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Incorporation of expanded vermiculite lightweight aggregate in cement mortar
Construction and Building Materials 179 (2018) 302–306
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Technical note
Incorporation of expanded vermiculite lightweight aggregate in cement mortar Kim Hung Mo a,⇑, Hong Jie Lee a, Michael Yong Jing Liu a, Tung-Chai Ling b,⇑ a
Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, Hunan, China b
a r t i c l e
i n f o
Article history: Received 26 July 2017 Received in revised form 7 May 2018 Accepted 26 May 2018
Keywords: Expanded vermiculite Lightweight aggregate Heat resistance Elevated temperature
a b s t r a c t This investigation presents an evaluation of the properties of cement mortars containing expanded vermiculite as partial sand replacement. When the expanded vermiculite was included at 30% and 60% replacement levels, the flow diameter was higher compared to the plain mortar without expanded vermiculite. The porous lightweight nature of the expanded vermiculite also contributed to the reduction in the unit weight and compressive strength of mortars, as well as increased water absorption. Although weight loss of the expanded vermiculite mortars subjected to elevated temperature was increased, the expanded vermiculite had positive effect in providing heat resistance and thermal stability to the mortars, observed by the reduction of compressive strength loss of mortars upon exposure to elevated temperatures. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Nowadays, there is increasing interest in the development of construction materials to resist high temperature, in particular for application in building structures. The resistance towards elevated temperature of building materials is of significant importance, particularly during the course of a fire event. For instance, in concrete or cement-based materials, fire could cause damage or in worse case, failure of building structures due to risk of spalling and significant loss of materials strength. Accordingly, plastering mortars with improved resistance towards elevated temperature could provide a solution for the aforementioned concern. One of the methods is through the introduction of thermally stable and porous aggregate in the mortar. This is because conventionally used siliceous aggregate may cause distress at temperature of about 570 °C and de-carbonation at temperature above 700 °C, resulting in significant loss of strength [1]. In the past, concrete with various porous lightweight aggregate materials such as pumice [2], scoria [3], expanded clay [4], palm oil clinker [5], oil palm shell [6] and plastic aggregate [7] were researched with the aim of investigating the performance when subjected to elevated temperatures.
⇑ Corresponding authors. E-mail addresses: [email protected] (K.H. Mo), [email protected] (T.-C. Ling). https://doi.org/10.1016/j.conbuildmat.2018.05.219 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
In recent times, non-structural lightweight aggregates such as vermiculite, perlite and expanded polystyrene aggregates which are very low in density were incorporated as partial sand replacement in cement-based mortars. The prime advantage of these materials is the good insulation properties owing to their highly porous nature. The improved thermal insulation performance of cement-based materials incorporating these aggregates were evidenced in literatures [8,9]. Based on this, because of the porous structure of these materials, there is also potential in utilizing these materials in plastering mortars for enhanced resistance towards elevated temperature. While the use of expanded perlite is more widespread [10], research on the utilization of vermiculite in cement-based materials is fairly limited and only recently garnering increased attention. Vermiculite is hydrated magnesiumaluminium-iron silicate, formed by the alteration of mica and appear in the forms of flakes. When exfoliated by heating to temperature of 900 °C or higher, water is released and the flakes expand into very lightweight porous material. The resulting expanded vermiculite is considered to be heat resistant and exhibits good sound and thermal insulation properties. Thus, this research aims on exploring the possibility of incorporating expanded vermiculite as partial sand replacement in cement-based plastering mortar, and focuses on the performance when subjected to elevated temperatures. Additionally, the effects of incorporating expanded vermiculite were investigated with
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K.H. Mo et al. / Construction and Building Materials 179 (2018) 302–306
regards to other properties of mortar relevant to plastering uses, such as consistency, compressive strength and water absorption.
River sand
Expanded vermiculite
100
2.1. Materials Type I Ordinary Portland cement with specific gravity of 3.15 was used for all mixes in the study. River sand with maximum size of 2.36 mm was selected as the fine aggregate used in the mortars. The specific gravity of river sand was found to be 2.62. Expanded vermiculite (Fig. 1) with specific gravity of 1.17 (maximum size of 2.36 mm) was used as partial river sand replacement. The expanded vermiculite was used in saturated surface dry condition for the prepared mortars. The particle size distributions of the river sand and expanded vermiculite are shown in Fig. 2. Mixing water was obtained from pipe water in the laboratory.
Percentage passing (%)
90
2. Materials and methods
80 70 60 50 40 30 20 10 0 0.1
1
10
Particle size (mm) Fig. 2. Particle size distribution of river sand and expanded vermiculite.
