- Email: [email protected]
Lightweight composite concrete produced with water treatment sludge and sawdust: Thermal properties and potential application
Construction and Building Materials 24 (2010) 2446–2453
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Lightweight composite concrete produced with water treatment sludge and sawdust: Thermal properties and potential application Almir Sales a,*, Francis Rodrigues de Souza b, Wilson Nunes dos Santos c, Alexsandro Mendes Zimer d, Fernando do Couto Rosa Almeida a a
Department of Civil Engineering, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil Department of Materials Science and Engineering, USP – University of São Paulo, Av. Trabalhador São-carlense, 400, São Carlos 13560-970, SP, Brazil Department of Materials Engineering, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil d Department of Chemistry, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil b c
a r t i c l e
i n f o
Article history: Received 9 July 2009 Received in revised form 13 April 2010 Accepted 7 June 2010 Available online 3 July 2010 Keywords: Lightweight concrete Thermal conductivity Water treatment sludge
a b s t r a c t The main objective of this study was to evaluate the potential application of a lightweight concrete produced with lightweight coarse aggregate made of the water treatment sludge and sawdust (lightweight composite), by determining the thermal properties and possible environmental impact of future residue of this concrete. Two types of concrete were prepared: concrete produced with the lightweight composite dosed with cement/sand/composite/water in a mass ratio of 1:2.5:0.67:0.6 and conventional concrete dosed with cement/sand/crushed stone/water in a mass ratio of 1:4.8:5.8:0.8. The thermal properties were determined by the hot wire parallel technique. The possible environmental impact was measured using the procedures and guidelines of the Brazilian Association of Technical Standards – ABNT. The concrete produced with the lightweight composite presented a 23% lower thermal conductivity than the conventional concrete. The concrete produced with the lightweight composite presented a set of thermal properties suitable for the application of this concrete in non-structural sealing elements. The concentration of aluminum in the solubilized extract of the concrete produced with the lightweight composite was much lower than the concentration of aluminum in the water treatment sludge, confirming the possible reduction of environmental impact of this composite for use in concrete. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The use of lightweight aggregates in concrete offers numerous advantages, including (a) foundations with smaller dimensions and lighter structures due to the reduction of the weight of buildings, which may result in a reduction of the amount of cement and steel; (b) lighter and smaller pre-molded elements that require smaller transportation equipment; (c) reduction of the dimensions of columns, beams and slabs, resulting in greater availability of space; (d) improved thermal insulation; and (e) improved fire resistance [1]. However, the most significant potential advantage of using lightweight aggregates in concrete is its environmental value, particularly when the raw material used in the production of lightweight aggregates is derived from wastes [2]. There are several types of lightweight aggregates, which can generally be classified into two groups: (a) natural (pumice stone, diatomite, volcanic slag, etc.) and (b) artificial (perlite, schist, expanded clay, slate, etc.) [3].
* Corresponding author. Tel.: +55 16 3351 9659; fax: +55 16 3351 8262. E-mail address: [email protected] (A. Sales). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.012
The lightweight aggregates used in the production of lightweight concretes are generally porous materials whose water absorption is usually higher than that of normal aggregate, which influences the microstructure of the hardened cement paste and the interfacial zone. The interfacial zone has been considered the weakest zone in composite concrete in terms of mechanical strength and permeability to fluids [4]. Both sewage sludge ash and sewage sludge can be used individually or in combination for the production of synthetic aggregates, provided they exhibit characteristics similar to those of expansive clays [5]. To achieve the properties of expansion, the raw material must meet the following requirements: (a) it must contain sufficient components to produce gas and (b) upon heating, pyroplasticity must occur simultaneously with the formation of gas [6]. These aggregates are produced in the rotary pelletizers at temperatures of 1050–1150 °C. A mixture of 20–30% of sewage sludge ash in sewage sludge is considered ideal for the production of lightweight aggregates of sewage sludge ash [7]. In developing countries such as Brazil, wastes generated in water supply treatment plant decanters and filters is discharged directly into the same rivers and streams from which water is drawn for treatment. These wastes, called water treatment sludge,
2447
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
are usually rich in aluminum, iron and other metals from the chemical products used in the treatment. The unregulated disposal of these wastes creates a major impact on the environment. Another environmental problem is the unregulated disposal of wood wastes. The forest products industry generates large quantities of these wastes, which are still rarely used in developing countries. A composite based on water treatment sludge and sawdust was developed in Brazil and applied as a coarse lightweight aggregate in the production of concrete. The concrete produced with a cement/sand/composite/water mass ratio of 1:2.5:0.67:0.6 attained an axial compression strength of 11.1 MPa, a tensile strength in diametral compression of 1.2 MPa, water absorption of 8.8% and a specific mass of 1847 kg/m3. The values of these mechanical properties are suitable for application in non-structural constructive elements [8]. Currently, greater attention is focusing on the reduction of energy consumed in maintaining or improving the conditions of thermal comfort in buildings. Aggregates with a crystalline structure have a higher thermal conductivity than amorphous or vitreous aggregates. Porosity and the contents of the mixture are also important factors that affect the thermal conductivity of concretes [19].
2. Objectives The objectives of this work are to: (1) determine the thermal properties of a lightweight concrete produced with a composite based on water treatment sludge and sawdust; (2) evaluate the possible environmental impact of the concrete produced with this composite by determining the concentration of metals in the solubilized and leached extracts of residue of this concrete and comparing the values obtained with those found in water treatment sludges.
3. Material and methods To determine the thermal properties and evaluate the possible environmental impact of the concrete produced with the composite, two types of concrete were prepared: (1) concrete produced with the composite containing a mass ratio of 1:2.5:0.67:0.6 of cement/sand/composite/water and (2) conventional reference concrete containing a mass ratio of 1:4.8:5.8:0.8 of cement/sand/ crushed stone/water. The concrete produced with the composite requires less water (water/cement ratio = 0.6) because the particle shape is rounded (Fig. 2), facilitating the workability. The conventional reference concrete requires more water (water/cement ratio = 0.8) because the crushed stone provides workability difficult. The rationale of this choice (water/cement different) was to maintain the same workability. 3.1. Materials employed The following materials were used in the production of the concretes: early high-strength Portland cement (CPV-ARI), quartz sand from the Mogi River, crushed basaltic stone and the lightweight composite produced with sludge from the São Carlos Water Supply Treatment Plant (São Paulo/Brazil), pine sawdust and boiled linseed oil. The early high-strength Portland cement (CPV-ARI) used in this research is the type of cement whose early high strength is due to its high fineness and not to the hydration products of tricalcium aluminate (C3A), whose maximum content is limited to 15%. The specific area of this cement, as determined by Blaine’s permeability meter, is approximately 5000 cm2/g, while the specific areas of
other cements are between 3000 and 4000 cm2/g. Table 1 summarizes the physicochemical properties of this cement. The natural aggregates used in the production of the concretes under study were quartz sand from the Mogi River and basaltic crushed stone. Table 2 shows the granulometric composition of these aggregates. The natural fine aggregate presented the following properties: maximum aggregate size of 2.4 mm; fineness modulus of 2.52; bulk density of the dry aggregate in condition not compacted of 1.53 kg/dm3; specific gravity of 4.82 kg/dm3; swelling coefficient equal 1.41 to water contained of 3.85%. The maximum aggregate size and fineness modulus measured agree with the NBR 7211:1983 [10]; the bulk density in condition not compacted was measured using the procedures and guidelines of the NBR 7251:1982 [11]. The specific gravity measured agrees with the NBR 9776:1987 [12]. The swelling coefficient and the water contained were measured using the procedures and guidelines of the NBR 6467:1987 [13]. The natural coarse aggregate presented the following properties: maximum aggregate size of 19 mm; fineness modulus of 3.89; bulk density of the dry aggregate in condition not compacted of 1.44 kg/dm3; specific gravity of 2.93 kg/dm3; water absorption of 1.12%. The maximum aggregate size and fineness modulus measured agree with the NBR 7211:1983 [10]; the bulk density in con-
Table 1 Physicochemical properties of Portland cement CPV-ARI. Data supplied by the manufacturer Ciminas. Physicochemical properties
Average values
Sieve residue # 400 Specific area (cm2/g) Consistency water (%) Initial setting (min) Final setting (min) Compressive strength at Compressive strength at Compressive strength at Compressive strength at Fire loss at 500 °C (%) Fire loss at 1000 °C (%) Insoluble residue (%) SiO2 (%) Al2O3 (%) Fe2O3 (%) CaO (%) MgO (%) SO3 (%) CO2 (%) K2O (%) C3A in clinker
2.71 4.66 30.00 148 198 30.3 42.0 46.3 54.6 0.80 3.32 0.45 18.9 5.06 2.95 63.9 1.02 2.72 1.80 0.76 7.70
1 day (MPa) 3 days (MPa) 7 days (MPa) 28 days (MPa)
Table 2 Granulometric composition of the natural aggregates used in the production of the concretes under study. Sieve (mm)
25 19 9.5 6.3 4.8 2.4 1.2 0.6 0.3 0.15 0
Percentage of retained and accumulated mass (%) Coarse aggregate
Fine aggregate
0 1.1 84.4 98.8 100 0 0 0 0 0 0
0 0 0 0.5 1.2 4.8 25.5 48.9 77.6 95.2 100
