Pavement Concrete with Air-Cooled Blast Furnace Slag and Dolomite ...

Pavement Concrete with Air-Cooled Blast Furnace Slag and Dolomite as Coarse Aggregates Effects of Deicers and Freeze–Thaw Cycles Kho Pin Verian, Parth Panchmatia, Jan Olek, and Tommy Nantung mining and transporting good quality natural aggregates, and with disposal of waste material (1). Blast furnace slag is a by-product generated during melting of iron ore. It is a glassy material consisting of silicates and aluminosilicates of calcium and magnesium together with compounds of iron, manganese, sulfur, and other trace elements. Blast furnace slag is classified as air-cooled, expanded, granulated, or pelletized, depending on the treatment it receives after being removed from the furnace. The air-cooled blast furnace slag (ACBFS) is a crystalline mineral produced by slow cooling of blast furnace slag under atmospheric condition. This paper focuses on the use of ACBFS as coarse aggregate in pavement concrete. During their lifetime, concrete pavements in the northern half of the United States are exposed to freezing temperatures. Various deicing salts, including sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2), are routinely used on pavement surfaces during winter season to ensure safe driving conditions. Previous studies have suggested that the effects of deicers on pavement concrete vary greatly, depending on such factors as the concentration of deicers, exposure conditions and the temperature (2–11). In some cases, the deicer reacts with concrete hydration products and weakens the cement paste matrix. Some of these reactions are described in more detail later in this paper. The deterioration of concrete pavements resulting from exposure to deicers in a freezing and thawing environment is thus a major concern in areas experiencing winter conditions. This paper discusses the effects of partial replacement of cement by Class C fly ash and the inclusion of slag aggregate as coarse aggregate on the fresh and hardened properties of pavement concrete. Specifically, this paper addresses the changes occurring in concrete at the macro scale (strength and elastic modulus) and micro scale (formation of secondary reactions products) owing to its exposure to freezing and thawing in the presence of three types of deicers (NaCl, MgCl2, and CaCl2) with nominal concentration of 5.5 molar.

This study evaluated the effects of substituting natural coarse aggregate (dolomite) with air-cooled blast furnace slag (ACBFS) on the strength and durability properties of pavement concretes. The scope of the study included evaluation and analysis of four types of concrete subjected to three deicers [calcium chloride (CaCl2), magnesium chloride (MgCl2), and sodium chloride (NaCl)] while undergoing freeze–thaw (FT) exposure. Of the four types of concrete mixtures, two were prepared with ACBFS and two with natural dolomite as coarse aggregate. For each aggregate type, one mixture was produced with Type 1 portland cement, while the second one was produced with a binder composed of Type 1 cement and Class C fly ash (20% replacement by weight). Fresh pro perties of concrete tested included slump, unit weight, and total air content, while compressive and flexural strengths were measured for hardened concrete. Durability of concrete exposed to FT was assessed by periodically measuring dynamic modulus of elasticity of concrete and average depth of chloride penetration. Concrete with ACBFS aggregates developed slightly higher (~6%) compressive strength but lower (~15%) flexural strength than did concrete with natural dolomite. Periodic measurements of dynamic modulus of elasticity and visual observations of test specimens showed that of the three deicers used, the CaCl2 was the most aggressive, followed by MgCl2 and NaCl. In regard to resistance to the FT cycles in the presence of deicers, fly ash concretes (with either ACBFS or dolomite as coarse aggregate) showed better performance than did corresponding plain cement concretes.

In recent years, interest has increased in the use of recycled materials in pavement concretes. Partial replacement of the ordinary portland cement (OPC) with blends containing either fly ash or slag cements in pavement concretes has been practiced since the early 1990s. More recently, recycled concrete and slag from metallurgical industries have been used as aggregates in concrete pavements in an effort to reduce the dependency on natural aggregates and to lower the amount of landfilled material. In addition to environmental benefits, the use of recycled aggregates in pavement concrete lowers the overall construction cost by eliminating the expenditure associated with

Materials, Mixture Proportions, and Experimental Program

K. P. Verian, P. Panchmatia, and J. Olek, School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907-2051. T. Nantung, Research Division, Indiana Department of Transportation, 1205 Montgomery Street, West Lafayette, IN 47906. Corresponding author: K. P. Verian, kverian@ purdue.edu.