2.2. Mix proportions A total of four mixes were prepared in this investigation as shown in Table 1. Mixes C0 and C1 were control mortars without expanded vermiculite as sand replacement with targeted 28-day compressive strength of 30 MPa and 15 MPa, respectively. On the other hand, mixes V30 and V60 were mortars prepared with expanded vermiculite at 30% and 60% of partial sand replacement (by volume), respectively. 2.3. Mixing
Table 1 Mix proportions. Mix
Water/cement ratio
Sand/cement ratio
Vermiculite/cement ratio
C0 C1 V30 V60
0.52 0.71 0.52 0.52
2.57 4.21 1.80 1.03
– – 0.19 0.67
Mixing of mortar was done using a table top mixer in the laboratory. The cement and fine aggregates (river sand and expanded vermiculite) were first allowed to mix homogenously for about 30 s. The water was then added without stopping the mix and the process lasted for 3 min to ensure thorough mixing. The fresh mortars were subjected to flow table test before poured into mortar moulds and compacted on a vibration table. 2.4. Test methods Flow table test was carried out on the fresh mortars in accordance with ASTM C1437-15 in order to determine the consistency of the mortars. The test was performed by filling, tamping of fresh mortars in the mould and dropping the mortar for 25 times within 15 s upon removal of the mould. The diameter of the flow spread of the fresh mortar was recorded subsequently (Fig. 3). Cubic mortars measuring 50 mm3 were de-moulded 24 h after casting and the hardened mortars were cured in laboratory condition until the age of testing. Compressive strength tests were carried out on the cubic mortars during the 7th and 28th days age, and the tests were performed according to BS EN 12390-3: 2009. Additionally, the residual compressive strength of the 28-day aged cubic mortars were evaluated upon exposure to elevated temperatures of 600 °C and 800 °C. The mortars were kept in a muffle furnace at the selected temperature for 1 h, and then allowed to cool internally for a further hour before the furnace was opened (Fig. 4). The heating curves of the muffle furnace up to 600 °C and 800 °C
Fig. 3. Measurement of flow spread diameter. are shown in Fig. 5. After the mortars were removed from the furnace, the mortars were allowed to cool in air in the laboratory for a further 2 h before the residual compressive strength of mortars were determined. Besides that, the cubic mortars at 28-day age were subjected to water absorption test. In order to remove moisture, the mortars were first dried in oven at 105 °C for 24 h. Subsequently, the dry weight of the mortars were taken and immersed in water. The saturated weights of the mortars after immersion for 30 min and 72 h were taken to determine the initial and final water absorption values, respectively. The water absorption of mortar was also similarly tested and calculated previously by Mo et al. [11].
3. Results and discussion 3.1. Consistency
Fig. 1. Expanded vermiculite.
The consistency of the fresh mortars presented in Fig. 6 were determined based on the flow diameter recorded from flow table
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the expanded vermiculite compared to the river sand, and hence reduced the water demand of the fresh mortar. Koksal et al. [13] reported that increase in vermiculite content in mortar containing only vermiculite as fine aggregate also increase flow of the mortars investigated. 3.2. Unit weight The unit weight of mixes C0, C1, V30 and V60 was found to be 2023 kg/m3, 1991 kg/m3, 1774 kg/m3 and 1485 kg/m3, respectively. The unit weight could be reduced by 12% and 27% when expanded vermiculite was incorporated as 30% and 60% volume replacement of sand. The reduction in weight is due to substitution of a lighter expanded vermiculite particle for the river sand, and the porous and lighter nature of the expanded vermiculite is caused by the exfoliation process during production of the material. The decrease in unit weight is beneficial towards self-weight reduction in wall system when utilized as plastering material. Fig. 4. Heating of mortars in a muffle furnace.
3.3. Compressive strength 900 800 700 600 500 400 300 200 100 0 0
20
40
60
80
100
120
140
160
Time (minutes) Fig. 5. Heating curves.