2448
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
dition not compacted was measured using the procedures and guidelines of the NBR 7251:1982 [11]. The specific gravity and water absorption measured agree with the NBR NM53:2003 [14]. The sludge used in the production of the composite was taken from the water supply treatment plant of the municipality of São Carlos, SP, Brazil. The sludge was removed during the cleaning process of one of the decanters of the treatment station. This water treatment station is characterized for treating water in a conventional system using aluminum sulfate as a coagulant. Table 3 lists the physicochemical characteristics of the sludge from this plant. The sawdust used in the development and production of the composite was wood from the genus Pinus. This wood, which is used in both the civil construction and the furniture industries, is highly water absorbent and has a low density, and its anatomical structure gives its fibers a uniform length. The sawdust presented the following properties: water contained factor of 11.6%, porosity of 12.22%, and medium diameter of pores equals 17.82 lm and bulk density of 0.507 g/cm3. Porosity, medium diameter of pores and density were measured by mercury porosimetry technique. Another material used in the development and production of the composite was boiled linseed oil. Linseed is a variety of flax, linum usitatissimum, which can be used for the production of both industrial and food oils. Boiled linseed oil is one of the products derived from the industrialization of flax seed. After the raw oil is extracted, it is boiled and an oil drying agent is added to hasten the drying process in air. Boiled linseed oil has a golden yellow, brown or amber color and is commonly applied on wood to protect, waterproof and enhance its natural colors. The boiled linseed oil used to produce the composite presented the following properties: water contained 60.2%; time to dry on glass surface 618 h; density of 928 kg/m3. The composite grains were submerged in the boiled linseed oil for one minute in temperature of 25 °C. This time was enough to reduce the water absorption of the composite during the concrete production. 3.2. Preparation of the composite The composite was prepared by mixing dried and ground water treatment sludge with water and sawdust and molding it by hand into rounded pellets with a diameter of 14 ± 2 mm (Fig. 1). The mass ratio of sawdust, sludge and water was, respectively, 1:6:4.5. The smallest amount of water necessary for the production of a mixture with good workability was considered the ideal. Table 4 presents the comparative average values of the physical properties of the composite and the crushed stone.
Fig. 1. Composite made of water treatment sludge and sawdust.
Table 4 Comparative average values of the properties of the composite and the crushed stone. Properties
Ratio of sawdust/sludge/water (kg) Geometric shape Specific mass (kg/dm3) Characteristic maximum dimension (mm) Unitary mass in the dry and loose state (kg/m3) Water absorption (%)
Coarse aggregate Composite
Crushed stone
1:6:4.5 Spherical 1.82 14 672 24.0
– Angular 2.93 19 1440 1.12
3.3. Preparation of the concretes under study Two types of concretes were prepared: concrete produced with the composite (Fig. 2) dosed with a mass ratio of 1:2.5:0.67:0.6 of cement/sand/composite/water and conventional concrete dosed with a mass ratio of 1:4.8:5.8:0.8 of cement/sand/crushed stone/ water. The proportion of materials was determined based on the consistency and workability of the concrete. The mechanical properties of the concrete produced with the composite were compared with those of the reference concrete produced with crushed stone (Table 5).
Table 3 Physicochemical characteristics of the sludge from the water supply treatment plant of São Carlos, SP, Brazil [8]. Physicochemical characteristics
Average values
Concentration of solids (%) pH Color (uC) Turbidity (uT) Chemical oxygen demand (mg/L) Total solids (mg/L) Suspended solids (mg/L) Dissolved solids (mg/L) Aluminum (mg/L) Iron (mg/L) Zinc (mg/L) Lead (mg/L) Cadmium (mg/L)
4.68 7.2 – – 4.80 58.63 26.52 32.11 11.10 5.00 4.25 1.6 0.02
Fig. 2. Concrete produced with the composite after testing to rupture under axial compression.
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453 Table 5 Average values of the mechanical properties of 15 concretes samples under study. Properties
Concrete produced with the composite
Conventional concrete of reference
Mass ratio cement/sand/ coarse aggregate/water Slump test (mm) Real specific mass (kg/m3) Apparent specific mass (kg/ m3) Water absorption (%) Air void index (%) Compressive strength (MPa) Modulus of elasticity (GPa) Modulus of drying creep tensile strength (GPa) Tensile strength (MPa)
1:2.5:0.67:0.6
1:4.8:5.8:0.8
70 ± 10 2200 1847
50 ± 10 2699 2373
8.8 16.2 11.1 15.9 9.9
5.1 12.1 20.9 27.9 7.3
1.2
2.2
3.4. Determination of the thermal properties of the concretes under study In this work, the thermal conductivity, specific heat and diffusivity of the concretes under study were determined: concrete produced with the composite (concrete ‘‘4”); conventional reference concrete (concrete ‘‘5”). These resulting values were compared with the density and thermal conductivity of the concretes with expanded clay (concretes ‘‘1”, ‘‘2” and ‘‘3”) presented by NBR 15220-2 [15]. These three properties, which are normally determined separately using individual techniques and equipment, are related to one another by the following equation:
k a¼ qc p
and measuring the temperature variation of the material with the help of the thermocouple [17]. The thermal conductivity is calculated from the angular coefficient of the straight line of temperature over time, according to the following equation:
k¼
While the composite presented water absorption of 24%, the crushed stone used in the production of the conventional concretes presented water absorption of 1.12% (Table 4). The water absorption of the composite required a large amount of water to mix the concrete. However, no cracking by plastic retraction was found in the concrete produced with the composite. The low compressive strength of the concrete produced with the composite compared with that of the conventional concrete (Table 5) was due to the higher water absorption and lower compressive strength of the composite in relation to the same properties of the crushed stone.
ð1Þ
where a = thermal diffusivity (m2/s); k = thermal conductivity (W/ mK); q = density (kg/m3) and cp = constant pressure specific heat (J/kgK). Today, several methods are known for determining the thermal conductivity and thermal diffusivity of a material. Recently, the transient heat exchange methods have been preferred for the determination of the thermal properties of materials [16]. In the present work, we used the hot wire parallel technique, which is applied to homogeneous, porous or dense samples with a density exceeding 500 kg/m3. This technique allows thermal conductivities of up to 25 W/mK to be measured [16]. The hot wire parallel technique consists of calculating the thermal conductivity from the temperature gradient generated by a heat source considered ideal, infinitely long and fine, in a material medium with dimensions that are considered infinite. The device has two wires, a central hot wire (Kanthal DS resistance) and a type K thermocouple wire positioned at a distance of 16 mm from the central hot wire. The thermal conductivity of the material is determined by applying a continuous electric current to the hot wire
2449
q0 4p a
ð2Þ
where q0 = RI2 is the linear power density (W/m), R is the hot wire resistance (X/m), I is the electric current (A), and a is the angular coefficient of the straight line. Prismatic test specimens with a width of 120 mm, length of 230 mm and height of 120 mm were molded for each dosage of the concretes under study. The molds of the prismatic test specimens, which were built especially for this purpose, were of plywood and dismountable on a vibrating table. The wires were positioned as illustrated in the diagram in Fig. 3 [18]. The chromel–alumel thermocouple was mounted using a Metal Inert Gas (MIG) probe, whose welded region is protected by an inert gas, in this case argon gas. The wires were threaded through the holes before molding and attached by connectors until demolding. The concrete dosed and prepared with the desired consistency was poured into the plywood molds and densified on the vibrating table for about 30 s. The test specimens were then covered with a plastic sheet to prevent rapid drying and allowed to rest in air at room temperature for 24 h until demolding. After demolding, the test specimens were placed in a humidity chamber at a temperature of 25 ± 2 °C and relative air humidity of 95% for a period of 7 days. After this period, the test specimens were exposed to the environmental conditions of the laboratory (temperature of 25 ± 4 °C and relative air humidity of 50 ± 10%) to approach the humidity content to the real conditions of application of the concrete. The thermal conductivity test was carried out 90 days after the preparation of the concrete. Based on the experimental results, a comparison was made of the thermal properties of the concretes under study in this research and the thermal properties of concretes produced with expanded clay. 3.5. Determination of the possible environmental impact of the concretes produced with the composite The possible environmental impact of the concretes under study was determined based on a classification of the environmental impact caused by the wastes of these concretes, as well as from a comparison of the metal concentrations of aluminum, iron and lead in the solubilized extract of the concretes and in the water treatment sludge. The wastes were classified based on the procedures and guidelines of the Brazilian Association of Technical Standards – ABNT: NBR 10004 [19], NBR 10005 [20], NBR 10006 [21] and NBR 10007 [22]. The NBR 10004 standard classifies solid wastes as follows: Class I Wastes (Harmful); Class II Wastes (Non-harmful); Class IIA Wastes (Non-harmful and Non-inert) and Class IIB Wastes (Nonharmful and Inert). This classification is done by analyzing the leached extract and the solubilized extract of the waste in order to ascertain the quantity and quality of the raw materials and substances that make up the waste or that participate in the process that cause the material to become a waste. The NBR 10005 standard establishes the requisites for obtaining leached extract from solid wastes. The qualitative and quantitative analysis of this extract and a comparison with the maximum limits established in Attachment F of the NBR 10004 standard serve to classify the wastes as Harmful (Class I) and Non-harmful (Class II).