Two types of Indiana Department of Transportation (DOT) No. 8 coarse aggregates [maximum diameter (Dmax) = 1 in.] were used in this study (12): natural dolomite (labeled NA) and air-cooled blast furnace slag (labeled ACBFS). The fine aggregate was Indiana DOT’s No. 23 (Dmax = 3∕8 in.) natural siliceous sand. Although the chemical composition of the ACBFS used in this study was not specifically

Transportation Research Record: Journal of the Transportation Research Board, No. 2508, Transportation Research Board, Washington, D.C., 2015, pp. 55–64. DOI: 10.3141/2508-07 55

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Transportation Research Record 2508

tested, such materials typically contain four major components: lime (CaO; 30% to 40%); silica (SiO2; 28% to 42%); alumina (Al2O3; 5% to 22%); and magnesia (MgO; 5% to 15%) (2). All concrete mixtures used in the study were designed to meet the requirements specified in Section 501 [Quality Control/Quality Assurance (QC/QA)] of Indiana DOT’s standard specification (12). These requirements are as follows: • Minimum amount of cement: 400 lb/yd3, • Maximum water-to-cementitious materials ratio (w/cm): 0.45, • Minimum portland cement–fly ash ratio: 3.2 by weight (mass), • Target air content: 6.5% (allowable range 5.3% to 9.8%), and • Minimum flexural strength at 7 days: 570 pounds per square inch [psi (4,000 kPa)]. In addition to the aforementioned requirements, for slip-formed concrete pavements, the Indiana DOT requires the slump to be in the range of 1.25 to 3.00 in. (32 to 76 mm). To achieve the target fresh properties (slump and air content), the dosage of water reducer and air entraining agent was adjusted within the limits suggested by the manufacturer. Four mixtures, two containing natural dolomite and two with ACBFS as coarse aggregate, were produced in the laboratory. One of the two mixtures employed a plain binder (100% OPC), while the other consisted of binary binder [80% OPC and 20% replacement by weight (wt. %) of Class C fly ash]. The labeling system used for the mixtures reflects the composition of the binder as well as the type of coarse aggregate used. As an example, the label M2-.8PC.2FAACBFS indicates that Mixture 2 (M2) was prepared with a binder consisting of 80% Type 1 Portland cement and 20% wt. % of Class C fly ash, and that ACBFS was used as the coarse aggregate. The specific mixture proportions are given in Table 1. Several tests were conducted to assess the properties of both the aggregates and concretes. The test performed on the aggregates included sieve analysis, determination of absorption, and determination of specific gravity (saturated surface dry). The measured fresh concrete properties included slump and air content (using volumetric method). These tests were conducted within 15 min after completion of the mixing cycle. The testing performed on hardened concrete included evaluation of compressive and flexural strengths,

determination of changes in dynamic modulus of elasticity (DME) resulting from exposure to freezing and thawing cycles, and evaluation of the changes in microstructure of concrete. Evaluation of freeze–thaw resistance of concrete was performed on 3 × 3 × 11-in. (76 × 76 × 279-mm) beams that were submerged in a 5.5 molar deicer solution and exposed to one freeze–thaw cycle a day for 350 days. A freeze–thaw cycle consisted of 11 h of freezing at −18°C and 11 h of thawing at 23°C and an hour each for changing the temperature from −18°C to 23°C and vice versa. Results and Discussion Aggregate Gradation, Specific Gravity, and Absorption The standard Indiana DOT’s gradations (12) and the sieve analysis results for aggregates used in this study are presented in Figure 1. The sieve analysis tests for fine and coarse aggregates were conducted following the procedure described in AASHTO T 27. As shown in Figure 1, the gradations of both types of coarse aggregates (No. 8 dolomite and No. 8 ACBFS) and sand used in this study were all between the upper and lower bounds required by Indiana DOT specifications (12). The No. 8 ACBFS aggregate had a slightly higher percentage of fine particles (i.e., those passing No. 8 sieve) than the dolomite did. Otherwise, the overall the gradations of ACBFS and dolomite aggregates are practically identical. The specific gravity (saturated surface dry) and absorption results of all aggregates are presented in Table 2. Slump, Air Content, and Unit Weight The slump of fresh concrete was measured in accordance with AASHTO T 119 and the results are presented in Figure 2a. As mentioned earlier, Indiana DOT’s QC/QA specification for pavement concrete requires the slump to be in the range of 1.25 to 3.00 in. The slump values vary with w/cm ratio and water reducer dosage. In this study, all mixtures have the same value of w/cm (0.42), but water reducing admixture dosage was slightly higher (2.2 fl. oz

