Slab fillers and methods for implementing fillers in two-way concrete slabs for building structures

A filler for use in a two-way concrete slab for building structures, the filler comprising:

• an upper keeper tray and a lower keeper tray with one or more spacers positioned on said keeper trays;
• a plurality of indicators positioned in all corners or at least one corner of the keeper trays supported via one or more buttress to indicate an amount or level of a concrete fed on the filler;
• one or more grooves at an end of the spacer, configured to securely hold one or more belts, wherein the spacer and belt in the keeper trays are configured to receive one or more rebar, said at least one belt is configured to attach at least one upper keeper tray, lower keeper tray, or both;
• a volumetric filling element arranged in between the upper keeper tray and the lower keeper tray, wherein the upper keeper tray is attached to a top of the volumetric filling element and the lower keeper tray is attached to a bottom of the volumetric filling element.