Evaluation of thermal conductivity, mechanical and transport properties of lightweight aggregate foamed geopolymer concrete

Accepted Manuscript Title: Evaluation of thermal conductivity, mechanical and transport properties of lightweight aggregate foamed geopolymer concrete Author: Michael Yong Jing Liu U. Johnson Alengaram Mohd Zamin Jumaat Kim Hung Mo PII: DOI: Reference:

S0378-7788(13)00846-3 http://dx.doi.org/doi:10.1016/j.enbuild.2013.12.029 ENB 4721

To appear in:

ENB

Received date: Revised date: Accepted date:

19-9-2013 28-11-2013 17-12-2013

Please cite this article as: M.Y.J. Liu, U.J. Alengaram, M.Z. Jumaat, K.H. Mo, Evaluation of thermal conductivity, mechanical and transport properties of lightweight aggregate foamed geopolymer concrete, Energy and Buildings (2014), http://dx.doi.org/10.1016/j.enbuild.2013.12.029 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Evaluation of thermal conductivity, mechanical and transport properties of geopolymer lightweight foamed concrete The highlights of the research work are as given below:

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The usage of industrial by-products FA and POFA as binder in geopolymer concrete Structural grade geopolymer foamed concrete using lightweight coarse aggregate, OPS Thermal conductivity of OPSFGC13 was 48% lower than the conventional brick  Strength to density ratio of the OPSFGC was 54% higher than the corresponding NWC

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Evaluation of thermal conductivity, mechanical and transport properties of lightweight aggregate foamed geopolymer concrete

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Michael Yong Jing Liu, U. Johnson Alengaram*, Mohd Zamin Jumaat, Kim Hung Mo

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Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

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Abstract

Energy efficiency is the predominant criterion in green building indices, which, in turn, contributes

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to sustainable development. One of the materials commonly used in the insulation of buildings is foamed concrete. This investigation presents the main objective of the experimental results

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concerning the thermal conductivity of oil palm shell foamed geopolymer concrete (OPSFGC), utilizing waste materials such as low-calcium fly ash (FA) and palm oil fuel ash (POFA) as

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cementitious materials, and oil palm shell (OPS) as lightweight coarse aggregate (LWA). Three

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OPSFGC mixtures with densities of 1300, 1500 and 1700 kg/m3 were prepared using an artificial

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foaming agent; a control mix without foam and conventional materials – block and brick – were used for comparison. The test results on the mechanical and transport properties are also discussed. The thermal conductivity of OPSFGC13 of about 0.47 W/mK was 22% and 48% lower than the conventional wall materials, block and brick, respectively. OPSFGC, with a density of 1300 and 1500 kg/m3, could be categorized as structural and insulating concrete, Class-II, whereas OPSFGC with a density of 1700 kg/m3 is classified as Class-I structural grade concrete with a compressive strength and thermal conductivity of about 30 MPa and 0.58 W/m K , respectively. Keywords: energy efficient building; lightweight aggregate foamed concrete; geopolymer; oil palm shell; palm oil fuel ash; structural and insulating concrete; thermal conductivity *Corresponding author. Tel.: +60 379677632. Fax: +60 379675318. E-mail address: [email protected] (U. Johnson Alengaram)

 

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1. Introduction

The concept of sustainable development is not a passing fad but rather a policy that will last

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and has become more relevant because the great ones of this world are breathing the same polluted air as the rest of us [1]. The need to optimize the energy behaviour of buildings’ has been enforced

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by the scientific and government policies. The public debates are focused on the quality of the

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urban environment, as more energy efficient buildings could reduce the quantities of fossil fuels consumed and thereby reduce the amount of carbon dioxide and sulphur dioxide emitted into the

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atmosphere, particularly on a micro- and mesoscale [2]. According to Mahlia et al. [3], a proper insulation material with the capacity to achieve acceptable comfort for the building occupants while

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reducing the cooling load is necessary as it would generate huge energy and cost savings as well as reduce environmental emissions from the power plants.

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As the construction industry is considered to be one of the fastest growing industries,

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reducing the heat loss in buildings by increasing its thermal insulation properties is important, as it

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would enable energy efficient buildings and improve environmental sustainability. In addition, the usage of industrial waste would be an added advantage. Ng and Low [4] discovered that sandwiched newspaper, which could be used as the wall envelope for energy efficient building construction, has a significant impact on the thermal conductivity performance of aerated lightweight concrete panels with a reduction of thermal conductivity of up to 22% compared to the control panels. Incorporation of 0.5 to 1.0% of the air-entraining agent in lightweight aggregate cellular concrete has shown an excellent characteristic as an architectural member due to its high acoustic shielding and thermal insulation properties [5]. Moreover, Alengaram et al. [6] reported that structural grade oil palm shell foamed concrete (OPSFC) has 39% reduced thermal conductivity compared to conventional brick. However, the spacing of cracks in the OPSFC beams was found to be closer than those found in normal weight concrete (NWC) beams; thus, OPSFC

 

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beams produced a higher modulus of elasticity (MOE) with smaller crack widths [7]. Furthermore, Ramírez et al. [8] determined that recycled coarse aggregate (RCA) concrete used in the construction of bio-digesters delivers significant savings in energy consumption with its good thermal behaviour and mechanical performance. Stalite aggregate has been presented as the most

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effective insulating RCA when 20 to 30% of glass bubbles are added, compared with normal concrete [9].

