Construction and Building Materials

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1 Construction and Building Materials 25 (211) 3 38 Contents lists available at ScienceDirect Construction and Building Materials journal omepage: Comparison of different metods for activation of ordinary Portland cement-slag mortars Fatolla Sajedi *, Hasim Abdul Razak Department of Civil Engineering, University of Malaya, 563 Kuala Lumpur, Malaysia article info abstract Article istory: Received 12 February 21 Received in revised form 13 May 21 Accepted 19 June 21 Available online 16 July 21 Keywords: OSM Grinding Termal treatment Cemical activators Early strengt Strengt loss Tis paper compares tree metods for activation of OPC-slag mortars (OSM): (1) prolonged grinding of binders (mecanical metod), (2) elevated temperature curing of mortars (termal metod), and (3) use of cemical activators suc as NaOH, KOH, and Na 2 SiO 3, 9.35H 2 O (cemical metod). Te proper reactivity of OSM was evaluated using a mixture of 5% OPC and 5% slag. Early and ultimate strengts were compared. All tree activation metods accelerated bot te slag reaction and strengt development rates. However, te cemical metod did not sow a significant effect on te ultimate strengt, wile termal activation increased te early strengt by 3 days. Mecanical activation increased te early strengts of te mortar significantly, but about 6% strengt loss occurred in te ultimate strengt. Altoug, te application of mecanical and termal activation metods needs extra equipment and energy, due to more significant of strengt improvement; based on current test results, it can be said tat mecanical activation is te most efficient and feasible metod for te activation of OSMs. Ó 21 Elsevier Ltd. All rigts reserved. 1. Introduction In tis experimental work, mecanical, termal, and cemical metods ave been used to improve te compressive strengt of OSMs. All tree metods can be used to activate te potential reactivity of cement constituents. Te mecanical activation is used to increase te specific surface area of te constituents and tus accelerates te ydration rate. Many results indicate tat te early strengt of a ardened cement paste is directly proportional to te fineness of te cement, but fineness cannot contribute to later-age strengt. In contrast, excessively ig fineness may increase te water requirement and cause a reduction in later strengt gain. In general, increased fineness results in better strengt development, but in practice, fineness is limited by economic and performance considerations and factors suc as setting time and srinkage [1]. For better performance, te fineness of GGBFS must be greater tan tat of cement [2]. At te same time, te requirement to increase fineness reduces productivity and consumes more energy. Prolonged grinding not only increases te surface area of a material, but also te number of imperfections or active centers wic exist at te edges, corners, projections and places were te inter-atomic distances are abnormal or are embedded wit foreign atoms. Tese centers are in a iger energy state tan in te normal structure. Te more of tese centers, te faster te rate of reactivity. Millers and Oulton * Corresponding autor. Tel.: address: f_sajedi@yaoo.com (F. Sajedi). (197) observed tat percussive dry grinding can cause obvious crystal distortion of kaolinite. It was also recently found tat impaction and friction milling of ig alumina cement alters its crystallinity and notably modifies its ydraulic beavior. A strengt test on 22 pozzolans (Catterjee and Lairi, 1967) indicated no general correlation between te compressive strengt of different materials (at 28 or 6 days) and surface area (eiter by Blain or BET metod). However, it was stated tat strengt increases as fineness increases, for a single material. Different pozzolans ave different quantities and nature of reactive components. It cannot be expected tat a unique relationsip exists between reactivity and surface area for all pozzolans. Prolonged grinding of natural pozzolan also consumes extra energy and reduces grinding productivity [3]. It as been reported [4] tat for eac 1 m 2 /kg increasing in Blain fineness, cost of grinding will be increased by about 1%. Elevated temperature curing needs additional equipment and is usually suitable for precast products. It also consumes a great amount of energy. Hydrated mortars and concretes can reac teir maximum strengt witin several ours troug elevated temperature curing. However, te ultimate strengt of ardened mortars and concretes as been sown to decrease wit curing temperature. Variations of mortar and concrete under ig temperature are mainly te result of two different mecanisms. One is te variation of material properties of te constituent pases under ig temperatures, and te oter is te transformation of constituent pases under different temperatures. Terefore, te property of mortar and concrete under ig temperatures must be studied from bot a mecanical and cemical point of view [5] /$ - see front matter Ó 21 Elsevier Ltd. All rigts reserved. doi:1.116/j.conbuildmat

