In this blog, we will establish an old concept not regularly used in concrete pavement. The use of “Maturity to Determine Opening to Traffic Concrete Strength.” This new section 40-1.03L in October 2021, 2018 Revised Standard Specifications (RSS), is completely new to the Caltrans construction process but is an old technology that was developed and used in the structural concrete industry over the last 35 years.
This process is still very new to the pavement industry but has been used very successfully in the private sector for when structural column forms may be stripped or loads may be placed on slabs on grade using construction equipment. The actual start of the development of maturity came in the 1970s when several bridges and their structures were collapsing even when the compressive strength showed it met its required strengths. The investigating engineers found the concrete specimen testing did not match the actual strength gain of the structures due to the cold ambient conditions which greatly slowed down hydration and was not represented by the concrete test specimens.
So, what is the maturity method? Maturity is a measurement of the relationship between concrete temperature, time, and strength gain. It is represented by an index value that can be measured in real-time in the field. The intent of the maturity method often referred to as maturity, is to measure newly in-place concrete pavement strength by correlating time and temperature readings to the actual strength values.
The new Section 40-1.03L “Use of the Maturity to Determine Opening to Traffic Concrete Strength,” uses the time/temperature to concrete strength to be developed during the mix study phase of 40-1.01C(4) Mix Design. During this process, as both flexural and compressive strength are tested, one extra bream and cylinder is fabricated and a sensor is placed inside each to measure the concrete temperature. The temperature and strength measurements are correlated at 3 days, 7 days, and 14 days.
With this curve developed in the laboratory or “in the field during the test strip or first day of production,” the data will then be used to estimate the strength of the in-place concrete without having to use concrete beam or cylinder results for approval to open to traffic. The use is very practical and not heavily reliant on test specimens that may or may not be cured properly or transported without damage. The concrete may be opened once the concrete has reached its temperature/strength relationship to the required 550 psi to allow traffic on the pavement.
There are different types of maturity equipment that may be purchased with the biggest innovation of the use of Bluetooth technology. This allows the reading to be taken without hooking up to a wire coming out of the concrete, and instead wirelessly from the embedded sensors during the duration of curing. The sensors are installed 1 1/2 feet from the edge of the pavement and approximately 2” from the surface, at the end of the day’s production. Most maturity equipment comes with a software application for smartphones or tablets that require you to be within 35 feet of the embedded sensor to retrieve the data. Once downloaded, a report will show the in-place strength and whether it has met the strength requirement. It is then delivered to the Caltrans engineer for approval to open the pavement to traffic.
For any project specification that bids prior to October of 2021, the contractor will have to request a change order to use the maturity method. It is strongly recommended to engage in conversation with the Caltrans team prior to requesting the change order to assure everyone agrees to the method and its use.
G3 Quality, Inc. is here to provide any further information you may need and how to implement this method on your current or upcoming projects. For more information, reach out to our Technical Services Director, Marc Robert by email at firstname.lastname@example.org or by phone at 562.321.5561.
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