The Effects of Aggregate Sizes on Strength and Permeability of Pervious Concrete Blended with Metakaolin
1,*Olosunde, O. E. and 2Ajamu, S. O.
1Department of Civil Engineering, Ladoke Akintola University of Technology, Ogbomoso, Oyo state, Nigeria.
DOI: 10.36108/laujoces/6202.61.0101
Abstract
Pervious concrete is a sustainable pavement material characterized by its high permeability, and it is increasingly adopted as an effective solution for storm water management in urban infrastructure by preventing flooding possibilities on our pavements and increasing water recharge to the underground. A major challenge lies in balancing its strength and permeability especially when partially replacing Portland Limestone Cement with supplementary cementitious materials for economic and environmental sustainability. This study investigates the combined effects of coarse aggregate size variation and partial substitution of Portland limestone cement with metakaolin, highly pozzolanic calcined clay, on the mechanical and permeability properties of pervious concrete. Concrete mixes were produced using three coarse aggregate gradations: 9.5-16, 16.5-20 and 20.5–25 mm. Aggregate properties were established through sieve analysis, water absorption and specific gravity test. For each of the size ranges, control mixes with 100% PLC and modified mixes with 10% metakaolin replacing cement by weight were prepared. A constant water–binder ratio of 0.35 and a binder aggregate ratio of 1:4 were recast. Workability tests (slump and compacting factor) were used to assess fresh concrete behavior. Mechanical properties were evaluated through permeability test, compressive and flexural strength tests and density assessments. These tests were conducted at 7, 28, and 56 days respectively to monitor the effects on the different aggregate
sizes and partial substitution of PLC with metakaolin over time. Sieve analysis confirmed the classification of coarse aggregate into the specified size ranges of 9.5-16, 16.5-20 and 20.5-25 mm. Slump values, ranged from 18-24 mm and 14-20 mm for the control and metakaolin modified mixes. Compacting factor values for all concrete mixes ranged from 0.68 to 0.82. The 9.5-16.0 mm mixes has compressive strength values, ranged from 9.78-16.44 MPa (Control mix) and 9.33-15.78 MPa (Blended mix) as against 9.11-16 Mpa, 8.67-15.33 Mpa in 20.0mm size range and 8.44-15.11 Mpa, 8-14.67 Mpa in 25.0 mm aggregate size range. It is recommended that 16.5-20 mm aggregate size range be used in pervious concrete where both strength and permeability are required. A 10% metakaolin replacement is also recommended to improve long-term strength.
Keywords: Compacting factor, Compressive strength, Flexural strength, Slump, Permeability.