RESISTANCE TO CHLORIDE-ION PENETRATION OF …

1

RESISTANCE TO CHLORIDE-ION PENETRATION OF LIGHTWEIGHT AGGREGATE

STRUCTURAL CONCRETE

João Filipe Martins Cortês

Introduction

Lightweight aggregate concrete (LWAC), with only coarse lightweight aggregates (LWA) has been used

for a long time, especially for structural applications in long-span bridges, high-rise buildings and buildings

founded on poor soil conditions.

Many authors argue that the resistance to chloride-ion penetration of LWAC is at least similar to the one

displayed by normal weight aggregate concrete (NWAC) (Chia and Zhang 2001; Kayali and Zhu 2004; Liu et al.

2010; Bogas 2011). According to Liu et al. (2010), the charge passed in Rapid Chloride Permeability Tests

(RCPT) was just about the same in LWAC of expanded clay and NWAC, for concretes with 0,38 w/c ratio and

28 days curing period. In fact, the authors report that the charge passed through NWAC was of 2528 Coulomb,

whereas the charge passed through LWAC was only of 2385 Coulomb. In the same study, similar results were

obtained in the Rapid Chloride Migration Tests (RCMT), determined by the NT Build 492 method, where 6,5

x10-12

m2/s and 8,8 x10

-12 m

2/s were the values registered for LWAC and NWAC respectively.

Kockal and Ozturam (2010) report that the charges passed through LWAC, with w/cm ratio of 0,26,

including silica fume, and 28 days curing period, were about the same, or even inferior to those passed through

the control NWAC mixtures. Bogas (2011) also verifies that the RCMT results of mixtures with 28 days curing

period and a w/c ratio of 0,35 and 0,45 tend to be same on LWAC and NWAC.

This results tend to indicate that the chloride penetration resistance, despite being influenced by the

diffusion of the aggregates, cement matrix and interface zones of the mixtures, could be manly ruled by the

quality of the last two, thus explaining the little differences between LWAC and NWAC (Liu et al. 2010; Bogas

2011). In fact, the incorporation of LWA often results in better quality of the cement paste and interface zones.

The type of w/c ratio and cimenticious materials incorporated in the admixture also seem to play an

important role in controlling the chloride-ion penetration. Kayali and Zhu (2004) verify that the addition of 23%

fly ash per cement mass, on slabs partially submerged in sodium chloride solution with various w/c ratios

(0,34;0,35 and 0,6), resulted in the reduction of the diffusion coefficients. Bogas (2011) also reports inferior

diffusion coefficients associated with the addition of fly ash. However, the author verifies that those results are

only valid for mixtures with a long curing period (365 days). In fact, various authors conclude that usually, long

curing periods lead to an improvement on the resistance to chloride-ion penetration (EuroLightCon 1999; Haque,

Khaiat, Kayali 2002; Bogas 2011).

Several authors report that the addition of silica fume also improves the chloride-ion penetration

resistance, even at an early age ( Kockal and Ozturam 2010; Bogas 2011; Güneyisi et al. 2013).

This paper aims to solidify the existing knowledge about the durability of LWAC, with special focus on

the chloride penetration resistance. In order to do so, the main properties of LWAC were studied and compared

with NWAC results, particularly its compressive strength, capillary absorption, electrical resistivity and chloride

penetration resistance.

2. Experimental program

2.1 Materials and methods

The experimental campaign involved the production of several LWAC with various water/binder ratios

(w/b) and additions. For the production of the admixtures four types of LWA were used - Leca and Argex

(expanded clay); Lytag (sintered fly-ash) and Stalite (expanded slate) - whose physical properties are

summarized in Table 1. Normal weight aggregates (NWA) consisted on crushed limestone composed by coarse

gravel (CG) and fine gravel (FG), and natural silica sand, composed by 30% fine sand (FS) and 70% coarse sand

(CS), such as resumed in Table 1.

Table 1 - Aggregate properties

Property

Normal weight aggregates Lightweight aggregates

Fine

sand

Coarse

sand

Fine

gravel

Coarse

gravel Leca Stalite Lytag Argex 2-4 Argex 3-8F

24h water absorption, wabs,24h (%) 0.19 0.26 0.73 0.35 15.81 3.57 17.92 21.38 19.28

Particle dry density, p (kg/m3) 2605 2617 2646 2683 1076 1483 1338 669 597

Loose bulk density, b (kg/m3) 1569 1708 1309 1346 624 760 750 377 330

Granulometric fraction (di/Di) 0/1 0/4 0/8 4/11.2 4/11.2 8/16 4/11.2 4/8 4/11.2

2

2.2 Mix proportions, concrete mixing and tests

Several mixtures were produced from the three w/b ratios studied (0,35; 0,45; 0,55), as indicated in Table

2. The maximum size of the aggregate was 12.5 mm. The effective water/ binder ratio (w/b) concerns the

effective water available for cement hydration, which means that it does not include the water absorbed by

aggregates. In NWAC, both CG and FG were combined in order to ensure a grading curve close to the one of

Leca. The same process was used for LWAC of Argex, where both Argex 2-4 and Argex 3-8F were combined.