TABLE 1 Proportions of Concrete Mixtures Value (lb/yd3), by Mix Design Material

M1-1PC-ACBFS

M2-.8PC.2FA-ACBFS

M3-1PC-NA

M3-.8PC.2FA-NA

586 0

470 118

586 0

470 118

0 1,620 1,220 247

0 1,620 1,220 247

1,720 0 1,320 247

1,710 0 1,310 247

Cement (Type 1) Fly ash (Class C) Coarse aggregate Dolomite ACBFS Fine aggregate Water w/cm Water reducera (Glenium 3030 NS) (2–6 fl. oz) Air entraining agenta (Microair) (0.5–3 fl. oz) a

Fluid ounce per 100-lb cementitious materials.

0.42 2

0.42 2

0.42 2.2

0.42 2.2

1

1

1

1

Verian, Panchmatia, Olek, and Nantung

57

100

Indiana DOT No. 8, upper limit

Percentage Passing

90 80

Indiana DOT No. 8, lower limit

70 No. 8, ACBFS

60 50

No. 8 dolomite

40 30

Indiana DOT No. 23, upper limit

20 Indiana DOT No. 23, lower limit

10 0 0.1

No. 23 sand

10

1 Sieve Size (mm)

FIGURE 1 Aggregate gradation curves.

Average Slump (in.)

3.0 2.5

Indiana DOT QC/QA range

2.0 1.5 1.0 0.5

Note: SSD = saturated surface dry; NA = not available. a Based on the QC data from aggregate producer.

A N

A

FA -

-N C

PC .2 .8 4-

155 150 145 140 135

C

PC .2

1P 3-

.8

M

4-

.8

M

FA PC .2

FA -N

A -N

S AC BF

BF

A

130

Mixture Design

(b) FIGURE 2 Average measurement results by fresh concrete mixture: (a) slump and (b) air content and unit weight.

Average Unit Weight (lb/ft3)

Indiana DOT QC/QA range

2-

5% Not specified NA

Unit weight 160

10 9 8 7 6 5 4 3 2 1 0

C -A C

1.1 3.4a 2.1

M Air content

M

No. 8 dolomite No. 8 ACBFS No. 23 sand

3-

(a)

1P

2.73 2.43 2.56

Indiana DOT’s Maximum Absorption Limit

M

Mixture Design

1-

Absorption (%)

1P

AC

M

2-

.8

M

1-

PC .2

1P

C

FA -

-A C

BF

BF

S

S

0.0

M

Aggregate

Specific Gravity (SSD)

Dolomite

3.5

S

TABLE 2 Specific Gravity and Absorption of Aggregates

ACBFS

Average Air Content (%)

versus 2.0 fl. oz per 100 lb of cementitious) for mixtures with dolomite as the coarse aggregate (M3 and M4) compared with mixtures with ACBFS (M1 and M2). This might be the reason for M3 having relatively higher slump (2.3 in.) compared with M1 (1.9 in.). For M2 and M4, the slumps are comparable (2.8 in. versus 2.7 in.). The role of fly ash with respect to increasing the workability can be clearly observed from the difference between the slumps of M1 and M2 (1.9 in. versus 2.8 in.) and M3 and M4 (2.3 in. versus 2.7 in.). However, the reported differences in the slump values fall within the variability limits of the testing procedure (AASHTO T 119) and are therefore considered insignificant (except for the differences in the slump values of M1 and M2). The air content of fresh concrete was measured following the procedure described in AASHTO T 196 (volumetric method). The volumetric (rather than pressure) test method of air determination was used because of slag aggregate being more porous than the natural aggregate. The unit weight of concrete was calculated by dividing the mass of fresh concrete required to completely fill the bowl of the air meter by the volume of the bowl. Figure 2b presents the values of air content and unit weight of four different concrete mixtures and the upper and lower air content limits specified by Indiana DOT for pavement concrete. Results shown in Figure 2b indicate that the air content of all mixtures was within the specified Indiana DOT’s limits for pavement concrete (target of 6.5%; allowable range 5.3% to 9.8%). All mixtures were prepared using the same amount (1.0 fl. oz./100 lb of cementitious) of air entraining admixture. As shown in Figure 2b, plain concrete with ACBFS (M1) has slightly higher (0.7%) air content compared to plain concrete with natural dolomite (M3),

