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Publication Number: FHWA-HRT-12-031
Date: August 2012

 

User’s Guide: Estimation of Key PCC, Base, Subbase, and Pavement Engineering Properties From Routine Tests and Physical Characteristics

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CHAPTER 5. Stabilized Materials Models

As the LTPP database contains limited data on modulus values and index properties of stabilized materials, the only prediction model that can be developed for modulus prediction is that for LCB materials, which is included in this section.

LCB Elastic Modulus Model

The model developed can be expressed as follows:

E subscript LCB equals 58,156 times the square root of f prime subscript c,28 d plus 716,886

Figure 97. Equation. Prediction model 17 for ELCB.

Where:

ELCB = Elastic modulus of the LCB layer. f'c, 28d = 28-day compressive strength of the LCB material.

The predicted versus measured and the residual errors plots for this relationship are presented in figure 98 and figure 99, respectively. The model has an R2 value of 41.24 percent, an RMSE of 541,600 psi, and uses 11 data points. The compressive strength values range from 770 to 2,800 psi with an average value of 1,400 psi.

This graph is an x-y scatter plot showing the predicted versus the measured values used in the lean concrete base (LCB) elastic modulus model. The x-axis shows the measured elastic modulus from 0E + 00 to 5.0E + 06 psi, and the y-axis shows the predicted elastic modulus from 0.0E 
+ 00 to 4.0E +06 psi. The plot contains 11 points, which correspond to the data points used in the model. The graph also shows a 45-degree line that represents the line of equality. The data are shown as solid diamonds, and they appear to demonstrate a good prediction. The measured values range from 1,862,500 to 4,266,667 psi. The graph also shows the model statistics as follows: N equals 11, R-squared equals 0.4124, root mean square error equals 541,619 psi, and 
y equals 0.4124x plus 2E plus 06.

Figure 98. Graph. Predicted versus measured for the LCB elastic modulus model.

This graph is an 
x-y scatter plot showing the residual errors in the predictions of the lean concrete base elastic modulus model. The x-axis shows the predicted elastic modulus from 0.0E + 00 to 4.0E + 06 psi, and the y-axis shows the error in prediction from -1.00E + 06 to 1.50E + 06 psi. The points are plotted as solid diamonds, and they appear to show no significant bias (i.e., the data are well distributed about the zero-error line). There appears to be no trend in the data, and the trend 
line is almost horizontal (i.e., zero slope). The following equations are provided in the graph: 
y equals -8E minus 06x plus 5.9484 and R-squared equals 4E minus 11.

Figure 99. Graph. Residual errors for the LCB elastic modulus model.


 


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