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Investigation of the compressive strength of pit sand, and sea sand mortar prisms produced with rice husk ash as additive
Construction and Building Materials 151 (2017) 383–387
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Investigation of the compressive strength of pit sand, and sea sand mortar prisms produced with rice husk ash as additive Samuel Kofi Tulashie a,⇑, Francis Kotoka a, David Mensah b, Anthony Kwame Kwablah a a b
University of Cape Coast, College of Agriculture and Natural Sciences, School of Physical Sciences, Department of Chemistry, Industrial Chemistry Unit, Cape Coast, Ghana Cape Coast Technical University, Department of Building Technology, Cape Coast, Ghana
h i g h l i g h t s Adding 11.11%–22.22% rice husk ash enhances the compressive strength of the cement. Pit sand is far better than sea sand for compressive strength enhancement. The rice husk ash impact on compressive strength can be defected by the source of sand used. Higher ash composition can potentially distort the desired mortar compressive strength.
a r t i c l e
i n f o
Article history: Received 9 March 2017 Received in revised form 18 May 2017 Accepted 15 June 2017
Keywords: Rice husk ash Compressive strength Mortar prisms Cement Pit sand Sea sand
a b s t r a c t This study investigates the compressive strength of ordinary Portland cement mortar prisms with rice husk ash (RHA). Pit sand–cement, and sea sand-cement mortar prisms were separately prepared using cement-sand mix ratio 1:3, and RHA composition of 0–44.44%. The optimum strength of the pit sandcement mortar prisms after 1, 2, 7, and 28 days was recorded at 11.11% RHA by the mass of the cement. However, the compressive strength of the sea sand-cement mortar prisms with 11.11% RHA decreased on the 7th and 28th day. Thus the inconsistencies in the compressive strength indicate that, sea sand is not a good candidate for constructions. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The addition of pozzolanic materials to cement to improve mortar and concrete properties has recently become an emerging issue in the cement and construction industries. The cement and construction industries would save energy and reduce cost when byproducts from industries which had the potential of improving cement properties were partially incorporated into Portland cement [1]. Some agricultural by-products had largely been noted to exhibit good pozzolanic characteristics which can significantly improve cement mortar and concrete properties, especially, the compressive strength [2]. Rice husk ash (Fig. 1) had been mentioned to be one of the common and abundant candidates that have such excellent pozzolanic characteristics [3]. The presence of amorphous silica (more than 80–85% silica) which reacts readily
⇑ Corresponding author. E-mail address: [email protected] (S.K. Tulashie). http://dx.doi.org/10.1016/j.conbuildmat.2017.06.082 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
with the cement lime [4–7], and its specific surface area [8] account for those characteristics. For instance, rice husk ash had been reported to have reduced the heat of hydration [9], improved corrosion resistance [10], improved workability [11], decreased permeability [12], and most importantly, elevated the compressive strength and flexural strength [13,14] of the mortar, and concrete studied. Significantly, several studies have been done on the effect of RHA on the compressive of cement mortal, concrete and bricks. For example, the compressive strength of bricks was improved in the range of 20.9–31.5 MPa when RHA was used as the main binder material [15]. Generally, the optimum replacement levels of cement with rice husk ash, which improved the compressive strength of the cement mortar and concrete had been reported to be 10% [13], 15% [12], 20% [16], 25% [17] and 30% [8]. Other studies too have considered combining different materials such as fly ash, wood fiber waste, fibers derived from fiber board, and rice stalk fiber with rice husk ash to improve compressive strength and other properties by 20–30% partial replacement of the cement [17–20].
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S.K. Tulashie et al. / Construction and Building Materials 151 (2017) 383–387
Fig. 1. (a) Rice husk heap captured at one of the rice refinery mini-factories in Ghana; and (b) Rice husk collected from the heap.
Obviously, most studies have focused on the partial replacement of cement with rice husk ash. However, little exploration had been done on the direct addition of the rice husk ash as additive to the cement to reinforce the compressive strength, considering the sources of sands used. Also, large quantities of rice husks are traditionally and industrially disposed as waste causing environmental nuisance [21]. This present study therefore investigates the compressive strength of ordinary Portland cement mortar prisms produced with varying composition of rice husk ash additive. The optimum compressive strength of the prisms will be presented and discussed. The effect on compressive strength of mortar prisms using pit sand, and sea sand will also be presented and discussed. 2. Materials and methods 2.1. Materials
Tables 1 and 2 show the physical and chemical properties of the ordinary Portland cement (grade 32.5 R), rice husk ash, pit sand and sea sand used for the study. 2.2. Determination of standard consistency and setting time of cement paste The IS: 4031-PART 4-1988 procedure was adopted [22]. The standard consistency of the cement paste, and mortar mixture were determined experimentally by Vicat apparatus. For the cement paste, 450 g of cement and 25% of water by weight of the cement were initially mixed vigorously on non-porous surface by means of two trowels for 240 s. The mold was filled immediately with the cement mixture paste and the surface of the mixture was smoothened in the mold. The plunger was lowered to touch the surface of the cement mixture paste and allowed to sink through the surface to examine the depth of penetration. The entire process was repeated and the water content was varied incrementally until the depth of penetration was within 33–35 mm during which the standard consistency was determined to be 32.9% (148.05 g of water). The setting times were determined at 27 °C and 65% relative humidity by adopting IS: 4031-PART 5-1988 procedure [23]. The standard consistency (P), and setting times (initial and final) were calculated as shown in Eqs. (1)–(3), respectively.