2 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) Te cemical activation refers to te use of some cemicals to activate te potential reactivity of cementitious components. Alkali-GGBFS is a typical, successful example of cemical activation. GGBFS sows little cementitious properties; neverteless, it gives very ig strengts in te presence of cemical activators suc as Na 2 SiO 3, NaOH, and Na 2 CO 3. Te activator(s) can be added during te milling of cement, or can be dissolved in te mixing water and added during mixing of mortars and concretes. Te tecnology is very simple and does not need extra equipment. However, in cemical activation metod tere is an important reality tat it cannot be used every activator to activate every type of slag, and ten for better performance by cemical activators it needs to ave many tests and materials for determination of te best activator. Tis is an improper point in cemical activation metod. Te objective of te current paper is to compare te efficacy of tree activation metods, as measured by strengt development and initial and ultimate compressive strengts. 2. Researc significance It is known tat a lot of slag is produced in te steel-iron industry every year, trougout te entire world. If some means of consumption for tese by-product materials can be found, it would elp in terms of being environment friendly and also provide significant economic benefits. Moreover, te results of several researces ave sown te use of te replacement materials in mortars and concretes as improved durability, wic as vital significance for te structures built in aggressive environments, suc as tose in marine structures, suc as big tunnels and bridges wit long life spans. However, tere is a problem in te use of te materials wit initial ydration being lower tan OPC and mortars and concretes aving low early strengts. Tere are several ways of resolving tis problem; including using mecanical, termal, and cemical metods of activation, wic is precisely te main purpose of tis study. 3. Experimental procedure 3.1. Properties of materials Te properties of te materials ave been used in te study are as follows Cement Te cement used in all mixes was OPC. ASTM C was used for determination of te compressive strengt of ydraulic cement mortars, by use of 5 mm sided cube specimens. Te specific gravity of cement used is by about Based on particle size analysis (PSA) tests, te specific surface area (SSA) for OPC was determined to be m 2 /kg. Te cemical compositions of OPC used in tis researc ave been determined by te testing metod X-ray fluorescence spectrometry (XRF). Te compositions of OPC are given in Table Slag Te specific gravity of te slag is approximately 2.87, wit its bulk density varying in te range of kg/m 3. Te color of ground granulated blast furnace slag (GGBFS) is normally witis (off-wite). Based on PSA tests, te SSA for GGBFS as been determined at m 2 /kg. It can be seen tat SSA slag = 1.9 SSA OPC, wic means tat particles of slag are 9% finer tan tat of OPC. Te compositions of slag are given in Tables 4a and 4b. As wit all cementing materials, te reactivity of te slag is determined by its SSA. Based on te definition of slag activity index (SAI) in ASTM C989 [5], it can be seen tat SAI = (SP/P) 1, were; SP = average compressive strengt of slag-reference cement mortar cubes; P = average compressive strengt of reference cement mortar cubes. Bot compressive strengts are in MPa. Based on tis definition, te slag used in te tests is classified into Grade 12. A result calculation is sown in te bottom of Table Aggregates Te fine aggregates used in te mixes are graded silica sands wit specific gravity, fineness modulus (FM) and water absorption (BS812: clause 21) 2.68%, 3.88% and.93%, respectively. Te maximum size of aggregate is 4.75 mm. Te PSA of te fine aggregates is given in Table 2, and te grain size distribution diagram is drawn in Fig Super plasticizer In order to ave appropriate consistency wit low a W/B ratio, super plasticizer (SP) is required to be used. Te SP used in tis investigation is Reobuild 11. Te specific gravity of SP is approximately 1.195, is dark brown in color, wit a ph in te range of Te consumed content of SP in te mortar depends on te replacement level of slag. Reobuild 11 is a cloride-free product. Meets ASTM C-494. Te basic components are syntetic polymers wic allow mixing water to be reduced considered. Te dosage of R11 generally varies from.8 to 1.2 l/(1 kg) Table 1 Composition of cementitious materials (% by mass). For OPC P2O5 SiO 2 Al 2 O 3 MgO Fe 2 O 3 CaO MnO K 2 O TiO 2 SO 3 CO 2 Cl For slag SrO SiO 2 Al 2 O 3 MgO Fe 2 O 3 CaO MnO K 2 O TiO 2 SO 3 CO 2 Na 2 O For 7 days; SAI = 47.57/47.76 = 1. >.95; For 28 days; SAI = 62.83/5.26 = 1.25 > 1.15; K b (basicity index) for slag = ( )/( ) = 1.3 > CaO/SiO 2 = C/S = 1.33 for slag [5]. Table 2 PSA for silica sand (SS) based on BS 822: Clause 11. Sieve size (lm) Sieve no. WSS + WS (g) WS (g) WSS (g) Ret. % Cum. Ret. % Pass. % 475 3/16 in No No No No No No Pan Total FM = /1 = 3.88 [6,7]. PSA for silica sand used in te mixes is as: 12% mes 5/1, 18% mes 3/6, 3% mes 16/3, 2% mes 8/16, and 2% mes 4/6.