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Although modern concretes are composite materials, cement is still an indispensable

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material in concrete production [1]. The production of cement is one of the main contributors towards global warming caused by the emission of carbon dioxide (CO2). Davidovits [10] was the

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pioneer in introducing binders other than cement that could be produced by the reaction between alkaline liquids and source materials that are rich in silica and alumina, commonly known as

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geopolymerization. The material has been termed ‘geopolymer’. The geopolymerization process is aided by heat curing and drying [11]. The use of geopolymer technology not only substantially

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reduces the CO2 emissions by the cement industry, but also utilizes waste materials, such as FA

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[11]. Low-calcium (ASTM Class-F) FA is preferred as a source material to high calcium (ASTM

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Class-C) F since the presence of a high amount of calcium interferes with the polymerization process and alters the microstructure [12]. Malaysia is the second largest palm oil producer through which it contributes large

quantities of waste, such as empty fruit bunches, palm oil clinker, oil palm shells (OPS) and palm oil fuel ash (POFA). These waste materials are unutilized and cause land and air pollution in the vicinity of the palm oil factories. Many researchers have taken the initiative to utilize some of these palm oil industry wastes, such as OPS and POFA, to develop sustainable construction materials [13-17]. Tangchirapat et al. [16] reported that a 20% replacement in ordinary Portland cement (OPC) concrete with medium size POFA as the pozzolanic material produced 90% of the compressive strength of the control concrete at the age of 90 days. Similarly, Ahmad et al. [17] investigated the optimum cement replacement of POFA and found that a replacement of 15%

 

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produced comparable strength to that of the control concrete. Shafigh et al. [14] used crushed OPS to produce high strength oil palm shell concrete (OPSC) with a compressive strength of up to 53 MPa with a density of 2000 kg/m3. The addition of polypropylene and nylon fibres in the OPSC enhanced the post-failure compressive strength [15]. Further, it was shown that the use of a sand to

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cement ratio of 1.6 in the OPSC enhanced the MOE up to 11 kN/mm2 [13]. Kupaei et al. [18] developed an optimum mix proportion for the 50-mm oil palm shell geopolymer concrete (OPSGC)

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with a compressive strength and density of 33 MPa and 1800 kg/m3, respectively.

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Although many researchers have attempted to utilize waste materials in geopolymer concrete, there has not been much research on the development of aerated or foamed geopolymer

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concrete. Raden and Hamidah [19] made an effort to utilize waste paper sludge ash as a source material to develop foamed geopolymer concrete (FGC). The density and the compressive strength

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of FGC were found to be approximately 1800 kg/m3 and 3 MPa, respectively. OPSFC with a density of 1100 kg/m3 is able to reduce 56% of the thermal conductivity when matched with the

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conventional brick in Malaysia [6]. However, there is no literature available on the thermal

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insulation characteristic of FGC. Furthermore, no research has been conducted on utilizing

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industrial waste such as OPS and POFA to replace the coarse aggregate and the binder in geopolymer concrete.

As a further research, artificially generated foam is introduced to produce both structural and

non-structural grade FGC in which OPS was used as the coarse aggregate. POFA and FA were used as cementitious materials (CM). The oven-dry density (ODD), porosity, sorptivity and compressive strength up to the age of 28 days were reported. This study focused on a comparison of the thermal conductivity effect of oil palm shell foamed geopolymer concrete (OPSFGC) for various ODDs with the conventional materials used for building walls in Malaysia, such as block and brick. The reported ODDs of OPSFGC ranged from 1300 to 1700 kg/m3, which were classified as lightweight concrete.

 

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2. Experimental programme

2.1.

Materials

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The binders used in this experimental work are Class-F FA and POFA. Class-F FA was supplied by Lafarge Cements, Malaysia, whereas POFA was collected from local palm oil mills.

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The chemical composition of FA and POFA conforming to ASTM C618-12a are shown in Table 1.

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The POFA collected from the mill was dried in an oven at 105 ± 5 ˚C for 24 hours, followed by sieving through 300 µm to remove any coarse foreign particles. Then, the POFA was ground in a

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Los Angeles abrasion machine for 30,000 cycles to a mean particle size of 45 µm to improve

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reactivity. For all mixtures, the binder consists of 20% POFA and 80% of FA.

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Table 1 Chemical composition of Class-F FA and POFA

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Crushed OPS of sizes between 2.36 and 9.5 mm was used as the coarse lightweight

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aggregate in this study. Table 2 shows the physical properties of the OPS. The OPS was washed and kept in a saturated surface dry (SSD) condition for about 24 hours before being used. Mining sand with a specific gravity of 2.67, passing through 2.36 mm and retained on 300 µm was used as fine aggregate for the OPSFGC; however, mining sand passing through 5 mm and retained on 300 µm was used as the fine aggregate for the oil palm shell non-foamed geopolymer concrete (OPSNFGC).

