Durability properties of a non-cement binder made up of pozzolans with sodium hydroxide

Construction and Building Materials 138 (2017) 174–184

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Durability properties of a non-cement binder made up of pozzolans with sodium hydroxide M.R. Karim a,b,⇑, M.M. Hossain a,⇑, M.F.M. Zain a,⇑, M. Jamil a, F.C. Lai c a

Faculty of Engineering and Built Environment, University Kebangsaan Malaysia (UKM), Malaysia Department of Civil Engineering, Dhaka University of Engineering & Technology, Gazipur, Bangladesh c Product Technology Lab Manager, Regional Technology Support Centre, Sika Kimia Sdn Bhd, Malaysia b

h i g h l i g h t s  Strength, water absorption and porosity of a non-cement mortar were determined.  Chloride penetration, sulfate, thermal and corrosion of mortar also investigated.  Non-cem was produced from slag, POFA and RHA with NaOH at 2.5 M solution.  Water absorption and porosity were found as 8.1% and 16.3% respectively at 28-days.  Chloride, sulfate, thermal and corrosion resistance of mortar were found well.

a r t i c l e

i n f o

Article history: Received 3 January 2015 Received in revised form 3 January 2017 Accepted 30 January 2017

Keywords: Non-cement mortar NaOH Water absorption Porosity Chloride penetration Sulfate Corrosion and thermal resistance

a b s t r a c t The durability property of a mortar is the second most important concerns next to its strength. This study investigates some durability properties of a Non-cement binder (Non-cem). The Non-cem was produced from pozzolans such as slag, palm oil fuel ash, and rice husk ash alongside a 2.5 M sodium hydroxide solution. The mortar of Non-cem was tested for its compressive strength, water absorption, porosity, chloride penetration, sulfate, corrosion, and thermal resistance (heated at 700 °C for 2 h) as well as compared to that of ordinary Portland cement (OPC) mortar. The results reveal that Non-cem mortar gains compressive strength of 42.84 MPa (93.36% of OPC) at 28 days. Water absorption and porosity at 28 days are found to be 8.1% and 16.3% for Non-cem mortar whereas 6.2% and 13.5% for OPC mortar, respectively. The chloride penetration of Non-cem and OPC mortars are found to be 11.5 mm and 10.1 mm respectively at 28 days. The sulfate resistance of Non-cem mortar is much higher than that of OPC (i.e., the reduction in compressive strength of Non-cem and OPC mortars were 12.6% and 14.1% respectively because of immersion in 5% magnesium sulfate solution after one month). In case of corrosion resistance, cracks are shown in OPC mortars earlier than Non-cem mortars and in case of thermal resistance of Noncem mortars lose their strengths by 19.21% whereas OPC mortars lose their strengths by 32.87%. These test results indicate that Non-cem could be used as an alternative of cement. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction The increasing demand and consumption of cement have necessitated the use of pozzolanic materials (e.g., slag, palm oil fuel ash (POFA), and rice husk ash (RHA)) in concrete construction. Besides the compressive strength of concrete, the durability properties are another vital engineering concern. Previous studies concluded that ⇑ Corresponding authors at: Faculty of Engineering and Built Environment, University Kebangsaan Malaysia (UKM), Malaysia (M.R. Karim; M.M. Hossain; M.F. M. Zain). E-mail addresses: [email protected] (M.R. Karim), shojib.ce_06@yahoo. com (M.M. Hossain), [email protected] (M.F.M. Zain). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.130 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

the strength and durability properties of concrete can be improved by the incorporation of pozzolans as a partial replacement of cement [1–4]. However, the present academic and industrial research are moving forward regarding the development of a cement-free new alternative sustainable binder by using pozzolans in the field of alkali-activated binder (AAB) or geopolymer concrete. It is well documented that compared with OPC, AAB has the potential to impart mechanical properties such as the compressive strength, elastic modulus and splitting tensile strength at early ages of curing with a low energy consumption and a low CO2 emission [5–7]. A number of researchers reported that AAB containing slag [8–13], POFA [14], RHA [15,16] show effective strength and

