Moreno-Cortés, Carla M.

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    Subsurface stormwater retention with pervious concrete pavement on UPRM campus master plan
    (2018-05) Moreno-Cortés, Carla M.; Hwang, Sangchul; College of Engineering; Morales Vélez, Alesandra C.; González Vélez, Enrique; Pagán Trinidad, Ismael; Department of Civil Engineering; Huérfano, Víctor
    Pervious concrete pavement constitutes an efficient Best Management Practice (BMP) stormwater management solution, since it serves to manage surface runoff quantitative and qualitative characteristics at its earliest stages. Since flash flooding occurs very often on campus of the University of Puerto Rico at Mayagüez (UPRM) under a normal rain event, the use of pervious concrete, results in the conservation and protection of water resources by leading to the reduction of flooding events downstream, non-point source pollutant transport, and on-site ponding. In order to implement the pervious concrete BMP system, a sustainability assessment was performed to identify possible sites in need of this practice, equipped with a subsurface water retention structure, hydrologic design, estimation of construction costs and resulting reduction of stormwater runoff volume. The sustainability assessment was done with a Multi-criteria Decision Analysis (MCDA) in conjunction with the Analytic Hierarchy Process (AHP) approach. The AHP approach, evaluated three sustainability categories, which are social, economic and environmental. Each one was ranked based on a particular and specific criteria, which was developed considering the input collected from a group of ten experts who were asked to fill a questionnaire comparing the different criteria under each sustainability category. These experts input was served to establish the ranking values for the criteria, resulting in the selection of social sustainability as the one with the highest value. Additionally, from the on site assessment of the campus, seven critical areas identified and the Mangual/Terrace and Faculty Building were identified as the ones in the most need of a PC system with overall ranked values of 4.1 and 4.0, respectively. Once the areas were identified, a study was made to attain an optimized mortar mixture incorporating glass and fly ash as partial replacement of cement. Since the main focus of the project is to incorporate sustainability in all aspects as possible, and given the lack of glass recycling and high quantities of fly ash that end up at landfills in P.R., the incorporation of both as construction materials was studied. X-ray diffraction (XRD) and a hydrometer test were also performed to analyze the chemical composition of the glass and the particle size distribution respectively. XRD revealed an amorphous pattern on the glass powder while the hydrometer test results showed that the cumulative measure for 50% of particles size was 8 μm. The optimization of the mixture was done using Response Surface Methodology (RSM) to get the highest possible compressive strength value with a targeted spread percentage of 110%. At 28 days of curing, the optimum values for a maximum compressive strength of 83 MPa and 110 spread percentage were 7.25% glass-to-binder ratio (G/B) and 14.30% fly ash-to-binder ratio (FA/B). After obtaining an optimized mix mortar containing glass powder and fly ash, it was incorporated to pervious concrete (PC). Because permeability and compressive strength are both important mechanical properties for PC and are inversely proportional to each other, a good balance between them is essential to attain the ideal design of PC. The measured values for compressive strength and permeability fell within the typical values specified by the National Ready Mix Concrete Association (NRMCA) and the American Concrete Institute (ACI). Since all the areas to be analyzed have different characteristics, for the implementation of the PC, the designs must be developed specifically for the selected area. Correspondingly, a hydrological study was carried out for the different areas in need of a pervious concrete system. The study was done using the National Resources Conservation Service (NRCS) method with a rainfall recurrence of 2 years and duration of 24 hours. Results of the analysis allowed evaluating the excess of runoff before and after the implementation of a PC system. A soil study was also performed on the Mangual/Terrace area to evaluate the soil properties specific to the site. The result from both studies allowed for the creation of a PC design that takes into consideration the site-specific characteristics. Furthermore, the design served not only as a stormwater subsurface storage structure but it also encompassed the safety of the students through a bicycle lane that would enhance the students’ daily commute.