INVESTIGATION OF DURABILITY OF WALL MATERIALS CONCRETE

PREPARED WITH FLY ASH

Jingliang Xia1,a, Zhuanqin Wu1, Renjie Shang1,b ,Beixing Li2,

Fangxin Jiang1,Zhiqiang Yin1

1Central Research Institute of Building and Construction，MCC Group Beijing，China；2 Wuhan

University of Technology，China

axiasnxia@126.com,bshangrj2000@yahoo.com

Keywords: fly ash; concrete; durability; wall material

Abstract. Based on durability of fly ash concrete, the freezing and thawing, impermeability and

cracking resistance of fly ash concrete were researched. The results show that the frost resistance of

concrete was reduced, impermeability and crack resistance were improved with increasing the fly

ash content.

Introduction

With development of the housing industry, wall reforms, as well as energy saving, environmental

protection requirements, fly ash concrete applied in the wall materials would become increasingly

widespread. Filling fly ash in the cement not only makes the recycling waste and improving

environment become true but also improves the workability, reduces the temperature up and

accelerates the growth of the strength in the latter time of concrete. The main points of concrete

durability are that in the condition of normal design, normal constructing and normal using, the

structures can remain the safety, common performance and acceptable appearance without

additional reinforcement during the service life[1,2]

.

The study of the durability of fly ash concrete used for wall material is very limited, therefore,

studying the durability of fly ash concrete used in the wall material is extremely important. The

effect of fly ash content on concrete durability was studied in the present paper.

Experiment

Raw materials

(1) Cement: 42.5R Portland cement. Chemical components, physical and mechanical properties are

shown in Table 1 and Table 2.

(2) Fly ash: Class I fly ash, chemical components is shown in Table 1. Fly ash fineness

(0.045mm square hole sieve) is 7.3%, specific surface area is 432.4m2/kg, water content is 0.21%,

water demand ratio is 95%.

(3) Coarse Aggregate: Grain size is 5 ~ 31.5mm graded limestone gravel, physical and

mechanical properties are shown in Table 3.

(4) Fine Aggregate: Fineness modulus 2.8, river sand, physical and mechanical properties were

shown in Table 3.

Applied Mechanics and Materials Vols. 174-177 (2012) pp 657-661Online available since 2012/May/14 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.174-177.657

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(5) Admixture: Shanxi Huang Teng efficient polycarboxylate superplasticizer, solid content

20%, alkali content0.75% , water-reducing rate 31%.

(6)Water: ordinary drinking water.

Table 1 The chemical composition of cement and fly ash

Material SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O Loss

P·O42.5 22.40 5.27 3.36 61.36 2.19 2.24 0.37 0.16 1.70

Class I

fly ash

52.04 29.23 5.45 2.72 1.06 0.64 2.41 0.53 3.89

Table 2 Main physical and mechanical properties of cement

Density

/g/cm3

Fineness

/%

Standard

consistency

/%

Setting time /

h:min Stability

Flexural

strength

/MPa

Compressive

strength

/MPa

Initial Final 3d 28d 3d 28d

3.15 6.8 29.4 2:12 3:18 Qualified 5.9 8.7 28.3 58.8

Table 3 Main physical and mechanical properties of Aggregate

Aggregate

Apparent

density

/( g/cm3)

Packing

density

/( g/m3)

Void

/%

Crushed

indicators

/%

Pin sheet

content

/%

Clay

content

/%

Lump of

clay

content

/%

Gravel 2.73 1.592 41.7 11.8 5.9 0.3 0

River

sand 2.67 1.589 40.0 \ \ 1.6 0

Test methods

Frost resistance and impermeability were measured according to GBT50082-2009 "Standard for test

methods of long-term performance and durability of ordinary concrete". Early crack resistance of

concrete experimental design and evaluation methods recommended by CCES01-2004"Guide to

Durability Design and Construction of Reinforced Structures" was used for crack resistance.

Experimental mixture

Concrete strength grade C40 was adopted in this study, which mixture and 28d compressive

strength were shown in Table 4.

Table 4 Concrete mixture and 28d compressive strength

NO. The amount of concrete material / kg·m

-3 Admixture

/% fc,28d/MPa

Cement Fly ash Water Sand Crushed

FA0 420 \ 168 616 1196 0.55 51.2

FA10 378 42 168 616 1196 0.55 50.3

FA20 336 84 168 616 1196 0.55 50.8

FA30 294 126 168 616 1196 0.55 49.5

FA40 252 168 168 616 1196 0.55 48.6

658 Advanced Building Materials and Sustainable Architecture

Results and discussion

Freeze and thaw resistance

Test results of fly ash effecting concrete frost resistance were shown in Figure 1. It showed that

relative dynamic elastic modulus of concrete freeze-thaw decline was not obvious at an early stage,

to reach a certain number of freeze-thaw times there would be a sudden drop, concrete without fly

ash appeared this phenomenon in 175 freeze-thaw cycles. Relative dynamic elastic modulus

declining increased with increasing fly ash content. 20% of fly ash admixture to resist freeze-thaw

cycle 225 times, and 40% fly ash concrete in freeze-thaw cycle 150 when relative dynamic elastic

modulus dropped to below 60%, so from the perspective of frost resistance considered fly ash

content could not be too high.

