Utilisation of crumb rubber as a soil amendment for sports turf Utilisation de granules de gomme comme amendement de sols de terrains de sport

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1 Scientific registration number : 496 Symposium number : 19 Presentation : oral Utilisation of crumb rubber as a soil amendment for sports turf Utilisation de granules de gomme comme amendement de sols de terrains de sport GROENEVELT P.H., GRUNTHAL P.E. Dept. of Land Resource Science, University of Guelph, N1G 2W1 - Guelph, Ontario CANADA 1 Introduction The use of scrap tire rubber for environmentally sound pedological or geotechnical applications has not received a great deal of attention. Recent problems with the use of chipped rubber as a lightweight aggregate in roadway construction has drastically reduced the amount of scrap rubber devoted to geotechnical research. Even less attention has been directed to the use of rubber crumb as a soil amendment to control downward mechanical forces that cause compaction. About 20 million car and truck tires are discarded in Canada annually. Of these, about 62% are landfilled (dumped), 14% are stockpiled, 18% are recycled and 4 % are converted into fuel. Clearly, there is a great opportunity and need to explore innovative uses of discarded rubber. Scrap tires may be shredded into crumbs of different sizes. The cost of the endproduct increases as the desired maximum size decreases. For the use of rubber crumbs in sports fields, it is absolutely essential that all the steel from the steel belts is removed. A United States patent by R.C.Malmgren et al. (1991) describes soil amendment methods using rubber crumb. The patent states that the rubber particles are mainly obtained from automotive tires, are of various sizes (it recommends 8 mm in diameter) and can be added in varying amounts (0-40%) depending on the soil type. Malmgren et al.(1991) suggests that the application of rubber crumb to soil decreases several negative impacts associated with compaction from heavy foot traffic, and that the ameliorative technique is especially useful for managing turfgrass in sports fields. Logsdon (1990) claims that the resiliency of the turf is not a direct factor of the elastic nature of rubber but rather the result of increased aeration which allows for the establishment of a thicker, more shock-absorbing, sward of turf. Researchers have also stated that the inclusion of rubber particles in soil can improve the use efficiency of water and fertilizers by up to 30% (Riggle, 1994). 1

2 The potential benefits of rubber amended soil for turfgrass performance and health include: increasing porosity, drainage, and resiliency of the soil so plant growth is not inhibited by water-logging or compaction reducing the probability of impact related injuries to athletes and thoroughbreds long-lasting soil enhancement from 10 to 25 years economical and longer-lasting than organic amendments beneficial recycling of resources 2 Materials and methods Forty field plots were established at the Guelph Turfgrass Institute at Guelph, Ontario. The plots were 4 m wide, 2.5 m in length, and excavated to a depth of 7.5 cm. Aisle ways separated the plots. Ten treatments were chosen to create different soil physical conditions. Very fine slightly alkaline sandy loam, the native soil, was used in all treatments. The treatment factors included: five concentrations of rubber crumb (0%, 10%, 20%, 30%, 40%) and 0% and 0.75% coconut fiber. Each of the ten treatments was replicated four times in this complete randomized block design. Twenty-four in-ground, bottom draining, turfgrass lysimeters were used to collect leachate from soils with and without crumb rubber, lime and/or peat moss. Each rectangular lysimeter was 0.65 m wide, 1.01 m long and 0.32 m deep. To allow rapid percolation, the lysimeters had a coarse gravel base of 0.09 m. The base was covered with fine mesh to maintain separation between the aggregate and the admixture. Leachate from each treatment plot was collected via tubing connected from the lysimeter drain to a container, located in a sunken bunker. Eight treatments were chosen to reflect different soil chemical conditions. Two different soil textures were used, a slightly alkaline very fine sandy loam and a slightly acidic loamy sand. Leachate was analyzed for volatile organic compounds (VOC) and base/neutral/acid extractable substances (BNA) as listed by the United States Environmental Protection Agency under schedules 624 and 625, respectively. Total concentrations of Al, Au, B, Ba, Be, Ca, Cd, Cr, Co, Cu, Fe, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, Ti, Va, Zn, and Zr were measured using inductively coupled plasma-atomic emission spectroscopy. 3 Results and discussion 3.1. Soil surface hardness Impact absorption values, to determine the strength or stiffness of the soil surface, were collected using a 2.25 kg Clegg Impact Soil Tester. Soil hardness is a measure of the shockabsorbing proper ties of a soil surface. An accelerometer in head of the hammer or missle measures the duration of impact. The shorter the time period, the greater the deceleration 2

