Development of construction specifications and quality assurance criteria for compacted fly ash-cement feedlot pads

Type F fly ash derived from the combustion of bituminous coal at power plants is a by-product that is typically disposed in landfills at a significant cost. However, numerous industrial uses have been identified for fly ash that economically benefits both the fly ash producer and the fly ash user. One such use is the construction of compacted fly ash-cement pads for hay storage and for livestock heavy traffic areas, including traffic lanes, feeding areas, watering sites, loafing lots, and feedlots. The use of a variety of pads (e.g. soil-cement, fly ash, geotextile-gravel) in feedlots has been shown to improve daily gain and reduce hoof disease in cattle. However, quality assurance methods for construction of such pads are lacking. Therefore, a laboratory study was performed to develop a quantitative approach to construction quality assurance (CQA) testing of compacted fly ash-cement pads. The study consisted of laboratory compaction testing using different combinations of compaction effort, water content, and cement content. Unconfined compressive strength (q(u)) testing of the different compacted specimens was performed to identify which combinations of parameters produced optimal results. Portland cement, hydrated lime, and quicklime were used as cementing agents. Results demonstrated that the maximum dry density (rho(dmax)) of the compacted fly ash-cement mixtures was achieved at an optimum water content (w(opt)) that ranged from 21% to 37%, depending on the compaction effort and cement type, with an average w(opt) of around 27%. Specimens compacted with portland cement were roughly twice as strong as those compacted with hydrated lime. Quicklime specimens were not as strong as the hydrated lime specimens, and the optimum water content of the quicklime specimens was 3% to 4% higher than the optimum water content of the hydrated lime specimens. To apply these results towards the development of construction specifications and CQA criteria, the q(u) data were superimposed onto the compaction data to associate combinations of dry density (rho(d)) and water content (w) with q(u). Using these plots, CQA criteria in the form of acceptance windows of rho(d) and w can be defined for any combination of cement type, cement content, and target q(u). CQA testing can be performed in the field using established methods to provide in situ measurement of rho(d) and w, which can be used with the plots to estimate q(u) and assess whether or not the compacted material has been constructed to design specifications.