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This paper presents the result of a study on the use of sawdust waste incineration fly ash (SWIFA) as supplementary cementing materials. Tests on the setting times and strength development of cement paste and mortar with up to 30 percent SWIFA were carried out. Results of the setting times and compressive strengths show that with increasing amounts of SWIFA, the setting times of the paste were extended and the compressive strengths decreased. Pozzolanic activity index of the material was also confirmed to be approximately 76 percent and that the material performed better in a nitric acid solution environment than in sulphuric acid solution. Keywords: sawdust ash; portland cement; pozzolana; compressive strength; durability Introduction Materials The use of waste in concrete manufacture may serve Sawdust is a waste from the timber industry. The as one of the solutions to the present problems sawdust waste used for this study was collected from encountered in waste management. Large quantities of the timber milling points in Bauchi. Bauchi is the State the conventional materials are used in the construction capital of Bauchi state in Nigeria. The dominant species industry and the cost of such conventional materials and at these milling points have been classified in an earlier other adverse environmental effects have necessitated works (Elinwa and Mahmood 2001). Burning of sawdust the search for adequate alternatives. into ash was by open burning using a drum. After Some industrial wastes have been used for a number cooling, the SWIFA was grinded using pestle and mortar of years as cement and concrete components such as fly before sieving using sieve size 212µm. Table 1 shows ash (Bilodeau and Malhotra 1998; Bouzoubaa et al the sieve analysis results while Figure 1 shows that the 1999), silica fume (Khedr and Abou-Zeid 1994), Slag material falls within zone 2 of the grading curve. (Olorunsogo and Wainwright 1998), and a host number Characterization of the material by physical and chemical a,b of others (Kim and Soh 2002; Remond et al 2001 ; analyses have been published earlier (Elinwa and Wang et al 2001). Performances of these materials have Mahmood 2001). Tables 2 and 3 show the physical and been improved using other supplementary cementing chemical characteristics of the SWIFA material. The materials (Ding Zhu 2002) or supper plasticizers (Page result of the X-ray analysis confirms that silica is and Spiratos 2000). dominant (Figure 2). There are other new materials such as agricultural The sand used for the study was river sand with a bulk wastes (Elinwa and Awari 2001), that could be used but density of 2.55 and a specific gravity of 1533kg/m . The their performance characteristics need be adequately sand was free from deleterious material. The sieve ascertained to satisfy the specifications determined by analysis of the sand is shown in Table 4 and Figure 3 its applications. It is also important that the use of wastes shows that the grading of the sand is within zone 2 (BS in concrete should not affect the durability of the 1881 1970). concrete. The coarse aggregate was a normal weight aggregate This study is on using sawdust waste incineration fly with a maximum size of 20mm. It was obtained from a ash (SWIFA) to produce cement pastes and concrete local supplier in Bauchi and has an average specific mortars. Simple preliminary tests have been conducted gravity of 2.50 and a bulk density of 1364 kg/m . The and its performance in an acidic enviroment evaluated. aggregate crushing value of the aggregate was 12.82. This was tested according to BS 1881 (1970) *Corresponding Authur: Associate Prof A.U.Elinwa, Civil Engineering Programme, Abubakar Tafawa Balewa University, Test on Cement Paste PMB 0248, Bauchi - Nigeria. email@example.com The pozzolanic activity index (PAI) of SWIFA with (Received August 29, 2003 ; accepted April 6, 2004) Portland cement was determined as per ASTM C618 - 78. A total of six specimens were cast and cured for 28 Journal of Asian Architecture and Building Engineering/May 2004/7 1 days. Three specimens were cast as the control (i.e. Table 1. Grain Size Distribution of SWIFA containing zero percent SWIFA), and the remaining three cast with 35 percent SWIFA as cement replacements. Table 5 shows details of the mix composition and the achieved strengths. The value of the PAI is 75.90 percent. This is greater than the 70.00 percent minimum specified by the code. Tests on Mortars To study the influence of SWIFA on the short - term and middle - term properties of mortars, certain performance characteristics of mortars containing increasing levels of SWIFA were studied. The consistency, setting times and soundness of Table 2. Physical Properties of SWIFA SWIFA mortar mix were studied using seven mixes as shown in Table 6 and according to BS 4550: Part 3 (1978) and BS 12 (1978). Consistency of Pozzolanic Mix The normal consistency of pastes of SWIFA/PC was determined as per ASTM C 143-78. SWIFA of 0, 