250
Flow diameter (mm)
200
150
100
50
The compressive strength of mortars at 7 and 28 days are presented in Fig. 7. For mortars without expanded vermiculite, the compressive strength at both ages was higher for the case of the C0 mortar due to the lower w/c ratio; when expanded vermiculite was included as partial sand replacement, the compressive strength was noticeably reduced as the replacement level was increased. The tendency of decrease in compressive strength in the expanded vermiculite mortars could be attributed to the porous soft structure and hence weaker strength of expanded vermiculite [14]. Weaker aggregate provides lower resistance towards crack propagation and therefore reduces the load-bearing capacity of the mortars. Besides that, the lower content of fines present in expanded vermiculite could result in less favourable particle packing and negatively affect the strength of the mortar. In this study, reduction of about 50% and 63% was found when expanded vermiculite was incorporated at volume replacements of 30% and 60%, respectively. Reduced strength of mortar due to increased volume of lightweight aggregates such as expanded perlite [15] and expanded polystyrene [16] were previously reported. Nevertheless, the 28-day compressive strength of expanded vermiculite mortars between 12.1 and 16.6 MPa obtained in this study is comparable with those observed by Schackow et al. [8]. It is worth noting that the gain in strength from 7 days to 28 days of mortars containing expanded vermiculite (V30 and V60), was generally higher than the mortars without expanded vermiculite (C0 and C1). The said strength gain was 35% and 24% respectively for V30 and V60 whereas it was only 19% and 12% for C0 and C1, respectively. A
0 C0
C1
V30
V60
Mix
35
test. The flow diameter recorded was 162 mm, 226 mm, 181 mm and 179 mm, respectively for mixes C0, C1, V30 and V60. The flow obtained for all of the mortars is considered to be sufficient, as Lucas et al. [12] reported that consistency of 175 mm is considered to be sufficient for mortars. Expectedly, the mix C1 exhibited higher flow compared to the mix C0 due to the higher water to cement (w/c) ratio. The inclusion of expanded vermiculite as partial sand replacement yielded improved flow, as demonstrated with the increase of about 11% in mixes V30 and V60 compared to the corresponding control mortar C0. This increase could be attributed to the lower fines content of sizes below 150 lm in
Compressive strength (MPa)
Fig. 6. Flow diameter of fresh mortars.
30 7 day 25 28 day 20 15 10 5 0 C0
C1
V30
V60
Mix Fig. 7. Compressive strength of mortars at 7 and 28 days.
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possible reason could be the releasing of water internally from the expanded vermiculite which facilitated the cement hydration as well as some minor pozzolanic activity of the expanded vermiculite. 3.4. Residual strength
3.5. Water absorption Table 3 shows the initial and final water absorption values of the 28-day age mortars. The water absorption values give indica-
Table 2 Residual compressive strength of mortars subjected to elevated temperatures. Mix
C0 C1 V30 V60 *
Fig. 8. Cracks observed in mortar exposed to 800 °C.
100 95 C0 90 V30
Weight (%)
Table 2 presents the residual compressive strength of mortars after exposure to elevated temperatures of 600 °C and 800 °C. For all mortars, it is clear that the compressive strength decreased when the mortars were exposed to higher temperatures. The strength loss at 600 °C was possibly caused by the decomposition of calcium hydroxide whereas at 800 °C, greater strength loss experience was could be due to disintegration of the calcium silicate hydrate gels. Very fine micro-cracks could only be observed in the mortars exposed to 600 °C whereas larger cracks could be found in the mortars exposed to 800 °C when the cracks were checked with a digital microscope as shown in Fig. 8. When compared with the mix C0, although the V30 and V60 mortars had lower residual strengths, the percentage in strength loss was lesser. It was found that the strength loss was about 30% and 70% respectively for exposure temperatures of 600 °C and 800 °C for the expanded vermiculite mortars whereas the strength loss was higher at 44% and 75% for C0 mortar at the corresponding temperatures (Table 2). An additional set of mortar C1 was prepared to facilitate comparison of mortars with similar 28-day compressive strength when exposed to elevated temperature. It could be seen that in this case, not only was the strength loss of expanded vermiculite mortars was lower than C1, the residual strength was at least equal, or higher (for the case of V30) at the elevated temperatures. The positive contribution of the expanded vermiculite in lowering the compressive strength decline could be attributed to the presence of voids within the aggregate, which act as heat insulator and relieve the internal pressure formation [17]. In addition, the expanded vermiculite could close and fill micro-cracks due to its expansion [13]. The thermal gravimetric analysis (TGA) results in Fig. 9 shows that the weight loss of mortar containing vermiculite, namely V30, was lower compared to the corresponding control mortar C0 when temperature was increased at a rate of 5 °C/min. This corresponds well to the residual strength results whereby the vermiculite mortars exhibited higher strength retention upon exposure to elevated temperature. From the TGA curves, it could be seen that the difference in weight loss between the V30 and C0 mortars increased as the heating temperature was increased. This implies that the vermiculite had positive effect in insulating heat, particularly at higher temperature. Based on the results shown, it could be said that the expanded vermiculite provided good thermal stability and enhanced the heat resistance of the mortars.
85 80 75 70 65 0
200
400
600
800
1000
1200
Fig. 9. Thermal gravimetric analysis of mortars.