2450
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
Fig. 3. Diagram of the position of the wires in the test specimens to measure the thermal conductivity by the hot wire parallel technique [18].
The NBR 10006 standard establishes the requisites for obtaining solubilized extract from solid wastes. The qualitative and quantitative analysis of this extract and a comparison of its parameters with the maximum limits established in Attachment G of the NBR 10004 standard serve to classify the wastes as Non-harmful and Non-inert (Class IIA) and Non-harmful and Inert (Class IIB). The NBR 10007 standard establishes the requisites for sampling of solid wastes. 3.5.1. Determination of the leached extract of the concrete produced with the composite A sample of the concrete produced with the composite was first collected and ground until its particles passed through a 9.5-mm mesh sieve, which is the condition in which the sample is ready for the extraction step, according to the NBR 10005 standard. Next, the extraction solution to be used in the leaching process was chosen. To this end, 5.0 g of the ground sample and 96.5 mL of deionized water were put into a beaker. The beaker was covered with a piece of glass and placed in a magnetic shaker, where it was shaken vigorously for 5 min, after which its pH was measured. If the pH of the mixture was 65.0, the number ‘‘1” extraction solution was used, with pH 4.93 ± 0.05, which was composed of 5.7 mL of glacial acetic acid, 64.3 mL + NaOH 1.0 N and distilled, deionized water devoid or organic substances up to a volume of 1 L. When the pH of the mixture was >5.0, 3.5 mL of HCl 1 N was added and the mixture was homogenized, covered with a piece of glass, heated to 50 °C for 10 min, cooled and its pH measured again. If the new solution had a pH of 65.0, the number ‘‘1” extraction solution was used. Otherwise, the number ‘‘2” extraction solution was used. This solution has a pH of 2.88 ± 0.05 and was composed of 5.7 mL of glacial acetic acid, distilled and deionized water devoid of organic substances up to a volume of L. The number ‘‘2” extraction solution was selected. After determining the extraction solution, 100 ± 0.1 g of the sample was transferred to a leaching flask for inert material. A quantity of extraction solution equivalent to 20 times the mass of the sample was added to the flask, which was then closed using PTFE tape to prevent leakage and the flask was shaken in a 30 ± 2 rpm rotary shaker for 18 ± 2 h at a temperature of 25 °C. The resulting solution was filtered through a 0.20-lm pore filtering membrane, its pH was determined, and it was defined as the leached extract of the waste.
The same procedure was carried out to obtain the leached extract of the conventional concrete, with the difference that the extraction solution selected was extraction solution number ‘‘1”. 3.5.2. Determination of the solubilized extract of the concrete produced with the composite Initially, a sample of the concrete produced with the composite was collected and ground until its particles passed through a 9.5mm mesh sieve. The sample that sifted through the sieve was oven-dried at a temperature of 42 °C, after which a representative amount of 250 g was placed in a 1500-mL flask. To this flask containing the 250 g of sample was added 1000 mL of distilled and deionized water devoid of organic substances. The flask was gently shaken by hand for 5 min, covered with a sheet of PVC film, and allowed to rest for 7 days at a temperature of up to 25 °C. After this period at rest, the solution was filtered through a 0.20-lm pore filtering membrane, its pH was measured and it was defined as the solubilized extract of the waste. The same procedure was performed to obtain the solubilized extract of the reference conventional concrete. 3.5.3. Determination of the concentration of metals in the leached and solubilized extracts of the concretes under study Aliquots of the leached and solubilized extracts of the concretes under study were removed, and the concentration of metals (aluminum, iron and lead) was determined using a Varian VISTA induction-coupled plasma optical emission mass spectrometer. The resulting values of the leached extracts were compared with maximum values established in Attachment F of the Brazilian NBR 10004 standard, while the values of the solubilized extracts were compared with maximum values established in Attachment G of the Brazilian NBR 10004 standard. 4. Results and discussion The concrete produced with the composite presented an axial compression strength of 11.1 MPa and an apparent specific mass of 1847 kg/m3 (Table 5) and was classified as a lightweight nonstructural concrete. This classification was based on the ACI 213R-87 guide for structural lightweight aggregate concrete [23], which defines structural lightweight aggregate concrete as concrete having a compressive strength of more than 17 MPa and an
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
apparent specific mass, dried in air, not exceeding 1.850 kg/m3, both at 28 days. Described below are the results obtained for the thermal properties and possible environmental impact of the concretes under study.
Table 6 Thermal properties of the concretes under study. Thermal properties
Concrete produced with the composite q = 1847 kg/m3
Conventional concrete of reference q = 2373 kg/m3
Thermal conductivity (W/m K) Specific heat (J/ kg K) Thermal diffusivity (m2/s)
1.89
2.46
839
851 6
1220 10
1233 106
Table 7 Comparison of the density and thermal conductivity of the concretes under study with the density and thermal conductivity of the concretes produced with expanded clay presented by NBR 15220-2 [15]. Concrete
Density (kg/m3)
Thermal conductivity (W/m K)
Typical production
1 2 3 4 5
1300 1500 1700 1847 2373
0.70 0.85 1.05 1.89 2.47
With expanded clay; dosage of cement >300 kg/m3 and density of the inert materials >350 kg/m3 [15] With the composite Conventional
1, 2 and 3 concretes ? values agree with the Brazilian Standard [15]. 4 ? concrete produced with the composite under study. 5 ? conventional concrete under study.
3
Density (kg/m ) 1, 2 and 3 concretes 4
2451
4.1. Thermal properties of the concretes under study The thermal conductivity, thermal diffusivity and specific heat, known as thermal or thermophysical properties, are the three most important physical properties from the standpoint of thermal calculations. These properties are directly related to the thermal insulation potential of a material. Table 6 lists the values of these three properties obtained for the concretes studied in this research. The concrete produced with the composite presented a thermal conductivity of 1.89 W/m K, which was 23.2% lower than that of the conventional concrete (Table 6). The thermal conductivity of concrete increases as the proportion of cement and the thermal conductivity of the aggregates increase [24]. In this study, the main cause of the lower thermal conductivity of the concrete produced with the composite than that of the conventional concrete was due to the higher water absorption of the composite (Table 3). This higher water absorption of the composite required a larger amount of water in the preparation of this concrete, which in turn increased not only the porosity of the hardened concrete but also its potential for water absorption (Table 4). Table 7 lists the values of density (q) and thermal conductivity (k) of the concretes under study and the corresponding values of the concretes with expanded clay presented by the NBR 15220-2 standard of the Brazilian Association of Technical Standards [15]. The graph in Fig. 4 illustrates the density and thermal conductivity of the concretes presented in Table 7. The thermal conductivity of the concrete produced with the composite (concrete ‘‘4”) was higher than that of the concrete produced with expanded clay (concretes ‘‘1”, ‘‘2” and ‘‘3”), but lower than that of the conventional concrete used as reference in this work (concrete ‘‘5”). The thermal properties obtained suggest the applicability of the concrete produced with the composite in lightweight non-structural elements for sealing and thermal insulation.
Thermal conductivity (W/m.K)
values agree with the Brazilian Standard [15]
concrete produced with the composite under study 5
conventional concrete under study
Fig. 4. Comparison of the density and thermal conductivity of the concretes under study against the same parameters of concretes produced with expanded clay.