That was because the incorporation of fly ash could be refined the pores within concrete,

increased the total porosity of the structure[3-4]

. At the same time the admixture of fly ash would

reduce freezing point of concrete pore water, frozen way to erosion by the hydrostatic pressure

changes in the osmotic pressure erosion. Total porosity increases and changes in freeze-thaw

mechanism to accelerate the freeze-thaw damage of fly ash concrete, made fly ash concrete had

lower frost resistance than pure cement concrete [5]

.

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

25 50 75 100 125 150 175 200 225 250

Times of Freeze-and-thaw

Relative dynamic modulus of elasticity

0%FA

10%FA

20%FA

30%FA

40%FA

Figure 1 Freeze-and-thaw ability

Impermeability

Concrete impermeability externalizes the ability to resist external erosion. Seepage experiment

results were shown in Figure 2 for specimens at 28d ages undergoing water pressure about 1.2MPa

for 24 hours for five different cases. It showed that after admixture of fly ash, water seepage height

decreased, indicated admixture of fly ash could improve the impermeability of concrete. And,

within a certain range, the concrete impermeability increased with fly ash content increase. This

was because the incorporation of fly ash improved the interfacial adhesion between the slurry and

aggregate, cement hydrate structure, the hydration of cement particles more uniform, hydrate

structure was denser.

Applied Mechanics and Materials Vols. 174-177 659

15

20

25

30

35

40

0 10% 20% 30% 40%

fly ash content(%)

hei

gh

t(m

m)

Figure 2 Height of water seepage

Crack resistance

Test method of plate-restraint was employed to detect concrete anti-cracking for different fly ash

content. Test photo was shown in figure 3. Test for 24 hours after the flat crack area was shown in

Figure 4. It showed that reduced the total area of cracks after admixture of fly ash, indicated the

admixture of fly ash to improve the early crack resistance of concrete. And, within a certain range,

the cracks area of concrete reduced with fly ash content increase.

Figure 3 Plate-restraint method test

The reasons as follows: (1) Unhydrated particles increased in concrete mixture after adding fly

ash, that could have a beneficial effect of the center circle, and enhanced interfacial transition zone

between aggregate and slurry, formed multi-gel system with high-quality cement-centric, to carry

out effectively inhibit the cracks[6]

. (2) Adding fly ash improved the performance of concrete

bleeding, and improved the crack resistance of concrete.

660 Advanced Building Materials and Sustainable Architecture

250

300

350

400

450

500

0 10% 20% 30% 40%

fly ash content(%)

Cra

ck

are

a(m

m2)

Figure 4 Crack development

Conclusions

To improve the durability of concrete, the effect of fly ash content on the properties of concrete was

investigated. The results show that:

(1)Filling fly ash could change the cavity structure of concrete, increased the cavity number per

unit volume and mainwhile accelerated freeze-thaw deterioration. Therefore, freeze-thaw resistance

of fly ash concrete decreases with increasing the fly ash content.

(2) Adding fly ash could improve the impermeability resistance and early crack resistance of

concrete. The impermeability resistance and early crack resistance increase with increasing fly ash

content.

(3) Considering the durability of fly ash concrete wall materials, content of fly ash can not be too

high, the appropriate content is 20%.

References

[1] Z.W. Wu and H.Z. Lian: High Performance Concrete. (Railway Publishing House of

China,1999)

[2] F.P. Zhou and Barr B.I.G: Fracture properties of high-strength concrete with varying silca fume

content and aggregates. Cement and Concrete Research Vol. 25, No.3(1995)

[3] X.L Yuan and B.X. Li and S.C. Zhao: Frost resistance of fly ash concrete and its mechanism,.

Concrete, 2008, Vol. 12,43-45

[4] Z. LIN AND Y.M. Chen: Study on the sub micro structure of the cement based materials after

adding grinding slag and fly ash. Journal of The Chinese Ceramic Society, 2000,28(1):6-10.

[5] G.H. Pan and S. Wei: Theoretical and experimental research on for resistance of high strength

concrete. Journal of The Chinese Ceramic Society, 1999,27(6):637-643.

[6] L.X. Zhang and Y.G. Tan: Study on crack resistance of high performance concrete for bulk

mass thin-wall structure. Water Resources and Power, 2010, 28(3):112- 114.

Applied Mechanics and Materials Vols. 174-177 661

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