Isothermal Calorimetry as a Tool to Evaluate Early Age Performance of 1

Fly Ash Mixtures 2

3 Jussara Tanesi, Ph.D. (Corresponding Author) 4 Global Consulting, Inc. 5 Turner-Fairbank Highway Research Center/FHWA 6 6300 Georgetown Pike - McLean VA 22101 7 Ph: 202 493 3485 8 Fax: (202) 493-3161 jussara.tanesi.ctr@dot.gov 9

Ahmad Ardani, P.E. 10 Turner-Fairbank Highway Research Center/FHWA 11 6300 Georgetown Pike - McLean VA 22101 12 Ph: 202 493 3422 13 Fax: (202) 493-3161 ahmad.ardani@dot.gov 14

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Number of words: Body: 3720, Figures: 2750 (11 figures), Tables: 750 (3 tables) = total: 7220 30

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Isothermal Calorimetry as a Tool to Evaluate Early Age 1

Performance of Fly Ash Mixtures 2

ABSTRACT 3

This paper documents the use of an isothermal calorimeter as scanning tool to evaluate early age behavior 4 of high volume fly ash (HVFA) mixtures. 5

A series of paste and mortar mixtures containing different fly ashes (one Class C fly ash and two 6 Class F fly ashes) with replacement levels ranging from 20% to 60%, with high and low alkali cement 7 were evaluated. Materials testing included ASTM C109, compressive strength of mortar cubes at 8 different ages; ASTM C1437, flow; ASTM C403, time of setting and ASTM C1679, isothermal 9 calorimetry. 10

In most cases, for the same water-binder ratio (0.40) and replacement level, Class C fly ash 11 mixtures exhibited higher strength but delayed setting when compared with Class F fly ash mixtures. 12 Isothermal calorimetry proved to be a good scanning tool for prediction of setting time, early age 13 compressive strength and identifying materials incompatibility. 14

1. INTRODUCTION 15 As the concept of sustainability gains momentum, many transportation agencies including State DOTs, 16 concrete industry and academia are exploring ways to make concrete more sustainable and 17 environmentally friendly. Supplementary cementitious materials (SCMs) such as fly ash, slag cement 18 and natural pozzolans have been used by many state DOTs/transportation agencies in achieving 19 sustainability through: 20

• Improved concrete performance and durability 21 • Improved rheological properties (workability, finishability, reduced water demand) 22 • Increased use of by products 23 • Reduced CO2 footprint associated with the production of cement and 24 • Reduced overall cost of concrete 25

Although, the use of fly ash has been steadily on the rise over the last couple of decades because 26 of the benefits they afford, their use in highway applications still poses many unanswered questions due 27 to the fact that there is no sound, systematic protocol that can be used to routinely evaluate and proportion 28 fly ash into concrete mixtures while ensuring that performance and durability are not compromised1. 29

Many transportation agencies have been using fly ash in their concrete pavement mixtures with 30 replacement levels ranging from 10 to 30 percent (typically 20 percent of the total cementitious material); 31 however, the basis for these specifications are often empirical estimates and lack sound engineering 32 evaluation. In an attempt to reduce the CO2 footprint associated with the production of the cement and 33 lessen its adverse impact on environment and ultimately improve concrete performance, many DOTs have 34 expressed interest in using higher dosages of fly ash in concrete infrastructure1. 35

While high volume fly ash (HVFA) concrete can be proportioned to produce durable concrete, 36 their use is not without problems. Some of the issues include slow strength gain at early age, delayed 37 setting2, and reduced bleeding, which results in extended curing time and eventually can slow down the 38 operation of concrete paving during construction. 39

Fly ash is a complex, heterogeneous material consisting of glassy and crystalline phases. The 40 glassy phase consists of 60 to 90 % of the total mass of fly ash, with the remaining fraction made up of 41 crystalline phases. The glassy phase is comprised of two types of spheres: solid and hollow (cenospheres). 42

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The glassy spheres and crystalline phases are not completely independent of one another and vary in their 1 proportions, which makes fly ash a complex material to classify and characterize (ACI 232.2R-6)3. 2