The concrete was produced in a vertical axis mixer. First, the aggregates were introduced in the mixer and

then moistened for 3 minutes with 1/3 of the mixing water. The absorption of lightweight aggregates was

estimated according to the method suggested by Bogas et al. (2012a). Then, the cement and additions, the

remaining water and, when needed, the superplasticizer, were added to the mixture. The final mixture time was

about 7 minutes.

For the physical and mechanical characterization of concrete the following specimens were produced for

each mix: two 100 mm cubic specimens for concrete density at 28 days; three 150 mm cubic specimens for

compressive strength tests at 28 days, according to EN 12390-3 (2003). For the durability tests, performed at 28

days, the following specimens were also produced: three sawed 105x25 mm cylindrical specimens for the rapid

chloride migration test, according to NTbuild492 (1999) and three sawed 150x50 mm cylindrical specimens for

the capillary absorption test, according to LNEC E393 (1993) and TC116- PCD (1999).

Table 2 - Mix proportions

Mixes w/b Cement Fly-ash

Silica

fume

Cement

content

(kg/m3)

Coarse

aggregate (l/m3)

Natural

sand

(l/m3)

Effective

water (l/m3)

Arg

ex

CEM I 0.35 100% - - 450 350 314 157.5

CEM I

0.45

100% - -

400 350

310

180 CEM II/A-V 85% 15% - 304

CEM II/B-V 70% 30% - 297

CEM I 0.55 100% - - 350 350 315 192.5

Lyta

g

CEM I 0.35 100% - - 450 350 314 157.5

CEM I

0.45

100% - -

400 350

310

180 CEM II/A-V 85% 15% - 304

CEM II/B-V 70% 30% - 297

CEM II/A-D(1) 94% - 6% 307

CEM I 0.55 100% - - 350 350 315 192.5

A.N

/ L

eca/

Sta

lite

CEM I

0.35

100% - -

450 350

314

157.5

CEM II/A-V 85% 15% - 307

CEM II/B-V 70% 30% - 300

CEM II/A-D(1) 94% - 6% 311

CEM II/A-D(2) 91% - 9% 309

CEM IV/A 70% 20% 10% 299

CEM IV/B 50% 40% 10% 290

CEM I

0.45

100% -

400 350

310

180

CEM II/A-V 85% 15%

304

CEM II/B-V 70% 30%

297

CEM II/A-D(1) 94% - 6% 307

CEM II/A-D(2) 91% - 9% 305

CEM IV/A 70% 20% 10% 296

CEM IV/B 50% 40% 10% 288

CEM I

0.55

100% - -

350 350

315

192.5

CEM II/A-V 85% 15% - 309

CEM II/B-V 70% 30% - 304

CEM II/A-D(1) 94% - 6% 312

CEM II/A-D(2) 91% - 9% 310

CEM IV/A 70% 20% 10% 303

CEM IV/B 50% 40% 10% 295

3

2.2.1 Curing process

All specimens were demoulded after 24 hours. The specimens used for compressive strength tests were

water cured until the age of testing. The specimens for the capillary absorption test water cured for 7 days;

followed by 7 days in a controlled chamber at 22± 2 ºC with 50 ± 5% relative humidity; then oven dried for 3

days at 60 °C; plus 10 days at 50 °C and 1 day at testing room temperature, without moisture exchange. This

procedure allows the redistribution of the water content across the specimen. The specimens used for electrical

resistivity tests were water cured for 21 days, then placed in a controlled chamber at a temperature of 22 ± 2 °C

and relative humidity of 50 ± 5% until testing. The specimens for chloride penetration tests were water cured for

7 days then placed in a controlled chamber at a temperature of 22 ± 2 °C and relative humidity of 50 ± 5% until

testing.

2.2.2 Capillary absorption

The absorption tests were carried out according to E393 (1993). This test basically consists of

determining the water absorption rate (sorptivity) of concrete by measuring the increase in mass of a specimen

due to absorption of water as a function of √time, when only one surface of the specimen is exposed to water.

The exposed surface of the specimen was immersed in 5 1 mm of water and the mass of the specimen was

recorded 10, 20, 30, 60 minutes and 3, 6, 24 and 72 hours after the initial contact with water. For each

composition, three specimens were tested at 28 days of age.