p¼
The pit sand sample as depicted in Fig. 2 was collected from a construction site on University of Cape Coast campus, geographically located in the Central region of Ghana. Sea sand sample was also collected from the Tema fishing harbor geographically located in the Greater Accra region of Ghana. Each of the sand samples were stored in polyethylene bags and carried to the laboratory for study. The rice husk used for this work was obtained from Oheamadwen, geographically located in the Shama district of Ghana. The husk sample was sun-dried for three days. The dried husk was burnt into ashes in a muffle furnace for 2 h at 1100 °C as shown in Fig. 3, which was then ground and kept ready for analysis.
Fig. 2. A heap of pit sand.
w 100 c
ð1Þ
Intitial setting time ¼ a b
ð2Þ
Final setting time ¼ c d
ð3Þ
where, W = Quantity of water added; C = Quantity of Cement used; a = time when water was first added to the cement; b = time at which the needle could not penetrate 5 mm–7 mm from the mold bottom; c = time at which the needle impressed but the attachment could not.
Fig. 3. Ground rice husk ash.
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S.K. Tulashie et al. / Construction and Building Materials 151 (2017) 383–387 Table 1 Physical properties of the ordinary Portland cement, rice husk ash, pit sand and sea sand. Material
Blaine fineness (m2/kg)
Specific gravity (g/cm3)
Particle size distribution
Standard consistency (%)
Setting times (min):Initial; Final
Soundness Le-Chatlier expansion (mm)
Cement Rice husk ash Pit sand Sea sand
446.0 875.7 2.671 2.43
3.16 2.19 2.66 2.70
– – 63 mm–1.18 mm 300 mm–2.36 mm
32.9 – – –
176; 325 – – –
1 – – –
Table 2 Chemical composition of the ordinary Portland cement, rice husk ash, and pit sand. Material
Chloride (v/w %)
SiO2 (wt.%)
CaO (wt.%)
MgO (wt.%)
Cement (32.5 R) Rice husk ash Pit sand Sea sand
0.01 0 0 0.145
17.20 92.80 99.10 81.23
61.3 1.26 0.06 0.05
2.36 0.52 0.01 0.11
2.3. Mortar preparation, and mortar prisms molding for compressive strength test This included two main steps, namely, mortar preparation, and molding of prisms with variable rice husk ash compositions. IS:4031-PART 6-1988 procedure was followed for this approach [24]. The mortar mixes were prepared by employing cement, sand, mass ratio of 1:3. Two prisms were first molded and used as the control. Thus 450 g, 1350 g, of cement and pit sand were respectively mixed sufficiently in dry-wet condition. ðp4 þ 3Þ% of water by combined mass of the cement and sand was completely mixed with the cement and sand mixture for 4 min to obtain a homogeneous color. The temperature of the mixing room was kept at 27 °C and relative humidity of 65%. The blends were cast into a completely cleaned and oiled mold of 40 mm 40 mm 160 mm dimension using a vibrating machine with speed 1200 rpm for 120 s in order to get a complete compact mortar prism. An additional replica was produced after which they were placed in a moist curing chamber for 24 h at a temperature of 27 °C and relative humidity of 90%. After 24 h, the prisms were stripped from their molds and placed in water curing tank at 27 °C until testing. The same procedure was followed to prepare the control prism from sea sand-cement mortar. In order to prepare pit sand-cement mortar prisms with rice husk additives (Fig. 4), 50 g, 100 g, 150 g, and 200 g of the rice husk ash were respectively added to four different mortars, each prepared from 450 g of cement, 1350 g of sand, and ðp4 þ 3Þ% water by the combined mass of the cement, pit sand, and RHA as listed in Table 3. The mass of the rice husk ash used respectively constituted 11.11%, 22.22%, 33.33%, and 44.44% of the total mass of the cement used. The moldings of the mortar prisms with variable rice husk ash compositions were then done in the same procedure and conditions as used for the control prisms. Also, the sea sand-cement mortar prisms with rice husk additives were prepared using the same procedure, conditions, and proportions outlined in the preparation of the pit sandcement mortar prisms with rice husk additives. All reproducible methods and measurements were duplicated and the average value reported. 2.4. Determination of the compressive strength of the prisms IS:4031-PART 6-1988 procedure was again adopted for this approach [24]. The compressive strength of the prisms was investigated using an ELE compressive strength machine with a load cell of 2500 kN. A loading rate of 24 kN/s. was used for the compressive strength. The compressive strength of the prisms was measured after 1, 2, 7 and 28 days. For each age, the compressive strength was tested, and was repeated twice.
