Validity of aggregate packing models in mixture design of interlocking concrete block pavers (ICBP)

Interlocking concrete block pavers (ICBP) are manufactured using a semi dry concrete mix and vibration and compression are applied by electrical or hydraulic machines to cast the blocks. Hence the concrete mixture characteristics differ from concrete mixtures that we use for general purposes. When determining the mix proportions for the mix design, several properties of the block need to be considered. Maintaining required strength and surface texture, producing mixes with optimum water content to maintain the green strength while avoiding slumping are some of the challenges faced by the industry. To overcome such challenges a mix design using aggregate packing optimisation can be used effectively. There are number of theoretical packing models available for concrete mix optimisations and each model has its own pros and cons. Most of the models are successfully used for more generalised concrete applications and these models have not been used for more specialised applications such as ICBP. This study considers Modified Toufar model, three parameter model and compressible packing model to determine the validity of applying for ICBP. The theoretical models are compared with laboratory and field packing density experiments and the results indicate that the models are not accurately predicting the packing density for mix design of ICBP. Hence the study suggests developing a new theoretical packing model that accommodates production procedures together with mixture performances to enhance the mix design procedure as well as the performance of ICBP.