58


concretes yielded slightly higher (up to 6%) compressive strength than concretes with dolomite. However, considering the accuracy of the method itself (15), this difference is considered to be statistically insignificant.

but this difference is not considered to be significant according to AASHTO T 196. However, the air contents of the two fly ash concretes (M2 and M4) were both the same. As expected, the unit weight of concrete with ACBFS was lower compared with similar concrete with natural dolomite. This is caused by differences in the specific gravity of these two aggregates. Specifically, the unit weights of M1 (136.3 lb/ft3) and M2 (135.6 lb/ft3) are, respectively, about 5% lower than the unit weights of M3 (143.4 lb/ft3) and M4 (142.9 lb/ft3).

Dynamic Modulus of Elasticity The DME was calculated by using measured values of mass and resonant frequency of prismatic specimens (3 in. × 3 in. × 11 in.) in accordance with ASTM E1876. It was calculated by using Equation 1:

Flexural and Compressive Strengths

f f2   L3   DME = 0.9465 p  m p  p  3  p T1  b t 

The flexural strength test was conducted using third-point loading method specified in AASHTO T 97. The Indiana DOT requires pavement concrete to develop a minimum 7-day flexural strength of 570 psi. That agency does not have a requirement for 28-day com pressive strength, but the Michigan DOT specifies the minimum 28-day compressive strength of 3,500 psi for pavement concrete (13). The values of both the flexural and compressive strengths for the mixtures used in this study are shown in Figure 3. The error bars indicate the spread of data points from their average. It can be seen that all mixtures satisfy Indiana DOT requirements for minimum 7-day flexural strength (570 psi) and all the 28-day compressive strengths were above 3,500 psi [the minimum value of the compressive strength specified by the Michigan DOT (13)]. Concretes made with ACBFS aggregate (M1 and M2) have lower (up to 15%) 7-day and 56-day flexural strengths when compared with concretes made with dolomite (M3 and M4). At early age (7 days), concretes with fly ash (M2 and M4) had lower flexural strength compared with plain concretes (M1 and M3). However, at later age (56 days), concretes with fly ash (M2 and M4) developed higher flexural strength than the corresponding plain concrete mixtures (M1 and M3). These later-age increases result from the pozzolanic reaction of fly ash (14). The pozzolanic reaction also leads to the higher compressive strength for M2 (5,655 psi) and M4 (5,474 psi) compared with M1 (5,488 psi) and M3 (5,160 psi). Unlike for the case of flexural strength, the ACBFS

where DME = dynamic modulus of elasticity (Pa), m = mass of specimen (g), b = width of specimen (mm), L = length of specimen (mm), t = thickness of specimen (mm), ff = fundamental resonant frequency of specimen in flexure (Hz), and T1 = correction factor for fundamental flexure mode to account for finite thickness of specimen and for Poisson’s ratio. 2

 t  t T1 = 1 + 6.585 p (1 + 0.0752µ + 0.8109µ 2 ) p   – 0.868 p    L  L

where µ is Poisson’s ratio.

7,000 6,000 5,000 4,000 3,000 2,000 1,000

A FA -

N

-N C

PC

.2

31P

Indiana DOT minimum flexural strength at 7 days

M

4-

.8

.2 M

2-

.8

M

PC

M

-A C FA

-A C C 11P

A

BF S

0

Compresive Strength (psi)

56-day flexural strength

28-day compressive strength

BF S

Flexural Strength (psi)

4

4

  t  2 8.34 p (1 + 0.2023µ + 2.173µ ) p    L  −  2   t  2 1 + 6.338 p (1 + 0.1408µ + 1.536µ ) p    L  

7-day flexural strength 1,000 900 800 700 600 500 400 300 200 100 0

(1)

Mixture Design FIGURE 3 Flexural and compressive strengths by concrete mixture.