Fig. 4. Mortar prisms with rice husk ash additive.
Table 3 Mortar mix proportions used. Cement mixture (g) Cement
Pit sand
Rice husk ash
Water
Proportion
450 450 450 450 450
1350 1350 1350 1350 1350
0 50 100 150 200
202.05 207.66 213.28 218.89 224.50
1:3:0:0.449 1:3:0.111:0.461 1:3:0.222:0.474 1:3:0.333:0.486 1:3:0.444:0.499
All statistical analyses, calculations, and graphs were done using Microsoft Excel 2010.
3. Results and discussion 3.1. Compressive strength of pit sand mortar prisms containing rice husk ash The results of the compressive strength tests on pit sand mortar prisms are shown in Table 4. Generally, the maximum compressive strength throughout the days was recorded from the prism that contained 11.11% rice husk ash composition by mass of the cement. Thus 8.5, 14.0, 24.4, and 37.2 N/mm2 were recorded in the 1st, 2nd, 7th, and the 28th day respectively. Secondly, the prisms that had 22.22% rice husk ash composition also showed Table 4 Mean compressive strength of pit sand-cement mortar prisms. %RHA
0 (control) 11.11 22.22 33.33 44.44
Weight of RHA (g)
0 50 100 150 200
Compressive strength (N/mm2) 1 day
2 days
7 days
28 days
8.1 8.5 6.3 5.1 3.1
15.5 14.0 12.8 11.6 7.4
22.5 24.4 25.2 20.9 9.4
30.7 37.2 36 26.3 13.3
Fig. 5. The effects of variable rice husk ash composition on compressive of pit sandcement mortar prisms.
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Table 5 Mean compressive strength of sea sand-cement mortar prisms. % RHA
Weight of RHA (g)
0 (control) 11.11 22.22 33.33 44.44
0 50 100 150 200
Compressive strength (N/mm2) 1 day
2 days
7 days
28 days
3.3 3.8 2.2 1.8 0.5
5.5 6.1 5.4 4.1 2.2
9.5 8.3 9.2 4.8 5.3
14.6 11.4 12.4 5.8 5.4
an appreciable increment in the compressive strength on the 7th, and the 28th day. As depicted in Fig. 5, the prisms with 11.11%, and 22.22% largely (excluding the 1st for the 22.22%, and 2nd day for both) portrayed higher compressive strength than the control ordinary Portland cement as the prisms were aging. The 11.11% RHA addition increased the compressive strength by 8.4% and 21.2% on the 7th and 28th day respectively whereas the 22.22% RHA increased it by 12% and 17.3%. This may imply that the utmost pozzolanic reaction induced by the rice husk ash in the mortar occurred in the range of 11.11–22.22% rice husk ash composition. This is consistent with other studies which reported 10%, 15%, 20%, and 25% rice husk ash composition by mass of the cement used to be the optimum incorporation into the cement to attain optimum compressive strength [12,13,16,17,25]. However, very low compressive strength was recorded throughout the days in the mortar prisms with 33.33% and 44.44% rice husk ash composition. This suggests that though rice husk ash may be used as pozzolanic material in cement, higher ash composition has the potential of distorting the desired mortar compressive strength, hence should be added in modulation. This result agrees with other literatures which observed general reduction in the compressive strength as the rice husk ash composition increased beyond 20% in the cement mixture [16,25].
3.2. Compressive strength of sea sand mortar prisms containing rice husk ash
Fig. 6. Compressive strengths of sea sand-cement mortar prisms with variable RHA.
In Table 5, the compressive strength of the prisms with 11.11% rice husk ash was higher than that of the control in the 1st and 2nd day, but steeply fell below that of the control on the 7th and 28th
Fig. 7. Comparison of the compressive strengths of pit sand-cement mortar prisms and sea sand–cement mortar prisms upon variable RHA additions. 0 g, 50 g, 100 g, and 150 g addition of RHA represent 0%, 11.11%, 22.22% and 33.33% RHA respectively.