During the test, the specimens were covered with a bell-glass in order to avoid the water evaporation. The

water absorption and the absorption coefficient were calculated for each age. The absorption coefficient was

obtained from the slope of the linear regression line between min and min of each tested specimen

and then averaged.

2.2.3 Electrical Resistivity

The electrical resistivity tests were carried out according to the standards proposed by Chlortest (2005) as

well as the DURAR (2000) manual and technical recommendation of TC 154 by RILEM (Polder 2000). This test

basically consists on the placement of a copre plak on both extremities of the specimens, through which an

electrical potential of 60 V is applied. The electrical charge passed through the specimen is then registered.

Based on these values the electrical resistivity is determined, as given from Eq. (1), where represents the

electrical resistivity ( , is the current intensity , is the applied voltage (V), is the area of the

specimens extremity (m2) and L is the length of the specimen (m). For each composition, three specimens were

tested at 28 days old.

(1)

2.2.4 Chloride-ion penetration resistance

The chloride penetration resistance was assessed by means of the non-steady state rapid chloride

migration test (RCMT) specified in NTDbuild492 (1999). An external electrical potential was applied, and the

chlorides ions were forced to migrate into the specimen. The testing time depends on the applied voltage. Then

the specimen was half-split and sprayed with a silver nitrate solution. The chloride penetration depth corresponds

to the visible limit of the white silver chloride precipitation. The non-steady-state chloride migration coefficient

of diffusion (Dnscm) was calculated from Eq. (2), where T represents the average value of the initial and final

temperature of the anodic solution (°C), L is the specimen’s thickness (mm), U is the absolute value of the

applied voltage (V), t is the test duration (hours) and Xd is the average value of the measured chloride penetration

depth (mm). For each composition, three specimens were tested at 28 days old.

nscm

t

t

m s (2)

3. Results and discussion

The dry density, d, the compressive strength, fcm, the structural efficiency (fcm/d), the 72 hours capillary

absorption, abs72h, the coefficient of capillary absorption, Cabs, the electrical resistivity, Res. and the coefficient

of chlorides diffusion at 28 days, Dnscm,28d, are listed in Table 3 for each composition.

4

Table 3 - Fresh density, dry density, compressive strength, structural efficiency, 72 hours capillary absorption, coefficient of capillary

absorption, electrical resistivity and coefficient of chlorides diffusion

Mixes Sump

cm

ρf ρd fc28d fc28d ρd Abs72h Cabs Res.

Dnscm,28d

kg/m3 kg/m3 Mpa 103.m kg/m2 x10-3m/min0,5 (Ω m) x10-12(m/s2)