It should be noted that chemical differences of fly ashes are as important as the mineralogical and 3 physical (particle size distribution and shape) differences in determining the influence of fly ash on 4 properties of concrete. Furthermore, pozzolanic properties of the fly ashes to a great extent are influenced 5 by their mineralogy and particle size and not so much by their chemistry4. 6

ASTM C618, “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan 7 for Use in Concrete5”, classifies ashes into two broad classes of F and C based on the sum of their three 8 principal oxides as follow: 9

• Class F 10 Pozzolanic 11 SiO2 + Al2O3 + Fe2O3 ≥ 70% 12

• Class C 13 Pozzolanic & Cementitious 14 SiO2 + Al2O3 + Fe2O3 ≥ 50% 15

The Canadian Standards Association (CSA) specification, CSA 3001-106, classifies fly ash into 16 three separate categories based on their lime content (percent of CaO) i.e., Type F (≤15 % CaO), Type CI 17 (>15 – ≤20 % CaO) and Type CH (>20% CaO), indicating low, intermediate or high calcium content 18 respectively. 19

One of the shortcomings of both of these specifications is the fact that mineralogical composition 20 and particle size distribution of the ashes are not required and, as a result, they are not determined in a 21 routine quality control. The ASTM C618 specifies the maximum retention of 34 percent on a 45 micron 22 sieve (no. 325); however, the particle size distribution (PSD) is rarely determined1. Laboratory 23 investigations around the world have shown that when the fly ash particle size is reduced, its performance 24 in concrete is improved7. Mehta’s study on the influence of particle size has also shown that majority of 25 the reactive particles in fly ash are actually less than 10 micrometers in diameter8. 26

Overall, both CSA 3001 and ASTM C618 are general in scope and intended only to provide fly 27 ash characteristics and are not robust indicators of early age or long-term hardened concrete performance, 28 especially when it comes to high volume fly ash (HVFA) concrete mixtures. More emphasis needs to be 29 placed on the performance requirements when designing a concrete mixture containing fly ash. It is 30 imperative to study the effects of fly ash on properties of fresh and hardened concrete by evaluating 31 workability, early age and long-term strength development and durability. 32

1.1. Objectives 33 The impetus behind this study is to evaluate the viability of using isothermal calorimetry to predict early 34 age properties of mixtures containing different amounts of fly ashes regardless of their types, source of 35 origin, physical properties and chemical composition. 36

2. EXPERIMENTAL PROGRAM 37 In this study, a total of 18 mortar mixtures and 19 paste mixtures were prepared. Two different Type I 38 portland cements (low alkali and high alkali), three different fly ashes (two Class F and one Class C) at 39 three replacement levels of 20, 40 and 60 percent were used. The two Class F fly ashes differ mainly on 40 their L.O.I. content. The lower L.O.I. Class F fly ash will be referred in this study as Class F fly ash, 41 while the second fly ash will be referred as Feed ash (FD). Feed ash is the ash that has its unburned 42 carbon separated from its mineral constituents of coal ash combustion through a triboelectrostatic 43

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separation process and then becomes a Class F fly ash. The feed ash and Class F fly ash were obtained 1 from the same source. 2

Table 1 shows a summary of the paste and mortar mixtures, Table 2 presents the chemical 3 analysis and Figure 1 presents the particle size distribution of the cements and fly ashes used in this study. 4 The two additional paste mixtures (LA and HA) were mixtures comprised of 100% low and high alkali 5 cement, respectively. For mortars, mixtures with 20% fly ash were considered controls. All mixtures had 6 a water-cementitious ratio of 0.40. 7

For the mortar mixtures, natural sand with an oven dry specific gravity of 2.57, absorption of 8 1.06% and fineness modulus of 2.76 was used. All mortar mixtures had 2.25 parts of sand for each part of 9 cementitious materials, on a mass basis. The water-cementitious ratio was kept constant at 0.40 for all 10 mixtures. 11

Mortar mixtures were mixed following ASTM C3059, except for the mixer requirements. The 12 mixer used had a 20 quart capacity, with speeds of 190 and 305 rpm, in order to accommodate bigger 13 batch sizes. Flow tests (ASTM C143710), modified unit weight using the base of the rollameter, setting 14 time (ASTM C40311) and compressive strength (ASTM C10911) at ages 3, 7, 28, 56, 91 and 119 days 15 were carried out. Three cubes were tested at each age. 16