M.R. Karim et al. / Construction and Building Materials 138 (2017) 174–184

mechanical properties as well as durability properties. AAB containing a binary composition with slag/fly ash [17–20], slag/silica fume [21], slag/metakaoline [22], Slag/Sugar Cane Bagasse ash [23], POFA/fly ash [24] and POFA/metakaoline [25] shows a very good strength, thermal and other durability properties compared to OPC mortar/concrete. In fact, the properties of mortar/concrete are greatly influenced by the doses of alkali and the curing temperature, duration, and methods employed [26,9]. It is time to an establish new technology using materials with binary, ternary and quaternary compositions with Alkaliactivated composites (AAC) which may really deal with the utilization of waste materials and also reduce the emission of greenhouse gases. Karim et al. reported a preliminary idea for the development of an alternative cementitious binder in the case of AAB by using slag and POFA and/or RHA (binary and/or ternary compositions among the materials) with sodium hydroxide (NaOH) [27] and calcium hydroxide (Ca(OH)2) [28] by weight of binder. Based on the preliminary observations of improved compressive strength and mechanical properties, authors concluded that in presence of chemical activator like NaOH and Ca(OH)2 a binary or ternary composition of slag, POFA, FA and RHA can be used as an alternative of OPC. Now the present situation demands the establishment of durability of composite binder which in turn depends on the interfacial transition zone characteristics and tortuosity of flow path of concrete [29]. Karim et al. [30] investigated water absorption, porosity and thermal resistance (heating at 700 °C) of composite binder produced from a ternary blend of slag 70%, POFA 20% and RHA 10% with NaOH solution of 1.0 M, 2.5 M and 5.0 M concentration. Although water absorption and porosity of the AAB mortar were slightly high, it shows an excellent thermal resistance compared to OPC mortar. The present study investigates the durability properties (i.e., water absorption, porosity, chloride penetration, sulfate, corrosion and thermal resistance) of Non-cement mortar which is produced from slag 42%, POFA 28%, and RHA 30% with 2.5 M NaOH solution. It is well known that mortar and concrete show different characteristics in the interfacial transition zone and tortuosity of flow path due to variation of their constituent ingredients [31]. The volume of void in concrete could be more than that of mortar because concrete contains coarse aggregate but mortar does not. Although the chemical and mineralogical effects of cementitious binders could be obtained by studying mortar, the durability of concrete cannot be quantified by studying mortar only [32]. However, instead of concrete, the durability of mortar was studied in this research due to the convenience of handling sample sizes, amount of activator (NaOH), slag, POFA, RHA. Moreover, it provides a scope to make comparison of few data with literature values [15,23,30,33] where mortar was used as the key component.

2. Materials and methodology 2.1. Materials and properties of materials Three different pozzolanic materials including ground granulated blast furnace slag, POFA, and RHA were used as constituents of Non-cement binder (Non-cem). OPC type I (42.5 N) was used as obtained from Tasek Cement Sdn Bhd, Malaysia, to compare the different properties of the Non-cem. The slag was provided by local industry named Slag Cement Sdn Bhd, Malaysia. POFA was taken from Ulu Langat palm oil mill, Selangor, Malaysia. RHA was made using a special type of furnace available in the concrete and structure lab at University Kebangsaan Malaysia. The details of the furnace were reported by Zain et al. [34]. The standard sand as required by BS EN196-1 [35] was used as fine aggregate for the preparation of mortar. As a chemical activator, NaOH flakes of

175

analytical grade were purchased from Merck. A superplasticizer (SP) Darex Super 20 brand obtained from Grace Manufacturer was used to increase and maintain sufficient flow of mortar. Tap water was used for the preparation and curing of mortar specimen. Fineness and grain size of materials were determined using automatic Blaine machine and Malvern Mastersizer respectively. Xray diffractometer (XRD) analysis was conducted to determine the amorphous or crystalline phase of materials using the Bruker AXS brand XRD machine, D8 advanced model using 40 kV power and 40 mA with Cu Ka source. The 2-theta angle ranges from 5 to 80 degree. Chemical composition of materials was determined using X-ray fluorescence (XRF). The morphological view and shape of the particles of materials were examined using scanning electron microscopy (SEM) images using Supra 55VP, ZEISS. The pore volumes of the materials were determined using Sorptomatic instrument. 2.2. Preparation of mortar The mixed proportions of the raw materials (i.e., slag, POFA, RHA, SP, NaOH, and sand) are presented in Table 1 for the preparation of Non-cem mortar, as suggested by Karim et al. [30]. The fineness of Non-cem was enhanced significantly by grinding of POFA and RHA in a ball-mill machine. However, the slag was used as received from the industry. A 2.5 M NaOH solution was used as chemical activators. The NaOH solution-to-binder ratio was used as 0.5, and sand-to-binder ratio was kept as 3.0. The required SP was used to maintain a flow of mortars at 70 ± 5% (to maintain the same flow as that of OPC). Mortar was mixed and prepared using a Hobart mixture machine according to ASTM C305 specification [36]. Mortar prism (40 mm  40 mm  160 mm) was compacted by using a mechanical shaking table for a uniform compaction. Shaking was done until mortar thoroughly spread inside the prism mold by two layers. Finally, the prism molds of the mortars were opened after one day. The mortar specimens were then immersed in a water tank at a temperature of 25 ± 2 °C for curing until the desired age of testing was achieved. 2.3. Tests on mortar 2.3.1. Flow and strength The mortar flow spread test was done by using a flow table based on the ASTM C1437 testing standard [37]. The compressive strength of the mortar prism (40 mm  40 mm  160 mm) was determined according to the BS EN196-1 [35] testing standard by using Universal testing machine (Unit test brand of capacity 500 kN). 2.3.2. Water absorption Water absorption of the mortar prism specimens (40 mm  40 mm  160 mm) was carried out according to ASTM C642 (1997) standard. Prism specimens (at the desired age of 14, 28, and 90 days) were dried until weight of specimen became constant (Wd). The specimens were then immersed in clean water for 30 min for 1, 3, 6, 24, 48, and 72 h. After the desired immersion period, the specimens were taken out and surfaces were wiped quickly with a wet cloth then weighed (Wa) immediately. Therefore, water absorption of the mortar specimen was determined as 100(Wa Wd)/Wd in percentage. Finally, water absorption of the mortar was taken as the average value of six specimens. This test method was also successfully used in a study by Qureshi et al. [38]. 2.3.3. Porosity For the determination of porosity of mortar, prism specimens of 40 mm  40 mm  160 mm size were cast according to BS EN196-