S.K. Tulashie et al. / Construction and Building Materials 151 (2017) 383–387
day. In fact, as shown in Fig. 6, the rice husk ash additive largely did not have significant improvement in the compressive strength of the sea sand-cement mortar prisms as the prisms were aging. The reduction in compressive strength might be due to the attack by MgSO4, and Cl ions present in the sea sand. These MgSO4, and Cl ions are known for causing set concrete to expand, resulting in spalling, cracking, and finally reducing the concrete strength [26]. This effect on the compressive strength is clearly depicted in Fig. 7. Conversely, the result obtained in this work was consistent with other work which reported that strength of the concrete appeared increasing at the early stage of attack but reduced as the concrete was aging [27].The result indicates that the impact of rice husk ash on compressive strength can be adversely affected by the source of sand used, hence the source of sand should also be considered when incorporating rice husk ash with the aim of enhancing compressive strength. Based on the observed results in Fig. 6, we, therefore, advise the general public against the usage of sea sand as a building material. Furthermore, with the current rising sea levels due to global warming, it becomes imperative to preserve the coastline with the sea sand, which would subsequently help prevent sea erosion. Fig. 7 compares the compressive strength of pit sand-cement mortar prisms with sea sand-cement mortar prisms. It was observed that the pit sand-cement mortar prisms completely had higher compressive strength than that of the sea sand-cement mortar prisms. The results therefore propose that in terms of compressive strength of mortar, pit sand is far better than sea sand. Pit sand must be largely used for mortar constructions instead of sea sand. 4. Conclusions This study focused on the compressive strength of ordinary Portland cement mortar prisms produced with rice husk ash additive. From the results of this study, the highest compressive strength of the pit sand-cement mortar prisms was achieved at 11.11% rice husk additive, indicating 8.4% and 21.2% improvement on the 7th and 28th day. Conversely, 22.22% rice husk ash addition also showed significant improvement (12% and 17.3%) in the compressive strength at 7, and 28 days old. The results suggest that a range of 11.11–22.22% rice husk ash by mass of cement can be incorporated into ordinary Portland cement together with pit sand to enhance the compressive strength. However, the compressive strength decreased at 33.33%, and 44.44% rice husk ash composition, implying that higher ash composition may not be desirable for compressive strength hence the ash must be added in modulation. Also, unlike the pit sand-cement mortar prisms, the compressive strength of the sea sand-cement mortar prisms decreased steeply on the 7th and 28th day. This proposes that so long as compressive strength of aging mortar is a very important property, pit sand is far better than sea sand. The results of this study will motivate the cement and construction industries to partly add rice husk ash to ordinary Portland cement to enhance the compressive strength of mortar structures, and also avoid the use of sea sand as a construction material due to its adverse effects on compressive strength, and use pit sand for mortar constructions instead of sea sand. Conflict of interest The authors have no conflict of interest regarding the publication of this paper.
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Acknowledgements We are grateful to the University of Cape Coast, Ghana, and Ghana Cement Limited for their laboratory assistance. References [1] P.P. Rao, A.P. Kumar, B.B. Singh, A study on use of rice husk ash in concrete, IJEAR 4 (spl-2) (2014). [2] P.K. Mehta, D. Pirtz, Use of rice husk ash to reduce temperature in high strength mass concrete, ACI J. Proc. 75 (2000) 60–63. [3] V.M. Malhotra, P.K. Mehta, Pozzolanic and Cementitious Materials, Taylor & Francis, London, 2004. [4] G.A. Habeeb, M.M. Fayyadh, Rice husk ash concrete: the effect of RHA average particle size on mechanical properties and drying shrinkage, Aust. J. Basic Appl. Sci. 3 (3) (2009) 1616–1622. [5] V.P. Della, I. Kuhn, D. Hotza, Rice husk ash as an alternate source for active silica production, Mater. Lett. 57 (4) (2002) 818–821. [6] R.B. Lin, S.M. Shih, C.F. Liu, Characteristics and relativities of Ca(OH)2/silica fume sorbents for low temperature flue gas desulfurization, Chem. Eng. Sci. 58 (16) (2003) 3659–3668. [7] F. Siddique, Waste Materials and By-Products in Concrete: With 174 Tables, Springer Press, 2008. [8] A.E. Dakroury, M.S. Gasser, Rice husk ash (RHA) as cement admixture for immobilization of liquid radioactive waste at different temperatures, J. Nucl. Mater. 381 (3) (2008) 271–277. [9] P.C. Hewlett, Chemistry of Cement and Concrete, Wiley, New York, 1998, pp. 471–601. [10] P. Chindaprasirt, S. Rukzon, Strength, porosity and corrosion resistance of ternary blend Portland cement, rice husk ash and fly ash mortar, Constr. Build. Mater. 22 (8) (2008) 1601–1606. [11] J.S. Coutinho, The combined benefits of CPF and RHA in improving the durability of concrete structures, Cem. Concr. Compos. 25 (1) (2002) 51–59. [12] K. Ganesan, K. Rajagopal, K. Thangavel, Rice husk ash blended cement: assessment of optimal level of replacement for strength and permeability properties of concrete, Constr. Build. Mater. 22 (8) (2008) 1675–1683. [13] M.H. Zhang, R. Lastra, V.M. Malhotra, Rice- husk ash paste and concrete: some aspects of hydration and the microstructure of the interfacial zone between the aggregate and paste, Cem. Concr. Res. 26 (6) (1996) 963–977. [14] G.S. Rodriguez, Strength development of concrete with rice-husk ash, Cem. Concr. Compos. 