5, 10, 15, 20, 25 and 30 percents was used to replace cement Table 3. Chemical Analysis of SWIFA and a total of 21 samples were prepared. An average of 3 samples was taken as the final value. The results are shown in Table 7. Fig.1. Particle size distribution of SWIFA Fig.2. X- Ray Diffraction Analysis of SWIFA 2 JAABE vol.3 no.1 May. 2004 A.U. Elinwa Table 4. Particle Size Distribution– Fine Aggregate Table 6. Summary of Mixes Fig.3. Particle size distribution of sand. Table 5. Pozzolanic Activity Index: Table 7. Consistency of Pozzolanic Mix: JAABE vol.3 no.1 May. 2004 A.U. Elinwa 3 Setting Time and Soundness of the Pozzolanic Mix presented in Tables 8 and 9 respectively for setting times Setting times and soundness tests were performed in and soundness. accordance with BS 12 (1978). The test results are Table 8. Setting Times of Pozzolanic Mix: Table 9. Soundness of Pozzolanic Mix: Compressive Strength Test: Durability Test To study the effects of the incorporation of sawdust To study the effect of the incorporation of sawdust waste incineration fly ash on compressive strength of waste incineration fly ash on the durability of cement cement mortar, a mix of 1:3 (cement: sand) was used. mortar, the same mix used for the compressive strength The mix had a cement content of 456kg/m , fine test was used for the experiment. Forty specimens were aggregate of 1366kg/m and a water-binder ratio of 0.60. cast and cured for 28 days before immersing in 20 percent Seventy two mortar cubes of 50mm were cast and cured concentrated solutions of hydrochloric acid (H SO ) and 2 4 for 3, 7, 28 and 60 days. Cement content was replaced nitric acid (HNO ); twenty for each concentration. They by SWIFA using replacement levels of 0, 5, 10, 15, 20 were immersed for a period of 5 (five) weeks and and 30 percent. Three cubes were crushed at the end of readings were taken at intervals of one week. The results each curing regime and the average crushing strength are as shown in Table 11. recorded. The results are shown in Table 10. Table 10. Mortar Compressive Strength Table 11. Durability Test 4 JAABE vol.3 no.1 May. 2004 A.U. Elinwa Water Absorption Test Table 12. Absorption Test. The water absorption test was carried out by casting 10 (ten) mortar cubes of dimensions 50mm and cured for 28 days. Five (5) of the mortar cubes were cast as the control and the remaining five using 15 percent of sawdust ash to replace cement. At the end of 28 days the specimens were removed and kept dry for 3 (three) days before immersing them completely in water for 24 hours and measurements taken by weighing and finding the difference in weight. The results are shown in Table 12. Discussion of Results Consistency of SWIFA Content Paste Normal consistency of the pastes increased as the proportions of SWIFA in the paste is increased (Fig.4). This means that with the addition of more and more SWIFA, an increased amount of water is required to obtain the desired consistency. Soundness of SWIFA Cement Paste Figure 5 shows the effect of adding SWIFA on the soundness. The soundness of the sample, which is, delayed expansion showed a gradual increase as the proportion of SWIFA is increased. A range of values from 0.70 to 1.45mm is recorded and this is within the limits specified by the British Standard Specifications (BS 12 1978). Setting Times of SWIFA Cement Paste Fig.4. Consistency of SWIFA The setting time of SWIFA cement paste is important for practical applications of the material. This was determined in accordance to BS 1881(1970) and shown in Fig.6. This shows there is retardation due to the effects of SWIFA. SWIFA is a latent hydraulic material and when it is incorporated with Portland cement its reaction has to be initiated by calcium hydroxide released from the portland cement hydration. Therefore, it defers the hydration of blended cement, and prolongs the setting time of cement. This observation was also made by Wang et al (2001) working with amorphous silica residues as supplementary cementing materials. Compressive Strength Fig.5. Soundness of SWIFA The compressive strength of the sawdust fly ash mortar cubes decreased as the ash content was increased. This is shown in Figure 7. An explanation to this can be given if the reaction mechanism of sawdust ash is divided into physical and chemical aspects (Ding Zhu 2000). The physical effect is that the ultra - fine particles fill the voids in cement, which makes the microstructure of cement paste denser. The chemical effect is the reaction of SWIFA with the cement hydrates. Ding Zhu (2002) working with metakaolin and slag has stressed that the slag reacted more slowly than the alite and thus strength development of slag was slow and that the strengthening effect of slag to the compressive strength of portland cement will be seen after the concrete was cast for a Fig.6. Setting times of SWIFA long time, for example, after 91 days. The same effect is JAABE vol.3 no.1 May. 2004 A.U. Elinwa 5 inferred for the sawdust ash and strength development is therefore slower