Suitability of some Ghanaian mineral admixtures for masonry mortar formulation

Construction and Building Materials 29 (2012) 667–671

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Suitability of some Ghanaian mineral admixtures for masonry mortar formulation Mark Bediako a,⇑, S.K.Y. Gawu b, A.A. Adjaottor c a

Building and Road Research Institute (BRRI) of Council for Scientific and Industrial Research (CSIR), Kumasi, Ghana Geological Engineering Department, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana c Materials Engineering Department, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana b

a r t i c l e

i n f o

Article history: Received 6 December 2010 Received in revised form 2 May 2011 Accepted 13 June 2011 Available online 31 December 2011 Keywords: Masonry mortar Ordinary Portland cement Compressive strength Mineral admixtures Clay pozzolana Limestone Water demand Setting times Binary Ternary

a b s t r a c t The suitability of masonry mortar for various constructional applications is dependent on some vital engineering properties and production cost. In a majority of masonry formulations, ordinary Portland cement (OPC) is the principal binding agent. However, the current trend of cement cost in Ghana has rendered masonry mortar formulation quite expensive. In this paper clay pozzolana produced from cost efficient local technology and limestone powder was used as mineral admixtures in cement. Physical and chemical properties of the mineral admixtures were analyzed. The particle sizes of the materials were also investigated. Binary and ternary pastes and mortars were formulated using some percentages of Clay Pozzolana (CP), Limestone (L) and Clay Pozzolana–Limestone (CP–L) to replace part of the expensive ordinary Portland cement. Water demand and setting time tests were determined on the binder paste whilst compressive strength test was performed on mortars cured in water for 7 and 28 days. Test results indicated that ASTM type M and S mortars could be formulated from binary and ternary mortar mixes. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The utilization of mineral admixtures as cement replacement materials is now widely adopted in USA, Europe and part of Asia for the production of mortars for masonry works like plastering, rendering and jointing of bricks, blocks and stones [1,2]. Examples of such mineral admixture commonly used are natural resources like pozzolans and limestone filler, heat-activated additions such as clay and metakaolin and industrial by-products like fly ash, blast-furnace and steel-making slag, silica fume, rice husk ash [3,4]. Many authors have found that the use of mineral admixtures in Portland cement for mortar formulation is very beneficial in areas like cost reduction, enhancement of mechanical properties, reduction in heat evolution, decreased permeability, increased chemical resistance and reduction in gas emission that contribute to green-house effect [5–7]. In most developing countries like Ghana, the technology of using mineral admixtures in mortar formulation is not well known. This is because Portland cement mortars are the most widely used traditional mortar for masonry works. However, Portland cement cost is among the limiting constraints for most builders and engineers in ⇑ Corresponding author. Address: CSIR-BRRI, UPO Box 40, KNUST-Kumasi, Ghana. Tel.: +233 302260064/5, mobile: +233 244745250; fax: +233 30260080. E-mail address: [email protected] (M. Bediako). 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.06.016

terms of construction cost. In 2005, Portland cement was sold for $5.50 per 50 kg bag and currently in 2010 is sold at $9.50 which represents about 80% increase in cost. It is estimated that by 2015 cement price per 50 kg bag will be between $18.00 and $25.00 depending on the location in Ghana due to proximity to Tema in Greater Accra Region and Takoradi in the Western Region where the clinker and gypsum milling plants are located. The annual price increase of Portland cement is attributed to the importation of clinker and gypsum, the main ingredients for cement production from Europe and Asia. Clinker and gypsum importation is said to cost the country about $200 million annually [8]. The need to develop alternative materials to reduce the cost of Portland cement mortar formulation in the country is thus necessary. Clay and limestone minerals are found in abundance in Ghana and could be processed into cementitious materials used in mortar formulation. It is estimated that about 1392 and 215 million tonnes of clay and limestone respectively exist untapped [9]. Previous studies by Atiemo [10] has identified and evaluated some clays in the country that are suitable for clay pozzolana formulation. Information regarding the use of limestone for masonry mortars is very rare. In this study clay pozzolana produced from Mankranso clay in Ashanti Region and limestone from Orterkpolu in the Eastern region were used to formulate binary and ternary mortars. Fig. 1 shows the map of Ghana which locates the position of both Ashanti