Table 2 Physical properties of OPS

A combination of sodium hydroxide in flake form and sodium silicate solution was used as the alkaline activator. The solution was prepared at least 1 day prior to its use to allow the  

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exothermically heated liquid to cool to ambient temperature. The ratios of the sodium silicate solution to sodium hydroxide solution and the alkaline solution to CM were 2.5 and 0.55 by mass, respectively. The molarity of the sodium hydroxide was 14M. In addition, a polycarboxylate ether (PCE) based superplasticizer (SP) was used at a dosage of 1.5% by mass of CM. Potable water was

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used in all the mixes. The commercially available foaming agent, Sika AER-50/50 was used in this investigation by using a foam generator. The air pressure of the foam generator was maintained at

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75 psi or 517 kN/mm2 and the generated foam was then added during the mixing of OPSFGC.

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2.2. Specimen preparation

In this investigation, the OPSFGC was cast based on the target ODD; namely, 1300, 1500

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and 1700 kg/m3. The control OPSNFGC specimen was cast for the purpose of comparison. The total CM used was 489 kg/m3, which consists of 20% of POFA and 80% of FA. The ratios of coarse

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aggregate to CM and fine aggregate to CM were kept at 0.6 and 1.7, respectively. The additional

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water to binder (w/b) ratio was kept constant at 0.1, whilst the SP was used at a dosage of 1.5% by

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mass of CM for all mixtures. The dosage of foam varied with the target densities of the OPSFGC. Table 3 showed the details of the mixture proportions of the OPSFGC and OPSNFGC.

Table 3 Mixture proportions of OPSFGC and OPSNFGC

The fine and coarse aggregates were mixed in a rotary mixer for about 2 minutes; this was

followed by the addition of CM with a further mixing of about 3 minutes. The alkaline solution, water and SP were then gradually added, and mixed for another 5 minutes. Finally, the foam was added to achieve the target density of OPSFGC. The concrete was then poured into the steel moulds and the specimens were covered with plastic sheets to prevent evaporation of the surface water. The specimens were then transferred to the curing chamber and cured at a temperature of 65˚C for 48 hours before being de-moulded and tested.  

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The concrete specimens were cast in 100-mm cubes for the compressive test, which was carried out at the ages of 3-, 7-, 14- and 28-days; the same size specimens were used for the ultrasonic pulse velocity (UPV) and sorptivity tests. The specimens of 100 mm φ x 200 mm height cylinders were prepared for the splitting tensile strength and porosity. The tests on the flexural

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strength and the modulus of elasticity (MOE) were carried out on prisms of size 100 x 100 x 500 mm and on 150 φ x 300 mm cylinders, respectively. For the thermal conductivity test, panels of size

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300 x 300 x 55 mm were used.

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2.3. Test method

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2.3.1. Thermal conductivity

The thermal conductivity test was performed at the age of 28 days, in accordance with BS

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EN 12664 [20]. The panels were oven-dried for 24 hours at a temperature of 105 ± 5 ˚C to remove

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any moisture present. Figs. 1 and 2 show the testing arrangements and schematic diagram of the

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apparatus. The panels were placed between hot and cold plates with a temperature of 40 ˚C and 18 ˚C, respectively, to stimulate the exterior and interior temperature. The temperatures on the hot and the cold plates were recorded at every 10 minutes for 24 hours and the data recorded. The mean values of the recorded temperatures were used in the calculation of the thermal conductivity. The thermal conductivity of the concrete specimen was calculated using Fourier’s law as given below in Eq. 1:

k = (Φ × t) / (A × ∆T)

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where k = thermal conductivity (W/m K ), Φ = heat flow (J/s), t = thickness of specimen (m), A = area of specimen (m2) and ∆T = temperature difference between hot and cold plates (˚C).

 

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Fig. 1. Thermal conductivity test equipment

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Fig. 2. The schematic diagram of the thermal conductivity test

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2.3.2. Transport properties

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The porosity test was done using disc specimens of size 100 φ x 50 mm at the age of 28 days for the geopolymer concrete. The vacuum saturation technique was applied for this test, which is

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based on ASTM C1202-12, and has been proven to be the most efficient [21]. The specimens were oven-dried for 48 hours before testing at 105 ± 5 ˚C to achieve constant weight. The equation (Eq.

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2) below was used to determine the porosity of the geopolymer concrete.

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where Ws = saturated surface-dry mass of the specimen in air, Wd = oven-dry mass of the specimen in air and Wb = buoyant mass of the saturated specimen in water.

The sorptivity test specimen (100 mm cube) cured for 28 days before being oven-dried at

105 ± 5 ˚C for 48 hours until a constant weight was achieved. Then the specimen was lightly greased and covered with cling film on its sides and placed in a container to absorb water vertically from its base. The weight of the specimen was observed at intervals of time of 1, 4, 9, 16, 25, 36, 49 and 64 minutes. The sorptivity of specimen was then calculated using the following equation (Eq. 3):

 

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i = A + St1/2

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where i = cumulative volume of water absorbed at time t (mm3/mm2), A = surface area of the

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specimen (mm2); S = sorptivity coefficient (mm/min1/2) and t = recorded time (min)

The UPV was done in accordance with ASTM C597-09 using a portable ultrasonic non-

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destructive digital indicating tester (PUNDIT) at the ages of 3-, 7-, 14- and 28-days on 100-mm

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cube specimens.

