Prepared for Ready Mixed Concrete (RMC) Research & Education Foundation by:
Somayeh Nassiri, Ph.D., P.Eng., Assistant Professor-Washington State University and Past ISCP Director
Othman AlShareedah, Ph.D. Student Washington State University
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SUMMARY Field installation of high-quality pervious concrete with the target void content and mechanical properties is a common challenge. The objective of this project was to set forth a model to forecast the physical and mechanical properties of field installations based on mixture composition and the compaction level. On this basis, compaction and mixture composition-based void content and strength models were developed in the laboratory in the first phase. For model development, the specimen size was confined to cylinders. Compaction was achieved with a lightweight deflectometer (LWD) with a load cell while simulating the proctor hammer compaction method. In the field study, the calibration parameters of the developed model were reevaluated based on the physical and mechanical results of field cores. As expected, it was seen that the model estimates would not match the void content and strength of field cores due to significantly higher compaction forces commonly used in the laboratory. Thus, the model was recalibrated to predict the properties of field cores accurately. Installers can use a database of their mixture composition, roller screed weight, revolution per minute, void content, and strength of cores from past projects to recalibrate the developed model. The calibrated model can then forecast the required compaction to produce the target void content and strength.
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Overview
In the laboratory phase of this study, an experiment was performed to develop correlations between the compaction force level, the void content, and compressive strength of cast pervious concrete cylindrical specimens. The objective of the field evaluation phase of the study was to evaluate the compaction model (Eq. 1-3) and update the calibration parameters of the laboratory model for field compaction, if needed.
Field Installation of Pervious Concrete Slabs
—Pervious Concrete Mixture Design Four 11-foot wide pervious concrete slabs were installed in the field on September 3, 2020. About 5-6 linear foot was installed using each compaction type, as will be described in the next section.
—Compaction Procedures: After placement, each of the four pervious concrete slabs was compacted by one of four methods
—Field Infiltration Rate Testing (ASTM C1701): The infiltration rate was measured on one location on each of the four slabs as per the ASTM C1701 test method.
Laboratory Testing of Field Cores
Three cores were extracted from each of the four slabs to evaluate the void content, infiltration rate, and compressive strength of pervious concrete as a function of compaction methods. Each core had a 4-inch diameter with varying depths based on the slab thickness at the specific location where the core was extracted. A total of 12 cores were obtained from the field.
—Void Content Testing (ASTM C1754): The void content was established according to the ASTM C1754 test method pre and post-cutting. In this method, the dry mass (Md, in g) and the cylinder’s dimensions (in cm) are taken.
—Laboratory Infiltration Rate Testing (modified ASTM C1701): A modified version of the ASTM C1701 was used to evaluate the infiltration rate of the cores in the laboratory.
—Compressive Strength Testing: The compressive strength of the cores was tested based on ASTM C39 with a modified loading rate of 15 psi/s to prevent premature failure of pervious concrete
—Results and Discussions: The design void content, the measured void content (ASTM C1754), and the measured infiltration rate (modified ASTM C1701) (infiltration rate normalized by cores’ depths) for the cores from the four slabs are presented in Fig. 8, including the results before and after trimming 1-inch from top and bottom.
Calibration of Compaction Model
The test results in this field study are used to validate the void content and compressive strength models shown earlier in Eqs. 1 and 2. To solve Eqs. 1 and 2, Fc (the compaction force) needs to be calculated using Eq. 3. The input parameters in Eq. 3 are the mass, radius, and angular velocity of the rotary roller screed used in the field.
Conclusions
Four pervious concrete slabs were installed with four compaction levels, and cores were extracted to study the effect of compaction on void content, infiltration rate, and compressive strength.
Acknowledgment
Funding and support from the RMC Research & Education Foundation are recognized.
References
For the paper, please go to: https://rmc-foundation.org/wp-content/uploads/2021/07/Predictive-Model-for-Void-Content-and-Strength-of-Pervious-Concrete-Pavements-FINAL.pdf