28 (2) (2006) 158–160. [15] C.L. Hwang, T.P. Huynh, Investigation into the use of unground rice husk ash to produce eco-friendly construction bricks, Constr. Build. Mater. 93 (2015) 335– 341, http://dx.doi.org/10.1016/j.conbuildmat.2015.04.061. [16] E.S. Aprianti, Effect of rice husk ash as additives in lime mortar, Int. J. Adv. Mech. Civil Eng. 2 (2) (2015) 2394–2827. [17] Y. Hamzeh, K. Pourhoshyar Ziabari, J. Torkaman, A. Ashori, M. Jafari, Study on the effects of white rice husk ash and fibrous materials variations on properties of fiber-cement composites, Environ. Manage. 117 (15) (2013) 263–267. [18] S.H. Sathawanea, V.S. Vairagadeb, K.S. Kenec, Combine effect of rice husk ash and fly ash on concrete by 30% cement replacement, Procedia Engineering, 51 (2013) 35–44. Available from: [19] M. Ghofrani, K. Nikkar Mokaram, A. Ashori, J. Torkaman, Fiber-cement composites using rice stalk and rice husk ash: mechanical and physical properties, Compos. Mater. 49 (26) (2015) 3317–3322. [20] J. Torkaman, A. Ashori, A. Sadr Momtazi, Using wood fiber waste, rice husk ash, and limestone powder waste as cement replacement materials for lightweight concrete blocks, Constr. Build. Mater. 50 (2014) 432–436. [21] V.T.A. Van, C. Rößler, D.D. Bui, et al. Pozzolanic reactiv-ity of mesoporous amorphous rice husk ash in portlandite solution, Constr. Build Mater. 59 (2014) 111–119. [22] IS: 4031(Part 4): 1988- Methods of physical tests for hydraulic cement (Determination of consistency of standard cement paste), , (accessed 15/12/2016). [23] IS: 4031(Part 5): 1988- Methods of physical tests for hydraulic cement (Determination of initial and final setting times), .
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Investigation of the compressive strength of pit sand, and sea sand mortar prisms produced with rice husk ash as additive Samuel Kofi Tulashie a,⇑, Francis Kotoka a, David Mensah b, Anthony Kwame Kwablah a a b
University of Cape Coast, College of Agriculture and Natural Sciences, School of Physical Sciences, Department of Chemistry, Industrial Chemistry Unit, Cape Coast, Ghana Cape Coast Technical University, Department of Building Technology, Cape Coast, Ghana
h i g h l i g h t s Adding 11.11%–22.22% rice husk ash enhances the compressive strength of the cement. Pit sand is far better than sea sand for compressive strength enhancement. The rice husk ash impact on compressive strength can be defected by the source of sand used. Higher ash composition can potentially distort the desired mortar compressive strength.
a r t i c l e
i n f o
Article history: Received 9 March 2017 Received in revised form 18 May 2017 Accepted 15 June 2017
Keywords: Rice husk ash Compressive strength Mortar prisms Cement Pit sand Sea sand
a b s t r a c t This study investigates the compressive strength of ordinary Portland cement mortar prisms with rice husk ash (RHA). Pit sand–cement, and sea sand-cement mortar prisms were separately prepared using cement-sand mix ratio 1:3, and RHA composition of 0–44.44%. The optimum strength of the pit sandcement mortar prisms after 1, 2, 7, and 28 days was recorded at 11.11% RHA by the mass of the cement. However, the compressive strength of the sea sand-cement mortar prisms with 11.11% RHA decreased on the 7th and 28th day. Thus the inconsistencies in the compressive strength indicate that, sea sand is not a good candidate for constructions. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The addition of pozzolanic materials to cement to improve mortar and concrete properties has recently become an emerging issue in the cement and construction industries. The cement and construction industries would save energy and reduce cost when byproducts from industries which had the potential of improving cement properties were partially incorporated into Portland cement [1]. Some agricultural by-products had largely been noted to exhibit good pozzolanic characteristics which can significantly improve cement mortar and concrete properties, especially, the compressive strength [2]. Rice husk ash (Fig. 1) had been mentioned to be one of the common and abundant candidates that have such excellent pozzolanic characteristics [3]. The presence of amorphous silica (more than 80–85% silica) which reacts readily
⇑ Corresponding author. E-mail address: [email protected] (S.K. Tulashie). http://dx.doi.org/10.1016/j.conbuildmat.2017.06.082 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
with the cement lime [4–7], and its specific surface area [8] account for those characteristics. For instance, rice husk ash had been reported to have reduced the heat of hydration [9], improved corrosion resistance [10], improved workability [11], decreased permeability [12], and most importantly, elevated the compressive strength and flexural strength [13,14] of the mortar, and concrete studied. Significantly, several studies have been done on the effect of RHA on the compressive of cement mortal, concrete and bricks. For example, the compressive strength of bricks was improved in the range of 20.9–31.5 MPa when RHA was used as the main binder material [15]. Generally, the optimum replacement levels of cement with rice husk ash, which improved the compressive strength of the cement mortar and concrete had been reported to be 10% [13], 15% [12], 20% [16], 25% [17] and 30% [8]. Other studies too have considered combining different materials such as fly ash, wood fiber waste, fibers derived from fiber board, and rice stalk fiber with rice husk ash to improve compressive strength and other properties by 20–30% partial replacement of the cement [17–20].