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Table 1 Materials used for the preparation of mortars (by weight). Binder

Non-cem Cement

Raw materials (% by weight) Slag

POFA

RHA

OPC

SP

42 0

28 0

30 0

0 100

4.5 –

Activator

Solution-to-binder ratio

Sand-to-binder ratio

Reference

NaOH –

0.5 0.5

3.0 3.0

Karim et al. [40] –

1 [35]. The porosity of mortar was determined at the age of 14, 28 and 90 days of curing age. Specimens were dried at 100 ± 5 °C until a constant weight (Wd) was achieved. The specimens were then immersed in clean water for full saturation for 3 days. The weight of specimens in water was recorded as Ww. Subsequently, the specimens were taken out, and their surfaces were wiped out by a wet cloth quickly and the specimens were weighed in air immediately (Wa). Then, the porosity of mortar specimen was calculated as 100(Wa Wd)/(Wa Ww) in percentage. Finally, the porosity of mortar was determined as the average value of six specimens. This method was used to measure the porosity of mortar/concrete in several previous studies [39,40].

+

2.3.4. Chloride penetration Chloride ion penetration test was carried out according to Japanese Industrial Standard (JIS A6203) for the prism specimens of size 40 mm  40 mm  160 mm. Specimens were tested for chloride ion penetration test at the age of 28 days. Before immersing the specimens in sodium chloride (NaCl) solution, the two smooth surfaces and two ends of the dry mortar specimens were coated with epoxy resin paint. The specimens were then immersed in 2.5% NaCl solution at 20 °C for 14 and 28 days for chloride ion penetration test. After the desired immersion period (14 and 28 days), the specimens were split, and the split cross-sections were sprayed with 0.1 N silver nitrate (AgNO3) solution. The depth of the rim of each cross-section that changed to white color was measured by using slide calipers and taken as a chloride ion penetration depth. The penetration was obtained as the average of six measured values. This method was also used successfully by Shaikh [41].

Mortar (40mm×40mm×160mm)

2.3.5. Sulfate resistance To perform the sulfate resistance of mortar, prism specimens of 40 mm  40 mm  160 mm in size were prepared according to BS EN196-1 [35]. Before immersion in 5% magnesium sulfate (MgSO4) solution, the strength of the mortar was measured as fc using three specimens at 28 days. Subsequently, another nine specimens were immersed in 5% MgSO4 solution for a period of 30, 60, and 90 days. At the desired age of testing, the three specimens were tested for compressive strength (fcs) at those specified ages. Compressive strength of mortar was taken as average of the six measured values from the three specimens. This test method was successfully used by El-Sayed et al. [13] for alkali-activated paste mixture and Bondar et al. [42] for concrete specimens. Finally, the loss in compressive strength was calculated as (fc fcs)/fc for those specimens because of sulfate attack. 2.3.6. Corrosion resistance Fig. 1 shows the schematic drawing of the corrosion testing procedure. In this regard, mortar prisms of 40 mm  40 mm  160 mm in size were prepared according to the BS EN196-1 [35] using 2.5 M NaOH solution. In addition, an embedded steel of 10 mm diameter and 160 mm in length was placed at the center of the prism. The steel was protected in such way that it protruded from the top surface of the prism by 15 mm. Thus it provides a sufficient mortar cover of 15 mm and 15 mm thick mortar at the end of steel bar and at the bottom of prism as shown in Fig. 1.

12 Volt DC power supply

Anode (steel bar) Cathode (Stainless steel mesh) Steel bar (10mm diameter and160mm long)

5% NaCl solution

Fig. 1. Test setup of corrosion resistance of mortar in 5% NaCl solution.

After completion of curing in water for the age of 28 days, they were taken for testing. Then the specimens were subjected to accelerated corrosion test with impressed voltage (ACTIV) using 5% sodium chloride (NaCl) solution and a constant 12 DC voltage. Then the condition of the prism was monitored continuously until the first crack was observed. Therefore, corrosion resistance of the mortar specimen was taken as the required time of the first crack. The measured results are the average value of six specimens. This method was used to measure the corrosion resistance by Chindaprasirt et al. [43]. 2.3.7. Thermal resistance To determine thermal resistance of mortar, prism specimens of 40 mm  40 mm  160 mm in size were prepared using 2.5 M NaOH solution according to the BS EN196-1 [35]. After the 28 days of curing age, the weight of specimens was recorded as Ws. Then they were put into electric furnace and heated at 700 °C for 2 h. The increment of temperature of the furnace was 9 °C per min. After completion of heating period, specimens were cooled to room temperature maintaining approximately the same period of time. Subsequently, specimens were taken out from the furnace and weighed (Wd). Then the weight loss of the specimens was calculated as (Ws Wd)/Ws. The strength of these specimens which heated at 700 °C was determined (fcf). This test method was successfully used in a study by Rahel et al. [44]. The loss in strength of the specimens due to thermal effect was determined as (fc fcf)/ fc; where, fc is the strength of ordinary specimen (without being heated). The measured results are the average value of six specimens. 3. Results and discussion 3.1. Physical properties of materials The different physical properties of the raw materials, OPC and Non-cem including specific gravity, fineness, XRD and SEM

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analysis were carried out. All of these properties are discussed in details using tables, graphs and photographs in the following sub-sections.