2452
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
Table 8 Concentration of metals in the leached and solubilized extracts of the concretes under study. Concrete
Extract
Aluminum (mg/L)
Iron (mg/L)
In the extract
Limit NBR 10004
Limit NBR 10004
In the extract
Limit NBR 10004
Produced with composite
Leached Solubilized
0.14 19.96
– 0.2
0.03 0.004
– 0.3
<0.01 <0.01
1.0 0.01
Conventional
Leached Solubilized
<0.02 1.12
– 0.2
<0.004 0.009
– 0.3
<0.01 <0.01
1.0 0.01
4.2. The possible environmental impact of the concretes under study The sludge from the São Carlos water supply treatment plant showed a high concentration of aluminum due to the fact that the treatment plant uses aluminum sulfate as a coagulant and also because its decanters and filters are cleaned at 3-month intervals. Table 8 lists the concentration of metals (aluminum, iron and lead) in the solubilized and leached extracts of the concretes under study (concrete produced with the composite and conventional concrete). Also listed in this table are the maximum values established by the NBR 10004 standard of the Brazilian Association of Technical Standards – ABNT. The evaluation of leaching was made in 18 samples extracted from concrete composite and 18 samples extracted from reference conventional concrete. The results presented in Table 8 are the highest values obtained in the evaluation of leaching. This laboratory test simulates as from concrete composite would behave in natural environment. All samples were studied during 3 months according to the Brazilian NBR 10004 standard [19]. Based on the concentration of metals (aluminum, iron and lead) in the leached and solubilized extracts of the concretes (Table 8), the solid wastes of the concrete produced with the composite of the conventional concrete were both classified, according to the Brazilian NBR 10004 standard [19], as non-harmful and non-inert solid wastes. The concentration of aluminum (19.96 mg/L) in the solubilized extract of the concrete produced with the composite is higher than the concentration of aluminum (1.12 mg/L) in the solubilized extract of the conventional concrete due the high concentration of aluminum (11.10 mg/L) in the sludge from the water supply treatment plant. The composite was produced with the sludge from the water supply treatment plant of São Carlos which uses aluminum sulfate as a coagulant in the treatment of the water. The comparison of the concentration of aluminum in the sludge (Table 3) and the concentration of aluminum in the solubilized extract of the concrete composite (Table 8) reveals a significant reduction in the concentration of the metal, which confirms the possible reduction environmental impact of this composite for use in concrete.
5. Conclusions The concretes of this study showed similar values for the properties of specific heat and thermal diffusivity. The concrete produced with the composite presented a specific heat of 839 J/kg K, while that of the conventional concrete was 851 J/kg K. In addition, the concrete with composite showed a thermal diffusivity of 1220 106 m2/s, whereas that of the conventional concrete was 1233 106 m2/s. However, the thermal conductivity of the concrete with composite was 1894 W/m K, which was 23% lower than the thermal conductivity of 2465 W/m K presented by the conventional concrete. Among the metals analyzed in this study, aluminum presented the highest concentration in the solubilized extract of the concrete containing the composite, with a value of 19.96 mg/L.
In the extract
Lead (mg/L)
Considering the thermal properties and physics measured, the concrete produced with the composite can be used to produce blocks and to stuff flagstones. These applications can reduce the weight of the buildings and increase the thermal comfort. The high concentration of aluminum in the solubilized extract of the concrete containing the composite was due to the fact that the composite was produced with sludge from the water supply treatment plant of São Carlos, which uses aluminum sulfate as a coagulant in the treatment of the water. The concentration of aluminum in the solubilized extract of the concrete with composite was found to be 19.96 mg/L, while the water treatment sludge has showed an aluminum concentration of 11.10 mg/L. The solid wastes of the concretes under study were classified according to the Brazilian ABNT NBR 10004 Standard [19] and were non-harmful and non-inert solid wastes. The possible reduction environmental impact of the production process of the composite for use as coarse aggregate in concrete was confirmed, based on the lower concentration of aluminum in the solubilized extract of the concrete containing the composite compared to the concentration of aluminum in the water treatment sludge as well as its classification as non-harmful and noninert. Therefore, the concrete produced with the composite of the sludge from water supply treatment plant and sawdust can be used in constructions and buildings and reduce the environmental degradation caused by irregular disposition of these wastes and by the use of the natural aggregate.
Acknowledgements The authors gratefully acknowledge the support of the Brazilian research funding agencies CAPES, USP (University of São Paulo), UFSCar (Federal University of São Carlos) and MCT/CNPq.
References [1] Kayali O. Fly ash lightweight aggregates in high performance concrete. Construct Build Mater 2008:2293–399. [2] Tanyildizi H, Coskun A. The effect of high temperature on compressive strength and splitting tensile strength of structural lightweight concrete containing fly ash. Construct Build Mater 2008;22:2269–75. [3] Dermirdag S, Gunduz L. Strength properties of volcanic slag aggregate lightweight concrete for high performance masonry units. Construct Build Mater 2008;22:135–42. [4] Lo TY, Cui HZ, Tang WC, Leung WM. The effect of aggregate absorption on pore area at the interfacial zone of lightweight concrete. Construct Build Mater 2008;22:623–8. [5] Qiao XC, Ng BR, Tyrer M, Poon CS, Cheeseman CR. Production of lightweight concrete using incinerator bottom ash. Construct Build Mater 2008;22:473–80. [6] Coatanlem P, Jauberthie R, Rendell F. Lightweight wood chipping concrete durability. Construct Build Mater 2006;30:776–81. [7] Chiou IJ, Wang KS, Chen CH, Lin YT. Lightweight aggregate made from sewage sludge and incinerated ash. Waste Manage 2006;26:1453–61. [8] Sales A, De Souza FR. Concretes and mortars recycled with water treatment sludge and construction and demolition rubble. Construct Build Mater 2009;23:2362–70. [10] NBR 7211:1983. Agregados para concreto – Especificação. (Aggregates for concretes – specification). Rio de Janeiro; 1983. 9p [available only in Portuguese].
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453 [11] NBR 7251:1982. Agregado em estado seco e solto – determinação da massa unitária. (Bulk density of the dry aggregate in condition not compacted – method of test). Rio de Janeiro; 1982. 3p. [available only in Portuguese]. [12] NBR 9776:1987. Agregados – Determinação da massa específica de agregados miúdos por meio do Frasco de Chapman. (Aggregates – determination of the specific mass of fine aggregates with the use of the Chapman Flask). Rio de Janeiro; 1987. 3p [available only in Portuguese]. [13] NBR 6467:1987. Agregados – Determinação do inchamento de agregado miúdo. (Swelling of the fine aggregate – method of test). Rio de Janeiro; 1987. 5p [available only in Portuguese]. [14] NBR NM53:2003. Agregado graúdo – Determinação da massa específica, da massa específica aparente e da absorção de água. (Specific gravity, bulk density and water absorption of the coarse aggregate – method of test). Rio de Janeiro; 2003. 8p [available only in Portuguese]. [15] NBR 15220-2:2005. Desempenho térmico de edificações – Métodos de cálculo da transmitância térmica, da capacidade térmica, do atraso térmico e do fator solar de elementos e componentes de edificações. (Thermal performance of buildings – methods for calculating thermal transmittance, thermal capacity, thermal delay and the solar factor of building elements and components). Rio de Janeiro; 2005. 34p [available only in Portuguese]. [16] Santos WN. Advances on the hot wire technique. J Eur Ceram Soc 2007;27: 1–5.