668

M. Bediako et al. / Construction and Building Materials 29 (2012) 667–671 Table 2 Chemical and mineralogical composition of OPC, CP and L. Compound (%)

OPC

CP

L

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI SiO2 + Al2O3 + Fe2O3 C3S C2S C3A C4AF

19.7 5 3.16 63.03 1.75 0.16 0.2 2.8 2.58 – 59.6 12.6 7.86 9.49

61.89 13.51 5.84 0.21 1.74 1.07 0.14 0.14 10 81.23 – – – –

17.65 3.45 1.56 49.57 2.11 0.78 0.3 0.3 23.43 – – – – –

Figs. 3 and 4 show the X-ray diffraction (XRD) patterns of CP and L. According to Fig. 3, CP contains mostly kaolinite and quartz whereas Fig. 3 shows the presence of calcite, dolomite and quartz in L. 2.2. Methods

Fig. 1. Regional map of Ghana.

Table 1 Physical properties of OPC, CP and L. Property

OPC

CP

L

Sp gravity Blaine fineness (m2/kg) Mean particle size (lm) % Passing 75 (lm)

3.14 338 4 92

2.58 410 30 99.6

2.56 420 32 98

Region and Eastern where the clay and limestone were respectively obtained. The aim was to produce suitable and alternative blended cement mortar for cost efficient masonry works. 2. Materials and methods 2.1. Materials Ordinary Portland cement (CEM I 42.5N) produced by Ghana cement manufacturers (Ghacem) that conformed to EN 197-1 and labelled OPC was used. Clay sample from Mankranso in the Ashanti Region of Ghana was used to produce the pozzolana (CP) through a calcination process whereas limestone from Orterkpolu (L) in the Eastern region of Ghana was crushed in a jaw crusher and milled for utilization. Tables 1 and 2 represent the physical and chemical properties of the powder mineral specimen. The particle size analysis of the powder samples determined by the sedimentation method in accordance with the BS 1377 [11] produced a graph as shown in Fig. 2. The mean particle size of CP and L were 30 lm and 32 lm respectively which values were higher than that of OPC which was 4 lm. The specific gravity values of CP and L are close being 2.58 and 2.56 respectively whilst that of OPC was much higher with a value of 3.14 as shown in Table 1. It could be deduced from the chemical properties shown in Table 2 that CP contained 81% of SiO2 + Al2O3 + Fe2O3, 0.14% of SO3 and 10% of LOI which can be classified as a class N pozzolan according to ASTM C618. Orterkpolu limestone (L) contained 88.5% CaCO3 in calcite form which was calculated from CaO content illustrated in Table 2 [12].

2.2.1. Clay pozzolana production The production process for Mankranso pozzolana involved clay winning and drying, dried clay and palm kernel shells milling with a hammer mill, mixing of dry clay and palm kernel shells in a mixer, formation of nodules, nodules drying, calcination of dried nodules in a locally fabricated brick kiln at 700–800 °C and finally milling the calcined nodules using a hammer mill. The flow diagram for the production process is shown in Fig. 5. The palm kernel shells which were mixed with the milled clay at a predefined ratio served as a source of fuel for the calcination process. The nodules formation enhanced the flow of hot air from the bottom of the kiln to the top part. Fig. 6 indicates the locally fabricated brick kiln used for calcining the clay nodules. The kiln is vertical, cylindrical in shape having a capacity of approximately three (3) tonnes, 3700 mm high and housed in a wooden structure. It was designed to contain two blowers placed at the bottom and middle part. Each blower is runned with a high speed motor (12 horsepower, 3000 rpm). The operation of the kiln starts by igniting fire at the bottom part using charcoal, dried sawdust and a small amount of kerosene sprinkled over the sawdust. Once ignition is started, the down blower starts to sustain the fire. Loading of the kiln with the dried nodules started at this stage for calcination from the top via a wooden stair case attached to the kiln. When loading of the nodules got to the middle part of the kiln, the middle blower was made to start in sustaining the calcination process till it was completed. The calcination process took between 18 and 21 h. Calcined nodules were left to cool down for about 6–8 h before pulverising it using the hammer mill. The production process for the limestone powder involved limestone digging and drying, limestone crushing in a jaw crusher, milling of the crushed limestone in a hammer mill into fine powder and finally sieving the powder through a 75 lm sieve size. The undersize was used for the study. 2.2.2. Specimen preparation, casting, curing and testing Binary binder pastes and mortars were prepared by using 10–40% Limestone (L) or Clay Pozzolana (CP) with the remainder being ordinary Portland cement (OPC). The ternary paste and mortars were also prepared using CP and L to replace up to 50% OPC. Table 3 shows the mix design for the binary and ternary mixes. A 1:3 binder to sand ratio was used for mortar preparation. The water to binder (w/b) ratio for OPC–L mortar batch mixes was 0.4 whilst 0.5 was used for OPC–CP and the ternary blend containing a mixture of OPC, CP, and L. The mortar was cast into 75 mm metallic cube moulds. Water demand and both initial and final setting times were determined on the binder paste by the vicat apparatus according to EN 197-1 standard. Compressive strength determination was performed on an average of three mortar specimens at 7 and 28 days of standard curing. This was determined in accordance with ASTM C109 standard [13].