120.0

Percentage Passing

100.0

3.1.1. Specific gravity of materials Specific gravity of any materials is one of the prime parameter to understand the relative density and weight of the material. Specific gravity of Non-cem was calculated based on the test results of specific gravity of raw materials used (i.e., slag, POFA and RHA). All of these test results are presented in Table 2. The table shows that the new composite binder is much lighter than OPC with a specific gravity of Non-cem is 2.45. 3.1.2. Fineness of materials It is well known that fineness of binder is an important property for strength development of mortar. It is also recognized that the greater the amount of fine particle, the higher is the fineness/surface area, which increases the rate of hydration leading to increase in strength development of mortar or concrete. For these reasons, POFA and RHA were ground in a ball-mill machine to obtain more fineness of the Non-cem, while slag was used as received from industries. The fineness values of the different materials and the Non-cem are presented in Table 3. The table indicates that grain size of the raw materials is larger based on parameters d10, d50 and d90 which are used to determine the size of a particle. To determine fineness modulus of sand, sieve analysis was performed according to ASTM C136 [45]. Fineness modulus of the sand is found to be 2.41. Using these sieve analysis data, a particle size distribution curve of the standard sand is presented in Fig. 2. The figure shows a well-defined particle size distribution curve. Table 3 shows that mean particle size (d50) of the unground POFA was the highest at 57 lm, while it is close to the OPC sample for the other materials. Particle size of POFA and RHA decreases after grinding that is shown in the Table 3. The mean particle sizes of the other materials are found to be 14.67 lm for slag, 6.63 lm for ground RHA, 16.08 lm for ground POFA, and 16.17 lm for OPC. Thus raw materials have lower particle size in comparison to that of the OPC. Specific surface area of the POFA samples was much lower as compared to OPC; but it can be improved greatly after grinding. The specific surface area of other materials shows

Table 2 Specific gravity of the materials. Name of materials

Specific gravity

Slag Ground RHA Ground POFA OPC Non-cem Standard sand

2.85 2.08 2.27 3.14 2.45 2.53

80.0 60.0 40.0 20.0 0.0 0.1

1.0

10.0

100.0

Sieve Size (mm) Fig. 2. Particle size distribution curve for standard sand used in this research.

a higher value and lower grain size other that unground POFA. Slag has an extensively high specific surface area of 1.136 m2/cm3, which is 1.5 times more than that for OPC. It is clearly understood that Non-cement binder shows 4 times higher surface area than OPC, because it is produced from a very fine slag, finely grounded POFA and RHA. 3.1.3. Strength activity index of materials The strength activity index is the ratio of the compressive strength of mortar containing substitute materials 20% by mass of binder to that of the average compressive strength of reference cement mortar at a designated age [46]. Strength activity of the materials was determined and the results are presented in Table 4. Experimental results show that the activity index of slag is more than 100% for both 7 days and 28 days age. Thus slag is considered as grade 100 based on ASTM C989 [47] classification. Activity indexes of unground RHA and POFA are below 50% and over 54% at 7 days respectively. They are found to be more than 63% at 28 days. Activity indexes of RHA and POFA are found lower due to the use of unground POFA and RHA in preparing testing mortar specimens. Usually, the strength activity index of any pozzolans can be improved by grinding or increasing their fineness [48] and can easily be seen from the Table 4. Thus activity indexes of grounded POFA and RHA are much higher than that of unground samples. Therefore, pozzolans can be more activated by improving their fineness. Similar observation was also reported by Givi et al. [49]. 3.2. Chemical properties of materials The chemical properties and oxide compositions are other important parameters for the activation of a binder. To determine the chemical properties, the raw materials and the Non-cem were examined through X-ray fluoresce (XRF). The oxide composition

Table 3 Fineness of the materials [40]. Materials

Slag POFA (UG) POFA (G) RHA (UG) RHA (G) OPC Non-cem

Grain size (lm)

Fineness (m2/g)

d10

d50

d90

Blaine

BET

Passing through 45 lm sieve

Specific surface area (m2/cm3)

Pore volume (cm3/g)

2.66 5.40 2.15 1.98 1.68 3.36 1.10

14.67 57.13 16.08 8.65 6.63 16.17 9.20

37.57 305.21 167.13 38.75 29.20 47.37 49.07

0.3919 0.1977 0.4582 0.5750 0.6964 0.2302 0.9299

1.99 2.89 12.57 – 12.68 1.52 8.16*

99.87 8.00 96.39 12.50 97.35 86.48 98.16

1.136 0.435 1.008 1.265 1.532 0.725 2.045

0.00619 0.00639 0.01724 – 0.00675 0.00310 –

UG – Unground, G – Ground. Calculated based on mix proportion as given in Table 1.