Table 3 Water absorption of mortars. Mix
Initial water absorption (%)
Final water absorption (%)
C0 C1 V30 V60
6.31 7.96 14.17 22.42
9.45 8.97 17.09 27.70
tion of the permeable voids present in the mortar. The increase in the water absorption of expanded vermiculite mortars is likely due to the porous nature of the expanded vermiculite. Moreover, since the expanded vermiculite used had lower finer particles and generally coarser than river sand, the packing of mortars could be less effective and hence the mortars exhibited higher water absorption values. Also, as suggested by Khonsari et al. [18] with the use of expanded perlite, the rise in water absorption can be caused by pores present in the weak cement-aggregate interface. The increase in water absorption with higher expanded vermiculite content was also reported in few researches [13,19]. 4. Conclusion
Compressive strength (MPa) Room temperature
600 °C
800 °C
33.03 13.77 16.62 12.11
18.62 ( 44%) 8.74 ( 37%) 11.61 ( 30%) 8.36 ( 31%)
8.42 3.93 4.97 3.99
Values in bracket represent percentage loss of compressive strength.
( ( ( (
75%) 71%) 70%) 67%)
Based on the experimental results obtained in this research, the following can be concluded: a. Incorporation of expanded vermiculite as partial sand replacement increased the flow diameter of the fresh mortars.
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b. Due to its lightweight nature, the presence of expanded vermiculite as partial sand substitute reduced the unit weight and compressive strength of mortar. c. The expanded vermiculite mortars exhibited enhanced resistance towards elevated temperature as lower compressive strength loss was observed compared to plain mortar. d. Water absorption of mortar was increased when the expanded vermiculite dosage as partial sand replacement was increased. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgement The authors is grateful for the funding provided by University of Malaya under the grants BK050-2016 and PG163-2015A. References [1] S. Aydin, Development of a high-temperature-resistant mortar by using slag and pumice, Fire Safe. J. 43 (8) (2008) 610–617. [2] T. Uygunoglu, I.B. Topcu, Thermal expansion of self-consolidating normal and lightweight aggregate concrete at elevated temperature, Constr. Build. Mater. 23 (9) (2009) 3063–3069. [3] H. Tanyildizi, A. Coskun, The effect of high temperature on compressive strength and splitting tensile strength of structural lightweight concrete containing fly ash, Constr. Build. Mater. 22 (11) (2008) 2269–2275. [4] O.A. Abdulkareem, A.M.M. Al Bakri, H. Kamarudin, K.I. Nizar, A.A. Saif, Effects of elevated temperatures on the thermal behavior and mechanical performance of fly ash geopolymer paste, mortar and lightweight concrete, Constr. Build. Mater. 50 (2014) 377–387. [5] M.Z. Jumaat, U.J. Alengaram, R. Ahmmad, S. Bahri, A.B.M.S. Islam, Characteristics of palm oil clinker as replacement for oil palm shell in lightweight concrete subjected to elevated temperature, Constr. Build. Mater. 101 (2015) 942–951.
[6] K.H. Mo, U.J. Alengaram, M.Z. Jumaat, M.Y.J. Liu, Contribution of acrylic fibre addition and ground granulated blast furnace slag on the properties of lightweight concrete, Constr. Build. Mater. 95 (2015) 686–695. [7] F. Colangelo, R. Cioffi, B. Liguori, F. Iucolano, Recycled polyolefins waste as aggregates for lightweight concrete, Compos. Part B: Eng. 106 (2016) 234–241. [8] A. Schackow, C. Effting, M.V. Folgueras, S. Guths, G.A. Mendes, Mechanical and thermal properties of lightweight concretes with vermiculite and EPS using air-entraining agent, Constr. Build. Mater. 57 (2014) 190–197. [9] O. Sengul, S. Azizi, F. Karaosmanoglu, M.A. Tasdemir, Effect of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete, Energy Build. 43 (2) (2011) 671–676. [10] A.M. Rashad, A synopsis about perlite as building material – a best practice guide for Civil Engineer, Constr. Build. Mater. 121 (2016) 338–353. [11] K.H. Mo, C.S. Bong, U.J. Alengaram, M.Z. Jumaat, S.P. Yap, Thermal conductivity, compressive and residual strength evaluation of polymer fibre-reinforced high volume palm oil fuel ash blended mortar, Constr. Build. Mater. 130 (2017) 113–121. [12] J. Lucas, J. de Brito, R. Veiga, C. Farinha, The effect of using sanitary ware as aggregates on rendering mortars’ performance, Mater. Des. 91 (2016) 155– 164. [13] F. Koksal, O. Gencel, M. Kaya, Combined effect of silica fume and expanded vermiculite on properties of lightweight mortars at ambient and elevated temperatures, Constr. Build. Mater. 88 (2015) 175–187. [14] H. Shoukry, M.F. Kotkata, S.A. Abo-El-Enein, M.S. Morsy, S.S. Shebl, Enhanced physical, mechanical and microstructural properties of lightweight vermiculite cement composites modified with nano metakaolin, Constr. Build. Mater. 112 (2016) 276–283. [15] M. Lanzon, P.A. Garcia-Ruiz, Lightweight cement mortars: advantages and inconveniences of expanded perlite and its influence on fresh and hardened state and durability, Constr. Build. Mater. 22 (8) (2008) 1798–1806. [16] V. Ferrandiz-Mas, T. Bond, E. Garcia-Alcocel, C.R. Cheeseman, Lightweight mortars containing expanded polystyrene and paper sludge ash, Constr. Build. Mater. 61 (2014) 282–292. [17] S.M.A. El-Gamal, F.S. Hashem, M.S. Amin, Thermal resistance of hardened cement pastes containing vermiculite and expanded vermiculite, J. Therm. Anal. Calorim. 109 (1) (2012) 217–226. [18] V. Khonsari, E. Eslami, A. Anvari, Effects of expanded perlite aggregate (EPA) on the mechanical behavior of lightweight concrete, in: B.H. Oh (Ed.), Fracture Mechanics of Concrete and Concrete Structures – high Performance, Fiber Reinforced Concrete, Special Loadings and Structural Applications, Korea Concrete Institute, 2010, pp. 1354–1361. [19] L. Li, X. Zhou, Y. Li, C. Gong, L. Lu, X. Fu, W. Tao, Water absorption and water/ fertilizer retention performance of vermiculite modified sulphoaluminate cementitious materials, Constr. Build. Mater. 137 (2017) 224–233.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Technical note