0,3

5 L

eca

CEM I 13 1899.6 1697.5 45.7 2.7 1.8 39.5 98.2 7.9

CEM II/A-V 15 1903.1 1666.7 40.4 2.4 2.9 68.7 76.1 10.1

CEM II/B-V 14 1823.6 1617.3 35.4 2.2 3.4 82.4 80.5 10.9

CEM II/A-D(1) 11 1945.2 1717.5 43.9 2.6 1.6 35.8 129.8 7.6

CEM II/A-D(2) 13 1905.8 1652.0 41.4 2.5 1.3 28.5 184.1 6.4

CEM IV/A 18 1891.3 1627.7 39.2 2.4 1.9 44.3 367.5 4.3

CEM IV/B 18 1762.8 1581.9 29.3 1.9 2.2 51.9 370.6 6.1

0,4

5 L

eca

CEM I 14 1886.8 1656.5 37.6 2.3 3.7 81.9 86.2 13.2

CEM II/A-V 18 1830.4 1594.4 33.5 2.1 3.8 81.5 62.3 13.3

CEM II/B-V 14 1958.1 1600.4 32.5 2.0 4.6 107.7 94.2 13.9

CEM II/A-D(1) 13 1778.7 1601.1 34.4 2.2 2.9 62.4 118.8 8.8

CEM II/A-D(2) 16 1803.0 1581.2 33.3 2.1 3.2 64.8 118.2 9.2

CEM IV/A 12 1853.5 1560.1 30.2 1.9 2.8 62.9 239.0 10.0

CEM IV/B 9 1795.3 1551.4 26.9 1.7 - 117.8 245.1 9.2

0,5

5 L

eca

CEM I 9 1893.0 - 33.8 - 3.9 83.2 100.5 18.6

CEM II/A-V 18 1900.0 1621.5 28.7 1.8 5.5 116.0 57.0 20.4

CEM II/B-V 16 1934.2 1593.4 25.2 1.6 7.0 149.9 64.9 22.3

CEM II/A-D(1) 10 1874.1 1595.2 31.3 2.0 5.2 106.6 87.3 17.0

CEM II/A-D(2) 8 1844.7 1574.3 29.8 1.9 4.7 107.9 87.8 16.4

CEM IV/A 8 1877.1 1570.7 26.1 1.7 5.4 115.6 119.8 -

CEM IV/B 10 1626.9 1563.7 16.9 1.1 8.0 199.8 110.6 17.6

0,3

5 S

tali

te

CEM I 18 1988.7 1893.5 66.8 3.5 1.8 38.9 133.7 7.1

CEM II/A-V 18 1929.8 1830.7 54.2 3.0 2.0 51.2 131.1 9.8

CEM II/B-V 18 1912.2 1824.2 44.9 2.5 2.1 55.9 151.9 8.4

CEM II/A-D(1) 17 1944.9 1869.4 65.3 3.5 1.6 32.5 277.5 4.2

CEM II/A-D(2) 18 1943.7 1831.4 61.3 3.3 1.4 30.7 372.8 3.8

CEM IV/A 12 1871.6 1784.8 52.9 3.0 1.7 42.2 326.0 4.6

CEM IV/B 13 1871.1 1761.9 42.3 2.4 1.9 51.3 356.9 5.4

0,4

5 S

tali

te

CEM I 12 1960.9 1793.7 49.9 2.8 3.3 65.7 59.4 13.0

CEM II/A-V 12 1930.1 1790.1 44.3 2.5 3.5 75.8 70.0 13.8

CEM II/B-V 9 1989.6 1795.0 40.1 2.2 4.0 93.1 96.4 15.6

CEM II/A-D(1) 12 1892.7 1763.5 45.7 2.6 3.5 80.2 119.6 11.0

CEM II/A-D(2) 13 1904.6 1750.1 43.8 2.5 3.3 68.7 185.2 9.9

CEM IV/A 18 1903.1 1711.6 40.4 2.4 3.1 7.9 245.8 11.8

CEM IV/B 17 1863.7 1673.9 28.6 1.7 5.3 127.2 260.7 7.9

0,5

5 S

tali

te

CEM I 13 1980.0 - 44.5 - 3.8 82.9 72.7 15.6

CEM II/A-V 11 1965.3 1803.1 36.7 2.0 4.6 101.3 67.1 19.3

CEM II/B-V 9 1957.9 1772.1 29.2 1.6 5.4 126.5 93.0 22.8

CEM II/A-D(1) 6 1939.8 1757.7 42.4 2.4 - - 101.8 15.2

CEM II/A-D(2) 5 1915.6 1743.9 39.9 2.3 5.5 111.8 102.2 15.0

CEM IV/A 3 1973.9 1777.1 32.3 1.8 6.1 149.5 129.3 18.2

CEM IV/B 4 1832.4 1733.0 21.3 1.2 7.2 236.1 157.8 -

5

Table 3 - Fresh density, dry density, compressive strength, structural efficiency, 72 hours capillary absorption, coefficient of capillary

absorption, electrical resistivity and coefficient of chlorides diffusion (continuation)

Mixes Sump

cm

ρf ρd fc28d fc28d ρd Abs72h Cabs Res. Dnscm,28d

kg/m3 kg/m3 Mpa 103.m kg/m2 x10-3m/min0,5 (Ω m) x10-12(m/s2)