*

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Table 4 Strength activity index of materials. Materials

Strength activity at 7 days

Slag RHA (UG) RHA (G) POFA (UG) POFA (G) Non-cem

Strength activity at 28 days

Index

ASTM requirement

Index

ASTM requirement

100.44 48.58 86.76 54.25 84.96 91.23

95 for 120 grade – – – – –

103.88 63.04 101.61 65.36 99.07 102.32

95 for 100 grade – – – – –

and loss on ignition (LOI) test results, as obtained from the experiments, are presented and discussed below in details. 3.2.1. Chemical composition Table 5 presents the chemical compositions of the materials. The table shows that among all types of raw materials, RHA contains 87.75% of silica which is responsible for the pozzolanic reaction or secondary hydration in mortar or concrete. The total percentage of SiO2 + Al2O3 + Fe2O3 is over 70% for RHA which is greater than the minimum (70%) as specified in ASTM C618 [46]. Thus RHA can be categorized as class-F pozzolan. While the sum of these oxides lies between 50% and 70% for both slag and POFA, accordingly, they may be considered as class-C pozzolan. But POFA does not possess any cementing property, thus it cannot be categorized as class-C pozzolan. The sulfur trioxide (SO3) content for these materials is less than 4% which is the maximum allowable content as prescribed by the ASTM C618 [46]. POFA contains 11.86% of K2O which is greater compared to the other materials because palm oil trees consume more potassium from soil during cultivation period [30]. However, the Non-cem shows a similar chemical composition to those of OPC, except it contains more than double the amount of SiO2 content and less than half the amount of CaO. 3.2.2. Loss on ignition The loss on ignition (LOI) is the weight lost when the material is heated to 1000 °C. Usually, at this temperature all moisture or CO2 present in the material is dried out and released. The LOI test data of the materials are shown in Table 4. The LOI is found higher for POFA, but it is less than the prescribed value of 10% by ASTM C618 [46]. While the value of LOI of Non-cem sample is nearly 7% which also falls within the prescribed ASTM limit. 3.3. Morphology and microstructure of materials The shape and size of the particles are important factors for the activation, bonding, flow and workability. Thus shape and physical appearance of the materials were examined through Scanning Electron Microscopy (SEM) analysis. The crystalline and amorphous state of the materials was analyzed using X-ray diffraction (XRD) analysis. The obtained results are discussed below.

3.3.1. SEM observation The SEM images of raw materials and Non-cem are shown in Fig. 3. Particles in the SEM view of RHA are found to be very porous and thus have high specific surface. The shape of unground RHA (as produced) particles is found to be angular and cellular. It can be observed from the SEM view of unground POFA (as received) that it contains mostly spherical particle with a small amount of spheroid and irregular-shaped particles. The SEM view of POFA (as received) also indicates that it consists of irregular-shaped particles with a sizeable fraction showing porous and cellular structure. Similar observation for RHA and POFA was reported in previous studies [27,43,48]. The particles in the SEM view of slag are observed to be square, triangular and diamond shaped and similar to the particles of OPC. The box and stone shaped particles are observed in the SEM view of OPC sample. On the other hand, the SEM image of Non-cem is presented in Fig. 3(f). This image reveals that after grinding, most of those spherical particles and large, irregular-shaped particles of POFA and RHA had been crushed and broken into a smaller shape. Therefore, Non-cem samples consist of very irregular-shaped particle with a porous cellular surface because they were produced from the mixture/combination of slag, ground RHA and POFA. Consequently, surface area of Non-cem increased and that can easily be viewed from the SEM image of Non-cem as shown in Fig. 3(f) and grain size (Table 4). 3.3.2. X-ray diffraction (XRD) analysis To know the amorphous and crystallographic structure of the materials, the X-ray diffraction (XRD) analysis was performed. The results from the test are shown in the Fig. 4. The figure indicates that slag contains amorphous silica. Amorphous silica present in these materials is responsible for the pozzolanic activity. The figure also demonstrates that the Non-cem exhibits mainly amorphous and few crystal forms of quartz and silica. This happens due to the grinding, because most of the crystal forms were transformed into the amorphous phases after grinding. The XRD view of POFA shows that the majority of crystalline phases consist of quartz, mullite, but different features have been found from the XRD of slag and RHA. The test data also indicate that the RHA contains mainly amorphous materials with a small quantity of crystalline phase as cristobalite which is the high temperature phase of SiO2 and sylvite. Only a few peaks are observed that could be identified as crystalline silica.

Table 5 Chemical composition of the materials. Material

Slag POFA RHA OPC Non-cem

Chemical properties, oxide compositions (wt.%) SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

P2O5

TiO2

MnO

LOI

33.05 47.22 87.75 20.99 53.43

16.36 2.24 0.38 4.60 7.61

0.53 2.65 0.19 4.44 1.02

45.0 6.48 1.04 67.17 21.03

6.41 5.86 0.69 2.53 4.54

1.21 3.34 0.56 2.98 1.61

0.13 1.22 0.05 0.03 0.41

0.42 11.86 2.83 0.16 4.35

– 5.37 1.31 – –

– 0.17 0.02 – –

– 0.10 0.07 – –

3.05 5.42 3.04 1.30 6.92

M.R. Karim et al. / Construction and Building Materials 138 (2017) 174–184

(b) POFA (UG)

(a) RHA (UG)

(c) RHA (G)

(d) POFA (G)

(e) Slag

(f) Non-cem

(g) OPC Fig. 3. SEM images of RHA, POFA, slag, Non-cem and OPC.

