Mix designs of self-compacting concrete using local materials

In the last several years, self- compacting concrete (SCC) has gained considerable attention in the concrete industry in order to overcome the problems associated with conventional vibrated concrete (CVC). The concept of SCC was originally advocated by Japanese researchers in the early 1980s and shortly thereafter developed and introduced as a construction material [1-3]. The term “self-compacting concrete” refers to a “new” special type of concrete mix characterized by high resistance to segregation that can spread into place, fill the formwork, and encapsulate reinforcement without any mechanical consolidation [4-5]. Such concrete should have a relatively low yield value to ensure a high degree of flowability and a moderate viscosity to resist segregation and bleeding. Furthermore, it must maintain its homogeneity during transportation, placing and curing to guarantee adequate structural performance and long-term durability. The successful development of SCC should be characterized by a good balance between deformability and stability. Researchers have established guidelines for the mix proportioning of SCC, which include a reduction in the volume ratio of aggregate to cementitious material [6], increasing the paste volume and water-cement ratio (w/c), carefully controlling the maximum coarse aggregate particle size and its total volume, and the use of various viscosity modified admixtures (VMA) [4-8]. For SCC, it is generally necessary to use superplasticizers in order to obtain a high flowability rate. Adding a large volume of powdered material or viscosity modifying admixture can eliminate segregation. The powdered materials that can be added are fly ash, silica fume, lime stone powder, glass filler and quartzite filler, and others [7]. One of the limitations of SCC is that there is no established mix design procedure yet. Literature available to date reveals that the general procedure for SCC design mixes is based on keeping the coarse aggregate and fine aggregate contents fixed at a certain ratio and that self -compactibility is to be achieved by adjusting the water/powder ratio and superplasticizer dosage [3 and 7]. A certain number of trial mixes is essentially required to determine the optimum water/powder ratio and other ingredients of SCC.

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