3 32 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) 3 38 Cumulative passing % Silica sand PSA diagram for Silica sand Sieve size (microns) Fig. 1. PSA diagram for silica sand. of cement. Oter dosages may be recommended in special cases according to specific job conditions. It is compatible wit all cements and admixtures meeting ASTM and UNI standards. Table 4a Mix proportions of OSMs for mecanical activation metod. No. Mix name OPC (g) Slag (g) Water (g) Flow (mm) SP (g) 1 OM OSM/ GS3C GSC GS3C GS6C GSC GS6C GS9.5C GSC GS9.5C GS13C GSC GS13C GSiCi = Mixes made by using te binders grounded in a period of i. For all mixes: W/B =.33, S/B = Water Te water used in all mixes was potable water in pipeline of te lab. It was assumed tat te specific gravity of te used water is about 1 g/cm Activators Cemical reagents NaOH, KOH, and Na 2 SiO 3, nh 2 were used as alkaline activators. Te dosage of alkaline activators were 2%, 4%, and 6% Na 2 O, K 2 O, and Na 2 O(% by mass), respectively. Based on te mass of slag, tese activators were dissolved into mixing water first and ten added to te mixing. Some pysical and cemical properties of te activators are sown in Table Mix proportions and curing Tables 4a, 5, and 6a and 6b represent te mix proportions for different activation metods. In all mixes, water-binder and sand-binder ratios are.33 and 2.25, respectively. Silica sands were used in te mixes. At first, based on PSA, five groups of silica sand were mixed. Two min following tat, cement and replacement slag were put into te mixture, followed by 3 4 min of mixing. Mixing water was ten added to te mix and mixing was continued for 5 min, following wic te required amount SP was added. Mixing was continued for 2 min before te moulds were filled wit fres mortar in two layers. Eac layer was compacted wit ten impacts by a rod wit 16 mm diameter. 24 after casting, te specimens were demoulded and cured proportionally in water wit 23 ± 3 C or in te room temperature 27 ± 3 C and 65 ± 18% relative umidity (RH) until te test day Test and mixing procedures Test for fres mortar In order to ave appropriate consistency for eac mortar mix after casting, a flow table test as been done. Te range of flow amounts were between 22 and 235 mm. Te test procedure is tat following casting, some mortar is put in te truncated brass cone in two layers. Eac layer is compacted 1 times by a steel rod wit a 16 mm diameter, before te cone is lifted and te mortar collapsed on te flow table. Following tat, bot te table and mortar are jolted 15 times in a period of 6 s. Jolting te table enables te mortar to consequently spread out and te maximum spread, to te two edges of te table, was ten recorded. Te average of bot records is calculated as flow (mm). Te potograp for mixture and flow table test is sown in Fig. 2. Table 4b SSA values (m 2 /kg) of OPC and slag. Duration of grinding () OPC Slag r = SSA slag /SAS OPC A ball mill grinder macine was used to grind te binders particles. Table 5 Mix proportions of OMs, OSMs/4, and OSMs/5 for termal activation metod. No. Mix name OPC (g) Slag (g) Water (g) SP (g) Flow (mm) For OMs, air and water cured 1 OM-air cure OM-water cure For OSMs/4, air and water cured 3 H/ H6/ H6/4, H6/8, H6/12, H6/ H6/18, H6/ For OSMs/5, air and water cured 11 H/ H6/ H6/4, H6/8, H6/12, H6/ H6/18, H6/ For optimum OSM/5 at 6 ages, only air cured 19 H6/ H6/i, j means 6 C temperature wit eating time i and j. PSA for silica sand used in te mixes is as: 12% mes 5/1, 18% mes 3/6, 3% mes 16/3, 2% mes 8/16, and 2% mes 4/6. Table 3 Some properties of activators used in te study. No. Activator name Type Formula/abbreviation Na 2 OorK 2 O (%) SiO 2 (%) H 2 O (%) M S M (g/mol) 1 Sodium silicate Solution Na 2 SiO 3, 1.11H 2 O/SSS Sodium silicate Solution Na 2 SiO 3, 9.35H 2 O/SSS Sodium silicate extra pure Solution Na 2 SiO 3, 12.58H 2 O/SSEP Sodium silicate Granular Na 2 SiO 3, 9.H 2 O/GSS Sodium ydroxide Pellet NaOH/SH Potassium ydroxide Pellet KOH/PH M s = Molar ratio = SiO 2 /Na 2 O.

