Abstract:
Particle packing optimization is a process of selecting optimum aggregate proportions that result in minimum voids and maximum density thus requirement of cement and water can be minimized. The concept of particle packing is adopted to determine sustainable concrete mix for interlocking concrete block pavers (ICBP). Typically the aggregates used for the ICBP are 12mm coarse aggregates with manufactured sand and natural sand as fine aggregates. Fresh concrete is poured into the mold and both vibration and compaction is applied to cast the block. The mold is removed soon after the block is cast. Hence a low water cement ratio and high green strength needs to prevent edge falling and cracking of freshly cast ICBP. Present industrial practice seems to be far less economical due to the use of high amount of cement, wastage of aggregates, and high energy consumption of machines due to improper mix proportions. Hence high strength variations within the same batch is visible. Theoretical packing models such as Toufar, De-Larrad, CPM, LPDM, Powers, Shilstone chart were analysed to determine the most suitable packing model. This study proposes improved sustainable mix design using packing density method by optimization of parameters such as water-cement ratio, coarse to fine aggregate ratio, quarry dust to natural sand ratio, cement content and compaction effort. Trial mixes were tested increasing excessive cement content from 20% to 40% in 5% intervals. The water cement ratio of 0.32-0.36 is suitable with 65-70% of fine aggregates. Further, 65-70% of manufactured sand (as a percentage of total fine aggregate) should be used to maintain green strength of the mix. Optimum vibration time should be 5-7 seconds with an optimum compression of 1.7 -2.0 MPa. The study reveals that optimization of mixture design parameters can reduce the cement content by 30% while maintaining the same concrete strength.