0.35 NWA

CEM I 14 2390.1 2298.7 76.3 3.3 1.9 42.2 111.0 8.1

CEM II/A-V 13 2351.6 2228.1 68.1 3.1 2.3 56.4 89.4 9.5

CEM II/B-V 15 2361.6 2234.0 63.7 2.9 2.5 61.6 115.4 10.4

CEM II/A-D(1) 14 2352.9 2241.4 74.3 3.3 1.7 39.7 201.6 7.2

CEM II/A-D(2) 10 2324.7 2258.5 84.2 3.7 1.2 28.9 240.7 4.1

CEM IV/A 13 2302.3 2225.7 71.4 3.2 1.7 43.3 310.3 4.6

CEM IV/B 15 2284.2 2210.6 58.2 2.6 2.5 63.3 387.7 7.1

0.45 NWA

CEM I 13 2367.4 2219.5 57.7 2.6 3.0 71.7 63.3 13.1

CEM II/A-V 19 2343.1 2188.9 51.4 2.4 3.2 75.1 74.1 14.2

CEM II/B-V 11 2326.8 2202.7 48.7 2.2 4.5 109.1 98.9 15.1

CEM II/A-D(1) 12 2307.6 2174.5 59.8 2.7 3.2 69.0 121.6 9.7

CEM II/A-D(2) 14 2281.5 2162.8 58.8 2.7 2.9 63.9 172.8 9.7

CEM IV/A 13 2253.3 2146.5 48.5 2.3 3.4 80.0 269.8 9.8

CEM IV/B 16 2218.8 2126.8 38.0 1.8 4.8 104.8 285.9 -

0.55 NWA

CEM I - 2199.5 - 47.8 - 3.9 87.0 103.0 15.8

CEM II/A-V 9 2370.1 2219.2 44.1 2.0 5.4 131.7 69.8 22.6

CEM II/B-V 10 2336.3 2203.4 36.0 1.6 5.8 154.7 81.2 -

CEM II/A-D(1) 2 2322.7 2186.8 47.0 2.1 4.7 107.9 119.9 12.9

CEM II/A-D(2) 2 2300.7 2166.3 45.0 2.1 5.1 118.2 150.7 11.8

CEM IV/A 3 2323.3 2178.6 40.1 1.8 5.3 124.9 171.0 13.1

CEM IV/B 5 2305.4 2135.2 25.9 1.2 6.7 227.3 208.9 19.1

0.35 CEM I 17 2010.4 1790.9 49.7 2.8 2.9 53.2 81.0 9.9

Lytag (0.45)

CEM I 13 1996.9 1733.2 41.2 2.4 - 90.5 40.4 15.3

CEM II/A-V 18 1943.3 1676.1 37.1 2.2 - - 52.0 18.1

CEM II/B-V 13 1947.1 1700.5 36.8 2.2 6.4 128.9 - 20.7

CEM II/A-D(1) 13 1912.3 1690.1 38.4 2.3 - - 77.1 15.1

0.55 CEM I 5,5 1746.3 - 36.2 - - - 52.1 20.1

0.35 CEM I 13 1676.2 1602.1 31.0 1.9 2.2 47.9 98.1 8.5

Argex

(0.45) CEM I

CEM II/A-V

CEM II/B-V

15

17

13

1635.9

1579.2

1608.3

1522.9

1430.0

1484.8

26.1

23.7

22.6

1.7

1.7

1.5

-

4.1

5.3

84.7

87.4

121.6

76.4

-

-

11.8

12.0

12.4

0.55 CEM I 13 1518.4 - 23.6 - 5.4 131.8 72.5 14.6

3.1 Compressive strength and dry density

The values of compressive strength and dry density, as shown in Table 3, suggest that the LWA of Stalite

are oriented to produce high strength concrete, while Leca and Lytag are better suited to produce medium to low

strength concrete and Argex can only be used for the production of very low strength concrete. Also, NWAC

and LWAC of Stalite exhibit the highest structural efficiency, no matter the w/b ratio. In fact, for concretes with

w/b above 0,35, most LWAC of Stalite actually have a structural efficiency superior to NWAC. As expected, the

structural efficiency tends to decrease with the increase of the w/b ratio.

3.2 Capillary absorption

The results show that the capillary absorption coefficients vary between 0.0285 and 0.236 mm/min0,5

,

which places the analysed concretes on the scale proposed by Browne (1991), between low and high quality.

This property seems to be mainly governed by the w/b ratio of the mixtures, given the major differences

registered among concretes with different w/b ratio. Other factors, like the kind of addition used and the type

6

LWA. Nonetheless, the differences between NWAC and LWAC are only significant on LWA with high open

porosity or weak outer shell (Argex and Lytag respectively). In the rest of the mixtures, generally, the water

absorption coefficient tends to be independent of the type of aggregate used, for a given w/c ratio and type of

cimenticious material (Figure 1). In some cases, the LWAC actually outmatches the results shown by NWAC,

probably due to better interface transition zones and improved internal curing.

For a given w/b ratio, the type of cimenticious material used is the main factor making the difference

between the mixtures results. According to the results shown on Table 3, and (Figures 2 to 4), the substitution of

cement by fly-ash resulted in the increase of the capillary absorption coefficients. That is probably due to the

short curing period and low pozzolanic reactivity of the material. On the other hand, the substitution of cement

by silica fume resulted on the decrease of the capillary absorption values, in most cases, due to its high

pozzolanic reactivity, since early ages, which causes the densification of the microstructure of the concrete

(Figures 5 to 7).