Incorporation of expanded vermiculite lightweight aggregate in cement mortar Kim Hung Mo a,⇑, Hong Jie Lee a, Michael Yong Jing Liu a, Tung-Chai Ling b,⇑ a
Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, Hunan, China b
a r t i c l e
i n f o
Article history: Received 26 July 2017 Received in revised form 7 May 2018 Accepted 26 May 2018
Keywords: Expanded vermiculite Lightweight aggregate Heat resistance Elevated temperature
a b s t r a c t This investigation presents an evaluation of the properties of cement mortars containing expanded vermiculite as partial sand replacement. When the expanded vermiculite was included at 30% and 60% replacement levels, the flow diameter was higher compared to the plain mortar without expanded vermiculite. The porous lightweight nature of the expanded vermiculite also contributed to the reduction in the unit weight and compressive strength of mortars, as well as increased water absorption. Although weight loss of the expanded vermiculite mortars subjected to elevated temperature was increased, the expanded vermiculite had positive effect in providing heat resistance and thermal stability to the mortars, observed by the reduction of compressive strength loss of mortars upon exposure to elevated temperatures. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Nowadays, there is increasing interest in the development of construction materials to resist high temperature, in particular for application in building structures. The resistance towards elevated temperature of building materials is of significant importance, particularly during the course of a fire event. For instance, in concrete or cement-based materials, fire could cause damage or in worse case, failure of building structures due to risk of spalling and significant loss of materials strength. Accordingly, plastering mortars with improved resistance towards elevated temperature could provide a solution for the aforementioned concern. One of the methods is through the introduction of thermally stable and porous aggregate in the mortar. This is because conventionally used siliceous aggregate may cause distress at temperature of about 570 °C and de-carbonation at temperature above 700 °C, resulting in significant loss of strength [1]. In the past, concrete with various porous lightweight aggregate materials such as pumice [2], scoria [3], expanded clay [4], palm oil clinker [5], oil palm shell [6] and plastic aggregate [7] were researched with the aim of investigating the performance when subjected to elevated temperatures.
⇑ Corresponding authors. E-mail addresses: [email protected] (K.H. Mo), [email protected] (T.-C. Ling). https://doi.org/10.1016/j.conbuildmat.2018.05.219 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
In recent times, non-structural lightweight aggregates such as vermiculite, perlite and expanded polystyrene aggregates which are very low in density were incorporated as partial sand replacement in cement-based mortars. The prime advantage of these materials is the good insulation properties owing to their highly porous nature. The improved thermal insulation performance of cement-based materials incorporating these aggregates were evidenced in literatures [8,9]. Based on this, because of the porous structure of these materials, there is also potential in utilizing these materials in plastering mortars for enhanced resistance towards elevated temperature. While the use of expanded perlite is more widespread [10], research on the utilization of vermiculite in cement-based materials is fairly limited and only recently garnering increased attention. Vermiculite is hydrated magnesiumaluminium-iron silicate, formed by the alteration of mica and appear in the forms of flakes. When exfoliated by heating to temperature of 900 °C or higher, water is released and the flakes expand into very lightweight porous material. The resulting expanded vermiculite is considered to be heat resistant and exhibits good sound and thermal insulation properties. Thus, this research aims on exploring the possibility of incorporating expanded vermiculite as partial sand replacement in cement-based plastering mortar, and focuses on the performance when subjected to elevated temperatures. Additionally, the effects of incorporating expanded vermiculite were investigated with
303
K.H. Mo et al. / Construction and Building Materials 179 (2018) 302–306
regards to other properties of mortar relevant to plastering uses, such as consistency, compressive strength and water absorption.