384
S.K. Tulashie et al. / Construction and Building Materials 151 (2017) 383–387
Fig. 1. (a) Rice husk heap captured at one of the rice refinery mini-factories in Ghana; and (b) Rice husk collected from the heap.
Obviously, most studies have focused on the partial replacement of cement with rice husk ash. However, little exploration had been done on the direct addition of the rice husk ash as additive to the cement to reinforce the compressive strength, considering the sources of sands used. Also, large quantities of rice husks are traditionally and industrially disposed as waste causing environmental nuisance [21]. This present study therefore investigates the compressive strength of ordinary Portland cement mortar prisms produced with varying composition of rice husk ash additive. The optimum compressive strength of the prisms will be presented and discussed. The effect on compressive strength of mortar prisms using pit sand, and sea sand will also be presented and discussed. 2. Materials and methods 2.1. Materials
Tables 1 and 2 show the physical and chemical properties of the ordinary Portland cement (grade 32.5 R), rice husk ash, pit sand and sea sand used for the study. 2.2. Determination of standard consistency and setting time of cement paste The IS: 4031-PART 4-1988 procedure was adopted [22]. The standard consistency of the cement paste, and mortar mixture were determined experimentally by Vicat apparatus. For the cement paste, 450 g of cement and 25% of water by weight of the cement were initially mixed vigorously on non-porous surface by means of two trowels for 240 s. The mold was filled immediately with the cement mixture paste and the surface of the mixture was smoothened in the mold. The plunger was lowered to touch the surface of the cement mixture paste and allowed to sink through the surface to examine the depth of penetration. The entire process was repeated and the water content was varied incrementally until the depth of penetration was within 33–35 mm during which the standard consistency was determined to be 32.9% (148.05 g of water). The setting times were determined at 27 °C and 65% relative humidity by adopting IS: 4031-PART 5-1988 procedure [23]. The standard consistency (P), and setting times (initial and final) were calculated as shown in Eqs. (1)–(3), respectively.
p¼
The pit sand sample as depicted in Fig. 2 was collected from a construction site on University of Cape Coast campus, geographically located in the Central region of Ghana. Sea sand sample was also collected from the Tema fishing harbor geographically located in the Greater Accra region of Ghana. Each of the sand samples were stored in polyethylene bags and carried to the laboratory for study. The rice husk used for this work was obtained from Oheamadwen, geographically located in the Shama district of Ghana. The husk sample was sun-dried for three days. The dried husk was burnt into ashes in a muffle furnace for 2 h at 1100 °C as shown in Fig. 3, which was then ground and kept ready for analysis.
Fig. 2. A heap of pit sand.
w 100 c
ð1Þ
Intitial setting time ¼ a b
ð2Þ
Final setting time ¼ c d
ð3Þ
where, W = Quantity of water added; C = Quantity of Cement used; a = time when water was first added to the cement; b = time at which the needle could not penetrate 5 mm–7 mm from the mold bottom; c = time at which the needle impressed but the attachment could not.
Fig. 3. Ground rice husk ash.