Table 1 Mixtures in the experimental program 17

Mixes Fly ash (%) Cement Type

Fly ash Class

LA* 0 Low alkali None LA20F 20 Low alkali Class F LA40F 40 Low alkali Class F LA60F 60 Low alkali Class F LA20C 20 Low alkali Class C LA40C 40 Low alkali Class C LA60C 60 Low alkali Class C

LA20FD 20 Low alkali Feed ash LA40FD 40 Low alkali Feed ash LA60FD 60 Low alkali Feed ash

HA* 0 High alkali None HA20F 20 High alkali Class F HA40F 40 High alkali Class F HA60F 60 High alkali Class F HA20C 20 High alkali Class C HA40C 40 High alkali Class C HA60C 60 High alkali Class C

HA20FD 20 High alkali Feed ash HA40FD 40 High alkali Feed ash

HA60FD** 60 High alkali Feed ash * Only paste mixtures were prepared. 18 ** Paste mixture could not be properly mixed. 19

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Table 2 Report on chemical analysis of cements and fly ashes 1

Analyte Low alkali cement

High alkali cement

Class F fly ash

Class C fly ash

Feed ash

Mass (%) Mass (%) Mass (%) Mass (%) Mass (%) SiO2 19.91 20.57 61.4 38.9 57.23 Al2O3 5.01 5.19 27.87 19.3 27.6 Fe2O3 3.47 2.27 2.91 6.89 3.87 CaO 63.56 62.07 0.48 23.3 0.7 MgO 2.5 3.03 0.9 5.28 0.97 SO3 2.52 3.12 <0.01 1.29 0.02

Na2O 0.11 0.23 0.27 1.55 0.33 K2O 0.67 0.87 2.84 0.64 2.73 TiO2 0.29 0.22 1.45 1.38 1.44 P2O5 0.19 0.12 0.13 1.15 0.19

Mn2O3 0.12 0.04 0.02 0.03 0.02 SrO 0.07 0.11 0.06 0.34 0.08

Cr2O3 0.01 <0.01 0.02 <0.01 0.02 ZnO 0.01 <0.01 0.01 0.03 0.02 BaO 0.13 0.95 0.15 L.O.I 1.98 2.55 0.95 0.28 4.13

Na2O equivalent 0.55 0.8 2.14 1.97 2.12

C3S** 62 49 C2S** 11 22 C3A** 7 10

C4AF** 11 7

SiO2+Al2O3+Fe2O3 92.2 64.1 88.7 Other properties Specific gravity 2.21 2.66 Mean size (µm)* 13.44 10.67 30.52 5.34 34.91

Specific area* (cm2/cm3)

15942 17504 7655 28863 5083

* Determined by LASER diffraction spectrometry using a Horiba LA-500 particle size analyzer and calculated by the Fraunhofer mathematical approximation. ** Based on Bogue calculation. NOTE: 1 inch = 25.4 mm.

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Figure 1 Particle size distribution of cements and fly ashes. 2

Paste mixtures were prepared according to ASTM C173812. All materials were kept at 23°C±3°C 3 at least for one day before mixing the paste. A commercial, eight-channel heat conduction calorimeter 4 was used to monitor heat flow and measure cumulative heat at 25°C for 72 hours, following ASTM 5 C167913, with four replicates per mixture and with masses ranging from 4.44g to 4.78g. 6

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3. RESULTS 1

3.1. Fresh Properties of Mortar 2

Table 3 shows the fresh property test results for mortar mixtures. 3

Table 3 Fresh properties of mortar mixtures 4

Mixes Flow (%)

Unit weight (lb/ft3)

Initial setting (min)

Final setting (min)

LA20F 94.5 139 214 311 LA40F 95.6 135 225 345 LA60F 88.1 132 232 363 LA20C 108.0 138 312 416 LA40C 125.7 137 423 562 LA60C 137.5 139 514 680

LA20FD 104.2 138 221 302 LA40FD 68.6 133 265 381 LA60FD 58.4 131 262 423 HA20F 99.5 136 205 302 HA40F 95.9 134 223 338 HA60F 84.8 131 247 421 HA20C 123.0 138 299 413 HA40C 138.0 138 422 567 HA60C 147.4 140 653 875