2453
[17] Santos WN, Cintra Filho JS. Application of the hot wire technique in the determination of the thermal properties of polymers. Polym: Sci Technol 2005;15:289–95 [available only in Portuguese]. [18] Sacht HM. Molded insulation panels in: evaluation of the thermal performance and development of concretes. Master’s Dissertation presented to the Department of Architecture and Urbanism, São Carlos School of Engineering, University of São Paulo; 2008. p. 120 [available only in Portuguese]. [19] NBR 10004:2004. Resíduos sólidos – Classificação. (Solid wastes – classification). Rio de Janeiro; 2004. 71p [available only in Portuguese]. [20] NBR 10005:2004. Procedimento para obtenção de extrato lixiviado de resíduos sólidos. (Procedure for obtaining leached extract from solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [21] NBR 10006:2004. Procedimento para obtenção de extrato solubilizado de resíduos sólidos. (Procedure for obtaining solubilized extract from solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [22] NBR 10007:2004. Amostragem de resíduos sólidos. (Sampling of solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [23] American Concrete Institute. Guide for structural lightweight aggregate concrete: reported by ACI Committee 213. ACI Mater J 1987;87(3):638–51. [24] Demirbog˘a R, Gül R. Thermal conductivity and compressive strength of expanded perlite aggregate concrete with mineral admixtures. Energy Build 2003;35:1155–9.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Lightweight composite concrete produced with water treatment sludge and sawdust: Thermal properties and potential application Almir Sales a,*, Francis Rodrigues de Souza b, Wilson Nunes dos Santos c, Alexsandro Mendes Zimer d, Fernando do Couto Rosa Almeida a a
Department of Civil Engineering, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil Department of Materials Science and Engineering, USP – University of São Paulo, Av. Trabalhador São-carlense, 400, São Carlos 13560-970, SP, Brazil Department of Materials Engineering, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil d Department of Chemistry, UFSCar – Federal University of São Carlos, Rod. Washington Luiz, km 235, São Carlos 13565-905, SP, Brazil b c
a r t i c l e
i n f o
Article history: Received 9 July 2009 Received in revised form 13 April 2010 Accepted 7 June 2010 Available online 3 July 2010 Keywords: Lightweight concrete Thermal conductivity Water treatment sludge
a b s t r a c t The main objective of this study was to evaluate the potential application of a lightweight concrete produced with lightweight coarse aggregate made of the water treatment sludge and sawdust (lightweight composite), by determining the thermal properties and possible environmental impact of future residue of this concrete. Two types of concrete were prepared: concrete produced with the lightweight composite dosed with cement/sand/composite/water in a mass ratio of 1:2.5:0.67:0.6 and conventional concrete dosed with cement/sand/crushed stone/water in a mass ratio of 1:4.8:5.8:0.8. The thermal properties were determined by the hot wire parallel technique. The possible environmental impact was measured using the procedures and guidelines of the Brazilian Association of Technical Standards – ABNT. The concrete produced with the lightweight composite presented a 23% lower thermal conductivity than the conventional concrete. The concrete produced with the lightweight composite presented a set of thermal properties suitable for the application of this concrete in non-structural sealing elements. The concentration of aluminum in the solubilized extract of the concrete produced with the lightweight composite was much lower than the concentration of aluminum in the water treatment sludge, confirming the possible reduction of environmental impact of this composite for use in concrete. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The use of lightweight aggregates in concrete offers numerous advantages, including (a) foundations with smaller dimensions and lighter structures due to the reduction of the weight of buildings, which may result in a reduction of the amount of cement and steel; (b) lighter and smaller pre-molded elements that require smaller transportation equipment; (c) reduction of the dimensions of columns, beams and slabs, resulting in greater availability of space; (d) improved thermal insulation; and (e) improved fire resistance [1]. However, the most significant potential advantage of using lightweight aggregates in concrete is its environmental value, particularly when the raw material used in the production of lightweight aggregates is derived from wastes [2]. There are several types of lightweight aggregates, which can generally be classified into two groups: (a) natural (pumice stone, diatomite, volcanic slag, etc.) and (b) artificial (perlite, schist, expanded clay, slate, etc.) [3].
* Corresponding author. Tel.: +55 16 3351 9659; fax: +55 16 3351 8262. E-mail address: [email protected] (A. Sales). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.012
The lightweight aggregates used in the production of lightweight concretes are generally porous materials whose water absorption is usually higher than that of normal aggregate, which influences the microstructure of the hardened cement paste and the interfacial zone. The interfacial zone has been considered the weakest zone in composite concrete in terms of mechanical strength and permeability to fluids [4]. Both sewage sludge ash and sewage sludge can be used individually or in combination for the production of synthetic aggregates, provided they exhibit characteristics similar to those of expansive clays [5]. To achieve the properties of expansion, the raw material must meet the following requirements: (a) it must contain sufficient components to produce gas and (b) upon heating, pyroplasticity must occur simultaneously with the formation of gas [6]. These aggregates are produced in the rotary pelletizers at temperatures of 1050–1150 °C. A mixture of 20–30% of sewage sludge ash in sewage sludge is considered ideal for the production of lightweight aggregates of sewage sludge ash [7]. In developing countries such as Brazil, wastes generated in water supply treatment plant decanters and filters is discharged directly into the same rivers and streams from which water is drawn for treatment. These wastes, called water treatment sludge,
2447
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
are usually rich in aluminum, iron and other metals from the chemical products used in the treatment. The unregulated disposal of these wastes creates a major impact on the environment. Another environmental problem is the unregulated disposal of wood wastes. The forest products industry generates large quantities of these wastes, which are still rarely used in developing countries. A composite based on water treatment sludge and sawdust was developed in Brazil and applied as a coarse lightweight aggregate in the production of concrete. The concrete produced with a cement/sand/composite/water mass ratio of 1:2.5:0.67:0.6 attained an axial compression strength of 11.1 MPa, a tensile strength in diametral compression of 1.2 MPa, water absorption of 8.8% and a specific mass of 1847 kg/m3. The values of these mechanical properties are suitable for application in non-structural constructive elements [8]. Currently, greater attention is focusing on the reduction of energy consumed in maintaining or improving the conditions of thermal comfort in buildings. Aggregates with a crystalline structure have a higher thermal conductivity than amorphous or vitreous aggregates. Porosity and the contents of the mixture are also important factors that affect the thermal conductivity of concretes [19].
2. Objectives The objectives of this work are to: (1) determine the thermal properties of a lightweight concrete produced with a composite based on water treatment sludge and sawdust; (2) evaluate the possible environmental impact of the concrete produced with this composite by determining the concentration of metals in the solubilized and leached extracts of residue of this concrete and comparing the values obtained with those found in water treatment sludges.
3. Material and methods To determine the thermal properties and evaluate the possible environmental impact of the concrete produced with the composite, two types of concrete were prepared: (1) concrete produced with the composite containing a mass ratio of 1:2.5:0.67:0.6 of cement/sand/composite/water and (2) conventional reference concrete containing a mass ratio of 1:4.8:5.8:0.8 of cement/sand/ crushed stone/water. The concrete produced with the composite requires less water (water/cement ratio = 0.6) because the particle shape is rounded (Fig. 2), facilitating the workability. The conventional reference concrete requires more water (water/cement ratio = 0.8) because the crushed stone provides workability difficult. The rationale of this choice (water/cement different) was to maintain the same workability. 3.1. Materials employed The following materials were used in the production of the concretes: early high-strength Portland cement (CPV-ARI), quartz sand from the Mogi River, crushed basaltic stone and the lightweight composite produced with sludge from the São Carlos Water Supply Treatment Plant (São Paulo/Brazil), pine sawdust and boiled linseed oil. The early high-strength Portland cement (CPV-ARI) used in this research is the type of cement whose early high strength is due to its high fineness and not to the hydration products of tricalcium aluminate (C3A), whose maximum content is limited to 15%. The specific area of this cement, as determined by Blaine’s permeability meter, is approximately 5000 cm2/g, while the specific areas of
other cements are between 3000 and 4000 cm2/g. Table 1 summarizes the physicochemical properties of this cement. The natural aggregates used in the production of the concretes under study were quartz sand from the Mogi River and basaltic crushed stone. Table 2 shows the granulometric composition of these aggregates. The natural fine aggregate presented the following properties: maximum aggregate size of 2.4 mm; fineness modulus of 2.52; bulk density of the dry aggregate in condition not compacted of 1.53 kg/dm3; specific gravity of 4.82 kg/dm3; swelling coefficient equal 1.41 to water contained of 3.85%. The maximum aggregate size and fineness modulus measured agree with the NBR 7211:1983 [10]; the bulk density in condition not compacted was measured using the procedures and guidelines of the NBR 7251:1982 [11]. The specific gravity measured agrees with the NBR 9776:1987 [12]. The swelling coefficient and the water contained were measured using the procedures and guidelines of the NBR 6467:1987 [13]. The natural coarse aggregate presented the following properties: maximum aggregate size of 19 mm; fineness modulus of 3.89; bulk density of the dry aggregate in condition not compacted of 1.44 kg/dm3; specific gravity of 2.93 kg/dm3; water absorption of 1.12%. The maximum aggregate size and fineness modulus measured agree with the NBR 7211:1983 [10]; the bulk density in con-
Table 1 Physicochemical properties of Portland cement CPV-ARI. Data supplied by the manufacturer Ciminas. Physicochemical properties
Average values
