1036-B4

USEFULNESS OF PULP INDUSTRIAL SOLID WASTE (WHITEWASH MUD) IN FOREST ROAD PAVEMENTS

Carlos Cardoso Machado; Reginaldo Sérgio Pereira; Dario Cardoso de Lima; Giovani Levi Sant´Anna; José Maurício Machado Pires, Gersonito da Silva Vieira ¹

Abstract

The present study had as objective the study the effects of industrial solid waste (whitewash mud) in geotechinical properties of soil samples from near by region of Alagoinhas, Bahia - Brazil. In seven soil samples collected, two where selected as having a greater geotecnical potential. The characterization, compacting, CBR and permeability essays where used in this study. The results indicated that the soil denominated Best Gravel as being the most promising one, when stabilized with whitewash mud, reaching the best results with dosage of 20 and 25% of whitewash mud.

1. INTRODUCTION

In many situations, natural state soils do not present adequate geotecnical properties for use in layers of service roads, from there, elapses the importance of the study of soil stabilization in order to adjust the geotechnical parameters of these, in compliance with the requirements contained in the technical specifications of road organizations. The problem in road supports is basically related to the type of soils to be used. When it is characterized as sand, it presents extreme conditions of the arenaceous soils, obtaining generally, elevated support capacity under service conditions, if adequately laterally confined. In other hand, the occurrence of dust in roads (vicinal) is generally associated with the presence of argillaceous, argilo-silt-arenaceous soils and even silt-argillaceous sands, since the fact that they present substantial loss of superficial particles under the action of traffics and local climatic factors.

In roads, considering the Brazilian experience and the relation cost-benefit of the road enterprises, the use of the chemical stabilization and the mechanical methods of soil stabilization is common. Historically, the cement and the whitewash have been used in pavement of highways, especially in layers of base and sub-base, usually texts of 6 to 10% for cement and 5 to 6% of whitewash (DNER, 1996). However, in forest roads, the associated costs of the use of these techniques can be considered impracticable. Thus, a technological solution of low cost for the forest road sector could be the application of residues generated in production processes, used as chemical additive, to improve the geotechnical characteristics of soil, fitting the technique constructive requirements of roads, as well as guaranteeing the withdrawal of industrial residues, many times, pollutant of the environmental, confining them under controlled conditions in the under structure of highways. A residue with great potential of use is the whitewash mud, sub-product of the pulp and paper industry.

The intention of this study was to analyze, in laboratory, the geotechnical behavior of whitewash mud-soil mixtures, on the basis of the results of characterization, consistence limit, CBR and permeability essays, looking for applications in highways.

2. MATERIAL AND METHODS

2.1. Soil samples

Seven soil samples, proceeding from the Klabin-Bacell company, located in Alagoinhas, Bahia - Brazil, have been characterized and classified geotechnically according to the system adopted by the Transportation Research Board (TRB). In function of the collection place, the most important samples had been identified as: a) Sand Subgrade - samples collected under forest road surface and; b) Best Gravel - samples collected from a mine.

2.2. Whitewash mud

It was evaluated the potential of the whitewash mud, generated in the process of production of pulp and paper, as chemical stabilizer for the soil samples, objectifying the classification as a chemical stabilizer in a geotecnical point of view. It was used the whitewash mud in its pure form, as it is disposed in the embankment by the company.

2.3. Soil samples collection

The field procedures adopted for soil samples collection consisted of extraction, storage in plastic bags and transportation to the Geotechnical Laboratory of the Federal University of Viçosa. After this point, the soil samples where dried to air, passed through a sieve with 4,8 mm mesh aperture, determined the humidity, after what they where stored in sealed up plastic bags. The preparation of deformed soil sample used in the geotechinical essays followed the recommendations of the Brazilian Association of Technical Standard (ABNT), in obedience to procedure NBR 6457/86.

2.4. Whitewash mud dosages

The Whitewash mud dosages used, in relation to the air dried soil mass was: 10, 15, 20 and 25%; dosages chosen on basis of preliminary essays.

