Polyacrylamide adsorption and aggregate stability

This study was to find a treatment technique to reduce the water absorption of Recycled Aggregates (RA) which involved preparing a coating to reduce the water penetration. The materials considered for the preparation of coating was Termite Mound Soil (TMS) and ordinary Portland cement. The objective was to find their optimum proportions and the slurry thickness for a coating that gives the lowest absorption. TMS was tested for pozzolanic properties. Chemical composition was tested using AAS and other analytical techniques. Mainly water absorption, particle size distribution, AIV, LAAV of RA was tested to ensure the suitability for construction purposes. Slurry was prepared using cement and TMS with cement replacement levels of 0, 20, 40, 60 and 80% of TMS. 3 sets of coatings were prepared with water to solid ratios of 1, 1.25 and 1.5. Slurries were prepared in a concrete mixture in which the aggregates were coated for 10 minutes. After air drying, coated aggregates were cured in water and tested for the absorption after 14 days. The absorption of treated aggregates was compared with those of natural and raw recycled aggregates. From the successful aggregate batches concrete test cubes were prepared and tested for the 28 day strength and compared the strength values with those prepared with natural aggregates. Aggregates Coated using 50% cement and 50% TMS showed a significant reduction in the water absorption up to 38.44%. The strength of concrete made from aggregates treated with 50%soil replacement along with the water solid ratio 1 was competitive as those from natural aggregates.

Irrigation Science, 1995

High levels of soil sodicity, resulting from intensive irrigation with saline-sodic waters, lead to an increased soil susceptibility to seal formation and to severe problems of runoff and soil erosion. The objective of this study was to investigate the efficacy of the addition of small amounts of an anionic polyacrylamide (PAM) to the irrigation water in controlling seal formation, runoff and soil erosion. Two predominantly montmorillonitic soils were studied, a grumusol (Typic Haploxerert) and a loess (Calcic Haploxeralf), having naturally occurring exchangeable sodium percentage (ESP) >12. The soils were exposed to 60 mm of simulated irrigation with commonly used tap water (TW, electrical conductivity=0.8 dS m-l; sodium adsorption ratio (SAR)=2), or saline water (SW, electrical conductivity=5.0 dS m-l; SAR> 12). PAM effectiveness in controlling runoff and erosion from the sodic soils was compared with runoff and erosion levels obtained from untreated soils having low ESPs (<4). For both soils and for both water qualities and polymer concentrations in the irrigation water, PAM was efficient in controlling runoff at low ESP levels and inefficient at high ESP levels. At moderate ESP levels, PAM's efficacy in controlling runoff was inconsistent and varied with water quality and polymer concentration. Conversely, in general, soil loss originating from rill erosion, was significantly and effectively reduced in moderate and high ESP soils by addition of PAM to the irrigation water, irrespective of water quality and polymer concentration. PAM was more effective in reducing rill erosion than in reducing runoff in the moderate and high ESP samples, because the energy involved in generating runoff is much higher than that involved in rill erosion. PAM treated surface aggregates were not stable against the distructive forces leading to seal formation and runoff production; but they were stableenough to resist the hydraulic shear exerted by the runoff flow.

Australian Journal of Soil Research, 2009

Soil surface application of dissolved linear polyacrylamide (PAM) of high molecular weight (MW) can mitigate seal formation, runoff, and erosion, especially when added with a source of electrolytes (e.g. gypsum). Practical difficulties associated with PAM solution application prohibited commercial use of PAM in dryland farming. An alternative practice of spreading dry granular PAM with high MW on the soil surface has been ineffective in reducing runoff while effectively reducing erosion. The objective of this study was to investigate the mechanism by which granular PAM (20 kg/ha), with moderate (2 Â 10 5 Da) or high (1.2 Â 10 7 Da) MW, mixed with phosphogypsum (PG) (4 Mg/ha) affects infiltration rate, runoff, and erosion. Five smectitic soils, treated with PAM and PG, were exposed to simulated rainfall of deionised water in the laboratory. Both dry PAMs, mixed with PG, increased final infiltration rate (3-5 times) and reduced erosion (2-4 times) relative to the control (no amendments). Whereas the polymers' effects on the infiltration rate and runoff relative to each other were inconsistent, PAM with moderate MW was consistently more effective in reducing soil loss than PAM with high MW. For example, in the sandy clay soil, soil losses were reduced from 840 g/m 2 , in the control, to 570 and 370 g/m 2 for the high and moderate MW PAM treatment, respectively. This greater capacity to control soil erosion was ascribed to the lower viscosity of the soil surface solution following dissolution of dry PAM granules in the case of moderate MW PAM, leading to more uniform, effective treatment of soil aggregates at the soil surface by the polymer.