4 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) Table 6a Mix proportions of control mixes and Abbreviations. No. Mix name Curing regime OPC (g) Slag (g) Water (g) SP (g) Flow (mm) (g) 1 OM Water OSM/4 Water OSM/5 Water OSM/6 Water List of abbreviations No. Original statement Abbr. 1 Ordinary Portland cement (OPC) mortar OM 2 Slag mortar SM 3 OPC-slag mortar wit i% level of slag OSM i 4 Potassium ydroxide wit i% content (based on mass of slag) PH i 5 Sodium ydroxide wit i% content (based on mass of slag) SH i 6 Solution sodium silicate wit i% content (based on mass of slag) SSS i 7 Granular sodium silicate wit i% content (based on mass of slag) GSS i 8 Sodium silicate extra pure wit i% content (based on mass of slag) SSEP i Table 6b Mix proportions of OSMs for cemical activation metod. No. Slag level Mix name Curing regime OPC (g) Slag (g) Water (g) SP (g) Flow (mm) 1 6 PH1 Air PH2 Air PH4 Air PH6 Air SH2 Air SH4 Air SH6 Air SSS2 Air SSS4 Air SSS6 Air GSS2 Air GSS2 Air SSEP2 Air SSS2 Water SSS3 Water SSS5 Water PH1.5 Air PH2 Air PH4 Air GSS SH3.35 Air GSS2.5 + SH2.33 Air SSS2 + SH.6 Air SSS3 + SH4.5 Air PH2 + SH3 Air PH2 + SH5 Air PH1 + SH1.5 Air PH.75 + SH1 Air PH.5 + SH.5 Air PH.5 + SH.5 Air PH.5 + SH.5 Air PH.5 + SH.5 Air PH1.5 + SH.75 Air For optimum OSM/5 at 6 ages 33 5 PH.5 + SH.5 Air For all mixes: W/B =.33 and S/B = PSA for silica sand used in te mixes is as: 12% mes 5/1, 18% mes 3/6, 3% mes 16/3, 2% mes 8/16, and 2% mes 4/ Test for ardened mortar Tree cubic samples, wit lengts of 5 mm, were used for eac age. Samples produced from fres mortar were demoulded after 24, and ten cured in room temperature wit 27 ± 3 C and 65 ± 18%RH, and in te water wit 23 ± 3 C before te samples were used for compressive strengt tests. Compressive strengt measurements were carried out using an ELE testing macine press wit a capacity of 2 KN, and a pacing rate of.5 KN/s. Compressive tests ave been done according to BS 1881, Part 116, Mortar mix metod Initially, five groups of silica sand are put in as a mixture and mixed for 2 min. Following tat, te cement and slag are added and mixing is continued for 3 4 min. Te activator is ten poured into te calculated water and mixed until completely dissolved. Te solution is ten added into te mixture and mixing is continued for 2 min. Finally, SP is added and mixing continued for 2 min; immediately following te completion of te mixing, te flow table test is done and te specimens are moulded. For eac mix, te duration of mixing time takes about 8 to 1 min. 4. Results and discussion 4.1. Mecanical metod In te mecanical metod, fourteen mix proportions of OSMs ave been used wit two mixes as control. For eac mix, it is important to ave ig early strengt. In tis metod, 5% of cement replacement as been selected as te optimum level of slag. Te main finding proves tat te use of ground slag and OPC,

5 34 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) 3 38 Fig. 2. Potograp for mixer and flow table test. maximum compressive strengt can be acieved for OSMs. It was found tat 65 MPa at 7-day and 8.8 MPa at 28-day strengt. Tese strengt levels ave been obtained for te mortar wenever te slag and OPC were ground for a period of 6, by a proper grinder macine. For grinding of OPC and slag particles a ball mill grinder macine was used. At first, OPC and GGBFS are weiged by a balance wit ±.1 g accuracy, and ten put in te cylinders of te grinder macine. Te macine used for grinding of te materials as tree cylinder boxes; eac cylinder as four sperical steel balls, eac wit a diameter of 5.6 mm and a mass of g. 65 g of materials are put in eac box; following tat, te macine is turned on for periods of 3, 6, 9.5, and 13. Te pacing rate of te grinder macine is around 11 rpm. In Table 4a tis mortar as been named as GS6C6 (optimum mortar). In tis part of study, tree groups of OSMs ave been used. In te first group, bot OPC and ground slag were used. In te second group, only ground slag was used, and in te tird group, only ground OPC used. For first group of mortars, it is seen tat te maximum strengts is attributed to r = It is noted tat te strengt levels of te first group are more tan tose of oter groups. At r = 1.35 te strengt at 28 days is 8.8 MPa. Te r factor is defined as te ratio of SSA slag to SSA OPC. Tis factor is dimensionless. For better performance of OSMs, it is generally accepted tat r sould be more tan 1.. From Table 4b it is clear tat te optimum mortar is attributed to minimum r = In tis case bot OPC and slag were separately ground in duration of 6. Te results of compressive strengt vs. age of curing, for all tree groups of OSMs used in mecanical metod, are sown in Fig. 3, Part A. Te best curve fitting of compressive strengt vs. age of mortar, for tree groups of OSMs, is sown in Fig. 3, Part B Termal metod A Compressive strengt-mpa B Compressive strengt (CS)- MPa st GROUP 2 nd GROUP 3 rd GROUP Age-day relationsip between compressive strengt and age CS(MPa,1 st group) = Ln(t) R 2 =.855 CS(MPa,2 nd group) = 9.478Ln(t) R 2 =.8835 CS(MPa,3 rd group) = Ln(t) R 2 = Age (t)- day Fig. 3. Compressive strengts vs. age for tree groups of mortars. Part A: relationsip; Part B: curve fitting. In te termal metod, 29 mix proportions of OSMs ave been used and two mixes as control. For eac mix, two points are important. Firstly, a iger percentage of slag is preferable because it as economic and environmental advantages and also elps to improve durability of te mortars. Secondly, it improves early strengt. It is apparent tat an increase of replacement slag causes early strengt to be reduced, since te slag as lower initial ydration eat tan tat of OPC. Moreover, for sort-term purposes te use of low levels of slag is neiter economic nor durable. It is clear tat te use of ig levels of slag in mortars and concretes as many benefits from standpoint of economic and environmental. By using ig levels of slag it can be said tat te use of cement will be more reduced. Tis means tat production and emission of carbon dioxide (CO 2 ) is significantly decreased, in due to it is generally accepted production of one ton of OPC is caused to produce one ton of (CO 2 ). In addition, wit use of iger levels of te slag, more compact structure can be obtained. In tis researc, it is