HA20FD 94.7 138 200 301 HA40FD 67.4 134 233 368 HA60FD 45.8 130 278 448

1 lb/ft3 = 16.02 kg/m3 5

As it can be observed, Class C fly ash mixtures presented the highest flow for all replacement 6 levels and for both cements, when compared to the mixtures containing the other two fly ashes, while 7 Feed ash mixtures exhibited the lowest flow. Since cement replacement was made on a mass basis, 8 mixtures with Class F fly ash, with a lower specific gravity, had a higher volume of cementitious 9 materials than mixtures with Class C fly ash, resulting in an increased water demand. 10

Although Feed ash was coarser than Class F fly ash (Figure 1), the flow of Feed ash mixtures was 11 much lower than the mixtures containing Class F fly ash, especially for higher fly ash contents. This may 12 be due to the higher L.O.I. content in the Feed ash. Unburned carbon can adsorb water14. This adsorption 13 may be governed by the unburned carbon surface area14 and porosity nature14,15 and the presence of 14 oxygen functional groups15. 15

The flow of mixtures containing Class C fly ash increased with the increase of fly ash content. 16 This trend was reversed in Class F fly ash mixtures, and mixtures with 60% Class F fly ash presented 17 lower flow than mixtures with 20% Class F. For feed ash, there was a considerable decrease in flow with 18 the increase of fly ash content. 19

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For the same replacement level, mixtures containing Class C fly ash and high alkali cement 1 presented a higher flow than the mixtures with low alkali cement, while mixtures containing Feed ash 2 presented opposite trend. No trend was observed in Class F fly ash mixtures. 3

In regards to setting, as expected, as the fly ash content increased, the initial and final setting 4 times also increased, but this trend was even more pronounced in Class C fly ash mixtures. Feed ash 5 mixtures presented slightly higher setting times than Class F fly ash mixtures. 6

3.2. Compressive Strength of Mortar 7 Figure 2 shows the strength development over time. As expected, the compressive strength decreased 8 with the increase of fly ash content, and this decrease is more pronounced at early ages. Nevertheless, the 9 compressive strengths achieved were acceptable for replacements of 20% and 40%, even at 3 days, 10 reaching at least 3000 psi. As it can be observed, there is little strength increase from 91 to 119 days. 11

As shown in Figure 2, in mixtures containing low alkali cement, mixtures with Class C fly ash 12 yielded the highest strengths, especially at longer ages, with exception of mixtures containing only 20% 13 of fly ash. On the other hand, in mixtures containing high alkali cement, there was no significant 14 difference between mixtures with Class F fly ash and Class C fly ash. Mixtures containing Feed ash 15 presented the lowest strengths, with exception of mixtures containing only 20% of Feed ash and low 16 alkali cement. 17

3.3. Isothermal Calorimetry 18

3.3.1. Effect of different fly ashes 19 The isothermal calorimetry results presented in this section represent the average of 4 channels. The heat 20 flow and the cumulative heat were normalized by the total cementitious mass. 21

A typical heat profile from isothermal calorimetry shows 3 peaks. An initial peak occurs 22 immediately after mixing the water with the cementitious materials, which is due to rapid dissolution of 23 C3A and initial formation of ettringite (Aft) phases16. Nevertheless, in the current experiments, this peak 24 is not shown since the mixtures were prepared externally prior to insertion into the calorimeter. The 25 second peak is related to the hydration of C3S and the third peak, also called sulfate depletion peak, 26 corresponds to the reaction of C3A and it has been suggested that it relates to the renewed formation of 27 ettringite17. 28

The heat flow over time for mixtures containing low alkali cement can be found in Figure 3. As 29 expected, the substitution of cement by fly ash caused a dilution effect, due to the fact that fly ashes are 30 normally inert during the first few hours. As a consequence, the maximum heat flow decreased with the 31 increase of fly ash content and, in some cases, there was retardation on the heat flow, shown as a shift of 32 the peaks to the right. For the same mass replacement, Class C fly ash mixtures yielded higher degrees of 33 retardation than Class F fly ash mixtures and Feed ash mixtures, although the volume of Class C fly ash 34 for the same mass was slightly lower than Class F fly ash due to a higher specific gravity and the Class C 35 fly ash used was finer than the Class F fly ash and Feed ash. Similar behavior was observed previously by 36 Bentz2, when using fly ashes from the same sources. 37