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2.3.3. Mechanical properties

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The mechanical properties tests that were carried out at the age of 28-day include splitting tensile strength (ASTM C496-11), flexural strength (ASTM C78-10e1) and MOE (ASTM C469-

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10). However, the compressive strength (BS EN 12390-3 [22]) test was done at 3-, 7-, 14- and 28-

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Results and discussion

3.1. Density

The ODD of OPSFGC and OPSNFGC range from 1291–1794 kg/m3, as summarized in

Table 4. The difference between the target and actual densities was within the range of ± 35 kg/m3, which is well within the range of ± 50 kg/m3 stipulated for foamed concrete. The pores introduced in the concrete due to the addition of foam played an important role in the density reduction. It has been reported that at a lower density range, it is the foam volume that controls the strength rather

 

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than the material properties [23]. Fig. 3 shows that the ODD of geopolymer concrete has a linear relationship with both the compressive strength and the UPV. Moreover, OPS itself is a porous aggregate, as it has a large number of micro pores of diverse sizes in the range of 16–24 µm, which might entrap air [18]. It can be seen from Table 4

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that the maximum density difference between the OPSFGC17 and OPSNFGC was only about 70 kg/m3, which might be attributed to the low quantity of foam added in the former. In addition, it can

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be observed from Table 4 that the ODD of 3-, 7-, 14- and 28-day specimens showed consistency.

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foam might be destroyed during the mixing process.

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The stability of the foam also plays an important role in maintaining the density as some of the

Table 4 ODD and compressive strength of OPSFGC and OPSNFGC

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3.2. Ultrasonic pulse velocity test

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Fig. 3. Relationship between the compressive strength, ODD and UPV

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The UPV test is a common technique employed for analysing the uniformity and relative quality of concrete to indicate the presence defects, such as voids and cracks, and to estimate the depth of cracks [15]. The measured 3-, 7-, 14- and 28-days UPV values for all geopolymer concrete specimens are presented in Fig. 4. It is observed that the UPV values of OPSFGC increased with the increase of density as well as the age of the geopolymer concrete. The presence of voids has been recognized to have an influence on the UPV transmission [24]. The earlier study performed by Karakurt et al. [25] showed that the increase of UPV values leads to a more solid form of the concrete. As suggested by Browne et al. [26], both the OPSFGC17 and OPSNFGC are considered as fair quality concrete as the UPV values fall between 3 and 4 km/s.

Fig. 4. Ultrasonic pulse velocity (UPV) of OPSFGC and OPSNFGC  

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3.3. Compressive strength

Fig. 5 shows the development of the compressive strength for the geopolymer concrete

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specimens. As known, the increase in the compressive strength over the period of 28 days is not high. In contrast to the well-established strength development of OPC concrete in which the

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hydration process takes place over a period of time along with strength gain, the geopolymer

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concrete does not gain strength exponentially over time [11]. The geopolymerization depends on the aluminosilicate contents in the source material, molarity and type of alkaline activator, curing

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condition and period, as well as the ratio of solution to binder among others. Xu and van Deventer [27] reported that silicon (Si) and aluminium (Al) appeared to be synchro-dissolving from the

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surface of the materials and yet, there is a higher extent of dissolution in concentrated NaOH alkaline solution.

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The compressive strength of OPSFGC and OPSNFGC specimens achieved high early

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strength due to the polymerization process that takes place during the first 48 hours of heat curing;

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as expected, the rate of strength gain decreased after 7 days and the strength gain between 7 and 28 days was about 11.3%.

It is evident from Figs. 3 and 5 that the compressive strength is proportional to the density of

the specimens, which is in agreement with the earlier findings reported by Alengaram et al. [6] for foamed concrete. The OPSFGC13 produced the lowest 28-day compressive strength of 8.3 MPa compared to 25.8 MPa for OPSFGC17. The non-foamed concrete, OPSNFGC, showed the highest 28-day compressive strength of about 30 MPa. The inclusion of different foam contents in the OPSFGC specimens produced tiny air-voids that lead to a lower strength in foamed specimens compared to the non-foamed specimen. At a higher foam volume, the merging of bubbles seemed to produce larger voids that result in a wide distribution of void size and lower strength [28].

 

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Alengaram et al. [6] reported that the oil palm shell concrete (OPSC) and oil palm shell foamed concrete (OPSFC) achieved the 28-day compressive strength of 28 MPa and 20.2 MPa, respectively. In this investigation, the OPSFGC with an ODD of 1700 kg/m3 was able to achieve about 26 MPa at the age of 3 days. Thus, with its ability to achieve as high as 90% of its 28-day

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compressive strength in 3 days, OPSFGC could be considered for the development of precast lightweight concrete. Moreover, by replacing highly siliceous POFA as CM in the geopolymer

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concrete, the polymerization of Si-Al might be attributed to the high compressive strength in the

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OPSFGC and OPSNFGC. The effect of POFA in conventional concrete has shown that 20% of cement replacement produced higher 90-day compressive strength compared to conventional

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concrete [29].

The OPSFGC17 with an ODD of 1700 kg/m3 is categorized as structural grade concrete.