6 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) Compressive strengt- MPa comparison of different activation tempratures for OSM/5 3 day 5/9-ac 5/9-wc Age- days 6/6-ac 6/6-wc 6/9-ac 6/9-wc 7day 7/9-ac 7/9-wc Fig. 4. Te effects of different temperatures on early-age strengts of OSM/5. desirable to know te optimum temperature and te duration tat will provide te igest early strengt at 3 and 7 days. In te study, te effects of 5 C, 6 C, and 7 C temperatures were considered on te early strengts at 3 and 7 days of OSM/5. Te results are sown in Fig. 4. It is apparent tat 6 C as te most enancing effects on early-age strengts, so it was selected as te optimum temperature. Te results obtained for compressive strengts based on eating time, are sown in Fig. 5. Based on te results, it can be seen tat 3 and 7 days strengts, for specimens cured in te water, bot witout being eated and wit 2 eating time, are greater tan wenever cured in room temperature. Tis reality as proven for bot OSM/5 and OSM/4. However, as soon as te eating time is increased to 4 and more, te aforementioned statement is reversed. Conversely, wenever eating time is increased to 4 and more, te strengt of specimens cured in room temperature is improved compared to te strengt of specimens cured in water. It appears tat tis is due to; room temperature and a ig RH of Compressive strengt-mpa Compressive strengt-mpa OSM/5-6 ºC Heating time- 3 day-a c day-w c OSM/4-6 ºC day-a c 7 day-w c 16 Heating time- 3 day-a c 3 day-w c 18 7 day-a c 7 day-w c Fig. 5. Compressive strengt vs. eating time for OSM/5 and OSM/4 cured in room temperature and water te room s air. Elevated curing temperature accelerates te cemical reactions of ydration, and increase te early-age strengt. However, during te initial period of ydration, an open and unfilled pore structure of cement paste forms and terefore negatively affects te properties of ardened mortar and concrete, especially at later ages [6,7]. Hardened mortars and concretes can reac teir maximum strengt witin several ours troug elevated temperature curing. However, te ultimate strengt of ardened mortars and concretes as been sown to decrease wit curing temperature. It was found tat by increasing curing temperature from 2 C to 6 C and te eating time up to 48 a continuous increase in compressive strengt occurred [8]. Studies ave sown tat tere is a tresold maximum, eat-curing temperature value in te range of 6 7 C, beyond wic eat treatment is of little or no benefit to te engineering properties of concrete. It is noted tat te maximum 3 and 7 days strengts of OSM/ 4s and OSM/5s specimens are 21.65%, 18.98% and 21.78%, 2.% greater tan tose of OM s specimens cured in room temperature. It is observed tat tere is strengt loss by about 2.2% wenever 56 days strengt is compared to 28 days strengt. Tis as been previously reported by oter researcers [9]. Wereas te main objective of elevated temperature curing is to acieve early strengt development, it is generally acknowledged tat tere is also strengt loss as a result of eat curing. Anoter mix of OSM/5 as te optimum mix as been designed for optimum temperature and eating time (H6 C 2 ) for six ages; 1, 3, 7, 28, 56, and 9 days. Te results of compressive strengt vs. age of te specimens cured in room temperature, is a logaritmic relationsip as: CS T ac = Ln(t) , wit R 2 =.9311; were CS is compressive strengt in MPa, t is curing age in days, and ac denotes curing regime in room temperature Cemical metod In tis metod, five groups of activators were used as follows. Te first group is a pellet of NaOH. Te second activator is a pellet of KOH, and te tird a solution of Na 2 SiO 3, 9.35H 2 O. Te fourt group is a combined activator as: (Na 2 SiO 3, nh 2 O) 2 + NaOH.583 wit te last being NaOH.5 + KOH.5 (% by mass of slag). Wit respect to te activators used, te NaOH.5 + KOH.5 mix leads, in all cases, to te igest strengts values, followed by te (Na 2 SiO 3, 9.35H 2 O) 2 + NaOH.583 solution and ten by KOH 1. NaOH gives te lowest strengt values wenever it is used alone. It was determined tat te effect of te combined activators being better tan tat of an individual one. Te activity of GGBFS is determined by te quantities and te properties of amorpous glass, as well as te cemical compositions. Facts ave been proven tat te iger te proportion of glass, te greater is te activity of slag at te same cemical compositions [1]. Te results obtained sow tat wen te aforementioned are considered, tey do not ave te same significance on te strengts. It seems te most relevant factor is te alkaline-activator nature. For compressive strengt, te relevant of factors may be attributed wit age. Tis order seems be as: activator nature, activator concentration, and specific surface of slag. Te last factor is curing temperature and is only significant at 3- and 7-day ages. Te significant role of an alkali activator is based on te fact tat slag alone reacts wit water very slowly, but ydroxyl ions (OH) are supplied by alkali activators. Tey are known to increase te ydration rate by promoting dissolution of aluminate and silicate network in te slag [11]. Te efficiency of an activator depends on several factors. Among tem, te type, ambient temperature, dosage and water/slag ratio are significant. Anoter significant factor is te pysico-cemical

