Project Information

 

BACKGROUND

 

-Pervious Concrete

The US Environmental Protection Agency (EPA) recommends pervious concrete pavement systems to manage surface storm-water runoff and treat the storm-water. When looking at the mix materials and the mixing techniques, the conventional concrete mix is similar to pervious concrete mix. Pervious concrete has a higher void ratio, which reduces its strength when compared to the conventional concrete. Pervious concrete has been applied in pavements for more than 20 years around the United States. Unfortunately, 25% of the installations have failed.

 

-The City of Flagstaff, Arizona

The City of Flagstaff is located in the northern part of the state of Arizona. Flagstaff has an elevation of 6,910 ft and an area of 63.9 square miles. The City of Flagstaff winter climate is often below freezing and experiences high frequency of freeze-thaw cycles which affects the performance of the mixes. The number of cycles is around 250 cycles. Northern Arizona University is located in the City of Flagstaff. A first attempt in using pervious concrete in the pavement was in 2007 when it was applied in the parking lot near the Applied Research and Development Building (ARD). NAU is the first institution in the State of Arizona to use pervious concrete in the parking lot pavement.

 

-Phase One

The parking lot located near the Applied Research and Development building (ARD) of the campus was made with pervious concrete in 2009. This parking lot failed after three years from the application and completion. A team in charge of Phase One developed pervious concrete mix formulas. The team members included Junyi Shen and Darius Ikan-tubui Ishaku. Then, based on the formulas, the team produced specimens. While a few pervious concrete mixes appeared to be a promising product, there is still a need to improve its performance in durability, strength, and air void. The information gathered from Phase One is necessary for applying the mix design formula and monitoring it. Also, the information is important to know the mistakes made by the Phase One team as well as the different mixes created in Phase One. This will help in avoiding the same mistakes and havin more ideas in creating more appropriate mix for the parking lots.

 

Project Description

 

-Project Understanding                   

Pervious concrete is a concrete mix that has a high void ratio to allow water to pass through the pavement to the ground in a short amount of time. This helps to manage storm water by reducing runoff and localized flooding. The purpose of Phase Two of the pervious concrete is to create a stronger mix of the pervious concrete by adding an admixture, silica fume, which increases the strength of concrete. The new mix includes fiber, aggregate, cement, water and silica fume. These mixes will be expected to increase the strength and void ratio of specimens, which will advance the performance of pervious concrete. Another purpose of this project is to compare the mixes in strength and void ratio with or without silica fume and fiber.

 

-Current Conditions

The ARD parking lot failed after three years from completion. The failure was due to shear force from large trucks. The failure of the parking lot motivated the project. Since then, specimens have been created in order to find the best concrete mix design formula and apply it to the parking lot. The new specimens have to withstand the high shear force from large trucks.

The specimens have different ratios of cement, coarse aggregate, water and sand. Also, the specimens have chemical admixtures added to them like Hydration Stabilizer (DELVO), Mid-range Water Reducer (P900), Viscosity Modifier (VMA), Air Entrainment (Micro Air). These chemical admixtures were added to the specimens for both phases; however, for the second phase and after looking up for more admixtures, silica fume admixture was added to the mix formulas. These admixtures are used to increase the quality of performance of concrete. Two different molds were used to test the specimens created. The first mold is a cylindrical mold with a diameter of 4 inches and a height of 8 inches. This mold is used for the Compression Strength Test and the Void Ratio Test. The second mold is rectangular mold that has a length of 16 inches, width of 4 inches and a height of 4 inches. These molds are used for the freeze-thaw cycle tests.

 

-Constraints and Limitations

There are several constraints and limitations for the concrete mix design formula. A water to cement ratio of 0.265-0.3 is required for the design. The resulted compression strength for the specimens must be no lower than 2500 psi. Moreover, the void ratio must exceed 17%. This is because having a lower percentage than 17 would decrease the chance of the seepage of water when applying pervious concrete on the pavement. The City of Flagstaff experiences around 250 freeze-thaw cycles in one year. The specimens must withstand the weather conditions and the high frequency of freeze-thaw cycles.

 

-Task Lists

A set of tasks was developed in order to complete the second phase of this research project. The tasks include all aspects related to finishing the second phase. This include deliverables, meetings, preparation, designing and testing. The list of tasks for the second phase of pervious concrete mix design formula are:

Task 1- Team Management

Task 2- Project Development

Task 3- State of the Art Literature Review

Task 4- Material Preparation

Task 5- Mix Formula Development

Task 6- Specimen Production

Task 7- Lab Testing

Task 8- Data Analysis

Task 9- Final Deliverable