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Another important factor is the strength to density ratio of the OPSFGC. The OPSFGC17 gives a strength to density ratio of 17, which is about 54% higher than the corresponding NWC [30]. The

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density reduction of about 29% of OPSFGC17 compared to NWC is advantageous as the structural

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elements with OPSFGC would reduce the overall cost of the structure. Both the OPSFGC17 and

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OPSNFGC achieved a 28-day compressive strength of about 26 MPa and 30 MPa, respectively, and hence could be categorized as lightweight structural concrete in accordance with ACI 213R [31].

Fig. 5. Development of compressive strength

3.4. Tensile strength and modulus of elasticity

The results for the mechanical properties of geopolymer concrete specimens are presented in Table 5. Jumaat et al. [7] reported that the OPSFC with a density range of 1653 to 1683 kg/m3 exhibited 28-day splitting tensile strength of 1.46 to 1.68 MPa. However, it can be seen from the results for the splitting tensile strength in Table 5 that the OPSFGC17 produced a higher 28-day

 

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splitting tensile strength of 1.79 MPa compared to the OPSFC of similar density; this might be attributed to the geopolymerization of OPSFGC. Nambiar and Ramamurthy [28] reported that FA helps in uniform distribution of air-voids by providing a good uniform coating on each bubble and prevents merging bubbles, which leads to a higher strength. Furthermore, it can be seen from Table

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5 that as the density decreases, there is a slight decrease in the tensile strength and MOE, which might be attributed to the amount of pore volume in the OPSFGC. The ratio of the 28-day splitting

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tensile strength to the corresponding compressive strength of the OPSFGC was about 7.2%; this is

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comparable to the OPS concrete reported by Alengaram et al. [32]. Furthermore, the equation (Eq. 4) proposed by Shafigh et al. [33] to estimate the splitting tensile strength can be used to predict the

(4)

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strength of OPSFGC as it gives close results.

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where ft = 28-day splitting tensile strength (MPa) and fcu = 28-day compressive strength (MPa).

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Table 5 Mechanical properties (as of 28-day)

A previous study [7] showed that the flexural strength of OPSFC varies between 1.76 and

2.15 MPa with a density of about 1700 kg/m3; however, OPSFGC17 exhibited a higher flexural strength of 50% compared to the OPSFC of similar density. The ratio of 28-day flexural strength of OPSGC to its compressive strength varied between 0.12 and 0.18. Similar to the results in Table 5, Yang et al. [34] stated that for air-entrained concrete, although the flexural strength is reduced with the increase in the air content, this reduction is very low compared to the compressive strength of the concrete. Also, foam concrete with narrower air-void distributions showed higher strength [28]. The equation proposed for OPSC (Eq. 5) [33] was found to predict the flexural strength close to the experimental results of the OPSFGC.  

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(5)

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where fr = 28-day flexural strength (MPa) and fcu = 28-day compressive strength (MPa).

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Jones and McCarthy [35] reported that the MOE of foamed concrete is significantly lower than that of normal weight concrete (NWC) and lightweight concrete, typically varying from 1–8

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GPa for dry densities varying between 500 and 1500 kg/m3, respectively. The results shown in this investigation (Table 5) were within the range of 4–5 GPa for similar densities. The pore volume and

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MOE have a linear relationship, as the increase in the density of the geopolymer concrete enhances

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the MOE.

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3.5. Porosity and sorptivity

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The relationship between the porosity and the ODD of the specimen at the age of 28-day is

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shown in Fig. 6. It can be seen that porosity is mainly influenced by the ODD, which, in turn, attributed to the pore volumes. For OPSFGC, the porosity varies between 25% and 40% for densities in the range of 1300–1700 kg/m3. In addition, the test results shown in Fig. 6 are consistent with the compressive strength shown in Fig. 5, where the compressive strength has a linear relationship with the ODD. The addition of foam reduced the density due to the creation of tiny air bubbles in the geopolymer matrix, which resulted in higher porosity in the concrete. The effect of the porosity can be seen in the reduced compressive strength of the geopolymer concrete. Neville [24] described that the strength of concrete is affected by the volume of its overall voids. Kearsley and Wainwright [36] reported that the porosity is largely dependent on dry density and not on the ash type or ash content. They reported a porosity of 40% for foamed concrete mixture with a density and ash/cement ratio of 1500 kg/m3 and 3, respectively [36], which is comparable with the  

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porosity of 34% for the OPSFGC with an ODD of 1500 kg/m3. However, the mix OPSFGC13 with ODD of about 1314 kg/m3 was found to have similar porosity as that of foamed concrete of density 1500 kg/m3 as reported by Kearsley and Wainwright [36]. In addition, the size, distribution and tortuosity of pores, the type and distribution of aggregates, and the nature and the thickness of

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interfacial transition zone also have considerable effects on the permeable porosity of concrete [37].