7 36 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) 3 38 nature of te material to be activated [11]. In tis activation metod, tree sets of activators ave been used. In te first set, te alkali activators, NaOH, KOH, and Na 2 SiO 3, 9.35H 2 O (solution/granular) were used for 2%, 4%, and 6% by mass of slag. In te second set, te combination of alkali activators NaOH and Na 2 SiO 3, 9.35H 2 O (solution/granular) used for different molar ratio (M s ).25,.5,.75, and 1.. In te tird set, te alkali activators NaOH and KOH ave been used for different combinations. Finally, by comparison of te results of te tree sets of activators used, te optimum set was acquired. Te optimum selected set of activators is sown in Fig. 6. It is noted tat in te first set of activators, te best activator is KOH wit a 1% content of K 2 O as mass of slag. Up to 6% slag replacement and use of KOH 1 as activator as yielded te best results. For te second set of activators, te best combination is (Na 2- SiO 3, 9.35H 2 O) 2 + NaOH.583 wit M s =.75. Up to 5% slag replacement and use of second set yielded te igest early strengts. In te tird set of activators, te best combination was NaOH.5 + KOH.5. Up to 5% slag substitution and use of a tird set of activators yielded te best results. By comparison of te obtained optimum results for te tree sets of activators; it was sown tat te optimum set is attributed to te tird set of activators. Te use of an optimum set of activators enabled te creation of anoter mix as an optimum mix proportion for specimens cured in room temperature. Tese were created for six ages 1, 3, 7, 28, 56, and 9 days. Te results of compressive strengt vs. age for optimum mix, as te best curve fitting as: CS C ac = Ln(t) , wit R 2 =.8169; were CS is compressive strengt in MPa, t is curing age in days, and ac denotes curing regime in room temperature Comparison of different metods From Fig. 7 it is observed tat SMs, OMs, and OSMs cured in te water do not ave strengt loss, but te OSMs activated by cemical, termal, and mecanical metods ave strengt loss at 9, 56, and 56 days, respectively. Te results sow tat strengt loss in alkali-activated mortars depends on te level of slag used, te type and dosage of alkali activator, and te regime of curing. Te reason for te loss of strengt can be due to internal or external reasons. Te internal reasons are tose linked to te cemical composition of te reacted products. Te external reasons are due to te variability of specimens, testing procedures, flatness of testing procedures. One oter factor tat as an important effect is te temperature. Te initial curing temperature as an important effect and can reduce or increase strengt at long curing times, i.e. advanced age. A strengt comparison of OMs and OSMs sowed tat OMs ave iger strengts until 7 days ages wen compared to OSMs, but Compressive strengt- MPa optimum set of activators 3 day-ac 3 day-wc 7 day-ac 7 day-wc Content and type of combination OSM/5- Control SSS 2+PSH.583 PPH.5+PSH.5-OSM/5 PPH1/-OSM/5 Fig. 6. Selection of optimum set of activators. Compressive strengt- MPa comparison between activation metods SM-WC OM-WC OSM/5-WC C-AC T-AC M-WC Age- days Fig. 7. Compressive strengt vs. age for different OSMs and activation metods. after 7 days tis statement is reversed. Additionally, te ultimate strengt of OSMs is more tan tat of OMs. From Fig. 8 it can be deduced tat wenever te cemical metod is used for activation of OSM/5 (for all ages except 1 day), not only did te strengt improve, but tat tere was also a strengt loss from 3 until 9 days compared to inactivated OSM/5. Tis is due to te presence of cement in OSM/5. Tis subject as been previously confirmed by oter researcers [12]. Te addition of alkalies to Portland cement results in a reduction of strengt after 3 or 7 days, because of te ydration cemistry and te morpology of te ydration products are canged due to te presence of alkalies [13]. Strengt development, due to te termal activation metod at a 3 days age, is more tan tat of te mecanical activation metod, but for 7 days and more, tis statement is reversed. Furtermore, it can be said tat use of te termal metod is better tan te mecanical metod until 3 days. After 3 days, te mecanical metod is te optimal metod. From Fig. 9 it can be observed tat: Te greatest strengt development at 1 day is attributed to mecanical, cemical, and termal activation metods. Te greatest strengt development at 3 days is attributed to termal, mecanical, and cemical metods of activation. Te igest strengt development at 7, 28, 56, and 9 days are attributed to mecanical, termal, and cemical activation metods. In summary, it can be said tose at all ages except 1 day, te cemical metod as te last rank of activation. At 1 day, te cemical metod as te second rank of activation. Moreover, te greatest strengt development at 3 days is related to te termal metod and for 7 days and more, te first rank of activation is attributed to te mecanical metod. Compressive strengt- MPa comparison between activation metods Age- days SM-WC OM-WC OSM/5-WC C-AC T-AC M-WC Fig. 8. Compressive strengt vs. separate ages for different OSMs and activation metods.