River sand
Expanded vermiculite
100
2.1. Materials Type I Ordinary Portland cement with specific gravity of 3.15 was used for all mixes in the study. River sand with maximum size of 2.36 mm was selected as the fine aggregate used in the mortars. The specific gravity of river sand was found to be 2.62. Expanded vermiculite (Fig. 1) with specific gravity of 1.17 (maximum size of 2.36 mm) was used as partial river sand replacement. The expanded vermiculite was used in saturated surface dry condition for the prepared mortars. The particle size distributions of the river sand and expanded vermiculite are shown in Fig. 2. Mixing water was obtained from pipe water in the laboratory.
Percentage passing (%)
90
2. Materials and methods
80 70 60 50 40 30 20 10 0 0.1
1
10
Particle size (mm) Fig. 2. Particle size distribution of river sand and expanded vermiculite.
2.2. Mix proportions A total of four mixes were prepared in this investigation as shown in Table 1. Mixes C0 and C1 were control mortars without expanded vermiculite as sand replacement with targeted 28-day compressive strength of 30 MPa and 15 MPa, respectively. On the other hand, mixes V30 and V60 were mortars prepared with expanded vermiculite at 30% and 60% of partial sand replacement (by volume), respectively. 2.3. Mixing
Table 1 Mix proportions. Mix
Water/cement ratio
Sand/cement ratio
Vermiculite/cement ratio
C0 C1 V30 V60
0.52 0.71 0.52 0.52
2.57 4.21 1.80 1.03
– – 0.19 0.67
Mixing of mortar was done using a table top mixer in the laboratory. The cement and fine aggregates (river sand and expanded vermiculite) were first allowed to mix homogenously for about 30 s. The water was then added without stopping the mix and the process lasted for 3 min to ensure thorough mixing. The fresh mortars were subjected to flow table test before poured into mortar moulds and compacted on a vibration table. 2.4. Test methods Flow table test was carried out on the fresh mortars in accordance with ASTM C1437-15 in order to determine the consistency of the mortars. The test was performed by filling, tamping of fresh mortars in the mould and dropping the mortar for 25 times within 15 s upon removal of the mould. The diameter of the flow spread of the fresh mortar was recorded subsequently (Fig. 3). Cubic mortars measuring 50 mm3 were de-moulded 24 h after casting and the hardened mortars were cured in laboratory condition until the age of testing. Compressive strength tests were carried out on the cubic mortars during the 7th and 28th days age, and the tests were performed according to BS EN 12390-3: 2009. Additionally, the residual compressive strength of the 28-day aged cubic mortars were evaluated upon exposure to elevated temperatures of 600 °C and 800 °C. The mortars were kept in a muffle furnace at the selected temperature for 1 h, and then allowed to cool internally for a further hour before the furnace was opened (Fig. 4). The heating curves of the muffle furnace up to 600 °C and 800 °C
Fig. 3. Measurement of flow spread diameter. are shown in Fig. 5. After the mortars were removed from the furnace, the mortars were allowed to cool in air in the laboratory for a further 2 h before the residual compressive strength of mortars were determined. Besides that, the cubic mortars at 28-day age were subjected to water absorption test. In order to remove moisture, the mortars were first dried in oven at 105 °C for 24 h. Subsequently, the dry weight of the mortars were taken and immersed in water. The saturated weights of the mortars after immersion for 30 min and 72 h were taken to determine the initial and final water absorption values, respectively. The water absorption of mortar was also similarly tested and calculated previously by Mo et al. [11].
3. Results and discussion 3.1. Consistency
Fig. 1. Expanded vermiculite.