Mississippi DOT minimum compressive strength at 28 days

(2)


59

7 6 5 4 3 2 1 0

M1-CaCl2-FT M1-MgCl2-FT M1-NaCl-FT M1-DST-FT M1-Control 0

provide a holistic measure of the durability of the bulk material. Therefore, the change in the DME of concrete was used to evaluate the durability of concrete in this study. The effects of fly ash in enhancing concrete performance can be observed by comparing the DME values of fly ash concrete specimens (M2 and M4) exposed to CaCl2 with DME values of plain concrete specimens (M1 and M3) exposed to the same deicer. To be specific, the fly ash concrete specimens did not fail after being exposed to, respectively, 321 and 350 freeze–thaw cycles. However, the plain concrete specimens failed after, respectively, 111 and 151 freeze haw cycles. The values of DME for other specimens (exposed to NaCl, DST, and control) were quite stable, indicating either intact concrete matrix or low deterioration level that could not be detected by the resonant frequency method. Physical Deterioration and Depth of Deicers Penetration: Visual Examination The depth of chloride penetration was measured by cutting the beam specimens at the end of freeze–thaw exposure. The presence of chlorides was indicated by the grayish color that appeared after spraying the cross section of the beam with silver nitrate solution. The reported depth of chloride penetration (dx) was calculated as the average of multiple measurements, each indicated by the red arrow lines shown in Figure 5. The examination of the average values of chloride penetration indicates that the penetrability of NaCl is higher than that of CaCl2 and MgCl2 (see Figure 6). Figure 6 indicates that fly ash concretes (M2 and M4) have lower chloride penetration depths compared with the plain concretes (M1 and M3). For plain concrete, slag aggregate mixture (M1) experienced lower penetration depth (dx) compared with concrete

Average DME (106 psi)


The measurements were taken periodically during the exposure to deicers and freeze–thaw cycles. One freeze–thaw cycle consisted of 11 h of freezing (at −18°C); 11 h of thawing (at 23°C); and 1 h of temperature ramping after each freezing and thawing phase. Three deicers were used in this study: NaCl (14% solution); MgCl2 (15% solution); and CaCl2 (17% solution). At these concentrations, all solutions contained the same total amount of ions; they also became partially frozen at the temperature of −18°C. In addition to being exposed to these deicers, one set of specimens from each mixture was exposed to distilled water (DST) while undergoing freeze–thaw cycles. Finally, the control set of specimens (labeled C) from each mixture was stored in the curing room (23°C ± 2; 95% relative humidity). The development of the dynamic modulus of elasticity (DME) for specimens from each mixture is presented in Figure 4. Figure 4 indicates that of all concrete mixtures, specimens exposed to CaCl2 have developed the lowest DME, except for M4 (fly ash mixture with dolomites shown in Figure 4d ). For this mixture, the DME of specimens exposed to CaCl2 was quite close to the DME of specimens exposed to MgCl2. Specimens from mixtures M1 and M5 failed (i.e., it was difficult to obtain consistent readings of frequencies) after being exposed to CaCl2 for 111 and 151 freeze–thaw cycles, respectively. In regard to the relative aggressiveness of deicers toward the specimens, the CaCl2 solution was the most aggressive, followed by MgCl2 and NaCl, respectively, as indicated by the development of DME for each set of specimens exposed to those deicers. As expected, all control specimens developed the highest DME since they were not exposed to any deicers or to freeze–thaw cycles. The only exception was mixture M1 (Figure 4a), for which the DME of DST-exposed specimen was slightly higher than that of the control. Inclusion of fly ash is known to reduce the scaling resistance of concrete. However, scaling is a surface phenomenon and does not

8 7 6 5 4 3 2 1 0

50 100 150 200 250 300 350 400


7 6 5 4 3 2 1 0


50 100 150 200 250 300 350 400 No. of Freeze–Thaw Cycles

(c)


(b) Average DME (106 psi)


No. of Freeze–Thaw Cycles (a) 8 7 6 5 4 3 2 1 0



(d)

FIGURE 4 Changes in DME of concretes exposed to various deicers while undergoing freeze–thaw (FT) cycles: (a) M1-1PC-ACBFS (plain, slag), (b) M3-1PC-NA (plain, dolomite), (c) M2-.8PC.2FA-ACBFS (fly ash, slag), and (d ) M4-.8PC.2FA-Dolomite (fly ash, dolomite) (No. 5 number).

60


Ml-CaCl2-FT davg = 17.4 mm

Ml-MgCl2-FT davg = 8.5 mm

Ml-NaCl-FT davg = 19.2 mm

Ml-DST-FT davg = 0 mm

(a)

M2-CaCl2-FT davg = 12.4 mm

M2-MgCl2-FT davg = 4.9 mm

M2-NaCl-FT davg = 17.8 mm

M2-DST-FT davg = 0 mm





(b)


M3-MgCl2-FT davg = 16.1 mm (c)


M4-MgCl2-FT davg = 5.0 mm (d)

FIGURE 5 Cross sections and depth of chloride penetration in beams from (a) M1 (plain–slag aggregate mixture), (b) M2 (fly ash–slag aggregate mixture), (c) M3 (plain–dolomite mixture), and (d ) M4 (fly ash– dolomite mixture).