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S.K. Tulashie et al. / Construction and Building Materials 151 (2017) 383–387 Table 1 Physical properties of the ordinary Portland cement, rice husk ash, pit sand and sea sand. Material
Blaine fineness (m2/kg)
Specific gravity (g/cm3)
Particle size distribution
Standard consistency (%)
Setting times (min):Initial; Final
Soundness Le-Chatlier expansion (mm)
Cement Rice husk ash Pit sand Sea sand
446.0 875.7 2.671 2.43
3.16 2.19 2.66 2.70
– – 63 mm–1.18 mm 300 mm–2.36 mm
32.9 – – –
176; 325 – – –
1 – – –
Table 2 Chemical composition of the ordinary Portland cement, rice husk ash, and pit sand. Material
Chloride (v/w %)
SiO2 (wt.%)
CaO (wt.%)
MgO (wt.%)
Cement (32.5 R) Rice husk ash Pit sand Sea sand
0.01 0 0 0.145
17.20 92.80 99.10 81.23
61.3 1.26 0.06 0.05
2.36 0.52 0.01 0.11
2.3. Mortar preparation, and mortar prisms molding for compressive strength test This included two main steps, namely, mortar preparation, and molding of prisms with variable rice husk ash compositions. IS:4031-PART 6-1988 procedure was followed for this approach [24]. The mortar mixes were prepared by employing cement, sand, mass ratio of 1:3. Two prisms were first molded and used as the control. Thus 450 g, 1350 g, of cement and pit sand were respectively mixed sufficiently in dry-wet condition. ðp4 þ 3Þ% of water by combined mass of the cement and sand was completely mixed with the cement and sand mixture for 4 min to obtain a homogeneous color. The temperature of the mixing room was kept at 27 °C and relative humidity of 65%. The blends were cast into a completely cleaned and oiled mold of 40 mm 40 mm 160 mm dimension using a vibrating machine with speed 1200 rpm for 120 s in order to get a complete compact mortar prism. An additional replica was produced after which they were placed in a moist curing chamber for 24 h at a temperature of 27 °C and relative humidity of 90%. After 24 h, the prisms were stripped from their molds and placed in water curing tank at 27 °C until testing. The same procedure was followed to prepare the control prism from sea sand-cement mortar. In order to prepare pit sand-cement mortar prisms with rice husk additives (Fig. 4), 50 g, 100 g, 150 g, and 200 g of the rice husk ash were respectively added to four different mortars, each prepared from 450 g of cement, 1350 g of sand, and ðp4 þ 3Þ% water by the combined mass of the cement, pit sand, and RHA as listed in Table 3. The mass of the rice husk ash used respectively constituted 11.11%, 22.22%, 33.33%, and 44.44% of the total mass of the cement used. The moldings of the mortar prisms with variable rice husk ash compositions were then done in the same procedure and conditions as used for the control prisms. Also, the sea sand-cement mortar prisms with rice husk additives were prepared using the same procedure, conditions, and proportions outlined in the preparation of the pit sandcement mortar prisms with rice husk additives. All reproducible methods and measurements were duplicated and the average value reported. 2.4. Determination of the compressive strength of the prisms IS:4031-PART 6-1988 procedure was again adopted for this approach [24]. The compressive strength of the prisms was investigated using an ELE compressive strength machine with a load cell of 2500 kN. A loading rate of 24 kN/s. was used for the compressive strength. The compressive strength of the prisms was measured after 1, 2, 7 and 28 days. For each age, the compressive strength was tested, and was repeated twice.
Fig. 4. Mortar prisms with rice husk ash additive.
Table 3 Mortar mix proportions used. Cement mixture (g) Cement
Pit sand
Rice husk ash
Water
Proportion
450 450 450 450 450
1350 1350 1350 1350 1350
0 50 100 150 200
202.05 207.66 213.28 218.89 224.50
1:3:0:0.449 1:3:0.111:0.461 1:3:0.222:0.474 1:3:0.333:0.486 1:3:0.444:0.499
All statistical analyses, calculations, and graphs were done using Microsoft Excel 2010.
3. Results and discussion 3.1. Compressive strength of pit sand mortar prisms containing rice husk ash The results of the compressive strength tests on pit sand mortar prisms are shown in Table 4. Generally, the maximum compressive strength throughout the days was recorded from the prism that contained 11.11% rice husk ash composition by mass of the cement. Thus 8.5, 14.0, 24.4, and 37.2 N/mm2 were recorded in the 1st, 2nd, 7th, and the 28th day respectively. Secondly, the prisms that had 22.22% rice husk ash composition also showed Table 4 Mean compressive strength of pit sand-cement mortar prisms. %RHA
0 (control) 11.11 22.22 33.33 44.44
Weight of RHA (g)
0 50 100 150 200
Compressive strength (N/mm2) 1 day
2 days
7 days
28 days
8.1 8.5 6.3 5.1 3.1
15.5 14.0 12.8 11.6 7.4
22.5 24.4 25.2 20.9 9.4
30.7 37.2 36 26.3 13.3
Fig. 5. The effects of variable rice husk ash composition on compressive of pit sandcement mortar prisms.