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Figure 2 Compressive strength development. a) mixtures containing low alkali cement and b) 5 mixtures containing high alkali cement. NOTE: 1 psi = 6.89 kPa. 6

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(b) 4 Figure 3 Heat flow, obtained through isothermal calorimetry, for the first 72 hours of mixtures 5 containing (a) low alkali cement and fly ashes Class F or Class C and (b) low alkali cement and 6 Class F fly ash or Feed ash. 7

A small fourth peak can be observed in mixtures containing only cement and mixtures containing 8 Class C fly ash. This peak increases with the increase of fly ash content and occurs between 22 and 23 9 hours. While this peak has been associated with the hydration of C4AF or the conversion of Aft to AFm 10 phase16 (ettringite to monosulfate), in the present study, this peak was found to increase with the increase 11 of Class C fly ash content. Consequently, it was presumed that, in mixtures containing Class C fly ash, 12 either the fly ash promotes the hydration of the cement and serves as nucleation site for the cement 13 hydration (and more specific to the hydration of C3A) or the pozzolanic reaction of the fly ash could 14

0

0.2

0.4

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0 1000 2000 3000 4000 5000

Heat

Flo

w (W

/g)

Time (min)

LA LA20F LA40F LA60F LA20C LA40C LA60C

Fourth peak

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manifest itself in the fourth hydration peak17. This peak appears slightly higher with the mixtures 1 containing low alkali cement, which has a lower C3A content and a higher C4AF (Table 2). 2

Figure 3 shows that Class F fly ash mixtures and Feed ash mixtures behaved similarly, since their 3 curves overlap. 4

The heat flow over time for mixtures containing high alkali cement can be found in Figure 4. The 5 same behavior regarding dilution effect and retardation observed in mixtures with low alkali cement was 6 observed in mixtures with high alkali cement. High alkali cement mixtures containing Class C fly ash 7 presented higher third peak when compared to mixtures with Class F and Feed ash. High alkali cement 8 mixtures containing Class F or Feed ash presented a fourth peak at around 12 hours. 9

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(b) 13 Figure 4 Heat flow, obtained through isothermal calorimetry, for the first 72 hours of mixtures 14 containing (a) high alkali cement and fly ashes Class F or Class C and (b) high alkali cement and 15 Class F fly ash or Feed ash. 16

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3.3.2. Effect of cement composition 1 Figure 5 shows the effect of the cement composition on the heat flow and Figure 6 shows the effect of the 2 cement composition on the cumulative heat for the first 72 hours of hydration. 3

The major differences between mixtures with low alkali cement and high alkali cement are 4 depicted below. High alkali cement mixtures: 5

a) presented sharper amplification of the third peak (associated with the reaction of calcium 6 aluminate phases) in mixtures containing 20% and 40% Class C fly ash; 7

b) containing Class C fly ash presented much higher peak than their respective mixtures containing 8 Class F fly ash or Feed ash; 9

c) presented higher cumulative heat in all cases but the mixtures with 60% Class C fly ash and 40% 10 Feed ash. The difference in cumulative heat between high alkali mixtures and low alkali mixtures 11 decreased with the increase in fly ash content. 12

d) curves were shifted to the right, indicating a delay in comparison with the low alkali cement 13 mixtures. The delay on the maximum heat flow when comparing low alkali and high alkali 14 mixtures varied from 24 minutes for plain mixtures to 223 minutes for mixtures containing 60% 15 of Class C fly ash. The difference between low alkali and high alkali cement mixtures containing 16 Class F fly or Feed ash was less pronounced ranging from 69 to 94 minutes. 17

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(c) 4 Figure 5 Heat flow comparison of low alkali cement mixtures and high alkali cement mixtures 5 containing (a) Class F fly ash, (b) Class C fly ash and (c) Feed ash. 6

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(c) 2 Figure 6 Cumulative heat comparison of low alkali cement mixtures and high alkali cement 3 mixtures containing (a) Class F fly ash, (b) Class C fly ash and (c) Feed ash. 4

