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Procedía Engineering 14(2011) 1157-1164
Procedía Engineering
www.elsevier.com/locate/procedia
The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction
Cellular Lightweight Concrete Containing Pozzolan Materials
Khamphee Jitchaiyaphuma*, Theerawat Sinsiria 1, Prinya Chindaprasirtb
a School of Civil Engineering, Suranaree University of Technology, Thailand bDepartment of Civil Engineering, Khon Kaen University, Thailand
Abstract
This research studies various properties of compressive strength, water absorption, and the porosity of cellular lightweight concrete or CLC, which is pre-formed foam method made from portland cement blended with foaming agent and pozzolan materials. Uses of fly ash replace cement in the proportions 10, 20 and 30 percent by weight of binder. Constant water to binder ratio of 0.5 and unit weight of 800 kg/m3 compared compressive strength at curing age 3, 14, 28 and 60 days. The study result that replacing cement with fly ash that is high strength on the early stage.
© 2011 Published by Elsevier Ltd.
Keywords: Cellular lightweight concrete, compressive strength, pozzolan material, foaming agent
1. INTRODUCTION
The cellular lightweight concrete (CLC) or sometimes might often call that foamed concrete is either a cement paste or mortar, classified as lightweight concrete, in which air voids are entrapped in mortar by suitable foaming agent. By proper control in dosage of foam content, a wide range of densities between 500 to 1600 kg/m3. A study on fineness of filler type on compressive strength of foamed concrete made with cement-fly ash mix, suggesting that the inclusion of fly ash helps in achieving more uniform distribution of air voids than fine sand, is a journal paper, reference (Nambiar and Ramamurthy, 2006). The cellular lightweight concrete can be obtained for application to structural, partition, insulation wall
* Presenter: Email: khampheej@yahoo.com t Corresponding author: Email: sinsiri@g.sut.ac.th
1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.145
and filling hole. Few studies report on the influence of pozzolan materials on the properties of cellular lightweight concrete. By using fly ash as filler (fine aggregate) instead of sand, the high volume utilization of fly ash becomes possible, thus providing a means of economic and safe disposal of this waste product. The pore system in based cement material is conventionally classified as gel pores, capillary pores, macro pores due to deliberately entrained air, and macro pore due to compaction has not enough. The gel pores not influence the strength of concrete through its porosity, although these pores are directly related to creep and shrinkage. Fly ash being finer, helps in uniform distribution of air voids by providing a well and uniform coating on each bubbles and preventing it from merging and overlapping, is a journal paper, reference (Nambiar and Ramamurthy, 2007). This paper discusses a systematic study on the influence of filler contents on the properties of cellular lightweight concrete made using pre-formed foam method.
2. EXPERIMENTAL
2.1. Parameters investigated and mix compositions
As the experimental program was aimed at studying the effect of the filler contents on the properties like density, flow behavior, water absorption and strength of cellular lightweight concrete, the following mixes were investigated by constant water to binder ratio of 0.5 by weight. The foam required for one density of cellular lightweight concrete of 800 kg/m3 was arrived as per ASTM C 796-97. In the fly ash mixes 0%, 10%, 20% and 30% by weight of binder are instead with fly ash by use symbols of C800, FA10, FA20 and FA30, respectively.
2.2. Materials
The foaming agent used was hydrolyzed protein foam and manufactured in Thailand. The mixture has used ordinary portland cement (OPC) which its particle is shown in Fig. 1(a), no fine river sand added and class F fly ash conforming to ASTM C 618 were used. The properties of cement and fly ash used in this study are presented in Table 1 and the scanning electron microscope (SEM) image of a fly ash particle is shown in Fig. 1(b).
2.3. Details of study
Foamed concrete is produced under controlled conditions from cement, filler, water and a liquid chemical that is diluted with water and aerated to form the foaming agent. The foaming agent was diluted with water in ratio of 1 : 40 by weight, and then aerating to a density of 45 kg/m3. The specimens were removed from the mould after 24 hours then wrapped with plastic film until near the time tests. The compressive strength, dry density and water absorption were determined. Even for mixes with fly ash at the age 3, 14, 28, and 60 days for five samples. Strength test was conducted so that comparison with the fly ash contents mixes would be possible. Size 100*100x100 mm cubic specimens, as the recommendations in ASTM standards, cast for the study of each parameter were used for the compressive strength test.
