Technological Advancements for Construction of Pervious Concrete Pavement Systems: EVOLUTION OF EQUIPMENT UTILITY

– Avishreshth Singh

Postdoctoral Researcher, Section of Pavement Engineering, Department of Engineering Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology,
The Netherlands

Pervious concrete pavement (PCP) systems are well known for their water-draining ability, which allow the mitigation of flashfloods and generation of stormwater runoff. Though PCP technology is widely utilized for the construction of parking lots and low-volume roads in developed countries, it is an evolving roadway system in emerging nations such as India. Further, the construction of PCPs requires the use of skilled labor and high-quality control, which restricts their implementation and use in emerging economies. It is worth mentioning that improper construction practices are consequential of pavement defects such as raveling, which are contributory to poor riding quality and premature failure.

Researchers at the Indian Institute of Technology Tirupati (IITT) developed and adopted a systematic methodology to construct PCP demonstration test sections at the Municipal Corporation of Tirupati, India in March 2018. The construction of subgrade and base layers involved similar approach used for conventional concrete pavements. In the absence of a standard construction methodology for PCP systems, the major challenge was to adequately compact the pervious concrete (PC) mix that was prepared on-site using a drum mixer. To accomplish this, alternate PC slabs (Figure 1a) were laid that were compacted with a plate vibratory compactor (Figure 1b), which is commonly used to compact soil and sand bed before placing the paver blocks as the surface wearing course. To avoid sticking of the aggregates onto the surface of a plate vibrator and prevent the formation of polished surface at the top; a thin, flat, and rigid aluminum sheet was placed over the PC surface after which the compactor was slowly moved over it for about 60-90 s. A lower compaction period was consequential of loose aggregates at the surface and higher compaction would result in the formation of cement patches over the surface. In another investigation, PCP test sections were constructed on-campus IITT using similar compaction approach, as described earlier. However, this study involved continuous construction of PC slabs (Figure 1c), and the mix was prepared in a ready-mix concrete plant and transported to the site through batch trucks. The isolation joints were provided by placing a wooden sheet between two adjacent PC slabs, which was removed once the slabs were compacted to the desired density. However, this resulted in low-to-severe raveling at the joints at distinct locations across the PCP system. Note that international practice has been to provide the joints using a pizza tool cutter immediately after construction. Further, different levels of raveling was common in both the PCP systems at multiple locations attributed to the fact that the compaction effort was not uniform throughout the length of PCP. Additional details relevant to the construction chronology and equipment can be found elsewhere.

To address the durability issues caused due to the utilization of a plate vibratory compactor, the research team at IITT decided to customize a roller screed and make use of it for all future preparation of the special PC mixtures. The roller screed comprised the following components: (a) 300 rpm and high speed gear box with variable speed options mounted on a power-end handle resting within an enclosure (Figure 2a) to allow for clockwise and counter clockwise rotations, (b) a roller tube 3.5 m long and with 170 mm diameter (Figure 2b), and (c) a handle placed at the opposite end of the motor assembly such that the roller could be adjusted for future extension. Further, provisions were made to place counterweights on the handle to prevent sinking of the roller on the motor end during operation and provide extra compaction effort. In addition, a joint cutter was customized having a groove at the center to hold circular blades with varying depths from 20-60 mm (Figure 2c). The joint cutter included a roller weighing between 7 and 10 kg having diameter of 100 mm and width of 750 mm. Finally, a push handle with provision of extension was attached to the joint cutter assembly for creating joints within the PCPs of different dimensions. Note that the roller had tapered ends to prevent the formation of roller marks on the PCP.

The customized screed was also used to compact the PC layer in the recently developed Pervious All-Road class All-weather Multilayered paver (PARAMpave) blocks. The utilization of screed roller resulted in a smooth PC surface without compromising the mix porosity. Note that the screed is capable of compacting thin PC layers (for conventional PCPs) under its own weight and can be operated at variable speeds to achieve the target mix density. For layer thicknesses greater than 100 mm, the roller screed can be used as an additional step to provide a uniform riding surface once the plate compaction step is completed. Further, the use of a pizza joint cutter (Figure 2b) is recommended to create joints in the PCP systems (Figure 2). To eliminate the use of a plate vibratory compactor for compacting PC surface layers with higher thicknesses, it is recommended to introduce the vibratory control function in the roller screed, which will help in achieving the desired densities to the best possible extent. Further, it is advised to provide joints using a joint cutter that is commonly used for conventional concrete between 36 and 72 h after the construction. In conclusions, there is an urgent need to evolve the way PCP systems are constructed by utilizing new and improvised equipment that will support construction of top-class PCPs, which possess consistence in quality without compromising durability and hydrological characteristics.

– Krishna Prapoorna Biligiri

Associate Professor and Head, Department of Civil and Environmental Engineering, Indian Institute of Technology Tirupati, India

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