61

M2-.8PC.2FA-ACBFS (fly ash–slag aggregate)-FT

M3-1PC-NA (plain–dolomite)-FT

M4-.8PC.2FA-NA (fly ash–dolomite)-FT

Average Cl Penetration Depth (mm)

M1-1PC-ACBFS (plain–slag aggregate)-FT

35 30 25 20 15 10 5 0

CaCl2

MgCl2 Type of Deicer

NaCl

FIGURE 6 Average depths of chloride penetration of four mixtures by type of deicer.

with dolomite (M3). This may indicate possible densification of the microstructure as a result of internal curing taking place in these mixtures (the slag aggregate was soaked overnight in water before being used to prepare the mixture). In regard to fly ash mixtures, the depth of chloride penetration was quite comparable (the difference being less than 3 mm) for concrete with ACBFS and concrete with dolomite. The deterioration of specimens (the result of chemical reactions coupled with physical damage caused by freeze–thaw exposure) manifested itself in the form of cracks that originated in the corners of specimens and propagated along edges of the beam in direction parallel to the long axis of the specimens. Plain concrete specimens exposed to CaCl2 deteriorated faster than any other specimens and (as mentioned earlier) failed after 111 freeze–thaw cycles for plain concrete with ACBFS aggregate and after 151 freeze–thaw cycles for plain concrete with natural dolomite aggregate. Among other specimens, there was no observable damage, with the exception of some minor cracks on the surface of plain concrete beams exposed to MgCl2. The physical appearances of plain concrete with ACBFS and plain concrete with natural dolomite aggregate exposed to freeze–thaw and CaCl2 are presented in Figure 7, a and b, respectively. Scanning Electron Microscopy Analysis and Results The detrimental chemical effects of chloride-based deicers such as sodium chloride, magnesium chloride, and calcium chloride on the microstructure of hardened concrete have been documented in the past [e.g., Ketcham et al. in FHWA-RD-95-202 (15) and Sutter et al. (16)]. The underlying deterioration mechanisms are chemical and involve reactions of deicers with various components of the hydrated cement matrix [i.e., calcium hydroxide, calcium silicate hydrate, or mono sulfate], as shown in Equations 3 through 7. These reactions result in an increase of porosity near the surface of the concrete (17, 18), thus making it more permeable and therefore susceptible to freeze–thaw damage (16). Sutter et al. reported formation of oxychloride phases when concrete is exposed to calcium and magnesium chlorides (16). Brucite [Mg(OH)2] and magnesium silicate hydrate (M-S-H) are

some other commonly encountered phases observed when concrete is exposed to magnesium chloride (8). Equations 4 through 6 show the chemical reactions for the formation of the aforementioned phases in cementitious systems exposed to CaCl2 and MgCl2 solutions. 2NaCl + Ca ( OH )2 → 2NaOH + CaCl 2

(3)

CaCl 2 + 3Ca ( OH )2 + 12H 2 O → 3CaO p CaCl 2 p 15H 2 O

(4)

MgCl 2 + Ca ( OH )2 → Mg ( OH )2 + CaCl 2

(5)

CaO i SiO 2 i H 2 O + MgCl 2 → CaCl 2 + MgO i SiO 2 i H 2 O

(6)

C4 A S H12 + 2Cl − → C3 A p CaCl 2 p 10H + CS H 2

(7)

where Ca(OH)2 = calcium hydroxide, NaOH = sodium hydroxide, H2O = water, 3CaO p CaCl2 p 15H2O = calcium oxychloride, CaO • SiO2 • H2O = calcium silicate hydrate, MgO • –SiO2 • H2O = M-S-H, C4AS H12 + 2Cl− = monosulfate, C3A p CaCl2 p 10H = Friedel’s salt, and – CSH2 = gypsum. Once the freezing–thawing testing was completed, small (∼0.8 in. × 0.8 in. × 0.8 in.) specimens were extracted from near the edge of the beams. These specimens were epoxy impregnated, lapped and polished before being examined in the scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) analyzer. The SEM observations revealed the presence of calcium chloride and Friedel’s salt deposits in samples extracted from the edge of the specimens exposed to all the aforementioned chloride based deicers. Friedel’s salt formation is a result of replacement of sulfate ions from the monosulfate phase (present abundantly in concrete) by chloride ions (see Equation 7). In addition to compromising the existing air void system (by Fridel’s salt deposits), the by-product of the formation