3. Results and discussions Table 3 indicates the mix design and mechanical properties of the binary and ternary paste and mortars. It can be deduced from Table 3 that on addition of between 10% and 40% CP to OPC, the water demand increased between 10.7% and 42.9% when compared with the control (C). Limestone addition within the same range increased the water demand between 3.6% and 7% compared

669

M. Bediako et al. / Construction and Building Materials 29 (2012) 667–671

Fig. 2. Particle size distribution of OPC, CP and L.

PALM KERNEL SHELLS CLAY WINNING

DRYING

PULVERISING

MILLING

MILLING

MIXING

CALCINATION

NODULISATION

Fig. 3. X-ray diffraction analysis of Mankranso clay pozzolana (CP).

Fig. 5. A flow diagram for the production of pozzolana from Mankranso clay.

Fig. 4. X-ray diffraction analysis of Orterkpolu limestone (L).

to the control. Again there was a slight increase in water demand when the percentage of limestone content was increased above 30%. For the ternary mixture, deductions from Table 3 showed that water demand increased by 17.6–35.7% compared to the control mortar. The results also showed that incorporating Orterkpolu limestone (L) from 10% to 40%, Clay Pozzolana (CP) from 10% to 40% or both at 30–50% mineral addition had a relatively high water

Fig. 6. Brick kiln used for calcining clay nodules.

670

M. Bediako et al. / Construction and Building Materials 29 (2012) 667–671

Table 3 Mix design, water demand, setting times and compressive strength of plain and blended pastes and mortars. Mix

C L1 L2 L3 L4 L5 L6 CP1 CP2 CP3 CP4 CP5 CP6 T1 T2 T3 T4

% Composition OPC

CP

L

100 90 80 75 70 65 60 90 80 75 70 65 60 70 70 70 50

– – – – – – – 10 20 25 30 35 40 10 20 15 30

– 10 20 25 30 35 40 – – – – – – 20 10 15 20

Water demand

0.28 0.29 0.29 0.29 0.29 0.3 0.3 0.31 0.33 0.35 0.36 0.38 0.4 0.36 0.33 0.35 0.38

Setting time

Compressive strength

Initial

Final

7 days

28 days

83 141 134 140 138 136 136 93 98 89 127 201 214 216 205 209 223

231 174 172 202 183 192 192 221 268 294 310 298 295 259 247 259 228

24.1 22.8 18.6 20.6 13.3 11.2 11.7 16.3 17.6 18.1 17.6 16.7 12.1 17.3 16.3 16.2 10.3

26.0 23.1 20.4 23.2 19.2 17.8 11.7 21.7 20.3 18.5 18.0 17.9 16.2 25.6 24.3 21.3 16.3

Fig. 9. Twenty-eight days compressive strength of OPC–CP–L masonry mortar compared to ASTM standard.