to an extent that increases with the proportion of sawdust ash. The maximum strength is obtained at 10 percent cement replacement. Figure 8 shows that as the curing proceeds, the compressive strength increases. Durability of Sawdust Fly Ash Mortar Cubes Figure 9 shows that the mortar with SWIFA offered better resistance to deterioration by nitric acids than Portland - cement mortar. Figure 10 shows that the effect of the sulphuric acid was very drastic both on the SWIFA Fig.7. Compressive strength of SWIFA mortar cube mortar and Portland cement mortar. This shows that SWIFA will not perform viably in such environment. A further confirmation on this issue is needed before final conclusion can be drawn. The rate of deterioration of the mortar cube in the nitric acid can be represented empirically by y = a – bx – cx , where y is the weight (kg) and a, b and c are coefficients. The values of the coefficients are 99.839, 1.7975 and0.6268 respectively.For such behaviour the correlation factor (R ) is 0.9585. The rate of deterioration of the mortar in sulphuric acid is exponential and can be –bx represented by y = ae , where y is the weight (kg) and a and b are the coefficients with the values of 100.75 and 0.3422 respectively. X in the two equations is the percentage sawdust ash. Fig.8. Compressive strength of SWIFA mortar cube Water Absorption The low water absorption exhibited by the mortar cube containing 15 percent SWIFA shows that a more dense microstructure was formed because the ultra - fine particles fill the void in cement and SWIFA can absorb CH to form C-S-H which is a continuum structure. Conclusion The conclusions of this study can be summarized as follows: a. Sawdust waste incineration fly ash can react with CH released by cement clinker hydration to produce secondary C-S-H gel inside the cement paste which improves the microstructure of cement paste matrix. b. The SWIFA can defer the reaction of cement hydration and prolong the setting time of cement paste. SWIFA has a pozzolanic activity Fig.9. Durability of SWIFA mortar cube in 20% nitric acid index of approximately 76% and thus can be used as supplementary cementing materials but its reaction is slow c. An increased amount of water is needed when using SWIFA in order to produce concrete that has consistent workability. d. The mortar compressive strength decreases as SWIFA content is increased. For this study 10% SWIFA is recommended. e. In acid environment, the rate of deterioration of SWIFA mortar cube is adversely affected in sulphuric acid than when in nitric acid and so SWIFA concrete or mortar should not be used in such environment. f. The rate of deterioration of SWIFA mortar cube in nitric acid environment can be evaluated using the empirical formula y = a – bx – cx and in sulphuric acid environment as –bx y = ae . Fig.10. Durability of SWIFA mortar cube in 20% sulphuric acid 6 JAABE vol.3 no.1 May. 2004 A.U. Elinwa 7) Wang, L., Seals, R.K. and Roy, A. (2001). Investigation of References: utilization of amorphous silica residues as supplementary cementing 1) Bilodeau A and Malhotra V.M. (1998). High volume fly ash system: materials. Advances in Cement Research, 13, (2), 85 -89. The concrete solution for sustainable development. CANMET/ACI 8) Ding Zhu, Z.L. (2002). Property improvement of porland cement International Symposium on Sustainable Development of the by incorporating with metakaolin and slag. Cement and Concrete Cement Industry, Ottawa, Canada, October 21 - 23, pp 1-22. Research, 33, 579 - 584. 2) Bouzoubaa, N; Zhang, M.H. and Malhotra, V.M. (1999). Production 9) Page, M. and Spiratos, N. (2000). The role of superplasticizers in and performance of laboratory produced high - volume fly ash the development of environmentally- friendly concrete. CANMET/ blended cements in concrete. 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Properties of unsaturated polyester fresh concrete, London; 1970. mortars using crushed waste glass. Journal of Asian Architecture 13) ASTM C 618 - 78. Specification for fly ash and raw or calcined and Building Engineering, 12, 7 - 12. natural pozzolana for use as a material admixture in Portland cement 6a) Remond, S., Pimienta, p. and Bentz, D.P. (2001). Effects of the concrete, 1978. incorporation of municipal solid waste incineration fly ash in 14) British Standard Specification BS 4550 Part 3: Methods of testing cement pastes and mortars I. Experimental. Cement and Concrete cement, London; 1978. Research, 32, 303 -311. 15) British Standard Specification BS 12: Ordinary and rapid Portland 6b) Remond, S., Bentz, D.P. and Pimienta P. (2001). Effects of the cement, London; 1978. incorporation of municipal solid waste incineration fly ash in cement pastes and mortars II. Modeling. Cement and Concrete Research, 32, 365 - 576. JAABE vol.3 no.1 May. 2004 A.U. Elinwa 7
Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: May 1, 2004
Keywords: sawdust ash; portland cement; pozzolana; compressive strength; durability
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