Journal of Environmental Management, 2014

The purpose of this study was to evaluate the effects of three agricultural processing wastes (APWs) on aggregate formation and aggregate stability in a sandy loam textured soil (Typic Xerofluvent) in Antalya, Turkey. The effects of APW applications on aggregate formation and aggregate stability were observed for different aggregate size groups (>4; 4e2; 2e1; 1e0.5; 0.5e0.25; 0.25e0.050 and <0.050 mm). Sugar Beet Pulp (SBP), Apple Pomace (AP) and Cotton Gin Waste (CGW) were applied to soil as fresh material (dry weight basis 0, 10, 20 and 40 t ha À1 ), and a greenhouse pot experiment was conducted using a completely randomized design with five replicates of each treatment. The study consisted of two periods. The first period (P1) consisted of a six-month incubation period (1st sample period). The second period (P2) is a six-month period and includes an eight-week green bean (Phaseolus vulgaris L.) growing process (2nd sample period). At the end of the first six months and fourteen months in total, aggregate formation and aggregate stability were determined and their correlation to different C sources was explained. At the end of the experiment, formation of aggregates was increased with increase in the application level of organic wastes in particular intermediate aggregates. Increase in the incubation time significantly enhanced the formation of particular macroaggregates. Soil aggregate stability of all aggregate sizes generally increased with the increasing in the level of implementation. In addition, incubation time effects on aggregate stability for macroaggregates were not significant, but significant for macro and microaggregates.

The presence of stable aggregates at the soil surface affects the potential for soil to be utilised for crop production, i.e. by affecting the ability of soil to receive and store water, and to enable the rapid and uniform emergence of crops. Considering this positive relationship between aggregation and crop production this paper offers a summary of numerous studies concerned with the mechanisms, associated physico-chemical properties and assessment of soil aggregate stability. It is perceived that such a summary facilitates a general understanding of the characteristics associated with aggregate stability that may be useful to agricultural industries to diagnose and manage structural degradation.

Transactions of the ASABE, 2012

Suspended sediment is the primary pollutant prevalent in runoff waters exiting construction sites with exposed and disturbed land. In this research, the effectiveness of a chemical stabilizer, known as anionic polyacrylamide (PAM), to prevent erosion and promote sedimentation was examined using different application methods (i.e., dry granular vs. semidissolved solution). In this study, the effectiveness of Silt Stop 712, a proprietary PAM product, was tested using different application methods at three different rates, i.e., 16.8, 28, and 39.2 kg ha-1 (15, 25, and 35 lbs acre-1), on bare, unseeded, unprotected 1.2 m × 0.6 m × 0.08 m (4 ft × 2 ft × 0.25 ft) laboratory-scale soil test plots. Laboratory-scale testing procedures using simulated rainfall were applied to mimic interrill erosion and sediment detachment scenarios similar to a highway embankment with a compacted 3H:1V fill slope. Our results showed that dry PAM treatments applied at the recommended rate of 39.2 kg ha-1 (35 lbs acre-1) were capable of reducing turbidity by 97% and net soil loss by approximately 50% in comparison to the bare soil control. Conversely, semi-dissolved PAM treatments applied at the same rate, i.e., 39.2 kg ha-1 (35 lbs acre-1), followed by a drying period of 48 h prior to the experiment, reduced turbidity by approximately 69% and soil loss by 76%. The lower application rates, i.e., 16.8 and 28 kg ha-1 (15 and 25 lbs acre-1), of semi-dissolved PAM without a drying time were observed to lose effectiveness after about 40 min; however, the higher application rate of 39.2 kg ha-1 (35 lbs acre-1) of semi-dissolved PAM provided consistent turbidity reductions throughout the entire experiment. Based on these results: (1) dry PAM applied directly to the surface at the manufacturer's recommended rate was more effective as a sediment control (i.e., turbidity reduction) measure, and (2) semi-dissolved PAM applied directly to the surface at the manufacturer's recommended rate and allowed to dry for 48 h prior to rainfall was a more effective erosion control (i.e., soil loss reduction) measure.

Soil & Tillage Research, 1998

The influence of the soil conditioner 'Agri-SC' on splash detachment and water-stable aggregation of an erodible clay Vertisol from Oahu, HI, was assessed. Laboratory rainfall Ž . simulation was used to assess splash detachment from soil treated with 0 untreated control , 0.3, 3.0, 30, and 300 l ha y1 of Agri-SC. Results indicated that the quantity of sediment splashed was y1 Ž significantly lower for Agri-SC application rates of 0.3 and 3.0 l ha rates are equivalent to 1 . and 10 times the manufacturer's recommended rates, respectively , than for the control, or for y1 Ž . Agri-SC applied at 30 and 300 l ha 100 and 1000 = , respectively . A second experiment was designed to test the influence of Agri-SC on water-stable aggregation of the Vertisol. Aggregates were subjected to rapid immersion in solution, shaken and washed through a series of sieves. Data indicated that there were no statistically significant differences in geometric mean aggregate diameter between the untreated and treated aggregates. The effect of the active ingredient, Ž . ammonium laureth sulfate an anionic surface active agent on splash and erodibility are discussed. These preliminary results indicate that further testing of Agri-SC is warranted on a variety of soils with different textures and mineralogies. q