3 and the harder the tested surface (Clegg, 1978). The greatest peak deceleration over four consecutive drops is recorded and measured in gravities (G). Four such recordings were collected from each plot. The mean hardness values are presented in Figure Soil Shear strength Shear strength of the turf surface was measured using a shear vane and electronic torque meter. The vane used was tapered with a vane width of 47.7 mm and a length of 97.2 mm. The diameter of the vane rod was 12.1 mm. Four readings were taken on each plot and the means are presented in Figure Soil Water Content Volumetric water contents were determined in situ using a Tektronix 1502C cable tester. Steel pins with a length of 200 mm, a diameter of 2.3 mm, and spaced 50 mm apart, were inserted into the soil at approximately 22 degrees to the surface, to determine the water content of the 7.5 cm depth of amended soil. Three readings were taken for each plot. Mean values are presented in Figure Zinc Content of Grass Tissue Approximately 100 grams of grass clippings were randomly collected from each of the 40 plots and analyzed for nitrogen, phosphorous, potassium, magnesium, calcium, manganese, copper, zinc, and boron. Zinc concentrations are presented in Figure Leachate analysis No elevated levels of VOC s or BNA s were detected in the leachate collected. Slightly elevated levels of boron, sodium and zinc, leached from acidic sandy loam soil amended with 30% rubber crumb. Concentrations of these elements from soil mixed with rubber crumb and lime, however, did not differ from those observed for control plots. The data are presented in Table 1, where H stands for acidic sandy loam soil, L = lime added, R = 30% rubber crumb added. 4. Conclusions Rubber crumb significantly reduced soil hardness, soil shear strength, and water content in non-compacted field tests. Rubber also significantly increased the concentration of zinc in turfgrass clippings. However, elevated concentrations were not sufficient to product zinc toxicity in turfgrass. Treatments consisting of an acidic soil and rubber crumb (HR) had elevated levels of zinc, boron and sodium. These effects were negated by the addition of lime to the soil admixture. 3

4 References CLEGG, B. (1978): An impact soil test for low cost roads. In: Proceedings of the 2 nd conference of the road engineers association of Asia and Australia. Australia, pp LOGSDON, G. (1990): New sports fields from old tires. Biocycle 31: & MALMGREN, R.C., PARVIZ, N., SOLTANPOUR, P.N. & CIPRA, J.E. (1991): Soil amendments with rubber particles. U.S. Patent 5,014,562. RIGGLE, D. (1994): Finding markets for scrap tires: utilization options. Biocycle 35: Keywords : crumb rubber, soil amendment, physical properties, sports turf Mots-clés : granules de gomme, amendement, sol, propriétés physiques, terrain de sport Figure 1: Effect of percent crumb rubber on soil surface hardness for treatments with and without coconut fibre % Fibre 0.75% Fibre Equation 1 illustrates the relationship between soil surface hardness and percent rubber crumb for all data. Similarly, the association between hardness and percent rubber crumb for treatments without fibre and treatments with 0.75% coconut fibre are shown in equations 2 and 3, respectively. 4

5 (1) (2) (3) G surface = (n= 40, α=0.0001, R 2 =0.623, MSE=5.152) G surface = (n= 20, α=0.0002, R 2 =0.557, MSE=5.297) G surface = (n= 20, α=0.0001, R 2 =0.700, MSE=4.997) where: G surface = impact absorption (G) RC = rubber crumb (%) Figure 2: Effect of percent crumb rubber on soil shear strength for treatments with and without coconut fibre % Fibre 0.75% Fibre Equation 4 illustrates the relationship between soil shear strength and percent rubber crumb for all data. Correspondingly, Equations 5 and 6 show the association between shear strength and percent rubber crumb for treatments without coconut fibre and for those containing 0.75% fibre, respectively. s = (n= 40, α=0.0001, R 2 =0.375, MSE=5.445) (4) s = (n= 20, α=0.002, R 2 =0.426, MSE=5.498) (5) s = (n= 20, α=0.009, R 2 =0.326, MSE=5.661) (6) 5

6 where: s = shear strength (kpa) RC = percent rubber crumb in amendment Figure 3: Effect of percent crumb rubber on soil water content for treatments with and without coconut fibre % Fibre 0.75% Fibre Equation 7 illustrates the relationship between soil water content and percent rubber crumb for all data, while equations 8 and 9 show the dependence of the factors for treatments without fibre and for those containing fibre, respectively. ( ) ( ) ( ) θ v = RC (n= 40, α=0.0001, R 2 =0.573, MSE=0.014) (7) θ v = RC (n= 20, α=0.0001, R 2 =0.625, MSE=0.015) (8) θ v = RC (n= 20, α=0.0002, R 2 =0.557, MSE=0.013) (9) where: θ v = soil water content (m 3 m -3 ) RC = rubber crumb (%) Figure 4: Effect of percent crumb rubber on mean zinc concentrations in turfgrass tissue. 6

7 % Fibre 0.75% Fibre Equation 10 illustrates the relationship between the concentration of zinc and percent rubber crumb for all data. [ Zn] = (n=40, α=0.05, R 2 =0.844, MSE=6.606) (10) where: [Zn]=concentration of zinc (mgkg -1 ) RC= rubber crumb (%) TABLE 1: Mean concentrations of B, Na, and Zn in leachate from acidic sandy loam (H) amended with lime (L) and rubber crumb (R). Note: Treatment B (mgkg -1 ) Na (mgkg -1 ) Zn (mgkg -1 ) H 0.05 B 4.10 B 0.03 B HL 0.05 B 2.23 B 0.02 B HR 0.14 A 8.77 A 0.18 A HLR 0.05 B 3.83 B 0.02 B Means in the same column with the same letter are not significantly different (α=0.05). 7

A Review of Environmental Impacts and Environmental Applications of Shredded Scrap Tires

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