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Figure 20: Concrete strength estimation for slab C1.1 two days after construction using the modified shear wave velocity
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(a) Modified shear wave velocity-based compressive strength estimation (psi) (b) Modified shear wave velocity-based flexural strength estimation
Figure 20: Concrete strength estimation for slab C1.1 two days after construction using the modified shear wave velocity
It should be noted that the maturity and shear wave velocity models developed for the long-life concrete mixture design are only valid for a pavement age of at least 1-day. Using these models to compute strength in the first few hours after paving might predict unrealistic, negative strength estimations.
4 Evaluation of Concrete Strength by Combined
Nondestructive Tests
In this study, the benefits of the maturity method and ultrasonic tomography are combined to create an efficient and accurate method of evaluating concrete strength. As discussed above, the shear wave velocity method permits better evaluation of the strength development of concrete, but it cannot be used to predict concrete strength development because the latter is affected by the ambient conditions. On the other hand, the maturity method is less accurate for the strength level determination but can be used for the prediction of strength development. A procedure was developed in this study to utilize the advantages of each method. The combined model also presents more realistic results when estimating strength right after placement.
4.1 Determining Maturity Curve
As previously discussed, maturity is a widely accepted method. The process of developing maturity curves is illustrated below using the data gathered in the field study aspect of this project. It must be noted that the coefficients obtained in this study are not the default values.
Separate maturity testing MUST be performed for every individual mixture design for accurate correlations.
Step 1: Obtaining Temperature Data
Maturity is based around the temperature variation as concrete cures; therefore, the initial step is setting up and obtaining temperature data over several days or weeks. The maturity measurements should be conducted according to ASTM C1074. Temperature sensors are imbedded in at least two cylinder and two beam specimens. In this example, three specimens of each were equipped. A data logger is used to gather the temperature data over the entirety of the laboratory testing period with the specimens containing the temperature sensors being testing for strength on the final day.
Figure 21 is an example of the gathered temperature data collected at the Golden Triangle Construction Company lab. The data logger creates a chart displaying the temperature every 5 minutes. The figure shows the temperature gain for the first 24 hours for all six equipped specimens.