Transactions of the ASAE, 2002

An indoor laboratory study was conducted to compare the dry versus sprayed application of polyacrylamide (PAM) and the use of different gypsiferous materials (gypsum and a class C ponded fly ash) on runoff and sediment yield. The six treatments incorporated in this study were: control, Nutra-Ash (NA), gypsum (G), sprayed PAM plus NA (PAMW+NA), sprayed PAM plus G (PAMW+G), and granular PAM plus G (PAMD+G). Simulated rainfall at an intensity of 70 mm hr-1 was applied for 2 hours to a silty clay loam soil packed into erosion pans. Only one of the two liquid PAM treatments (PAMW+G) significantly reduced runoff (35%), while both liquid PAM treatments (PAMW+G and PAMW+NA) significantly reduced sediment yield (74% and 77%) compared to the control. Sprayed PAM was more effective than granular application in terms of total runoff, but there was no statistical difference with regard to total sediment yield. Differences between the effects of sprayed and granular PAM are explained by the mechanisms by which they reduce erosion. Sprayed PAM, in combination with gypsum, increases infiltration during the first part of a rainfall event until sufficient rainfall has occurred to break down the PAM-treated aggregates, at which time runoff rate and sediment yield rate approach those of the control. Runoff and sediment yield rates from the granular PAM application were initially similar to those from the control. However, as time increased, sediment yield reached a maximum and then decreased without a corresponding decrease in runoff. This likely occurred because the PAM particles became activated during the rainfall and acted as a mortar to stabilize the soil matrix. Gypsum was a better source of electrolyte than a class C ponded fly ash, commercially known as Nutra-Ash (NA), likely due to its greater solubility. Addition of PAM decreased soil erodibility and may be a viable erosion control practice for soils susceptible to flow detachment. Choice of application method should be based on the expected amount and severity of precipitation before vegetation establishment. These results indicate that sprayed PAM, in combination with gypsum or Nutra-Ash, provides immediate erosion control, but its effectiveness decreases over time, as indicated by steadily increasing sediment yield rate. Dry PAM application was not as effective in the beginning of the experiment, but after sufficient rainfall it became "activated" and sediment yield continuously decreased over the remainder of the experiment.

European Journal of Soil Science, 1986

When natural soil aggregates were destroyed by crushing, techniques traditionally used for re-forming aggregates, such as wetting/drying and freezing/thawing cycles, did not produce any stable re-formed aggregates. Incubation without amendment, was similarly unsuccessful, whereas incubation with glucose amendment did produce stable aggregates, and their stability was related both to the natural soil organic matter levels and to the original stability of the natural aggregates. However, the stability induced by incubation with glucose was of a transient nature and declined over a period of 12 weeks. This behaviour was attributed to the production of microbial, extracellular polysaccharides and their subsequent decomposition. Addition of microbial polysaccharides of known structure confirmed that such polymers were capable of producing stable re-formed aggregates without the assistance of further microbial activity. Longer term incubation showed that the stability of the re-formed aggregates also declined as soil microorganisms broke down the polysaccharide material.

Paste ..., 2018

Tailings rehabilitation, using soil-like properties with chemical and physical stability, can be influenced by surface forces on a particle scale and microstructure. Non-homogeneous structures, manifesting as particle aggregation, alter the permeability/porosity and improve the balance of aerated and water-filled pores that then favours plant growth. Polymer flocculation in tailings thickeners yields large, weak aggregates that are sheared in beds and on pumping. While low-level residual structure may remain, sizes are small and downstream polymer impacts are minor. However, high polymer dosages added in-pipe to high-solids streams lead to further water recovery on deposition, and while this process is poorly understood, it gives aggregates that are likely denser and stronger. If such structures persist, they could potentially offer closure and rehabilitation benefits in some applications. A high-solids (50 wt%) thickener underflow analogue (kaolin, silt, and fine sand) was treated with anionic polyacrylamide (PAM) polymers at elevated dosages (up to 1,000 g t-1) to establish if aggregate structures created during inline tailings flocculation survive or change over longer-term consolidation. Low and high molecular weight (MW) PAM polymers of fixed anionicity (30%) were tested. Focused beam reflectance measurement (FBRM) provided real-time monitoring of the aggregation state after polymer addition. The compressibility of the inline flocculated tailings was assessed over an eight week period. Variations in the size-density relationship of aggregate structures were determined over this period using an image analysis technique, revealing that the shorter polymer chains produced denser, more compact structures immediately after deposition, whereas the longer chains resulted in a much slower re-conformation of the partially adsorbed polymer, leading to additional densification over time. Eight weeks after deposition, inline flocculated tailings produced with the low MW polymer were characterised by a higher compressive yield stress compared with the high MW polymer, consistent with the formation of smaller, more rigid aggregate structures with the shorter chains. The potential impact of such structures on longer-term rehabilitation properties (e.g. metal/metalloid ion adsorption and surface exchange capacity) of the treated tailings is discussed.