3.3.3. Relationship between calorimetry and setting time 5 Figure 7 and Figure 8 show the zoomed-in view of the heat flow of pastes during the first 15 hours of 6 hydration. In each curve, with the exception of the mixtures containing only cement, two markers are 7 shown: the first represents the initial set of the respective mortar mixture and the second marker 8 represents the time of the maximum heat flow of the paste mixture. When two curves and their markers 9 overlap, only one of the markers labels is shown. 10

In Figure 9, these two markers are plotted against each other, correlating the time of maximum 11 heat flow of pastes and the initial or final setting time of the mortars containing the same proportions of 12 cementitious materials and the same water-cementitious ratio. As it can be observed, there is a very good 13 correlation (R2 = 0.89), indicating that the calorimetry measurements could be used to predict the initial 14 setting time. A similar correlation (R2 = 0.87) was obtained between final setting time and time of the 15 maximum heat flow. This shows that isothermal calorimetry can be used as a tool to identify 16 incompatibilities and a surrogate test for setting time, which is very labor intensive. It is important to 17 emphasize that the linear regressions shown in Figure 9 need to be validated for different water-18 cementitious ratio and different cements and fly ashes. 19

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(b) 4 Figure 7 Zoomed in - heat flow of mixtures containing (a) low alkali cement and Class F fly ash or 5 Class C fly ash and (b) low alkali cement and Class F fly ash or Feed ash. 6

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(a) 2

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(b) 4 Figure 8 Zoomed in - heat flow of mixtures containing (a) high alkali cement and Class F fly ash or 5 Class C fly ash and (b) high alkali cement and Class F fly ash or Feed ash. 6

In a study on incompatibility of combinations of concrete materials, Taylor et al.18 suggested a 7 test protocol where a combination of materials would be considered incompatible when the time of 8 maximum heat flow is delayed by more than 60 minutes. Figure 10 presents the delay on time of 9 maximum heat flow of each of the 17 mixtures evaluated, in relation to a mixture with the same water to 10 cementitious ratio and 100% of low alkali cement (mixes LA20F, LA40F, LA60F, LA20C, LA40C, 11 LA60C, LA20FD, LA40FD and LA60FD) or 100% of high alkali cement (HA20F, HA40F, HA60F, 12 HA20C, HA40C, HA60C, HA20FD and HA40FD). 13

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Figure 9 Relation between time of maximum heat flow of pastes and the initial and final setting 2 time of respective mortar. 3

According to the criteria presented by Taylor et al.18, mixtures LA20F, LA40F, LA60F, LA20FD, 4 LA40FD, LA60FD, HA20F, HA40F, HA20FD and HA40FD would be considered compatible. All the 5 mixtures containing Class C fly ash, as well as mixture HA60F would be considered incompatible. 6

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Figure 10 Delay on time of maximum heat flow. 8

3.3.4. Relationship between calorimetry and compressive strength 9

Figure 11 shows the relation between the cumulative heat for the first 72 hours of paste hydration and the 10 3-day compressive strength of mortar cubes made with the same cementitious proportions and the same 11 water to cementitious ratio. It is important to emphasize that the linear regression shown in Figure 11 12 needs to be validated for different water-cementitious ratio and different cements and fly ashes. 13

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Nevertheless, once again isothermal calorimetry appears as a very reliable screening tool in selecting 1 mixture proportions. 2

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Figure 11 Relationship between cumulative heat for the first 72 hours of hydration of pastes and 3-5 day compressive strength of respective mortars. NOTE: 1 psi = 6.89 kPa. 6

4. CONCLUSIONS 7 From the results presented and discussed above, the following general conclusions can be made: 8 • Isothermal calorimetry was confirmed to be a good screening tool to detect problems related to 9

delayed setting time; 10 • Isothermal calorimetry was found to be a good tool for setting time prediction and compressive 11

strength prediction at early ages; 12 13

From the results presented and discussed above, the following conclusions can be made for the 14 materials used in this study: 15 • Class F fly ash did not significantly affect setting time, even at 60% fly ash content, with the 16

exception of the mixture containing high alkali cement. 17 • Feed ash did not significantly affect setting time for up to 40% fly ash content. 18 • Class C fly ash significantly affected setting time, even at 20% fly ash content and mixtures 19

containing high alkali cement were more affected. 20 • Compressive strength of mixtures with up to 40% Class F fly ash, Class C fly ash or Feed ash was 21

found to be satisfactory at 3 days; 22 • Mixtures containing Class C fly ash presented higher flow when compared to mixtures containing 23