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Fig. 6. Porosity as a function of ODD of OPSFGC and OPSNFGC

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Fig. 7 shows the result of the sorptivity for the OPSFGC and OPSNFGC specimens and it can be seen from the figure that the correlation coefficients (R2) exceed 0.97 for all the sorptivity

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data. An increase in the sorptivity was observed as the density of geopolymer concrete specimens increased, particularly at a density of 1300 kg/m3 with a sorptivity of 0.208 mm/min1/2. The

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sorptivity for FGC1500, FGC1700 and NFGC were 0.142, 0.111 and 0.109 mm/min1/2,

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respectively. It can be seen from the results of the OPSFGC17 and OPSNFGC, the sorptivity values

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are similar and this could be attributed to less number of pore volumes in the OPSFGC17. Further, the density difference between these two specimens was found about 50 kg/m3. Although the difference in the density between OPSFGC15 and OPSFGC13 was about 150 kg/m3, the sorptivity of the latter was found much higher when compared to the sorptivity between OPSFGC17 and OPSFGC15. Thus, it can be concluded that the foam volume plays a significant role in the sorptivity of the concrete. The sorptivity increases with an increase in foam volume for OPSFGC; this is similar to the findings reported by Panesar [38]. Nambiar and Ramamurthy [39] also opined that the sorptivity of foamed concrete is dependent on the number of pores in the capillary suction process. Therefore, as the foam volume increases, more capillary pores are formed that increased of the sorptivity, especially in the mix OPSFGC13. Besides that, it can be observed from Figs. 5 and 7 that as the sorptivity of geopolymer

 

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concrete increases, the compressive strength decreases. Tasdemir [40] reported similar findings as the capillary sorptivity coefficient of concrete decreased with the increase in the compressive strength. Further, Polat et al. [41] showed a strong correlation between the inverse proportion of the

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sorptivity and the density of the concrete.

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Fig. 7. Sorptivity of geopolymer concrete specimens at 28 days

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3.6. Thermal conductivity

The thermal conductivity of a material is the quantity of heat transmitted through a unit

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thickness in a direction perpendicular to a surface of unit area, due to a unit temperature gradient under given conditions [42]. The thermal conductivity of the four specimens of foamed and non-

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foamed concrete was compared with the conventional materials – block and brick. As seen from

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Fig. 8, the foamed and non-foamed OPSGC exhibited lower thermal conductivity compared to the

Ac ce p

conventional materials, block and brick. As for OPSGC, its lower density resulted in lower conductivity, which is comparable to the results reported by other researchers [4, 42, 43]. The results prove that the foamed and non-foamed OPSGC is superior in thermal resistivity compared to the conventional materials used, such as block and brick. The reduction in the conductivity was about 22%, 17%, 10% and 3% for OPSFGC13, OPSFGC15, OPSFGC17 and OPSNFGC, respectively, compared to the block. However, higher resistivity was found for foamed and nonfoamed concretes compared to brick; the reduction in percentage was 48%, 44%, 40% and 36% for OPSFGC13, OPSFGC15, OPSFGC17 and OPSNFGC specimens, respectively. The fine capillary pores present in clay bricks are responsible for transporting the moisture content through the brick, which increases the conductivity [6]. Saygılı and Baykal [43] reported that the decrease in the thermal conductivity is due to the increase of void ratio that decreased the unit weight of concrete.

 

Page 17 of 32

Since air is the poorest conductor compared to the solid and liquid due to its molecular structure [4], it contributes to the lower thermal conductivity in porous concrete. Also, Ramamurthy et al. [44] reported that foamed concrete has excellent thermal insulating properties due to its cellular microstructure. Another parallel is also drawn between the thermal conductivity and UPV; the

ip t

thermal conductivity is directly proportional to UPV as the concrete with low UPV value possesses

cr

a high air content.

an

us

Fig. 8. Thermal conductivity of specimens

M

Fig. 9. Relationship between thermal conductivity and compressive strength of specimens

The superior thermal resistivity of the OPSFGC compared to conventional materials would

d

enable foamed geopolymer concrete to be a viable material for energy efficiency. The comparison

te

of the thermal conductivity and its trend with the compressive strength is shown in Fig. 9. The

Ac ce p

compressive strength and the thermal conductivity were found to reduce with a decrease in the density of the concrete [45]. Alengaram et al. [6] have shown that the low density specimen has high air content inside due to the high quantity of foam, thus reducing the rate of heat transfer through the specimen. According to RILEM [46], OPSFGC17 and OPSNFGC can be categorized as structural grade concrete – Class-I with a compressive strength of more than 15 MPa; OPSFGC13 and OPSFGC15 fall under the category of

structural and insulating concrete – Class-II

(compressive strength between 3.5 and 15 MPa and the thermal conductivity is less than 0.75 W/m K ) .

Conclusions

 

Page 18 of 32

Thermal insulating materials play a vital role in reducing the power requirement, and, hence, reduce greenhouse gas emissions. This research focused on the development of structural and thermal insulating lightweight geopolymer concrete using locally available waste materials for sustainable development. Three types of foamed and one non-foamed geopolymer were produced

ip t

using OPS as lightweight aggregate; the thermal conductivity of the geopolymer concrete was compared with conventional materials, such as brick and block. From the experimental results, the

us

i.

cr

following conclusions can be drawn:

The addition of foam decreases the density of OPSFGC owing to the pore volume. All the

ii.

an

ODD of the OPSFGC specimens were within ± 50 kg/m3 of the target density. The UPV varied inversely with the density of geopolymer concrete and the UPV between 3

iii.