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12 Water Absorption (%)

11 10 9 8 7 6 OPC

(a) Water absorption at 14 days

5

Non-Cem

4 3 0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

Time (Hours)

Fig. 4. X-ray diffraction (XRD) pattern of OPC, slag, Non-cem, POFA and RHA.

Water Absorption (%)

9

3.4. Compressive strength

8 7 6 5

0

3.5. Water absorption

Compressive Strength (MPa)

The water absorption of mortar at 14, 28, and 90 days of curing age is presented in Fig. 6. The figure shows that water absorption of Non-cem mortar was over 10% whereas that obtained for OPC mortar was 7.4% at 14 days. Interestingly, the rate of water absorption was higher at the beginning of immersion period (i.e., within

50 40 30 20 10

Non-Cem OPC

3 Days 24.62 25.10

Non-Cem

3

7 Days 30.20 30.84

28 Days 42.84 45.73

Fig. 5. Compressive strength of OPC and Non-cem mortar with 2.5 M NaOH solution.

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

Time (Hours) Water Absorption (%)

The compressive strength of Non-cem mortar containing 2.5 M NaOH solution was determined at 3, 7, and 28 days, and the results are shown in Fig. 5. The figure shows that the strength of Non-cem mortar increases with curing age which are similar to OPC mortar. The strength of Non-cem is very close to OPC at all ages up to 28 days. Non-cem containing 2.5 M NaOH solution achieved compressive strength of 24.62 and 30.20 MPa at 3 and 7 days respectively. The compressive strength of Non-cem mortar was within the ASTM C150 standard [50] (the minimum strength of OPC type I cement was 12 and 19 MPa at 3 and 7 days respectively). In addition, Non-cem mortar with 2.5 M NaOH solution achieved compressive strength of 42.84 MPa at 28 days which was greater than those required for OPC (42.5 N). The strength of Non-cem was determined for the mixed proportions of Non-cem (42% slag, 28% POFA, and 30% RHA) using 2.5 M NaOH solution. This mix ratio gave the highest strength as recommended by Karim et al. [27]. However, this study focuses on the durability property of Noncem mortar only. In fact, the strengths of the Non-cem mortar are greatly influenced by the mixed proportion, fineness of the materials and doses (amount/concentration) of activators, as reported in several previous studies [17,18,27].

00

OPC

(b) Water absorption at 28 days 4

9 8 7 6 5 4 3

OPC

(c) Water absorption at 90 days

Non-Cem

2 1 0 0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

Time (Hours) Fig. 6. Water absorption of mortar at 14, 28 and 90 days.

30 min to 3 h) at 14 days of testing age. Water absorption of Non-cem and OPC specimen was 6.7% and 4.4% respectively after 30 min. However, rate of water absorption was lower at 90 days of testing age (i.e., absorption was 4.3% for Non-cem and that for OPC was only 1.8% after 30 min). This result can most likely be attributed to the lower strength of Non-cem mortar at 14 days. Thus the mortar absorbed water quickly after immersion into water. Mortar specimens achieved more strength at 90 days, and consequently, absorption rate was reduced. The water absorption of Non-cem specimens was higher than that of OPC mortar at all testing ages. Differences in water absorption of Non-cem specimens and OPC mortar were 2.0% and 1.9% at 28 and 90 days respectively. In addition, the water absorption of Non-cem and OPC mortar reduced at longer age, at 90 days. This could happen because mortar became denser and compacted at later age because of hydration effect. In contrast, Adam [19] concluded that durability properties including water sorptivity of the alkali-activated slag concrete did not perform well. He [19] also reported that the fly ash-based geopolymer concrete performed better than the OPC, blended, and alkali-activated slag concrete in terms of water sorptivity. In case of alkali-activated binder, Chi and Huang [17] obtained water absorption of 7.5% for OPC specimen. However, they found that absorption reduced significantly for the alkali-activated binder (1.1%–6.1%), which depends on the ratio of slag-to-fly ash and activator contents. Chi and Huang [17] obtained high performance in terms of water absorption most probably due to the higher compressive strength (20 MPa–80 MPa) of mortar. Nonetheless, in the present study,

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water absorption of the Non-cem mortar was found slightly a higher than OPC. Non-cem mortar showed higher water absorption most likely because of porous microstructure as reported by Karim et al. [27] as revealed in scanning electron microscopy (SEM) views of mortar and observed slightly lower strength than OPC at the same ages. In addition, Non-cem had fine particles and a larger surface area and consequently absorbed more water than OPC [27].

figure also shows that porosity of the mortar reduced gradually and systematically with the increasing strength of mortar. This happened most likely because of the reduced pores of the mortars with the increasing strength. Hence, water absorption reduced with decreasing porosity. Similar observation was reported by Chindaprasirt and Rukzon [43]. Therefore, the observed porosity of Non-cem seems to be rational. 3.7. Chloride penetration