Sieve residue # 400 Specific area (cm2/g) Consistency water (%) Initial setting (min) Final setting (min) Compressive strength at Compressive strength at Compressive strength at Compressive strength at Fire loss at 500 °C (%) Fire loss at 1000 °C (%) Insoluble residue (%) SiO2 (%) Al2O3 (%) Fe2O3 (%) CaO (%) MgO (%) SO3 (%) CO2 (%) K2O (%) C3A in clinker
2.71 4.66 30.00 148 198 30.3 42.0 46.3 54.6 0.80 3.32 0.45 18.9 5.06 2.95 63.9 1.02 2.72 1.80 0.76 7.70
1 day (MPa) 3 days (MPa) 7 days (MPa) 28 days (MPa)
Table 2 Granulometric composition of the natural aggregates used in the production of the concretes under study. Sieve (mm)
25 19 9.5 6.3 4.8 2.4 1.2 0.6 0.3 0.15 0
Percentage of retained and accumulated mass (%) Coarse aggregate
Fine aggregate
0 1.1 84.4 98.8 100 0 0 0 0 0 0
0 0 0 0.5 1.2 4.8 25.5 48.9 77.6 95.2 100
2448
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
dition not compacted was measured using the procedures and guidelines of the NBR 7251:1982 [11]. The specific gravity and water absorption measured agree with the NBR NM53:2003 [14]. The sludge used in the production of the composite was taken from the water supply treatment plant of the municipality of São Carlos, SP, Brazil. The sludge was removed during the cleaning process of one of the decanters of the treatment station. This water treatment station is characterized for treating water in a conventional system using aluminum sulfate as a coagulant. Table 3 lists the physicochemical characteristics of the sludge from this plant. The sawdust used in the development and production of the composite was wood from the genus Pinus. This wood, which is used in both the civil construction and the furniture industries, is highly water absorbent and has a low density, and its anatomical structure gives its fibers a uniform length. The sawdust presented the following properties: water contained factor of 11.6%, porosity of 12.22%, and medium diameter of pores equals 17.82 lm and bulk density of 0.507 g/cm3. Porosity, medium diameter of pores and density were measured by mercury porosimetry technique. Another material used in the development and production of the composite was boiled linseed oil. Linseed is a variety of flax, linum usitatissimum, which can be used for the production of both industrial and food oils. Boiled linseed oil is one of the products derived from the industrialization of flax seed. After the raw oil is extracted, it is boiled and an oil drying agent is added to hasten the drying process in air. Boiled linseed oil has a golden yellow, brown or amber color and is commonly applied on wood to protect, waterproof and enhance its natural colors. The boiled linseed oil used to produce the composite presented the following properties: water contained 60.2%; time to dry on glass surface 618 h; density of 928 kg/m3. The composite grains were submerged in the boiled linseed oil for one minute in temperature of 25 °C. This time was enough to reduce the water absorption of the composite during the concrete production. 3.2. Preparation of the composite The composite was prepared by mixing dried and ground water treatment sludge with water and sawdust and molding it by hand into rounded pellets with a diameter of 14 ± 2 mm (Fig. 1). The mass ratio of sawdust, sludge and water was, respectively, 1:6:4.5. The smallest amount of water necessary for the production of a mixture with good workability was considered the ideal. Table 4 presents the comparative average values of the physical properties of the composite and the crushed stone.
Fig. 1. Composite made of water treatment sludge and sawdust.
Table 4 Comparative average values of the properties of the composite and the crushed stone. Properties
Ratio of sawdust/sludge/water (kg) Geometric shape Specific mass (kg/dm3) Characteristic maximum dimension (mm) Unitary mass in the dry and loose state (kg/m3) Water absorption (%)
Coarse aggregate Composite
Crushed stone
1:6:4.5 Spherical 1.82 14 672 24.0
– Angular 2.93 19 1440 1.12
3.3. Preparation of the concretes under study Two types of concretes were prepared: concrete produced with the composite (Fig. 2) dosed with a mass ratio of 1:2.5:0.67:0.6 of cement/sand/composite/water and conventional concrete dosed with a mass ratio of 1:4.8:5.8:0.8 of cement/sand/crushed stone/ water. The proportion of materials was determined based on the consistency and workability of the concrete. The mechanical properties of the concrete produced with the composite were compared with those of the reference concrete produced with crushed stone (Table 5).
Table 3 Physicochemical characteristics of the sludge from the water supply treatment plant of São Carlos, SP, Brazil [8]. Physicochemical characteristics
Average values
Concentration of solids (%) pH Color (uC) Turbidity (uT) Chemical oxygen demand (mg/L) Total solids (mg/L) Suspended solids (mg/L) Dissolved solids (mg/L) Aluminum (mg/L) Iron (mg/L) Zinc (mg/L) Lead (mg/L) Cadmium (mg/L)
4.68 7.2 – – 4.80 58.63 26.52 32.11 11.10 5.00 4.25 1.6 0.02
Fig. 2. Concrete produced with the composite after testing to rupture under axial compression.
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453 Table 5 Average values of the mechanical properties of 15 concretes samples under study. Properties
Concrete produced with the composite
Conventional concrete of reference
Mass ratio cement/sand/ coarse aggregate/water Slump test (mm) Real specific mass (kg/m3) Apparent specific mass (kg/ m3) Water absorption (%) Air void index (%) Compressive strength (MPa) Modulus of elasticity (GPa) Modulus of drying creep tensile strength (GPa) Tensile strength (MPa)
1:2.5:0.67:0.6
1:4.8:5.8:0.8
70 ± 10 2200 1847
50 ± 10 2699 2373
8.8 16.2 11.1 15.9 9.9
5.1 12.1 20.9 27.9 7.3
1.2
2.2
3.4. Determination of the thermal properties of the concretes under study In this work, the thermal conductivity, specific heat and diffusivity of the concretes under study were determined: concrete produced with the composite (concrete ‘‘4”); conventional reference concrete (concrete ‘‘5”). These resulting values were compared with the density and thermal conductivity of the concretes with expanded clay (concretes ‘‘1”, ‘‘2” and ‘‘3”) presented by NBR 15220-2 [15]. These three properties, which are normally determined separately using individual techniques and equipment, are related to one another by the following equation:
k a¼ qc p
and measuring the temperature variation of the material with the help of the thermocouple [17]. The thermal conductivity is calculated from the angular coefficient of the straight line of temperature over time, according to the following equation:
k¼
While the composite presented water absorption of 24%, the crushed stone used in the production of the conventional concretes presented water absorption of 1.12% (Table 4). The water absorption of the composite required a large amount of water to mix the concrete. However, no cracking by plastic retraction was found in the concrete produced with the composite. The low compressive strength of the concrete produced with the composite compared with that of the conventional concrete (Table 5) was due to the higher water absorption and lower compressive strength of the composite in relation to the same properties of the crushed stone.
ð1Þ
where a = thermal diffusivity (m2/s); k = thermal conductivity (W/ mK); q = density (kg/m3) and cp = constant pressure specific heat (J/kgK). Today, several methods are known for determining the thermal conductivity and thermal diffusivity of a material. Recently, the transient heat exchange methods have been preferred for the determination of the thermal properties of materials [16]. In the present work, we used the hot wire parallel technique, which is applied to homogeneous, porous or dense samples with a density exceeding 500 kg/m3. This technique allows thermal conductivities of up to 25 W/mK to be measured [16]. The hot wire parallel technique consists of calculating the thermal conductivity from the temperature gradient generated by a heat source considered ideal, infinitely long and fine, in a material medium with dimensions that are considered infinite. The device has two wires, a central hot wire (Kanthal DS resistance) and a type K thermocouple wire positioned at a distance of 16 mm from the central hot wire. The thermal conductivity of the material is determined by applying a continuous electric current to the hot wire
2449
q0 4p a
ð2Þ
where q0 = RI2 is the linear power density (W/m), R is the hot wire resistance (X/m), I is the electric current (A), and a is the angular coefficient of the straight line. Prismatic test specimens with a width of 120 mm, length of 230 mm and height of 120 mm were molded for each dosage of the concretes under study. The molds of the prismatic test specimens, which were built especially for this purpose, were of plywood and dismountable on a vibrating table. The wires were positioned as illustrated in the diagram in Fig. 3 [18]. The chromel–alumel thermocouple was mounted using a Metal Inert Gas (MIG) probe, whose welded region is protected by an inert gas, in this case argon gas. The wires were threaded through the holes before molding and attached by connectors until demolding. The concrete dosed and prepared with the desired consistency was poured into the plywood molds and densified on the vibrating table for about 30 s. The test specimens were then covered with a plastic sheet to prevent rapid drying and allowed to rest in air at room temperature for 24 h until demolding. After demolding, the test specimens were placed in a humidity chamber at a temperature of 25 ± 2 °C and relative air humidity of 95% for a period of 7 days. After this period, the test specimens were exposed to the environmental conditions of the laboratory (temperature of 25 ± 4 °C and relative air humidity of 50 ± 10%) to approach the humidity content to the real conditions of application of the concrete. The thermal conductivity test was carried out 90 days after the preparation of the concrete. Based on the experimental results, a comparison was made of the thermal properties of the concretes under study in this research and the thermal properties of concretes produced with expanded clay. 3.5. Determination of the possible environmental impact of the concretes produced with the composite The possible environmental impact of the concretes under study was determined based on a classification of the environmental impact caused by the wastes of these concretes, as well as from a comparison of the metal concentrations of aluminum, iron and lead in the solubilized extract of the concretes and in the water treatment sludge. The wastes were classified based on the procedures and guidelines of the Brazilian Association of Technical Standards – ABNT: NBR 10004 [19], NBR 10005 [20], NBR 10006 [21] and NBR 10007 [22]. The NBR 10004 standard classifies solid wastes as follows: Class I Wastes (Harmful); Class II Wastes (Non-harmful); Class IIA Wastes (Non-harmful and Non-inert) and Class IIB Wastes (Nonharmful and Inert). This classification is done by analyzing the leached extract and the solubilized extract of the waste in order to ascertain the quantity and quality of the raw materials and substances that make up the waste or that participate in the process that cause the material to become a waste. The NBR 10005 standard establishes the requisites for obtaining leached extract from solid wastes. The qualitative and quantitative analysis of this extract and a comparison with the maximum limits established in Attachment F of the NBR 10004 standard serve to classify the wastes as Harmful (Class I) and Non-harmful (Class II).