62


35 FT cycles

42 FT cycles

59 FT cycles (a)

65 FT cycles

102 FT cycles

118 FT cycles

139 FT cycles

(b) FIGURE 7 Physical changes in plain concrete specimens exposed to freezing and thawing cycles and CaCl 2 deicer: (a) with ACBFS and (b) with dolomite.

of Friedel’s salt, that is, gypsum, is expansive and increases the potential for delayed ettringite formation. A lot of chloride was detected in paste of samples extracted from the edge of the specimen. However, little or no evidence of chlorides or Friedel’s salt was detected in samples extracted from the center of the specimen. Samples exposed to MgCl2 solution showed evidence of brucite deposits (see Figure 8a) at the edge of the sample. The deposits of M-S-H and oxychloridelike phases were also observed near the edges (as shown in Figure 8, b and c). The frequency of appearance of these phases decreased in areas away from the edge of the specimen. Samples extracted from the center of the beam showed no signs of the aforementioned phases. These observations agree well with the penetration depth tests results reported in an earlier section of this paper. Samples exposed to CaCl2 solution showed the maximum deterioration and the SEM analysis of those samples showed presence of phases that appeared similar to oxychloride phases as shown in Figure 8d and as observed by Sutter et al. (16). Summary and Conclusions The results of this study can be summarized as follows: • Concrete prepared with ACBFS developed slightly higher (although statistically insignificant) compressive strength than con-

crete prepared with natural dolomite. At the same time, ACBFS concretes had lower flexural strength and lower values of DME compared with their counterparts with natural aggregate. • Fly ash improved the strength of concretes at later ages (28-day compressive strength and 56-day flexural strength), reduced concretes permeability, and improved concrete durability with respect to deicer attack and freeze–thaw damage. • At the same level of total ion concentration (5.5 molal), CaCl2 has been found to cause more concrete deterioration than MgCl2 and NaCl. • In regard to CaCl2 exposure combined with freeze–thaw cycles, plain concrete with dolomite as coarse aggregate performed better than similar concrete with ACBFS as coarse aggregate. However, for specimens exposed to MgCl2, plain concrete with dolomite had inferior performance compared with the same concrete with ACBFS. • In regard to depth of penetration of chlorides, the observed values were largest for chloride derived from NaCl, followed by chlorides derived from CaCl2. The chlorides derived from MgCl2 penetrated the least, most likely because of formation of protective surface layer of brucite at the surface of the specimens. • Friedel’s salt and ettringite deposits were encountered in all samples exposed to chloride-based deicers. In addition to those phases, the presence of M-S-H and brucite was evident in samples exposed to MgCl2. In addition, calcium oxychloride-like phase was detected in samples exposed to both, MgCl2 and CaCl2 solution.


63

(a)

(b)

(c)

(d)

FIGURE 8 SEM–EDX images: (a) brucite, (b) M-S-H, (c) Mg-O-Cl phase surrounded by calcium hydroxide (samples extracted from edge of specimen exposed to MgCl 2 solution), and (d ) image magnified 1,000 times of void filled with calcium oxychloride-like phase in sample exposed to CaCl 2 solution.