Figure 1 - Capillary absorption coefficients of CEM I concretes

Figure 2 - Capillary absorption coefficient Vs % substitution by fly

ash (w/b = 0.35)

Figure 3 - Capillary absorption coefficient Vs % substitution by fly

ash (w/b = 0.45)

Figure 4 - Capillary absorption coefficient Vs % substitution by fly ash (w/b = 0.55)

0

20

40

60

80

100

120

140

A.N

0,35

Leca

0,35

Stalite

0,35

Lytag

0,35

Argex

0,35

A.N

0,45

Leca

0,45

Stalite

0,45

Lytag

0,45

Argex

0,45

A.N

0,55

Leca

0,55

Stalite

0,55

Argex

0,55

Cab

s

(x10

-3 m

m/m

in0.5

)

Argex 0,35

Argex 0,45

Argex 0,55

a/b=0.35

a/b=0.45

a/b=0.55

0

20

40

60

80

100

0 15 30

Cab

s

(x10

-3 m

m/m

in0.5

)

% Fly ash

N.A 0.35

Leca 0.35

Stalite 0.35

0

20

40

60

80

100

120

140

0 15 30

Cab

s

(x10

-3 m

m/m

in0.5

)

% Fly ash

N.A 0,45

Leca 0,45

Stalite 0,45

Lytag 0,45

Argex 0,45

0

50

100

150

200

0 15 30

Cab

s

(x10

-3 m

m/m

in0.5

)

% Fly ash

N.A 0,55

Leca 0,55

Stalite 0,55

7

Figure 5 - Capillary absorption coefficient Vs % substitution by

silica fume (w/b = 0.35)

Figure 6 - Capillary absorption coefficient Vs % substitution by

silica fume (w/b = 0.45)

Figure 7 - Capillary absorption coefficient Vs % substitution by silica fume (w/b = 0.55)

3.3 Electrical resistivity

The analysis of the electrical resistivity results was very troublesome, due to the constraints associated

with this kind of test. Nonetheless, the general tendencies seem to follow the same standards as the ones shown

by the capillary absorption tests. The results vary from 40.4 to 387.7 Ωm, where the higher values referer to low

porosity concretes (Figures 8 to 10 ). Once again, the w/b ratio is responsible for the major differences

registered amongst the mixtures. The only significant difference between the capillary absorption tests and the

resistivity ones is the distinct effect of the substitution of cement by fly-ash. Unlike seen on the capillary

absorption tests, the substitution of cement by fly-ash tends to increase the resistivity of the admixtures. This

results should be due to the longer curing period of these mixtures, as well as the possible change of the ionic

composition of the pore fluid solution. Like seen in the capillary absorption tests, the substitution of cement by

silica fume improves significantly the performance of the concretes.

Figure 8 - Electrical resistivity for CEM I concretes

0

10

20

30

40

50

0 6

Cab

s

(x10

-3 m

m/m

in0.5

)

% Sílica fume

N.A 0,35

Leca 0,35

Stalite 0,35

9

0

20

40

60

80

100

0 6

Cab

s

(x10

-3 m

m/m

in0.5

)

% Sílica fume

N.A 0,45

Leca 0,45

Stalite 0,45

9

0

20

40

60

80

100

120

140

0 6

Cab

s

(x10

-3 m

m/m

in0.5

% Sílica fume

N.A 0,55

Leca 0,55

Stalite 0,55

9

0 20 40 60 80

100 120 140 160

Ele

ctri

cal

resi

stiv

ity

(Ω.m

)

Leca 0,35

Leca 0,45

Leca 0,55

w/b = 0.35

w/b = 0.45

w/b = 0.55

8

Figure 9 - Electrical resistivity for concretes with several percentages of fly-ash

Figure 10 - Electrical resistivity for concretes with several percentages of silica fume

3.4 Chloride-ion penetration resistance

Results show that, once again, there is no significant differences between the behaviour of LWAC and

NWAC. The diffusion coefficients vary between 3.8 a 37.6 x10-12

m2/s which, according to the classification

proposed by Gjorv (1996), match concretes with chloride penetration resistance from very high to very low

(Figure 12). Generally, the additions and the w/b ratio used, specially this last one, are responsible for the most

expressive differences among the various concretes studied. In fact, for a given w/b ratio, the type of aggregate

used has very little significance. Nonetheless, for high w/b ratios, above 0,55, the participation of LWA with

more superficial porosity (Argex and Lytag) can be visible.