2.4. Scanning electron microscope image
The microstructure of cellular lightweight concrete was investigated using SEM (JOEL JSM-6400). The sample were split middle portion hardened blended cement paste. Samples were submerged directly
into liquid nitrogen for 5 minutes then are evacuation under pressure of 0.5 N/m2 at temperature of -40 °C for 2 days (Galle, 2001, Konecny and Naqvi, 1993).
3. RESULTS AND DISCUSSION
3.1. Characteristic of OPC and fly ash
Physical properties of the materials are shown in Table 1. The specific gravity of fly ash is 3.15. The median particle size of fly ash (D50) is 14.52 ^m, particle size has small sized and nearby cement particle. The chemical compositions of OPC and fly ash are given in Table 2. The main chemical composition of fly ash has total amount of SiO2, Al2O3 and Fe2O3 more than 70 %.
Table 1: Physical properties of materials used
Sample Specific gravity Median particle size Blaine fineness (cm2/g)
OPC 3.15 14.75 3,600
Fly ash 2.02 14.52 -
Table 2: Chemical composition of materials used
Chemical composition (% by weight) OPC Fly ash
Silicon dioxide (SiO2) 19.85 43.87
Aluminum oxide (Al2O3) 4.49 26.33
Iron oxide (Fe2O3) 3.56 10.81
Calcium oxide (CaO) 66.96 12.69
Magnesium oxide (MgO) 1.36 1.23
Sodium oxide (Na2O) - -
Potassium oxide (K2O) 0.34 1.10
Sulfur trioxide (SO3) 2.46 2.74
Loss on ignition (LOI) 0.98 1.23
SiO2 + Al2O3 + Fe2O3 - 81.01
a) OPC (x500) b) Fly ash (x1,500)
Figure 1: Scanning electron microscope images of particle
3.2. Compressive strength
The effect of fly ash contents on the compressive strength of cellular lightweight concrete is presented in Fig. 2(a). For a given density, the mix with high contents resulted in higher strength than the mix with low contents and the variation is higher at higher density. Similar results have been reported in literature as (Kearsley and Wainwright, 2001, Nambiar and Ramamurthy, 2006). Fracture surface of the specimens viewed through a scanning electronic microscope with magnification factor of 100 showed that there was a comparatively uniform distribution of pore in the case of cellular lightweight concrete with low contents, while the pores were connected mostly and irregular for mixes with high contents. This indicates that high contents causes clustering of bubbles to form irregular small pores and concrete is slump while it is setting. Thus it can be concluded that low contents results in uniform distribution of bubbles and hence results in lower strength than high contents at a given density, (Kearsley and Wainwright, 2002) reported similar observations on the effect of density on the strength of lightweight concrete.
In order to study the effect of replacement of cement with fly ash, the relationship between pore size and compressive strength for cellular lightweight concrete mixes with fly ash as filler is shown in Fig. 2(b). For a given density, an increase in fly ash content results in higher strength. Apart from pozzolanic activity of fly ash, the lower requirement of foam volume for a given density of foam concrete will also contribute to strength enhancement by reducing the pore volume and facilitating uniform distribution of pores. Reference (Chindaprasirt et al., 2005, Nambiar and Ramamurthy, 2007) observed a similar enhancement in strength due to fly ash and this was attributed to the development of strong inter particle bond between the gel matrix and the fly ash particles.
i ! i ! i I i ! i ! i _ _ - "
- jr --------0
_ J -O- C800 -
If -■- FA 10
—A— FA 20 -
,1.1.1,1 . i .
10 20 30 40 Age (days)
a) Strength vs age Figure 2: Effect of fly ash content on strength and pore size
• FA10
▲ FA20
♦ FA30
20 40 60
Pore size (im)
b) Strength vs pore size at 28 days
3.3. Water absorption and porosity
Table 3 shows the variation of compressive strength with water absorption of cellular lightweight concrete. It is noted that, unlike conventional concrete, water absorption increases with compressive strength. A possible explanation can be that for a given cellular lightweight concrete mix, increased density corresponds to an increase in paste volume of capillary pore and reduction in foam volume of artificial pore. However, the compressive strength and water absorption increase with density of cellular lightweight concrete. Therefore, for a given cellular lightweight concrete mix, water absorption mainly depends on capillary pore volume and the volume of artificial pores governs the compressive strength and density, (Narayanan and Ramamurthy, 2000) reported similar conclusions on strength of artificial pore dependency for autoclave aerated concrete.