Class F or Feed ash. Feed ash significantly decreased the flow of the mixtures. 24

5. REFERENCES 25 1. Rao, C.; Stehly, D., and Ardani, A., “Proportioning Fly Ash as Cementitious Materials in Airfield 26

Pavement Concrete Mixtures,” Mix Optimization Catalog for Project IPRF-01-G-002-06-2, April 27 2011. 28

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2. Bentz, D. Blending Different Fineness Cements to Engineer the Properties of Cement Based 1 Materials. Magazine of Concrete Research, 62 (5), 327-338, 2010. 2

3. ACI 232.2R-03, “Use of Fly Ash in Concrete”, Reported by ACI Committee 226, ACI Materials 3 Journal, American Concrete Institute, Volume 84, Issue 5, 1987. 4

4. Malhotra, V.M., Mehta, P.K., “High-Performance, High-volume Fly Ash Concrete: Materials, 5 Mixture Proportioning, Properties, Construction Practice, and Case Histories,” August 2002. 6

5. ASTM C618, “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for 7 Use in Concrete,” 2012. 8

6. CSA, “A3001-10 Cementitious Materials for Use in Concrete”, 2010. 9

7. Obla, K.H., Hill, R.L., Thomas, M.D., Shashiprakash, S.G., and Perebatova, O., “Properties of 10 Concrete Containing Ultra-Fine Fly Ash,” ACI Materials Journal, Technical Paper, Title no. 100-11 M49, September 2003. 12

8. Mehta, P.K., “Influence of Fly Ash Characteristics on Strength of portland Cement-Fly Ash 13 Mixtures,” Cement and Concrete Research, V. 15, No. 4, July 1985. 14

9. ASTM C305-06 Standard Practice for Mechanical Mixing Hydraulic Cement Pastes and Mortars of 15 Plastic Consistency. ASTM International, West Conshohocken, PA, 2006. 16

10. ASTM C1437 - 07 Standard Test Method for Flow of Hydraulic Cement Mortar. ASTM 17 International, West Conshohocken, PA, 2007. 18

11. ASTM C403 / C403M - 08 Standard Test Method for Time of Setting of Concrete Mixtures by 19 Penetration Resistance. ASTM International, West Conshohocken, PA, 2008. 20

11. ASTM C109 / C109M - 08 Standard Test Method for Compressive Strength of Hydraulic Cement 21 Mortars (Using 2-in. or [50-mm] Cube Specimens). ASTM International, West Conshohocken, PA, 22 2008. 23

12. ASTM C1738 - 11a Standard Practice for High-Shear Mixing of Hydraulic Cement Paste. ASTM 24 International, West Conshohocken, PA, 2011. 25

13. ASTM C1679 - 09 Standard Practice for Measuring Hydration Kinetics of Hydraulic Cementitious 26 Mixtures Using Isothermal Calorimetry. ASTM International, West Conshohocken, PA, 2009. 27

14. Külaots, I; Hurt, R.; Suuberg, E. Size distribution of unburned carbon in coal fly ash and its 28 implications. Fuel 83, 223–230, 2004. 29

15. Maroto-Valer, M.; Taulbee, D.; Hower,J. Characterization of differing forms of unburned carbon 30 present in fly ash separated by density gradient centrifugation. Fuel 80, 795-800, 2001. 31

16. Lagier, F.; Kurtis, K. Influence of portland cement composition on early age reactions with 32 metakaolin. Cement and Concrete Research, 37, 1411-1417, 2007. 33

17. Baert, G., Van Driessche, I., Hoste, S., De Schutter, G., De Belie, N. Interaction between the 34 Pozzolanic Reaction of Fly Ash and the Hydration of Cement. In: 12th International Congress on the 35 Chemistry of Cement, 12th International Congress on the Chemistry of Cement. 36

18. Taylor, P; Johansen, V.; Graf, L.; Kozikowski, R.; Zemajtis, J; Ferraris, C. Identifying Incompatible 37 Combinations of Concrete Materials: Volume II-Test Protocol. Federal Highway Administration, 38 Publication No HRT-06-080, 2006. 39

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