Lightweight Fly Ash-Plastic Aggregates in Concrete

Abstract

The potential of using a synthetic lightweight aggregate (SLA) in concrete is examined. The aggregates are manufactured through thermal processing using plastic to encapsulate and bind fly ash particles. Nominal maximum-size aggregates of 9.5 mm were produced with fly ash contents of 0 percent, 35 percent, and 80 percent by total mass of the aggregate. The plastic used was high-density polyethylene, and the fly ash had a carbon content of 12 percent. An expanded clay lightweight aggregate and a normal-weight aggregate were used as comparison. Gradation, specific gravity, and absorption capacity are reported for the aggregates. Five batches of concrete were made with the different coarse aggregate types. Volume fractions of cement, water, fine aggregates, and coarse aggregates were kept the same for comparative purposes. Mechanical properties of the concrete determined included density, compressive strength, elastic modulus, splitting tensile strength, fracture toughness, and fracture energy. Salt-scaling resistance, a concrete durability property, was also examined. Compressive and tensile strengths were lower for the synthetic aggregates than for the normal-weight and expanded clay lightweight aggregates; however, comparable fracture properties were obtained. Relatively low compressive modulus of elasticity was found for concretes with the SLAs, although high ductility was also obtained. As fly ash content of the SLAs increased, all properties of the concrete were improved. Excellent salt-scaling resistance was obtained with the SLA containing 80 percent fly ash.

Novel lightweight concrete containing manufactured plastic aggregate

“…to 23% (25 to 50 mm) as the replacement level was increased from 25 to 100%. This result is comparable to those of Jansen et al [30] and Slabaugh et al [33] who reported slump reduction of 7 to 16% due to replacing CA with SLA. The decrease in the slump of the RP2F1C mixes is due to the sub-angular shape and fibrous surface texture of the RP2F1A particles.…”

“…As can be seen in Figure 12, RP2F1C100 had the most ductile behaviour. A similar finding was reported by Kashi et al [29], Jansen et al Lateral strain (mm/mm) Axial strain (mm/mm) [30] and Malloy et al [31]; who all observed that concrete made with SLA kept deforming at the peak load before fully disintegrating. The ductility, or reduced brittleness, of the RP2F1C mixes is a unique feature not shared by conventional lightweight concrete.…”

“…Conversely, a reduction in slump (ranging from 7 to 28%) was also observed by other researchers [30,31,33] when lightweight CA was fully replaced with synthetic lightweight aggregate (SLA). However, the plastic-based aggregates developed in these studies [27][28][29][30][31][32][33][34] were of the same shape and size. Additionally, these aggregates were either a composite made from plastic and fly ash, or plastic coated with either river sand or granulated blast furnace slag (GBFS).…”

“…Other studies [27][28][29][30][31][32][33][34] have showed a similar decreasing trend in the mechanical properties of concrete with an increase in synthetic lightweight aggregate content; while workability increased in some instances and in others it is decreased. For instance, Choi et al [27,28] reported that the slump of concrete made with waste PET lightweight aggregate (WPLA), at a 75% replacement level of FA, was 46% higher compared to conventional concrete.…”

“…Several studies [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] were conducted on the effect of replacing coarse (CA) and/or fine aggregate (FA) in concrete with plastic. However, few studies have reported on the influence of manufactured plastic aggregate on the performance of concrete, when it is used as a replacement for aggregate [27][28][29][30][31][32][33][34].…”