Effect of Water Content on Relative Flow Area and Hence Predicted Flow Values of Controlled Low Strength Materials

Abstract

Urban cities are embracing new innovations in built-up spaces and thereby necessitating renovations or constructions for new buildings either by demolition of obsolete buildings or at new places to expand the city itself. In this regard natural stones are converted to aggregates and hence generate stone dust as a waste. Construction and demolition wastes include brickbats which are used as in-fills. Many attempts have been made to re-use these wastes but still the problem persists and large percentages of these wastes reach landfills. Controlled low strength materials (CLSM) are an obvious choice for use of these wastes in large quantities, required for sustainable city objectives. CLSM is a cementitious and self-flowing backfill material. Design of CLSM mixes involves iteration process mainly to satisfy the flow and strength requirements. Phenomenological models are an effective tool in the design of CLSM mixtures with a single trial. In this paper Class F fly ash was used as secondary cementitious material along with powdered brickbats, stone dust as fine aggregates in complete replacement to natural sand; to produce sustainable CLSM mixtures with varying Class F fly ash to cement ratios and water contents. Spread flow and marsh cone flow tests were conducted on fresh CLSM mixtures and compressive strength tests were carried out on hardened cylindrical specimens at 3, 7, 28, and 56 day age. Spread flow values were converted to relative flow area values. Phenomenological models (flow and strength) were generated using wide range of experimental data to predict flow and strength values. The water demand of quarry dust mixes was more compared to brickbats mixes and this resulted in lesser flow values and hence non-flow results. Incorporation of these non-flow values in the generation of flow prediction models resulted in poor prediction of flow results; however strength prediction was not influenced. Discarded brick bats and quarry dust are hence recommended for use as fine aggregates along with Class F fly ash as secondary cementitious material in CLSM to overcome urbanization challenge for sustainable development. © 2018 American Society of Civil Engineers.