2.4. Laboratory Essays

The soil samples characterization essays accomplished embrace these determinations: combined grain-size analysis (ABNT, 1984a), liquid limit (ABNT, 1984b), plastic limit (ABNT, 1984c) and determination of the specific mass of the soil grains (ABNT, 1984c). After this stage, it was made a technical analysis of the results, in order to define which soil samples could be considered as representative, for usage in stabilization process and, consequently, in the determination of the parameters of compacting, CBR and permeability of the soil and whitewash mud mixtures. The following indexes were determined on the selected samples: optimum compacting parameters (ABNT, 1986), in the medium energy compacting AASHTO essay; California Bearing Ratio - CBR (ABNT, 1987); and permeability (HEAD, 1982). The sequence of execution for the compacting, CBR and permeability essays were: Soil as is, dried to air humidity plus water - rest of 24 hours before the compacting; Soil plus whitewash mud: addition of whitewash mud to the soil, after that, it was proceeded the addition of water and then the mixtures was passed through a sieve with 4,8 mm mesh aperture, until it reached a homogenization of at least 80%, then initiated the compacting.

3- RESULTS AND DISCUSSIONS

3.1. Classification and geotechnical characterization of soil

The table 1 present a synthesis of the results of the geotechnical characterization essays, as well as the respective classification of the soil samples of the region of Alagoinhas - Bahia, Brazil, by the TRB (DNER, 1996) process. Analyzing the results in table 1 following the TRB recommendations, it is verified that the studied soil samples, with exception of that called high subgrade collected in the Klabin Farm, integrates the group of granular materials that have a potential of use in roads construction, foreseeing, a good to excellent behavior as a material for subgrade forest road pavement. In relation to high subgrade, this one fits the group of fine soil of the related system of classification, being able to present a weak to poor behavior as a material for subgrade.

The analysis of the results presented in Table 1 leads, also to the conclusion that the samples Sand Subgrade and Best Gravel, on the point of view of grain size and from considerations to the plasticity (NP, for the first one, and with IP equal to 6%, the second) can be considered as representative of the set of essayed soil, being able to be used as component of the mixtures soil + whitewash mud. The Figure 1 presents the grain size curves of these samples. It is noticed that in table 1 the assigned grain sized fractions as gravel, sand, silt and clay are related to the following diameters: fraction gravel with diameter between 76 to 2 mm, fraction sand with diameter between 2 to 0,074 mm, fraction silt with diameter between 0,074 to 0,005 mm and fraction clay with diameter under 0,005 mm.

3.2. Compacting and CBR essays of soil and soil plus whitewash mud mixtures

The table 2 presents the compacting and CBR parameters and expansion measured in CBR essay of soil and soil plus whitewash mud mixtures for the Sand Subgrade and Best Gravel samples. In the mixtures case, it is noticed that there was a one-day cure period before performing the CBR essay. The soil compacting parameters suffered little variation in the optimum humidity and the maximum specific mass in relation to the addition of different dosages of the whitewash mud. The values of CBR, for some whitewash mud texts, had been superior to the ones of soil as is, being the best resulted reached for the Best Gravel sample in the dosages of 20% and 25%, with profits respectively in the order of 14% and 46%.

Table 1 - Results of the grain size essays, Atterberg limits and TRB classification

However, it must be evidenced that the addition of whitewash to a soil is, generally, responsible for action of cationic exchange, flocculation and cementation as pozolanic reactions. The first two, are responsible for small immediate profits of mechanic resistance of the stabilized mixture, and the third for the development of the mechanic resistance as the time goes by. Therefore, it must be considered the gain of resistance of mixtures of soil-whitewash, separating the mechanic resistance of cured mixture and the mechanic resistance of the mixture not cured. In this context, the parameters CBR and Expansion_CBR presented in table 2 could be understood as corresponding to the values of mechanic resistance of the mixture not cured, foreseen that with the elapse of time, it will have a trend of significant increase in CBR and decrease in the Expansion_CBR values.

FIGURE 1 - Particle size distruibution of Sand Subgrade and Best Gravel.

Table 2 - Geotecnical Parameters: Moisture content (Wot), maximum specific dry gravity (Ydmax), CBR and Expansion _CBR (%), for the period of one day cure before the execution of CBR essay.