8 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) Relative compressive strengt day 3day 7day 28day 56day 9day Age of curing wit type of activation metod OSM/5-Con. C T M Fig. 9. Relative Compressive strengt vs. age and type of activation metod. Regardless of te iger expenses for mecanical and termal metods, due to bot metods aving te igest strengts, tey can be proposed as simple and feasible first and second rank metods of activation. Te cemical metod ad a positive effect on strengt at only 1 day by about 8%. Tis metod also sowed strengt loss from 3 until 9 days instead of strengt development, so it is not proposed as a feasible metod of activation. From Fig. 1 it can be observed tat: Te cemical activation metod developed strengt at only te first day and reduced it at all oter ages until 9 days, compared to OSM s strengts for same ages. Te termal activation metod as been developed at all ages, except at 1 day age. It can be remembered tat te specimens eated after 1 day. It is noted tat strengt growt is te igest (32%) at 3 days, and ten from 7 until 9 days te increments are reduced. Te strengt growt at 9 days is 3%. Te mecanical activation metod ad te igest strengt growt at te first day (5%) and about 3% at 3 days. From 7 days wit 36% of strengt growt until 9 days, te increment of strengt development as been gradually reduced. At 9 days te strengt growt was only about 6%. Some diagrams are drawn in Fig. 11. Tese diagrams are a curve fitting of compressive strengt vs. curing age for SMs, OMs, and OSMs and also te activation metods of OSM/5, namely Cemical (C), Termal (T), and Mecanical (M) metods. From tis Figure it can be seen tat te best curves fittings are logaritmic relations as, a Ln(t)+b. Comparison of regression relations sow tat te best curve fitting is related to te termal activation metod. Additionally, it is observed tat tere is a logaritmic relation for estimation of strengt, based on te Relative compressive strengt OSM/5-Con. C T M Type of activation metod 1 day 3 day 7 day 28 day 56 day 9 day Fig. 1. Relative Compressive strengt vs. type of activation metod. curing age for OSM/5. Te value of te correlation factor of te relation is R 2 = Conclusions 5.1. For mecanical metod All tree groups of mortars ave significant effects on strengt improvement, especially at early ages, wilst te greatest effect is related to te first group. Te maximum strengts obtained are attributed to te first group of OSMs. Te strengt obtained at 28-day of optimum OSM (GS6C6) is 8.8 MPa. It is noted tat tis strengt was obtained only by using 25 kg/m 3 of cement. Tis sows igly importance of te researc, because of te strengt is very ig and as many benefits from standpoint of economic and environmental. In fact, tis is a novelty. For all groups of mortars, strengt loss as occurred only at long ages. Fine grinding leads to te generation of a larger surface area, but due to te agglomeration penomenon tere is limitation on te SSA of OPC and slag. Te results obtained sow tat ground slag as a greater effect on strengt improvement at early and long ages compared to ground OPC For termal metod Based on te experimental results obtained in te study it was specified tere is an optimum temperature to obtain ig early strengt for te materials used in tis study. It is determined tat 6 C is te optimum temperature. Duration of eating time is also very important to gain ig early strengt. For te slag used in tis study, 2 is te optimum eating time. Usually, as eating time increases towards te optimum, te compressive strengt will increase. Te maximum strengts obtained of OSM/5 cured in room temperature at 3 and 7 days, are and MPa, respectively. It can be seen tat tese strengt levels are 21.78% and 2.% more tan tose for OPC s specimens cured in room temperature and 26.12% and 29.4% more tan tose for OPC s specimens cured in te water, respectively. If te mortar is eated more tan te optimum eating time, it is specified tat tis will not lead to increasing early strengt of mortar. According to te results of study and oter researces [14,15],it can always be said tat termal activation is one of te applicable metods for te activation of OSMs. It is well known tat tis metod is usually used in precast concrete plants. It as been sown tat te specimens strengts at 3- and 7-day of OSM/4 and OSM/5 cured in water witout eating and wit use of 2 eating after demoulding, are more tan tose cured in room temperature. However, as soon as te eating time is increased towards 4 and above, tis statement is reversed. Tis is a new finding, as muc importance in precast industry wit many advantages in arid regions to cure concrete structures For cemical metod In tis study te activators sodium ydroxide, potassium ydroxide, and sodium silicate ave been used. It was determined tat te igest effect is attributed to sodium silicate and te lowest for sodium ydroxide, wenever te activators were used alone.

