MTC research brief: Pervious Concrete Physical Characteristics and Effectiveness in Stormwater Pollution Reduction

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July 06, 2016

The Midwest Transportation Center (MTC) sponsors a competitive research program to fund projects focused on State of Good Repair in infrastructure with attention to safety and Data Driven Performance Measures for Enhanced Infrastructure Condition.

The following details one project led by Iowa State University. Stay up to date on research conducted by the MTC here.

 

Iowa State University

Pervious Concrete Physical Characteristics and Effectiveness in Stormwater Pollution Reduction

Project PI: Say Kee Ong                  Project Co-PI: Kejin Wang   

The objective of this research was to investigate the physical/chemical and water flow characteristics of various previous concrete mixes made of different concrete materials and their effectiveness in attenuating water pollution. Four pervious concrete mixes were prepared with Portland cement and with 15% cementitious materials (slag, limestone powder, and fly ash) as a Portland cement replacement.

All four pervious concrete mixtures had acceptable workability. The unit weight of the fresh pervious concrete mixtures ranged from 115.9 lb/yd3 to 119.6 lb/yd3, while the 28 day compressive strength of the pervious concrete mixes ranged from 1858 psi (mix with 15% slag) to 2285 psi (pure cement mix). The compressive strength generally increased with unit weight and decreased with total porosity (air void ratio). The permeability of the four mixes generally decreased with unit weight and increased with total porosity. The permeability coefficients ranged from 340 in./hr for the pure cement mix to 642 in./hr for the mix with 15% slag. The total porosities of the four pervious concrete mixes ranged from 24.00% (mix with 15% slag) to 31.41% (pure cement mix) as measured by the flatbed scanner test method, while the porosities ranged from 18.93% (mix with 15% slag) to 24.15% (pure cement mix) as measured by the RapidAir method. The total porosities of the four pervious concrete mixes measured by the flatbed scanner method were higher than those measured by the Rapid Air method, but the specific surface areas measured by the flatbed scanner method were all lower than those measured by the Rapid Air method. For the pollution abatement experiments, mixes with fly ash and limestone powder removed about 30% of the input naphthalene concentration, while the mix with slag only removed 0.5% of the influent naphthalene concentration. The water volume balance showed that less than 1% of the water added was retained in the experimental column setup.

Some key findings of this research included the following:

  •  All four pervious concrete mixes had acceptable workability. The mixes made with pure Portland cement and 15% fly ash replacement appeared to have better workability than the other two mixes.
  • The unit weights of the fresh mixes ranged from 115.9 lb/yd3 (15% slag mix) to 119.6 lb/yd3 (15% fly ash mix).
  • The 28 day compressive strengths ranged from 1858 psi (15% slag mix) to 2285 psi (pure cement mix). The compressive strength generally increased with unit weight and decreased with total porosity.
  • The hydraulic permeabilities ranged from 340 in./hr (pure cement mix) to 642 in./hr (15% slag mix). The permeability generally decreased with unit weight and increased with total porosity.
  • The total porosities (air void ratios) ranged from 24% (15% slag mix) to 31.41% (pure cement mix) using the flatbed scanner test method. The total porosities ranged from 18.93% (15% slag mix) to 24.15% (pure cement mix) using the RapidAir method.
  • The total porosities of the mixes measured by the flatbed scanner method were all higher than those measured by the RapidAir method, but the specific surface areas measured by the flatbed scanner method were all lower than those measured by the RapidAir method.
  • The pollutant abatement experiments showed that the mixes with fly ash and limestone powder removed about 30% of the influent naphthalene concentration. The mix with pure cement removed 10% of the influent naphthalene concentration and the mix with slag removed only 0.5% of the influent naphthalene concentration. Less than 1% of the water was retained in the experimental column setup.

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