2450
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
Fig. 3. Diagram of the position of the wires in the test specimens to measure the thermal conductivity by the hot wire parallel technique [18].
The NBR 10006 standard establishes the requisites for obtaining solubilized extract from solid wastes. The qualitative and quantitative analysis of this extract and a comparison of its parameters with the maximum limits established in Attachment G of the NBR 10004 standard serve to classify the wastes as Non-harmful and Non-inert (Class IIA) and Non-harmful and Inert (Class IIB). The NBR 10007 standard establishes the requisites for sampling of solid wastes. 3.5.1. Determination of the leached extract of the concrete produced with the composite A sample of the concrete produced with the composite was first collected and ground until its particles passed through a 9.5-mm mesh sieve, which is the condition in which the sample is ready for the extraction step, according to the NBR 10005 standard. Next, the extraction solution to be used in the leaching process was chosen. To this end, 5.0 g of the ground sample and 96.5 mL of deionized water were put into a beaker. The beaker was covered with a piece of glass and placed in a magnetic shaker, where it was shaken vigorously for 5 min, after which its pH was measured. If the pH of the mixture was 65.0, the number ‘‘1” extraction solution was used, with pH 4.93 ± 0.05, which was composed of 5.7 mL of glacial acetic acid, 64.3 mL + NaOH 1.0 N and distilled, deionized water devoid or organic substances up to a volume of 1 L. When the pH of the mixture was >5.0, 3.5 mL of HCl 1 N was added and the mixture was homogenized, covered with a piece of glass, heated to 50 °C for 10 min, cooled and its pH measured again. If the new solution had a pH of 65.0, the number ‘‘1” extraction solution was used. Otherwise, the number ‘‘2” extraction solution was used. This solution has a pH of 2.88 ± 0.05 and was composed of 5.7 mL of glacial acetic acid, distilled and deionized water devoid of organic substances up to a volume of L. The number ‘‘2” extraction solution was selected. After determining the extraction solution, 100 ± 0.1 g of the sample was transferred to a leaching flask for inert material. A quantity of extraction solution equivalent to 20 times the mass of the sample was added to the flask, which was then closed using PTFE tape to prevent leakage and the flask was shaken in a 30 ± 2 rpm rotary shaker for 18 ± 2 h at a temperature of 25 °C. The resulting solution was filtered through a 0.20-lm pore filtering membrane, its pH was determined, and it was defined as the leached extract of the waste.
The same procedure was carried out to obtain the leached extract of the conventional concrete, with the difference that the extraction solution selected was extraction solution number ‘‘1”. 3.5.2. Determination of the solubilized extract of the concrete produced with the composite Initially, a sample of the concrete produced with the composite was collected and ground until its particles passed through a 9.5mm mesh sieve. The sample that sifted through the sieve was oven-dried at a temperature of 42 °C, after which a representative amount of 250 g was placed in a 1500-mL flask. To this flask containing the 250 g of sample was added 1000 mL of distilled and deionized water devoid of organic substances. The flask was gently shaken by hand for 5 min, covered with a sheet of PVC film, and allowed to rest for 7 days at a temperature of up to 25 °C. After this period at rest, the solution was filtered through a 0.20-lm pore filtering membrane, its pH was measured and it was defined as the solubilized extract of the waste. The same procedure was performed to obtain the solubilized extract of the reference conventional concrete. 3.5.3. Determination of the concentration of metals in the leached and solubilized extracts of the concretes under study Aliquots of the leached and solubilized extracts of the concretes under study were removed, and the concentration of metals (aluminum, iron and lead) was determined using a Varian VISTA induction-coupled plasma optical emission mass spectrometer. The resulting values of the leached extracts were compared with maximum values established in Attachment F of the Brazilian NBR 10004 standard, while the values of the solubilized extracts were compared with maximum values established in Attachment G of the Brazilian NBR 10004 standard. 4. Results and discussion The concrete produced with the composite presented an axial compression strength of 11.1 MPa and an apparent specific mass of 1847 kg/m3 (Table 5) and was classified as a lightweight nonstructural concrete. This classification was based on the ACI 213R-87 guide for structural lightweight aggregate concrete [23], which defines structural lightweight aggregate concrete as concrete having a compressive strength of more than 17 MPa and an
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
apparent specific mass, dried in air, not exceeding 1.850 kg/m3, both at 28 days. Described below are the results obtained for the thermal properties and possible environmental impact of the concretes under study.
Table 6 Thermal properties of the concretes under study. Thermal properties
Concrete produced with the composite q = 1847 kg/m3
Conventional concrete of reference q = 2373 kg/m3
Thermal conductivity (W/m K) Specific heat (J/ kg K) Thermal diffusivity (m2/s)
1.89
2.46
839
851 6
1220 10
1233 106
Table 7 Comparison of the density and thermal conductivity of the concretes under study with the density and thermal conductivity of the concretes produced with expanded clay presented by NBR 15220-2 [15]. Concrete
Density (kg/m3)
Thermal conductivity (W/m K)
Typical production
1 2 3 4 5
1300 1500 1700 1847 2373
0.70 0.85 1.05 1.89 2.47
With expanded clay; dosage of cement >300 kg/m3 and density of the inert materials >350 kg/m3 [15] With the composite Conventional
1, 2 and 3 concretes ? values agree with the Brazilian Standard [15]. 4 ? concrete produced with the composite under study. 5 ? conventional concrete under study.
3
Density (kg/m ) 1, 2 and 3 concretes 4
2451
4.1. Thermal properties of the concretes under study The thermal conductivity, thermal diffusivity and specific heat, known as thermal or thermophysical properties, are the three most important physical properties from the standpoint of thermal calculations. These properties are directly related to the thermal insulation potential of a material. Table 6 lists the values of these three properties obtained for the concretes studied in this research. The concrete produced with the composite presented a thermal conductivity of 1.89 W/m K, which was 23.2% lower than that of the conventional concrete (Table 6). The thermal conductivity of concrete increases as the proportion of cement and the thermal conductivity of the aggregates increase [24]. In this study, the main cause of the lower thermal conductivity of the concrete produced with the composite than that of the conventional concrete was due to the higher water absorption of the composite (Table 3). This higher water absorption of the composite required a larger amount of water in the preparation of this concrete, which in turn increased not only the porosity of the hardened concrete but also its potential for water absorption (Table 4). Table 7 lists the values of density (q) and thermal conductivity (k) of the concretes under study and the corresponding values of the concretes with expanded clay presented by the NBR 15220-2 standard of the Brazilian Association of Technical Standards [15]. The graph in Fig. 4 illustrates the density and thermal conductivity of the concretes presented in Table 7. The thermal conductivity of the concrete produced with the composite (concrete ‘‘4”) was higher than that of the concrete produced with expanded clay (concretes ‘‘1”, ‘‘2” and ‘‘3”), but lower than that of the conventional concrete used as reference in this work (concrete ‘‘5”). The thermal properties obtained suggest the applicability of the concrete produced with the composite in lightweight non-structural elements for sealing and thermal insulation.
Thermal conductivity (W/m.K)
values agree with the Brazilian Standard [15]
concrete produced with the composite under study 5
conventional concrete under study
Fig. 4. Comparison of the density and thermal conductivity of the concretes under study against the same parameters of concretes produced with expanded clay.