3.6. Porosity The results of porosity of mortars at 14, 28, and 90 days are shown in Fig. 7(a). These results confirm that porosity of mortar containing Non-cem was 3.0% higher than that of OPC at 28 days. Siliceous admixture (POFA, RHA and slag) particles had more surface area because of small particle size; hence, they absorbed more water. In addition, Non-cem mortar showed porous microstructure as shown in Fig. 3 (f). Consequently, the porosity of Non-cem mortar increased. The porosity of the mortars reduced with an increase in age up to 28 days significantly, and then porosity reduced slightly. This happens because of an increase in the hydration of binding materials. Porosity of the Non-cem mortar reduced by a pattern similar to that of OPC mortar at the age of 14–90 days. The porosities of the Non-cem mortar were found to be 16.0% 16.3%, whereas that of OPC was 13.3% at 90 days. Al-Otaib [51] reported that alkali-activated slag concrete has higher porosity value compared with OPC. This researcher obtained a range of porosity of 13%–10% at the age of 7–360 days, depending on the slag replacement; whereas OPC concrete showed a porosity of 10.4%–8% for the same age. Nevertheless, the relationship between the porosity and strength of mortar follows the conventional pattern as shown in Fig. 7(b). The figure shows a strength-toporosity relationship of y = 574.91x 0.953 for OPC mortar, and the relation is y = 220.09x 0.742 for Non-cem mortar, where ‘y’ is the porosity and ‘x’ is the compressive strength of mortar. Chindaprasirt and Rukzon [43] obtained a porosity-to-strength relation of y = 457.63x 0.87 for blended mortar with fly ash and RHA. The

Porosity (%)

25

OPC

Non-Cem

20

15

10 0

20

40 60 Curing Age (Days)

80

100

The chloride ion penetration test data for the OPC and Non-cem mortars as carried out in this study are shown in Fig. 8. The results show that OPC specimens already had a chloride ion penetration of 24.55% (i.e., chloride penetration of 9.82 mm in 40 mm section of mortar specimen) after 14 days of testing age. On the contrary, specimens containing Non-cem shows a slight increase in chloride ion penetration depth of 25.50% (i.e., chloride penetration 10.20 mm in 40 mm section of mortar specimen). The Non-cem mortars show slightly less/reduced resistance to accelerated chloride penetration test compared with OPC mortar. Accelerated chloride penetration depth of OPC and Non-cem mortars were 9.82 and 10.65 mm respectively at 14 days. However, the chloride penetration depth was slightly higher at 28 days of testing age. These results confirm that Non-cem mortar shows slightly less chloride penetration resistance compared with that of OPC, but depth of chloride penetration for OPC and Non-cem specimens was found very close in the present study. For alkali-activated slag (OPC:slag = 40:60), Roy et al. [52] reported that alkali-activated blended cement mortar shows a high early strength, rapid hardening, high-ultimate strength, low permeability in alkali-activated cement concrete, and resistance to the effects resulting from high chloride diffusion rates or chemical attack. Al-Otaib [51] concluded that alkali-activated slag concrete (either 100% slag and/or OPC:slag = 40:60) shows a very good result against chloride ion penetration. This researcher obtained a good result which may be due to a higher compressive strength (over 80 MPa) of concrete. By contrast, Adam [19] concluded that the durability properties including chloride resistance of the alkali-activated slag concrete did not perform well. He also reported that the fly ash-based geopolymer concrete performed better than the OPC, blended, and alkali-activated slag concrete in chloride penetration. However, the chloride penetration depth of Non-cem mortar was found to be slightly greater than OPC, which may be most probably because of its reduced compressive strength and larger porosity values. Therefore, chloride penetration of Non-cem mortar seems to be normal. 3.8. Sulfate resistance The reduction in compressive strength of mortars by immersion in 5% MgSO4 solution for different periods is shown in Fig. 9. The

(a) Porosity of mortar at different age 24.0 y = 574.91x-0.953 R² = 0.97

Non-Cem

OPC

Chloride Penetration (mm)

Porosity (%)

22.0 20.0 18.0 16.0 14.0

220.09x-0.742

y= R² = 0.98

12.0 10.0 30.0

35.0 40.0 Compressive Strength (MPa)

45.0

(b) Relation between porosity and strength of mortar Fig. 7. Porosity of OPC and Non-cem mortar at different ages.

12 11 10 9 8 7 6 5

50.0

14 Days 28 days

OPC 9.82 10.10

Non-Cem 10.65 11.38

Fig. 8. Chloride ion penetration test results for the Non-cem and OPC mortars.

M.R. Karim et al. / Construction and Building Materials 138 (2017) 174–184

Reduction in Compressive Strength (%)

182 30 OPC

Non-Cem

20

10

0 30

60

90

Age (Days)

Fig. 9. Reduction in compressive strength of mortar due to immersed in 5% MgSO4 solution.