The porosity and the water absorption at 28 days of cellular lightweight concrete can be seen in Table 3 and Table 4. From these Tables it can be seen that the relationship is not significantly influenced by the use of fly ash. Mixtures with replace fly ash of 30 % seem to yield marginally higher absorption than mixtures with fly ash replacement of 20 % while replace fly ash of 30 % has lower porosity. However, these differences are only small and it can be concluded that for the results available, the volume of ash used does not significantly influence the porosity strength relationship of cellular lightweight concrete.
Table 3: Compressive strength and water absorption of cellular lightweight concrete with variation of fly ash replacement
Fly ash content Compressive strength (MPa) Water absorption
Symbol (% by weight) - (% by weight)
3 days 14 days 28 days 60 days
C800 0 1.65 2.46 2.64 2.79 31
FA10 10 2.45 3.25 3.29 3.32 35
FA20 20 2.53 3.11 3.38 3.57 39
FA30 30 2.45 3.73 3.92 4.08 47
3.4. Pore size distribution and microstructure
From the total pore volume and pore size distribution of cellular lightweight concrete shown in Table 4. It explained that total pore volume of 0.33 to 0.76 cc/g. The capillary pore (>0.01 ^m) took 56 to 91% of total pore volume. The pore size distribution in Fig. 3, it was known that hydration reactions of cement mainly generated pores smaller than 0.1 ^m. Similar results have been reported in reference as (Chindaprasirt et al., 2005). However, during foaming insert of air bubble foam, the pores generated were mostly larger than 100 ^m. In adding fly ash increased the volume of pores smaller than 30 ^m. This meant that cellular lightweight concrete with foaming agent mostly produced pores larger than 30 ^m and thus to result in a flowable structure due to its open and connected pores. Similar results have been reported in reference as (Wang et al., 2005). Thus it can be proved in SEM micrograph.
Table 4: Porous structure of cellular lightweight concrete at 28 days
Fly ash content Pore size Total pore volume Porosity
Symbol (% by weight) (^m) (cc/g) (%)
FA10 10 54.78 0.3379 59.15
FA20 20 37.23 0.7651 90.03
FA30 30 27.53 0.3325 56.38
Fig. 4 shows the scanning electron microscope images of fractured surface of cellular lightweight concrete at 28 days. In Fig. 4(a) is shown the plain cement paste, all porous structure has smoothly surface seen under the higher power microscope (*100). In Fig. 4(b),(c), there are close pores and it proved that cellular lightweight concrete had the characteristic of low water absorption under the higher power microscope (*100). In Fig. 4(d), there are connecting pores and small pores which are proved that cellular lightweight concrete had the characteristic of high water absorption.
1 1 1 1 f 1 \ FA 10 ----FA 20 -----FA 30
1 - 1 N JK \ - ; x\ </ w « " ■ » n
// \ K A. IN -
inl..-^ 1 1
0.001 0.01 0.1
Pore size (^m)
100 1000
Figure 3: Effect of fly ash content on cellular lightweight concrete.
a) C800 b) FA10
c) FA20 d) FA30
Figure 4: Fractured surface of cellular lightweight concrete at 28 days (x 100).
4. CONCLUSIONS
The conclusions drawn from this study and summarized below are applicable to the characteristics of the materials used and the range of parameters investigated:
1. For a given density, an increase in fly ash content of the mix results in increased strength.
2. Replacing cement with high fly ash not affect the compressive strength in early age.
3. Replacing cement with high fly ash affects the pore size decrease and cause compressive strength increased.
Acknowledgements
The authors would like to acknowledge the financial supports of the Commission by Rajamangala University of Technology Isan of Thailand for support given through a grant fund under the Strategic Scholarships for Frontier Research Network for the Join Ph.D. Program, Thai Doctoral degree.
References
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[2] ASTM. Standard specification for fly ash and raw or calcined natural pozzolana for use as a mineral admixture in portland cement concrete, ASTM C 618-89, Philadelphia, 1989.
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