An Alternate Test Method for the Void Content of Pervious Concrete

Abstract

Abstract In recent years, pervious concrete has become an emerging material for healthier ground water recharge and superior control of high stormwater runoff. This is facilitated by the high void content of the material. The void content percentage is an important design variable, as it correlates permeability as well as the strength of the material. Therefore, an accurate quantification of the void content is needed. A recently developed ASTM standard (ASTM C1754/C1754M-12) presents a method for determining the density and void content of hardened pervious concrete; however, there are still some issues apparent with this standard. The main issue is that the standard does not consider the absorption of the aggregate or the paste, which could adversely affect the results. Other concerns include the buoyant force due to trapped air when submerging the specimens, the high drying temperature in drying method B, which causes cracking and renders the specimen unusable for other testing, and the lengthy time requirement. This study further articulated these issues and presented two alternative testing techniques, one novel technique (Torres method) and one modified ASTM C1754 test method that can be used to better determine the void content of pervious concrete. The Torres method developed in this study placed the pervious concrete specimen in saturated surface dry (SSD) condition prior to determining the void percentage, such that the absorbed water mass was removed from the calculation. Additionally, a modified ASTM C1754 was developed that also placed the specimens in an SSD condition while still using the water tank used in ASTM C1754. The results from both of the developed methods showed lower void percentages for the specimens tested than with the current ASTM C1754 (drying method A and B) standard. The results indicated that including the absorbed water mass into the calculation ultimately resulted in higher void percentages.