OPC-Specimens results confirm that Non-cem has a better resistance against sulfate attack compared to OPC mortar. The reduction in compressive strength of the OPC and Non-cem was 14.1% and 12.6% respectively after immersion for 30 days whereas the strength reductions after 60 and 90 days of immersion periods were found higher. Chi [53] reported that sulfate resistance of slag-activated concrete is better than OPC concrete. In the present study, the greater resistance of the Non-cem mortar against sulfate attack seems to be customary which may be because of the better chemical action of NaOH. 3.9. Corrosion resistance The time of formation of the first crack of mortar subjected to accelerated corrosion test with impressed voltage (ACTIV) was investigated on the Non-cem and OPC mortars. The time of the first crack of OPC mortar was observed at 37 h. It is interesting to note that crack was seen in a number of the Non-cem mortar after 132 h of testing time. In addition, there was no crack formed in most of the Non-cem mortars but the reinforcement was found fully corroded and disconnected from the mortar after 94 h of testing time. Fig. 10 shows the physical appearance of the mortars after ACTIV test. The figure indicates a clear crack formation in the OPC mortar specimens with the existence of extended portion of the reinforcement. On the contrary, Non-cem mortar shows no appearance of crack formation but the extended portion of the reinforcement is found completely corroded and disconnected from mortar. The extended portion of the reinforcement also suffered corrosion and that may be due to chemical reaction occurred for the ACTIV testing arrangement (cathodic and anodic reactions due to flow of electricity). However, for alkali-activated cement with slag (OPC:slag = 40:60), Roy et al. [52] reported that blended alkali-activated cement mortar exhibited a low corrosion rate of the steel reinforcement. Adam [19] concluded that geopolymer concrete might have a comparable or even better performance in terms of corrosion resistance. Nonetheless, in the present study corrosion resistance of Noncem mortar is found to be more than double compared to OPC. Therefore, corrosion resistance of the Non-cem mortar seems to be rational. 3.10. Thermal resistance The losses obtained in both weight and strength of mortars are presented in Fig. 11. The weight loss of OPC, Non-cem specimens was found to be 10.26, and 11.71% respectively. The figure also indicates that loss in strength of OPC mortar is 32.87% while Non-cem shows a very good result against thermal resistance – they lose their strengths by 19.21%. Rahel et al. [44] found that

Non-cem Specimens Fig. 10. Pictures of the mortars after accelerated corrosion test with impressed voltage (ACTIV).

OPC Losses in weight (%) Losses in strength (%) Non-cem

0

5

10

15

20

25

30

35

% Losses in Weight and Strength of Mortar after Heated at 700°C Fig. 11. Losses in weight and strength of mortars due to being heated at 700 °C.

OPC specimens exhibited a reduced strength by 32% under the same conditions. In case of full replacement of cement, Rashad [54] reported that alkali-activated metakaolin based concrete shows a very good result against heat resistance up to 1200– 1400 °C. Alkali-activated binders slag with metakaolin blended showed a very strong against heat/thermal resistance as reported by Bernal et al. [55]. In present study, Non-cem mortar exhibits a very strong thermal resistance compared to that of OPC up to 700 °C which seems to be practical. This better thermal resistance of Non-cem mortar may be due to the strong bond formed by NaOH solution in the mortar and also its high boiling point

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(1388 °C). Thus the strength of Non-cem mortar did not reduce significantly due to exposure at 700 °C. Therefore, it can be concluded that thermal resistance of Non-cem mortar is found to be rational. 4. Conclusions Based on the durability test results of the Non-cem mortar, the following conclusions are drawn from the present study:  Water absorption of Non-cem mortar (e.g., 8.1% at 28 days) was found slightly higher compared to that of OPC (e.g., 6.2% at 28 days) mortar. Water absorption of Non-cem mortar can be minimized by improving its compressive strength.  Non-cem mortar showed a porosity of 16.3% at 28 days which was slightly higher than that of OPC mortar (e.g., 13.5% at 28 days). Porosity of Non-cem mortar can be reduced by increasing its compressive strength.  Chloride penetration of Non-cem mortar was found as 11.3 mm, whereas OPC showed 10.1 mm at 28 days, and these results were very close. Chloride penetration of Non-cem mortar seems to be reasonable compared to OPC.  The reduction in compressive strength of Non-cem mortar was found to be 12.6% when immersed in 5% MgSO4 solution for 30 days, whereas that in OPC mortar case was found to be 14.1% under the same conditions. Thus sulfate resistance of Non-cem mortar shows a good result.  Corrosion resistance of Non-cem mortar was found very well when evaluated against OPC mortar. The time of formation of the first crack in mortar when subjected to accelerated corrosion test with impressed voltage (ACTIV) was found after 37 h in OPC mortar, while no crack was observed in Non-cem mortar even after 94 h of testing time.  An excellent thermal resistance was shown by the Non-cem mortar when it was exposed to 700 °C for two hours. Only 19.2% strength reduced in case of Non-cem mortar while OPC lost more than 32% strength under the same conditions.  Based on the overall test results, Non-cem could be used as a potential alternative of cement. The utilization of Non-cem would not only save the OPC consumption but it also emerges as a sustainable binder for the production of sustainable concrete.  Moreover, Non-cem can also contribute to reduced CO2 emission by using it as a supplement of the conventional cement.

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