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Table 5 Mean compressive strength of sea sand-cement mortar prisms. % RHA
Weight of RHA (g)
0 (control) 11.11 22.22 33.33 44.44
0 50 100 150 200
Compressive strength (N/mm2) 1 day
2 days
7 days
28 days
3.3 3.8 2.2 1.8 0.5
5.5 6.1 5.4 4.1 2.2
9.5 8.3 9.2 4.8 5.3
14.6 11.4 12.4 5.8 5.4
an appreciable increment in the compressive strength on the 7th, and the 28th day. As depicted in Fig. 5, the prisms with 11.11%, and 22.22% largely (excluding the 1st for the 22.22%, and 2nd day for both) portrayed higher compressive strength than the control ordinary Portland cement as the prisms were aging. The 11.11% RHA addition increased the compressive strength by 8.4% and 21.2% on the 7th and 28th day respectively whereas the 22.22% RHA increased it by 12% and 17.3%. This may imply that the utmost pozzolanic reaction induced by the rice husk ash in the mortar occurred in the range of 11.11–22.22% rice husk ash composition. This is consistent with other studies which reported 10%, 15%, 20%, and 25% rice husk ash composition by mass of the cement used to be the optimum incorporation into the cement to attain optimum compressive strength [12,13,16,17,25]. However, very low compressive strength was recorded throughout the days in the mortar prisms with 33.33% and 44.44% rice husk ash composition. This suggests that though rice husk ash may be used as pozzolanic material in cement, higher ash composition has the potential of distorting the desired mortar compressive strength, hence should be added in modulation. This result agrees with other literatures which observed general reduction in the compressive strength as the rice husk ash composition increased beyond 20% in the cement mixture [16,25].
3.2. Compressive strength of sea sand mortar prisms containing rice husk ash
Fig. 6. Compressive strengths of sea sand-cement mortar prisms with variable RHA.
In Table 5, the compressive strength of the prisms with 11.11% rice husk ash was higher than that of the control in the 1st and 2nd day, but steeply fell below that of the control on the 7th and 28th
Fig. 7. Comparison of the compressive strengths of pit sand-cement mortar prisms and sea sand–cement mortar prisms upon variable RHA additions. 0 g, 50 g, 100 g, and 150 g addition of RHA represent 0%, 11.11%, 22.22% and 33.33% RHA respectively.
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day. In fact, as shown in Fig. 6, the rice husk ash additive largely did not have significant improvement in the compressive strength of the sea sand-cement mortar prisms as the prisms were aging. The reduction in compressive strength might be due to the attack by MgSO4, and Cl ions present in the sea sand. These MgSO4, and Cl ions are known for causing set concrete to expand, resulting in spalling, cracking, and finally reducing the concrete strength [26]. This effect on the compressive strength is clearly depicted in Fig. 7. Conversely, the result obtained in this work was consistent with other work which reported that strength of the concrete appeared increasing at the early stage of attack but reduced as the concrete was aging [27].The result indicates that the impact of rice husk ash on compressive strength can be adversely affected by the source of sand used, hence the source of sand should also be considered when incorporating rice husk ash with the aim of enhancing compressive strength. Based on the observed results in Fig. 6, we, therefore, advise the general public against the usage of sea sand as a building material. Furthermore, with the current rising sea levels due to global warming, it becomes imperative to preserve the coastline with the sea sand, which would subsequently help prevent sea erosion. Fig. 7 compares the compressive strength of pit sand-cement mortar prisms with sea sand-cement mortar prisms. It was observed that the pit sand-cement mortar prisms completely had higher compressive strength than that of the sea sand-cement mortar prisms. The results therefore propose that in terms of compressive strength of mortar, pit sand is far better than sea sand. Pit sand must be largely used for mortar constructions instead of sea sand. 4. Conclusions This study focused on the compressive strength of ordinary Portland cement mortar prisms produced with rice husk ash additive. From the results of this study, the highest compressive strength of the pit sand-cement mortar prisms was achieved at 11.11% rice husk additive, indicating 8.4% and 21.2% improvement on the 7th and 28th day. Conversely, 22.22% rice husk ash addition also showed significant improvement (12% and 17.3%) in the compressive strength at 7, and 28 days old. The results suggest that a range of 11.11–22.22% rice husk ash by mass of cement can be incorporated into ordinary Portland cement together with pit sand to enhance the compressive strength. However, the compressive strength decreased at 33.33%, and 44.44% rice husk ash composition, implying that higher ash composition may not be desirable for compressive strength hence the ash must be added in modulation. Also, unlike the pit sand-cement mortar prisms, the compressive strength of the sea sand-cement mortar prisms decreased steeply on the 7th and 28th day. This proposes that so long as compressive strength of aging mortar is a very important property, pit sand is far better than sea sand. The results of this study will motivate the cement and construction industries to partly add rice husk ash to ordinary Portland cement to enhance the compressive strength of mortar structures, and also avoid the use of sea sand as a construction material due to its adverse effects on compressive strength, and use pit sand for mortar constructions instead of sea sand. Conflict of interest The authors have no conflict of interest regarding the publication of this paper.
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