M

and 4 for the specimens of OPSFGC17 and OPSNFGC showed fair quality concrete. The porosity varied between 25% and 40% for the OPSFGC of densities in the range of

d

1300–1700 kg/m3 and high porosity of concrete lowered the compressive strength. In

The mechanical properties of OPSFGC and OPSNFGC, such as compressive, splitting

Ac ce p

iv.

te

addition, the sorptivity linearly decreased as the density increased.

tensile and flexural strengths, generally reduced with the reduction in the ODD; the MOE also followed a similar trend. The strength to density ratio of 17 for the OPSFGC17 was 54% higher than the corresponding normal weight concrete

v.

The thermal conductivity of OPSFGC and OPSNFGC results showed that an increase in the quantity of foam enabled its resistivity. The thermal conductivity of OPSFGC13 of about 0.47 W/mK was 22% and 48% lower than the conventional materials, block and brick, respectively used in walls.

vi.

The range of compressive strengths and the thermal conductivity of OPSFGC13 and OPSFGC15 were found to be about 8 and 13 MPa, and 0.47 and 0.50 W/m K , respectively, and hence these could be categorized as structural and insulating concrete. The non-foamed

 

Page 19 of 32

OPSNFGC produced a higher compressive strength of about 30 MPa and falls under the structural concrete as per the RILEM classification.

Acknowledgement

ip t

This research work was funded by the University of Malaya under the High Impact Research Grant

cr

(HIRG) No. UM.C/625/1/HIR/206 (Synthesis of Energy Redeemable Material from Local Wastes for Buildings). The authors are grateful to the Vice-Chancellor of University of Malaya for his

us

noteworthy effort in securing the funding for the above said project.

P.C. Aı tcin, Cements of yesterday and today: Concrete of tomorrow, Cement and Concrete Research, 30 (9) (2000) 1349-1359.

A.M. Papadopoulos, E. Giama, Environmental performance evaluation of thermal insulation

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[2]

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[1]

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materials and its impact on the building, Building and Environment, 42 (5) (2007) 2178-

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properties of lightweight aggregate concrete with a high volume of entrained air, Construction and Building Materials, 29 (2012) 193-200. [6]

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elasticity of palm kernel shell concrete, Materials & Design, 32 (4) (2011) 2143-2148. P. Shafigh, M.Z. Jumaat, H. Mahmud, U.J. Alengaram, A new method of producing high

strength oil palm shell lightweight concrete, Materials & Design, 32 (10) (2011) 4839-4843.

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W. Tangchirapat, T. Saeting, C. Jaturapitakkul, K. Kiattikomol, A. Siripanichgorn, Use of waste ash from palm oil industry in concrete, Waste Management, 27 (1) (2007) 81-88.

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of thermal resistance by means of guarded hot plate and heat flow meter methods. Dry and moist products of medium and low thermal resistance, British Standards Institution, London,

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permeable porosity of concrete, Cement and Concrete Research, 35 (5) (2005) 1008-1013. BS EN 12390-3, Testing hardened concrete, in: Compressive strength of test specimens,

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E.K.K. Nambiar, K. Ramamurthy, Air‐void characterisation of foam concrete, Cement and

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concrete containing palm oil fuel ash and rice husk–bark ash, Construction and Building Materials, 21 (7) (2007) 1492-1499.

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Structural lightweight aggregate concrete, Blackie Academic and Professional, Glassgow,

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1993, pp. 19-44.

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shell as lightweight aggregate in concrete – A review, Construction and Building Materials,

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shell lightweight aggregate concrete: A review, International Journal of Physical Sciences, 5 (14) (2010) 2127-2134.

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entraining agent, Cement and Concrete Research, 30 (8) (2000) 1313-1317. [35]

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sorptivity coefficient of concrete, Cement and Concrete Research, 33 (10) (2003) 16371642.

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on the physico-mechanical properties of concrete exposed to freeze–thaw cycles, Cold

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Regions Science and Technology, 60 (1) (2010) 51-56.

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mechanical properties and thermal conductivity of lightweight concrete, Energy and

A. Saygılı, G. Baykal, A new method for improving the thermal insulation properties of fly

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Buildings, 43 (2-3) (2011) 671-676.

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of foam concrete, Cement and Concrete Composites, 31 (6) (2009) 388-396.

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Page 24 of 32

     

Table 1 Chemical composition of Class-F FA and POFA POFA

ASTM C618

Silica (SiO2)

57.6

63.4

-

Ferric oxide (Fe2O3)

5.8

4.2

-

Calcium oxide (CaO)

0.2

4.3

-

Magnesium oxide (MgO)

0.9

3.7

Potassium oxide (K2O)

0.9

6.3

Sulphuric anhydride (SO3)

0.2

0.9

≤ 4.0

Alumina (Al2O3)

28.9

5.5

-

Loss of ignition (LOI)

3.6

6.0

≤ 10.0

SiO2 + Al2O3 + Fe2O3

92.3

73.1

≥ 70.0

Physical property

cr -

-

us

M

Table 2 Physical properties of OPS

OPS 1.36

Bulk density (loose) (kg/m3)

589

d

Specific gravity (saturated surface dry) 3

652

Fineness modulus

5.90

Water absorption (24 h) (%)

24.39

te

Bulk density (compacted) (kg/m )

Ac ce p

ip t

Class-F FA

an

Chemical composition (%)

Table 3 Mixture proportions of OPSFGC and OPSNFGC Mix

Target density

OPS

Sand

FA

POFA

Alkaline Water solution

SP

Foam volume

(kg/m3)

