Properties Of High-Lime Fly Ash Concrete

PROPERTIES OF HIGH-LIME FLY ASH CONCRETE

Senel Artirma

Erdem Tandirli

ABSTRACT

Fly ash is a waste product from coal based thermal power stations. About seven million tons of fly ash is being produced annually from these thermal power stations in Turkey. Concerted efforts are needed to make the material used to a great extent.

These paper give the results of an investigation on the performance of fly ash concrete made with ASTM C class fly ashes from two sources. PC42,5 cement used in the experiments conforms to TS19 (Turkish Standards).

A comparison between concretes with and without fly ash was provided for various aspects. All the concrete mixtures contained polyhydroxy carbon salt plasticizer which complies with ASTM C 494-81 Type D. Their workabilities were kept constant.

As freshly-mixed concrete properties slump, unit weight, air content, setting time and bleeding values were determined.

As mechanical properties compressive strength and were measured after 24 hours, 7, 28 and 90 days.

Durability in terms of freezing and thawing resistance (ASTM C 666 Procedure A), and permeability were also investigated.

Keywords: Fly ash, concrete properties, binder material, micro-structure

Senel Artirma, Geophysics Engineer, Quality Assurance Manager of Nuh Beton Ready-Mixed Concrete Company, Turkey.

Erdem Tandirli, Civil Engineer, Quality Control Chief of Nuh Beton Ready-Mixed Concrete Company, Turkey.

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1. INTRODUCTION

Environmental hazards and over-comsumption of energy resources has been and still are the most concerning issues for the modern world. In this respect the usage of fly ash which is a waste product of the thermal power stations by ready-mixed concrete industry as a binder material can be an effective way both of decreasing the ash discharge out to the environment and of cement consumption thus of saving the resources on a national scale.

From the concrete technology's point of view, the usage of fly ash causes qualitative changes in concrete properties. The answer to whether these changes were improvement or not can be given only by knowing the intentions of usage.

For this purpose fly ashes were added both in addition to and as a substitute for some part of the cement, and fresh and hardened concrete properties were investigated.

2. EXPERIMENTAL STUDIES

2.1 Materials

2.1.1 Cement

The cement used is Turkish, portland cement (PC 42.5) and comforms to Turkish standart TS19 while approximately corresponds to ASTM C 150-89 Type I. Its chemical composition, and principal compounds are summarized in Table 1.a, physical and mechanical properties in Table 1.b along with standart limits.

Table 1.a - Chemical properties of cement

Chemical Composition

Components, % PC 42.5 TS 19 ASTM Type I

SiO2 21.16 - -

Al2O3 3.60 - -

Fe2O3 4.50 - -

CaO 64.90 - -

MgO 1.20 5 max. 6 max.

SO3 1.97 3.5 max. 3 max.

Total Alkalies: Na2O+0.658x K2O 0.00 - 0.6 max.

Insoluble Residue 0.83 1.5 max. 0.75 max.

Loss on Ignition 1.15 4 max. 3 max.

Principal Compounds

C3S 64.27 - -

C2S 11.11 - -

C3A 1.93 - -

C4AF 13.69 - -

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Table 1.b - Physical and mechanical properties of cement

Physical Properties

PC 42.5 TS 19 ASTM Type I

Specific Gravity, gr/cm3 3.12 - -

Specific Surface, cm2/gr 3268 2800 min. 2800 min.

Setting Times, minutes

Initial 195 60 min. 45 min.

Final 216 600 max. 375 max.

Mechanical Properties

Compressive Strength, MPa

1 day 166 - -

2 days 271 20 min -

7 days 442 31.5 min. 19.3 min.

28 days - 42.5 min 27.6 min.

2.1.2 Fly ashes

Fly ashes were from two different thermal power plants using lignite as combustible, namely Seyitomer and Cayirhan both of which are located in western Turkey. Their chemical compositions are given in Table 2.a, physical and mechanical properties in Table 2.b, in comparison with ASTM C 618-89a limits and relevant Turkish standart TS 639 limits.

Table 2.a - Chemical properties of fly ashes

Chemical Composition

Components, % Seyitцmer Fly Ash (F1) Cayэrhan Fly Ash (F2) ASTM C 618 Spec.Class C TS 639

Spec.Class C

SiO2 50.05 48.65 - -

Al2O3 8.65 18.66 - -

Fe2O3 5.85 6.34 - -

Total, SiO2+Al2O3+Fe2O3 64.55 73.65 50.5 min. -

CaO 23.65 19.18 - -

MgO 2.83 1.77 5.0 max. -

SO3 - - 5.0 max. 3.0 max.

Na2O 1.90 1.60 1.5 max. -

K2O 2.82 2.10 - -

Insoluble Residue - - -

Loss