The consistency of the fresh mortars presented in Fig. 6 were determined based on the flow diameter recorded from flow table
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K.H. Mo et al. / Construction and Building Materials 179 (2018) 302–306
the expanded vermiculite compared to the river sand, and hence reduced the water demand of the fresh mortar. Koksal et al. [13] reported that increase in vermiculite content in mortar containing only vermiculite as fine aggregate also increase flow of the mortars investigated. 3.2. Unit weight The unit weight of mixes C0, C1, V30 and V60 was found to be 2023 kg/m3, 1991 kg/m3, 1774 kg/m3 and 1485 kg/m3, respectively. The unit weight could be reduced by 12% and 27% when expanded vermiculite was incorporated as 30% and 60% volume replacement of sand. The reduction in weight is due to substitution of a lighter expanded vermiculite particle for the river sand, and the porous and lighter nature of the expanded vermiculite is caused by the exfoliation process during production of the material. The decrease in unit weight is beneficial towards self-weight reduction in wall system when utilized as plastering material. Fig. 4. Heating of mortars in a muffle furnace.
3.3. Compressive strength 900 800 700 600 500 400 300 200 100 0 0
20
40
60
80
100
120
140
160
Time (minutes) Fig. 5. Heating curves.
250
Flow diameter (mm)
200
150
100
50
The compressive strength of mortars at 7 and 28 days are presented in Fig. 7. For mortars without expanded vermiculite, the compressive strength at both ages was higher for the case of the C0 mortar due to the lower w/c ratio; when expanded vermiculite was included as partial sand replacement, the compressive strength was noticeably reduced as the replacement level was increased. The tendency of decrease in compressive strength in the expanded vermiculite mortars could be attributed to the porous soft structure and hence weaker strength of expanded vermiculite [14]. Weaker aggregate provides lower resistance towards crack propagation and therefore reduces the load-bearing capacity of the mortars. Besides that, the lower content of fines present in expanded vermiculite could result in less favourable particle packing and negatively affect the strength of the mortar. In this study, reduction of about 50% and 63% was found when expanded vermiculite was incorporated at volume replacements of 30% and 60%, respectively. Reduced strength of mortar due to increased volume of lightweight aggregates such as expanded perlite [15] and expanded polystyrene [16] were previously reported. Nevertheless, the 28-day compressive strength of expanded vermiculite mortars between 12.1 and 16.6 MPa obtained in this study is comparable with those observed by Schackow et al. [8]. It is worth noting that the gain in strength from 7 days to 28 days of mortars containing expanded vermiculite (V30 and V60), was generally higher than the mortars without expanded vermiculite (C0 and C1). The said strength gain was 35% and 24% respectively for V30 and V60 whereas it was only 19% and 12% for C0 and C1, respectively. A
0 C0
C1
V30
V60
Mix
35
test. The flow diameter recorded was 162 mm, 226 mm, 181 mm and 179 mm, respectively for mixes C0, C1, V30 and V60. The flow obtained for all of the mortars is considered to be sufficient, as Lucas et al. [12] reported that consistency of 175 mm is considered to be sufficient for mortars. Expectedly, the mix C1 exhibited higher flow compared to the mix C0 due to the higher water to cement (w/c) ratio. The inclusion of expanded vermiculite as partial sand replacement yielded improved flow, as demonstrated with the increase of about 11% in mixes V30 and V60 compared to the corresponding control mortar C0. This increase could be attributed to the lower fines content of sizes below 150 lm in
Compressive strength (MPa)
Fig. 6. Flow diameter of fresh mortars.
30 7 day 25 28 day 20 15 10 5 0 C0
C1
V30
V60
Mix Fig. 7. Compressive strength of mortars at 7 and 28 days.
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possible reason could be the releasing of water internally from the expanded vermiculite which facilitated the cement hydration as well as some minor pozzolanic activity of the expanded vermiculite. 3.4. Residual strength
3.5. Water absorption Table 3 shows the initial and final water absorption values of the 28-day age mortars. The water absorption values give indica-
Table 2 Residual compressive strength of mortars subjected to elevated temperatures. Mix
C0 C1 V30 V60 *
Fig. 8. Cracks observed in mortar exposed to 800 °C.