9 38 F. Sajedi, H.A. Razak / Construction and Building Materials 25 (211) 3 38 Fig. 11. Curve fittings of Compressive strengt vs. age for OSMs and teir activation metods. It as been considered tat te greatest strengt improvement is related to combination of sodium ydroxide and potassium ydroxide, followed by combination of sodium silicate and sodium ydroxide. Te best curve fitting of te strengt of optimum combination of activators is a logaritmic relation as: CS- C- ac = Ln(t) , wit R 2 =.8169; Were CS is compressive strengt in MPa, t is curing age in days, and ac denotes curing regime in room temperature. Te maximum strengt obtained due to cemical activation is 85% of OM s strengt at 56 days. Due to leacing in te water cured regime, te strengt of specimens cured in te water were less tan tose cured in room temperature. In some mixes, strengt loss as been observed. Te results obtained sow tat strengt loss in alkali-activated mortars depends on te level of slag used, te type and dosage of te alkali activator, and te curing regime Specific results (a) Te best curve fitting to sow te relationsip between strengt development and age of curing of OSMs and teir activation metods, are logaritmic relations in te form a Ln(t)+b; Were a and b are constants for eac specific relationsip. (b) At all ages except 1 day, te cemical metod as te last order of activation. At 1 day, it as second order. Additionally, te igest strengt development at 3 days is attributed to te termal metod; and at 7 days and more te first order of activation is related to te mecanical metod. (c) In summary, regardless of te greater expenses of te mecanical and termal metods; due to bot metods aving te igest strengts, tey can be recommended as simple References and feasible first and second orders metods of activation. Te cemical metod ad a positive effect on strengt at only 1 day by about 8%. Tis metod sowed strengt loss in duration of 3 9 days instead of strengt improvement, so it is not proposed as a feasible metod of activation. [1] Caijun Si, Robert L Day. Comparison of different metods for enancing reactivity of pozzolans. Cem Concr Res 21;31(5): [2] Nanjing Institute of Cemical Tecnology, Cement Tecnology. Beijing: Cinese Construction Press; [3] Lee Jaesung. Experimental studies and teoretical modeling of concrete subjected to ig temperatures. P.D. Tesis, University of Colorado, USA; 26. [4] Jin-Keun Kim, Sang Hun Han, Seok Kyun Park. Effect of temperature and aging on te mecanical properties of concrete, Part II. Prediction model. Cem Concr Res 22;32(7): [5] Pal SC, Mukerjee A, Patak SR. Investigation of ydration activity of ground granulated blast furnace slag in concrete. Cem Concr Res 23;33(9): [6] Neville AM. Properties of concrete, Fourt and final ed. Malaysia: Prentice Hall; 28. [7] Neville AM, Brooks JJ. Concrete tecnology. Malaysia: Prentice Hall; 28. [8] Brooks JJ, AL-kaisi AF. Early strengt development of Portland and slag cement concretes cured at elevated temperatures. ACI Mater J 199;87(5):53 7. [9] Si C. Strengt, pore structure and permeability of alkali-activated slag mortars. Cem Concr Res 1996;26(12): [1] Bougara A, Lynsdale C, Ezziane K. Activation of Algerian slag in mortars. Constr Build Mater 29;23(1): [11] Xingua Fu, Wenping Hou, Cunxia Yang, Dongux Li, Xuequan Wu. Studies on Portland cement wit large amount of slag. Cem Concr Res 2;3(4): [12] Vladimir Zivica. Effectiveness of new silica fumes alkali activator. Cem Concr Compos 26;28(1):21 5. [13] Caijun Si, Activation of natural pozzolanz, fly ases and blast furnace slag. P.D. Tesis, Te University of Calgary, Canada; [14] Barnet SJ, Soutsos MN, Millard SG, Bungey JH. Strengt development of mortars containing ground granulated blast-furnace slag: effect of curing temperature and determination of apparent activation energies. Cem Concr Res 26;36(3): [15] Zain MFM, Radin SS. Pysical Properties of ig-performance concrete wit admixtures to a medium temperature range 2 5 C. Cem Concr Res 2;3(8):