The table 3 summarizes the technical requirements of the method of dimensioning flexible pavements used by Brazilian National Department of Highway (DNER, 1996), that it is based on the results of the soil characterization and CBR essays. In the case of the region of Alagoinhas - Bahia, Brazil, where there is a deficiency of materials for the construction of roads and the number of solicitation of the standard axle of 8.2 tons can be esteem as equal or inferior 5x10 ⁶ , is distinguished that the DNER recommends the use of base layers with CBR equal or under 60% and Expansion_CBR under 0.5%. Therefore, considering the data presented in table 2, none of the essayed mixtures attended to either requirements, reason for which it is not recommended the use of this material as base layer, even so it was verified significant profits of mechanic resistance for the mixtures Best Gravel plus whitewash mud of 20% and 25%. It is important to mention that the Sand Sub Grade and the Best Gravel, in the natural state, attends the requirements for sub base materials, for presenting index of CBR above of 20% (26,4 and 35,5%, respectively) and lese 1% expansion.

3.3. Results of the permeability of soil and the whitewash mud mixture essays

Table 4 presents the values of the coefficients of hydraulic conductivity of the body-of-test molded of the soil Sand Subgrade, Best Gravel, mixtures of Sand Subgrade + 20% whitewash mud and Best Gravel + 25% whitewash mud, compacted in AASHTO medium energy, humidity texts of 8.1% and 11.0%, respectively. In the case of the Sand Subgrade, it is observed that there is no significant modification in the values of the hydraulic conductivity and the emptiness index of the samples of the soil as it is in comparison with soil stabilized with whitewash mud; other wise, occurred a variation of 10% in the hydraulic conductivity and 63% in emptiness index of the Best Gravel after the stabilization with whitewash mud. It is distinguished, also, that the coefficients of permeability of the studied soil fit in the characteristic band of silt, by PINTO (2000).

Table 3 - Requirements techniques of the DNER set of wheels to be used as layers of reinforcement, sub-base and base of flexible road floors

Table 4 - Values of the hydraulic conductivity coefficient, K₂₀ (cm/s), of the Sand Subgrade, Best Gravel and Sand Subgrade + 20% whitewash mud and Best Gravel + 25% of whitewash mud soil mixtures compacted in the medium energy.

4. CONCLUSIONS

The best effect of the whitewash mud in the mechanical characteristics of soil, had been reached with the Best Gravel in the dosages of 20% and 25% of whitewash mud, where it was achieved values of 40 and 53% of CBR, respectively. It is observed, also the occurrence of small or insignificant variation in the hydraulic conductivity coefficients of the mixtures in comparison with soils as they are. The current study on the whitewash mud added "in natura" in the maximum dosage of 25% demonstrated the potential of the product as chemical soil stabilizer, considering that in this work, it was used a period of cure of one day. Certainly, greater mechanic resistance profits can be waited for larger periods of cure. It is shimmer, therefore, that better resulted can be obtained with a deeper study of the reactivity of soil/whitewash mud, including in the study, the variable, period of cure, in the mixtures for the periods of 7 and 28 days at least, and with the possibility of improvement of the product, by thermal treatments with high temperatures.

5. REFERENCES

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT.1984b. NBR 6459/84 Solo; determinação do Limite de Liquidez. Rio de Janeiro. 6p.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT.1984d. NBR 6508/84 Solo; determinação da massa específica aparente. Rio de Janeiro. 8p.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT. 1984c. NBR 7180/84 Solo; determinação do Limite de Plasticidade. Rio de Janeiro. 3p.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT. 1984a.NBR 7181/84 Solo; análise granulométrica. Rio de Janeiro. 13p.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT. 1986 NBR 7182/86 Solo; ensaio de compactação. Rio de Janeiro. 10p.

DNER. 1986. Manual de Pavimentação. Ministério dos Transportes, Departamento Nacional de Estradas de Rodagem, 2 ^a ed., Rio de Janeiro, 320p.

HEAD, K. H. 1982. Manual of Soil Laboratóry Testing, Volume 2: Permeability, Shear Strength and Compressibility Tests. New York, Halsted Press Book, p. 335-747.

PINTO, C.S. 2000. Curso básico de mecânica dos solos. São Paulo, 347p.

¹ FederalUniversity of Viçosa, Full Professor-Viçosa, MG, Brazil- [email protected]; [email protected]
Federal University of Viçosa, Graduate Student - Viçosa - MG - Brazil - [email protected]
Federal University of Viçosa, Master - Viçosa - MG - Brazil - [email protected]
Federal University of Viçosa, Civil Engineer - Viçosa - MG - Brazil - [email protected]