Figure 11 - Chloride diffusion coefficients of CEM I concretes

The comparison of the concretes with mortars of equal composition (Figure 11) shows that the inclusion

of LWA does not worsen the chloride penetration resistance of the mixtures. Since the diffusion coefficients of

the concretes tend to be similar to the ones registered for the mortars, it seems that the quality of the porous

microstructure of the paste is the main ruler of the diffusion process. Nonetheless, a careful observation of the

results shows that the LWA with high open porosity and weak outer shell tend to have higher diffusion

coefficients than the reference NWAC, whilst the LWAC of Stalite can produce diffusion coefficients even

0 20 40 60 80

100 120 140 160

A.N

15%

Lec

a 15%

Sta

lite

15%

A.N

30%

Lec

a 30%

Sta

lite

30%

A.N

15%

Lec

a 15%

Sta

lite

15%

Lyt

ag 1

5%

A.N

30%

Lec

a 30%

Sta

lite

30%

A.N

15%

Lec

a 15%

Sta

lite

15%

A.N

30%

Lec

a 30%

Sta

lite

30%

Ele

ctri

cal

resi

stiv

ity

(Ω.m

)

Leca 15%

Leca 15%

Leca 15%

w/b = 0.35

w/b = 0.45

w/b = 0.55

0

100

200

300

400

A.N

6%

Lec

a 6%

Sta

lite

6%

A.N

9%

Lec

a 9%

Sta

lite

9%

A.N

6%

Lec

a 6%

Sta

lite

6%

Lyt

ag 6

%

A.N

9%

Lec

a 9%

Sta

lite

9%

A.N

6%

Lec

a 6%

Sta

lite

6%

A.N

9%

Lec

a 9%

Sta

lite

9%

Ele

ctri

cal

resi

stiv

ity

(Ω.m

)

Leca 6%

Leca 6%

Leca 6%

w/b = 0.35

w/b = 0.45

w/b = 0.55

0

5

10

15

20

25

A.N

…

Lec

a …

Sta

lit…

Lyt

a…

Arg

e…

Arg

a…

A.N

…

Lec

a …

Sta

lit…

Lyt

a…

Arg

e…

Arg

a…

A.N

…

Lec

a …

Sta

lit…

Lyt

a…

Arg

e…

Arg

a…

Dcl

,RC

MT

(x 1

0-1

2m

2/s

) Argex 0,35

Argamassa 0,35

Argex 0,45

Argamassa 0,45

Argex 0,55

Argamassa 0,55

w/c=0.35

w/c=0.45

w/c=0.55

mortar w/c =0.35

mortar w/c =0.45

mortar w/c =0.55

9

lower than those of the reference concretes. This could be due to the low pore interconnectivity of the

microstructure and the high quality of the cement paste of these concretes, especially their interface transition

zones.

The type of addition used can also influence the quality of the cement paste, thus the chloride penetration

resistance, although on a smaller scale when compared to the sway of the w/b ratio. The substitution of cement

by fly-ash, for any given w/b ratio, results on the increase of the diffusion coefficients (Figures 12 to 14). Once

again, this effect is supposed to be related with the low curing period of the mixtures, that combined with the low

pozzolanic reactivity of the fly-ash, results on the formation of less C-H-S than needed to cause the densification

of the microstructure. The negative effect of the substitution of cement by fly-ash tends to be increase with the

increase of the w/b ratio.

The substitution of cement by silica fume results, as long as the dispersion is effective, on the reduction of

the diffusion coefficients (Figures 15 to 17). This shows, like seen in the capillary absorption results, that the

addition of silica fume can lead to the denser, less porous microstructures, which can cause reductions on the

diffusion that can ascend to 50% of the reference values. Just like in the capillary tests, the silica fume seems to

be more effective on the NWA concretes.

Nonetheless, considering fly ash and silica fume working as additions, both materials resulted in the

decrease of the chloride diffusion coefficients, as shown in Figure 18 .

Figure 14- Chloride diffusion coefficient Vs % substitution of cement by fly ash (w/b =0.55)

0

5

10

15

20

25

0 15 30 Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Fly ash

NA 0,55

Leca 0,55

Stalite 0,55

Figure 12 - Chloride diffusion coefficient Vs % substitution of

cement by fly ash (w/b =0.35)


cement by fly ash (w/b =0.45)


cement by silica fume (w/b =0.35)


cement by silica fume (w/b =0.45)

0

2

4

6

8

10

12

0 15 30

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Fly ash

NA 0,35

Leca 0,35

Stalite 0,35

0

5

10

15

20

25

0 15 30

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Fly ash

NA 0,45

Leca 0,45

Stalite 0,45

Lytag 0,45

Argex 0,45

0

2

4

6

8

10

12

0 6

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Sílica fume

NA 0,35

Leca 0,35

Stalite

0,35

9 0

5

10

15

20

25

30

0 6

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Sílica fume

NA 0,45

Leca 0,45

Stalite 0,45

Lytag 0,45

9

10

Figure 17 - Chloride diffusion coefficient Vs % substitution of cement by silica fume (w/b =0.55)

Figure 18 - Diffusion curves according to the w/c variation

The correlation between the compressive strength and the chloride diffusion coefficients is very weak,

since it's only a slight tendency is visible for the decrease of the diffusion with the increase of the compressive

strength, for a given aggregate type (Figure 19). This is expected, since the influence of the type of aggregate is

very different on these two properties.

