Evaluation of suitability of voidcon slab as an alternative slab solution for the Ugandan construction industry

Abstract

The VoidCon slab deck is a new type of slab system being introduced and marketed into the Ugandan construction industry as an alternative to the already existing and conventional slab types namely; the solid slab and the hollow block slab. However since this is a new system, it has not yet really been proven whether the benefits alleged with its use truly stand when used in the Ugandan setting or whether the design parameters that the decking bases off are indeed applicable within the construction industry. This study was aimed at confirming whether the VoidCon system is an appropriate alternative to the conventional slab methods typically used in the Ugandan construction industry through the assessment of the design parameters stated by the deck manufacturer, comparative analysis of the costing of the major slab materials, the deadweight component and the eco-friendly aspect of the slab type options. The concrete strength class of C30 was stated to be used during the design of the VoidCon slab by the deck manufacturer which was discredited following the determination of the most commonly used strength class for casting of slabs in the Ugandan construction industry. Lab results on concrete cube strength tests were obtained and these showed that for most of the cubes, the strength of 30MPa after 28 days age was not being hit for concrete works done for slabs. A few Site Engineers were also interviewed and the most commonly used concrete class determined as C25. Mix design was done for the C25 and the C30 to obtain the cement content which was used to prove the expectations of the C25 concrete strength class being cheaper and if so, to what extent. New load-span tables were created with a change in the dead load and application of new factors in accordance with Eurocode 1 (BS EN 1991-1-1:2002). The conventional slabs and the VoidCon slab were designed for varying span so as to note out the trend in reduction percentages when the design of the slab is altered. The quantities of the concrete constituents were determined using the quantities from the mix design of the C25 and the volume of the slabs with the VoidCon slab coming out as the cheapest of the slab options with a 30% reduction from the solid slab and a 16.5% reduction from the hollow block slab. The total rebar required for each of the three slab options was determined and this resulted in 30% reduction in cost for the hollow block slab from the solid slab while the VoidCon slab had a 69% reduction from the solid slab and a 59% reduction from the hollow block slab. From the design of the slabs, the self-weight of the three slab options was obtained and the VoidCon slab was seen to be the lighter of the slab alternatives. The total cement required to cast the three slabs was calculated to see which would release the least amount of CO2 and the VoidCon slab was seen as the most eco-friendly due to the fact that it requires less cement than the conventional slab options with a 30.5% reduction in carbon dioxide emitted.