Table 4 General recommendation on masonry mortar type selection by ASTM C270. Masonry mortar type

Location

Building segment

28 days compressive strength (MPa)

Type M

Exterior above grade Interior

Load bearing walls

20.0

Exterior at or below grade

Foundation walls, retaining walls Manholes, sewers, pavements, Patio, parapet walls

Type S

Fig. 7. Twenty-eight days compressive strength of OPC–L masonry mortar compared to ASTM standard.

Fig. 8. Twenty-eight days compressive strength of OPC–CP masonry mortar compared to ASTM standard.

absorption capability as compared to the plain cement paste. This was in conformity with the investigations done by Ahmed and Shakh [14]. The results of the setting times as shown in Table 3 indicated that between 10% and 25% CP content, initial setting time got nearer to the control OPC paste. However, further CP addition delayed the initial setting time of the binder paste up to 40%.

Load/nonload bearing walls 14.5

The ternary mixture which contained both CP and L up to 30% and 50% generally caused a delay in both initial and final setting times as compared to the control paste. Meanwhile OPC replacement at 30% CP and L content showed that at 10% CP and 20% L, both the initial and final setting times delayed compared to 20% CP and 10% L batch mixes. The decrease in final setting time of limestone replacement in the mix was consistent with work studied by Helal [15]. He explained that, the observation was mainly due to the formation of increased amounts of calcium carboaluminate hydrates, which have a high rate of formation during the early stages of the hydration process. Heikal et al. [16] explained that limestone addition enhances the formation of Ca(OH)2 at early ages because it provides nucleating sites for its growth. Irassar et al. [17] also reported that this effect accelerates the cement hydration process at the early stages. The percentage clay pozzolana replacement levels which caused retardation in the setting times were similar to the work done by Brooks et al [18]. This was also evident in 30% CP and 20% L batch ternary mix where there was more pozzolana. Chindaprasirt et al. [19] reported that generally delayed setting times, particularly initial setting time could be beneficial in hot tropical climates since early stiffening of mortar in hot conditions can lead to cracking and delamination of masonry mortar. Figs. 7–9 and Table 4 indicate the compressive strength figures of OPC–L, OPC–CP and OPC–CP–L and general recommendations for masonry mortar selection respectively. Fig. 7 shows that 10–30% L content satisfied type M mortars whilst 35% L satisfied mortar type S. In Fig. 8, 10% and 20% CP was good for type M mortars whilst 25%, 30%, 35% and 40% CP satisfied type S mortars. Fig. 9 also illustrated that a ternary blend containing T1, T2 and T3 could produce a type M mortar whilst T4 produced a type S mortar. Binary mortars that contained 30% L or 20% CP and 35% L or 40% CP best satisfied type M and S mortars respectively. Again in a ternary mixture system containing L and CP, up to 30% of the mineral

M. Bediako et al. / Construction and Building Materials 29 (2012) 667–671 Table 5 Cost analysis of 1:3 mortar/m3 of plain and blended mortar. Cost (US $)

Admixture OPC Sand Total

1:3 Mortar mix Plain

CP

0%

25%

40%

L 30%

35%

0 162.09 33.53 195.63

20.26 121.57 31.44 173.27

32.42 97.26 30.18 159.86

24.34 113.41 31.02 168.77

28.34 105.41 30.60 164.35

671

 Final setting time of binary mixture containing limestone up to 40% occurred faster than clay pozzolana mixture.  In a ternary mixture containing clay pozzolana and limestone, increasing limestone up to 20% caused a faster setting of the paste.  Utilization of Orterkpolu limestone or Mankranso clay pozzolana as mineral admixtures in a ternary or binary mixture has economic benefits when used for masonry mortar formulation.

Acknowledgement admixtures could be suitable for a type M mortar. T4 which contained 30% CP and 20% L was more appropriate for a type S mortar class.

The authors acknowledge the support from the Materials development and engineering division of CSIR-Building and Road Research Institute in Kumasi–Ghana.