Figure 19 - Correlation between chloride diffusion coefficients and compressive strength

The correlation between the electrical resistance and the chloride diffusion coefficients is also very weak.

The main reasons for that are the variability of the electrical resistivity tests, as well as the different influence of

the microstructure and ionic composition of pore fluid solution on both tests (Figure 20).

0

5

10

15

20

25

30

0 6

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

% Sílica fume

NA 0,55

Leca 0,55

Stalite 0,55

9

0

5

10

15

20

25

30

35

40

0,20 0,40 0,60 0,80 1,00

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

w/c

NA

Leca

Stalite

Lytag

Argex

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

fcm,28dias (MPa)

NA

Leca

stalite

Lytag

Argex

11

Figure 20 - Correlation between chloride diffusion coefficients and electrical resistivity

Even though a linear tendency is visible between the capillary absorption and the chloride penetration

coefficients, the correlation between the two is relatively weak. In fact, these two properties are differently

affected by other factors, like the moist content of the mixtures, for instance (Figure 21).

Figure 21 - Correlation between chloride diffusion coefficients and capillary absorption coefficients

4. Conclusions

In the present study, the main mechanical and physical properties (compressive strength and concrete density)

and the durability behaviour of lightweight concretes, specially the chloride-ion penetration resistance, were

analysed, as well as the capillary absorption and electrical resistivity. The following main conclusions have been

drawn:

- Stalite aggregates can be used to produce high strength concrete. For w/b ratios above 0,35, their structural

efficiency is even higher than the one shown by NWA.

- Every mechanism studied (capillary absorption, electrical resistivity and chloride-ion penetration resistance)

was primarily affected by the w/b ratio, followed by the type and amount of additions used.

- Generally, of all the types of additions studied (fly ash and silica fume with several substitution percentages),

the best performing concretes were either CEM I concretes or concretes with silica fume incorporation.

- In the durability tests (capillary absorption, electrical resistivity and chloride-ion penetration resistance), no

significant differences were ever observed between the behaviour of LWAC and NWAC. Even so, the more

porous and less dense LWA (Argex and Lytag respectively), shown the tendency to be outmatched by the denser

ones.

4. References

Bogas JA. Characterization of structural lightweight expanded clay aggregate concrete (in Portuguese). PhD

thesis in Civil Engineering. Technical University of Lisbon, Instituto Superior Técnico, Lisbon, 2011;

Bogas J.A., Gomes M.G., Real S. "Capillary absorption of structural lightweight aggregate concrete", MATER.

STRUCT. 2014; M10. 1617

0

5

10

15

20

25

30

35

40

0 200 400 600

Dcl

,RC

MT

(x 1

0-1

2m

2/s

) Electrical resistivity (Ω.m)

NA

Leca

Stalite

Lytag

Argex

0

5

10

15

20

25

30

35

40

0 100 200 300

Dcl

,RC

MT

(x 1

0-1

2m

2/s

)

Capillary absorption coefficient (x103 mm/min0,5)

NA

Leca

Stalite

Lytag

Argex

12

Chia K. S., Zhang M. "Water permeability and chloride penetrability of high-strength lightweight aggregate

concrete", CEM. CONCR. RES. 2001; (32):639-645

Euro ightConR “Chlori e penetration into concrete with lightweight aggregates ” European nion – Brite

EuRam III, BE96-3942/R3, 1999. 120p.

Güneyisi E., Gesoglu M., Pürsünlü Ö., Mermedas K. "Durability aspects of concretes composed of cold bonded

and sintered fly ash lightweight aggregates", Composites: Part B 2013; (53):258-266

Haque M. N., Al- Khaiat H., Kayali O. "Strength and durability of lightweight concrete", CEM. & CONCR.

COMP. 2002; (26): 307-314

Kayali, O., e B. Zhu. “Chlori e in uce reinforcement corrosion in lightweight aggregate high- strength fly ash

concrete ” Construction an Buil ing Materials, Volume 19, Issue 4, 2004: pp 327-336.

Kockal N. U., Ozturan T. "Durability of lightweight concretes with lightweight fly ash aggregates", Const. and

Build. Mat., 2010; (25):1430-1438

Liu X., Chia K. S., Zhang M. "Water absorption, permeability and resistance to chloride-ion penetration of

lightweight aggregate concrete", Const. and Build. Mat., 2010; (25):335-343

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