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In conclusion, the observed fresh properties and strength values of concrete incorporating ACBFS aggregate were satisfactory for paving applications. Additionally, ACBFS concrete with fly ash (M2) provided adequate resistance (similar to concrete incorporating dolomite aggregate) to freeze–thaw damage in presence of chloride-based deicers. Therefore, the use of ACBFS as coarse aggregate in pavement concrete is a viable option with respect to reducing the dependency on natural aggregates and environmental damage associated with mining natural aggregate sources. Acknowledgments This work was supported in part by the Joint Transportation Research Program administered by the Indiana Department of Transportation and Purdue University. References 1. Verian, K. P. Using Recycled Concrete as Coarse Aggregate in Pavement Concrete. MS thesis. Purdue University, West Lafayette, Ind., 2012. 2. Morian, D., T. Van Dam, and R. Perera. Use of Air-Cooled Blast Furnace Slag as Coarse Aggregate in Concrete Pavements. Final report, FHWAHIF-12-008. FHWA, U.S. Department of Transportation, 2012. 3. Chatterji, S. Mechanism of the CaCl2 Attack on Portland Cement Concrete. Cement and Concrete Research, Vol. 8, 1978, pp. 461–467. 4. Collepardi, C., M. Coppola, and L. Pistolesi. Durability of Concrete Structures Exposed to CaCl2 Based Deicing Salts. SP-145: Durability of Concrete—Proceedings of the 3rd CANMET, Nice, France, American Concrete Institute, Farmington Hills, Mich., 1994, pp. 107–120. 5. Ghafoori, R. P., and N. Mathis. Scaling Resistance of Concrete Paving Block Surface Exposed to Deicing Chemicals. ACI Materials Journal, Vol. 94, 1997, pp. 32–38. 6. Harnik, A. B., U. Meier, and A. Rösli. Combined Influence of Freezing and Deicing Salt on Concrete—Physical Aspects. Durability of Building Materials and Component. Proc., 1st International Conference, Ottawa, Ontario, Canada, 1978, Issue 69, pp. 474–484. 7. Hudec, S. P., P. P. Maclnnis, and C. McCann. Investigation of Alternate Concrete Deicers. SP-145: Durability of Concrete—Proceedings of the 3rd CANMET, Nice, France, American Concrete Institute, Farmington Hills, Mich., 1994, pp. 65–84. 8. Janusz, A. Investigation of Deicing Chemicals and Their Interactions with Concrete Materials. MS thesis. Purdue University, West Lafayette, Ind., 2010.


9. Marchand, M., L. Sellevold, and E. J. Pigeon. The Deicer Salt Scaling Deterioration of Concrete—An Overview. SP-145: Durability of Concrete—Proceedings of the 3rd CANMET, ACI International Conference, Nice, France, American Concrete Institute, Farmington Hills, Mich., 1994, pp. 1–46. 10. McDonald, W. F., and D. B. Perenchio. Effects of Salt Type on Concrete Scaling. Concrete International, Vol. 19, 1997, pp. 23–26. 11. Sutter, L. Investigation of the Long Term Effects of Magnesium Chloride and Other Concentrated Salt Solutions on Pavement and Structural Portland Cement Concrete. http://www.mse.mtu.edu/∼llsutter /pdf/SDDOTsum.pdf. Accessed April 12, 2014. 12. Indiana Department of Transportation. Standards Specification, 2010. http://www.in.gov/dot/div/contracts/standards/book/sep09/5-2010.pdf. Accessed May 13, 2014. 13. Michigan Department of Transportation. Standard Specifications for Construction, 2012. http://mdotcf.state.mi.us/public/specbook/2012/. Accessed April 20, 2014. 14. Abo-El-Enein, S. A., G. El-kady, T. M. El-Sokkary, and M. Gharieb. Physico-Mechanical Properties of Composite Cement Pastes Containing Silica Fume and Fly Ash. HBRC Journal, Vol. 11, No. 1, 2015, pp. 7–15. http://dx.doi.org/10.1016/j.hbrcj.2014.02.003. Accessed Nov. 11, 2014. 15. Ketcham, S., L. D. Minsk, R. R. Blackburn, and E. J. Fleege. Manual of Practice for an Effective Anti-Icing Program—A Guide for Highway Winter Maintenance Personnel. Report FHWA-RD-95-202. U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H. https://www.fhwa.dot.gov/publications/research/safety/95202 /index.cfm. 16. Sutter, L. L., T. J. Van Dam, K. R. Peterson, and D. P. Johnston. LongTerm Effects of Magnesium Chloride and Other Concentrated Salt Solutions on Pavement and Structural Portland Cement Concrete: Phase I Results. In Transportation Research Record: Journal of the Transportation Research Board, No. 1979, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 60–68. 17. Dirk, W. Change in Structure and Chemistry of Cement Mortars Stressed by a Sodium Chloride Solution. Cement and Concrete Research, Vol. 14, 1984, pp. 49–56. 18. Gegout, G. M. P., and E. Revertegat. Action of Chloride Ions on Hydrated Cement Pastes: Influence of the Cement Type and Long Time Effect of the Concentration of Chlorides. Cement and Concrete Research, Vol. 22, 1992, pp. 451–457. The contents of this paper reflect the views of the authors, who are responsible for the facts and the accuracy of the data, and do not necessarily reflect the official views or policies of the sponsoring organizations. The contents do not constitute a standard, specification, or regulation. The Standing Committee on the Durability of Concrete peer-reviewed this paper.