3.1. Economic analysis of plain and blended mortars

References

As already illustrated in Figs. 7 and 8, the optimum mix for a type M mortar was at either 30% L or 25% CP whereas that for a type S mortar was at 35% L or 40% CP respectively. Table 5 represents the cost analysis of the formulation using 1:3 binder to sand ratio of plain and the optimum percentages for CP and L mortar mixes. The cost analysis was based on the following assumptions:

[1] Saad MNA, de Andrade WP, Paulon VA. Properties of mass concrete containing active pozzolana made from clay. Concr Int 1982:59–65. [2] Malhotra VM, Hemmings RT. Blended cements in North America – a review. Cem Concr Compos 1995:23–35. [3] Mehta PK, Monteiro PJM. Concrete structure, properties and materials. New Jersey Prentice Hall; 1993. [4] Kim H-S, Lee S-H, Moon H-Y. Strength properties and durability aspects of high strength concrete using Korean metakaolin. Constr Build Mater 2007;21:1229–37. [5] Carrasco MF, Menendez G, Bonavetti V, Irassar EF. Strength optimization of ‘‘tailor-made cement’’ with limestone filler and blast furnace slag. Cem Concr Res 2005;35:1324–31. [6] Tagnit-Hamou A, Pertove N, Luke K. Properties of concrete containing diatomaceous earth. ACI Mater J 2003;100(1):73–8. [7] Kadri E-H, Duval R. Effect of ultrafine particles on heat of hydration of cement mortars. ACI Mater J 2002;99(11):138–42. [8] Anonymous. Minerals in Ghana. A Report of the Ministry of Trade and Industry, Ghana; 2007. [9] Kesse GO. The mineral and rock resources of Ghana. Netherlands: Balkema; 1985. [10] Atiemo E. Production of pozzolana from some local clays-prospects for application in housing construction. J Build Road Res Inst 2005;9(1&2):34–7. [11] British Standard Institution. Composition, specifications and conformity criteria for common cements, BS EN 197-1(Part 1), BSI, London; 2000. [12] ASTM C618-03. Standard specification for coal fly ash and raw or calcined natural pozzolana for use in concrete. PA: ASTM International; 2003. [13] ASTM C109-77. Compressive strength of hydraulic cement mortars (using 2-in or 50 mm cube specimen)1. PA: ASTM Standards; 1979. [14] Ahmed SY, Shakh Z. Portland-pozzolana cement from bagasse: In: Hill Neville, editor. Lime and other alternative cements; 1992. p. 172–9. [15] Helal MA. Effect of curing time on the physicomechanical characteristics of the hardened cement pastes containing limestone. Cem Concr Res 2002;32(3):447–50. [16] Heikal M, El-Didamony H, Morsy MS. Limestone-filled pozzolanic cement. Cem Concr Res 2000;30:1827–34. [17] Brooks JJ, Megat Johari MA, Mazloom M. Effects of admixtures on the setting times of high strength concrete. Cem Concr Compos 2000;22:293–301. [18] Irassar EF, Gonzalez M, Rahhal V. Sulphate resistance of type V cements with limestone filler and natural pozzolana. Cem Concr Compos 2000;22:361–8. [19] Chindaprasirt P, Buapa N, Cao HT. Mixed cement containing fly ash for masonry and plastering work. Construct Build Mater 2005;19:612–8.

 Cost of OPC per 50 kg = $8.60.  Cost of CP or L = $4.31. From Table 5, it is indicated that for a type M mortar containing either 25% CP or 30% L could make a savings of 11.43% and 13.7% over plain mortar whilst type S mortar formulation containing either 40% CP or 35% L could also make a savings of 18.3% and 16% over plain mortar respectively.

4. Conclusions Based on the studies the following conclusions were drawn:  Mankranso clay was suitable to produce a class N pozzolan according to ASTM C618.  Orterkpolu limestone contained 88.5% CaCO3 as calcite.  At 1:3 binder to sand ratio, binary mixture containing up to 30% Orterkpolu limestone (L) or 25% Mankranso clay pozzolana (CP) produced type M mortars whereas up to 40% of OL or MCP produced a type S mortar.  Addition of limestone, clay pozzolana or both had a relatively high water absorption capability compared to the control.  Mankranso clay pozzolana (CP) blends between 10% and 40% had a higher absorption capability than limestone (L) blends.