2452
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453
Table 8 Concentration of metals in the leached and solubilized extracts of the concretes under study. Concrete
Extract
Aluminum (mg/L)
Iron (mg/L)
In the extract
Limit NBR 10004
Limit NBR 10004
In the extract
Limit NBR 10004
Produced with composite
Leached Solubilized
0.14 19.96
– 0.2
0.03 0.004
– 0.3
<0.01 <0.01
1.0 0.01
Conventional
Leached Solubilized
<0.02 1.12
– 0.2
<0.004 0.009
– 0.3
<0.01 <0.01
1.0 0.01
4.2. The possible environmental impact of the concretes under study The sludge from the São Carlos water supply treatment plant showed a high concentration of aluminum due to the fact that the treatment plant uses aluminum sulfate as a coagulant and also because its decanters and filters are cleaned at 3-month intervals. Table 8 lists the concentration of metals (aluminum, iron and lead) in the solubilized and leached extracts of the concretes under study (concrete produced with the composite and conventional concrete). Also listed in this table are the maximum values established by the NBR 10004 standard of the Brazilian Association of Technical Standards – ABNT. The evaluation of leaching was made in 18 samples extracted from concrete composite and 18 samples extracted from reference conventional concrete. The results presented in Table 8 are the highest values obtained in the evaluation of leaching. This laboratory test simulates as from concrete composite would behave in natural environment. All samples were studied during 3 months according to the Brazilian NBR 10004 standard [19]. Based on the concentration of metals (aluminum, iron and lead) in the leached and solubilized extracts of the concretes (Table 8), the solid wastes of the concrete produced with the composite of the conventional concrete were both classified, according to the Brazilian NBR 10004 standard [19], as non-harmful and non-inert solid wastes. The concentration of aluminum (19.96 mg/L) in the solubilized extract of the concrete produced with the composite is higher than the concentration of aluminum (1.12 mg/L) in the solubilized extract of the conventional concrete due the high concentration of aluminum (11.10 mg/L) in the sludge from the water supply treatment plant. The composite was produced with the sludge from the water supply treatment plant of São Carlos which uses aluminum sulfate as a coagulant in the treatment of the water. The comparison of the concentration of aluminum in the sludge (Table 3) and the concentration of aluminum in the solubilized extract of the concrete composite (Table 8) reveals a significant reduction in the concentration of the metal, which confirms the possible reduction environmental impact of this composite for use in concrete.
5. Conclusions The concretes of this study showed similar values for the properties of specific heat and thermal diffusivity. The concrete produced with the composite presented a specific heat of 839 J/kg K, while that of the conventional concrete was 851 J/kg K. In addition, the concrete with composite showed a thermal diffusivity of 1220 106 m2/s, whereas that of the conventional concrete was 1233 106 m2/s. However, the thermal conductivity of the concrete with composite was 1894 W/m K, which was 23% lower than the thermal conductivity of 2465 W/m K presented by the conventional concrete. Among the metals analyzed in this study, aluminum presented the highest concentration in the solubilized extract of the concrete containing the composite, with a value of 19.96 mg/L.
In the extract
Lead (mg/L)
Considering the thermal properties and physics measured, the concrete produced with the composite can be used to produce blocks and to stuff flagstones. These applications can reduce the weight of the buildings and increase the thermal comfort. The high concentration of aluminum in the solubilized extract of the concrete containing the composite was due to the fact that the composite was produced with sludge from the water supply treatment plant of São Carlos, which uses aluminum sulfate as a coagulant in the treatment of the water. The concentration of aluminum in the solubilized extract of the concrete with composite was found to be 19.96 mg/L, while the water treatment sludge has showed an aluminum concentration of 11.10 mg/L. The solid wastes of the concretes under study were classified according to the Brazilian ABNT NBR 10004 Standard [19] and were non-harmful and non-inert solid wastes. The possible reduction environmental impact of the production process of the composite for use as coarse aggregate in concrete was confirmed, based on the lower concentration of aluminum in the solubilized extract of the concrete containing the composite compared to the concentration of aluminum in the water treatment sludge as well as its classification as non-harmful and noninert. Therefore, the concrete produced with the composite of the sludge from water supply treatment plant and sawdust can be used in constructions and buildings and reduce the environmental degradation caused by irregular disposition of these wastes and by the use of the natural aggregate.
Acknowledgements The authors gratefully acknowledge the support of the Brazilian research funding agencies CAPES, USP (University of São Paulo), UFSCar (Federal University of São Carlos) and MCT/CNPq.
References [1] Kayali O. Fly ash lightweight aggregates in high performance concrete. Construct Build Mater 2008:2293–399. [2] Tanyildizi H, Coskun A. The effect of high temperature on compressive strength and splitting tensile strength of structural lightweight concrete containing fly ash. Construct Build Mater 2008;22:2269–75. [3] Dermirdag S, Gunduz L. Strength properties of volcanic slag aggregate lightweight concrete for high performance masonry units. Construct Build Mater 2008;22:135–42. [4] Lo TY, Cui HZ, Tang WC, Leung WM. The effect of aggregate absorption on pore area at the interfacial zone of lightweight concrete. Construct Build Mater 2008;22:623–8. [5] Qiao XC, Ng BR, Tyrer M, Poon CS, Cheeseman CR. Production of lightweight concrete using incinerator bottom ash. Construct Build Mater 2008;22:473–80. [6] Coatanlem P, Jauberthie R, Rendell F. Lightweight wood chipping concrete durability. Construct Build Mater 2006;30:776–81. [7] Chiou IJ, Wang KS, Chen CH, Lin YT. Lightweight aggregate made from sewage sludge and incinerated ash. Waste Manage 2006;26:1453–61. [8] Sales A, De Souza FR. Concretes and mortars recycled with water treatment sludge and construction and demolition rubble. Construct Build Mater 2009;23:2362–70. [10] NBR 7211:1983. Agregados para concreto – Especificação. (Aggregates for concretes – specification). Rio de Janeiro; 1983. 9p [available only in Portuguese].
A. Sales et al. / Construction and Building Materials 24 (2010) 2446–2453 [11] NBR 7251:1982. Agregado em estado seco e solto – determinação da massa unitária. (Bulk density of the dry aggregate in condition not compacted – method of test). Rio de Janeiro; 1982. 3p. [available only in Portuguese]. [12] NBR 9776:1987. Agregados – Determinação da massa específica de agregados miúdos por meio do Frasco de Chapman. (Aggregates – determination of the specific mass of fine aggregates with the use of the Chapman Flask). Rio de Janeiro; 1987. 3p [available only in Portuguese]. [13] NBR 6467:1987. Agregados – Determinação do inchamento de agregado miúdo. (Swelling of the fine aggregate – method of test). Rio de Janeiro; 1987. 5p [available only in Portuguese]. [14] NBR NM53:2003. Agregado graúdo – Determinação da massa específica, da massa específica aparente e da absorção de água. (Specific gravity, bulk density and water absorption of the coarse aggregate – method of test). Rio de Janeiro; 2003. 8p [available only in Portuguese]. [15] NBR 15220-2:2005. Desempenho térmico de edificações – Métodos de cálculo da transmitância térmica, da capacidade térmica, do atraso térmico e do fator solar de elementos e componentes de edificações. (Thermal performance of buildings – methods for calculating thermal transmittance, thermal capacity, thermal delay and the solar factor of building elements and components). Rio de Janeiro; 2005. 34p [available only in Portuguese]. [16] Santos WN. Advances on the hot wire technique. J Eur Ceram Soc 2007;27: 1–5.
2453
[17] Santos WN, Cintra Filho JS. Application of the hot wire technique in the determination of the thermal properties of polymers. Polym: Sci Technol 2005;15:289–95 [available only in Portuguese]. [18] Sacht HM. Molded insulation panels in: evaluation of the thermal performance and development of concretes. Master’s Dissertation presented to the Department of Architecture and Urbanism, São Carlos School of Engineering, University of São Paulo; 2008. p. 120 [available only in Portuguese]. [19] NBR 10004:2004. Resíduos sólidos – Classificação. (Solid wastes – classification). Rio de Janeiro; 2004. 71p [available only in Portuguese]. [20] NBR 10005:2004. Procedimento para obtenção de extrato lixiviado de resíduos sólidos. (Procedure for obtaining leached extract from solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [21] NBR 10006:2004. Procedimento para obtenção de extrato solubilizado de resíduos sólidos. (Procedure for obtaining solubilized extract from solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [22] NBR 10007:2004. Amostragem de resíduos sólidos. (Sampling of solid wastes). Rio de Janeiro; 2004 [available only in Portuguese]. [23] American Concrete Institute. Guide for structural lightweight aggregate concrete: reported by ACI Committee 213. ACI Mater J 1987;87(3):638–51. [24] Demirbog˘a R, Gül R. Thermal conductivity and compressive strength of expanded perlite aggregate concrete with mineral admixtures. Energy Build 2003;35:1155–9.