OPSFGC13

1300

294

832

392

98

269

73.4

7.3

31.7

OPSFGC15

1500

294

832

392

98

269

73.4

7.3

25.6

OPSFGC17

1700

294

832

392

98

269

73.4

7.3

16.5

OPSNFGC

-

294

832

392

98

269

73.4

7.3

-

       

Page 25 of 32

   

Table 4 ODD and compressive strength of OPSFGC and OPSNFGC

OPSFGC15

Oven-dry density (kg/m3)

3

1331

7

1309

14

1327

28

1291

3

1469

7

1466

14

1465

28

1467

1500

1700

OPSNFGC

1735

14

1723

28

1721

3

1762

7

1783

14

1794

28

1791

Ac ce p

OPSFGC17

te

7

1730

d

3

-

Strength/density ratio (N/mm2 kg/m3) x 1000 5.5 6.0

6.1

us

cr

1300

Compressive strength (MPa) 7.3 (0.2) 7.8 (0.6) 8.1 (0.9) 8.3 (0.7) 9.8 (1.2) 11.5 (0.9) 12.9 (0.6) 13.5 (1.1) 23.5 (1.3) 24.7 (0.6) 24.9 (1.8) 25.8 (0.5) 22.4 (1.7) 25.7 (0.8) 25.8 (1.5) 30.1 (1.30)

ip t

Age (days)

an

OPSFGC13

Target density (kg/m3)

M

Specimen

6.4

6.7 7.8 8.8 9.2 13.6 14.2 14.4 15.0 13.4 14.4 14.4 16.8

Note: The standard deviations (in MPa) of the corresponding compressive strengths are shown in the brackets.

         

 

Page 26 of 32

 

Table 5 Mechanical properties (as of 28-day)

Specimen

Compressive strength

Splitting tensile strength

Flexural strength

Modulus of elasticity (x103)

0.62

1.48

OPSFGC15

13.46

0.99

2.16

OPSFGC17

25.83

1.79

3.23

OPSNFGC

30.06

2.41

3.53

6.13

7.44

an

3.74

4.67

cr

8.32

us

OPSFGC13

ip t

(MPa)

Ac ce p

te

d

M

 

 

Page 27 of 32

ip t cr us an

 

Ac ce p

te

d

 

M

Fig. 1. Thermal conductivity test equipment

Fig. 2. The schematic diagram of thermal conductivity test

 

 

Page 28 of 32

3.5 3.0

R² = 0.994

2.5

20

2.0

ip t

25

28-day UPV (km/s)

30

R² = 0.9697

1.5

15

cr

28-day compressive strength (MPa)

35

1.0

10

Compressive strength

us

5

0.5

UPV 1300

1400

1500

1600

1700

an

0 1200

1800

0.0 1900

Oven-dry density (kg/m3)

3.0

7-day UPV 14-day UPV

Ac ce p

UPV (km/s)

2.8

3-day UPV

te

3.2

d

M

Fig. 3. Relationship between the compressive strength, ODD and UPV

2.6

28-day UPV

2.4 2.2 2.0 1.8 1.6

OPSFGC13

OPSFGC15

OPSFGC17

OPSNFGC

Specimen Fig. 4. Ultrasonic pulse velocity (UPV) of OPSFGC and OPSNFGC

 

Page 29 of 32

OPSFGC13

OPSFGC15

OPSFGC17

OPSNFGC

30 25 20

ip t

15 10

cr

Compressive strength (MPa)

35

0 0

5

10

15

us

5

20

an

Age (Days)

25

30

Fig. 5. Development of compressive strength

Ac ce p

te

d

M

 

 

Page 30 of 32

45.0

35.0 R² = 0.9713

ip t

Porosity (%)

40.0

30.0

20.0 1200

1300

1400

1500

1600

1700

1800

1900

an

Oven-dry density (kg/m3)

us

cr

25.0

Fig. 6. Porosity as a function of ODD of OPSFGC and OPSNFGC

M

OPSFGC13 OPSFGC15

2.0

d

OPSFGC17 OPSNFGC

te

1.5

1.0

Ac ce p

Cumulative absorption (mm3/mm2)

2.5

0.5

0.0

0

1

2

3

4

5

6

7

8

9

Time (min1/2)

Fig. 7 Sorptivity of geopolymer concrete specimens at 28 days

 

Page 31 of 32

0.90

0.9 0.8 0.7

0.60

0.58

0.6

ip t

0.47

0.5

0.54

0.50

0.4

cr

Thermal conductivity (W/mK)

1.0

0.2 OPSFGC13

OPSFGC15

OPSFGC17

us

0.3 OPSNFGC

Specimen

Block

Brick

an

Fig. 8. Thermal conductivity of specimens

0.6

OPSFGC15

0.5

OPSFGC17

0.5

OPSNFGC

R² = 0.9646

te

0.5

M

OPSFGC13

d

0.6

0.5 0.5

Ac ce p

Thermal conductivity (W/m K )

0.6

0.4 0.4 0.4

0

5

10

15

20

25

30

35

28-day compressive strength (MPa)

Fig. 9. Relationship between thermal conductivity and compressive strength of specimens  

 

 

Page 32 of 32