100 95 C0 90 V30
Weight (%)
Table 2 presents the residual compressive strength of mortars after exposure to elevated temperatures of 600 °C and 800 °C. For all mortars, it is clear that the compressive strength decreased when the mortars were exposed to higher temperatures. The strength loss at 600 °C was possibly caused by the decomposition of calcium hydroxide whereas at 800 °C, greater strength loss experience was could be due to disintegration of the calcium silicate hydrate gels. Very fine micro-cracks could only be observed in the mortars exposed to 600 °C whereas larger cracks could be found in the mortars exposed to 800 °C when the cracks were checked with a digital microscope as shown in Fig. 8. When compared with the mix C0, although the V30 and V60 mortars had lower residual strengths, the percentage in strength loss was lesser. It was found that the strength loss was about 30% and 70% respectively for exposure temperatures of 600 °C and 800 °C for the expanded vermiculite mortars whereas the strength loss was higher at 44% and 75% for C0 mortar at the corresponding temperatures (Table 2). An additional set of mortar C1 was prepared to facilitate comparison of mortars with similar 28-day compressive strength when exposed to elevated temperature. It could be seen that in this case, not only was the strength loss of expanded vermiculite mortars was lower than C1, the residual strength was at least equal, or higher (for the case of V30) at the elevated temperatures. The positive contribution of the expanded vermiculite in lowering the compressive strength decline could be attributed to the presence of voids within the aggregate, which act as heat insulator and relieve the internal pressure formation [17]. In addition, the expanded vermiculite could close and fill micro-cracks due to its expansion [13]. The thermal gravimetric analysis (TGA) results in Fig. 9 shows that the weight loss of mortar containing vermiculite, namely V30, was lower compared to the corresponding control mortar C0 when temperature was increased at a rate of 5 °C/min. This corresponds well to the residual strength results whereby the vermiculite mortars exhibited higher strength retention upon exposure to elevated temperature. From the TGA curves, it could be seen that the difference in weight loss between the V30 and C0 mortars increased as the heating temperature was increased. This implies that the vermiculite had positive effect in insulating heat, particularly at higher temperature. Based on the results shown, it could be said that the expanded vermiculite provided good thermal stability and enhanced the heat resistance of the mortars.
85 80 75 70 65 0
200
400
600
800
1000
1200
Fig. 9. Thermal gravimetric analysis of mortars.
Table 3 Water absorption of mortars. Mix
Initial water absorption (%)
Final water absorption (%)
C0 C1 V30 V60
6.31 7.96 14.17 22.42
9.45 8.97 17.09 27.70
tion of the permeable voids present in the mortar. The increase in the water absorption of expanded vermiculite mortars is likely due to the porous nature of the expanded vermiculite. Moreover, since the expanded vermiculite used had lower finer particles and generally coarser than river sand, the packing of mortars could be less effective and hence the mortars exhibited higher water absorption values. Also, as suggested by Khonsari et al. [18] with the use of expanded perlite, the rise in water absorption can be caused by pores present in the weak cement-aggregate interface. The increase in water absorption with higher expanded vermiculite content was also reported in few researches [13,19]. 4. Conclusion
Compressive strength (MPa) Room temperature
600 °C
800 °C
33.03 13.77 16.62 12.11
18.62 ( 44%) 8.74 ( 37%) 11.61 ( 30%) 8.36 ( 31%)
8.42 3.93 4.97 3.99
Values in bracket represent percentage loss of compressive strength.
( ( ( (
75%) 71%) 70%) 67%)
Based on the experimental results obtained in this research, the following can be concluded: a. Incorporation of expanded vermiculite as partial sand replacement increased the flow diameter of the fresh mortars.
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b. Due to its lightweight nature, the presence of expanded vermiculite as partial sand substitute reduced the unit weight and compressive strength of mortar. c. The expanded vermiculite mortars exhibited enhanced resistance towards elevated temperature as lower compressive strength loss was observed compared to plain mortar. d. Water absorption of mortar was increased when the expanded vermiculite dosage as partial sand replacement was increased. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgement The authors is grateful for the funding provided by University of Malaya under the grants BK050-2016 and PG163-2015A. References [1] S. Aydin, Development of a high-temperature-resistant mortar by using slag and pumice, Fire Safe. J. 43 (8) (2008) 610–617. [2] T. Uygunoglu, I.B. Topcu, Thermal expansion of self-consolidating normal and lightweight aggregate concrete at elevated temperature, Constr. Build. Mater. 23 (9) (2009) 3063–3069. [3] H. Tanyildizi, A. Coskun, The effect of high temperature on compressive strength and splitting tensile strength of structural lightweight concrete containing fly ash, Constr. Build. Mater. 22 (11) (2008) 2269–2275. [4] O.A. Abdulkareem, A.M.M. Al Bakri, H. Kamarudin, K.I. Nizar, A.A. Saif, Effects of elevated temperatures on the thermal behavior and mechanical performance of fly ash geopolymer paste, mortar and lightweight concrete, Constr. Build. Mater. 50 (2014) 377–387. [5] M.Z. Jumaat, U.J. Alengaram, R. Ahmmad, S. Bahri, A.B.M.S. Islam, Characteristics of palm oil clinker as replacement for oil palm shell in lightweight concrete subjected to elevated temperature, Constr. Build. Mater. 101 (2015) 942–951.
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