficient and reliable method for quality control in industrial concrete construction. The data from the sensors also provided measurement of the non-uniform strength gains of in-situ concrete, thereby providing more precise control to the contractor and engineer in determining when a newly placed concrete structure can be exposed to live loads and formwork can be removed (E4-15, page 26).

Since this was a pilot test of a relatively new technology, the contractor in the beginning continued to do all of the concrete testing that they normally would have done without the loggers. It was not possible during the pilot test to quantify the schedule and cost savings that resulted from the use of the maturity sensors. However, as the pilot study progressed, the engineer of record authorized the use of the maturity system to determine the timing of the following:

1. Place live loads on elevated slabs.
2. Remove forms from precast panels.
3. Proceed with non-destructive testing to clear non-conformance reports (E4-15, page 26).

Another field study of the concrete maturity method in very cold weather was conducted and it was found that these methods could be used to reduce the overall total cost of any construction project. Although the concrete maturity method was not the government quality control procedure on the project observed in this study, it provided timely and accurate field concrete maturity information, which could potentially lead to significant time savings if the method were used as the governing quality control procedure (E4-2, page 40).

Heating and hoarding cost is a relatively small part of the total cost savings that could be realized using the concrete maturity method. The forms that become available from early removal can be used for other concrete activities in the project, or returned to the suppliers, which results in savings in the shoring and forms rental cost per day. If the overall project duration is reduced, the supervisory and overhead costs of the project are also reduced. A time savings of 28% could have been achieved if the concrete maturity method had been fully adopted. Therefore, the indirect cost savings equivalent to the 28% time reduction could have reasonable been expected (E4-2, page 41).

In summary, this research project provided experience for the contractor in the use of the maturity system technology that enabled real-time estimates of concrete strength using sacrificial sensors embedded in concrete placements. The pilot results depict the high degree of correlation obtainable between the maturity method calculation and the actual concrete strength.